1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002
4 @c Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
25 @c readline appendices use @vindex, @findex and @ftable,
26 @c annotate.texi and gdbmi use @findex.
30 @c !!set GDB manual's edition---not the same as GDB version!
33 @c !!set GDB manual's revision date
34 @set DATE December 2001
36 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Programming & development tools.
42 * Gdb: (gdb). The @sc{gnu} debugger.
46 This file documents the @sc{gnu} debugger @value{GDBN}.
49 This is the @value{EDITION} Edition, @value{DATE},
50 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
51 for @value{GDBN} Version @value{GDBVN}.
53 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,@*
54 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
56 Permission is granted to copy, distribute and/or modify this document
57 under the terms of the GNU Free Documentation License, Version 1.1 or
58 any later version published by the Free Software Foundation; with the
59 Invariant Sections being ``Free Software'' and ``Free Software Needs
60 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
61 and with the Back-Cover Texts as in (a) below.
63 (a) The Free Software Foundation's Back-Cover Text is: ``You have
64 freedom to copy and modify this GNU Manual, like GNU software. Copies
65 published by the Free Software Foundation raise funds for GNU
70 @title Debugging with @value{GDBN}
71 @subtitle The @sc{gnu} Source-Level Debugger
73 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
74 @subtitle @value{DATE}
75 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
79 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
80 \hfill {\it Debugging with @value{GDBN}}\par
81 \hfill \TeX{}info \texinfoversion\par
85 @vskip 0pt plus 1filll
86 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
87 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
89 Published by the Free Software Foundation @*
90 59 Temple Place - Suite 330, @*
91 Boston, MA 02111-1307 USA @*
94 Permission is granted to copy, distribute and/or modify this document
95 under the terms of the GNU Free Documentation License, Version 1.1 or
96 any later version published by the Free Software Foundation; with the
97 Invariant Sections being ``Free Software'' and ``Free Software Needs
98 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
99 and with the Back-Cover Texts as in (a) below.
101 (a) The Free Software Foundation's Back-Cover Text is: ``You have
102 freedom to copy and modify this GNU Manual, like GNU software. Copies
103 published by the Free Software Foundation raise funds for GNU
109 @node Top, Summary, (dir), (dir)
111 @top Debugging with @value{GDBN}
113 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
115 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
118 Copyright (C) 1988-2002 Free Software Foundation, Inc.
121 * Summary:: Summary of @value{GDBN}
122 * Sample Session:: A sample @value{GDBN} session
124 * Invocation:: Getting in and out of @value{GDBN}
125 * Commands:: @value{GDBN} commands
126 * Running:: Running programs under @value{GDBN}
127 * Stopping:: Stopping and continuing
128 * Stack:: Examining the stack
129 * Source:: Examining source files
130 * Data:: Examining data
131 * Macros:: Preprocessor Macros
132 * Tracepoints:: Debugging remote targets non-intrusively
133 * Overlays:: Debugging programs that use overlays
135 * Languages:: Using @value{GDBN} with different languages
137 * Symbols:: Examining the symbol table
138 * Altering:: Altering execution
139 * GDB Files:: @value{GDBN} files
140 * Targets:: Specifying a debugging target
141 * Remote Debugging:: Debugging remote programs
142 * Configurations:: Configuration-specific information
143 * Controlling GDB:: Controlling @value{GDBN}
144 * Sequences:: Canned sequences of commands
145 * TUI:: @value{GDBN} Text User Interface
146 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
147 * Annotations:: @value{GDBN}'s annotation interface.
148 * GDB/MI:: @value{GDBN}'s Machine Interface.
150 * GDB Bugs:: Reporting bugs in @value{GDBN}
151 * Formatting Documentation:: How to format and print @value{GDBN} documentation
153 * Command Line Editing:: Command Line Editing
154 * Using History Interactively:: Using History Interactively
155 * Installing GDB:: Installing GDB
156 * Maintenance Commands:: Maintenance Commands
157 * Remote Protocol:: GDB Remote Serial Protocol
158 * Copying:: GNU General Public License says
159 how you can copy and share GDB
160 * GNU Free Documentation License:: The license for this documentation
169 @unnumbered Summary of @value{GDBN}
171 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
172 going on ``inside'' another program while it executes---or what another
173 program was doing at the moment it crashed.
175 @value{GDBN} can do four main kinds of things (plus other things in support of
176 these) to help you catch bugs in the act:
180 Start your program, specifying anything that might affect its behavior.
183 Make your program stop on specified conditions.
186 Examine what has happened, when your program has stopped.
189 Change things in your program, so you can experiment with correcting the
190 effects of one bug and go on to learn about another.
193 You can use @value{GDBN} to debug programs written in C and C++.
194 For more information, see @ref{Support,,Supported languages}.
195 For more information, see @ref{C,,C and C++}.
197 @c OBSOLETE @cindex Chill
200 @c OBSOLETE and Chill
201 is partial. For information on Modula-2, see @ref{Modula-2,,Modula-2}.
202 @c OBSOLETE For information on Chill, see @ref{Chill}.
205 Debugging Pascal programs which use sets, subranges, file variables, or
206 nested functions does not currently work. @value{GDBN} does not support
207 entering expressions, printing values, or similar features using Pascal
211 @value{GDBN} can be used to debug programs written in Fortran, although
212 it may be necessary to refer to some variables with a trailing
216 * Free Software:: Freely redistributable software
217 * Contributors:: Contributors to GDB
221 @unnumberedsec Free software
223 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
224 General Public License
225 (GPL). The GPL gives you the freedom to copy or adapt a licensed
226 program---but every person getting a copy also gets with it the
227 freedom to modify that copy (which means that they must get access to
228 the source code), and the freedom to distribute further copies.
229 Typical software companies use copyrights to limit your freedoms; the
230 Free Software Foundation uses the GPL to preserve these freedoms.
232 Fundamentally, the General Public License is a license which says that
233 you have these freedoms and that you cannot take these freedoms away
236 @unnumberedsec Free Software Needs Free Documentation
238 The biggest deficiency in the free software community today is not in
239 the software---it is the lack of good free documentation that we can
240 include with the free software. Many of our most important
241 programs do not come with free reference manuals and free introductory
242 texts. Documentation is an essential part of any software package;
243 when an important free software package does not come with a free
244 manual and a free tutorial, that is a major gap. We have many such
247 Consider Perl, for instance. The tutorial manuals that people
248 normally use are non-free. How did this come about? Because the
249 authors of those manuals published them with restrictive terms---no
250 copying, no modification, source files not available---which exclude
251 them from the free software world.
253 That wasn't the first time this sort of thing happened, and it was far
254 from the last. Many times we have heard a GNU user eagerly describe a
255 manual that he is writing, his intended contribution to the community,
256 only to learn that he had ruined everything by signing a publication
257 contract to make it non-free.
259 Free documentation, like free software, is a matter of freedom, not
260 price. The problem with the non-free manual is not that publishers
261 charge a price for printed copies---that in itself is fine. (The Free
262 Software Foundation sells printed copies of manuals, too.) The
263 problem is the restrictions on the use of the manual. Free manuals
264 are available in source code form, and give you permission to copy and
265 modify. Non-free manuals do not allow this.
267 The criteria of freedom for a free manual are roughly the same as for
268 free software. Redistribution (including the normal kinds of
269 commercial redistribution) must be permitted, so that the manual can
270 accompany every copy of the program, both on-line and on paper.
272 Permission for modification of the technical content is crucial too.
273 When people modify the software, adding or changing features, if they
274 are conscientious they will change the manual too---so they can
275 provide accurate and clear documentation for the modified program. A
276 manual that leaves you no choice but to write a new manual to document
277 a changed version of the program is not really available to our
280 Some kinds of limits on the way modification is handled are
281 acceptable. For example, requirements to preserve the original
282 author's copyright notice, the distribution terms, or the list of
283 authors, are ok. It is also no problem to require modified versions
284 to include notice that they were modified. Even entire sections that
285 may not be deleted or changed are acceptable, as long as they deal
286 with nontechnical topics (like this one). These kinds of restrictions
287 are acceptable because they don't obstruct the community's normal use
290 However, it must be possible to modify all the @emph{technical}
291 content of the manual, and then distribute the result in all the usual
292 media, through all the usual channels. Otherwise, the restrictions
293 obstruct the use of the manual, it is not free, and we need another
294 manual to replace it.
296 Please spread the word about this issue. Our community continues to
297 lose manuals to proprietary publishing. If we spread the word that
298 free software needs free reference manuals and free tutorials, perhaps
299 the next person who wants to contribute by writing documentation will
300 realize, before it is too late, that only free manuals contribute to
301 the free software community.
303 If you are writing documentation, please insist on publishing it under
304 the GNU Free Documentation License or another free documentation
305 license. Remember that this decision requires your approval---you
306 don't have to let the publisher decide. Some commercial publishers
307 will use a free license if you insist, but they will not propose the
308 option; it is up to you to raise the issue and say firmly that this is
309 what you want. If the publisher you are dealing with refuses, please
310 try other publishers. If you're not sure whether a proposed license
311 is free, write to @email{licensing@@gnu.org}.
313 You can encourage commercial publishers to sell more free, copylefted
314 manuals and tutorials by buying them, and particularly by buying
315 copies from the publishers that paid for their writing or for major
316 improvements. Meanwhile, try to avoid buying non-free documentation
317 at all. Check the distribution terms of a manual before you buy it,
318 and insist that whoever seeks your business must respect your freedom.
319 Check the history of the book, and try to reward the publishers that
320 have paid or pay the authors to work on it.
322 The Free Software Foundation maintains a list of free documentation
323 published by other publishers, at
324 @url{http://www.fsf.org/doc/other-free-books.html}.
327 @unnumberedsec Contributors to @value{GDBN}
329 Richard Stallman was the original author of @value{GDBN}, and of many
330 other @sc{gnu} programs. Many others have contributed to its
331 development. This section attempts to credit major contributors. One
332 of the virtues of free software is that everyone is free to contribute
333 to it; with regret, we cannot actually acknowledge everyone here. The
334 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
335 blow-by-blow account.
337 Changes much prior to version 2.0 are lost in the mists of time.
340 @emph{Plea:} Additions to this section are particularly welcome. If you
341 or your friends (or enemies, to be evenhanded) have been unfairly
342 omitted from this list, we would like to add your names!
345 So that they may not regard their many labors as thankless, we
346 particularly thank those who shepherded @value{GDBN} through major
348 Andrew Cagney (releases 5.3, 5.2, 5.1 and 5.0);
349 Jim Blandy (release 4.18);
350 Jason Molenda (release 4.17);
351 Stan Shebs (release 4.14);
352 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
353 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
354 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
355 Jim Kingdon (releases 3.5, 3.4, and 3.3);
356 and Randy Smith (releases 3.2, 3.1, and 3.0).
358 Richard Stallman, assisted at various times by Peter TerMaat, Chris
359 Hanson, and Richard Mlynarik, handled releases through 2.8.
361 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
362 in @value{GDBN}, with significant additional contributions from Per
363 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
364 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
365 much general update work leading to release 3.0).
367 @value{GDBN} uses the BFD subroutine library to examine multiple
368 object-file formats; BFD was a joint project of David V.
369 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
371 David Johnson wrote the original COFF support; Pace Willison did
372 the original support for encapsulated COFF.
374 Brent Benson of Harris Computer Systems contributed DWARF2 support.
376 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
377 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
379 Jean-Daniel Fekete contributed Sun 386i support.
380 Chris Hanson improved the HP9000 support.
381 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
382 David Johnson contributed Encore Umax support.
383 Jyrki Kuoppala contributed Altos 3068 support.
384 Jeff Law contributed HP PA and SOM support.
385 Keith Packard contributed NS32K support.
386 Doug Rabson contributed Acorn Risc Machine support.
387 Bob Rusk contributed Harris Nighthawk CX-UX support.
388 Chris Smith contributed Convex support (and Fortran debugging).
389 Jonathan Stone contributed Pyramid support.
390 Michael Tiemann contributed SPARC support.
391 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
392 Pace Willison contributed Intel 386 support.
393 Jay Vosburgh contributed Symmetry support.
395 Andreas Schwab contributed M68K Linux support.
397 Rich Schaefer and Peter Schauer helped with support of SunOS shared
400 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
401 about several machine instruction sets.
403 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
404 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
405 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
406 and RDI targets, respectively.
408 Brian Fox is the author of the readline libraries providing
409 command-line editing and command history.
411 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
412 Modula-2 support, and contributed the Languages chapter of this manual.
414 Fred Fish wrote most of the support for Unix System Vr4.
415 He also enhanced the command-completion support to cover C@t{++} overloaded
418 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
421 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
423 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
425 Toshiba sponsored the support for the TX39 Mips processor.
427 Matsushita sponsored the support for the MN10200 and MN10300 processors.
429 Fujitsu sponsored the support for SPARClite and FR30 processors.
431 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
434 Michael Snyder added support for tracepoints.
436 Stu Grossman wrote gdbserver.
438 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
439 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
441 The following people at the Hewlett-Packard Company contributed
442 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
443 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
444 compiler, and the terminal user interface: Ben Krepp, Richard Title,
445 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
446 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
447 information in this manual.
449 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
450 Robert Hoehne made significant contributions to the DJGPP port.
452 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
453 development since 1991. Cygnus engineers who have worked on @value{GDBN}
454 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
455 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
456 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
457 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
458 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
459 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
460 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
461 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
462 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
463 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
464 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
465 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
466 Zuhn have made contributions both large and small.
468 Jim Blandy added support for preprocessor macros, while working for Red
472 @chapter A Sample @value{GDBN} Session
474 You can use this manual at your leisure to read all about @value{GDBN}.
475 However, a handful of commands are enough to get started using the
476 debugger. This chapter illustrates those commands.
479 In this sample session, we emphasize user input like this: @b{input},
480 to make it easier to pick out from the surrounding output.
483 @c FIXME: this example may not be appropriate for some configs, where
484 @c FIXME...primary interest is in remote use.
486 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
487 processor) exhibits the following bug: sometimes, when we change its
488 quote strings from the default, the commands used to capture one macro
489 definition within another stop working. In the following short @code{m4}
490 session, we define a macro @code{foo} which expands to @code{0000}; we
491 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
492 same thing. However, when we change the open quote string to
493 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
494 procedure fails to define a new synonym @code{baz}:
503 @b{define(bar,defn(`foo'))}
507 @b{changequote(<QUOTE>,<UNQUOTE>)}
509 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
512 m4: End of input: 0: fatal error: EOF in string
516 Let us use @value{GDBN} to try to see what is going on.
519 $ @b{@value{GDBP} m4}
520 @c FIXME: this falsifies the exact text played out, to permit smallbook
521 @c FIXME... format to come out better.
522 @value{GDBN} is free software and you are welcome to distribute copies
523 of it under certain conditions; type "show copying" to see
525 There is absolutely no warranty for @value{GDBN}; type "show warranty"
528 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
533 @value{GDBN} reads only enough symbol data to know where to find the
534 rest when needed; as a result, the first prompt comes up very quickly.
535 We now tell @value{GDBN} to use a narrower display width than usual, so
536 that examples fit in this manual.
539 (@value{GDBP}) @b{set width 70}
543 We need to see how the @code{m4} built-in @code{changequote} works.
544 Having looked at the source, we know the relevant subroutine is
545 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
546 @code{break} command.
549 (@value{GDBP}) @b{break m4_changequote}
550 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
554 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
555 control; as long as control does not reach the @code{m4_changequote}
556 subroutine, the program runs as usual:
559 (@value{GDBP}) @b{run}
560 Starting program: /work/Editorial/gdb/gnu/m4/m4
568 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
569 suspends execution of @code{m4}, displaying information about the
570 context where it stops.
573 @b{changequote(<QUOTE>,<UNQUOTE>)}
575 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
577 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
581 Now we use the command @code{n} (@code{next}) to advance execution to
582 the next line of the current function.
586 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
591 @code{set_quotes} looks like a promising subroutine. We can go into it
592 by using the command @code{s} (@code{step}) instead of @code{next}.
593 @code{step} goes to the next line to be executed in @emph{any}
594 subroutine, so it steps into @code{set_quotes}.
598 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
600 530 if (lquote != def_lquote)
604 The display that shows the subroutine where @code{m4} is now
605 suspended (and its arguments) is called a stack frame display. It
606 shows a summary of the stack. We can use the @code{backtrace}
607 command (which can also be spelled @code{bt}), to see where we are
608 in the stack as a whole: the @code{backtrace} command displays a
609 stack frame for each active subroutine.
612 (@value{GDBP}) @b{bt}
613 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
615 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
617 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
618 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
620 #4 0x79dc in expand_input () at macro.c:40
621 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
625 We step through a few more lines to see what happens. The first two
626 times, we can use @samp{s}; the next two times we use @code{n} to avoid
627 falling into the @code{xstrdup} subroutine.
631 0x3b5c 532 if (rquote != def_rquote)
633 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
634 def_lquote : xstrdup(lq);
636 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
639 538 len_lquote = strlen(rquote);
643 The last line displayed looks a little odd; we can examine the variables
644 @code{lquote} and @code{rquote} to see if they are in fact the new left
645 and right quotes we specified. We use the command @code{p}
646 (@code{print}) to see their values.
649 (@value{GDBP}) @b{p lquote}
650 $1 = 0x35d40 "<QUOTE>"
651 (@value{GDBP}) @b{p rquote}
652 $2 = 0x35d50 "<UNQUOTE>"
656 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
657 To look at some context, we can display ten lines of source
658 surrounding the current line with the @code{l} (@code{list}) command.
664 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
666 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
669 538 len_lquote = strlen(rquote);
670 539 len_rquote = strlen(lquote);
677 Let us step past the two lines that set @code{len_lquote} and
678 @code{len_rquote}, and then examine the values of those variables.
682 539 len_rquote = strlen(lquote);
685 (@value{GDBP}) @b{p len_lquote}
687 (@value{GDBP}) @b{p len_rquote}
692 That certainly looks wrong, assuming @code{len_lquote} and
693 @code{len_rquote} are meant to be the lengths of @code{lquote} and
694 @code{rquote} respectively. We can set them to better values using
695 the @code{p} command, since it can print the value of
696 any expression---and that expression can include subroutine calls and
700 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
702 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
707 Is that enough to fix the problem of using the new quotes with the
708 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
709 executing with the @code{c} (@code{continue}) command, and then try the
710 example that caused trouble initially:
716 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
723 Success! The new quotes now work just as well as the default ones. The
724 problem seems to have been just the two typos defining the wrong
725 lengths. We allow @code{m4} exit by giving it an EOF as input:
729 Program exited normally.
733 The message @samp{Program exited normally.} is from @value{GDBN}; it
734 indicates @code{m4} has finished executing. We can end our @value{GDBN}
735 session with the @value{GDBN} @code{quit} command.
738 (@value{GDBP}) @b{quit}
742 @chapter Getting In and Out of @value{GDBN}
744 This chapter discusses how to start @value{GDBN}, and how to get out of it.
748 type @samp{@value{GDBP}} to start @value{GDBN}.
750 type @kbd{quit} or @kbd{C-d} to exit.
754 * Invoking GDB:: How to start @value{GDBN}
755 * Quitting GDB:: How to quit @value{GDBN}
756 * Shell Commands:: How to use shell commands inside @value{GDBN}
760 @section Invoking @value{GDBN}
762 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
763 @value{GDBN} reads commands from the terminal until you tell it to exit.
765 You can also run @code{@value{GDBP}} with a variety of arguments and options,
766 to specify more of your debugging environment at the outset.
768 The command-line options described here are designed
769 to cover a variety of situations; in some environments, some of these
770 options may effectively be unavailable.
772 The most usual way to start @value{GDBN} is with one argument,
773 specifying an executable program:
776 @value{GDBP} @var{program}
780 You can also start with both an executable program and a core file
784 @value{GDBP} @var{program} @var{core}
787 You can, instead, specify a process ID as a second argument, if you want
788 to debug a running process:
791 @value{GDBP} @var{program} 1234
795 would attach @value{GDBN} to process @code{1234} (unless you also have a file
796 named @file{1234}; @value{GDBN} does check for a core file first).
798 Taking advantage of the second command-line argument requires a fairly
799 complete operating system; when you use @value{GDBN} as a remote
800 debugger attached to a bare board, there may not be any notion of
801 ``process'', and there is often no way to get a core dump. @value{GDBN}
802 will warn you if it is unable to attach or to read core dumps.
804 You can optionally have @code{@value{GDBP}} pass any arguments after the
805 executable file to the inferior using @code{--args}. This option stops
808 gdb --args gcc -O2 -c foo.c
810 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
811 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
813 You can run @code{@value{GDBP}} without printing the front material, which describes
814 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
821 You can further control how @value{GDBN} starts up by using command-line
822 options. @value{GDBN} itself can remind you of the options available.
832 to display all available options and briefly describe their use
833 (@samp{@value{GDBP} -h} is a shorter equivalent).
835 All options and command line arguments you give are processed
836 in sequential order. The order makes a difference when the
837 @samp{-x} option is used.
841 * File Options:: Choosing files
842 * Mode Options:: Choosing modes
846 @subsection Choosing files
848 When @value{GDBN} starts, it reads any arguments other than options as
849 specifying an executable file and core file (or process ID). This is
850 the same as if the arguments were specified by the @samp{-se} and
851 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
852 first argument that does not have an associated option flag as
853 equivalent to the @samp{-se} option followed by that argument; and the
854 second argument that does not have an associated option flag, if any, as
855 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
856 If the second argument begins with a decimal digit, @value{GDBN} will
857 first attempt to attach to it as a process, and if that fails, attempt
858 to open it as a corefile. If you have a corefile whose name begins with
859 a digit, you can prevent @value{GDBN} from treating it as a pid by
860 prefixing it with @file{./}, eg. @file{./12345}.
862 If @value{GDBN} has not been configured to included core file support,
863 such as for most embedded targets, then it will complain about a second
864 argument and ignore it.
866 Many options have both long and short forms; both are shown in the
867 following list. @value{GDBN} also recognizes the long forms if you truncate
868 them, so long as enough of the option is present to be unambiguous.
869 (If you prefer, you can flag option arguments with @samp{--} rather
870 than @samp{-}, though we illustrate the more usual convention.)
872 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
873 @c way, both those who look for -foo and --foo in the index, will find
877 @item -symbols @var{file}
879 @cindex @code{--symbols}
881 Read symbol table from file @var{file}.
883 @item -exec @var{file}
885 @cindex @code{--exec}
887 Use file @var{file} as the executable file to execute when appropriate,
888 and for examining pure data in conjunction with a core dump.
892 Read symbol table from file @var{file} and use it as the executable
895 @item -core @var{file}
897 @cindex @code{--core}
899 Use file @var{file} as a core dump to examine.
901 @item -c @var{number}
902 @item -pid @var{number}
903 @itemx -p @var{number}
906 Connect to process ID @var{number}, as with the @code{attach} command.
907 If there is no such process, @value{GDBN} will attempt to open a core
908 file named @var{number}.
910 @item -command @var{file}
912 @cindex @code{--command}
914 Execute @value{GDBN} commands from file @var{file}. @xref{Command
915 Files,, Command files}.
917 @item -directory @var{directory}
918 @itemx -d @var{directory}
919 @cindex @code{--directory}
921 Add @var{directory} to the path to search for source files.
925 @cindex @code{--mapped}
927 @emph{Warning: this option depends on operating system facilities that are not
928 supported on all systems.}@*
929 If memory-mapped files are available on your system through the @code{mmap}
930 system call, you can use this option
931 to have @value{GDBN} write the symbols from your
932 program into a reusable file in the current directory. If the program you are debugging is
933 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
934 Future @value{GDBN} debugging sessions notice the presence of this file,
935 and can quickly map in symbol information from it, rather than reading
936 the symbol table from the executable program.
938 The @file{.syms} file is specific to the host machine where @value{GDBN}
939 is run. It holds an exact image of the internal @value{GDBN} symbol
940 table. It cannot be shared across multiple host platforms.
944 @cindex @code{--readnow}
946 Read each symbol file's entire symbol table immediately, rather than
947 the default, which is to read it incrementally as it is needed.
948 This makes startup slower, but makes future operations faster.
952 You typically combine the @code{-mapped} and @code{-readnow} options in
953 order to build a @file{.syms} file that contains complete symbol
954 information. (@xref{Files,,Commands to specify files}, for information
955 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
956 but build a @file{.syms} file for future use is:
959 gdb -batch -nx -mapped -readnow programname
963 @subsection Choosing modes
965 You can run @value{GDBN} in various alternative modes---for example, in
966 batch mode or quiet mode.
973 Do not execute commands found in any initialization files. Normally,
974 @value{GDBN} executes the commands in these files after all the command
975 options and arguments have been processed. @xref{Command Files,,Command
981 @cindex @code{--quiet}
982 @cindex @code{--silent}
984 ``Quiet''. Do not print the introductory and copyright messages. These
985 messages are also suppressed in batch mode.
988 @cindex @code{--batch}
989 Run in batch mode. Exit with status @code{0} after processing all the
990 command files specified with @samp{-x} (and all commands from
991 initialization files, if not inhibited with @samp{-n}). Exit with
992 nonzero status if an error occurs in executing the @value{GDBN} commands
993 in the command files.
995 Batch mode may be useful for running @value{GDBN} as a filter, for
996 example to download and run a program on another computer; in order to
997 make this more useful, the message
1000 Program exited normally.
1004 (which is ordinarily issued whenever a program running under
1005 @value{GDBN} control terminates) is not issued when running in batch
1010 @cindex @code{--nowindows}
1012 ``No windows''. If @value{GDBN} comes with a graphical user interface
1013 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1014 interface. If no GUI is available, this option has no effect.
1018 @cindex @code{--windows}
1020 If @value{GDBN} includes a GUI, then this option requires it to be
1023 @item -cd @var{directory}
1025 Run @value{GDBN} using @var{directory} as its working directory,
1026 instead of the current directory.
1030 @cindex @code{--fullname}
1032 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1033 subprocess. It tells @value{GDBN} to output the full file name and line
1034 number in a standard, recognizable fashion each time a stack frame is
1035 displayed (which includes each time your program stops). This
1036 recognizable format looks like two @samp{\032} characters, followed by
1037 the file name, line number and character position separated by colons,
1038 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1039 @samp{\032} characters as a signal to display the source code for the
1043 @cindex @code{--epoch}
1044 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1045 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1046 routines so as to allow Epoch to display values of expressions in a
1049 @item -annotate @var{level}
1050 @cindex @code{--annotate}
1051 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1052 effect is identical to using @samp{set annotate @var{level}}
1053 (@pxref{Annotations}).
1054 Annotation level controls how much information does @value{GDBN} print
1055 together with its prompt, values of expressions, source lines, and other
1056 types of output. Level 0 is the normal, level 1 is for use when
1057 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1058 maximum annotation suitable for programs that control @value{GDBN}.
1061 @cindex @code{--async}
1062 Use the asynchronous event loop for the command-line interface.
1063 @value{GDBN} processes all events, such as user keyboard input, via a
1064 special event loop. This allows @value{GDBN} to accept and process user
1065 commands in parallel with the debugged process being
1066 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1067 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1068 suspended when the debuggee runs.}, so you don't need to wait for
1069 control to return to @value{GDBN} before you type the next command.
1070 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1071 operation is not yet in place, so @samp{-async} does not work fully
1073 @c FIXME: when the target side of the event loop is done, the above NOTE
1074 @c should be removed.
1076 When the standard input is connected to a terminal device, @value{GDBN}
1077 uses the asynchronous event loop by default, unless disabled by the
1078 @samp{-noasync} option.
1081 @cindex @code{--noasync}
1082 Disable the asynchronous event loop for the command-line interface.
1085 @cindex @code{--args}
1086 Change interpretation of command line so that arguments following the
1087 executable file are passed as command line arguments to the inferior.
1088 This option stops option processing.
1090 @item -baud @var{bps}
1092 @cindex @code{--baud}
1094 Set the line speed (baud rate or bits per second) of any serial
1095 interface used by @value{GDBN} for remote debugging.
1097 @item -tty @var{device}
1098 @itemx -t @var{device}
1099 @cindex @code{--tty}
1101 Run using @var{device} for your program's standard input and output.
1102 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1104 @c resolve the situation of these eventually
1106 @cindex @code{--tui}
1107 Activate the Terminal User Interface when starting.
1108 The Terminal User Interface manages several text windows on the terminal,
1109 showing source, assembly, registers and @value{GDBN} command outputs
1110 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1111 Do not use this option if you run @value{GDBN} from Emacs
1112 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1115 @c @cindex @code{--xdb}
1116 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1117 @c For information, see the file @file{xdb_trans.html}, which is usually
1118 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1121 @item -interpreter @var{interp}
1122 @cindex @code{--interpreter}
1123 Use the interpreter @var{interp} for interface with the controlling
1124 program or device. This option is meant to be set by programs which
1125 communicate with @value{GDBN} using it as a back end.
1127 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1128 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1129 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1130 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1133 @cindex @code{--write}
1134 Open the executable and core files for both reading and writing. This
1135 is equivalent to the @samp{set write on} command inside @value{GDBN}
1139 @cindex @code{--statistics}
1140 This option causes @value{GDBN} to print statistics about time and
1141 memory usage after it completes each command and returns to the prompt.
1144 @cindex @code{--version}
1145 This option causes @value{GDBN} to print its version number and
1146 no-warranty blurb, and exit.
1151 @section Quitting @value{GDBN}
1152 @cindex exiting @value{GDBN}
1153 @cindex leaving @value{GDBN}
1156 @kindex quit @r{[}@var{expression}@r{]}
1157 @kindex q @r{(@code{quit})}
1158 @item quit @r{[}@var{expression}@r{]}
1160 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1161 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1162 do not supply @var{expression}, @value{GDBN} will terminate normally;
1163 otherwise it will terminate using the result of @var{expression} as the
1168 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1169 terminates the action of any @value{GDBN} command that is in progress and
1170 returns to @value{GDBN} command level. It is safe to type the interrupt
1171 character at any time because @value{GDBN} does not allow it to take effect
1172 until a time when it is safe.
1174 If you have been using @value{GDBN} to control an attached process or
1175 device, you can release it with the @code{detach} command
1176 (@pxref{Attach, ,Debugging an already-running process}).
1178 @node Shell Commands
1179 @section Shell commands
1181 If you need to execute occasional shell commands during your
1182 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1183 just use the @code{shell} command.
1187 @cindex shell escape
1188 @item shell @var{command string}
1189 Invoke a standard shell to execute @var{command string}.
1190 If it exists, the environment variable @code{SHELL} determines which
1191 shell to run. Otherwise @value{GDBN} uses the default shell
1192 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1195 The utility @code{make} is often needed in development environments.
1196 You do not have to use the @code{shell} command for this purpose in
1201 @cindex calling make
1202 @item make @var{make-args}
1203 Execute the @code{make} program with the specified
1204 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1208 @chapter @value{GDBN} Commands
1210 You can abbreviate a @value{GDBN} command to the first few letters of the command
1211 name, if that abbreviation is unambiguous; and you can repeat certain
1212 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1213 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1214 show you the alternatives available, if there is more than one possibility).
1217 * Command Syntax:: How to give commands to @value{GDBN}
1218 * Completion:: Command completion
1219 * Help:: How to ask @value{GDBN} for help
1222 @node Command Syntax
1223 @section Command syntax
1225 A @value{GDBN} command is a single line of input. There is no limit on
1226 how long it can be. It starts with a command name, which is followed by
1227 arguments whose meaning depends on the command name. For example, the
1228 command @code{step} accepts an argument which is the number of times to
1229 step, as in @samp{step 5}. You can also use the @code{step} command
1230 with no arguments. Some commands do not allow any arguments.
1232 @cindex abbreviation
1233 @value{GDBN} command names may always be truncated if that abbreviation is
1234 unambiguous. Other possible command abbreviations are listed in the
1235 documentation for individual commands. In some cases, even ambiguous
1236 abbreviations are allowed; for example, @code{s} is specially defined as
1237 equivalent to @code{step} even though there are other commands whose
1238 names start with @code{s}. You can test abbreviations by using them as
1239 arguments to the @code{help} command.
1241 @cindex repeating commands
1242 @kindex RET @r{(repeat last command)}
1243 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1244 repeat the previous command. Certain commands (for example, @code{run})
1245 will not repeat this way; these are commands whose unintentional
1246 repetition might cause trouble and which you are unlikely to want to
1249 The @code{list} and @code{x} commands, when you repeat them with
1250 @key{RET}, construct new arguments rather than repeating
1251 exactly as typed. This permits easy scanning of source or memory.
1253 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1254 output, in a way similar to the common utility @code{more}
1255 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1256 @key{RET} too many in this situation, @value{GDBN} disables command
1257 repetition after any command that generates this sort of display.
1259 @kindex # @r{(a comment)}
1261 Any text from a @kbd{#} to the end of the line is a comment; it does
1262 nothing. This is useful mainly in command files (@pxref{Command
1263 Files,,Command files}).
1265 @cindex repeating command sequences
1266 @kindex C-o @r{(operate-and-get-next)}
1267 The @kbd{C-o} binding is useful for repeating a complex sequence of
1268 commands. This command accepts the current line, like @kbd{RET}, and
1269 then fetches the next line relative to the current line from the history
1273 @section Command completion
1276 @cindex word completion
1277 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1278 only one possibility; it can also show you what the valid possibilities
1279 are for the next word in a command, at any time. This works for @value{GDBN}
1280 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1282 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1283 of a word. If there is only one possibility, @value{GDBN} fills in the
1284 word, and waits for you to finish the command (or press @key{RET} to
1285 enter it). For example, if you type
1287 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1288 @c complete accuracy in these examples; space introduced for clarity.
1289 @c If texinfo enhancements make it unnecessary, it would be nice to
1290 @c replace " @key" by "@key" in the following...
1292 (@value{GDBP}) info bre @key{TAB}
1296 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1297 the only @code{info} subcommand beginning with @samp{bre}:
1300 (@value{GDBP}) info breakpoints
1304 You can either press @key{RET} at this point, to run the @code{info
1305 breakpoints} command, or backspace and enter something else, if
1306 @samp{breakpoints} does not look like the command you expected. (If you
1307 were sure you wanted @code{info breakpoints} in the first place, you
1308 might as well just type @key{RET} immediately after @samp{info bre},
1309 to exploit command abbreviations rather than command completion).
1311 If there is more than one possibility for the next word when you press
1312 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1313 characters and try again, or just press @key{TAB} a second time;
1314 @value{GDBN} displays all the possible completions for that word. For
1315 example, you might want to set a breakpoint on a subroutine whose name
1316 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1317 just sounds the bell. Typing @key{TAB} again displays all the
1318 function names in your program that begin with those characters, for
1322 (@value{GDBP}) b make_ @key{TAB}
1323 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1324 make_a_section_from_file make_environ
1325 make_abs_section make_function_type
1326 make_blockvector make_pointer_type
1327 make_cleanup make_reference_type
1328 make_command make_symbol_completion_list
1329 (@value{GDBP}) b make_
1333 After displaying the available possibilities, @value{GDBN} copies your
1334 partial input (@samp{b make_} in the example) so you can finish the
1337 If you just want to see the list of alternatives in the first place, you
1338 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1339 means @kbd{@key{META} ?}. You can type this either by holding down a
1340 key designated as the @key{META} shift on your keyboard (if there is
1341 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1343 @cindex quotes in commands
1344 @cindex completion of quoted strings
1345 Sometimes the string you need, while logically a ``word'', may contain
1346 parentheses or other characters that @value{GDBN} normally excludes from
1347 its notion of a word. To permit word completion to work in this
1348 situation, you may enclose words in @code{'} (single quote marks) in
1349 @value{GDBN} commands.
1351 The most likely situation where you might need this is in typing the
1352 name of a C@t{++} function. This is because C@t{++} allows function
1353 overloading (multiple definitions of the same function, distinguished
1354 by argument type). For example, when you want to set a breakpoint you
1355 may need to distinguish whether you mean the version of @code{name}
1356 that takes an @code{int} parameter, @code{name(int)}, or the version
1357 that takes a @code{float} parameter, @code{name(float)}. To use the
1358 word-completion facilities in this situation, type a single quote
1359 @code{'} at the beginning of the function name. This alerts
1360 @value{GDBN} that it may need to consider more information than usual
1361 when you press @key{TAB} or @kbd{M-?} to request word completion:
1364 (@value{GDBP}) b 'bubble( @kbd{M-?}
1365 bubble(double,double) bubble(int,int)
1366 (@value{GDBP}) b 'bubble(
1369 In some cases, @value{GDBN} can tell that completing a name requires using
1370 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1371 completing as much as it can) if you do not type the quote in the first
1375 (@value{GDBP}) b bub @key{TAB}
1376 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1377 (@value{GDBP}) b 'bubble(
1381 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1382 you have not yet started typing the argument list when you ask for
1383 completion on an overloaded symbol.
1385 For more information about overloaded functions, see @ref{C plus plus
1386 expressions, ,C@t{++} expressions}. You can use the command @code{set
1387 overload-resolution off} to disable overload resolution;
1388 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1392 @section Getting help
1393 @cindex online documentation
1396 You can always ask @value{GDBN} itself for information on its commands,
1397 using the command @code{help}.
1400 @kindex h @r{(@code{help})}
1403 You can use @code{help} (abbreviated @code{h}) with no arguments to
1404 display a short list of named classes of commands:
1408 List of classes of commands:
1410 aliases -- Aliases of other commands
1411 breakpoints -- Making program stop at certain points
1412 data -- Examining data
1413 files -- Specifying and examining files
1414 internals -- Maintenance commands
1415 obscure -- Obscure features
1416 running -- Running the program
1417 stack -- Examining the stack
1418 status -- Status inquiries
1419 support -- Support facilities
1420 tracepoints -- Tracing of program execution without@*
1421 stopping the program
1422 user-defined -- User-defined commands
1424 Type "help" followed by a class name for a list of
1425 commands in that class.
1426 Type "help" followed by command name for full
1428 Command name abbreviations are allowed if unambiguous.
1431 @c the above line break eliminates huge line overfull...
1433 @item help @var{class}
1434 Using one of the general help classes as an argument, you can get a
1435 list of the individual commands in that class. For example, here is the
1436 help display for the class @code{status}:
1439 (@value{GDBP}) help status
1444 @c Line break in "show" line falsifies real output, but needed
1445 @c to fit in smallbook page size.
1446 info -- Generic command for showing things
1447 about the program being debugged
1448 show -- Generic command for showing things
1451 Type "help" followed by command name for full
1453 Command name abbreviations are allowed if unambiguous.
1457 @item help @var{command}
1458 With a command name as @code{help} argument, @value{GDBN} displays a
1459 short paragraph on how to use that command.
1462 @item apropos @var{args}
1463 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1464 commands, and their documentation, for the regular expression specified in
1465 @var{args}. It prints out all matches found. For example:
1476 set symbol-reloading -- Set dynamic symbol table reloading
1477 multiple times in one run
1478 show symbol-reloading -- Show dynamic symbol table reloading
1479 multiple times in one run
1484 @item complete @var{args}
1485 The @code{complete @var{args}} command lists all the possible completions
1486 for the beginning of a command. Use @var{args} to specify the beginning of the
1487 command you want completed. For example:
1493 @noindent results in:
1504 @noindent This is intended for use by @sc{gnu} Emacs.
1507 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1508 and @code{show} to inquire about the state of your program, or the state
1509 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1510 manual introduces each of them in the appropriate context. The listings
1511 under @code{info} and under @code{show} in the Index point to
1512 all the sub-commands. @xref{Index}.
1517 @kindex i @r{(@code{info})}
1519 This command (abbreviated @code{i}) is for describing the state of your
1520 program. For example, you can list the arguments given to your program
1521 with @code{info args}, list the registers currently in use with @code{info
1522 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1523 You can get a complete list of the @code{info} sub-commands with
1524 @w{@code{help info}}.
1528 You can assign the result of an expression to an environment variable with
1529 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1530 @code{set prompt $}.
1534 In contrast to @code{info}, @code{show} is for describing the state of
1535 @value{GDBN} itself.
1536 You can change most of the things you can @code{show}, by using the
1537 related command @code{set}; for example, you can control what number
1538 system is used for displays with @code{set radix}, or simply inquire
1539 which is currently in use with @code{show radix}.
1542 To display all the settable parameters and their current
1543 values, you can use @code{show} with no arguments; you may also use
1544 @code{info set}. Both commands produce the same display.
1545 @c FIXME: "info set" violates the rule that "info" is for state of
1546 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1547 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1551 Here are three miscellaneous @code{show} subcommands, all of which are
1552 exceptional in lacking corresponding @code{set} commands:
1555 @kindex show version
1556 @cindex version number
1558 Show what version of @value{GDBN} is running. You should include this
1559 information in @value{GDBN} bug-reports. If multiple versions of
1560 @value{GDBN} are in use at your site, you may need to determine which
1561 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1562 commands are introduced, and old ones may wither away. Also, many
1563 system vendors ship variant versions of @value{GDBN}, and there are
1564 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1565 The version number is the same as the one announced when you start
1568 @kindex show copying
1570 Display information about permission for copying @value{GDBN}.
1572 @kindex show warranty
1574 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1575 if your version of @value{GDBN} comes with one.
1580 @chapter Running Programs Under @value{GDBN}
1582 When you run a program under @value{GDBN}, you must first generate
1583 debugging information when you compile it.
1585 You may start @value{GDBN} with its arguments, if any, in an environment
1586 of your choice. If you are doing native debugging, you may redirect
1587 your program's input and output, debug an already running process, or
1588 kill a child process.
1591 * Compilation:: Compiling for debugging
1592 * Starting:: Starting your program
1593 * Arguments:: Your program's arguments
1594 * Environment:: Your program's environment
1596 * Working Directory:: Your program's working directory
1597 * Input/Output:: Your program's input and output
1598 * Attach:: Debugging an already-running process
1599 * Kill Process:: Killing the child process
1601 * Threads:: Debugging programs with multiple threads
1602 * Processes:: Debugging programs with multiple processes
1606 @section Compiling for debugging
1608 In order to debug a program effectively, you need to generate
1609 debugging information when you compile it. This debugging information
1610 is stored in the object file; it describes the data type of each
1611 variable or function and the correspondence between source line numbers
1612 and addresses in the executable code.
1614 To request debugging information, specify the @samp{-g} option when you run
1617 Most compilers do not include information about preprocessor macros in
1618 the debugging information if you specify the @option{-g} flag alone,
1619 because this information is rather large. Version 3.1 of @value{NGCC},
1620 the @sc{gnu} C compiler, provides macro information if you specify the
1621 options @option{-gdwarf-2} and @option{-g3}; the former option requests
1622 debugging information in the Dwarf 2 format, and the latter requests
1623 ``extra information''. In the future, we hope to find more compact ways
1624 to represent macro information, so that it can be included with
1627 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1628 options together. Using those compilers, you cannot generate optimized
1629 executables containing debugging information.
1631 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1632 without @samp{-O}, making it possible to debug optimized code. We
1633 recommend that you @emph{always} use @samp{-g} whenever you compile a
1634 program. You may think your program is correct, but there is no sense
1635 in pushing your luck.
1637 @cindex optimized code, debugging
1638 @cindex debugging optimized code
1639 When you debug a program compiled with @samp{-g -O}, remember that the
1640 optimizer is rearranging your code; the debugger shows you what is
1641 really there. Do not be too surprised when the execution path does not
1642 exactly match your source file! An extreme example: if you define a
1643 variable, but never use it, @value{GDBN} never sees that
1644 variable---because the compiler optimizes it out of existence.
1646 Some things do not work as well with @samp{-g -O} as with just
1647 @samp{-g}, particularly on machines with instruction scheduling. If in
1648 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1649 please report it to us as a bug (including a test case!).
1651 Older versions of the @sc{gnu} C compiler permitted a variant option
1652 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1653 format; if your @sc{gnu} C compiler has this option, do not use it.
1657 @section Starting your program
1663 @kindex r @r{(@code{run})}
1666 Use the @code{run} command to start your program under @value{GDBN}.
1667 You must first specify the program name (except on VxWorks) with an
1668 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1669 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1670 (@pxref{Files, ,Commands to specify files}).
1674 If you are running your program in an execution environment that
1675 supports processes, @code{run} creates an inferior process and makes
1676 that process run your program. (In environments without processes,
1677 @code{run} jumps to the start of your program.)
1679 The execution of a program is affected by certain information it
1680 receives from its superior. @value{GDBN} provides ways to specify this
1681 information, which you must do @emph{before} starting your program. (You
1682 can change it after starting your program, but such changes only affect
1683 your program the next time you start it.) This information may be
1684 divided into four categories:
1687 @item The @emph{arguments.}
1688 Specify the arguments to give your program as the arguments of the
1689 @code{run} command. If a shell is available on your target, the shell
1690 is used to pass the arguments, so that you may use normal conventions
1691 (such as wildcard expansion or variable substitution) in describing
1693 In Unix systems, you can control which shell is used with the
1694 @code{SHELL} environment variable.
1695 @xref{Arguments, ,Your program's arguments}.
1697 @item The @emph{environment.}
1698 Your program normally inherits its environment from @value{GDBN}, but you can
1699 use the @value{GDBN} commands @code{set environment} and @code{unset
1700 environment} to change parts of the environment that affect
1701 your program. @xref{Environment, ,Your program's environment}.
1703 @item The @emph{working directory.}
1704 Your program inherits its working directory from @value{GDBN}. You can set
1705 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1706 @xref{Working Directory, ,Your program's working directory}.
1708 @item The @emph{standard input and output.}
1709 Your program normally uses the same device for standard input and
1710 standard output as @value{GDBN} is using. You can redirect input and output
1711 in the @code{run} command line, or you can use the @code{tty} command to
1712 set a different device for your program.
1713 @xref{Input/Output, ,Your program's input and output}.
1716 @emph{Warning:} While input and output redirection work, you cannot use
1717 pipes to pass the output of the program you are debugging to another
1718 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1722 When you issue the @code{run} command, your program begins to execute
1723 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1724 of how to arrange for your program to stop. Once your program has
1725 stopped, you may call functions in your program, using the @code{print}
1726 or @code{call} commands. @xref{Data, ,Examining Data}.
1728 If the modification time of your symbol file has changed since the last
1729 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1730 table, and reads it again. When it does this, @value{GDBN} tries to retain
1731 your current breakpoints.
1734 @section Your program's arguments
1736 @cindex arguments (to your program)
1737 The arguments to your program can be specified by the arguments of the
1739 They are passed to a shell, which expands wildcard characters and
1740 performs redirection of I/O, and thence to your program. Your
1741 @code{SHELL} environment variable (if it exists) specifies what shell
1742 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1743 the default shell (@file{/bin/sh} on Unix).
1745 On non-Unix systems, the program is usually invoked directly by
1746 @value{GDBN}, which emulates I/O redirection via the appropriate system
1747 calls, and the wildcard characters are expanded by the startup code of
1748 the program, not by the shell.
1750 @code{run} with no arguments uses the same arguments used by the previous
1751 @code{run}, or those set by the @code{set args} command.
1756 Specify the arguments to be used the next time your program is run. If
1757 @code{set args} has no arguments, @code{run} executes your program
1758 with no arguments. Once you have run your program with arguments,
1759 using @code{set args} before the next @code{run} is the only way to run
1760 it again without arguments.
1764 Show the arguments to give your program when it is started.
1768 @section Your program's environment
1770 @cindex environment (of your program)
1771 The @dfn{environment} consists of a set of environment variables and
1772 their values. Environment variables conventionally record such things as
1773 your user name, your home directory, your terminal type, and your search
1774 path for programs to run. Usually you set up environment variables with
1775 the shell and they are inherited by all the other programs you run. When
1776 debugging, it can be useful to try running your program with a modified
1777 environment without having to start @value{GDBN} over again.
1781 @item path @var{directory}
1782 Add @var{directory} to the front of the @code{PATH} environment variable
1783 (the search path for executables) that will be passed to your program.
1784 The value of @code{PATH} used by @value{GDBN} does not change.
1785 You may specify several directory names, separated by whitespace or by a
1786 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1787 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1788 is moved to the front, so it is searched sooner.
1790 You can use the string @samp{$cwd} to refer to whatever is the current
1791 working directory at the time @value{GDBN} searches the path. If you
1792 use @samp{.} instead, it refers to the directory where you executed the
1793 @code{path} command. @value{GDBN} replaces @samp{.} in the
1794 @var{directory} argument (with the current path) before adding
1795 @var{directory} to the search path.
1796 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1797 @c document that, since repeating it would be a no-op.
1801 Display the list of search paths for executables (the @code{PATH}
1802 environment variable).
1804 @kindex show environment
1805 @item show environment @r{[}@var{varname}@r{]}
1806 Print the value of environment variable @var{varname} to be given to
1807 your program when it starts. If you do not supply @var{varname},
1808 print the names and values of all environment variables to be given to
1809 your program. You can abbreviate @code{environment} as @code{env}.
1811 @kindex set environment
1812 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1813 Set environment variable @var{varname} to @var{value}. The value
1814 changes for your program only, not for @value{GDBN} itself. @var{value} may
1815 be any string; the values of environment variables are just strings, and
1816 any interpretation is supplied by your program itself. The @var{value}
1817 parameter is optional; if it is eliminated, the variable is set to a
1819 @c "any string" here does not include leading, trailing
1820 @c blanks. Gnu asks: does anyone care?
1822 For example, this command:
1829 tells the debugged program, when subsequently run, that its user is named
1830 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1831 are not actually required.)
1833 @kindex unset environment
1834 @item unset environment @var{varname}
1835 Remove variable @var{varname} from the environment to be passed to your
1836 program. This is different from @samp{set env @var{varname} =};
1837 @code{unset environment} removes the variable from the environment,
1838 rather than assigning it an empty value.
1841 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1843 by your @code{SHELL} environment variable if it exists (or
1844 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1845 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1846 @file{.bashrc} for BASH---any variables you set in that file affect
1847 your program. You may wish to move setting of environment variables to
1848 files that are only run when you sign on, such as @file{.login} or
1851 @node Working Directory
1852 @section Your program's working directory
1854 @cindex working directory (of your program)
1855 Each time you start your program with @code{run}, it inherits its
1856 working directory from the current working directory of @value{GDBN}.
1857 The @value{GDBN} working directory is initially whatever it inherited
1858 from its parent process (typically the shell), but you can specify a new
1859 working directory in @value{GDBN} with the @code{cd} command.
1861 The @value{GDBN} working directory also serves as a default for the commands
1862 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1867 @item cd @var{directory}
1868 Set the @value{GDBN} working directory to @var{directory}.
1872 Print the @value{GDBN} working directory.
1876 @section Your program's input and output
1881 By default, the program you run under @value{GDBN} does input and output to
1882 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1883 to its own terminal modes to interact with you, but it records the terminal
1884 modes your program was using and switches back to them when you continue
1885 running your program.
1888 @kindex info terminal
1890 Displays information recorded by @value{GDBN} about the terminal modes your
1894 You can redirect your program's input and/or output using shell
1895 redirection with the @code{run} command. For example,
1902 starts your program, diverting its output to the file @file{outfile}.
1905 @cindex controlling terminal
1906 Another way to specify where your program should do input and output is
1907 with the @code{tty} command. This command accepts a file name as
1908 argument, and causes this file to be the default for future @code{run}
1909 commands. It also resets the controlling terminal for the child
1910 process, for future @code{run} commands. For example,
1917 directs that processes started with subsequent @code{run} commands
1918 default to do input and output on the terminal @file{/dev/ttyb} and have
1919 that as their controlling terminal.
1921 An explicit redirection in @code{run} overrides the @code{tty} command's
1922 effect on the input/output device, but not its effect on the controlling
1925 When you use the @code{tty} command or redirect input in the @code{run}
1926 command, only the input @emph{for your program} is affected. The input
1927 for @value{GDBN} still comes from your terminal.
1930 @section Debugging an already-running process
1935 @item attach @var{process-id}
1936 This command attaches to a running process---one that was started
1937 outside @value{GDBN}. (@code{info files} shows your active
1938 targets.) The command takes as argument a process ID. The usual way to
1939 find out the process-id of a Unix process is with the @code{ps} utility,
1940 or with the @samp{jobs -l} shell command.
1942 @code{attach} does not repeat if you press @key{RET} a second time after
1943 executing the command.
1946 To use @code{attach}, your program must be running in an environment
1947 which supports processes; for example, @code{attach} does not work for
1948 programs on bare-board targets that lack an operating system. You must
1949 also have permission to send the process a signal.
1951 When you use @code{attach}, the debugger finds the program running in
1952 the process first by looking in the current working directory, then (if
1953 the program is not found) by using the source file search path
1954 (@pxref{Source Path, ,Specifying source directories}). You can also use
1955 the @code{file} command to load the program. @xref{Files, ,Commands to
1958 The first thing @value{GDBN} does after arranging to debug the specified
1959 process is to stop it. You can examine and modify an attached process
1960 with all the @value{GDBN} commands that are ordinarily available when
1961 you start processes with @code{run}. You can insert breakpoints; you
1962 can step and continue; you can modify storage. If you would rather the
1963 process continue running, you may use the @code{continue} command after
1964 attaching @value{GDBN} to the process.
1969 When you have finished debugging the attached process, you can use the
1970 @code{detach} command to release it from @value{GDBN} control. Detaching
1971 the process continues its execution. After the @code{detach} command,
1972 that process and @value{GDBN} become completely independent once more, and you
1973 are ready to @code{attach} another process or start one with @code{run}.
1974 @code{detach} does not repeat if you press @key{RET} again after
1975 executing the command.
1978 If you exit @value{GDBN} or use the @code{run} command while you have an
1979 attached process, you kill that process. By default, @value{GDBN} asks
1980 for confirmation if you try to do either of these things; you can
1981 control whether or not you need to confirm by using the @code{set
1982 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1986 @section Killing the child process
1991 Kill the child process in which your program is running under @value{GDBN}.
1994 This command is useful if you wish to debug a core dump instead of a
1995 running process. @value{GDBN} ignores any core dump file while your program
1998 On some operating systems, a program cannot be executed outside @value{GDBN}
1999 while you have breakpoints set on it inside @value{GDBN}. You can use the
2000 @code{kill} command in this situation to permit running your program
2001 outside the debugger.
2003 The @code{kill} command is also useful if you wish to recompile and
2004 relink your program, since on many systems it is impossible to modify an
2005 executable file while it is running in a process. In this case, when you
2006 next type @code{run}, @value{GDBN} notices that the file has changed, and
2007 reads the symbol table again (while trying to preserve your current
2008 breakpoint settings).
2011 @section Debugging programs with multiple threads
2013 @cindex threads of execution
2014 @cindex multiple threads
2015 @cindex switching threads
2016 In some operating systems, such as HP-UX and Solaris, a single program
2017 may have more than one @dfn{thread} of execution. The precise semantics
2018 of threads differ from one operating system to another, but in general
2019 the threads of a single program are akin to multiple processes---except
2020 that they share one address space (that is, they can all examine and
2021 modify the same variables). On the other hand, each thread has its own
2022 registers and execution stack, and perhaps private memory.
2024 @value{GDBN} provides these facilities for debugging multi-thread
2028 @item automatic notification of new threads
2029 @item @samp{thread @var{threadno}}, a command to switch among threads
2030 @item @samp{info threads}, a command to inquire about existing threads
2031 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2032 a command to apply a command to a list of threads
2033 @item thread-specific breakpoints
2037 @emph{Warning:} These facilities are not yet available on every
2038 @value{GDBN} configuration where the operating system supports threads.
2039 If your @value{GDBN} does not support threads, these commands have no
2040 effect. For example, a system without thread support shows no output
2041 from @samp{info threads}, and always rejects the @code{thread} command,
2045 (@value{GDBP}) info threads
2046 (@value{GDBP}) thread 1
2047 Thread ID 1 not known. Use the "info threads" command to
2048 see the IDs of currently known threads.
2050 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2051 @c doesn't support threads"?
2054 @cindex focus of debugging
2055 @cindex current thread
2056 The @value{GDBN} thread debugging facility allows you to observe all
2057 threads while your program runs---but whenever @value{GDBN} takes
2058 control, one thread in particular is always the focus of debugging.
2059 This thread is called the @dfn{current thread}. Debugging commands show
2060 program information from the perspective of the current thread.
2062 @cindex @code{New} @var{systag} message
2063 @cindex thread identifier (system)
2064 @c FIXME-implementors!! It would be more helpful if the [New...] message
2065 @c included GDB's numeric thread handle, so you could just go to that
2066 @c thread without first checking `info threads'.
2067 Whenever @value{GDBN} detects a new thread in your program, it displays
2068 the target system's identification for the thread with a message in the
2069 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2070 whose form varies depending on the particular system. For example, on
2071 LynxOS, you might see
2074 [New process 35 thread 27]
2078 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2079 the @var{systag} is simply something like @samp{process 368}, with no
2082 @c FIXME!! (1) Does the [New...] message appear even for the very first
2083 @c thread of a program, or does it only appear for the
2084 @c second---i.e.@: when it becomes obvious we have a multithread
2086 @c (2) *Is* there necessarily a first thread always? Or do some
2087 @c multithread systems permit starting a program with multiple
2088 @c threads ab initio?
2090 @cindex thread number
2091 @cindex thread identifier (GDB)
2092 For debugging purposes, @value{GDBN} associates its own thread
2093 number---always a single integer---with each thread in your program.
2096 @kindex info threads
2098 Display a summary of all threads currently in your
2099 program. @value{GDBN} displays for each thread (in this order):
2102 @item the thread number assigned by @value{GDBN}
2104 @item the target system's thread identifier (@var{systag})
2106 @item the current stack frame summary for that thread
2110 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2111 indicates the current thread.
2115 @c end table here to get a little more width for example
2118 (@value{GDBP}) info threads
2119 3 process 35 thread 27 0x34e5 in sigpause ()
2120 2 process 35 thread 23 0x34e5 in sigpause ()
2121 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2127 @cindex thread number
2128 @cindex thread identifier (GDB)
2129 For debugging purposes, @value{GDBN} associates its own thread
2130 number---a small integer assigned in thread-creation order---with each
2131 thread in your program.
2133 @cindex @code{New} @var{systag} message, on HP-UX
2134 @cindex thread identifier (system), on HP-UX
2135 @c FIXME-implementors!! It would be more helpful if the [New...] message
2136 @c included GDB's numeric thread handle, so you could just go to that
2137 @c thread without first checking `info threads'.
2138 Whenever @value{GDBN} detects a new thread in your program, it displays
2139 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2140 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2141 whose form varies depending on the particular system. For example, on
2145 [New thread 2 (system thread 26594)]
2149 when @value{GDBN} notices a new thread.
2152 @kindex info threads
2154 Display a summary of all threads currently in your
2155 program. @value{GDBN} displays for each thread (in this order):
2158 @item the thread number assigned by @value{GDBN}
2160 @item the target system's thread identifier (@var{systag})
2162 @item the current stack frame summary for that thread
2166 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2167 indicates the current thread.
2171 @c end table here to get a little more width for example
2174 (@value{GDBP}) info threads
2175 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2177 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2178 from /usr/lib/libc.2
2179 1 system thread 27905 0x7b003498 in _brk () \@*
2180 from /usr/lib/libc.2
2184 @kindex thread @var{threadno}
2185 @item thread @var{threadno}
2186 Make thread number @var{threadno} the current thread. The command
2187 argument @var{threadno} is the internal @value{GDBN} thread number, as
2188 shown in the first field of the @samp{info threads} display.
2189 @value{GDBN} responds by displaying the system identifier of the thread
2190 you selected, and its current stack frame summary:
2193 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2194 (@value{GDBP}) thread 2
2195 [Switching to process 35 thread 23]
2196 0x34e5 in sigpause ()
2200 As with the @samp{[New @dots{}]} message, the form of the text after
2201 @samp{Switching to} depends on your system's conventions for identifying
2204 @kindex thread apply
2205 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2206 The @code{thread apply} command allows you to apply a command to one or
2207 more threads. Specify the numbers of the threads that you want affected
2208 with the command argument @var{threadno}. @var{threadno} is the internal
2209 @value{GDBN} thread number, as shown in the first field of the @samp{info
2210 threads} display. To apply a command to all threads, use
2211 @code{thread apply all} @var{args}.
2214 @cindex automatic thread selection
2215 @cindex switching threads automatically
2216 @cindex threads, automatic switching
2217 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2218 signal, it automatically selects the thread where that breakpoint or
2219 signal happened. @value{GDBN} alerts you to the context switch with a
2220 message of the form @samp{[Switching to @var{systag}]} to identify the
2223 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2224 more information about how @value{GDBN} behaves when you stop and start
2225 programs with multiple threads.
2227 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2228 watchpoints in programs with multiple threads.
2231 @section Debugging programs with multiple processes
2233 @cindex fork, debugging programs which call
2234 @cindex multiple processes
2235 @cindex processes, multiple
2236 On most systems, @value{GDBN} has no special support for debugging
2237 programs which create additional processes using the @code{fork}
2238 function. When a program forks, @value{GDBN} will continue to debug the
2239 parent process and the child process will run unimpeded. If you have
2240 set a breakpoint in any code which the child then executes, the child
2241 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2242 will cause it to terminate.
2244 However, if you want to debug the child process there is a workaround
2245 which isn't too painful. Put a call to @code{sleep} in the code which
2246 the child process executes after the fork. It may be useful to sleep
2247 only if a certain environment variable is set, or a certain file exists,
2248 so that the delay need not occur when you don't want to run @value{GDBN}
2249 on the child. While the child is sleeping, use the @code{ps} program to
2250 get its process ID. Then tell @value{GDBN} (a new invocation of
2251 @value{GDBN} if you are also debugging the parent process) to attach to
2252 the child process (@pxref{Attach}). From that point on you can debug
2253 the child process just like any other process which you attached to.
2255 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2256 debugging programs that create additional processes using the
2257 @code{fork} or @code{vfork} function.
2259 By default, when a program forks, @value{GDBN} will continue to debug
2260 the parent process and the child process will run unimpeded.
2262 If you want to follow the child process instead of the parent process,
2263 use the command @w{@code{set follow-fork-mode}}.
2266 @kindex set follow-fork-mode
2267 @item set follow-fork-mode @var{mode}
2268 Set the debugger response to a program call of @code{fork} or
2269 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2270 process. The @var{mode} can be:
2274 The original process is debugged after a fork. The child process runs
2275 unimpeded. This is the default.
2278 The new process is debugged after a fork. The parent process runs
2282 The debugger will ask for one of the above choices.
2285 @item show follow-fork-mode
2286 Display the current debugger response to a @code{fork} or @code{vfork} call.
2289 If you ask to debug a child process and a @code{vfork} is followed by an
2290 @code{exec}, @value{GDBN} executes the new target up to the first
2291 breakpoint in the new target. If you have a breakpoint set on
2292 @code{main} in your original program, the breakpoint will also be set on
2293 the child process's @code{main}.
2295 When a child process is spawned by @code{vfork}, you cannot debug the
2296 child or parent until an @code{exec} call completes.
2298 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2299 call executes, the new target restarts. To restart the parent process,
2300 use the @code{file} command with the parent executable name as its
2303 You can use the @code{catch} command to make @value{GDBN} stop whenever
2304 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2305 Catchpoints, ,Setting catchpoints}.
2308 @chapter Stopping and Continuing
2310 The principal purposes of using a debugger are so that you can stop your
2311 program before it terminates; or so that, if your program runs into
2312 trouble, you can investigate and find out why.
2314 Inside @value{GDBN}, your program may stop for any of several reasons,
2315 such as a signal, a breakpoint, or reaching a new line after a
2316 @value{GDBN} command such as @code{step}. You may then examine and
2317 change variables, set new breakpoints or remove old ones, and then
2318 continue execution. Usually, the messages shown by @value{GDBN} provide
2319 ample explanation of the status of your program---but you can also
2320 explicitly request this information at any time.
2323 @kindex info program
2325 Display information about the status of your program: whether it is
2326 running or not, what process it is, and why it stopped.
2330 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2331 * Continuing and Stepping:: Resuming execution
2333 * Thread Stops:: Stopping and starting multi-thread programs
2337 @section Breakpoints, watchpoints, and catchpoints
2340 A @dfn{breakpoint} makes your program stop whenever a certain point in
2341 the program is reached. For each breakpoint, you can add conditions to
2342 control in finer detail whether your program stops. You can set
2343 breakpoints with the @code{break} command and its variants (@pxref{Set
2344 Breaks, ,Setting breakpoints}), to specify the place where your program
2345 should stop by line number, function name or exact address in the
2348 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2349 breakpoints in shared libraries before the executable is run. There is
2350 a minor limitation on HP-UX systems: you must wait until the executable
2351 is run in order to set breakpoints in shared library routines that are
2352 not called directly by the program (for example, routines that are
2353 arguments in a @code{pthread_create} call).
2356 @cindex memory tracing
2357 @cindex breakpoint on memory address
2358 @cindex breakpoint on variable modification
2359 A @dfn{watchpoint} is a special breakpoint that stops your program
2360 when the value of an expression changes. You must use a different
2361 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2362 watchpoints}), but aside from that, you can manage a watchpoint like
2363 any other breakpoint: you enable, disable, and delete both breakpoints
2364 and watchpoints using the same commands.
2366 You can arrange to have values from your program displayed automatically
2367 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2371 @cindex breakpoint on events
2372 A @dfn{catchpoint} is another special breakpoint that stops your program
2373 when a certain kind of event occurs, such as the throwing of a C@t{++}
2374 exception or the loading of a library. As with watchpoints, you use a
2375 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2376 catchpoints}), but aside from that, you can manage a catchpoint like any
2377 other breakpoint. (To stop when your program receives a signal, use the
2378 @code{handle} command; see @ref{Signals, ,Signals}.)
2380 @cindex breakpoint numbers
2381 @cindex numbers for breakpoints
2382 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2383 catchpoint when you create it; these numbers are successive integers
2384 starting with one. In many of the commands for controlling various
2385 features of breakpoints you use the breakpoint number to say which
2386 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2387 @dfn{disabled}; if disabled, it has no effect on your program until you
2390 @cindex breakpoint ranges
2391 @cindex ranges of breakpoints
2392 Some @value{GDBN} commands accept a range of breakpoints on which to
2393 operate. A breakpoint range is either a single breakpoint number, like
2394 @samp{5}, or two such numbers, in increasing order, separated by a
2395 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2396 all breakpoint in that range are operated on.
2399 * Set Breaks:: Setting breakpoints
2400 * Set Watchpoints:: Setting watchpoints
2401 * Set Catchpoints:: Setting catchpoints
2402 * Delete Breaks:: Deleting breakpoints
2403 * Disabling:: Disabling breakpoints
2404 * Conditions:: Break conditions
2405 * Break Commands:: Breakpoint command lists
2406 * Breakpoint Menus:: Breakpoint menus
2407 * Error in Breakpoints:: ``Cannot insert breakpoints''
2411 @subsection Setting breakpoints
2413 @c FIXME LMB what does GDB do if no code on line of breakpt?
2414 @c consider in particular declaration with/without initialization.
2416 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2419 @kindex b @r{(@code{break})}
2420 @vindex $bpnum@r{, convenience variable}
2421 @cindex latest breakpoint
2422 Breakpoints are set with the @code{break} command (abbreviated
2423 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2424 number of the breakpoint you've set most recently; see @ref{Convenience
2425 Vars,, Convenience variables}, for a discussion of what you can do with
2426 convenience variables.
2428 You have several ways to say where the breakpoint should go.
2431 @item break @var{function}
2432 Set a breakpoint at entry to function @var{function}.
2433 When using source languages that permit overloading of symbols, such as
2434 C@t{++}, @var{function} may refer to more than one possible place to break.
2435 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2437 @item break +@var{offset}
2438 @itemx break -@var{offset}
2439 Set a breakpoint some number of lines forward or back from the position
2440 at which execution stopped in the currently selected @dfn{stack frame}.
2441 (@xref{Frames, ,Frames}, for a description of stack frames.)
2443 @item break @var{linenum}
2444 Set a breakpoint at line @var{linenum} in the current source file.
2445 The current source file is the last file whose source text was printed.
2446 The breakpoint will stop your program just before it executes any of the
2449 @item break @var{filename}:@var{linenum}
2450 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2452 @item break @var{filename}:@var{function}
2453 Set a breakpoint at entry to function @var{function} found in file
2454 @var{filename}. Specifying a file name as well as a function name is
2455 superfluous except when multiple files contain similarly named
2458 @item break *@var{address}
2459 Set a breakpoint at address @var{address}. You can use this to set
2460 breakpoints in parts of your program which do not have debugging
2461 information or source files.
2464 When called without any arguments, @code{break} sets a breakpoint at
2465 the next instruction to be executed in the selected stack frame
2466 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2467 innermost, this makes your program stop as soon as control
2468 returns to that frame. This is similar to the effect of a
2469 @code{finish} command in the frame inside the selected frame---except
2470 that @code{finish} does not leave an active breakpoint. If you use
2471 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2472 the next time it reaches the current location; this may be useful
2475 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2476 least one instruction has been executed. If it did not do this, you
2477 would be unable to proceed past a breakpoint without first disabling the
2478 breakpoint. This rule applies whether or not the breakpoint already
2479 existed when your program stopped.
2481 @item break @dots{} if @var{cond}
2482 Set a breakpoint with condition @var{cond}; evaluate the expression
2483 @var{cond} each time the breakpoint is reached, and stop only if the
2484 value is nonzero---that is, if @var{cond} evaluates as true.
2485 @samp{@dots{}} stands for one of the possible arguments described
2486 above (or no argument) specifying where to break. @xref{Conditions,
2487 ,Break conditions}, for more information on breakpoint conditions.
2490 @item tbreak @var{args}
2491 Set a breakpoint enabled only for one stop. @var{args} are the
2492 same as for the @code{break} command, and the breakpoint is set in the same
2493 way, but the breakpoint is automatically deleted after the first time your
2494 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2497 @item hbreak @var{args}
2498 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2499 @code{break} command and the breakpoint is set in the same way, but the
2500 breakpoint requires hardware support and some target hardware may not
2501 have this support. The main purpose of this is EPROM/ROM code
2502 debugging, so you can set a breakpoint at an instruction without
2503 changing the instruction. This can be used with the new trap-generation
2504 provided by SPARClite DSU and some x86-based targets. These targets
2505 will generate traps when a program accesses some data or instruction
2506 address that is assigned to the debug registers. However the hardware
2507 breakpoint registers can take a limited number of breakpoints. For
2508 example, on the DSU, only two data breakpoints can be set at a time, and
2509 @value{GDBN} will reject this command if more than two are used. Delete
2510 or disable unused hardware breakpoints before setting new ones
2511 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2514 @item thbreak @var{args}
2515 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2516 are the same as for the @code{hbreak} command and the breakpoint is set in
2517 the same way. However, like the @code{tbreak} command,
2518 the breakpoint is automatically deleted after the
2519 first time your program stops there. Also, like the @code{hbreak}
2520 command, the breakpoint requires hardware support and some target hardware
2521 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2522 See also @ref{Conditions, ,Break conditions}.
2525 @cindex regular expression
2526 @item rbreak @var{regex}
2527 Set breakpoints on all functions matching the regular expression
2528 @var{regex}. This command sets an unconditional breakpoint on all
2529 matches, printing a list of all breakpoints it set. Once these
2530 breakpoints are set, they are treated just like the breakpoints set with
2531 the @code{break} command. You can delete them, disable them, or make
2532 them conditional the same way as any other breakpoint.
2534 The syntax of the regular expression is the standard one used with tools
2535 like @file{grep}. Note that this is different from the syntax used by
2536 shells, so for instance @code{foo*} matches all functions that include
2537 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2538 @code{.*} leading and trailing the regular expression you supply, so to
2539 match only functions that begin with @code{foo}, use @code{^foo}.
2541 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2542 breakpoints on overloaded functions that are not members of any special
2545 @kindex info breakpoints
2546 @cindex @code{$_} and @code{info breakpoints}
2547 @item info breakpoints @r{[}@var{n}@r{]}
2548 @itemx info break @r{[}@var{n}@r{]}
2549 @itemx info watchpoints @r{[}@var{n}@r{]}
2550 Print a table of all breakpoints, watchpoints, and catchpoints set and
2551 not deleted, with the following columns for each breakpoint:
2554 @item Breakpoint Numbers
2556 Breakpoint, watchpoint, or catchpoint.
2558 Whether the breakpoint is marked to be disabled or deleted when hit.
2559 @item Enabled or Disabled
2560 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2561 that are not enabled.
2563 Where the breakpoint is in your program, as a memory address.
2565 Where the breakpoint is in the source for your program, as a file and
2570 If a breakpoint is conditional, @code{info break} shows the condition on
2571 the line following the affected breakpoint; breakpoint commands, if any,
2572 are listed after that.
2575 @code{info break} with a breakpoint
2576 number @var{n} as argument lists only that breakpoint. The
2577 convenience variable @code{$_} and the default examining-address for
2578 the @code{x} command are set to the address of the last breakpoint
2579 listed (@pxref{Memory, ,Examining memory}).
2582 @code{info break} displays a count of the number of times the breakpoint
2583 has been hit. This is especially useful in conjunction with the
2584 @code{ignore} command. You can ignore a large number of breakpoint
2585 hits, look at the breakpoint info to see how many times the breakpoint
2586 was hit, and then run again, ignoring one less than that number. This
2587 will get you quickly to the last hit of that breakpoint.
2590 @value{GDBN} allows you to set any number of breakpoints at the same place in
2591 your program. There is nothing silly or meaningless about this. When
2592 the breakpoints are conditional, this is even useful
2593 (@pxref{Conditions, ,Break conditions}).
2595 @cindex negative breakpoint numbers
2596 @cindex internal @value{GDBN} breakpoints
2597 @value{GDBN} itself sometimes sets breakpoints in your program for
2598 special purposes, such as proper handling of @code{longjmp} (in C
2599 programs). These internal breakpoints are assigned negative numbers,
2600 starting with @code{-1}; @samp{info breakpoints} does not display them.
2601 You can see these breakpoints with the @value{GDBN} maintenance command
2602 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
2605 @node Set Watchpoints
2606 @subsection Setting watchpoints
2608 @cindex setting watchpoints
2609 @cindex software watchpoints
2610 @cindex hardware watchpoints
2611 You can use a watchpoint to stop execution whenever the value of an
2612 expression changes, without having to predict a particular place where
2615 Depending on your system, watchpoints may be implemented in software or
2616 hardware. @value{GDBN} does software watchpointing by single-stepping your
2617 program and testing the variable's value each time, which is hundreds of
2618 times slower than normal execution. (But this may still be worth it, to
2619 catch errors where you have no clue what part of your program is the
2622 On some systems, such as HP-UX, Linux and some other x86-based targets,
2623 @value{GDBN} includes support for
2624 hardware watchpoints, which do not slow down the running of your
2629 @item watch @var{expr}
2630 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2631 is written into by the program and its value changes.
2634 @item rwatch @var{expr}
2635 Set a watchpoint that will break when watch @var{expr} is read by the program.
2638 @item awatch @var{expr}
2639 Set a watchpoint that will break when @var{expr} is either read or written into
2642 @kindex info watchpoints
2643 @item info watchpoints
2644 This command prints a list of watchpoints, breakpoints, and catchpoints;
2645 it is the same as @code{info break}.
2648 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2649 watchpoints execute very quickly, and the debugger reports a change in
2650 value at the exact instruction where the change occurs. If @value{GDBN}
2651 cannot set a hardware watchpoint, it sets a software watchpoint, which
2652 executes more slowly and reports the change in value at the next
2653 statement, not the instruction, after the change occurs.
2655 When you issue the @code{watch} command, @value{GDBN} reports
2658 Hardware watchpoint @var{num}: @var{expr}
2662 if it was able to set a hardware watchpoint.
2664 Currently, the @code{awatch} and @code{rwatch} commands can only set
2665 hardware watchpoints, because accesses to data that don't change the
2666 value of the watched expression cannot be detected without examining
2667 every instruction as it is being executed, and @value{GDBN} does not do
2668 that currently. If @value{GDBN} finds that it is unable to set a
2669 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2670 will print a message like this:
2673 Expression cannot be implemented with read/access watchpoint.
2676 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2677 data type of the watched expression is wider than what a hardware
2678 watchpoint on the target machine can handle. For example, some systems
2679 can only watch regions that are up to 4 bytes wide; on such systems you
2680 cannot set hardware watchpoints for an expression that yields a
2681 double-precision floating-point number (which is typically 8 bytes
2682 wide). As a work-around, it might be possible to break the large region
2683 into a series of smaller ones and watch them with separate watchpoints.
2685 If you set too many hardware watchpoints, @value{GDBN} might be unable
2686 to insert all of them when you resume the execution of your program.
2687 Since the precise number of active watchpoints is unknown until such
2688 time as the program is about to be resumed, @value{GDBN} might not be
2689 able to warn you about this when you set the watchpoints, and the
2690 warning will be printed only when the program is resumed:
2693 Hardware watchpoint @var{num}: Could not insert watchpoint
2697 If this happens, delete or disable some of the watchpoints.
2699 The SPARClite DSU will generate traps when a program accesses some data
2700 or instruction address that is assigned to the debug registers. For the
2701 data addresses, DSU facilitates the @code{watch} command. However the
2702 hardware breakpoint registers can only take two data watchpoints, and
2703 both watchpoints must be the same kind. For example, you can set two
2704 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2705 @strong{or} two with @code{awatch} commands, but you cannot set one
2706 watchpoint with one command and the other with a different command.
2707 @value{GDBN} will reject the command if you try to mix watchpoints.
2708 Delete or disable unused watchpoint commands before setting new ones.
2710 If you call a function interactively using @code{print} or @code{call},
2711 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2712 kind of breakpoint or the call completes.
2714 @value{GDBN} automatically deletes watchpoints that watch local
2715 (automatic) variables, or expressions that involve such variables, when
2716 they go out of scope, that is, when the execution leaves the block in
2717 which these variables were defined. In particular, when the program
2718 being debugged terminates, @emph{all} local variables go out of scope,
2719 and so only watchpoints that watch global variables remain set. If you
2720 rerun the program, you will need to set all such watchpoints again. One
2721 way of doing that would be to set a code breakpoint at the entry to the
2722 @code{main} function and when it breaks, set all the watchpoints.
2725 @cindex watchpoints and threads
2726 @cindex threads and watchpoints
2727 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2728 usefulness. With the current watchpoint implementation, @value{GDBN}
2729 can only watch the value of an expression @emph{in a single thread}. If
2730 you are confident that the expression can only change due to the current
2731 thread's activity (and if you are also confident that no other thread
2732 can become current), then you can use watchpoints as usual. However,
2733 @value{GDBN} may not notice when a non-current thread's activity changes
2736 @c FIXME: this is almost identical to the previous paragraph.
2737 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2738 have only limited usefulness. If @value{GDBN} creates a software
2739 watchpoint, it can only watch the value of an expression @emph{in a
2740 single thread}. If you are confident that the expression can only
2741 change due to the current thread's activity (and if you are also
2742 confident that no other thread can become current), then you can use
2743 software watchpoints as usual. However, @value{GDBN} may not notice
2744 when a non-current thread's activity changes the expression. (Hardware
2745 watchpoints, in contrast, watch an expression in all threads.)
2748 @node Set Catchpoints
2749 @subsection Setting catchpoints
2750 @cindex catchpoints, setting
2751 @cindex exception handlers
2752 @cindex event handling
2754 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2755 kinds of program events, such as C@t{++} exceptions or the loading of a
2756 shared library. Use the @code{catch} command to set a catchpoint.
2760 @item catch @var{event}
2761 Stop when @var{event} occurs. @var{event} can be any of the following:
2765 The throwing of a C@t{++} exception.
2769 The catching of a C@t{++} exception.
2773 A call to @code{exec}. This is currently only available for HP-UX.
2777 A call to @code{fork}. This is currently only available for HP-UX.
2781 A call to @code{vfork}. This is currently only available for HP-UX.
2784 @itemx load @var{libname}
2786 The dynamic loading of any shared library, or the loading of the library
2787 @var{libname}. This is currently only available for HP-UX.
2790 @itemx unload @var{libname}
2791 @kindex catch unload
2792 The unloading of any dynamically loaded shared library, or the unloading
2793 of the library @var{libname}. This is currently only available for HP-UX.
2796 @item tcatch @var{event}
2797 Set a catchpoint that is enabled only for one stop. The catchpoint is
2798 automatically deleted after the first time the event is caught.
2802 Use the @code{info break} command to list the current catchpoints.
2804 There are currently some limitations to C@t{++} exception handling
2805 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2809 If you call a function interactively, @value{GDBN} normally returns
2810 control to you when the function has finished executing. If the call
2811 raises an exception, however, the call may bypass the mechanism that
2812 returns control to you and cause your program either to abort or to
2813 simply continue running until it hits a breakpoint, catches a signal
2814 that @value{GDBN} is listening for, or exits. This is the case even if
2815 you set a catchpoint for the exception; catchpoints on exceptions are
2816 disabled within interactive calls.
2819 You cannot raise an exception interactively.
2822 You cannot install an exception handler interactively.
2825 @cindex raise exceptions
2826 Sometimes @code{catch} is not the best way to debug exception handling:
2827 if you need to know exactly where an exception is raised, it is better to
2828 stop @emph{before} the exception handler is called, since that way you
2829 can see the stack before any unwinding takes place. If you set a
2830 breakpoint in an exception handler instead, it may not be easy to find
2831 out where the exception was raised.
2833 To stop just before an exception handler is called, you need some
2834 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2835 raised by calling a library function named @code{__raise_exception}
2836 which has the following ANSI C interface:
2839 /* @var{addr} is where the exception identifier is stored.
2840 @var{id} is the exception identifier. */
2841 void __raise_exception (void **addr, void *id);
2845 To make the debugger catch all exceptions before any stack
2846 unwinding takes place, set a breakpoint on @code{__raise_exception}
2847 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2849 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2850 that depends on the value of @var{id}, you can stop your program when
2851 a specific exception is raised. You can use multiple conditional
2852 breakpoints to stop your program when any of a number of exceptions are
2857 @subsection Deleting breakpoints
2859 @cindex clearing breakpoints, watchpoints, catchpoints
2860 @cindex deleting breakpoints, watchpoints, catchpoints
2861 It is often necessary to eliminate a breakpoint, watchpoint, or
2862 catchpoint once it has done its job and you no longer want your program
2863 to stop there. This is called @dfn{deleting} the breakpoint. A
2864 breakpoint that has been deleted no longer exists; it is forgotten.
2866 With the @code{clear} command you can delete breakpoints according to
2867 where they are in your program. With the @code{delete} command you can
2868 delete individual breakpoints, watchpoints, or catchpoints by specifying
2869 their breakpoint numbers.
2871 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2872 automatically ignores breakpoints on the first instruction to be executed
2873 when you continue execution without changing the execution address.
2878 Delete any breakpoints at the next instruction to be executed in the
2879 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2880 the innermost frame is selected, this is a good way to delete a
2881 breakpoint where your program just stopped.
2883 @item clear @var{function}
2884 @itemx clear @var{filename}:@var{function}
2885 Delete any breakpoints set at entry to the function @var{function}.
2887 @item clear @var{linenum}
2888 @itemx clear @var{filename}:@var{linenum}
2889 Delete any breakpoints set at or within the code of the specified line.
2891 @cindex delete breakpoints
2893 @kindex d @r{(@code{delete})}
2894 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2895 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2896 ranges specified as arguments. If no argument is specified, delete all
2897 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2898 confirm off}). You can abbreviate this command as @code{d}.
2902 @subsection Disabling breakpoints
2904 @kindex disable breakpoints
2905 @kindex enable breakpoints
2906 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2907 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2908 it had been deleted, but remembers the information on the breakpoint so
2909 that you can @dfn{enable} it again later.
2911 You disable and enable breakpoints, watchpoints, and catchpoints with
2912 the @code{enable} and @code{disable} commands, optionally specifying one
2913 or more breakpoint numbers as arguments. Use @code{info break} or
2914 @code{info watch} to print a list of breakpoints, watchpoints, and
2915 catchpoints if you do not know which numbers to use.
2917 A breakpoint, watchpoint, or catchpoint can have any of four different
2918 states of enablement:
2922 Enabled. The breakpoint stops your program. A breakpoint set
2923 with the @code{break} command starts out in this state.
2925 Disabled. The breakpoint has no effect on your program.
2927 Enabled once. The breakpoint stops your program, but then becomes
2930 Enabled for deletion. The breakpoint stops your program, but
2931 immediately after it does so it is deleted permanently. A breakpoint
2932 set with the @code{tbreak} command starts out in this state.
2935 You can use the following commands to enable or disable breakpoints,
2936 watchpoints, and catchpoints:
2939 @kindex disable breakpoints
2941 @kindex dis @r{(@code{disable})}
2942 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2943 Disable the specified breakpoints---or all breakpoints, if none are
2944 listed. A disabled breakpoint has no effect but is not forgotten. All
2945 options such as ignore-counts, conditions and commands are remembered in
2946 case the breakpoint is enabled again later. You may abbreviate
2947 @code{disable} as @code{dis}.
2949 @kindex enable breakpoints
2951 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2952 Enable the specified breakpoints (or all defined breakpoints). They
2953 become effective once again in stopping your program.
2955 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2956 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2957 of these breakpoints immediately after stopping your program.
2959 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2960 Enable the specified breakpoints to work once, then die. @value{GDBN}
2961 deletes any of these breakpoints as soon as your program stops there.
2964 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2965 @c confusing: tbreak is also initially enabled.
2966 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2967 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2968 subsequently, they become disabled or enabled only when you use one of
2969 the commands above. (The command @code{until} can set and delete a
2970 breakpoint of its own, but it does not change the state of your other
2971 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2975 @subsection Break conditions
2976 @cindex conditional breakpoints
2977 @cindex breakpoint conditions
2979 @c FIXME what is scope of break condition expr? Context where wanted?
2980 @c in particular for a watchpoint?
2981 The simplest sort of breakpoint breaks every time your program reaches a
2982 specified place. You can also specify a @dfn{condition} for a
2983 breakpoint. A condition is just a Boolean expression in your
2984 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2985 a condition evaluates the expression each time your program reaches it,
2986 and your program stops only if the condition is @emph{true}.
2988 This is the converse of using assertions for program validation; in that
2989 situation, you want to stop when the assertion is violated---that is,
2990 when the condition is false. In C, if you want to test an assertion expressed
2991 by the condition @var{assert}, you should set the condition
2992 @samp{! @var{assert}} on the appropriate breakpoint.
2994 Conditions are also accepted for watchpoints; you may not need them,
2995 since a watchpoint is inspecting the value of an expression anyhow---but
2996 it might be simpler, say, to just set a watchpoint on a variable name,
2997 and specify a condition that tests whether the new value is an interesting
3000 Break conditions can have side effects, and may even call functions in
3001 your program. This can be useful, for example, to activate functions
3002 that log program progress, or to use your own print functions to
3003 format special data structures. The effects are completely predictable
3004 unless there is another enabled breakpoint at the same address. (In
3005 that case, @value{GDBN} might see the other breakpoint first and stop your
3006 program without checking the condition of this one.) Note that
3007 breakpoint commands are usually more convenient and flexible than break
3009 purpose of performing side effects when a breakpoint is reached
3010 (@pxref{Break Commands, ,Breakpoint command lists}).
3012 Break conditions can be specified when a breakpoint is set, by using
3013 @samp{if} in the arguments to the @code{break} command. @xref{Set
3014 Breaks, ,Setting breakpoints}. They can also be changed at any time
3015 with the @code{condition} command.
3017 You can also use the @code{if} keyword with the @code{watch} command.
3018 The @code{catch} command does not recognize the @code{if} keyword;
3019 @code{condition} is the only way to impose a further condition on a
3024 @item condition @var{bnum} @var{expression}
3025 Specify @var{expression} as the break condition for breakpoint,
3026 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3027 breakpoint @var{bnum} stops your program only if the value of
3028 @var{expression} is true (nonzero, in C). When you use
3029 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3030 syntactic correctness, and to determine whether symbols in it have
3031 referents in the context of your breakpoint. If @var{expression} uses
3032 symbols not referenced in the context of the breakpoint, @value{GDBN}
3033 prints an error message:
3036 No symbol "foo" in current context.
3041 not actually evaluate @var{expression} at the time the @code{condition}
3042 command (or a command that sets a breakpoint with a condition, like
3043 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3045 @item condition @var{bnum}
3046 Remove the condition from breakpoint number @var{bnum}. It becomes
3047 an ordinary unconditional breakpoint.
3050 @cindex ignore count (of breakpoint)
3051 A special case of a breakpoint condition is to stop only when the
3052 breakpoint has been reached a certain number of times. This is so
3053 useful that there is a special way to do it, using the @dfn{ignore
3054 count} of the breakpoint. Every breakpoint has an ignore count, which
3055 is an integer. Most of the time, the ignore count is zero, and
3056 therefore has no effect. But if your program reaches a breakpoint whose
3057 ignore count is positive, then instead of stopping, it just decrements
3058 the ignore count by one and continues. As a result, if the ignore count
3059 value is @var{n}, the breakpoint does not stop the next @var{n} times
3060 your program reaches it.
3064 @item ignore @var{bnum} @var{count}
3065 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3066 The next @var{count} times the breakpoint is reached, your program's
3067 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3070 To make the breakpoint stop the next time it is reached, specify
3073 When you use @code{continue} to resume execution of your program from a
3074 breakpoint, you can specify an ignore count directly as an argument to
3075 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3076 Stepping,,Continuing and stepping}.
3078 If a breakpoint has a positive ignore count and a condition, the
3079 condition is not checked. Once the ignore count reaches zero,
3080 @value{GDBN} resumes checking the condition.
3082 You could achieve the effect of the ignore count with a condition such
3083 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3084 is decremented each time. @xref{Convenience Vars, ,Convenience
3088 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3091 @node Break Commands
3092 @subsection Breakpoint command lists
3094 @cindex breakpoint commands
3095 You can give any breakpoint (or watchpoint or catchpoint) a series of
3096 commands to execute when your program stops due to that breakpoint. For
3097 example, you might want to print the values of certain expressions, or
3098 enable other breakpoints.
3103 @item commands @r{[}@var{bnum}@r{]}
3104 @itemx @dots{} @var{command-list} @dots{}
3106 Specify a list of commands for breakpoint number @var{bnum}. The commands
3107 themselves appear on the following lines. Type a line containing just
3108 @code{end} to terminate the commands.
3110 To remove all commands from a breakpoint, type @code{commands} and
3111 follow it immediately with @code{end}; that is, give no commands.
3113 With no @var{bnum} argument, @code{commands} refers to the last
3114 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3115 recently encountered).
3118 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3119 disabled within a @var{command-list}.
3121 You can use breakpoint commands to start your program up again. Simply
3122 use the @code{continue} command, or @code{step}, or any other command
3123 that resumes execution.
3125 Any other commands in the command list, after a command that resumes
3126 execution, are ignored. This is because any time you resume execution
3127 (even with a simple @code{next} or @code{step}), you may encounter
3128 another breakpoint---which could have its own command list, leading to
3129 ambiguities about which list to execute.
3132 If the first command you specify in a command list is @code{silent}, the
3133 usual message about stopping at a breakpoint is not printed. This may
3134 be desirable for breakpoints that are to print a specific message and
3135 then continue. If none of the remaining commands print anything, you
3136 see no sign that the breakpoint was reached. @code{silent} is
3137 meaningful only at the beginning of a breakpoint command list.
3139 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3140 print precisely controlled output, and are often useful in silent
3141 breakpoints. @xref{Output, ,Commands for controlled output}.
3143 For example, here is how you could use breakpoint commands to print the
3144 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3150 printf "x is %d\n",x
3155 One application for breakpoint commands is to compensate for one bug so
3156 you can test for another. Put a breakpoint just after the erroneous line
3157 of code, give it a condition to detect the case in which something
3158 erroneous has been done, and give it commands to assign correct values
3159 to any variables that need them. End with the @code{continue} command
3160 so that your program does not stop, and start with the @code{silent}
3161 command so that no output is produced. Here is an example:
3172 @node Breakpoint Menus
3173 @subsection Breakpoint menus
3175 @cindex symbol overloading
3177 Some programming languages (notably C@t{++}) permit a single function name
3178 to be defined several times, for application in different contexts.
3179 This is called @dfn{overloading}. When a function name is overloaded,
3180 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3181 a breakpoint. If you realize this is a problem, you can use
3182 something like @samp{break @var{function}(@var{types})} to specify which
3183 particular version of the function you want. Otherwise, @value{GDBN} offers
3184 you a menu of numbered choices for different possible breakpoints, and
3185 waits for your selection with the prompt @samp{>}. The first two
3186 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3187 sets a breakpoint at each definition of @var{function}, and typing
3188 @kbd{0} aborts the @code{break} command without setting any new
3191 For example, the following session excerpt shows an attempt to set a
3192 breakpoint at the overloaded symbol @code{String::after}.
3193 We choose three particular definitions of that function name:
3195 @c FIXME! This is likely to change to show arg type lists, at least
3198 (@value{GDBP}) b String::after
3201 [2] file:String.cc; line number:867
3202 [3] file:String.cc; line number:860
3203 [4] file:String.cc; line number:875
3204 [5] file:String.cc; line number:853
3205 [6] file:String.cc; line number:846
3206 [7] file:String.cc; line number:735
3208 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3209 Breakpoint 2 at 0xb344: file String.cc, line 875.
3210 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3211 Multiple breakpoints were set.
3212 Use the "delete" command to delete unwanted
3218 @c @ifclear BARETARGET
3219 @node Error in Breakpoints
3220 @subsection ``Cannot insert breakpoints''
3222 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3224 Under some operating systems, breakpoints cannot be used in a program if
3225 any other process is running that program. In this situation,
3226 attempting to run or continue a program with a breakpoint causes
3227 @value{GDBN} to print an error message:
3230 Cannot insert breakpoints.
3231 The same program may be running in another process.
3234 When this happens, you have three ways to proceed:
3238 Remove or disable the breakpoints, then continue.
3241 Suspend @value{GDBN}, and copy the file containing your program to a new
3242 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3243 that @value{GDBN} should run your program under that name.
3244 Then start your program again.
3247 Relink your program so that the text segment is nonsharable, using the
3248 linker option @samp{-N}. The operating system limitation may not apply
3249 to nonsharable executables.
3253 A similar message can be printed if you request too many active
3254 hardware-assisted breakpoints and watchpoints:
3256 @c FIXME: the precise wording of this message may change; the relevant
3257 @c source change is not committed yet (Sep 3, 1999).
3259 Stopped; cannot insert breakpoints.
3260 You may have requested too many hardware breakpoints and watchpoints.
3264 This message is printed when you attempt to resume the program, since
3265 only then @value{GDBN} knows exactly how many hardware breakpoints and
3266 watchpoints it needs to insert.
3268 When this message is printed, you need to disable or remove some of the
3269 hardware-assisted breakpoints and watchpoints, and then continue.
3272 @node Continuing and Stepping
3273 @section Continuing and stepping
3277 @cindex resuming execution
3278 @dfn{Continuing} means resuming program execution until your program
3279 completes normally. In contrast, @dfn{stepping} means executing just
3280 one more ``step'' of your program, where ``step'' may mean either one
3281 line of source code, or one machine instruction (depending on what
3282 particular command you use). Either when continuing or when stepping,
3283 your program may stop even sooner, due to a breakpoint or a signal. (If
3284 it stops due to a signal, you may want to use @code{handle}, or use
3285 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3289 @kindex c @r{(@code{continue})}
3290 @kindex fg @r{(resume foreground execution)}
3291 @item continue @r{[}@var{ignore-count}@r{]}
3292 @itemx c @r{[}@var{ignore-count}@r{]}
3293 @itemx fg @r{[}@var{ignore-count}@r{]}
3294 Resume program execution, at the address where your program last stopped;
3295 any breakpoints set at that address are bypassed. The optional argument
3296 @var{ignore-count} allows you to specify a further number of times to
3297 ignore a breakpoint at this location; its effect is like that of
3298 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3300 The argument @var{ignore-count} is meaningful only when your program
3301 stopped due to a breakpoint. At other times, the argument to
3302 @code{continue} is ignored.
3304 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3305 debugged program is deemed to be the foreground program) are provided
3306 purely for convenience, and have exactly the same behavior as
3310 To resume execution at a different place, you can use @code{return}
3311 (@pxref{Returning, ,Returning from a function}) to go back to the
3312 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3313 different address}) to go to an arbitrary location in your program.
3315 A typical technique for using stepping is to set a breakpoint
3316 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3317 beginning of the function or the section of your program where a problem
3318 is believed to lie, run your program until it stops at that breakpoint,
3319 and then step through the suspect area, examining the variables that are
3320 interesting, until you see the problem happen.
3324 @kindex s @r{(@code{step})}
3326 Continue running your program until control reaches a different source
3327 line, then stop it and return control to @value{GDBN}. This command is
3328 abbreviated @code{s}.
3331 @c "without debugging information" is imprecise; actually "without line
3332 @c numbers in the debugging information". (gcc -g1 has debugging info but
3333 @c not line numbers). But it seems complex to try to make that
3334 @c distinction here.
3335 @emph{Warning:} If you use the @code{step} command while control is
3336 within a function that was compiled without debugging information,
3337 execution proceeds until control reaches a function that does have
3338 debugging information. Likewise, it will not step into a function which
3339 is compiled without debugging information. To step through functions
3340 without debugging information, use the @code{stepi} command, described
3344 The @code{step} command only stops at the first instruction of a source
3345 line. This prevents the multiple stops that could otherwise occur in
3346 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3347 to stop if a function that has debugging information is called within
3348 the line. In other words, @code{step} @emph{steps inside} any functions
3349 called within the line.
3351 Also, the @code{step} command only enters a function if there is line
3352 number information for the function. Otherwise it acts like the
3353 @code{next} command. This avoids problems when using @code{cc -gl}
3354 on MIPS machines. Previously, @code{step} entered subroutines if there
3355 was any debugging information about the routine.
3357 @item step @var{count}
3358 Continue running as in @code{step}, but do so @var{count} times. If a
3359 breakpoint is reached, or a signal not related to stepping occurs before
3360 @var{count} steps, stepping stops right away.
3363 @kindex n @r{(@code{next})}
3364 @item next @r{[}@var{count}@r{]}
3365 Continue to the next source line in the current (innermost) stack frame.
3366 This is similar to @code{step}, but function calls that appear within
3367 the line of code are executed without stopping. Execution stops when
3368 control reaches a different line of code at the original stack level
3369 that was executing when you gave the @code{next} command. This command
3370 is abbreviated @code{n}.
3372 An argument @var{count} is a repeat count, as for @code{step}.
3375 @c FIX ME!! Do we delete this, or is there a way it fits in with
3376 @c the following paragraph? --- Vctoria
3378 @c @code{next} within a function that lacks debugging information acts like
3379 @c @code{step}, but any function calls appearing within the code of the
3380 @c function are executed without stopping.
3382 The @code{next} command only stops at the first instruction of a
3383 source line. This prevents multiple stops that could otherwise occur in
3384 @code{switch} statements, @code{for} loops, etc.
3386 @kindex set step-mode
3388 @cindex functions without line info, and stepping
3389 @cindex stepping into functions with no line info
3390 @itemx set step-mode on
3391 The @code{set step-mode on} command causes the @code{step} command to
3392 stop at the first instruction of a function which contains no debug line
3393 information rather than stepping over it.
3395 This is useful in cases where you may be interested in inspecting the
3396 machine instructions of a function which has no symbolic info and do not
3397 want @value{GDBN} to automatically skip over this function.
3399 @item set step-mode off
3400 Causes the @code{step} command to step over any functions which contains no
3401 debug information. This is the default.
3405 Continue running until just after function in the selected stack frame
3406 returns. Print the returned value (if any).
3408 Contrast this with the @code{return} command (@pxref{Returning,
3409 ,Returning from a function}).
3412 @kindex u @r{(@code{until})}
3415 Continue running until a source line past the current line, in the
3416 current stack frame, is reached. This command is used to avoid single
3417 stepping through a loop more than once. It is like the @code{next}
3418 command, except that when @code{until} encounters a jump, it
3419 automatically continues execution until the program counter is greater
3420 than the address of the jump.
3422 This means that when you reach the end of a loop after single stepping
3423 though it, @code{until} makes your program continue execution until it
3424 exits the loop. In contrast, a @code{next} command at the end of a loop
3425 simply steps back to the beginning of the loop, which forces you to step
3426 through the next iteration.
3428 @code{until} always stops your program if it attempts to exit the current
3431 @code{until} may produce somewhat counterintuitive results if the order
3432 of machine code does not match the order of the source lines. For
3433 example, in the following excerpt from a debugging session, the @code{f}
3434 (@code{frame}) command shows that execution is stopped at line
3435 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3439 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3441 (@value{GDBP}) until
3442 195 for ( ; argc > 0; NEXTARG) @{
3445 This happened because, for execution efficiency, the compiler had
3446 generated code for the loop closure test at the end, rather than the
3447 start, of the loop---even though the test in a C @code{for}-loop is
3448 written before the body of the loop. The @code{until} command appeared
3449 to step back to the beginning of the loop when it advanced to this
3450 expression; however, it has not really gone to an earlier
3451 statement---not in terms of the actual machine code.
3453 @code{until} with no argument works by means of single
3454 instruction stepping, and hence is slower than @code{until} with an
3457 @item until @var{location}
3458 @itemx u @var{location}
3459 Continue running your program until either the specified location is
3460 reached, or the current stack frame returns. @var{location} is any of
3461 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3462 ,Setting breakpoints}). This form of the command uses breakpoints,
3463 and hence is quicker than @code{until} without an argument.
3466 @kindex si @r{(@code{stepi})}
3468 @itemx stepi @var{arg}
3470 Execute one machine instruction, then stop and return to the debugger.
3472 It is often useful to do @samp{display/i $pc} when stepping by machine
3473 instructions. This makes @value{GDBN} automatically display the next
3474 instruction to be executed, each time your program stops. @xref{Auto
3475 Display,, Automatic display}.
3477 An argument is a repeat count, as in @code{step}.
3481 @kindex ni @r{(@code{nexti})}
3483 @itemx nexti @var{arg}
3485 Execute one machine instruction, but if it is a function call,
3486 proceed until the function returns.
3488 An argument is a repeat count, as in @code{next}.
3495 A signal is an asynchronous event that can happen in a program. The
3496 operating system defines the possible kinds of signals, and gives each
3497 kind a name and a number. For example, in Unix @code{SIGINT} is the
3498 signal a program gets when you type an interrupt character (often @kbd{C-c});
3499 @code{SIGSEGV} is the signal a program gets from referencing a place in
3500 memory far away from all the areas in use; @code{SIGALRM} occurs when
3501 the alarm clock timer goes off (which happens only if your program has
3502 requested an alarm).
3504 @cindex fatal signals
3505 Some signals, including @code{SIGALRM}, are a normal part of the
3506 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3507 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3508 program has not specified in advance some other way to handle the signal.
3509 @code{SIGINT} does not indicate an error in your program, but it is normally
3510 fatal so it can carry out the purpose of the interrupt: to kill the program.
3512 @value{GDBN} has the ability to detect any occurrence of a signal in your
3513 program. You can tell @value{GDBN} in advance what to do for each kind of
3516 @cindex handling signals
3517 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3518 @code{SIGALRM} be silently passed to your program
3519 (so as not to interfere with their role in the program's functioning)
3520 but to stop your program immediately whenever an error signal happens.
3521 You can change these settings with the @code{handle} command.
3524 @kindex info signals
3527 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3528 handle each one. You can use this to see the signal numbers of all
3529 the defined types of signals.
3531 @code{info handle} is an alias for @code{info signals}.
3534 @item handle @var{signal} @var{keywords}@dots{}
3535 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3536 can be the number of a signal or its name (with or without the
3537 @samp{SIG} at the beginning); a list of signal numbers of the form
3538 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3539 known signals. The @var{keywords} say what change to make.
3543 The keywords allowed by the @code{handle} command can be abbreviated.
3544 Their full names are:
3548 @value{GDBN} should not stop your program when this signal happens. It may
3549 still print a message telling you that the signal has come in.
3552 @value{GDBN} should stop your program when this signal happens. This implies
3553 the @code{print} keyword as well.
3556 @value{GDBN} should print a message when this signal happens.
3559 @value{GDBN} should not mention the occurrence of the signal at all. This
3560 implies the @code{nostop} keyword as well.
3564 @value{GDBN} should allow your program to see this signal; your program
3565 can handle the signal, or else it may terminate if the signal is fatal
3566 and not handled. @code{pass} and @code{noignore} are synonyms.
3570 @value{GDBN} should not allow your program to see this signal.
3571 @code{nopass} and @code{ignore} are synonyms.
3575 When a signal stops your program, the signal is not visible to the
3577 continue. Your program sees the signal then, if @code{pass} is in
3578 effect for the signal in question @emph{at that time}. In other words,
3579 after @value{GDBN} reports a signal, you can use the @code{handle}
3580 command with @code{pass} or @code{nopass} to control whether your
3581 program sees that signal when you continue.
3583 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3584 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3585 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3588 You can also use the @code{signal} command to prevent your program from
3589 seeing a signal, or cause it to see a signal it normally would not see,
3590 or to give it any signal at any time. For example, if your program stopped
3591 due to some sort of memory reference error, you might store correct
3592 values into the erroneous variables and continue, hoping to see more
3593 execution; but your program would probably terminate immediately as
3594 a result of the fatal signal once it saw the signal. To prevent this,
3595 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3599 @section Stopping and starting multi-thread programs
3601 When your program has multiple threads (@pxref{Threads,, Debugging
3602 programs with multiple threads}), you can choose whether to set
3603 breakpoints on all threads, or on a particular thread.
3606 @cindex breakpoints and threads
3607 @cindex thread breakpoints
3608 @kindex break @dots{} thread @var{threadno}
3609 @item break @var{linespec} thread @var{threadno}
3610 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3611 @var{linespec} specifies source lines; there are several ways of
3612 writing them, but the effect is always to specify some source line.
3614 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3615 to specify that you only want @value{GDBN} to stop the program when a
3616 particular thread reaches this breakpoint. @var{threadno} is one of the
3617 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3618 column of the @samp{info threads} display.
3620 If you do not specify @samp{thread @var{threadno}} when you set a
3621 breakpoint, the breakpoint applies to @emph{all} threads of your
3624 You can use the @code{thread} qualifier on conditional breakpoints as
3625 well; in this case, place @samp{thread @var{threadno}} before the
3626 breakpoint condition, like this:
3629 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3634 @cindex stopped threads
3635 @cindex threads, stopped
3636 Whenever your program stops under @value{GDBN} for any reason,
3637 @emph{all} threads of execution stop, not just the current thread. This
3638 allows you to examine the overall state of the program, including
3639 switching between threads, without worrying that things may change
3642 @cindex continuing threads
3643 @cindex threads, continuing
3644 Conversely, whenever you restart the program, @emph{all} threads start
3645 executing. @emph{This is true even when single-stepping} with commands
3646 like @code{step} or @code{next}.
3648 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3649 Since thread scheduling is up to your debugging target's operating
3650 system (not controlled by @value{GDBN}), other threads may
3651 execute more than one statement while the current thread completes a
3652 single step. Moreover, in general other threads stop in the middle of a
3653 statement, rather than at a clean statement boundary, when the program
3656 You might even find your program stopped in another thread after
3657 continuing or even single-stepping. This happens whenever some other
3658 thread runs into a breakpoint, a signal, or an exception before the
3659 first thread completes whatever you requested.
3661 On some OSes, you can lock the OS scheduler and thus allow only a single
3665 @item set scheduler-locking @var{mode}
3666 Set the scheduler locking mode. If it is @code{off}, then there is no
3667 locking and any thread may run at any time. If @code{on}, then only the
3668 current thread may run when the inferior is resumed. The @code{step}
3669 mode optimizes for single-stepping. It stops other threads from
3670 ``seizing the prompt'' by preempting the current thread while you are
3671 stepping. Other threads will only rarely (or never) get a chance to run
3672 when you step. They are more likely to run when you @samp{next} over a
3673 function call, and they are completely free to run when you use commands
3674 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3675 thread hits a breakpoint during its timeslice, they will never steal the
3676 @value{GDBN} prompt away from the thread that you are debugging.
3678 @item show scheduler-locking
3679 Display the current scheduler locking mode.
3684 @chapter Examining the Stack
3686 When your program has stopped, the first thing you need to know is where it
3687 stopped and how it got there.
3690 Each time your program performs a function call, information about the call
3692 That information includes the location of the call in your program,
3693 the arguments of the call,
3694 and the local variables of the function being called.
3695 The information is saved in a block of data called a @dfn{stack frame}.
3696 The stack frames are allocated in a region of memory called the @dfn{call
3699 When your program stops, the @value{GDBN} commands for examining the
3700 stack allow you to see all of this information.
3702 @cindex selected frame
3703 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3704 @value{GDBN} commands refer implicitly to the selected frame. In
3705 particular, whenever you ask @value{GDBN} for the value of a variable in
3706 your program, the value is found in the selected frame. There are
3707 special @value{GDBN} commands to select whichever frame you are
3708 interested in. @xref{Selection, ,Selecting a frame}.
3710 When your program stops, @value{GDBN} automatically selects the
3711 currently executing frame and describes it briefly, similar to the
3712 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3715 * Frames:: Stack frames
3716 * Backtrace:: Backtraces
3717 * Selection:: Selecting a frame
3718 * Frame Info:: Information on a frame
3723 @section Stack frames
3725 @cindex frame, definition
3727 The call stack is divided up into contiguous pieces called @dfn{stack
3728 frames}, or @dfn{frames} for short; each frame is the data associated
3729 with one call to one function. The frame contains the arguments given
3730 to the function, the function's local variables, and the address at
3731 which the function is executing.
3733 @cindex initial frame
3734 @cindex outermost frame
3735 @cindex innermost frame
3736 When your program is started, the stack has only one frame, that of the
3737 function @code{main}. This is called the @dfn{initial} frame or the
3738 @dfn{outermost} frame. Each time a function is called, a new frame is
3739 made. Each time a function returns, the frame for that function invocation
3740 is eliminated. If a function is recursive, there can be many frames for
3741 the same function. The frame for the function in which execution is
3742 actually occurring is called the @dfn{innermost} frame. This is the most
3743 recently created of all the stack frames that still exist.
3745 @cindex frame pointer
3746 Inside your program, stack frames are identified by their addresses. A
3747 stack frame consists of many bytes, each of which has its own address; each
3748 kind of computer has a convention for choosing one byte whose
3749 address serves as the address of the frame. Usually this address is kept
3750 in a register called the @dfn{frame pointer register} while execution is
3751 going on in that frame.
3753 @cindex frame number
3754 @value{GDBN} assigns numbers to all existing stack frames, starting with
3755 zero for the innermost frame, one for the frame that called it,
3756 and so on upward. These numbers do not really exist in your program;
3757 they are assigned by @value{GDBN} to give you a way of designating stack
3758 frames in @value{GDBN} commands.
3760 @c The -fomit-frame-pointer below perennially causes hbox overflow
3761 @c underflow problems.
3762 @cindex frameless execution
3763 Some compilers provide a way to compile functions so that they operate
3764 without stack frames. (For example, the @value{GCC} option
3766 @samp{-fomit-frame-pointer}
3768 generates functions without a frame.)
3769 This is occasionally done with heavily used library functions to save
3770 the frame setup time. @value{GDBN} has limited facilities for dealing
3771 with these function invocations. If the innermost function invocation
3772 has no stack frame, @value{GDBN} nevertheless regards it as though
3773 it had a separate frame, which is numbered zero as usual, allowing
3774 correct tracing of the function call chain. However, @value{GDBN} has
3775 no provision for frameless functions elsewhere in the stack.
3778 @kindex frame@r{, command}
3779 @cindex current stack frame
3780 @item frame @var{args}
3781 The @code{frame} command allows you to move from one stack frame to another,
3782 and to print the stack frame you select. @var{args} may be either the
3783 address of the frame or the stack frame number. Without an argument,
3784 @code{frame} prints the current stack frame.
3786 @kindex select-frame
3787 @cindex selecting frame silently
3789 The @code{select-frame} command allows you to move from one stack frame
3790 to another without printing the frame. This is the silent version of
3799 @cindex stack traces
3800 A backtrace is a summary of how your program got where it is. It shows one
3801 line per frame, for many frames, starting with the currently executing
3802 frame (frame zero), followed by its caller (frame one), and on up the
3807 @kindex bt @r{(@code{backtrace})}
3810 Print a backtrace of the entire stack: one line per frame for all
3811 frames in the stack.
3813 You can stop the backtrace at any time by typing the system interrupt
3814 character, normally @kbd{C-c}.
3816 @item backtrace @var{n}
3818 Similar, but print only the innermost @var{n} frames.
3820 @item backtrace -@var{n}
3822 Similar, but print only the outermost @var{n} frames.
3827 @kindex info s @r{(@code{info stack})}
3828 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3829 are additional aliases for @code{backtrace}.
3831 Each line in the backtrace shows the frame number and the function name.
3832 The program counter value is also shown---unless you use @code{set
3833 print address off}. The backtrace also shows the source file name and
3834 line number, as well as the arguments to the function. The program
3835 counter value is omitted if it is at the beginning of the code for that
3838 Here is an example of a backtrace. It was made with the command
3839 @samp{bt 3}, so it shows the innermost three frames.
3843 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3845 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3846 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3848 (More stack frames follow...)
3853 The display for frame zero does not begin with a program counter
3854 value, indicating that your program has stopped at the beginning of the
3855 code for line @code{993} of @code{builtin.c}.
3858 @section Selecting a frame
3860 Most commands for examining the stack and other data in your program work on
3861 whichever stack frame is selected at the moment. Here are the commands for
3862 selecting a stack frame; all of them finish by printing a brief description
3863 of the stack frame just selected.
3866 @kindex frame@r{, selecting}
3867 @kindex f @r{(@code{frame})}
3870 Select frame number @var{n}. Recall that frame zero is the innermost
3871 (currently executing) frame, frame one is the frame that called the
3872 innermost one, and so on. The highest-numbered frame is the one for
3875 @item frame @var{addr}
3877 Select the frame at address @var{addr}. This is useful mainly if the
3878 chaining of stack frames has been damaged by a bug, making it
3879 impossible for @value{GDBN} to assign numbers properly to all frames. In
3880 addition, this can be useful when your program has multiple stacks and
3881 switches between them.
3883 On the SPARC architecture, @code{frame} needs two addresses to
3884 select an arbitrary frame: a frame pointer and a stack pointer.
3886 On the MIPS and Alpha architecture, it needs two addresses: a stack
3887 pointer and a program counter.
3889 On the 29k architecture, it needs three addresses: a register stack
3890 pointer, a program counter, and a memory stack pointer.
3891 @c note to future updaters: this is conditioned on a flag
3892 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3893 @c as of 27 Jan 1994.
3897 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3898 advances toward the outermost frame, to higher frame numbers, to frames
3899 that have existed longer. @var{n} defaults to one.
3902 @kindex do @r{(@code{down})}
3904 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3905 advances toward the innermost frame, to lower frame numbers, to frames
3906 that were created more recently. @var{n} defaults to one. You may
3907 abbreviate @code{down} as @code{do}.
3910 All of these commands end by printing two lines of output describing the
3911 frame. The first line shows the frame number, the function name, the
3912 arguments, and the source file and line number of execution in that
3913 frame. The second line shows the text of that source line.
3921 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3923 10 read_input_file (argv[i]);
3927 After such a printout, the @code{list} command with no arguments
3928 prints ten lines centered on the point of execution in the frame.
3929 @xref{List, ,Printing source lines}.
3932 @kindex down-silently
3934 @item up-silently @var{n}
3935 @itemx down-silently @var{n}
3936 These two commands are variants of @code{up} and @code{down},
3937 respectively; they differ in that they do their work silently, without
3938 causing display of the new frame. They are intended primarily for use
3939 in @value{GDBN} command scripts, where the output might be unnecessary and
3944 @section Information about a frame
3946 There are several other commands to print information about the selected
3952 When used without any argument, this command does not change which
3953 frame is selected, but prints a brief description of the currently
3954 selected stack frame. It can be abbreviated @code{f}. With an
3955 argument, this command is used to select a stack frame.
3956 @xref{Selection, ,Selecting a frame}.
3959 @kindex info f @r{(@code{info frame})}
3962 This command prints a verbose description of the selected stack frame,
3967 the address of the frame
3969 the address of the next frame down (called by this frame)
3971 the address of the next frame up (caller of this frame)
3973 the language in which the source code corresponding to this frame is written
3975 the address of the frame's arguments
3977 the address of the frame's local variables
3979 the program counter saved in it (the address of execution in the caller frame)
3981 which registers were saved in the frame
3984 @noindent The verbose description is useful when
3985 something has gone wrong that has made the stack format fail to fit
3986 the usual conventions.
3988 @item info frame @var{addr}
3989 @itemx info f @var{addr}
3990 Print a verbose description of the frame at address @var{addr}, without
3991 selecting that frame. The selected frame remains unchanged by this
3992 command. This requires the same kind of address (more than one for some
3993 architectures) that you specify in the @code{frame} command.
3994 @xref{Selection, ,Selecting a frame}.
3998 Print the arguments of the selected frame, each on a separate line.
4002 Print the local variables of the selected frame, each on a separate
4003 line. These are all variables (declared either static or automatic)
4004 accessible at the point of execution of the selected frame.
4007 @cindex catch exceptions, list active handlers
4008 @cindex exception handlers, how to list
4010 Print a list of all the exception handlers that are active in the
4011 current stack frame at the current point of execution. To see other
4012 exception handlers, visit the associated frame (using the @code{up},
4013 @code{down}, or @code{frame} commands); then type @code{info catch}.
4014 @xref{Set Catchpoints, , Setting catchpoints}.
4020 @chapter Examining Source Files
4022 @value{GDBN} can print parts of your program's source, since the debugging
4023 information recorded in the program tells @value{GDBN} what source files were
4024 used to build it. When your program stops, @value{GDBN} spontaneously prints
4025 the line where it stopped. Likewise, when you select a stack frame
4026 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4027 execution in that frame has stopped. You can print other portions of
4028 source files by explicit command.
4030 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4031 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4032 @value{GDBN} under @sc{gnu} Emacs}.
4035 * List:: Printing source lines
4036 * Search:: Searching source files
4037 * Source Path:: Specifying source directories
4038 * Machine Code:: Source and machine code
4042 @section Printing source lines
4045 @kindex l @r{(@code{list})}
4046 To print lines from a source file, use the @code{list} command
4047 (abbreviated @code{l}). By default, ten lines are printed.
4048 There are several ways to specify what part of the file you want to print.
4050 Here are the forms of the @code{list} command most commonly used:
4053 @item list @var{linenum}
4054 Print lines centered around line number @var{linenum} in the
4055 current source file.
4057 @item list @var{function}
4058 Print lines centered around the beginning of function
4062 Print more lines. If the last lines printed were printed with a
4063 @code{list} command, this prints lines following the last lines
4064 printed; however, if the last line printed was a solitary line printed
4065 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4066 Stack}), this prints lines centered around that line.
4069 Print lines just before the lines last printed.
4072 By default, @value{GDBN} prints ten source lines with any of these forms of
4073 the @code{list} command. You can change this using @code{set listsize}:
4076 @kindex set listsize
4077 @item set listsize @var{count}
4078 Make the @code{list} command display @var{count} source lines (unless
4079 the @code{list} argument explicitly specifies some other number).
4081 @kindex show listsize
4083 Display the number of lines that @code{list} prints.
4086 Repeating a @code{list} command with @key{RET} discards the argument,
4087 so it is equivalent to typing just @code{list}. This is more useful
4088 than listing the same lines again. An exception is made for an
4089 argument of @samp{-}; that argument is preserved in repetition so that
4090 each repetition moves up in the source file.
4093 In general, the @code{list} command expects you to supply zero, one or two
4094 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4095 of writing them, but the effect is always to specify some source line.
4096 Here is a complete description of the possible arguments for @code{list}:
4099 @item list @var{linespec}
4100 Print lines centered around the line specified by @var{linespec}.
4102 @item list @var{first},@var{last}
4103 Print lines from @var{first} to @var{last}. Both arguments are
4106 @item list ,@var{last}
4107 Print lines ending with @var{last}.
4109 @item list @var{first},
4110 Print lines starting with @var{first}.
4113 Print lines just after the lines last printed.
4116 Print lines just before the lines last printed.
4119 As described in the preceding table.
4122 Here are the ways of specifying a single source line---all the
4127 Specifies line @var{number} of the current source file.
4128 When a @code{list} command has two linespecs, this refers to
4129 the same source file as the first linespec.
4132 Specifies the line @var{offset} lines after the last line printed.
4133 When used as the second linespec in a @code{list} command that has
4134 two, this specifies the line @var{offset} lines down from the
4138 Specifies the line @var{offset} lines before the last line printed.
4140 @item @var{filename}:@var{number}
4141 Specifies line @var{number} in the source file @var{filename}.
4143 @item @var{function}
4144 Specifies the line that begins the body of the function @var{function}.
4145 For example: in C, this is the line with the open brace.
4147 @item @var{filename}:@var{function}
4148 Specifies the line of the open-brace that begins the body of the
4149 function @var{function} in the file @var{filename}. You only need the
4150 file name with a function name to avoid ambiguity when there are
4151 identically named functions in different source files.
4153 @item *@var{address}
4154 Specifies the line containing the program address @var{address}.
4155 @var{address} may be any expression.
4159 @section Searching source files
4161 @kindex reverse-search
4163 There are two commands for searching through the current source file for a
4168 @kindex forward-search
4169 @item forward-search @var{regexp}
4170 @itemx search @var{regexp}
4171 The command @samp{forward-search @var{regexp}} checks each line,
4172 starting with the one following the last line listed, for a match for
4173 @var{regexp}. It lists the line that is found. You can use the
4174 synonym @samp{search @var{regexp}} or abbreviate the command name as
4177 @item reverse-search @var{regexp}
4178 The command @samp{reverse-search @var{regexp}} checks each line, starting
4179 with the one before the last line listed and going backward, for a match
4180 for @var{regexp}. It lists the line that is found. You can abbreviate
4181 this command as @code{rev}.
4185 @section Specifying source directories
4188 @cindex directories for source files
4189 Executable programs sometimes do not record the directories of the source
4190 files from which they were compiled, just the names. Even when they do,
4191 the directories could be moved between the compilation and your debugging
4192 session. @value{GDBN} has a list of directories to search for source files;
4193 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4194 it tries all the directories in the list, in the order they are present
4195 in the list, until it finds a file with the desired name. Note that
4196 the executable search path is @emph{not} used for this purpose. Neither is
4197 the current working directory, unless it happens to be in the source
4200 If @value{GDBN} cannot find a source file in the source path, and the
4201 object program records a directory, @value{GDBN} tries that directory
4202 too. If the source path is empty, and there is no record of the
4203 compilation directory, @value{GDBN} looks in the current directory as a
4206 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4207 any information it has cached about where source files are found and where
4208 each line is in the file.
4212 When you start @value{GDBN}, its source path includes only @samp{cdir}
4213 and @samp{cwd}, in that order.
4214 To add other directories, use the @code{directory} command.
4217 @item directory @var{dirname} @dots{}
4218 @item dir @var{dirname} @dots{}
4219 Add directory @var{dirname} to the front of the source path. Several
4220 directory names may be given to this command, separated by @samp{:}
4221 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4222 part of absolute file names) or
4223 whitespace. You may specify a directory that is already in the source
4224 path; this moves it forward, so @value{GDBN} searches it sooner.
4228 @vindex $cdir@r{, convenience variable}
4229 @vindex $cwdr@r{, convenience variable}
4230 @cindex compilation directory
4231 @cindex current directory
4232 @cindex working directory
4233 @cindex directory, current
4234 @cindex directory, compilation
4235 You can use the string @samp{$cdir} to refer to the compilation
4236 directory (if one is recorded), and @samp{$cwd} to refer to the current
4237 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4238 tracks the current working directory as it changes during your @value{GDBN}
4239 session, while the latter is immediately expanded to the current
4240 directory at the time you add an entry to the source path.
4243 Reset the source path to empty again. This requires confirmation.
4245 @c RET-repeat for @code{directory} is explicitly disabled, but since
4246 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4248 @item show directories
4249 @kindex show directories
4250 Print the source path: show which directories it contains.
4253 If your source path is cluttered with directories that are no longer of
4254 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4255 versions of source. You can correct the situation as follows:
4259 Use @code{directory} with no argument to reset the source path to empty.
4262 Use @code{directory} with suitable arguments to reinstall the
4263 directories you want in the source path. You can add all the
4264 directories in one command.
4268 @section Source and machine code
4270 You can use the command @code{info line} to map source lines to program
4271 addresses (and vice versa), and the command @code{disassemble} to display
4272 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4273 mode, the @code{info line} command causes the arrow to point to the
4274 line specified. Also, @code{info line} prints addresses in symbolic form as
4279 @item info line @var{linespec}
4280 Print the starting and ending addresses of the compiled code for
4281 source line @var{linespec}. You can specify source lines in any of
4282 the ways understood by the @code{list} command (@pxref{List, ,Printing
4286 For example, we can use @code{info line} to discover the location of
4287 the object code for the first line of function
4288 @code{m4_changequote}:
4290 @c FIXME: I think this example should also show the addresses in
4291 @c symbolic form, as they usually would be displayed.
4293 (@value{GDBP}) info line m4_changequote
4294 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4298 We can also inquire (using @code{*@var{addr}} as the form for
4299 @var{linespec}) what source line covers a particular address:
4301 (@value{GDBP}) info line *0x63ff
4302 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4305 @cindex @code{$_} and @code{info line}
4306 @kindex x@r{(examine), and} info line
4307 After @code{info line}, the default address for the @code{x} command
4308 is changed to the starting address of the line, so that @samp{x/i} is
4309 sufficient to begin examining the machine code (@pxref{Memory,
4310 ,Examining memory}). Also, this address is saved as the value of the
4311 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4316 @cindex assembly instructions
4317 @cindex instructions, assembly
4318 @cindex machine instructions
4319 @cindex listing machine instructions
4321 This specialized command dumps a range of memory as machine
4322 instructions. The default memory range is the function surrounding the
4323 program counter of the selected frame. A single argument to this
4324 command is a program counter value; @value{GDBN} dumps the function
4325 surrounding this value. Two arguments specify a range of addresses
4326 (first inclusive, second exclusive) to dump.
4329 The following example shows the disassembly of a range of addresses of
4330 HP PA-RISC 2.0 code:
4333 (@value{GDBP}) disas 0x32c4 0x32e4
4334 Dump of assembler code from 0x32c4 to 0x32e4:
4335 0x32c4 <main+204>: addil 0,dp
4336 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4337 0x32cc <main+212>: ldil 0x3000,r31
4338 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4339 0x32d4 <main+220>: ldo 0(r31),rp
4340 0x32d8 <main+224>: addil -0x800,dp
4341 0x32dc <main+228>: ldo 0x588(r1),r26
4342 0x32e0 <main+232>: ldil 0x3000,r31
4343 End of assembler dump.
4346 Some architectures have more than one commonly-used set of instruction
4347 mnemonics or other syntax.
4350 @kindex set disassembly-flavor
4351 @cindex assembly instructions
4352 @cindex instructions, assembly
4353 @cindex machine instructions
4354 @cindex listing machine instructions
4355 @cindex Intel disassembly flavor
4356 @cindex AT&T disassembly flavor
4357 @item set disassembly-flavor @var{instruction-set}
4358 Select the instruction set to use when disassembling the
4359 program via the @code{disassemble} or @code{x/i} commands.
4361 Currently this command is only defined for the Intel x86 family. You
4362 can set @var{instruction-set} to either @code{intel} or @code{att}.
4363 The default is @code{att}, the AT&T flavor used by default by Unix
4364 assemblers for x86-based targets.
4369 @chapter Examining Data
4371 @cindex printing data
4372 @cindex examining data
4375 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4376 @c document because it is nonstandard... Under Epoch it displays in a
4377 @c different window or something like that.
4378 The usual way to examine data in your program is with the @code{print}
4379 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4380 evaluates and prints the value of an expression of the language your
4381 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4382 Different Languages}).
4385 @item print @var{expr}
4386 @itemx print /@var{f} @var{expr}
4387 @var{expr} is an expression (in the source language). By default the
4388 value of @var{expr} is printed in a format appropriate to its data type;
4389 you can choose a different format by specifying @samp{/@var{f}}, where
4390 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4394 @itemx print /@var{f}
4395 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4396 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4397 conveniently inspect the same value in an alternative format.
4400 A more low-level way of examining data is with the @code{x} command.
4401 It examines data in memory at a specified address and prints it in a
4402 specified format. @xref{Memory, ,Examining memory}.
4404 If you are interested in information about types, or about how the
4405 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4406 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4410 * Expressions:: Expressions
4411 * Variables:: Program variables
4412 * Arrays:: Artificial arrays
4413 * Output Formats:: Output formats
4414 * Memory:: Examining memory
4415 * Auto Display:: Automatic display
4416 * Print Settings:: Print settings
4417 * Value History:: Value history
4418 * Convenience Vars:: Convenience variables
4419 * Registers:: Registers
4420 * Floating Point Hardware:: Floating point hardware
4421 * Vector Unit:: Vector Unit
4422 * Memory Region Attributes:: Memory region attributes
4423 * Dump/Restore Files:: Copy between memory and a file
4427 @section Expressions
4430 @code{print} and many other @value{GDBN} commands accept an expression and
4431 compute its value. Any kind of constant, variable or operator defined
4432 by the programming language you are using is valid in an expression in
4433 @value{GDBN}. This includes conditional expressions, function calls,
4434 casts, and string constants. It also includes preprocessor macros, if
4435 you compiled your program to include this information; see
4438 @value{GDBN} supports array constants in expressions input by
4439 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4440 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4441 memory that is @code{malloc}ed in the target program.
4443 Because C is so widespread, most of the expressions shown in examples in
4444 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4445 Languages}, for information on how to use expressions in other
4448 In this section, we discuss operators that you can use in @value{GDBN}
4449 expressions regardless of your programming language.
4451 Casts are supported in all languages, not just in C, because it is so
4452 useful to cast a number into a pointer in order to examine a structure
4453 at that address in memory.
4454 @c FIXME: casts supported---Mod2 true?
4456 @value{GDBN} supports these operators, in addition to those common
4457 to programming languages:
4461 @samp{@@} is a binary operator for treating parts of memory as arrays.
4462 @xref{Arrays, ,Artificial arrays}, for more information.
4465 @samp{::} allows you to specify a variable in terms of the file or
4466 function where it is defined. @xref{Variables, ,Program variables}.
4468 @cindex @{@var{type}@}
4469 @cindex type casting memory
4470 @cindex memory, viewing as typed object
4471 @cindex casts, to view memory
4472 @item @{@var{type}@} @var{addr}
4473 Refers to an object of type @var{type} stored at address @var{addr} in
4474 memory. @var{addr} may be any expression whose value is an integer or
4475 pointer (but parentheses are required around binary operators, just as in
4476 a cast). This construct is allowed regardless of what kind of data is
4477 normally supposed to reside at @var{addr}.
4481 @section Program variables
4483 The most common kind of expression to use is the name of a variable
4486 Variables in expressions are understood in the selected stack frame
4487 (@pxref{Selection, ,Selecting a frame}); they must be either:
4491 global (or file-static)
4498 visible according to the scope rules of the
4499 programming language from the point of execution in that frame
4502 @noindent This means that in the function
4517 you can examine and use the variable @code{a} whenever your program is
4518 executing within the function @code{foo}, but you can only use or
4519 examine the variable @code{b} while your program is executing inside
4520 the block where @code{b} is declared.
4522 @cindex variable name conflict
4523 There is an exception: you can refer to a variable or function whose
4524 scope is a single source file even if the current execution point is not
4525 in this file. But it is possible to have more than one such variable or
4526 function with the same name (in different source files). If that
4527 happens, referring to that name has unpredictable effects. If you wish,
4528 you can specify a static variable in a particular function or file,
4529 using the colon-colon notation:
4531 @cindex colon-colon, context for variables/functions
4533 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4534 @cindex @code{::}, context for variables/functions
4537 @var{file}::@var{variable}
4538 @var{function}::@var{variable}
4542 Here @var{file} or @var{function} is the name of the context for the
4543 static @var{variable}. In the case of file names, you can use quotes to
4544 make sure @value{GDBN} parses the file name as a single word---for example,
4545 to print a global value of @code{x} defined in @file{f2.c}:
4548 (@value{GDBP}) p 'f2.c'::x
4551 @cindex C@t{++} scope resolution
4552 This use of @samp{::} is very rarely in conflict with the very similar
4553 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4554 scope resolution operator in @value{GDBN} expressions.
4555 @c FIXME: Um, so what happens in one of those rare cases where it's in
4558 @cindex wrong values
4559 @cindex variable values, wrong
4561 @emph{Warning:} Occasionally, a local variable may appear to have the
4562 wrong value at certain points in a function---just after entry to a new
4563 scope, and just before exit.
4565 You may see this problem when you are stepping by machine instructions.
4566 This is because, on most machines, it takes more than one instruction to
4567 set up a stack frame (including local variable definitions); if you are
4568 stepping by machine instructions, variables may appear to have the wrong
4569 values until the stack frame is completely built. On exit, it usually
4570 also takes more than one machine instruction to destroy a stack frame;
4571 after you begin stepping through that group of instructions, local
4572 variable definitions may be gone.
4574 This may also happen when the compiler does significant optimizations.
4575 To be sure of always seeing accurate values, turn off all optimization
4578 @cindex ``No symbol "foo" in current context''
4579 Another possible effect of compiler optimizations is to optimize
4580 unused variables out of existence, or assign variables to registers (as
4581 opposed to memory addresses). Depending on the support for such cases
4582 offered by the debug info format used by the compiler, @value{GDBN}
4583 might not be able to display values for such local variables. If that
4584 happens, @value{GDBN} will print a message like this:
4587 No symbol "foo" in current context.
4590 To solve such problems, either recompile without optimizations, or use a
4591 different debug info format, if the compiler supports several such
4592 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4593 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4594 in a format that is superior to formats such as COFF. You may be able
4595 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4596 debug info. See @ref{Debugging Options,,Options for Debugging Your
4597 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4602 @section Artificial arrays
4604 @cindex artificial array
4605 @kindex @@@r{, referencing memory as an array}
4606 It is often useful to print out several successive objects of the
4607 same type in memory; a section of an array, or an array of
4608 dynamically determined size for which only a pointer exists in the
4611 You can do this by referring to a contiguous span of memory as an
4612 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4613 operand of @samp{@@} should be the first element of the desired array
4614 and be an individual object. The right operand should be the desired length
4615 of the array. The result is an array value whose elements are all of
4616 the type of the left argument. The first element is actually the left
4617 argument; the second element comes from bytes of memory immediately
4618 following those that hold the first element, and so on. Here is an
4619 example. If a program says
4622 int *array = (int *) malloc (len * sizeof (int));
4626 you can print the contents of @code{array} with
4632 The left operand of @samp{@@} must reside in memory. Array values made
4633 with @samp{@@} in this way behave just like other arrays in terms of
4634 subscripting, and are coerced to pointers when used in expressions.
4635 Artificial arrays most often appear in expressions via the value history
4636 (@pxref{Value History, ,Value history}), after printing one out.
4638 Another way to create an artificial array is to use a cast.
4639 This re-interprets a value as if it were an array.
4640 The value need not be in memory:
4642 (@value{GDBP}) p/x (short[2])0x12345678
4643 $1 = @{0x1234, 0x5678@}
4646 As a convenience, if you leave the array length out (as in
4647 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4648 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4650 (@value{GDBP}) p/x (short[])0x12345678
4651 $2 = @{0x1234, 0x5678@}
4654 Sometimes the artificial array mechanism is not quite enough; in
4655 moderately complex data structures, the elements of interest may not
4656 actually be adjacent---for example, if you are interested in the values
4657 of pointers in an array. One useful work-around in this situation is
4658 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4659 variables}) as a counter in an expression that prints the first
4660 interesting value, and then repeat that expression via @key{RET}. For
4661 instance, suppose you have an array @code{dtab} of pointers to
4662 structures, and you are interested in the values of a field @code{fv}
4663 in each structure. Here is an example of what you might type:
4673 @node Output Formats
4674 @section Output formats
4676 @cindex formatted output
4677 @cindex output formats
4678 By default, @value{GDBN} prints a value according to its data type. Sometimes
4679 this is not what you want. For example, you might want to print a number
4680 in hex, or a pointer in decimal. Or you might want to view data in memory
4681 at a certain address as a character string or as an instruction. To do
4682 these things, specify an @dfn{output format} when you print a value.
4684 The simplest use of output formats is to say how to print a value
4685 already computed. This is done by starting the arguments of the
4686 @code{print} command with a slash and a format letter. The format
4687 letters supported are:
4691 Regard the bits of the value as an integer, and print the integer in
4695 Print as integer in signed decimal.
4698 Print as integer in unsigned decimal.
4701 Print as integer in octal.
4704 Print as integer in binary. The letter @samp{t} stands for ``two''.
4705 @footnote{@samp{b} cannot be used because these format letters are also
4706 used with the @code{x} command, where @samp{b} stands for ``byte'';
4707 see @ref{Memory,,Examining memory}.}
4710 @cindex unknown address, locating
4711 @cindex locate address
4712 Print as an address, both absolute in hexadecimal and as an offset from
4713 the nearest preceding symbol. You can use this format used to discover
4714 where (in what function) an unknown address is located:
4717 (@value{GDBP}) p/a 0x54320
4718 $3 = 0x54320 <_initialize_vx+396>
4722 The command @code{info symbol 0x54320} yields similar results.
4723 @xref{Symbols, info symbol}.
4726 Regard as an integer and print it as a character constant.
4729 Regard the bits of the value as a floating point number and print
4730 using typical floating point syntax.
4733 For example, to print the program counter in hex (@pxref{Registers}), type
4740 Note that no space is required before the slash; this is because command
4741 names in @value{GDBN} cannot contain a slash.
4743 To reprint the last value in the value history with a different format,
4744 you can use the @code{print} command with just a format and no
4745 expression. For example, @samp{p/x} reprints the last value in hex.
4748 @section Examining memory
4750 You can use the command @code{x} (for ``examine'') to examine memory in
4751 any of several formats, independently of your program's data types.
4753 @cindex examining memory
4755 @kindex x @r{(examine memory)}
4756 @item x/@var{nfu} @var{addr}
4759 Use the @code{x} command to examine memory.
4762 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4763 much memory to display and how to format it; @var{addr} is an
4764 expression giving the address where you want to start displaying memory.
4765 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4766 Several commands set convenient defaults for @var{addr}.
4769 @item @var{n}, the repeat count
4770 The repeat count is a decimal integer; the default is 1. It specifies
4771 how much memory (counting by units @var{u}) to display.
4772 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4775 @item @var{f}, the display format
4776 The display format is one of the formats used by @code{print},
4777 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4778 The default is @samp{x} (hexadecimal) initially.
4779 The default changes each time you use either @code{x} or @code{print}.
4781 @item @var{u}, the unit size
4782 The unit size is any of
4788 Halfwords (two bytes).
4790 Words (four bytes). This is the initial default.
4792 Giant words (eight bytes).
4795 Each time you specify a unit size with @code{x}, that size becomes the
4796 default unit the next time you use @code{x}. (For the @samp{s} and
4797 @samp{i} formats, the unit size is ignored and is normally not written.)
4799 @item @var{addr}, starting display address
4800 @var{addr} is the address where you want @value{GDBN} to begin displaying
4801 memory. The expression need not have a pointer value (though it may);
4802 it is always interpreted as an integer address of a byte of memory.
4803 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4804 @var{addr} is usually just after the last address examined---but several
4805 other commands also set the default address: @code{info breakpoints} (to
4806 the address of the last breakpoint listed), @code{info line} (to the
4807 starting address of a line), and @code{print} (if you use it to display
4808 a value from memory).
4811 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4812 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4813 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4814 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4815 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4817 Since the letters indicating unit sizes are all distinct from the
4818 letters specifying output formats, you do not have to remember whether
4819 unit size or format comes first; either order works. The output
4820 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4821 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4823 Even though the unit size @var{u} is ignored for the formats @samp{s}
4824 and @samp{i}, you might still want to use a count @var{n}; for example,
4825 @samp{3i} specifies that you want to see three machine instructions,
4826 including any operands. The command @code{disassemble} gives an
4827 alternative way of inspecting machine instructions; see @ref{Machine
4828 Code,,Source and machine code}.
4830 All the defaults for the arguments to @code{x} are designed to make it
4831 easy to continue scanning memory with minimal specifications each time
4832 you use @code{x}. For example, after you have inspected three machine
4833 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4834 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4835 the repeat count @var{n} is used again; the other arguments default as
4836 for successive uses of @code{x}.
4838 @cindex @code{$_}, @code{$__}, and value history
4839 The addresses and contents printed by the @code{x} command are not saved
4840 in the value history because there is often too much of them and they
4841 would get in the way. Instead, @value{GDBN} makes these values available for
4842 subsequent use in expressions as values of the convenience variables
4843 @code{$_} and @code{$__}. After an @code{x} command, the last address
4844 examined is available for use in expressions in the convenience variable
4845 @code{$_}. The contents of that address, as examined, are available in
4846 the convenience variable @code{$__}.
4848 If the @code{x} command has a repeat count, the address and contents saved
4849 are from the last memory unit printed; this is not the same as the last
4850 address printed if several units were printed on the last line of output.
4853 @section Automatic display
4854 @cindex automatic display
4855 @cindex display of expressions
4857 If you find that you want to print the value of an expression frequently
4858 (to see how it changes), you might want to add it to the @dfn{automatic
4859 display list} so that @value{GDBN} prints its value each time your program stops.
4860 Each expression added to the list is given a number to identify it;
4861 to remove an expression from the list, you specify that number.
4862 The automatic display looks like this:
4866 3: bar[5] = (struct hack *) 0x3804
4870 This display shows item numbers, expressions and their current values. As with
4871 displays you request manually using @code{x} or @code{print}, you can
4872 specify the output format you prefer; in fact, @code{display} decides
4873 whether to use @code{print} or @code{x} depending on how elaborate your
4874 format specification is---it uses @code{x} if you specify a unit size,
4875 or one of the two formats (@samp{i} and @samp{s}) that are only
4876 supported by @code{x}; otherwise it uses @code{print}.
4880 @item display @var{expr}
4881 Add the expression @var{expr} to the list of expressions to display
4882 each time your program stops. @xref{Expressions, ,Expressions}.
4884 @code{display} does not repeat if you press @key{RET} again after using it.
4886 @item display/@var{fmt} @var{expr}
4887 For @var{fmt} specifying only a display format and not a size or
4888 count, add the expression @var{expr} to the auto-display list but
4889 arrange to display it each time in the specified format @var{fmt}.
4890 @xref{Output Formats,,Output formats}.
4892 @item display/@var{fmt} @var{addr}
4893 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4894 number of units, add the expression @var{addr} as a memory address to
4895 be examined each time your program stops. Examining means in effect
4896 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4899 For example, @samp{display/i $pc} can be helpful, to see the machine
4900 instruction about to be executed each time execution stops (@samp{$pc}
4901 is a common name for the program counter; @pxref{Registers, ,Registers}).
4904 @kindex delete display
4906 @item undisplay @var{dnums}@dots{}
4907 @itemx delete display @var{dnums}@dots{}
4908 Remove item numbers @var{dnums} from the list of expressions to display.
4910 @code{undisplay} does not repeat if you press @key{RET} after using it.
4911 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4913 @kindex disable display
4914 @item disable display @var{dnums}@dots{}
4915 Disable the display of item numbers @var{dnums}. A disabled display
4916 item is not printed automatically, but is not forgotten. It may be
4917 enabled again later.
4919 @kindex enable display
4920 @item enable display @var{dnums}@dots{}
4921 Enable display of item numbers @var{dnums}. It becomes effective once
4922 again in auto display of its expression, until you specify otherwise.
4925 Display the current values of the expressions on the list, just as is
4926 done when your program stops.
4928 @kindex info display
4930 Print the list of expressions previously set up to display
4931 automatically, each one with its item number, but without showing the
4932 values. This includes disabled expressions, which are marked as such.
4933 It also includes expressions which would not be displayed right now
4934 because they refer to automatic variables not currently available.
4937 If a display expression refers to local variables, then it does not make
4938 sense outside the lexical context for which it was set up. Such an
4939 expression is disabled when execution enters a context where one of its
4940 variables is not defined. For example, if you give the command
4941 @code{display last_char} while inside a function with an argument
4942 @code{last_char}, @value{GDBN} displays this argument while your program
4943 continues to stop inside that function. When it stops elsewhere---where
4944 there is no variable @code{last_char}---the display is disabled
4945 automatically. The next time your program stops where @code{last_char}
4946 is meaningful, you can enable the display expression once again.
4948 @node Print Settings
4949 @section Print settings
4951 @cindex format options
4952 @cindex print settings
4953 @value{GDBN} provides the following ways to control how arrays, structures,
4954 and symbols are printed.
4957 These settings are useful for debugging programs in any language:
4960 @kindex set print address
4961 @item set print address
4962 @itemx set print address on
4963 @value{GDBN} prints memory addresses showing the location of stack
4964 traces, structure values, pointer values, breakpoints, and so forth,
4965 even when it also displays the contents of those addresses. The default
4966 is @code{on}. For example, this is what a stack frame display looks like with
4967 @code{set print address on}:
4972 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4974 530 if (lquote != def_lquote)
4978 @item set print address off
4979 Do not print addresses when displaying their contents. For example,
4980 this is the same stack frame displayed with @code{set print address off}:
4984 (@value{GDBP}) set print addr off
4986 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4987 530 if (lquote != def_lquote)
4991 You can use @samp{set print address off} to eliminate all machine
4992 dependent displays from the @value{GDBN} interface. For example, with
4993 @code{print address off}, you should get the same text for backtraces on
4994 all machines---whether or not they involve pointer arguments.
4996 @kindex show print address
4997 @item show print address
4998 Show whether or not addresses are to be printed.
5001 When @value{GDBN} prints a symbolic address, it normally prints the
5002 closest earlier symbol plus an offset. If that symbol does not uniquely
5003 identify the address (for example, it is a name whose scope is a single
5004 source file), you may need to clarify. One way to do this is with
5005 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5006 you can set @value{GDBN} to print the source file and line number when
5007 it prints a symbolic address:
5010 @kindex set print symbol-filename
5011 @item set print symbol-filename on
5012 Tell @value{GDBN} to print the source file name and line number of a
5013 symbol in the symbolic form of an address.
5015 @item set print symbol-filename off
5016 Do not print source file name and line number of a symbol. This is the
5019 @kindex show print symbol-filename
5020 @item show print symbol-filename
5021 Show whether or not @value{GDBN} will print the source file name and
5022 line number of a symbol in the symbolic form of an address.
5025 Another situation where it is helpful to show symbol filenames and line
5026 numbers is when disassembling code; @value{GDBN} shows you the line
5027 number and source file that corresponds to each instruction.
5029 Also, you may wish to see the symbolic form only if the address being
5030 printed is reasonably close to the closest earlier symbol:
5033 @kindex set print max-symbolic-offset
5034 @item set print max-symbolic-offset @var{max-offset}
5035 Tell @value{GDBN} to only display the symbolic form of an address if the
5036 offset between the closest earlier symbol and the address is less than
5037 @var{max-offset}. The default is 0, which tells @value{GDBN}
5038 to always print the symbolic form of an address if any symbol precedes it.
5040 @kindex show print max-symbolic-offset
5041 @item show print max-symbolic-offset
5042 Ask how large the maximum offset is that @value{GDBN} prints in a
5046 @cindex wild pointer, interpreting
5047 @cindex pointer, finding referent
5048 If you have a pointer and you are not sure where it points, try
5049 @samp{set print symbol-filename on}. Then you can determine the name
5050 and source file location of the variable where it points, using
5051 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5052 For example, here @value{GDBN} shows that a variable @code{ptt} points
5053 at another variable @code{t}, defined in @file{hi2.c}:
5056 (@value{GDBP}) set print symbol-filename on
5057 (@value{GDBP}) p/a ptt
5058 $4 = 0xe008 <t in hi2.c>
5062 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5063 does not show the symbol name and filename of the referent, even with
5064 the appropriate @code{set print} options turned on.
5067 Other settings control how different kinds of objects are printed:
5070 @kindex set print array
5071 @item set print array
5072 @itemx set print array on
5073 Pretty print arrays. This format is more convenient to read,
5074 but uses more space. The default is off.
5076 @item set print array off
5077 Return to compressed format for arrays.
5079 @kindex show print array
5080 @item show print array
5081 Show whether compressed or pretty format is selected for displaying
5084 @kindex set print elements
5085 @item set print elements @var{number-of-elements}
5086 Set a limit on how many elements of an array @value{GDBN} will print.
5087 If @value{GDBN} is printing a large array, it stops printing after it has
5088 printed the number of elements set by the @code{set print elements} command.
5089 This limit also applies to the display of strings.
5090 When @value{GDBN} starts, this limit is set to 200.
5091 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5093 @kindex show print elements
5094 @item show print elements
5095 Display the number of elements of a large array that @value{GDBN} will print.
5096 If the number is 0, then the printing is unlimited.
5098 @kindex set print null-stop
5099 @item set print null-stop
5100 Cause @value{GDBN} to stop printing the characters of an array when the first
5101 @sc{null} is encountered. This is useful when large arrays actually
5102 contain only short strings.
5105 @kindex set print pretty
5106 @item set print pretty on
5107 Cause @value{GDBN} to print structures in an indented format with one member
5108 per line, like this:
5123 @item set print pretty off
5124 Cause @value{GDBN} to print structures in a compact format, like this:
5128 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5129 meat = 0x54 "Pork"@}
5134 This is the default format.
5136 @kindex show print pretty
5137 @item show print pretty
5138 Show which format @value{GDBN} is using to print structures.
5140 @kindex set print sevenbit-strings
5141 @item set print sevenbit-strings on
5142 Print using only seven-bit characters; if this option is set,
5143 @value{GDBN} displays any eight-bit characters (in strings or
5144 character values) using the notation @code{\}@var{nnn}. This setting is
5145 best if you are working in English (@sc{ascii}) and you use the
5146 high-order bit of characters as a marker or ``meta'' bit.
5148 @item set print sevenbit-strings off
5149 Print full eight-bit characters. This allows the use of more
5150 international character sets, and is the default.
5152 @kindex show print sevenbit-strings
5153 @item show print sevenbit-strings
5154 Show whether or not @value{GDBN} is printing only seven-bit characters.
5156 @kindex set print union
5157 @item set print union on
5158 Tell @value{GDBN} to print unions which are contained in structures. This
5159 is the default setting.
5161 @item set print union off
5162 Tell @value{GDBN} not to print unions which are contained in structures.
5164 @kindex show print union
5165 @item show print union
5166 Ask @value{GDBN} whether or not it will print unions which are contained in
5169 For example, given the declarations
5172 typedef enum @{Tree, Bug@} Species;
5173 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5174 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5185 struct thing foo = @{Tree, @{Acorn@}@};
5189 with @code{set print union on} in effect @samp{p foo} would print
5192 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5196 and with @code{set print union off} in effect it would print
5199 $1 = @{it = Tree, form = @{...@}@}
5205 These settings are of interest when debugging C@t{++} programs:
5209 @kindex set print demangle
5210 @item set print demangle
5211 @itemx set print demangle on
5212 Print C@t{++} names in their source form rather than in the encoded
5213 (``mangled'') form passed to the assembler and linker for type-safe
5214 linkage. The default is on.
5216 @kindex show print demangle
5217 @item show print demangle
5218 Show whether C@t{++} names are printed in mangled or demangled form.
5220 @kindex set print asm-demangle
5221 @item set print asm-demangle
5222 @itemx set print asm-demangle on
5223 Print C@t{++} names in their source form rather than their mangled form, even
5224 in assembler code printouts such as instruction disassemblies.
5227 @kindex show print asm-demangle
5228 @item show print asm-demangle
5229 Show whether C@t{++} names in assembly listings are printed in mangled
5232 @kindex set demangle-style
5233 @cindex C@t{++} symbol decoding style
5234 @cindex symbol decoding style, C@t{++}
5235 @item set demangle-style @var{style}
5236 Choose among several encoding schemes used by different compilers to
5237 represent C@t{++} names. The choices for @var{style} are currently:
5241 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5244 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5245 This is the default.
5248 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5251 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5254 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5255 @strong{Warning:} this setting alone is not sufficient to allow
5256 debugging @code{cfront}-generated executables. @value{GDBN} would
5257 require further enhancement to permit that.
5260 If you omit @var{style}, you will see a list of possible formats.
5262 @kindex show demangle-style
5263 @item show demangle-style
5264 Display the encoding style currently in use for decoding C@t{++} symbols.
5266 @kindex set print object
5267 @item set print object
5268 @itemx set print object on
5269 When displaying a pointer to an object, identify the @emph{actual}
5270 (derived) type of the object rather than the @emph{declared} type, using
5271 the virtual function table.
5273 @item set print object off
5274 Display only the declared type of objects, without reference to the
5275 virtual function table. This is the default setting.
5277 @kindex show print object
5278 @item show print object
5279 Show whether actual, or declared, object types are displayed.
5281 @kindex set print static-members
5282 @item set print static-members
5283 @itemx set print static-members on
5284 Print static members when displaying a C@t{++} object. The default is on.
5286 @item set print static-members off
5287 Do not print static members when displaying a C@t{++} object.
5289 @kindex show print static-members
5290 @item show print static-members
5291 Show whether C@t{++} static members are printed, or not.
5293 @c These don't work with HP ANSI C++ yet.
5294 @kindex set print vtbl
5295 @item set print vtbl
5296 @itemx set print vtbl on
5297 Pretty print C@t{++} virtual function tables. The default is off.
5298 (The @code{vtbl} commands do not work on programs compiled with the HP
5299 ANSI C@t{++} compiler (@code{aCC}).)
5301 @item set print vtbl off
5302 Do not pretty print C@t{++} virtual function tables.
5304 @kindex show print vtbl
5305 @item show print vtbl
5306 Show whether C@t{++} virtual function tables are pretty printed, or not.
5310 @section Value history
5312 @cindex value history
5313 Values printed by the @code{print} command are saved in the @value{GDBN}
5314 @dfn{value history}. This allows you to refer to them in other expressions.
5315 Values are kept until the symbol table is re-read or discarded
5316 (for example with the @code{file} or @code{symbol-file} commands).
5317 When the symbol table changes, the value history is discarded,
5318 since the values may contain pointers back to the types defined in the
5323 @cindex history number
5324 The values printed are given @dfn{history numbers} by which you can
5325 refer to them. These are successive integers starting with one.
5326 @code{print} shows you the history number assigned to a value by
5327 printing @samp{$@var{num} = } before the value; here @var{num} is the
5330 To refer to any previous value, use @samp{$} followed by the value's
5331 history number. The way @code{print} labels its output is designed to
5332 remind you of this. Just @code{$} refers to the most recent value in
5333 the history, and @code{$$} refers to the value before that.
5334 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5335 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5336 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5338 For example, suppose you have just printed a pointer to a structure and
5339 want to see the contents of the structure. It suffices to type
5345 If you have a chain of structures where the component @code{next} points
5346 to the next one, you can print the contents of the next one with this:
5353 You can print successive links in the chain by repeating this
5354 command---which you can do by just typing @key{RET}.
5356 Note that the history records values, not expressions. If the value of
5357 @code{x} is 4 and you type these commands:
5365 then the value recorded in the value history by the @code{print} command
5366 remains 4 even though the value of @code{x} has changed.
5371 Print the last ten values in the value history, with their item numbers.
5372 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5373 values} does not change the history.
5375 @item show values @var{n}
5376 Print ten history values centered on history item number @var{n}.
5379 Print ten history values just after the values last printed. If no more
5380 values are available, @code{show values +} produces no display.
5383 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5384 same effect as @samp{show values +}.
5386 @node Convenience Vars
5387 @section Convenience variables
5389 @cindex convenience variables
5390 @value{GDBN} provides @dfn{convenience variables} that you can use within
5391 @value{GDBN} to hold on to a value and refer to it later. These variables
5392 exist entirely within @value{GDBN}; they are not part of your program, and
5393 setting a convenience variable has no direct effect on further execution
5394 of your program. That is why you can use them freely.
5396 Convenience variables are prefixed with @samp{$}. Any name preceded by
5397 @samp{$} can be used for a convenience variable, unless it is one of
5398 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5399 (Value history references, in contrast, are @emph{numbers} preceded
5400 by @samp{$}. @xref{Value History, ,Value history}.)
5402 You can save a value in a convenience variable with an assignment
5403 expression, just as you would set a variable in your program.
5407 set $foo = *object_ptr
5411 would save in @code{$foo} the value contained in the object pointed to by
5414 Using a convenience variable for the first time creates it, but its
5415 value is @code{void} until you assign a new value. You can alter the
5416 value with another assignment at any time.
5418 Convenience variables have no fixed types. You can assign a convenience
5419 variable any type of value, including structures and arrays, even if
5420 that variable already has a value of a different type. The convenience
5421 variable, when used as an expression, has the type of its current value.
5424 @kindex show convenience
5425 @item show convenience
5426 Print a list of convenience variables used so far, and their values.
5427 Abbreviated @code{show conv}.
5430 One of the ways to use a convenience variable is as a counter to be
5431 incremented or a pointer to be advanced. For example, to print
5432 a field from successive elements of an array of structures:
5436 print bar[$i++]->contents
5440 Repeat that command by typing @key{RET}.
5442 Some convenience variables are created automatically by @value{GDBN} and given
5443 values likely to be useful.
5446 @vindex $_@r{, convenience variable}
5448 The variable @code{$_} is automatically set by the @code{x} command to
5449 the last address examined (@pxref{Memory, ,Examining memory}). Other
5450 commands which provide a default address for @code{x} to examine also
5451 set @code{$_} to that address; these commands include @code{info line}
5452 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5453 except when set by the @code{x} command, in which case it is a pointer
5454 to the type of @code{$__}.
5456 @vindex $__@r{, convenience variable}
5458 The variable @code{$__} is automatically set by the @code{x} command
5459 to the value found in the last address examined. Its type is chosen
5460 to match the format in which the data was printed.
5463 @vindex $_exitcode@r{, convenience variable}
5464 The variable @code{$_exitcode} is automatically set to the exit code when
5465 the program being debugged terminates.
5468 On HP-UX systems, if you refer to a function or variable name that
5469 begins with a dollar sign, @value{GDBN} searches for a user or system
5470 name first, before it searches for a convenience variable.
5476 You can refer to machine register contents, in expressions, as variables
5477 with names starting with @samp{$}. The names of registers are different
5478 for each machine; use @code{info registers} to see the names used on
5482 @kindex info registers
5483 @item info registers
5484 Print the names and values of all registers except floating-point
5485 registers (in the selected stack frame).
5487 @kindex info all-registers
5488 @cindex floating point registers
5489 @item info all-registers
5490 Print the names and values of all registers, including floating-point
5493 @item info registers @var{regname} @dots{}
5494 Print the @dfn{relativized} value of each specified register @var{regname}.
5495 As discussed in detail below, register values are normally relative to
5496 the selected stack frame. @var{regname} may be any register name valid on
5497 the machine you are using, with or without the initial @samp{$}.
5500 @value{GDBN} has four ``standard'' register names that are available (in
5501 expressions) on most machines---whenever they do not conflict with an
5502 architecture's canonical mnemonics for registers. The register names
5503 @code{$pc} and @code{$sp} are used for the program counter register and
5504 the stack pointer. @code{$fp} is used for a register that contains a
5505 pointer to the current stack frame, and @code{$ps} is used for a
5506 register that contains the processor status. For example,
5507 you could print the program counter in hex with
5514 or print the instruction to be executed next with
5521 or add four to the stack pointer@footnote{This is a way of removing
5522 one word from the stack, on machines where stacks grow downward in
5523 memory (most machines, nowadays). This assumes that the innermost
5524 stack frame is selected; setting @code{$sp} is not allowed when other
5525 stack frames are selected. To pop entire frames off the stack,
5526 regardless of machine architecture, use @code{return};
5527 see @ref{Returning, ,Returning from a function}.} with
5533 Whenever possible, these four standard register names are available on
5534 your machine even though the machine has different canonical mnemonics,
5535 so long as there is no conflict. The @code{info registers} command
5536 shows the canonical names. For example, on the SPARC, @code{info
5537 registers} displays the processor status register as @code{$psr} but you
5538 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5539 is an alias for the @sc{eflags} register.
5541 @value{GDBN} always considers the contents of an ordinary register as an
5542 integer when the register is examined in this way. Some machines have
5543 special registers which can hold nothing but floating point; these
5544 registers are considered to have floating point values. There is no way
5545 to refer to the contents of an ordinary register as floating point value
5546 (although you can @emph{print} it as a floating point value with
5547 @samp{print/f $@var{regname}}).
5549 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5550 means that the data format in which the register contents are saved by
5551 the operating system is not the same one that your program normally
5552 sees. For example, the registers of the 68881 floating point
5553 coprocessor are always saved in ``extended'' (raw) format, but all C
5554 programs expect to work with ``double'' (virtual) format. In such
5555 cases, @value{GDBN} normally works with the virtual format only (the format
5556 that makes sense for your program), but the @code{info registers} command
5557 prints the data in both formats.
5559 Normally, register values are relative to the selected stack frame
5560 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5561 value that the register would contain if all stack frames farther in
5562 were exited and their saved registers restored. In order to see the
5563 true contents of hardware registers, you must select the innermost
5564 frame (with @samp{frame 0}).
5566 However, @value{GDBN} must deduce where registers are saved, from the machine
5567 code generated by your compiler. If some registers are not saved, or if
5568 @value{GDBN} is unable to locate the saved registers, the selected stack
5569 frame makes no difference.
5571 @node Floating Point Hardware
5572 @section Floating point hardware
5573 @cindex floating point
5575 Depending on the configuration, @value{GDBN} may be able to give
5576 you more information about the status of the floating point hardware.
5581 Display hardware-dependent information about the floating
5582 point unit. The exact contents and layout vary depending on the
5583 floating point chip. Currently, @samp{info float} is supported on
5584 the ARM and x86 machines.
5588 @section Vector Unit
5591 Depending on the configuration, @value{GDBN} may be able to give you
5592 more information about the status of the vector unit.
5597 Display information about the vector unit. The exact contents and
5598 layout vary depending on the hardware.
5601 @node Memory Region Attributes
5602 @section Memory region attributes
5603 @cindex memory region attributes
5605 @dfn{Memory region attributes} allow you to describe special handling
5606 required by regions of your target's memory. @value{GDBN} uses attributes
5607 to determine whether to allow certain types of memory accesses; whether to
5608 use specific width accesses; and whether to cache target memory.
5610 Defined memory regions can be individually enabled and disabled. When a
5611 memory region is disabled, @value{GDBN} uses the default attributes when
5612 accessing memory in that region. Similarly, if no memory regions have
5613 been defined, @value{GDBN} uses the default attributes when accessing
5616 When a memory region is defined, it is given a number to identify it;
5617 to enable, disable, or remove a memory region, you specify that number.
5621 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
5622 Define memory region bounded by @var{lower} and @var{upper} with
5623 attributes @var{attributes}@dots{}. Note that @var{upper} == 0 is a
5624 special case: it is treated as the the target's maximum memory address.
5625 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
5628 @item delete mem @var{nums}@dots{}
5629 Remove memory regions @var{nums}@dots{}.
5632 @item disable mem @var{nums}@dots{}
5633 Disable memory regions @var{nums}@dots{}.
5634 A disabled memory region is not forgotten.
5635 It may be enabled again later.
5638 @item enable mem @var{nums}@dots{}
5639 Enable memory regions @var{nums}@dots{}.
5643 Print a table of all defined memory regions, with the following columns
5647 @item Memory Region Number
5648 @item Enabled or Disabled.
5649 Enabled memory regions are marked with @samp{y}.
5650 Disabled memory regions are marked with @samp{n}.
5653 The address defining the inclusive lower bound of the memory region.
5656 The address defining the exclusive upper bound of the memory region.
5659 The list of attributes set for this memory region.
5664 @subsection Attributes
5666 @subsubsection Memory Access Mode
5667 The access mode attributes set whether @value{GDBN} may make read or
5668 write accesses to a memory region.
5670 While these attributes prevent @value{GDBN} from performing invalid
5671 memory accesses, they do nothing to prevent the target system, I/O DMA,
5672 etc. from accessing memory.
5676 Memory is read only.
5678 Memory is write only.
5680 Memory is read/write. This is the default.
5683 @subsubsection Memory Access Size
5684 The acccess size attributes tells @value{GDBN} to use specific sized
5685 accesses in the memory region. Often memory mapped device registers
5686 require specific sized accesses. If no access size attribute is
5687 specified, @value{GDBN} may use accesses of any size.
5691 Use 8 bit memory accesses.
5693 Use 16 bit memory accesses.
5695 Use 32 bit memory accesses.
5697 Use 64 bit memory accesses.
5700 @c @subsubsection Hardware/Software Breakpoints
5701 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5702 @c will use hardware or software breakpoints for the internal breakpoints
5703 @c used by the step, next, finish, until, etc. commands.
5707 @c Always use hardware breakpoints
5708 @c @item swbreak (default)
5711 @subsubsection Data Cache
5712 The data cache attributes set whether @value{GDBN} will cache target
5713 memory. While this generally improves performance by reducing debug
5714 protocol overhead, it can lead to incorrect results because @value{GDBN}
5715 does not know about volatile variables or memory mapped device
5720 Enable @value{GDBN} to cache target memory.
5722 Disable @value{GDBN} from caching target memory. This is the default.
5725 @c @subsubsection Memory Write Verification
5726 @c The memory write verification attributes set whether @value{GDBN}
5727 @c will re-reads data after each write to verify the write was successful.
5731 @c @item noverify (default)
5734 @node Dump/Restore Files
5735 @section Copy between memory and a file
5736 @cindex dump/restore files
5737 @cindex append data to a file
5738 @cindex dump data to a file
5739 @cindex restore data from a file
5744 The commands @code{dump}, @code{append}, and @code{restore} are used
5745 for copying data between target memory and a file. Data is written
5746 into a file using @code{dump} or @code{append}, and restored from a
5747 file into memory by using @code{restore}. Files may be binary, srec,
5748 intel hex, or tekhex (but only binary files can be appended).
5752 @kindex append binary
5753 @item dump binary memory @var{filename} @var{start_addr} @var{end_addr}
5754 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5755 raw binary format file @var{filename}.
5757 @item append binary memory @var{filename} @var{start_addr} @var{end_addr}
5758 Append contents of memory from @var{start_addr} to @var{end_addr} to
5759 raw binary format file @var{filename}.
5761 @item dump binary value @var{filename} @var{expression}
5762 Dump value of @var{expression} into raw binary format file @var{filename}.
5764 @item append binary memory @var{filename} @var{expression}
5765 Append value of @var{expression} to raw binary format file @var{filename}.
5768 @item dump ihex memory @var{filename} @var{start_addr} @var{end_addr}
5769 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5770 intel hex format file @var{filename}.
5772 @item dump ihex value @var{filename} @var{expression}
5773 Dump value of @var{expression} into intel hex format file @var{filename}.
5776 @item dump srec memory @var{filename} @var{start_addr} @var{end_addr}
5777 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5778 srec format file @var{filename}.
5780 @item dump srec value @var{filename} @var{expression}
5781 Dump value of @var{expression} into srec format file @var{filename}.
5784 @item dump tekhex memory @var{filename} @var{start_addr} @var{end_addr}
5785 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5786 tekhex format file @var{filename}.
5788 @item dump tekhex value @var{filename} @var{expression}
5789 Dump value of @var{expression} into tekhex format file @var{filename}.
5791 @item restore @var{filename} [@var{binary}] @var{bias} @var{start} @var{end}
5792 Restore the contents of file @var{filename} into memory. The @code{restore}
5793 command can automatically recognize any known bfd file format, except for
5794 raw binary. To restore a raw binary file you must use the optional argument
5795 @var{binary} after the filename.
5797 If @var{bias} is non-zero, its value will be added to the addresses
5798 contained in the file. Binary files always start at address zero, so
5799 they will be restored at address @var{bias}. Other bfd files have
5800 a built-in location; they will be restored at offset @var{bias}
5803 If @var{start} and/or @var{end} are non-zero, then only data between
5804 file offset @var{start} and file offset @var{end} will be restored.
5805 These offsets are relative to the addresses in the file, before
5806 the @var{bias} argument is applied.
5811 @chapter C Preprocessor Macros
5813 Some languages, such as C and C++, provide a way to define and invoke
5814 ``preprocessor macros'' which expand into strings of tokens.
5815 @value{GDBN} can evaluate expressions containing macro invocations, show
5816 the result of macro expansion, and show a macro's definition, including
5817 where it was defined.
5819 You may need to compile your program specially to provide @value{GDBN}
5820 with information about preprocessor macros. Most compilers do not
5821 include macros in their debugging information, even when you compile
5822 with the @option{-g} flag. @xref{Compilation}.
5824 A program may define a macro at one point, remove that definition later,
5825 and then provide a different definition after that. Thus, at different
5826 points in the program, a macro may have different definitions, or have
5827 no definition at all. If there is a current stack frame, @value{GDBN}
5828 uses the macros in scope at that frame's source code line. Otherwise,
5829 @value{GDBN} uses the macros in scope at the current listing location;
5832 At the moment, @value{GDBN} does not support the @code{##}
5833 token-splicing operator, the @code{#} stringification operator, or
5834 variable-arity macros.
5836 Whenever @value{GDBN} evaluates an expression, it always expands any
5837 macro invocations present in the expression. @value{GDBN} also provides
5838 the following commands for working with macros explicitly.
5842 @kindex macro expand
5843 @cindex macro expansion, showing the results of preprocessor
5844 @cindex preprocessor macro expansion, showing the results of
5845 @cindex expanding preprocessor macros
5846 @item macro expand @var{expression}
5847 @itemx macro exp @var{expression}
5848 Show the results of expanding all preprocessor macro invocations in
5849 @var{expression}. Since @value{GDBN} simply expands macros, but does
5850 not parse the result, @var{expression} need not be a valid expression;
5851 it can be any string of tokens.
5853 @kindex macro expand-once
5854 @item macro expand-once @var{expression}
5855 @itemx macro exp1 @var{expression}
5856 @i{(This command is not yet implemented.)} Show the results of
5857 expanding those preprocessor macro invocations that appear explicitly in
5858 @var{expression}. Macro invocations appearing in that expansion are
5859 left unchanged. This command allows you to see the effect of a
5860 particular macro more clearly, without being confused by further
5861 expansions. Since @value{GDBN} simply expands macros, but does not
5862 parse the result, @var{expression} need not be a valid expression; it
5863 can be any string of tokens.
5866 @cindex macro definition, showing
5867 @cindex definition, showing a macro's
5868 @item info macro @var{macro}
5869 Show the definition of the macro named @var{macro}, and describe the
5870 source location where that definition was established.
5872 @kindex macro define
5873 @cindex user-defined macros
5874 @cindex defining macros interactively
5875 @cindex macros, user-defined
5876 @item macro define @var{macro} @var{replacement-list}
5877 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
5878 @i{(This command is not yet implemented.)} Introduce a definition for a
5879 preprocessor macro named @var{macro}, invocations of which are replaced
5880 by the tokens given in @var{replacement-list}. The first form of this
5881 command defines an ``object-like'' macro, which takes no arguments; the
5882 second form defines a ``function-like'' macro, which takes the arguments
5883 given in @var{arglist}.
5885 A definition introduced by this command is in scope in every expression
5886 evaluated in @value{GDBN}, until it is removed with the @command{macro
5887 undef} command, described below. The definition overrides all
5888 definitions for @var{macro} present in the program being debugged, as
5889 well as any previous user-supplied definition.
5892 @item macro undef @var{macro}
5893 @i{(This command is not yet implemented.)} Remove any user-supplied
5894 definition for the macro named @var{macro}. This command only affects
5895 definitions provided with the @command{macro define} command, described
5896 above; it cannot remove definitions present in the program being
5901 @cindex macros, example of debugging with
5902 Here is a transcript showing the above commands in action. First, we
5903 show our source files:
5911 #define ADD(x) (M + x)
5916 printf ("Hello, world!\n");
5918 printf ("We're so creative.\n");
5920 printf ("Goodbye, world!\n");
5927 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
5928 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
5929 compiler includes information about preprocessor macros in the debugging
5933 $ gcc -gdwarf-2 -g3 sample.c -o sample
5937 Now, we start @value{GDBN} on our sample program:
5941 GNU gdb 2002-05-06-cvs
5942 Copyright 2002 Free Software Foundation, Inc.
5943 GDB is free software, @dots{}
5947 We can expand macros and examine their definitions, even when the
5948 program is not running. @value{GDBN} uses the current listing position
5949 to decide which macro definitions are in scope:
5955 5 #define ADD(x) (M + x)
5960 10 printf ("Hello, world!\n");
5962 12 printf ("We're so creative.\n");
5963 (gdb) info macro ADD
5964 Defined at /home/jimb/gdb/macros/play/sample.c:5
5965 #define ADD(x) (M + x)
5967 Defined at /home/jimb/gdb/macros/play/sample.h:1
5968 included at /home/jimb/gdb/macros/play/sample.c:2
5970 (gdb) macro expand ADD(1)
5971 expands to: (42 + 1)
5972 (gdb) macro expand-once ADD(1)
5973 expands to: once (M + 1)
5977 In the example above, note that @command{macro expand-once} expands only
5978 the macro invocation explicit in the original text --- the invocation of
5979 @code{ADD} --- but does not expand the invocation of the macro @code{M},
5980 which was introduced by @code{ADD}.
5982 Once the program is running, GDB uses the macro definitions in force at
5983 the source line of the current stack frame:
5987 Breakpoint 1 at 0x8048370: file sample.c, line 10.
5989 Starting program: /home/jimb/gdb/macros/play/sample
5991 Breakpoint 1, main () at sample.c:10
5992 10 printf ("Hello, world!\n");
5996 At line 10, the definition of the macro @code{N} at line 9 is in force:
6000 Defined at /home/jimb/gdb/macros/play/sample.c:9
6002 (gdb) macro expand N Q M
6009 As we step over directives that remove @code{N}'s definition, and then
6010 give it a new definition, @value{GDBN} finds the definition (or lack
6011 thereof) in force at each point:
6016 12 printf ("We're so creative.\n");
6018 The symbol `N' has no definition as a C/C++ preprocessor macro
6019 at /home/jimb/gdb/macros/play/sample.c:12
6022 14 printf ("Goodbye, world!\n");
6024 Defined at /home/jimb/gdb/macros/play/sample.c:13
6026 (gdb) macro expand N Q M
6027 expands to: 1729 < 42
6035 @chapter Tracepoints
6036 @c This chapter is based on the documentation written by Michael
6037 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
6040 In some applications, it is not feasible for the debugger to interrupt
6041 the program's execution long enough for the developer to learn
6042 anything helpful about its behavior. If the program's correctness
6043 depends on its real-time behavior, delays introduced by a debugger
6044 might cause the program to change its behavior drastically, or perhaps
6045 fail, even when the code itself is correct. It is useful to be able
6046 to observe the program's behavior without interrupting it.
6048 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
6049 specify locations in the program, called @dfn{tracepoints}, and
6050 arbitrary expressions to evaluate when those tracepoints are reached.
6051 Later, using the @code{tfind} command, you can examine the values
6052 those expressions had when the program hit the tracepoints. The
6053 expressions may also denote objects in memory---structures or arrays,
6054 for example---whose values @value{GDBN} should record; while visiting
6055 a particular tracepoint, you may inspect those objects as if they were
6056 in memory at that moment. However, because @value{GDBN} records these
6057 values without interacting with you, it can do so quickly and
6058 unobtrusively, hopefully not disturbing the program's behavior.
6060 The tracepoint facility is currently available only for remote
6061 targets. @xref{Targets}. In addition, your remote target must know how
6062 to collect trace data. This functionality is implemented in the remote
6063 stub; however, none of the stubs distributed with @value{GDBN} support
6064 tracepoints as of this writing.
6066 This chapter describes the tracepoint commands and features.
6070 * Analyze Collected Data::
6071 * Tracepoint Variables::
6074 @node Set Tracepoints
6075 @section Commands to Set Tracepoints
6077 Before running such a @dfn{trace experiment}, an arbitrary number of
6078 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
6079 tracepoint has a number assigned to it by @value{GDBN}. Like with
6080 breakpoints, tracepoint numbers are successive integers starting from
6081 one. Many of the commands associated with tracepoints take the
6082 tracepoint number as their argument, to identify which tracepoint to
6085 For each tracepoint, you can specify, in advance, some arbitrary set
6086 of data that you want the target to collect in the trace buffer when
6087 it hits that tracepoint. The collected data can include registers,
6088 local variables, or global data. Later, you can use @value{GDBN}
6089 commands to examine the values these data had at the time the
6092 This section describes commands to set tracepoints and associated
6093 conditions and actions.
6096 * Create and Delete Tracepoints::
6097 * Enable and Disable Tracepoints::
6098 * Tracepoint Passcounts::
6099 * Tracepoint Actions::
6100 * Listing Tracepoints::
6101 * Starting and Stopping Trace Experiment::
6104 @node Create and Delete Tracepoints
6105 @subsection Create and Delete Tracepoints
6108 @cindex set tracepoint
6111 The @code{trace} command is very similar to the @code{break} command.
6112 Its argument can be a source line, a function name, or an address in
6113 the target program. @xref{Set Breaks}. The @code{trace} command
6114 defines a tracepoint, which is a point in the target program where the
6115 debugger will briefly stop, collect some data, and then allow the
6116 program to continue. Setting a tracepoint or changing its commands
6117 doesn't take effect until the next @code{tstart} command; thus, you
6118 cannot change the tracepoint attributes once a trace experiment is
6121 Here are some examples of using the @code{trace} command:
6124 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
6126 (@value{GDBP}) @b{trace +2} // 2 lines forward
6128 (@value{GDBP}) @b{trace my_function} // first source line of function
6130 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
6132 (@value{GDBP}) @b{trace *0x2117c4} // an address
6136 You can abbreviate @code{trace} as @code{tr}.
6139 @cindex last tracepoint number
6140 @cindex recent tracepoint number
6141 @cindex tracepoint number
6142 The convenience variable @code{$tpnum} records the tracepoint number
6143 of the most recently set tracepoint.
6145 @kindex delete tracepoint
6146 @cindex tracepoint deletion
6147 @item delete tracepoint @r{[}@var{num}@r{]}
6148 Permanently delete one or more tracepoints. With no argument, the
6149 default is to delete all tracepoints.
6154 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
6156 (@value{GDBP}) @b{delete trace} // remove all tracepoints
6160 You can abbreviate this command as @code{del tr}.
6163 @node Enable and Disable Tracepoints
6164 @subsection Enable and Disable Tracepoints
6167 @kindex disable tracepoint
6168 @item disable tracepoint @r{[}@var{num}@r{]}
6169 Disable tracepoint @var{num}, or all tracepoints if no argument
6170 @var{num} is given. A disabled tracepoint will have no effect during
6171 the next trace experiment, but it is not forgotten. You can re-enable
6172 a disabled tracepoint using the @code{enable tracepoint} command.
6174 @kindex enable tracepoint
6175 @item enable tracepoint @r{[}@var{num}@r{]}
6176 Enable tracepoint @var{num}, or all tracepoints. The enabled
6177 tracepoints will become effective the next time a trace experiment is
6181 @node Tracepoint Passcounts
6182 @subsection Tracepoint Passcounts
6186 @cindex tracepoint pass count
6187 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
6188 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
6189 automatically stop a trace experiment. If a tracepoint's passcount is
6190 @var{n}, then the trace experiment will be automatically stopped on
6191 the @var{n}'th time that tracepoint is hit. If the tracepoint number
6192 @var{num} is not specified, the @code{passcount} command sets the
6193 passcount of the most recently defined tracepoint. If no passcount is
6194 given, the trace experiment will run until stopped explicitly by the
6200 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
6201 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
6203 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
6204 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
6205 (@value{GDBP}) @b{trace foo}
6206 (@value{GDBP}) @b{pass 3}
6207 (@value{GDBP}) @b{trace bar}
6208 (@value{GDBP}) @b{pass 2}
6209 (@value{GDBP}) @b{trace baz}
6210 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
6211 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
6212 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
6213 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
6217 @node Tracepoint Actions
6218 @subsection Tracepoint Action Lists
6222 @cindex tracepoint actions
6223 @item actions @r{[}@var{num}@r{]}
6224 This command will prompt for a list of actions to be taken when the
6225 tracepoint is hit. If the tracepoint number @var{num} is not
6226 specified, this command sets the actions for the one that was most
6227 recently defined (so that you can define a tracepoint and then say
6228 @code{actions} without bothering about its number). You specify the
6229 actions themselves on the following lines, one action at a time, and
6230 terminate the actions list with a line containing just @code{end}. So
6231 far, the only defined actions are @code{collect} and
6232 @code{while-stepping}.
6234 @cindex remove actions from a tracepoint
6235 To remove all actions from a tracepoint, type @samp{actions @var{num}}
6236 and follow it immediately with @samp{end}.
6239 (@value{GDBP}) @b{collect @var{data}} // collect some data
6241 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
6243 (@value{GDBP}) @b{end} // signals the end of actions.
6246 In the following example, the action list begins with @code{collect}
6247 commands indicating the things to be collected when the tracepoint is
6248 hit. Then, in order to single-step and collect additional data
6249 following the tracepoint, a @code{while-stepping} command is used,
6250 followed by the list of things to be collected while stepping. The
6251 @code{while-stepping} command is terminated by its own separate
6252 @code{end} command. Lastly, the action list is terminated by an
6256 (@value{GDBP}) @b{trace foo}
6257 (@value{GDBP}) @b{actions}
6258 Enter actions for tracepoint 1, one per line:
6267 @kindex collect @r{(tracepoints)}
6268 @item collect @var{expr1}, @var{expr2}, @dots{}
6269 Collect values of the given expressions when the tracepoint is hit.
6270 This command accepts a comma-separated list of any valid expressions.
6271 In addition to global, static, or local variables, the following
6272 special arguments are supported:
6276 collect all registers
6279 collect all function arguments
6282 collect all local variables.
6285 You can give several consecutive @code{collect} commands, each one
6286 with a single argument, or one @code{collect} command with several
6287 arguments separated by commas: the effect is the same.
6289 The command @code{info scope} (@pxref{Symbols, info scope}) is
6290 particularly useful for figuring out what data to collect.
6292 @kindex while-stepping @r{(tracepoints)}
6293 @item while-stepping @var{n}
6294 Perform @var{n} single-step traces after the tracepoint, collecting
6295 new data at each step. The @code{while-stepping} command is
6296 followed by the list of what to collect while stepping (followed by
6297 its own @code{end} command):
6301 > collect $regs, myglobal
6307 You may abbreviate @code{while-stepping} as @code{ws} or
6311 @node Listing Tracepoints
6312 @subsection Listing Tracepoints
6315 @kindex info tracepoints
6316 @cindex information about tracepoints
6317 @item info tracepoints @r{[}@var{num}@r{]}
6318 Display information about the tracepoint @var{num}. If you don't specify
6319 a tracepoint number, displays information about all the tracepoints
6320 defined so far. For each tracepoint, the following information is
6327 whether it is enabled or disabled
6331 its passcount as given by the @code{passcount @var{n}} command
6333 its step count as given by the @code{while-stepping @var{n}} command
6335 where in the source files is the tracepoint set
6337 its action list as given by the @code{actions} command
6341 (@value{GDBP}) @b{info trace}
6342 Num Enb Address PassC StepC What
6343 1 y 0x002117c4 0 0 <gdb_asm>
6344 2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
6345 3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
6350 This command can be abbreviated @code{info tp}.
6353 @node Starting and Stopping Trace Experiment
6354 @subsection Starting and Stopping Trace Experiment
6358 @cindex start a new trace experiment
6359 @cindex collected data discarded
6361 This command takes no arguments. It starts the trace experiment, and
6362 begins collecting data. This has the side effect of discarding all
6363 the data collected in the trace buffer during the previous trace
6367 @cindex stop a running trace experiment
6369 This command takes no arguments. It ends the trace experiment, and
6370 stops collecting data.
6372 @strong{Note:} a trace experiment and data collection may stop
6373 automatically if any tracepoint's passcount is reached
6374 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6377 @cindex status of trace data collection
6378 @cindex trace experiment, status of
6380 This command displays the status of the current trace data
6384 Here is an example of the commands we described so far:
6387 (@value{GDBP}) @b{trace gdb_c_test}
6388 (@value{GDBP}) @b{actions}
6389 Enter actions for tracepoint #1, one per line.
6390 > collect $regs,$locals,$args
6395 (@value{GDBP}) @b{tstart}
6396 [time passes @dots{}]
6397 (@value{GDBP}) @b{tstop}
6401 @node Analyze Collected Data
6402 @section Using the collected data
6404 After the tracepoint experiment ends, you use @value{GDBN} commands
6405 for examining the trace data. The basic idea is that each tracepoint
6406 collects a trace @dfn{snapshot} every time it is hit and another
6407 snapshot every time it single-steps. All these snapshots are
6408 consecutively numbered from zero and go into a buffer, and you can
6409 examine them later. The way you examine them is to @dfn{focus} on a
6410 specific trace snapshot. When the remote stub is focused on a trace
6411 snapshot, it will respond to all @value{GDBN} requests for memory and
6412 registers by reading from the buffer which belongs to that snapshot,
6413 rather than from @emph{real} memory or registers of the program being
6414 debugged. This means that @strong{all} @value{GDBN} commands
6415 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6416 behave as if we were currently debugging the program state as it was
6417 when the tracepoint occurred. Any requests for data that are not in
6418 the buffer will fail.
6421 * tfind:: How to select a trace snapshot
6422 * tdump:: How to display all data for a snapshot
6423 * save-tracepoints:: How to save tracepoints for a future run
6427 @subsection @code{tfind @var{n}}
6430 @cindex select trace snapshot
6431 @cindex find trace snapshot
6432 The basic command for selecting a trace snapshot from the buffer is
6433 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6434 counting from zero. If no argument @var{n} is given, the next
6435 snapshot is selected.
6437 Here are the various forms of using the @code{tfind} command.
6441 Find the first snapshot in the buffer. This is a synonym for
6442 @code{tfind 0} (since 0 is the number of the first snapshot).
6445 Stop debugging trace snapshots, resume @emph{live} debugging.
6448 Same as @samp{tfind none}.
6451 No argument means find the next trace snapshot.
6454 Find the previous trace snapshot before the current one. This permits
6455 retracing earlier steps.
6457 @item tfind tracepoint @var{num}
6458 Find the next snapshot associated with tracepoint @var{num}. Search
6459 proceeds forward from the last examined trace snapshot. If no
6460 argument @var{num} is given, it means find the next snapshot collected
6461 for the same tracepoint as the current snapshot.
6463 @item tfind pc @var{addr}
6464 Find the next snapshot associated with the value @var{addr} of the
6465 program counter. Search proceeds forward from the last examined trace
6466 snapshot. If no argument @var{addr} is given, it means find the next
6467 snapshot with the same value of PC as the current snapshot.
6469 @item tfind outside @var{addr1}, @var{addr2}
6470 Find the next snapshot whose PC is outside the given range of
6473 @item tfind range @var{addr1}, @var{addr2}
6474 Find the next snapshot whose PC is between @var{addr1} and
6475 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6477 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6478 Find the next snapshot associated with the source line @var{n}. If
6479 the optional argument @var{file} is given, refer to line @var{n} in
6480 that source file. Search proceeds forward from the last examined
6481 trace snapshot. If no argument @var{n} is given, it means find the
6482 next line other than the one currently being examined; thus saying
6483 @code{tfind line} repeatedly can appear to have the same effect as
6484 stepping from line to line in a @emph{live} debugging session.
6487 The default arguments for the @code{tfind} commands are specifically
6488 designed to make it easy to scan through the trace buffer. For
6489 instance, @code{tfind} with no argument selects the next trace
6490 snapshot, and @code{tfind -} with no argument selects the previous
6491 trace snapshot. So, by giving one @code{tfind} command, and then
6492 simply hitting @key{RET} repeatedly you can examine all the trace
6493 snapshots in order. Or, by saying @code{tfind -} and then hitting
6494 @key{RET} repeatedly you can examine the snapshots in reverse order.
6495 The @code{tfind line} command with no argument selects the snapshot
6496 for the next source line executed. The @code{tfind pc} command with
6497 no argument selects the next snapshot with the same program counter
6498 (PC) as the current frame. The @code{tfind tracepoint} command with
6499 no argument selects the next trace snapshot collected by the same
6500 tracepoint as the current one.
6502 In addition to letting you scan through the trace buffer manually,
6503 these commands make it easy to construct @value{GDBN} scripts that
6504 scan through the trace buffer and print out whatever collected data
6505 you are interested in. Thus, if we want to examine the PC, FP, and SP
6506 registers from each trace frame in the buffer, we can say this:
6509 (@value{GDBP}) @b{tfind start}
6510 (@value{GDBP}) @b{while ($trace_frame != -1)}
6511 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6512 $trace_frame, $pc, $sp, $fp
6516 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6517 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6518 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6519 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6520 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6521 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6522 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6523 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6524 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6525 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6526 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6529 Or, if we want to examine the variable @code{X} at each source line in
6533 (@value{GDBP}) @b{tfind start}
6534 (@value{GDBP}) @b{while ($trace_frame != -1)}
6535 > printf "Frame %d, X == %d\n", $trace_frame, X
6545 @subsection @code{tdump}
6547 @cindex dump all data collected at tracepoint
6548 @cindex tracepoint data, display
6550 This command takes no arguments. It prints all the data collected at
6551 the current trace snapshot.
6554 (@value{GDBP}) @b{trace 444}
6555 (@value{GDBP}) @b{actions}
6556 Enter actions for tracepoint #2, one per line:
6557 > collect $regs, $locals, $args, gdb_long_test
6560 (@value{GDBP}) @b{tstart}
6562 (@value{GDBP}) @b{tfind line 444}
6563 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6565 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6567 (@value{GDBP}) @b{tdump}
6568 Data collected at tracepoint 2, trace frame 1:
6569 d0 0xc4aa0085 -995491707
6573 d4 0x71aea3d 119204413
6578 a1 0x3000668 50333288
6581 a4 0x3000698 50333336
6583 fp 0x30bf3c 0x30bf3c
6584 sp 0x30bf34 0x30bf34
6586 pc 0x20b2c8 0x20b2c8
6590 p = 0x20e5b4 "gdb-test"
6597 gdb_long_test = 17 '\021'
6602 @node save-tracepoints
6603 @subsection @code{save-tracepoints @var{filename}}
6604 @kindex save-tracepoints
6605 @cindex save tracepoints for future sessions
6607 This command saves all current tracepoint definitions together with
6608 their actions and passcounts, into a file @file{@var{filename}}
6609 suitable for use in a later debugging session. To read the saved
6610 tracepoint definitions, use the @code{source} command (@pxref{Command
6613 @node Tracepoint Variables
6614 @section Convenience Variables for Tracepoints
6615 @cindex tracepoint variables
6616 @cindex convenience variables for tracepoints
6619 @vindex $trace_frame
6620 @item (int) $trace_frame
6621 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6622 snapshot is selected.
6625 @item (int) $tracepoint
6626 The tracepoint for the current trace snapshot.
6629 @item (int) $trace_line
6630 The line number for the current trace snapshot.
6633 @item (char []) $trace_file
6634 The source file for the current trace snapshot.
6637 @item (char []) $trace_func
6638 The name of the function containing @code{$tracepoint}.
6641 Note: @code{$trace_file} is not suitable for use in @code{printf},
6642 use @code{output} instead.
6644 Here's a simple example of using these convenience variables for
6645 stepping through all the trace snapshots and printing some of their
6649 (@value{GDBP}) @b{tfind start}
6651 (@value{GDBP}) @b{while $trace_frame != -1}
6652 > output $trace_file
6653 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6659 @chapter Debugging Programs That Use Overlays
6662 If your program is too large to fit completely in your target system's
6663 memory, you can sometimes use @dfn{overlays} to work around this
6664 problem. @value{GDBN} provides some support for debugging programs that
6668 * How Overlays Work:: A general explanation of overlays.
6669 * Overlay Commands:: Managing overlays in @value{GDBN}.
6670 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
6671 mapped by asking the inferior.
6672 * Overlay Sample Program:: A sample program using overlays.
6675 @node How Overlays Work
6676 @section How Overlays Work
6677 @cindex mapped overlays
6678 @cindex unmapped overlays
6679 @cindex load address, overlay's
6680 @cindex mapped address
6681 @cindex overlay area
6683 Suppose you have a computer whose instruction address space is only 64
6684 kilobytes long, but which has much more memory which can be accessed by
6685 other means: special instructions, segment registers, or memory
6686 management hardware, for example. Suppose further that you want to
6687 adapt a program which is larger than 64 kilobytes to run on this system.
6689 One solution is to identify modules of your program which are relatively
6690 independent, and need not call each other directly; call these modules
6691 @dfn{overlays}. Separate the overlays from the main program, and place
6692 their machine code in the larger memory. Place your main program in
6693 instruction memory, but leave at least enough space there to hold the
6694 largest overlay as well.
6696 Now, to call a function located in an overlay, you must first copy that
6697 overlay's machine code from the large memory into the space set aside
6698 for it in the instruction memory, and then jump to its entry point
6701 @c NB: In the below the mapped area's size is greater or equal to the
6702 @c size of all overlays. This is intentional to remind the developer
6703 @c that overlays don't necessarily need to be the same size.
6707 Data Instruction Larger
6708 Address Space Address Space Address Space
6709 +-----------+ +-----------+ +-----------+
6711 +-----------+ +-----------+ +-----------+<-- overlay 1
6712 | program | | main | .----| overlay 1 | load address
6713 | variables | | program | | +-----------+
6714 | and heap | | | | | |
6715 +-----------+ | | | +-----------+<-- overlay 2
6716 | | +-----------+ | | | load address
6717 +-----------+ | | | .-| overlay 2 |
6719 mapped --->+-----------+ | | +-----------+
6721 | overlay | <-' | | |
6722 | area | <---' +-----------+<-- overlay 3
6723 | | <---. | | load address
6724 +-----------+ `--| overlay 3 |
6731 @anchor{A code overlay}A code overlay
6735 The diagram (@pxref{A code overlay}) shows a system with separate data
6736 and instruction address spaces. To map an overlay, the program copies
6737 its code from the larger address space to the instruction address space.
6738 Since the overlays shown here all use the same mapped address, only one
6739 may be mapped at a time. For a system with a single address space for
6740 data and instructions, the diagram would be similar, except that the
6741 program variables and heap would share an address space with the main
6742 program and the overlay area.
6744 An overlay loaded into instruction memory and ready for use is called a
6745 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
6746 instruction memory. An overlay not present (or only partially present)
6747 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
6748 is its address in the larger memory. The mapped address is also called
6749 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
6750 called the @dfn{load memory address}, or @dfn{LMA}.
6752 Unfortunately, overlays are not a completely transparent way to adapt a
6753 program to limited instruction memory. They introduce a new set of
6754 global constraints you must keep in mind as you design your program:
6759 Before calling or returning to a function in an overlay, your program
6760 must make sure that overlay is actually mapped. Otherwise, the call or
6761 return will transfer control to the right address, but in the wrong
6762 overlay, and your program will probably crash.
6765 If the process of mapping an overlay is expensive on your system, you
6766 will need to choose your overlays carefully to minimize their effect on
6767 your program's performance.
6770 The executable file you load onto your system must contain each
6771 overlay's instructions, appearing at the overlay's load address, not its
6772 mapped address. However, each overlay's instructions must be relocated
6773 and its symbols defined as if the overlay were at its mapped address.
6774 You can use GNU linker scripts to specify different load and relocation
6775 addresses for pieces of your program; see @ref{Overlay Description,,,
6776 ld.info, Using ld: the GNU linker}.
6779 The procedure for loading executable files onto your system must be able
6780 to load their contents into the larger address space as well as the
6781 instruction and data spaces.
6785 The overlay system described above is rather simple, and could be
6786 improved in many ways:
6791 If your system has suitable bank switch registers or memory management
6792 hardware, you could use those facilities to make an overlay's load area
6793 contents simply appear at their mapped address in instruction space.
6794 This would probably be faster than copying the overlay to its mapped
6795 area in the usual way.
6798 If your overlays are small enough, you could set aside more than one
6799 overlay area, and have more than one overlay mapped at a time.
6802 You can use overlays to manage data, as well as instructions. In
6803 general, data overlays are even less transparent to your design than
6804 code overlays: whereas code overlays only require care when you call or
6805 return to functions, data overlays require care every time you access
6806 the data. Also, if you change the contents of a data overlay, you
6807 must copy its contents back out to its load address before you can copy a
6808 different data overlay into the same mapped area.
6813 @node Overlay Commands
6814 @section Overlay Commands
6816 To use @value{GDBN}'s overlay support, each overlay in your program must
6817 correspond to a separate section of the executable file. The section's
6818 virtual memory address and load memory address must be the overlay's
6819 mapped and load addresses. Identifying overlays with sections allows
6820 @value{GDBN} to determine the appropriate address of a function or
6821 variable, depending on whether the overlay is mapped or not.
6823 @value{GDBN}'s overlay commands all start with the word @code{overlay};
6824 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
6829 Disable @value{GDBN}'s overlay support. When overlay support is
6830 disabled, @value{GDBN} assumes that all functions and variables are
6831 always present at their mapped addresses. By default, @value{GDBN}'s
6832 overlay support is disabled.
6834 @item overlay manual
6835 @kindex overlay manual
6836 @cindex manual overlay debugging
6837 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
6838 relies on you to tell it which overlays are mapped, and which are not,
6839 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
6840 commands described below.
6842 @item overlay map-overlay @var{overlay}
6843 @itemx overlay map @var{overlay}
6844 @kindex overlay map-overlay
6845 @cindex map an overlay
6846 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
6847 be the name of the object file section containing the overlay. When an
6848 overlay is mapped, @value{GDBN} assumes it can find the overlay's
6849 functions and variables at their mapped addresses. @value{GDBN} assumes
6850 that any other overlays whose mapped ranges overlap that of
6851 @var{overlay} are now unmapped.
6853 @item overlay unmap-overlay @var{overlay}
6854 @itemx overlay unmap @var{overlay}
6855 @kindex overlay unmap-overlay
6856 @cindex unmap an overlay
6857 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
6858 must be the name of the object file section containing the overlay.
6859 When an overlay is unmapped, @value{GDBN} assumes it can find the
6860 overlay's functions and variables at their load addresses.
6863 @kindex overlay auto
6864 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
6865 consults a data structure the overlay manager maintains in the inferior
6866 to see which overlays are mapped. For details, see @ref{Automatic
6869 @item overlay load-target
6871 @kindex overlay load-target
6872 @cindex reloading the overlay table
6873 Re-read the overlay table from the inferior. Normally, @value{GDBN}
6874 re-reads the table @value{GDBN} automatically each time the inferior
6875 stops, so this command should only be necessary if you have changed the
6876 overlay mapping yourself using @value{GDBN}. This command is only
6877 useful when using automatic overlay debugging.
6879 @item overlay list-overlays
6881 @cindex listing mapped overlays
6882 Display a list of the overlays currently mapped, along with their mapped
6883 addresses, load addresses, and sizes.
6887 Normally, when @value{GDBN} prints a code address, it includes the name
6888 of the function the address falls in:
6892 $3 = @{int ()@} 0x11a0 <main>
6895 When overlay debugging is enabled, @value{GDBN} recognizes code in
6896 unmapped overlays, and prints the names of unmapped functions with
6897 asterisks around them. For example, if @code{foo} is a function in an
6898 unmapped overlay, @value{GDBN} prints it this way:
6902 No sections are mapped.
6904 $5 = @{int (int)@} 0x100000 <*foo*>
6907 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
6912 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
6913 mapped at 0x1016 - 0x104a
6915 $6 = @{int (int)@} 0x1016 <foo>
6918 When overlay debugging is enabled, @value{GDBN} can find the correct
6919 address for functions and variables in an overlay, whether or not the
6920 overlay is mapped. This allows most @value{GDBN} commands, like
6921 @code{break} and @code{disassemble}, to work normally, even on unmapped
6922 code. However, @value{GDBN}'s breakpoint support has some limitations:
6926 @cindex breakpoints in overlays
6927 @cindex overlays, setting breakpoints in
6928 You can set breakpoints in functions in unmapped overlays, as long as
6929 @value{GDBN} can write to the overlay at its load address.
6931 @value{GDBN} can not set hardware or simulator-based breakpoints in
6932 unmapped overlays. However, if you set a breakpoint at the end of your
6933 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
6934 you are using manual overlay management), @value{GDBN} will re-set its
6935 breakpoints properly.
6939 @node Automatic Overlay Debugging
6940 @section Automatic Overlay Debugging
6941 @cindex automatic overlay debugging
6943 @value{GDBN} can automatically track which overlays are mapped and which
6944 are not, given some simple co-operation from the overlay manager in the
6945 inferior. If you enable automatic overlay debugging with the
6946 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
6947 looks in the inferior's memory for certain variables describing the
6948 current state of the overlays.
6950 Here are the variables your overlay manager must define to support
6951 @value{GDBN}'s automatic overlay debugging:
6955 @item @code{_ovly_table}:
6956 This variable must be an array of the following structures:
6961 /* The overlay's mapped address. */
6964 /* The size of the overlay, in bytes. */
6967 /* The overlay's load address. */
6970 /* Non-zero if the overlay is currently mapped;
6972 unsigned long mapped;
6976 @item @code{_novlys}:
6977 This variable must be a four-byte signed integer, holding the total
6978 number of elements in @code{_ovly_table}.
6982 To decide whether a particular overlay is mapped or not, @value{GDBN}
6983 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
6984 @code{lma} members equal the VMA and LMA of the overlay's section in the
6985 executable file. When @value{GDBN} finds a matching entry, it consults
6986 the entry's @code{mapped} member to determine whether the overlay is
6989 In addition, your overlay manager may define a function called
6990 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
6991 will silently set a breakpoint there. If the overlay manager then
6992 calls this function whenever it has changed the overlay table, this
6993 will enable @value{GDBN} to accurately keep track of which overlays
6994 are in program memory, and update any breakpoints that may be set
6995 in overlays. This will allow breakpoints to work even if the
6996 overlays are kept in ROM or other non-writable memory while they
6997 are not being executed.
6999 @node Overlay Sample Program
7000 @section Overlay Sample Program
7001 @cindex overlay example program
7003 When linking a program which uses overlays, you must place the overlays
7004 at their load addresses, while relocating them to run at their mapped
7005 addresses. To do this, you must write a linker script (@pxref{Overlay
7006 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
7007 since linker scripts are specific to a particular host system, target
7008 architecture, and target memory layout, this manual cannot provide
7009 portable sample code demonstrating @value{GDBN}'s overlay support.
7011 However, the @value{GDBN} source distribution does contain an overlaid
7012 program, with linker scripts for a few systems, as part of its test
7013 suite. The program consists of the following files from
7014 @file{gdb/testsuite/gdb.base}:
7018 The main program file.
7020 A simple overlay manager, used by @file{overlays.c}.
7025 Overlay modules, loaded and used by @file{overlays.c}.
7028 Linker scripts for linking the test program on the @code{d10v-elf}
7029 and @code{m32r-elf} targets.
7032 You can build the test program using the @code{d10v-elf} GCC
7033 cross-compiler like this:
7036 $ d10v-elf-gcc -g -c overlays.c
7037 $ d10v-elf-gcc -g -c ovlymgr.c
7038 $ d10v-elf-gcc -g -c foo.c
7039 $ d10v-elf-gcc -g -c bar.c
7040 $ d10v-elf-gcc -g -c baz.c
7041 $ d10v-elf-gcc -g -c grbx.c
7042 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
7043 baz.o grbx.o -Wl,-Td10v.ld -o overlays
7046 The build process is identical for any other architecture, except that
7047 you must substitute the appropriate compiler and linker script for the
7048 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
7052 @chapter Using @value{GDBN} with Different Languages
7055 Although programming languages generally have common aspects, they are
7056 rarely expressed in the same manner. For instance, in ANSI C,
7057 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
7058 Modula-2, it is accomplished by @code{p^}. Values can also be
7059 represented (and displayed) differently. Hex numbers in C appear as
7060 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
7062 @cindex working language
7063 Language-specific information is built into @value{GDBN} for some languages,
7064 allowing you to express operations like the above in your program's
7065 native language, and allowing @value{GDBN} to output values in a manner
7066 consistent with the syntax of your program's native language. The
7067 language you use to build expressions is called the @dfn{working
7071 * Setting:: Switching between source languages
7072 * Show:: Displaying the language
7073 * Checks:: Type and range checks
7074 * Support:: Supported languages
7078 @section Switching between source languages
7080 There are two ways to control the working language---either have @value{GDBN}
7081 set it automatically, or select it manually yourself. You can use the
7082 @code{set language} command for either purpose. On startup, @value{GDBN}
7083 defaults to setting the language automatically. The working language is
7084 used to determine how expressions you type are interpreted, how values
7087 In addition to the working language, every source file that
7088 @value{GDBN} knows about has its own working language. For some object
7089 file formats, the compiler might indicate which language a particular
7090 source file is in. However, most of the time @value{GDBN} infers the
7091 language from the name of the file. The language of a source file
7092 controls whether C@t{++} names are demangled---this way @code{backtrace} can
7093 show each frame appropriately for its own language. There is no way to
7094 set the language of a source file from within @value{GDBN}, but you can
7095 set the language associated with a filename extension. @xref{Show, ,
7096 Displaying the language}.
7098 This is most commonly a problem when you use a program, such
7099 as @code{cfront} or @code{f2c}, that generates C but is written in
7100 another language. In that case, make the
7101 program use @code{#line} directives in its C output; that way
7102 @value{GDBN} will know the correct language of the source code of the original
7103 program, and will display that source code, not the generated C code.
7106 * Filenames:: Filename extensions and languages.
7107 * Manually:: Setting the working language manually
7108 * Automatically:: Having @value{GDBN} infer the source language
7112 @subsection List of filename extensions and languages
7114 If a source file name ends in one of the following extensions, then
7115 @value{GDBN} infers that its language is the one indicated.
7134 @c OBSOLETE @item .ch
7135 @c OBSOLETE @itemx .c186
7136 @c OBSOLETE @itemx .c286
7137 @c OBSOLETE CHILL source file
7140 Modula-2 source file
7144 Assembler source file. This actually behaves almost like C, but
7145 @value{GDBN} does not skip over function prologues when stepping.
7148 In addition, you may set the language associated with a filename
7149 extension. @xref{Show, , Displaying the language}.
7152 @subsection Setting the working language
7154 If you allow @value{GDBN} to set the language automatically,
7155 expressions are interpreted the same way in your debugging session and
7158 @kindex set language
7159 If you wish, you may set the language manually. To do this, issue the
7160 command @samp{set language @var{lang}}, where @var{lang} is the name of
7162 @code{c} or @code{modula-2}.
7163 For a list of the supported languages, type @samp{set language}.
7165 Setting the language manually prevents @value{GDBN} from updating the working
7166 language automatically. This can lead to confusion if you try
7167 to debug a program when the working language is not the same as the
7168 source language, when an expression is acceptable to both
7169 languages---but means different things. For instance, if the current
7170 source file were written in C, and @value{GDBN} was parsing Modula-2, a
7178 might not have the effect you intended. In C, this means to add
7179 @code{b} and @code{c} and place the result in @code{a}. The result
7180 printed would be the value of @code{a}. In Modula-2, this means to compare
7181 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
7184 @subsection Having @value{GDBN} infer the source language
7186 To have @value{GDBN} set the working language automatically, use
7187 @samp{set language local} or @samp{set language auto}. @value{GDBN}
7188 then infers the working language. That is, when your program stops in a
7189 frame (usually by encountering a breakpoint), @value{GDBN} sets the
7190 working language to the language recorded for the function in that
7191 frame. If the language for a frame is unknown (that is, if the function
7192 or block corresponding to the frame was defined in a source file that
7193 does not have a recognized extension), the current working language is
7194 not changed, and @value{GDBN} issues a warning.
7196 This may not seem necessary for most programs, which are written
7197 entirely in one source language. However, program modules and libraries
7198 written in one source language can be used by a main program written in
7199 a different source language. Using @samp{set language auto} in this
7200 case frees you from having to set the working language manually.
7203 @section Displaying the language
7205 The following commands help you find out which language is the
7206 working language, and also what language source files were written in.
7208 @kindex show language
7209 @kindex info frame@r{, show the source language}
7210 @kindex info source@r{, show the source language}
7213 Display the current working language. This is the
7214 language you can use with commands such as @code{print} to
7215 build and compute expressions that may involve variables in your program.
7218 Display the source language for this frame. This language becomes the
7219 working language if you use an identifier from this frame.
7220 @xref{Frame Info, ,Information about a frame}, to identify the other
7221 information listed here.
7224 Display the source language of this source file.
7225 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
7226 information listed here.
7229 In unusual circumstances, you may have source files with extensions
7230 not in the standard list. You can then set the extension associated
7231 with a language explicitly:
7233 @kindex set extension-language
7234 @kindex info extensions
7236 @item set extension-language @var{.ext} @var{language}
7237 Set source files with extension @var{.ext} to be assumed to be in
7238 the source language @var{language}.
7240 @item info extensions
7241 List all the filename extensions and the associated languages.
7245 @section Type and range checking
7248 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
7249 checking are included, but they do not yet have any effect. This
7250 section documents the intended facilities.
7252 @c FIXME remove warning when type/range code added
7254 Some languages are designed to guard you against making seemingly common
7255 errors through a series of compile- and run-time checks. These include
7256 checking the type of arguments to functions and operators, and making
7257 sure mathematical overflows are caught at run time. Checks such as
7258 these help to ensure a program's correctness once it has been compiled
7259 by eliminating type mismatches, and providing active checks for range
7260 errors when your program is running.
7262 @value{GDBN} can check for conditions like the above if you wish.
7263 Although @value{GDBN} does not check the statements in your program, it
7264 can check expressions entered directly into @value{GDBN} for evaluation via
7265 the @code{print} command, for example. As with the working language,
7266 @value{GDBN} can also decide whether or not to check automatically based on
7267 your program's source language. @xref{Support, ,Supported languages},
7268 for the default settings of supported languages.
7271 * Type Checking:: An overview of type checking
7272 * Range Checking:: An overview of range checking
7275 @cindex type checking
7276 @cindex checks, type
7278 @subsection An overview of type checking
7280 Some languages, such as Modula-2, are strongly typed, meaning that the
7281 arguments to operators and functions have to be of the correct type,
7282 otherwise an error occurs. These checks prevent type mismatch
7283 errors from ever causing any run-time problems. For example,
7291 The second example fails because the @code{CARDINAL} 1 is not
7292 type-compatible with the @code{REAL} 2.3.
7294 For the expressions you use in @value{GDBN} commands, you can tell the
7295 @value{GDBN} type checker to skip checking;
7296 to treat any mismatches as errors and abandon the expression;
7297 or to only issue warnings when type mismatches occur,
7298 but evaluate the expression anyway. When you choose the last of
7299 these, @value{GDBN} evaluates expressions like the second example above, but
7300 also issues a warning.
7302 Even if you turn type checking off, there may be other reasons
7303 related to type that prevent @value{GDBN} from evaluating an expression.
7304 For instance, @value{GDBN} does not know how to add an @code{int} and
7305 a @code{struct foo}. These particular type errors have nothing to do
7306 with the language in use, and usually arise from expressions, such as
7307 the one described above, which make little sense to evaluate anyway.
7309 Each language defines to what degree it is strict about type. For
7310 instance, both Modula-2 and C require the arguments to arithmetical
7311 operators to be numbers. In C, enumerated types and pointers can be
7312 represented as numbers, so that they are valid arguments to mathematical
7313 operators. @xref{Support, ,Supported languages}, for further
7314 details on specific languages.
7316 @value{GDBN} provides some additional commands for controlling the type checker:
7318 @kindex set check@r{, type}
7319 @kindex set check type
7320 @kindex show check type
7322 @item set check type auto
7323 Set type checking on or off based on the current working language.
7324 @xref{Support, ,Supported languages}, for the default settings for
7327 @item set check type on
7328 @itemx set check type off
7329 Set type checking on or off, overriding the default setting for the
7330 current working language. Issue a warning if the setting does not
7331 match the language default. If any type mismatches occur in
7332 evaluating an expression while type checking is on, @value{GDBN} prints a
7333 message and aborts evaluation of the expression.
7335 @item set check type warn
7336 Cause the type checker to issue warnings, but to always attempt to
7337 evaluate the expression. Evaluating the expression may still
7338 be impossible for other reasons. For example, @value{GDBN} cannot add
7339 numbers and structures.
7342 Show the current setting of the type checker, and whether or not @value{GDBN}
7343 is setting it automatically.
7346 @cindex range checking
7347 @cindex checks, range
7348 @node Range Checking
7349 @subsection An overview of range checking
7351 In some languages (such as Modula-2), it is an error to exceed the
7352 bounds of a type; this is enforced with run-time checks. Such range
7353 checking is meant to ensure program correctness by making sure
7354 computations do not overflow, or indices on an array element access do
7355 not exceed the bounds of the array.
7357 For expressions you use in @value{GDBN} commands, you can tell
7358 @value{GDBN} to treat range errors in one of three ways: ignore them,
7359 always treat them as errors and abandon the expression, or issue
7360 warnings but evaluate the expression anyway.
7362 A range error can result from numerical overflow, from exceeding an
7363 array index bound, or when you type a constant that is not a member
7364 of any type. Some languages, however, do not treat overflows as an
7365 error. In many implementations of C, mathematical overflow causes the
7366 result to ``wrap around'' to lower values---for example, if @var{m} is
7367 the largest integer value, and @var{s} is the smallest, then
7370 @var{m} + 1 @result{} @var{s}
7373 This, too, is specific to individual languages, and in some cases
7374 specific to individual compilers or machines. @xref{Support, ,
7375 Supported languages}, for further details on specific languages.
7377 @value{GDBN} provides some additional commands for controlling the range checker:
7379 @kindex set check@r{, range}
7380 @kindex set check range
7381 @kindex show check range
7383 @item set check range auto
7384 Set range checking on or off based on the current working language.
7385 @xref{Support, ,Supported languages}, for the default settings for
7388 @item set check range on
7389 @itemx set check range off
7390 Set range checking on or off, overriding the default setting for the
7391 current working language. A warning is issued if the setting does not
7392 match the language default. If a range error occurs and range checking is on,
7393 then a message is printed and evaluation of the expression is aborted.
7395 @item set check range warn
7396 Output messages when the @value{GDBN} range checker detects a range error,
7397 but attempt to evaluate the expression anyway. Evaluating the
7398 expression may still be impossible for other reasons, such as accessing
7399 memory that the process does not own (a typical example from many Unix
7403 Show the current setting of the range checker, and whether or not it is
7404 being set automatically by @value{GDBN}.
7408 @section Supported languages
7410 @value{GDBN} supports C, C@t{++}, Fortran, Java,
7412 assembly, and Modula-2.
7413 @c This is false ...
7414 Some @value{GDBN} features may be used in expressions regardless of the
7415 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7416 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7417 ,Expressions}) can be used with the constructs of any supported
7420 The following sections detail to what degree each source language is
7421 supported by @value{GDBN}. These sections are not meant to be language
7422 tutorials or references, but serve only as a reference guide to what the
7423 @value{GDBN} expression parser accepts, and what input and output
7424 formats should look like for different languages. There are many good
7425 books written on each of these languages; please look to these for a
7426 language reference or tutorial.
7430 * Modula-2:: Modula-2
7431 @c OBSOLETE * Chill:: Chill
7435 @subsection C and C@t{++}
7437 @cindex C and C@t{++}
7438 @cindex expressions in C or C@t{++}
7440 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7441 to both languages. Whenever this is the case, we discuss those languages
7445 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7446 @cindex @sc{gnu} C@t{++}
7447 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7448 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7449 effectively, you must compile your C@t{++} programs with a supported
7450 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7451 compiler (@code{aCC}).
7453 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7454 format. You can select that format explicitly with the @code{g++}
7455 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7456 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7457 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7460 * C Operators:: C and C@t{++} operators
7461 * C Constants:: C and C@t{++} constants
7462 * C plus plus expressions:: C@t{++} expressions
7463 * C Defaults:: Default settings for C and C@t{++}
7464 * C Checks:: C and C@t{++} type and range checks
7465 * Debugging C:: @value{GDBN} and C
7466 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7470 @subsubsection C and C@t{++} operators
7472 @cindex C and C@t{++} operators
7474 Operators must be defined on values of specific types. For instance,
7475 @code{+} is defined on numbers, but not on structures. Operators are
7476 often defined on groups of types.
7478 For the purposes of C and C@t{++}, the following definitions hold:
7483 @emph{Integral types} include @code{int} with any of its storage-class
7484 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7487 @emph{Floating-point types} include @code{float}, @code{double}, and
7488 @code{long double} (if supported by the target platform).
7491 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7494 @emph{Scalar types} include all of the above.
7499 The following operators are supported. They are listed here
7500 in order of increasing precedence:
7504 The comma or sequencing operator. Expressions in a comma-separated list
7505 are evaluated from left to right, with the result of the entire
7506 expression being the last expression evaluated.
7509 Assignment. The value of an assignment expression is the value
7510 assigned. Defined on scalar types.
7513 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7514 and translated to @w{@code{@var{a} = @var{a op b}}}.
7515 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7516 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7517 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7520 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7521 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7525 Logical @sc{or}. Defined on integral types.
7528 Logical @sc{and}. Defined on integral types.
7531 Bitwise @sc{or}. Defined on integral types.
7534 Bitwise exclusive-@sc{or}. Defined on integral types.
7537 Bitwise @sc{and}. Defined on integral types.
7540 Equality and inequality. Defined on scalar types. The value of these
7541 expressions is 0 for false and non-zero for true.
7543 @item <@r{, }>@r{, }<=@r{, }>=
7544 Less than, greater than, less than or equal, greater than or equal.
7545 Defined on scalar types. The value of these expressions is 0 for false
7546 and non-zero for true.
7549 left shift, and right shift. Defined on integral types.
7552 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7555 Addition and subtraction. Defined on integral types, floating-point types and
7558 @item *@r{, }/@r{, }%
7559 Multiplication, division, and modulus. Multiplication and division are
7560 defined on integral and floating-point types. Modulus is defined on
7564 Increment and decrement. When appearing before a variable, the
7565 operation is performed before the variable is used in an expression;
7566 when appearing after it, the variable's value is used before the
7567 operation takes place.
7570 Pointer dereferencing. Defined on pointer types. Same precedence as
7574 Address operator. Defined on variables. Same precedence as @code{++}.
7576 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7577 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7578 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7579 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7583 Negative. Defined on integral and floating-point types. Same
7584 precedence as @code{++}.
7587 Logical negation. Defined on integral types. Same precedence as
7591 Bitwise complement operator. Defined on integral types. Same precedence as
7596 Structure member, and pointer-to-structure member. For convenience,
7597 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7598 pointer based on the stored type information.
7599 Defined on @code{struct} and @code{union} data.
7602 Dereferences of pointers to members.
7605 Array indexing. @code{@var{a}[@var{i}]} is defined as
7606 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7609 Function parameter list. Same precedence as @code{->}.
7612 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7613 and @code{class} types.
7616 Doubled colons also represent the @value{GDBN} scope operator
7617 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7621 If an operator is redefined in the user code, @value{GDBN} usually
7622 attempts to invoke the redefined version instead of using the operator's
7630 @subsubsection C and C@t{++} constants
7632 @cindex C and C@t{++} constants
7634 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7639 Integer constants are a sequence of digits. Octal constants are
7640 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
7641 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7642 @samp{l}, specifying that the constant should be treated as a
7646 Floating point constants are a sequence of digits, followed by a decimal
7647 point, followed by a sequence of digits, and optionally followed by an
7648 exponent. An exponent is of the form:
7649 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7650 sequence of digits. The @samp{+} is optional for positive exponents.
7651 A floating-point constant may also end with a letter @samp{f} or
7652 @samp{F}, specifying that the constant should be treated as being of
7653 the @code{float} (as opposed to the default @code{double}) type; or with
7654 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7658 Enumerated constants consist of enumerated identifiers, or their
7659 integral equivalents.
7662 Character constants are a single character surrounded by single quotes
7663 (@code{'}), or a number---the ordinal value of the corresponding character
7664 (usually its @sc{ascii} value). Within quotes, the single character may
7665 be represented by a letter or by @dfn{escape sequences}, which are of
7666 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
7667 of the character's ordinal value; or of the form @samp{\@var{x}}, where
7668 @samp{@var{x}} is a predefined special character---for example,
7669 @samp{\n} for newline.
7672 String constants are a sequence of character constants surrounded by
7673 double quotes (@code{"}). Any valid character constant (as described
7674 above) may appear. Double quotes within the string must be preceded by
7675 a backslash, so for instance @samp{"a\"b'c"} is a string of five
7679 Pointer constants are an integral value. You can also write pointers
7680 to constants using the C operator @samp{&}.
7683 Array constants are comma-separated lists surrounded by braces @samp{@{}
7684 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
7685 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
7686 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
7690 * C plus plus expressions::
7697 @node C plus plus expressions
7698 @subsubsection C@t{++} expressions
7700 @cindex expressions in C@t{++}
7701 @value{GDBN} expression handling can interpret most C@t{++} expressions.
7703 @cindex C@t{++} support, not in @sc{coff}
7704 @cindex @sc{coff} versus C@t{++}
7705 @cindex C@t{++} and object formats
7706 @cindex object formats and C@t{++}
7707 @cindex a.out and C@t{++}
7708 @cindex @sc{ecoff} and C@t{++}
7709 @cindex @sc{xcoff} and C@t{++}
7710 @cindex @sc{elf}/stabs and C@t{++}
7711 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
7712 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
7713 @c periodically whether this has happened...
7715 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
7716 proper compiler. Typically, C@t{++} debugging depends on the use of
7717 additional debugging information in the symbol table, and thus requires
7718 special support. In particular, if your compiler generates a.out, MIPS
7719 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
7720 symbol table, these facilities are all available. (With @sc{gnu} CC,
7721 you can use the @samp{-gstabs} option to request stabs debugging
7722 extensions explicitly.) Where the object code format is standard
7723 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
7724 support in @value{GDBN} does @emph{not} work.
7729 @cindex member functions
7731 Member function calls are allowed; you can use expressions like
7734 count = aml->GetOriginal(x, y)
7737 @vindex this@r{, inside C@t{++} member functions}
7738 @cindex namespace in C@t{++}
7740 While a member function is active (in the selected stack frame), your
7741 expressions have the same namespace available as the member function;
7742 that is, @value{GDBN} allows implicit references to the class instance
7743 pointer @code{this} following the same rules as C@t{++}.
7745 @cindex call overloaded functions
7746 @cindex overloaded functions, calling
7747 @cindex type conversions in C@t{++}
7749 You can call overloaded functions; @value{GDBN} resolves the function
7750 call to the right definition, with some restrictions. @value{GDBN} does not
7751 perform overload resolution involving user-defined type conversions,
7752 calls to constructors, or instantiations of templates that do not exist
7753 in the program. It also cannot handle ellipsis argument lists or
7756 It does perform integral conversions and promotions, floating-point
7757 promotions, arithmetic conversions, pointer conversions, conversions of
7758 class objects to base classes, and standard conversions such as those of
7759 functions or arrays to pointers; it requires an exact match on the
7760 number of function arguments.
7762 Overload resolution is always performed, unless you have specified
7763 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7764 ,@value{GDBN} features for C@t{++}}.
7766 You must specify @code{set overload-resolution off} in order to use an
7767 explicit function signature to call an overloaded function, as in
7769 p 'foo(char,int)'('x', 13)
7772 The @value{GDBN} command-completion facility can simplify this;
7773 see @ref{Completion, ,Command completion}.
7775 @cindex reference declarations
7777 @value{GDBN} understands variables declared as C@t{++} references; you can use
7778 them in expressions just as you do in C@t{++} source---they are automatically
7781 In the parameter list shown when @value{GDBN} displays a frame, the values of
7782 reference variables are not displayed (unlike other variables); this
7783 avoids clutter, since references are often used for large structures.
7784 The @emph{address} of a reference variable is always shown, unless
7785 you have specified @samp{set print address off}.
7788 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7789 expressions can use it just as expressions in your program do. Since
7790 one scope may be defined in another, you can use @code{::} repeatedly if
7791 necessary, for example in an expression like
7792 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7793 resolving name scope by reference to source files, in both C and C@t{++}
7794 debugging (@pxref{Variables, ,Program variables}).
7797 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7798 calling virtual functions correctly, printing out virtual bases of
7799 objects, calling functions in a base subobject, casting objects, and
7800 invoking user-defined operators.
7803 @subsubsection C and C@t{++} defaults
7805 @cindex C and C@t{++} defaults
7807 If you allow @value{GDBN} to set type and range checking automatically, they
7808 both default to @code{off} whenever the working language changes to
7809 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7810 selects the working language.
7812 If you allow @value{GDBN} to set the language automatically, it
7813 recognizes source files whose names end with @file{.c}, @file{.C}, or
7814 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7815 these files, it sets the working language to C or C@t{++}.
7816 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7817 for further details.
7819 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7820 @c unimplemented. If (b) changes, it might make sense to let this node
7821 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7824 @subsubsection C and C@t{++} type and range checks
7826 @cindex C and C@t{++} checks
7828 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7829 is not used. However, if you turn type checking on, @value{GDBN}
7830 considers two variables type equivalent if:
7834 The two variables are structured and have the same structure, union, or
7838 The two variables have the same type name, or types that have been
7839 declared equivalent through @code{typedef}.
7842 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7845 The two @code{struct}, @code{union}, or @code{enum} variables are
7846 declared in the same declaration. (Note: this may not be true for all C
7851 Range checking, if turned on, is done on mathematical operations. Array
7852 indices are not checked, since they are often used to index a pointer
7853 that is not itself an array.
7856 @subsubsection @value{GDBN} and C
7858 The @code{set print union} and @code{show print union} commands apply to
7859 the @code{union} type. When set to @samp{on}, any @code{union} that is
7860 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7861 appears as @samp{@{...@}}.
7863 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7864 with pointers and a memory allocation function. @xref{Expressions,
7868 * Debugging C plus plus::
7871 @node Debugging C plus plus
7872 @subsubsection @value{GDBN} features for C@t{++}
7874 @cindex commands for C@t{++}
7876 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7877 designed specifically for use with C@t{++}. Here is a summary:
7880 @cindex break in overloaded functions
7881 @item @r{breakpoint menus}
7882 When you want a breakpoint in a function whose name is overloaded,
7883 @value{GDBN} breakpoint menus help you specify which function definition
7884 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7886 @cindex overloading in C@t{++}
7887 @item rbreak @var{regex}
7888 Setting breakpoints using regular expressions is helpful for setting
7889 breakpoints on overloaded functions that are not members of any special
7891 @xref{Set Breaks, ,Setting breakpoints}.
7893 @cindex C@t{++} exception handling
7896 Debug C@t{++} exception handling using these commands. @xref{Set
7897 Catchpoints, , Setting catchpoints}.
7900 @item ptype @var{typename}
7901 Print inheritance relationships as well as other information for type
7903 @xref{Symbols, ,Examining the Symbol Table}.
7905 @cindex C@t{++} symbol display
7906 @item set print demangle
7907 @itemx show print demangle
7908 @itemx set print asm-demangle
7909 @itemx show print asm-demangle
7910 Control whether C@t{++} symbols display in their source form, both when
7911 displaying code as C@t{++} source and when displaying disassemblies.
7912 @xref{Print Settings, ,Print settings}.
7914 @item set print object
7915 @itemx show print object
7916 Choose whether to print derived (actual) or declared types of objects.
7917 @xref{Print Settings, ,Print settings}.
7919 @item set print vtbl
7920 @itemx show print vtbl
7921 Control the format for printing virtual function tables.
7922 @xref{Print Settings, ,Print settings}.
7923 (The @code{vtbl} commands do not work on programs compiled with the HP
7924 ANSI C@t{++} compiler (@code{aCC}).)
7926 @kindex set overload-resolution
7927 @cindex overloaded functions, overload resolution
7928 @item set overload-resolution on
7929 Enable overload resolution for C@t{++} expression evaluation. The default
7930 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7931 and searches for a function whose signature matches the argument types,
7932 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7933 expressions}, for details). If it cannot find a match, it emits a
7936 @item set overload-resolution off
7937 Disable overload resolution for C@t{++} expression evaluation. For
7938 overloaded functions that are not class member functions, @value{GDBN}
7939 chooses the first function of the specified name that it finds in the
7940 symbol table, whether or not its arguments are of the correct type. For
7941 overloaded functions that are class member functions, @value{GDBN}
7942 searches for a function whose signature @emph{exactly} matches the
7945 @item @r{Overloaded symbol names}
7946 You can specify a particular definition of an overloaded symbol, using
7947 the same notation that is used to declare such symbols in C@t{++}: type
7948 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7949 also use the @value{GDBN} command-line word completion facilities to list the
7950 available choices, or to finish the type list for you.
7951 @xref{Completion,, Command completion}, for details on how to do this.
7955 @subsection Modula-2
7957 @cindex Modula-2, @value{GDBN} support
7959 The extensions made to @value{GDBN} to support Modula-2 only support
7960 output from the @sc{gnu} Modula-2 compiler (which is currently being
7961 developed). Other Modula-2 compilers are not currently supported, and
7962 attempting to debug executables produced by them is most likely
7963 to give an error as @value{GDBN} reads in the executable's symbol
7966 @cindex expressions in Modula-2
7968 * M2 Operators:: Built-in operators
7969 * Built-In Func/Proc:: Built-in functions and procedures
7970 * M2 Constants:: Modula-2 constants
7971 * M2 Defaults:: Default settings for Modula-2
7972 * Deviations:: Deviations from standard Modula-2
7973 * M2 Checks:: Modula-2 type and range checks
7974 * M2 Scope:: The scope operators @code{::} and @code{.}
7975 * GDB/M2:: @value{GDBN} and Modula-2
7979 @subsubsection Operators
7980 @cindex Modula-2 operators
7982 Operators must be defined on values of specific types. For instance,
7983 @code{+} is defined on numbers, but not on structures. Operators are
7984 often defined on groups of types. For the purposes of Modula-2, the
7985 following definitions hold:
7990 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7994 @emph{Character types} consist of @code{CHAR} and its subranges.
7997 @emph{Floating-point types} consist of @code{REAL}.
8000 @emph{Pointer types} consist of anything declared as @code{POINTER TO
8004 @emph{Scalar types} consist of all of the above.
8007 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
8010 @emph{Boolean types} consist of @code{BOOLEAN}.
8014 The following operators are supported, and appear in order of
8015 increasing precedence:
8019 Function argument or array index separator.
8022 Assignment. The value of @var{var} @code{:=} @var{value} is
8026 Less than, greater than on integral, floating-point, or enumerated
8030 Less than or equal to, greater than or equal to
8031 on integral, floating-point and enumerated types, or set inclusion on
8032 set types. Same precedence as @code{<}.
8034 @item =@r{, }<>@r{, }#
8035 Equality and two ways of expressing inequality, valid on scalar types.
8036 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
8037 available for inequality, since @code{#} conflicts with the script
8041 Set membership. Defined on set types and the types of their members.
8042 Same precedence as @code{<}.
8045 Boolean disjunction. Defined on boolean types.
8048 Boolean conjunction. Defined on boolean types.
8051 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
8054 Addition and subtraction on integral and floating-point types, or union
8055 and difference on set types.
8058 Multiplication on integral and floating-point types, or set intersection
8062 Division on floating-point types, or symmetric set difference on set
8063 types. Same precedence as @code{*}.
8066 Integer division and remainder. Defined on integral types. Same
8067 precedence as @code{*}.
8070 Negative. Defined on @code{INTEGER} and @code{REAL} data.
8073 Pointer dereferencing. Defined on pointer types.
8076 Boolean negation. Defined on boolean types. Same precedence as
8080 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
8081 precedence as @code{^}.
8084 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
8087 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
8091 @value{GDBN} and Modula-2 scope operators.
8095 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
8096 treats the use of the operator @code{IN}, or the use of operators
8097 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
8098 @code{<=}, and @code{>=} on sets as an error.
8102 @node Built-In Func/Proc
8103 @subsubsection Built-in functions and procedures
8104 @cindex Modula-2 built-ins
8106 Modula-2 also makes available several built-in procedures and functions.
8107 In describing these, the following metavariables are used:
8112 represents an @code{ARRAY} variable.
8115 represents a @code{CHAR} constant or variable.
8118 represents a variable or constant of integral type.
8121 represents an identifier that belongs to a set. Generally used in the
8122 same function with the metavariable @var{s}. The type of @var{s} should
8123 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
8126 represents a variable or constant of integral or floating-point type.
8129 represents a variable or constant of floating-point type.
8135 represents a variable.
8138 represents a variable or constant of one of many types. See the
8139 explanation of the function for details.
8142 All Modula-2 built-in procedures also return a result, described below.
8146 Returns the absolute value of @var{n}.
8149 If @var{c} is a lower case letter, it returns its upper case
8150 equivalent, otherwise it returns its argument.
8153 Returns the character whose ordinal value is @var{i}.
8156 Decrements the value in the variable @var{v} by one. Returns the new value.
8158 @item DEC(@var{v},@var{i})
8159 Decrements the value in the variable @var{v} by @var{i}. Returns the
8162 @item EXCL(@var{m},@var{s})
8163 Removes the element @var{m} from the set @var{s}. Returns the new
8166 @item FLOAT(@var{i})
8167 Returns the floating point equivalent of the integer @var{i}.
8170 Returns the index of the last member of @var{a}.
8173 Increments the value in the variable @var{v} by one. Returns the new value.
8175 @item INC(@var{v},@var{i})
8176 Increments the value in the variable @var{v} by @var{i}. Returns the
8179 @item INCL(@var{m},@var{s})
8180 Adds the element @var{m} to the set @var{s} if it is not already
8181 there. Returns the new set.
8184 Returns the maximum value of the type @var{t}.
8187 Returns the minimum value of the type @var{t}.
8190 Returns boolean TRUE if @var{i} is an odd number.
8193 Returns the ordinal value of its argument. For example, the ordinal
8194 value of a character is its @sc{ascii} value (on machines supporting the
8195 @sc{ascii} character set). @var{x} must be of an ordered type, which include
8196 integral, character and enumerated types.
8199 Returns the size of its argument. @var{x} can be a variable or a type.
8201 @item TRUNC(@var{r})
8202 Returns the integral part of @var{r}.
8204 @item VAL(@var{t},@var{i})
8205 Returns the member of the type @var{t} whose ordinal value is @var{i}.
8209 @emph{Warning:} Sets and their operations are not yet supported, so
8210 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
8214 @cindex Modula-2 constants
8216 @subsubsection Constants
8218 @value{GDBN} allows you to express the constants of Modula-2 in the following
8224 Integer constants are simply a sequence of digits. When used in an
8225 expression, a constant is interpreted to be type-compatible with the
8226 rest of the expression. Hexadecimal integers are specified by a
8227 trailing @samp{H}, and octal integers by a trailing @samp{B}.
8230 Floating point constants appear as a sequence of digits, followed by a
8231 decimal point and another sequence of digits. An optional exponent can
8232 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
8233 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
8234 digits of the floating point constant must be valid decimal (base 10)
8238 Character constants consist of a single character enclosed by a pair of
8239 like quotes, either single (@code{'}) or double (@code{"}). They may
8240 also be expressed by their ordinal value (their @sc{ascii} value, usually)
8241 followed by a @samp{C}.
8244 String constants consist of a sequence of characters enclosed by a
8245 pair of like quotes, either single (@code{'}) or double (@code{"}).
8246 Escape sequences in the style of C are also allowed. @xref{C
8247 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
8251 Enumerated constants consist of an enumerated identifier.
8254 Boolean constants consist of the identifiers @code{TRUE} and
8258 Pointer constants consist of integral values only.
8261 Set constants are not yet supported.
8265 @subsubsection Modula-2 defaults
8266 @cindex Modula-2 defaults
8268 If type and range checking are set automatically by @value{GDBN}, they
8269 both default to @code{on} whenever the working language changes to
8270 Modula-2. This happens regardless of whether you or @value{GDBN}
8271 selected the working language.
8273 If you allow @value{GDBN} to set the language automatically, then entering
8274 code compiled from a file whose name ends with @file{.mod} sets the
8275 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8276 the language automatically}, for further details.
8279 @subsubsection Deviations from standard Modula-2
8280 @cindex Modula-2, deviations from
8282 A few changes have been made to make Modula-2 programs easier to debug.
8283 This is done primarily via loosening its type strictness:
8287 Unlike in standard Modula-2, pointer constants can be formed by
8288 integers. This allows you to modify pointer variables during
8289 debugging. (In standard Modula-2, the actual address contained in a
8290 pointer variable is hidden from you; it can only be modified
8291 through direct assignment to another pointer variable or expression that
8292 returned a pointer.)
8295 C escape sequences can be used in strings and characters to represent
8296 non-printable characters. @value{GDBN} prints out strings with these
8297 escape sequences embedded. Single non-printable characters are
8298 printed using the @samp{CHR(@var{nnn})} format.
8301 The assignment operator (@code{:=}) returns the value of its right-hand
8305 All built-in procedures both modify @emph{and} return their argument.
8309 @subsubsection Modula-2 type and range checks
8310 @cindex Modula-2 checks
8313 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8316 @c FIXME remove warning when type/range checks added
8318 @value{GDBN} considers two Modula-2 variables type equivalent if:
8322 They are of types that have been declared equivalent via a @code{TYPE
8323 @var{t1} = @var{t2}} statement
8326 They have been declared on the same line. (Note: This is true of the
8327 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8330 As long as type checking is enabled, any attempt to combine variables
8331 whose types are not equivalent is an error.
8333 Range checking is done on all mathematical operations, assignment, array
8334 index bounds, and all built-in functions and procedures.
8337 @subsubsection The scope operators @code{::} and @code{.}
8339 @cindex @code{.}, Modula-2 scope operator
8340 @cindex colon, doubled as scope operator
8342 @vindex colon-colon@r{, in Modula-2}
8343 @c Info cannot handle :: but TeX can.
8346 @vindex ::@r{, in Modula-2}
8349 There are a few subtle differences between the Modula-2 scope operator
8350 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8355 @var{module} . @var{id}
8356 @var{scope} :: @var{id}
8360 where @var{scope} is the name of a module or a procedure,
8361 @var{module} the name of a module, and @var{id} is any declared
8362 identifier within your program, except another module.
8364 Using the @code{::} operator makes @value{GDBN} search the scope
8365 specified by @var{scope} for the identifier @var{id}. If it is not
8366 found in the specified scope, then @value{GDBN} searches all scopes
8367 enclosing the one specified by @var{scope}.
8369 Using the @code{.} operator makes @value{GDBN} search the current scope for
8370 the identifier specified by @var{id} that was imported from the
8371 definition module specified by @var{module}. With this operator, it is
8372 an error if the identifier @var{id} was not imported from definition
8373 module @var{module}, or if @var{id} is not an identifier in
8377 @subsubsection @value{GDBN} and Modula-2
8379 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8380 Five subcommands of @code{set print} and @code{show print} apply
8381 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8382 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8383 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8384 analogue in Modula-2.
8386 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8387 with any language, is not useful with Modula-2. Its
8388 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8389 created in Modula-2 as they can in C or C@t{++}. However, because an
8390 address can be specified by an integral constant, the construct
8391 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8393 @cindex @code{#} in Modula-2
8394 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8395 interpreted as the beginning of a comment. Use @code{<>} instead.
8397 @c OBSOLETE @node Chill
8398 @c OBSOLETE @subsection Chill
8400 @c OBSOLETE The extensions made to @value{GDBN} to support Chill only support output
8401 @c OBSOLETE from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
8402 @c OBSOLETE supported, and attempting to debug executables produced by them is most
8403 @c OBSOLETE likely to give an error as @value{GDBN} reads in the executable's symbol
8406 @c OBSOLETE @c This used to say "... following Chill related topics ...", but since
8407 @c OBSOLETE @c menus are not shown in the printed manual, it would look awkward.
8408 @c OBSOLETE This section covers the Chill related topics and the features
8409 @c OBSOLETE of @value{GDBN} which support these topics.
8412 @c OBSOLETE * How modes are displayed:: How modes are displayed
8413 @c OBSOLETE * Locations:: Locations and their accesses
8414 @c OBSOLETE * Values and their Operations:: Values and their Operations
8415 @c OBSOLETE * Chill type and range checks::
8416 @c OBSOLETE * Chill defaults::
8417 @c OBSOLETE @end menu
8419 @c OBSOLETE @node How modes are displayed
8420 @c OBSOLETE @subsubsection How modes are displayed
8422 @c OBSOLETE The Chill Datatype- (Mode) support of @value{GDBN} is directly related
8423 @c OBSOLETE with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
8424 @c OBSOLETE slightly from the standard specification of the Chill language. The
8425 @c OBSOLETE provided modes are:
8427 @c OBSOLETE @c FIXME: this @table's contents effectively disable @code by using @r
8428 @c OBSOLETE @c on every @item. So why does it need @code?
8429 @c OBSOLETE @table @code
8430 @c OBSOLETE @item @r{@emph{Discrete modes:}}
8431 @c OBSOLETE @itemize @bullet
8433 @c OBSOLETE @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
8434 @c OBSOLETE UINT, LONG, ULONG},
8436 @c OBSOLETE @emph{Boolean Mode} which is predefined by @code{BOOL},
8438 @c OBSOLETE @emph{Character Mode} which is predefined by @code{CHAR},
8440 @c OBSOLETE @emph{Set Mode} which is displayed by the keyword @code{SET}.
8441 @c OBSOLETE @smallexample
8442 @c OBSOLETE (@value{GDBP}) ptype x
8443 @c OBSOLETE type = SET (karli = 10, susi = 20, fritzi = 100)
8444 @c OBSOLETE @end smallexample
8445 @c OBSOLETE If the type is an unnumbered set the set element values are omitted.
8447 @c OBSOLETE @emph{Range Mode} which is displayed by
8448 @c OBSOLETE @smallexample
8449 @c OBSOLETE @code{type = <basemode>(<lower bound> : <upper bound>)}
8450 @c OBSOLETE @end smallexample
8451 @c OBSOLETE where @code{<lower bound>, <upper bound>} can be of any discrete literal
8452 @c OBSOLETE expression (e.g. set element names).
8453 @c OBSOLETE @end itemize
8455 @c OBSOLETE @item @r{@emph{Powerset Mode:}}
8456 @c OBSOLETE A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
8457 @c OBSOLETE the member mode of the powerset. The member mode can be any discrete mode.
8458 @c OBSOLETE @smallexample
8459 @c OBSOLETE (@value{GDBP}) ptype x
8460 @c OBSOLETE type = POWERSET SET (egon, hugo, otto)
8461 @c OBSOLETE @end smallexample
8463 @c OBSOLETE @item @r{@emph{Reference Modes:}}
8464 @c OBSOLETE @itemize @bullet
8466 @c OBSOLETE @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
8467 @c OBSOLETE followed by the mode name to which the reference is bound.
8469 @c OBSOLETE @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
8470 @c OBSOLETE @end itemize
8472 @c OBSOLETE @item @r{@emph{Procedure mode}}
8473 @c OBSOLETE The procedure mode is displayed by @code{type = PROC(<parameter list>)
8474 @c OBSOLETE <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
8475 @c OBSOLETE list>} is a list of the parameter modes. @code{<return mode>} indicates
8476 @c OBSOLETE the mode of the result of the procedure if any. The exceptionlist lists
8477 @c OBSOLETE all possible exceptions which can be raised by the procedure.
8480 @c OBSOLETE @item @r{@emph{Instance mode}}
8481 @c OBSOLETE The instance mode is represented by a structure, which has a static
8482 @c OBSOLETE type, and is therefore not really of interest.
8483 @c OBSOLETE @end ignore
8485 @c OBSOLETE @item @r{@emph{Synchronization Modes:}}
8486 @c OBSOLETE @itemize @bullet
8488 @c OBSOLETE @emph{Event Mode} which is displayed by
8489 @c OBSOLETE @smallexample
8490 @c OBSOLETE @code{EVENT (<event length>)}
8491 @c OBSOLETE @end smallexample
8492 @c OBSOLETE where @code{(<event length>)} is optional.
8494 @c OBSOLETE @emph{Buffer Mode} which is displayed by
8495 @c OBSOLETE @smallexample
8496 @c OBSOLETE @code{BUFFER (<buffer length>)<buffer element mode>}
8497 @c OBSOLETE @end smallexample
8498 @c OBSOLETE where @code{(<buffer length>)} is optional.
8499 @c OBSOLETE @end itemize
8501 @c OBSOLETE @item @r{@emph{Timing Modes:}}
8502 @c OBSOLETE @itemize @bullet
8504 @c OBSOLETE @emph{Duration Mode} which is predefined by @code{DURATION}
8506 @c OBSOLETE @emph{Absolute Time Mode} which is predefined by @code{TIME}
8507 @c OBSOLETE @end itemize
8509 @c OBSOLETE @item @r{@emph{Real Modes:}}
8510 @c OBSOLETE Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
8512 @c OBSOLETE @item @r{@emph{String Modes:}}
8513 @c OBSOLETE @itemize @bullet
8515 @c OBSOLETE @emph{Character String Mode} which is displayed by
8516 @c OBSOLETE @smallexample
8517 @c OBSOLETE @code{CHARS(<string length>)}
8518 @c OBSOLETE @end smallexample
8519 @c OBSOLETE followed by the keyword @code{VARYING} if the String Mode is a varying
8522 @c OBSOLETE @emph{Bit String Mode} which is displayed by
8523 @c OBSOLETE @smallexample
8524 @c OBSOLETE @code{BOOLS(<string
8525 @c OBSOLETE length>)}
8526 @c OBSOLETE @end smallexample
8527 @c OBSOLETE @end itemize
8529 @c OBSOLETE @item @r{@emph{Array Mode:}}
8530 @c OBSOLETE The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
8531 @c OBSOLETE followed by the element mode (which may in turn be an array mode).
8532 @c OBSOLETE @smallexample
8533 @c OBSOLETE (@value{GDBP}) ptype x
8534 @c OBSOLETE type = ARRAY (1:42)
8535 @c OBSOLETE ARRAY (1:20)
8536 @c OBSOLETE SET (karli = 10, susi = 20, fritzi = 100)
8537 @c OBSOLETE @end smallexample
8539 @c OBSOLETE @item @r{@emph{Structure Mode}}
8540 @c OBSOLETE The Structure mode is displayed by the keyword @code{STRUCT(<field
8541 @c OBSOLETE list>)}. The @code{<field list>} consists of names and modes of fields
8542 @c OBSOLETE of the structure. Variant structures have the keyword @code{CASE <field>
8543 @c OBSOLETE OF <variant fields> ESAC} in their field list. Since the current version
8544 @c OBSOLETE of the GNU Chill compiler doesn't implement tag processing (no runtime
8545 @c OBSOLETE checks of variant fields, and therefore no debugging info), the output
8546 @c OBSOLETE always displays all variant fields.
8547 @c OBSOLETE @smallexample
8548 @c OBSOLETE (@value{GDBP}) ptype str
8549 @c OBSOLETE type = STRUCT (
8552 @c OBSOLETE CASE bs OF
8553 @c OBSOLETE (karli):
8559 @c OBSOLETE @end smallexample
8560 @c OBSOLETE @end table
8562 @c OBSOLETE @node Locations
8563 @c OBSOLETE @subsubsection Locations and their accesses
8565 @c OBSOLETE A location in Chill is an object which can contain values.
8567 @c OBSOLETE A value of a location is generally accessed by the (declared) name of
8568 @c OBSOLETE the location. The output conforms to the specification of values in
8569 @c OBSOLETE Chill programs. How values are specified
8570 @c OBSOLETE is the topic of the next section, @ref{Values and their Operations}.
8572 @c OBSOLETE The pseudo-location @code{RESULT} (or @code{result}) can be used to
8573 @c OBSOLETE display or change the result of a currently-active procedure:
8575 @c OBSOLETE @smallexample
8576 @c OBSOLETE set result := EXPR
8577 @c OBSOLETE @end smallexample
8579 @c OBSOLETE @noindent
8580 @c OBSOLETE This does the same as the Chill action @code{RESULT EXPR} (which
8581 @c OBSOLETE is not available in @value{GDBN}).
8583 @c OBSOLETE Values of reference mode locations are printed by @code{PTR(<hex
8584 @c OBSOLETE value>)} in case of a free reference mode, and by @code{(REF <reference
8585 @c OBSOLETE mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
8586 @c OBSOLETE represents the address where the reference points to. To access the
8587 @c OBSOLETE value of the location referenced by the pointer, use the dereference
8588 @c OBSOLETE operator @samp{->}.
8590 @c OBSOLETE Values of procedure mode locations are displayed by
8591 @c OBSOLETE @smallexample
8592 @c OBSOLETE @code{@{ PROC
8593 @c OBSOLETE (<argument modes> ) <return mode> @} <address> <name of procedure
8594 @c OBSOLETE location>}
8595 @c OBSOLETE @end smallexample
8596 @c OBSOLETE @code{<argument modes>} is a list of modes according to the parameter
8597 @c OBSOLETE specification of the procedure and @code{<address>} shows the address of
8598 @c OBSOLETE the entry point.
8601 @c OBSOLETE Locations of instance modes are displayed just like a structure with two
8602 @c OBSOLETE fields specifying the @emph{process type} and the @emph{copy number} of
8603 @c OBSOLETE the investigated instance location@footnote{This comes from the current
8604 @c OBSOLETE implementation of instances. They are implemented as a structure (no
8605 @c OBSOLETE na). The output should be something like @code{[<name of the process>;
8606 @c OBSOLETE <instance number>]}.}. The field names are @code{__proc_type} and
8607 @c OBSOLETE @code{__proc_copy}.
8609 @c OBSOLETE Locations of synchronization modes are displayed like a structure with
8610 @c OBSOLETE the field name @code{__event_data} in case of a event mode location, and
8611 @c OBSOLETE like a structure with the field @code{__buffer_data} in case of a buffer
8612 @c OBSOLETE mode location (refer to previous paragraph).
8614 @c OBSOLETE Structure Mode locations are printed by @code{[.<field name>: <value>,
8615 @c OBSOLETE ...]}. The @code{<field name>} corresponds to the structure mode
8616 @c OBSOLETE definition and the layout of @code{<value>} varies depending of the mode
8617 @c OBSOLETE of the field. If the investigated structure mode location is of variant
8618 @c OBSOLETE structure mode, the variant parts of the structure are enclosed in curled
8619 @c OBSOLETE braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
8620 @c OBSOLETE on the same memory location and represent the current values of the
8621 @c OBSOLETE memory location in their specific modes. Since no tag processing is done
8622 @c OBSOLETE all variants are displayed. A variant field is printed by
8623 @c OBSOLETE @code{(<variant name>) = .<field name>: <value>}. (who implements the
8624 @c OBSOLETE stuff ???)
8625 @c OBSOLETE @smallexample
8626 @c OBSOLETE (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
8627 @c OBSOLETE [.cs: []], (susi) = [.ds: susi]}]
8628 @c OBSOLETE @end smallexample
8629 @c OBSOLETE @end ignore
8631 @c OBSOLETE Substructures of string mode-, array mode- or structure mode-values
8632 @c OBSOLETE (e.g. array slices, fields of structure locations) are accessed using
8633 @c OBSOLETE certain operations which are described in the next section, @ref{Values
8634 @c OBSOLETE and their Operations}.
8636 @c OBSOLETE A location value may be interpreted as having a different mode using the
8637 @c OBSOLETE location conversion. This mode conversion is written as @code{<mode
8638 @c OBSOLETE name>(<location>)}. The user has to consider that the sizes of the modes
8639 @c OBSOLETE have to be equal otherwise an error occurs. Furthermore, no range
8640 @c OBSOLETE checking of the location against the destination mode is performed, and
8641 @c OBSOLETE therefore the result can be quite confusing.
8643 @c OBSOLETE @smallexample
8644 @c OBSOLETE (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
8645 @c OBSOLETE @end smallexample
8647 @c OBSOLETE @node Values and their Operations
8648 @c OBSOLETE @subsubsection Values and their Operations
8650 @c OBSOLETE Values are used to alter locations, to investigate complex structures in
8651 @c OBSOLETE more detail or to filter relevant information out of a large amount of
8652 @c OBSOLETE data. There are several (mode dependent) operations defined which enable
8653 @c OBSOLETE such investigations. These operations are not only applicable to
8654 @c OBSOLETE constant values but also to locations, which can become quite useful
8655 @c OBSOLETE when debugging complex structures. During parsing the command line
8656 @c OBSOLETE (e.g. evaluating an expression) @value{GDBN} treats location names as
8657 @c OBSOLETE the values behind these locations.
8659 @c OBSOLETE This section describes how values have to be specified and which
8660 @c OBSOLETE operations are legal to be used with such values.
8662 @c OBSOLETE @table @code
8663 @c OBSOLETE @item Literal Values
8664 @c OBSOLETE Literal values are specified in the same manner as in @sc{gnu} Chill programs.
8665 @c OBSOLETE For detailed specification refer to the @sc{gnu} Chill implementation Manual
8666 @c OBSOLETE chapter 1.5.
8667 @c OBSOLETE @c FIXME: if the Chill Manual is a Texinfo documents, the above should
8668 @c OBSOLETE @c be converted to a @ref.
8671 @c OBSOLETE @itemize @bullet
8673 @c OBSOLETE @emph{Integer Literals} are specified in the same manner as in Chill
8674 @c OBSOLETE programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
8676 @c OBSOLETE @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
8678 @c OBSOLETE @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
8679 @c OBSOLETE @code{'M'})
8681 @c OBSOLETE @emph{Set Literals} are defined by a name which was specified in a set
8682 @c OBSOLETE mode. The value delivered by a Set Literal is the set value. This is
8683 @c OBSOLETE comparable to an enumeration in C/C@t{++} language.
8685 @c OBSOLETE @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
8686 @c OBSOLETE emptiness literal delivers either the empty reference value, the empty
8687 @c OBSOLETE procedure value or the empty instance value.
8690 @c OBSOLETE @emph{Character String Literals} are defined by a sequence of characters
8691 @c OBSOLETE enclosed in single- or double quotes. If a single- or double quote has
8692 @c OBSOLETE to be part of the string literal it has to be stuffed (specified twice).
8694 @c OBSOLETE @emph{Bitstring Literals} are specified in the same manner as in Chill
8695 @c OBSOLETE programs (refer z200/88 chpt 5.2.4.8).
8697 @c OBSOLETE @emph{Floating point literals} are specified in the same manner as in
8698 @c OBSOLETE (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
8699 @c OBSOLETE @end itemize
8700 @c OBSOLETE @end ignore
8702 @c OBSOLETE @item Tuple Values
8703 @c OBSOLETE A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
8704 @c OBSOLETE name>} can be omitted if the mode of the tuple is unambiguous. This
8705 @c OBSOLETE unambiguity is derived from the context of a evaluated expression.
8706 @c OBSOLETE @code{<tuple>} can be one of the following:
8708 @c OBSOLETE @itemize @bullet
8709 @c OBSOLETE @item @emph{Powerset Tuple}
8710 @c OBSOLETE @item @emph{Array Tuple}
8711 @c OBSOLETE @item @emph{Structure Tuple}
8712 @c OBSOLETE Powerset tuples, array tuples and structure tuples are specified in the
8713 @c OBSOLETE same manner as in Chill programs refer to z200/88 chpt 5.2.5.
8714 @c OBSOLETE @end itemize
8716 @c OBSOLETE @item String Element Value
8717 @c OBSOLETE A string element value is specified by
8718 @c OBSOLETE @smallexample
8719 @c OBSOLETE @code{<string value>(<index>)}
8720 @c OBSOLETE @end smallexample
8721 @c OBSOLETE where @code{<index>} is a integer expression. It delivers a character
8722 @c OBSOLETE value which is equivalent to the character indexed by @code{<index>} in
8723 @c OBSOLETE the string.
8725 @c OBSOLETE @item String Slice Value
8726 @c OBSOLETE A string slice value is specified by @code{<string value>(<slice
8727 @c OBSOLETE spec>)}, where @code{<slice spec>} can be either a range of integer
8728 @c OBSOLETE expressions or specified by @code{<start expr> up <size>}.
8729 @c OBSOLETE @code{<size>} denotes the number of elements which the slice contains.
8730 @c OBSOLETE The delivered value is a string value, which is part of the specified
8733 @c OBSOLETE @item Array Element Values
8734 @c OBSOLETE An array element value is specified by @code{<array value>(<expr>)} and
8735 @c OBSOLETE delivers a array element value of the mode of the specified array.
8737 @c OBSOLETE @item Array Slice Values
8738 @c OBSOLETE An array slice is specified by @code{<array value>(<slice spec>)}, where
8739 @c OBSOLETE @code{<slice spec>} can be either a range specified by expressions or by
8740 @c OBSOLETE @code{<start expr> up <size>}. @code{<size>} denotes the number of
8741 @c OBSOLETE arrayelements the slice contains. The delivered value is an array value
8742 @c OBSOLETE which is part of the specified array.
8744 @c OBSOLETE @item Structure Field Values
8745 @c OBSOLETE A structure field value is derived by @code{<structure value>.<field
8746 @c OBSOLETE name>}, where @code{<field name>} indicates the name of a field specified
8747 @c OBSOLETE in the mode definition of the structure. The mode of the delivered value
8748 @c OBSOLETE corresponds to this mode definition in the structure definition.
8750 @c OBSOLETE @item Procedure Call Value
8751 @c OBSOLETE The procedure call value is derived from the return value of the
8752 @c OBSOLETE procedure@footnote{If a procedure call is used for instance in an
8753 @c OBSOLETE expression, then this procedure is called with all its side
8754 @c OBSOLETE effects. This can lead to confusing results if used carelessly.}.
8756 @c OBSOLETE Values of duration mode locations are represented by @code{ULONG} literals.
8758 @c OBSOLETE Values of time mode locations appear as
8759 @c OBSOLETE @smallexample
8760 @c OBSOLETE @code{TIME(<secs>:<nsecs>)}
8761 @c OBSOLETE @end smallexample
8765 @c OBSOLETE This is not implemented yet:
8766 @c OBSOLETE @item Built-in Value
8767 @c OBSOLETE @noindent
8768 @c OBSOLETE The following built in functions are provided:
8770 @c OBSOLETE @table @code
8771 @c OBSOLETE @item @code{ADDR()}
8772 @c OBSOLETE @item @code{NUM()}
8773 @c OBSOLETE @item @code{PRED()}
8774 @c OBSOLETE @item @code{SUCC()}
8775 @c OBSOLETE @item @code{ABS()}
8776 @c OBSOLETE @item @code{CARD()}
8777 @c OBSOLETE @item @code{MAX()}
8778 @c OBSOLETE @item @code{MIN()}
8779 @c OBSOLETE @item @code{SIZE()}
8780 @c OBSOLETE @item @code{UPPER()}
8781 @c OBSOLETE @item @code{LOWER()}
8782 @c OBSOLETE @item @code{LENGTH()}
8783 @c OBSOLETE @item @code{SIN()}
8784 @c OBSOLETE @item @code{COS()}
8785 @c OBSOLETE @item @code{TAN()}
8786 @c OBSOLETE @item @code{ARCSIN()}
8787 @c OBSOLETE @item @code{ARCCOS()}
8788 @c OBSOLETE @item @code{ARCTAN()}
8789 @c OBSOLETE @item @code{EXP()}
8790 @c OBSOLETE @item @code{LN()}
8791 @c OBSOLETE @item @code{LOG()}
8792 @c OBSOLETE @item @code{SQRT()}
8793 @c OBSOLETE @end table
8795 @c OBSOLETE For a detailed description refer to the GNU Chill implementation manual
8796 @c OBSOLETE chapter 1.6.
8797 @c OBSOLETE @end ignore
8799 @c OBSOLETE @item Zero-adic Operator Value
8800 @c OBSOLETE The zero-adic operator value is derived from the instance value for the
8801 @c OBSOLETE current active process.
8803 @c OBSOLETE @item Expression Values
8804 @c OBSOLETE The value delivered by an expression is the result of the evaluation of
8805 @c OBSOLETE the specified expression. If there are error conditions (mode
8806 @c OBSOLETE incompatibility, etc.) the evaluation of expressions is aborted with a
8807 @c OBSOLETE corresponding error message. Expressions may be parenthesised which
8808 @c OBSOLETE causes the evaluation of this expression before any other expression
8809 @c OBSOLETE which uses the result of the parenthesised expression. The following
8810 @c OBSOLETE operators are supported by @value{GDBN}:
8812 @c OBSOLETE @table @code
8813 @c OBSOLETE @item @code{OR, ORIF, XOR}
8814 @c OBSOLETE @itemx @code{AND, ANDIF}
8815 @c OBSOLETE @itemx @code{NOT}
8816 @c OBSOLETE Logical operators defined over operands of boolean mode.
8818 @c OBSOLETE @item @code{=, /=}
8819 @c OBSOLETE Equality and inequality operators defined over all modes.
8821 @c OBSOLETE @item @code{>, >=}
8822 @c OBSOLETE @itemx @code{<, <=}
8823 @c OBSOLETE Relational operators defined over predefined modes.
8825 @c OBSOLETE @item @code{+, -}
8826 @c OBSOLETE @itemx @code{*, /, MOD, REM}
8827 @c OBSOLETE Arithmetic operators defined over predefined modes.
8829 @c OBSOLETE @item @code{-}
8830 @c OBSOLETE Change sign operator.
8832 @c OBSOLETE @item @code{//}
8833 @c OBSOLETE String concatenation operator.
8835 @c OBSOLETE @item @code{()}
8836 @c OBSOLETE String repetition operator.
8838 @c OBSOLETE @item @code{->}
8839 @c OBSOLETE Referenced location operator which can be used either to take the
8840 @c OBSOLETE address of a location (@code{->loc}), or to dereference a reference
8841 @c OBSOLETE location (@code{loc->}).
8843 @c OBSOLETE @item @code{OR, XOR}
8844 @c OBSOLETE @itemx @code{AND}
8845 @c OBSOLETE @itemx @code{NOT}
8846 @c OBSOLETE Powerset and bitstring operators.
8848 @c OBSOLETE @item @code{>, >=}
8849 @c OBSOLETE @itemx @code{<, <=}
8850 @c OBSOLETE Powerset inclusion operators.
8852 @c OBSOLETE @item @code{IN}
8853 @c OBSOLETE Membership operator.
8854 @c OBSOLETE @end table
8855 @c OBSOLETE @end table
8857 @c OBSOLETE @node Chill type and range checks
8858 @c OBSOLETE @subsubsection Chill type and range checks
8860 @c OBSOLETE @value{GDBN} considers two Chill variables mode equivalent if the sizes
8861 @c OBSOLETE of the two modes are equal. This rule applies recursively to more
8862 @c OBSOLETE complex datatypes which means that complex modes are treated
8863 @c OBSOLETE equivalent if all element modes (which also can be complex modes like
8864 @c OBSOLETE structures, arrays, etc.) have the same size.
8866 @c OBSOLETE Range checking is done on all mathematical operations, assignment, array
8867 @c OBSOLETE index bounds and all built in procedures.
8869 @c OBSOLETE Strong type checks are forced using the @value{GDBN} command @code{set
8870 @c OBSOLETE check strong}. This enforces strong type and range checks on all
8871 @c OBSOLETE operations where Chill constructs are used (expressions, built in
8872 @c OBSOLETE functions, etc.) in respect to the semantics as defined in the z.200
8873 @c OBSOLETE language specification.
8875 @c OBSOLETE All checks can be disabled by the @value{GDBN} command @code{set check
8879 @c OBSOLETE @c Deviations from the Chill Standard Z200/88
8880 @c OBSOLETE see last paragraph ?
8881 @c OBSOLETE @end ignore
8883 @c OBSOLETE @node Chill defaults
8884 @c OBSOLETE @subsubsection Chill defaults
8886 @c OBSOLETE If type and range checking are set automatically by @value{GDBN}, they
8887 @c OBSOLETE both default to @code{on} whenever the working language changes to
8888 @c OBSOLETE Chill. This happens regardless of whether you or @value{GDBN}
8889 @c OBSOLETE selected the working language.
8891 @c OBSOLETE If you allow @value{GDBN} to set the language automatically, then entering
8892 @c OBSOLETE code compiled from a file whose name ends with @file{.ch} sets the
8893 @c OBSOLETE working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8894 @c OBSOLETE the language automatically}, for further details.
8897 @chapter Examining the Symbol Table
8899 The commands described in this chapter allow you to inquire about the
8900 symbols (names of variables, functions and types) defined in your
8901 program. This information is inherent in the text of your program and
8902 does not change as your program executes. @value{GDBN} finds it in your
8903 program's symbol table, in the file indicated when you started @value{GDBN}
8904 (@pxref{File Options, ,Choosing files}), or by one of the
8905 file-management commands (@pxref{Files, ,Commands to specify files}).
8907 @cindex symbol names
8908 @cindex names of symbols
8909 @cindex quoting names
8910 Occasionally, you may need to refer to symbols that contain unusual
8911 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8912 most frequent case is in referring to static variables in other
8913 source files (@pxref{Variables,,Program variables}). File names
8914 are recorded in object files as debugging symbols, but @value{GDBN} would
8915 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8916 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8917 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8924 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8927 @kindex info address
8928 @cindex address of a symbol
8929 @item info address @var{symbol}
8930 Describe where the data for @var{symbol} is stored. For a register
8931 variable, this says which register it is kept in. For a non-register
8932 local variable, this prints the stack-frame offset at which the variable
8935 Note the contrast with @samp{print &@var{symbol}}, which does not work
8936 at all for a register variable, and for a stack local variable prints
8937 the exact address of the current instantiation of the variable.
8940 @cindex symbol from address
8941 @item info symbol @var{addr}
8942 Print the name of a symbol which is stored at the address @var{addr}.
8943 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8944 nearest symbol and an offset from it:
8947 (@value{GDBP}) info symbol 0x54320
8948 _initialize_vx + 396 in section .text
8952 This is the opposite of the @code{info address} command. You can use
8953 it to find out the name of a variable or a function given its address.
8956 @item whatis @var{expr}
8957 Print the data type of expression @var{expr}. @var{expr} is not
8958 actually evaluated, and any side-effecting operations (such as
8959 assignments or function calls) inside it do not take place.
8960 @xref{Expressions, ,Expressions}.
8963 Print the data type of @code{$}, the last value in the value history.
8966 @item ptype @var{typename}
8967 Print a description of data type @var{typename}. @var{typename} may be
8968 the name of a type, or for C code it may have the form @samp{class
8969 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8970 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8972 @item ptype @var{expr}
8974 Print a description of the type of expression @var{expr}. @code{ptype}
8975 differs from @code{whatis} by printing a detailed description, instead
8976 of just the name of the type.
8978 For example, for this variable declaration:
8981 struct complex @{double real; double imag;@} v;
8985 the two commands give this output:
8989 (@value{GDBP}) whatis v
8990 type = struct complex
8991 (@value{GDBP}) ptype v
8992 type = struct complex @{
9000 As with @code{whatis}, using @code{ptype} without an argument refers to
9001 the type of @code{$}, the last value in the value history.
9004 @item info types @var{regexp}
9006 Print a brief description of all types whose names match @var{regexp}
9007 (or all types in your program, if you supply no argument). Each
9008 complete typename is matched as though it were a complete line; thus,
9009 @samp{i type value} gives information on all types in your program whose
9010 names include the string @code{value}, but @samp{i type ^value$} gives
9011 information only on types whose complete name is @code{value}.
9013 This command differs from @code{ptype} in two ways: first, like
9014 @code{whatis}, it does not print a detailed description; second, it
9015 lists all source files where a type is defined.
9018 @cindex local variables
9019 @item info scope @var{addr}
9020 List all the variables local to a particular scope. This command
9021 accepts a location---a function name, a source line, or an address
9022 preceded by a @samp{*}, and prints all the variables local to the
9023 scope defined by that location. For example:
9026 (@value{GDBP}) @b{info scope command_line_handler}
9027 Scope for command_line_handler:
9028 Symbol rl is an argument at stack/frame offset 8, length 4.
9029 Symbol linebuffer is in static storage at address 0x150a18, length 4.
9030 Symbol linelength is in static storage at address 0x150a1c, length 4.
9031 Symbol p is a local variable in register $esi, length 4.
9032 Symbol p1 is a local variable in register $ebx, length 4.
9033 Symbol nline is a local variable in register $edx, length 4.
9034 Symbol repeat is a local variable at frame offset -8, length 4.
9038 This command is especially useful for determining what data to collect
9039 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
9044 Show information about the current source file---that is, the source file for
9045 the function containing the current point of execution:
9048 the name of the source file, and the directory containing it,
9050 the directory it was compiled in,
9052 its length, in lines,
9054 which programming language it is written in,
9056 whether the executable includes debugging information for that file, and
9057 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
9059 whether the debugging information includes information about
9060 preprocessor macros.
9064 @kindex info sources
9066 Print the names of all source files in your program for which there is
9067 debugging information, organized into two lists: files whose symbols
9068 have already been read, and files whose symbols will be read when needed.
9070 @kindex info functions
9071 @item info functions
9072 Print the names and data types of all defined functions.
9074 @item info functions @var{regexp}
9075 Print the names and data types of all defined functions
9076 whose names contain a match for regular expression @var{regexp}.
9077 Thus, @samp{info fun step} finds all functions whose names
9078 include @code{step}; @samp{info fun ^step} finds those whose names
9079 start with @code{step}. If a function name contains characters
9080 that conflict with the regular expression language (eg.
9081 @samp{operator*()}), they may be quoted with a backslash.
9083 @kindex info variables
9084 @item info variables
9085 Print the names and data types of all variables that are declared
9086 outside of functions (i.e.@: excluding local variables).
9088 @item info variables @var{regexp}
9089 Print the names and data types of all variables (except for local
9090 variables) whose names contain a match for regular expression
9094 This was never implemented.
9095 @kindex info methods
9097 @itemx info methods @var{regexp}
9098 The @code{info methods} command permits the user to examine all defined
9099 methods within C@t{++} program, or (with the @var{regexp} argument) a
9100 specific set of methods found in the various C@t{++} classes. Many
9101 C@t{++} classes provide a large number of methods. Thus, the output
9102 from the @code{ptype} command can be overwhelming and hard to use. The
9103 @code{info-methods} command filters the methods, printing only those
9104 which match the regular-expression @var{regexp}.
9107 @cindex reloading symbols
9108 Some systems allow individual object files that make up your program to
9109 be replaced without stopping and restarting your program. For example,
9110 in VxWorks you can simply recompile a defective object file and keep on
9111 running. If you are running on one of these systems, you can allow
9112 @value{GDBN} to reload the symbols for automatically relinked modules:
9115 @kindex set symbol-reloading
9116 @item set symbol-reloading on
9117 Replace symbol definitions for the corresponding source file when an
9118 object file with a particular name is seen again.
9120 @item set symbol-reloading off
9121 Do not replace symbol definitions when encountering object files of the
9122 same name more than once. This is the default state; if you are not
9123 running on a system that permits automatic relinking of modules, you
9124 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
9125 may discard symbols when linking large programs, that may contain
9126 several modules (from different directories or libraries) with the same
9129 @kindex show symbol-reloading
9130 @item show symbol-reloading
9131 Show the current @code{on} or @code{off} setting.
9134 @kindex set opaque-type-resolution
9135 @item set opaque-type-resolution on
9136 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
9137 declared as a pointer to a @code{struct}, @code{class}, or
9138 @code{union}---for example, @code{struct MyType *}---that is used in one
9139 source file although the full declaration of @code{struct MyType} is in
9140 another source file. The default is on.
9142 A change in the setting of this subcommand will not take effect until
9143 the next time symbols for a file are loaded.
9145 @item set opaque-type-resolution off
9146 Tell @value{GDBN} not to resolve opaque types. In this case, the type
9147 is printed as follows:
9149 @{<no data fields>@}
9152 @kindex show opaque-type-resolution
9153 @item show opaque-type-resolution
9154 Show whether opaque types are resolved or not.
9156 @kindex maint print symbols
9158 @kindex maint print psymbols
9159 @cindex partial symbol dump
9160 @item maint print symbols @var{filename}
9161 @itemx maint print psymbols @var{filename}
9162 @itemx maint print msymbols @var{filename}
9163 Write a dump of debugging symbol data into the file @var{filename}.
9164 These commands are used to debug the @value{GDBN} symbol-reading code. Only
9165 symbols with debugging data are included. If you use @samp{maint print
9166 symbols}, @value{GDBN} includes all the symbols for which it has already
9167 collected full details: that is, @var{filename} reflects symbols for
9168 only those files whose symbols @value{GDBN} has read. You can use the
9169 command @code{info sources} to find out which files these are. If you
9170 use @samp{maint print psymbols} instead, the dump shows information about
9171 symbols that @value{GDBN} only knows partially---that is, symbols defined in
9172 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
9173 @samp{maint print msymbols} dumps just the minimal symbol information
9174 required for each object file from which @value{GDBN} has read some symbols.
9175 @xref{Files, ,Commands to specify files}, for a discussion of how
9176 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
9180 @chapter Altering Execution
9182 Once you think you have found an error in your program, you might want to
9183 find out for certain whether correcting the apparent error would lead to
9184 correct results in the rest of the run. You can find the answer by
9185 experiment, using the @value{GDBN} features for altering execution of the
9188 For example, you can store new values into variables or memory
9189 locations, give your program a signal, restart it at a different
9190 address, or even return prematurely from a function.
9193 * Assignment:: Assignment to variables
9194 * Jumping:: Continuing at a different address
9195 * Signaling:: Giving your program a signal
9196 * Returning:: Returning from a function
9197 * Calling:: Calling your program's functions
9198 * Patching:: Patching your program
9202 @section Assignment to variables
9205 @cindex setting variables
9206 To alter the value of a variable, evaluate an assignment expression.
9207 @xref{Expressions, ,Expressions}. For example,
9214 stores the value 4 into the variable @code{x}, and then prints the
9215 value of the assignment expression (which is 4).
9216 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
9217 information on operators in supported languages.
9219 @kindex set variable
9220 @cindex variables, setting
9221 If you are not interested in seeing the value of the assignment, use the
9222 @code{set} command instead of the @code{print} command. @code{set} is
9223 really the same as @code{print} except that the expression's value is
9224 not printed and is not put in the value history (@pxref{Value History,
9225 ,Value history}). The expression is evaluated only for its effects.
9227 If the beginning of the argument string of the @code{set} command
9228 appears identical to a @code{set} subcommand, use the @code{set
9229 variable} command instead of just @code{set}. This command is identical
9230 to @code{set} except for its lack of subcommands. For example, if your
9231 program has a variable @code{width}, you get an error if you try to set
9232 a new value with just @samp{set width=13}, because @value{GDBN} has the
9233 command @code{set width}:
9236 (@value{GDBP}) whatis width
9238 (@value{GDBP}) p width
9240 (@value{GDBP}) set width=47
9241 Invalid syntax in expression.
9245 The invalid expression, of course, is @samp{=47}. In
9246 order to actually set the program's variable @code{width}, use
9249 (@value{GDBP}) set var width=47
9252 Because the @code{set} command has many subcommands that can conflict
9253 with the names of program variables, it is a good idea to use the
9254 @code{set variable} command instead of just @code{set}. For example, if
9255 your program has a variable @code{g}, you run into problems if you try
9256 to set a new value with just @samp{set g=4}, because @value{GDBN} has
9257 the command @code{set gnutarget}, abbreviated @code{set g}:
9261 (@value{GDBP}) whatis g
9265 (@value{GDBP}) set g=4
9269 The program being debugged has been started already.
9270 Start it from the beginning? (y or n) y
9271 Starting program: /home/smith/cc_progs/a.out
9272 "/home/smith/cc_progs/a.out": can't open to read symbols:
9274 (@value{GDBP}) show g
9275 The current BFD target is "=4".
9280 The program variable @code{g} did not change, and you silently set the
9281 @code{gnutarget} to an invalid value. In order to set the variable
9285 (@value{GDBP}) set var g=4
9288 @value{GDBN} allows more implicit conversions in assignments than C; you can
9289 freely store an integer value into a pointer variable or vice versa,
9290 and you can convert any structure to any other structure that is the
9291 same length or shorter.
9292 @comment FIXME: how do structs align/pad in these conversions?
9293 @comment /doc@cygnus.com 18dec1990
9295 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9296 construct to generate a value of specified type at a specified address
9297 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9298 to memory location @code{0x83040} as an integer (which implies a certain size
9299 and representation in memory), and
9302 set @{int@}0x83040 = 4
9306 stores the value 4 into that memory location.
9309 @section Continuing at a different address
9311 Ordinarily, when you continue your program, you do so at the place where
9312 it stopped, with the @code{continue} command. You can instead continue at
9313 an address of your own choosing, with the following commands:
9317 @item jump @var{linespec}
9318 Resume execution at line @var{linespec}. Execution stops again
9319 immediately if there is a breakpoint there. @xref{List, ,Printing
9320 source lines}, for a description of the different forms of
9321 @var{linespec}. It is common practice to use the @code{tbreak} command
9322 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9325 The @code{jump} command does not change the current stack frame, or
9326 the stack pointer, or the contents of any memory location or any
9327 register other than the program counter. If line @var{linespec} is in
9328 a different function from the one currently executing, the results may
9329 be bizarre if the two functions expect different patterns of arguments or
9330 of local variables. For this reason, the @code{jump} command requests
9331 confirmation if the specified line is not in the function currently
9332 executing. However, even bizarre results are predictable if you are
9333 well acquainted with the machine-language code of your program.
9335 @item jump *@var{address}
9336 Resume execution at the instruction at address @var{address}.
9339 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9340 On many systems, you can get much the same effect as the @code{jump}
9341 command by storing a new value into the register @code{$pc}. The
9342 difference is that this does not start your program running; it only
9343 changes the address of where it @emph{will} run when you continue. For
9351 makes the next @code{continue} command or stepping command execute at
9352 address @code{0x485}, rather than at the address where your program stopped.
9353 @xref{Continuing and Stepping, ,Continuing and stepping}.
9355 The most common occasion to use the @code{jump} command is to back
9356 up---perhaps with more breakpoints set---over a portion of a program
9357 that has already executed, in order to examine its execution in more
9362 @section Giving your program a signal
9366 @item signal @var{signal}
9367 Resume execution where your program stopped, but immediately give it the
9368 signal @var{signal}. @var{signal} can be the name or the number of a
9369 signal. For example, on many systems @code{signal 2} and @code{signal
9370 SIGINT} are both ways of sending an interrupt signal.
9372 Alternatively, if @var{signal} is zero, continue execution without
9373 giving a signal. This is useful when your program stopped on account of
9374 a signal and would ordinary see the signal when resumed with the
9375 @code{continue} command; @samp{signal 0} causes it to resume without a
9378 @code{signal} does not repeat when you press @key{RET} a second time
9379 after executing the command.
9383 Invoking the @code{signal} command is not the same as invoking the
9384 @code{kill} utility from the shell. Sending a signal with @code{kill}
9385 causes @value{GDBN} to decide what to do with the signal depending on
9386 the signal handling tables (@pxref{Signals}). The @code{signal} command
9387 passes the signal directly to your program.
9391 @section Returning from a function
9394 @cindex returning from a function
9397 @itemx return @var{expression}
9398 You can cancel execution of a function call with the @code{return}
9399 command. If you give an
9400 @var{expression} argument, its value is used as the function's return
9404 When you use @code{return}, @value{GDBN} discards the selected stack frame
9405 (and all frames within it). You can think of this as making the
9406 discarded frame return prematurely. If you wish to specify a value to
9407 be returned, give that value as the argument to @code{return}.
9409 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9410 frame}), and any other frames inside of it, leaving its caller as the
9411 innermost remaining frame. That frame becomes selected. The
9412 specified value is stored in the registers used for returning values
9415 The @code{return} command does not resume execution; it leaves the
9416 program stopped in the state that would exist if the function had just
9417 returned. In contrast, the @code{finish} command (@pxref{Continuing
9418 and Stepping, ,Continuing and stepping}) resumes execution until the
9419 selected stack frame returns naturally.
9422 @section Calling program functions
9424 @cindex calling functions
9427 @item call @var{expr}
9428 Evaluate the expression @var{expr} without displaying @code{void}
9432 You can use this variant of the @code{print} command if you want to
9433 execute a function from your program, but without cluttering the output
9434 with @code{void} returned values. If the result is not void, it
9435 is printed and saved in the value history.
9438 @section Patching programs
9440 @cindex patching binaries
9441 @cindex writing into executables
9442 @cindex writing into corefiles
9444 By default, @value{GDBN} opens the file containing your program's
9445 executable code (or the corefile) read-only. This prevents accidental
9446 alterations to machine code; but it also prevents you from intentionally
9447 patching your program's binary.
9449 If you'd like to be able to patch the binary, you can specify that
9450 explicitly with the @code{set write} command. For example, you might
9451 want to turn on internal debugging flags, or even to make emergency
9457 @itemx set write off
9458 If you specify @samp{set write on}, @value{GDBN} opens executable and
9459 core files for both reading and writing; if you specify @samp{set write
9460 off} (the default), @value{GDBN} opens them read-only.
9462 If you have already loaded a file, you must load it again (using the
9463 @code{exec-file} or @code{core-file} command) after changing @code{set
9464 write}, for your new setting to take effect.
9468 Display whether executable files and core files are opened for writing
9473 @chapter @value{GDBN} Files
9475 @value{GDBN} needs to know the file name of the program to be debugged,
9476 both in order to read its symbol table and in order to start your
9477 program. To debug a core dump of a previous run, you must also tell
9478 @value{GDBN} the name of the core dump file.
9481 * Files:: Commands to specify files
9482 * Symbol Errors:: Errors reading symbol files
9486 @section Commands to specify files
9488 @cindex symbol table
9489 @cindex core dump file
9491 You may want to specify executable and core dump file names. The usual
9492 way to do this is at start-up time, using the arguments to
9493 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9494 Out of @value{GDBN}}).
9496 Occasionally it is necessary to change to a different file during a
9497 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9498 a file you want to use. In these situations the @value{GDBN} commands
9499 to specify new files are useful.
9502 @cindex executable file
9504 @item file @var{filename}
9505 Use @var{filename} as the program to be debugged. It is read for its
9506 symbols and for the contents of pure memory. It is also the program
9507 executed when you use the @code{run} command. If you do not specify a
9508 directory and the file is not found in the @value{GDBN} working directory,
9509 @value{GDBN} uses the environment variable @code{PATH} as a list of
9510 directories to search, just as the shell does when looking for a program
9511 to run. You can change the value of this variable, for both @value{GDBN}
9512 and your program, using the @code{path} command.
9514 On systems with memory-mapped files, an auxiliary file named
9515 @file{@var{filename}.syms} may hold symbol table information for
9516 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9517 @file{@var{filename}.syms}, starting up more quickly. See the
9518 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9519 (available on the command line, and with the commands @code{file},
9520 @code{symbol-file}, or @code{add-symbol-file}, described below),
9521 for more information.
9524 @code{file} with no argument makes @value{GDBN} discard any information it
9525 has on both executable file and the symbol table.
9528 @item exec-file @r{[} @var{filename} @r{]}
9529 Specify that the program to be run (but not the symbol table) is found
9530 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9531 if necessary to locate your program. Omitting @var{filename} means to
9532 discard information on the executable file.
9535 @item symbol-file @r{[} @var{filename} @r{]}
9536 Read symbol table information from file @var{filename}. @code{PATH} is
9537 searched when necessary. Use the @code{file} command to get both symbol
9538 table and program to run from the same file.
9540 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9541 program's symbol table.
9543 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9544 of its convenience variables, the value history, and all breakpoints and
9545 auto-display expressions. This is because they may contain pointers to
9546 the internal data recording symbols and data types, which are part of
9547 the old symbol table data being discarded inside @value{GDBN}.
9549 @code{symbol-file} does not repeat if you press @key{RET} again after
9552 When @value{GDBN} is configured for a particular environment, it
9553 understands debugging information in whatever format is the standard
9554 generated for that environment; you may use either a @sc{gnu} compiler, or
9555 other compilers that adhere to the local conventions.
9556 Best results are usually obtained from @sc{gnu} compilers; for example,
9557 using @code{@value{GCC}} you can generate debugging information for
9560 For most kinds of object files, with the exception of old SVR3 systems
9561 using COFF, the @code{symbol-file} command does not normally read the
9562 symbol table in full right away. Instead, it scans the symbol table
9563 quickly to find which source files and which symbols are present. The
9564 details are read later, one source file at a time, as they are needed.
9566 The purpose of this two-stage reading strategy is to make @value{GDBN}
9567 start up faster. For the most part, it is invisible except for
9568 occasional pauses while the symbol table details for a particular source
9569 file are being read. (The @code{set verbose} command can turn these
9570 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9571 warnings and messages}.)
9573 We have not implemented the two-stage strategy for COFF yet. When the
9574 symbol table is stored in COFF format, @code{symbol-file} reads the
9575 symbol table data in full right away. Note that ``stabs-in-COFF''
9576 still does the two-stage strategy, since the debug info is actually
9580 @cindex reading symbols immediately
9581 @cindex symbols, reading immediately
9583 @cindex memory-mapped symbol file
9584 @cindex saving symbol table
9585 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9586 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9587 You can override the @value{GDBN} two-stage strategy for reading symbol
9588 tables by using the @samp{-readnow} option with any of the commands that
9589 load symbol table information, if you want to be sure @value{GDBN} has the
9590 entire symbol table available.
9592 If memory-mapped files are available on your system through the
9593 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9594 cause @value{GDBN} to write the symbols for your program into a reusable
9595 file. Future @value{GDBN} debugging sessions map in symbol information
9596 from this auxiliary symbol file (if the program has not changed), rather
9597 than spending time reading the symbol table from the executable
9598 program. Using the @samp{-mapped} option has the same effect as
9599 starting @value{GDBN} with the @samp{-mapped} command-line option.
9601 You can use both options together, to make sure the auxiliary symbol
9602 file has all the symbol information for your program.
9604 The auxiliary symbol file for a program called @var{myprog} is called
9605 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9606 than the corresponding executable), @value{GDBN} always attempts to use
9607 it when you debug @var{myprog}; no special options or commands are
9610 The @file{.syms} file is specific to the host machine where you run
9611 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9612 symbol table. It cannot be shared across multiple host platforms.
9614 @c FIXME: for now no mention of directories, since this seems to be in
9615 @c flux. 13mar1992 status is that in theory GDB would look either in
9616 @c current dir or in same dir as myprog; but issues like competing
9617 @c GDB's, or clutter in system dirs, mean that in practice right now
9618 @c only current dir is used. FFish says maybe a special GDB hierarchy
9619 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9624 @item core-file @r{[} @var{filename} @r{]}
9625 Specify the whereabouts of a core dump file to be used as the ``contents
9626 of memory''. Traditionally, core files contain only some parts of the
9627 address space of the process that generated them; @value{GDBN} can access the
9628 executable file itself for other parts.
9630 @code{core-file} with no argument specifies that no core file is
9633 Note that the core file is ignored when your program is actually running
9634 under @value{GDBN}. So, if you have been running your program and you
9635 wish to debug a core file instead, you must kill the subprocess in which
9636 the program is running. To do this, use the @code{kill} command
9637 (@pxref{Kill Process, ,Killing the child process}).
9639 @kindex add-symbol-file
9640 @cindex dynamic linking
9641 @item add-symbol-file @var{filename} @var{address}
9642 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9643 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9644 The @code{add-symbol-file} command reads additional symbol table
9645 information from the file @var{filename}. You would use this command
9646 when @var{filename} has been dynamically loaded (by some other means)
9647 into the program that is running. @var{address} should be the memory
9648 address at which the file has been loaded; @value{GDBN} cannot figure
9649 this out for itself. You can additionally specify an arbitrary number
9650 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9651 section name and base address for that section. You can specify any
9652 @var{address} as an expression.
9654 The symbol table of the file @var{filename} is added to the symbol table
9655 originally read with the @code{symbol-file} command. You can use the
9656 @code{add-symbol-file} command any number of times; the new symbol data
9657 thus read keeps adding to the old. To discard all old symbol data
9658 instead, use the @code{symbol-file} command without any arguments.
9660 @cindex relocatable object files, reading symbols from
9661 @cindex object files, relocatable, reading symbols from
9662 @cindex reading symbols from relocatable object files
9663 @cindex symbols, reading from relocatable object files
9664 @cindex @file{.o} files, reading symbols from
9665 Although @var{filename} is typically a shared library file, an
9666 executable file, or some other object file which has been fully
9667 relocated for loading into a process, you can also load symbolic
9668 information from relocatable @file{.o} files, as long as:
9672 the file's symbolic information refers only to linker symbols defined in
9673 that file, not to symbols defined by other object files,
9675 every section the file's symbolic information refers to has actually
9676 been loaded into the inferior, as it appears in the file, and
9678 you can determine the address at which every section was loaded, and
9679 provide these to the @code{add-symbol-file} command.
9683 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9684 relocatable files into an already running program; such systems
9685 typically make the requirements above easy to meet. However, it's
9686 important to recognize that many native systems use complex link
9687 procedures (@code{.linkonce} section factoring and C++ constructor table
9688 assembly, for example) that make the requirements difficult to meet. In
9689 general, one cannot assume that using @code{add-symbol-file} to read a
9690 relocatable object file's symbolic information will have the same effect
9691 as linking the relocatable object file into the program in the normal
9694 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9696 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9697 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9698 table information for @var{filename}.
9700 @kindex add-shared-symbol-file
9701 @item add-shared-symbol-file
9702 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9703 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9704 shared libraries, however if @value{GDBN} does not find yours, you can run
9705 @code{add-shared-symbol-file}. It takes no arguments.
9709 The @code{section} command changes the base address of section SECTION of
9710 the exec file to ADDR. This can be used if the exec file does not contain
9711 section addresses, (such as in the a.out format), or when the addresses
9712 specified in the file itself are wrong. Each section must be changed
9713 separately. The @code{info files} command, described below, lists all
9714 the sections and their addresses.
9720 @code{info files} and @code{info target} are synonymous; both print the
9721 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9722 including the names of the executable and core dump files currently in
9723 use by @value{GDBN}, and the files from which symbols were loaded. The
9724 command @code{help target} lists all possible targets rather than
9727 @kindex maint info sections
9728 @item maint info sections
9729 Another command that can give you extra information about program sections
9730 is @code{maint info sections}. In addition to the section information
9731 displayed by @code{info files}, this command displays the flags and file
9732 offset of each section in the executable and core dump files. In addition,
9733 @code{maint info sections} provides the following command options (which
9734 may be arbitrarily combined):
9738 Display sections for all loaded object files, including shared libraries.
9739 @item @var{sections}
9740 Display info only for named @var{sections}.
9741 @item @var{section-flags}
9742 Display info only for sections for which @var{section-flags} are true.
9743 The section flags that @value{GDBN} currently knows about are:
9746 Section will have space allocated in the process when loaded.
9747 Set for all sections except those containing debug information.
9749 Section will be loaded from the file into the child process memory.
9750 Set for pre-initialized code and data, clear for @code{.bss} sections.
9752 Section needs to be relocated before loading.
9754 Section cannot be modified by the child process.
9756 Section contains executable code only.
9758 Section contains data only (no executable code).
9760 Section will reside in ROM.
9762 Section contains data for constructor/destructor lists.
9764 Section is not empty.
9766 An instruction to the linker to not output the section.
9767 @item COFF_SHARED_LIBRARY
9768 A notification to the linker that the section contains
9769 COFF shared library information.
9771 Section contains common symbols.
9774 @kindex set trust-readonly-sections
9775 @item set trust-readonly-sections on
9776 Tell @value{GDBN} that readonly sections in your object file
9777 really are read-only (i.e.@: that their contents will not change).
9778 In that case, @value{GDBN} can fetch values from these sections
9779 out of the object file, rather than from the target program.
9780 For some targets (notably embedded ones), this can be a significant
9781 enhancement to debugging performance.
9785 @item set trust-readonly-sections off
9786 Tell @value{GDBN} not to trust readonly sections. This means that
9787 the contents of the section might change while the program is running,
9788 and must therefore be fetched from the target when needed.
9791 All file-specifying commands allow both absolute and relative file names
9792 as arguments. @value{GDBN} always converts the file name to an absolute file
9793 name and remembers it that way.
9795 @cindex shared libraries
9796 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9799 @value{GDBN} automatically loads symbol definitions from shared libraries
9800 when you use the @code{run} command, or when you examine a core file.
9801 (Before you issue the @code{run} command, @value{GDBN} does not understand
9802 references to a function in a shared library, however---unless you are
9803 debugging a core file).
9805 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9806 automatically loads the symbols at the time of the @code{shl_load} call.
9808 @c FIXME: some @value{GDBN} release may permit some refs to undef
9809 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9810 @c FIXME...lib; check this from time to time when updating manual
9812 There are times, however, when you may wish to not automatically load
9813 symbol definitions from shared libraries, such as when they are
9814 particularly large or there are many of them.
9816 To control the automatic loading of shared library symbols, use the
9820 @kindex set auto-solib-add
9821 @item set auto-solib-add @var{mode}
9822 If @var{mode} is @code{on}, symbols from all shared object libraries
9823 will be loaded automatically when the inferior begins execution, you
9824 attach to an independently started inferior, or when the dynamic linker
9825 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9826 is @code{off}, symbols must be loaded manually, using the
9827 @code{sharedlibrary} command. The default value is @code{on}.
9829 @kindex show auto-solib-add
9830 @item show auto-solib-add
9831 Display the current autoloading mode.
9834 To explicitly load shared library symbols, use the @code{sharedlibrary}
9838 @kindex info sharedlibrary
9841 @itemx info sharedlibrary
9842 Print the names of the shared libraries which are currently loaded.
9844 @kindex sharedlibrary
9846 @item sharedlibrary @var{regex}
9847 @itemx share @var{regex}
9848 Load shared object library symbols for files matching a
9849 Unix regular expression.
9850 As with files loaded automatically, it only loads shared libraries
9851 required by your program for a core file or after typing @code{run}. If
9852 @var{regex} is omitted all shared libraries required by your program are
9856 On some systems, such as HP-UX systems, @value{GDBN} supports
9857 autoloading shared library symbols until a limiting threshold size is
9858 reached. This provides the benefit of allowing autoloading to remain on
9859 by default, but avoids autoloading excessively large shared libraries,
9860 up to a threshold that is initially set, but which you can modify if you
9863 Beyond that threshold, symbols from shared libraries must be explicitly
9864 loaded. To load these symbols, use the command @code{sharedlibrary
9865 @var{filename}}. The base address of the shared library is determined
9866 automatically by @value{GDBN} and need not be specified.
9868 To display or set the threshold, use the commands:
9871 @kindex set auto-solib-limit
9872 @item set auto-solib-limit @var{threshold}
9873 Set the autoloading size threshold, in an integral number of megabytes.
9874 If @var{threshold} is nonzero and shared library autoloading is enabled,
9875 symbols from all shared object libraries will be loaded until the total
9876 size of the loaded shared library symbols exceeds this threshold.
9877 Otherwise, symbols must be loaded manually, using the
9878 @code{sharedlibrary} command. The default threshold is 100 (i.e.@: 100
9881 @kindex show auto-solib-limit
9882 @item show auto-solib-limit
9883 Display the current autoloading size threshold, in megabytes.
9887 @section Errors reading symbol files
9889 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9890 such as symbol types it does not recognize, or known bugs in compiler
9891 output. By default, @value{GDBN} does not notify you of such problems, since
9892 they are relatively common and primarily of interest to people
9893 debugging compilers. If you are interested in seeing information
9894 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9895 only one message about each such type of problem, no matter how many
9896 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9897 to see how many times the problems occur, with the @code{set
9898 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9901 The messages currently printed, and their meanings, include:
9904 @item inner block not inside outer block in @var{symbol}
9906 The symbol information shows where symbol scopes begin and end
9907 (such as at the start of a function or a block of statements). This
9908 error indicates that an inner scope block is not fully contained
9909 in its outer scope blocks.
9911 @value{GDBN} circumvents the problem by treating the inner block as if it had
9912 the same scope as the outer block. In the error message, @var{symbol}
9913 may be shown as ``@code{(don't know)}'' if the outer block is not a
9916 @item block at @var{address} out of order
9918 The symbol information for symbol scope blocks should occur in
9919 order of increasing addresses. This error indicates that it does not
9922 @value{GDBN} does not circumvent this problem, and has trouble
9923 locating symbols in the source file whose symbols it is reading. (You
9924 can often determine what source file is affected by specifying
9925 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9928 @item bad block start address patched
9930 The symbol information for a symbol scope block has a start address
9931 smaller than the address of the preceding source line. This is known
9932 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9934 @value{GDBN} circumvents the problem by treating the symbol scope block as
9935 starting on the previous source line.
9937 @item bad string table offset in symbol @var{n}
9940 Symbol number @var{n} contains a pointer into the string table which is
9941 larger than the size of the string table.
9943 @value{GDBN} circumvents the problem by considering the symbol to have the
9944 name @code{foo}, which may cause other problems if many symbols end up
9947 @item unknown symbol type @code{0x@var{nn}}
9949 The symbol information contains new data types that @value{GDBN} does
9950 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9951 uncomprehended information, in hexadecimal.
9953 @value{GDBN} circumvents the error by ignoring this symbol information.
9954 This usually allows you to debug your program, though certain symbols
9955 are not accessible. If you encounter such a problem and feel like
9956 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9957 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9958 and examine @code{*bufp} to see the symbol.
9960 @item stub type has NULL name
9962 @value{GDBN} could not find the full definition for a struct or class.
9964 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9965 The symbol information for a C@t{++} member function is missing some
9966 information that recent versions of the compiler should have output for
9969 @item info mismatch between compiler and debugger
9971 @value{GDBN} could not parse a type specification output by the compiler.
9976 @chapter Specifying a Debugging Target
9978 @cindex debugging target
9981 A @dfn{target} is the execution environment occupied by your program.
9983 Often, @value{GDBN} runs in the same host environment as your program;
9984 in that case, the debugging target is specified as a side effect when
9985 you use the @code{file} or @code{core} commands. When you need more
9986 flexibility---for example, running @value{GDBN} on a physically separate
9987 host, or controlling a standalone system over a serial port or a
9988 realtime system over a TCP/IP connection---you can use the @code{target}
9989 command to specify one of the target types configured for @value{GDBN}
9990 (@pxref{Target Commands, ,Commands for managing targets}).
9993 * Active Targets:: Active targets
9994 * Target Commands:: Commands for managing targets
9995 * Byte Order:: Choosing target byte order
9996 * Remote:: Remote debugging
9997 * KOD:: Kernel Object Display
10001 @node Active Targets
10002 @section Active targets
10004 @cindex stacking targets
10005 @cindex active targets
10006 @cindex multiple targets
10008 There are three classes of targets: processes, core files, and
10009 executable files. @value{GDBN} can work concurrently on up to three
10010 active targets, one in each class. This allows you to (for example)
10011 start a process and inspect its activity without abandoning your work on
10014 For example, if you execute @samp{gdb a.out}, then the executable file
10015 @code{a.out} is the only active target. If you designate a core file as
10016 well---presumably from a prior run that crashed and coredumped---then
10017 @value{GDBN} has two active targets and uses them in tandem, looking
10018 first in the corefile target, then in the executable file, to satisfy
10019 requests for memory addresses. (Typically, these two classes of target
10020 are complementary, since core files contain only a program's
10021 read-write memory---variables and so on---plus machine status, while
10022 executable files contain only the program text and initialized data.)
10024 When you type @code{run}, your executable file becomes an active process
10025 target as well. When a process target is active, all @value{GDBN}
10026 commands requesting memory addresses refer to that target; addresses in
10027 an active core file or executable file target are obscured while the
10028 process target is active.
10030 Use the @code{core-file} and @code{exec-file} commands to select a new
10031 core file or executable target (@pxref{Files, ,Commands to specify
10032 files}). To specify as a target a process that is already running, use
10033 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
10036 @node Target Commands
10037 @section Commands for managing targets
10040 @item target @var{type} @var{parameters}
10041 Connects the @value{GDBN} host environment to a target machine or
10042 process. A target is typically a protocol for talking to debugging
10043 facilities. You use the argument @var{type} to specify the type or
10044 protocol of the target machine.
10046 Further @var{parameters} are interpreted by the target protocol, but
10047 typically include things like device names or host names to connect
10048 with, process numbers, and baud rates.
10050 The @code{target} command does not repeat if you press @key{RET} again
10051 after executing the command.
10053 @kindex help target
10055 Displays the names of all targets available. To display targets
10056 currently selected, use either @code{info target} or @code{info files}
10057 (@pxref{Files, ,Commands to specify files}).
10059 @item help target @var{name}
10060 Describe a particular target, including any parameters necessary to
10063 @kindex set gnutarget
10064 @item set gnutarget @var{args}
10065 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
10066 knows whether it is reading an @dfn{executable},
10067 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
10068 with the @code{set gnutarget} command. Unlike most @code{target} commands,
10069 with @code{gnutarget} the @code{target} refers to a program, not a machine.
10072 @emph{Warning:} To specify a file format with @code{set gnutarget},
10073 you must know the actual BFD name.
10077 @xref{Files, , Commands to specify files}.
10079 @kindex show gnutarget
10080 @item show gnutarget
10081 Use the @code{show gnutarget} command to display what file format
10082 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
10083 @value{GDBN} will determine the file format for each file automatically,
10084 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
10087 Here are some common targets (available, or not, depending on the GDB
10091 @kindex target exec
10092 @item target exec @var{program}
10093 An executable file. @samp{target exec @var{program}} is the same as
10094 @samp{exec-file @var{program}}.
10096 @kindex target core
10097 @item target core @var{filename}
10098 A core dump file. @samp{target core @var{filename}} is the same as
10099 @samp{core-file @var{filename}}.
10101 @kindex target remote
10102 @item target remote @var{dev}
10103 Remote serial target in GDB-specific protocol. The argument @var{dev}
10104 specifies what serial device to use for the connection (e.g.
10105 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
10106 supports the @code{load} command. This is only useful if you have
10107 some other way of getting the stub to the target system, and you can put
10108 it somewhere in memory where it won't get clobbered by the download.
10112 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
10120 works; however, you cannot assume that a specific memory map, device
10121 drivers, or even basic I/O is available, although some simulators do
10122 provide these. For info about any processor-specific simulator details,
10123 see the appropriate section in @ref{Embedded Processors, ,Embedded
10128 Some configurations may include these targets as well:
10132 @kindex target nrom
10133 @item target nrom @var{dev}
10134 NetROM ROM emulator. This target only supports downloading.
10138 Different targets are available on different configurations of @value{GDBN};
10139 your configuration may have more or fewer targets.
10141 Many remote targets require you to download the executable's code
10142 once you've successfully established a connection.
10146 @kindex load @var{filename}
10147 @item load @var{filename}
10148 Depending on what remote debugging facilities are configured into
10149 @value{GDBN}, the @code{load} command may be available. Where it exists, it
10150 is meant to make @var{filename} (an executable) available for debugging
10151 on the remote system---by downloading, or dynamic linking, for example.
10152 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
10153 the @code{add-symbol-file} command.
10155 If your @value{GDBN} does not have a @code{load} command, attempting to
10156 execute it gets the error message ``@code{You can't do that when your
10157 target is @dots{}}''
10159 The file is loaded at whatever address is specified in the executable.
10160 For some object file formats, you can specify the load address when you
10161 link the program; for other formats, like a.out, the object file format
10162 specifies a fixed address.
10163 @c FIXME! This would be a good place for an xref to the GNU linker doc.
10165 @code{load} does not repeat if you press @key{RET} again after using it.
10169 @section Choosing target byte order
10171 @cindex choosing target byte order
10172 @cindex target byte order
10174 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
10175 offer the ability to run either big-endian or little-endian byte
10176 orders. Usually the executable or symbol will include a bit to
10177 designate the endian-ness, and you will not need to worry about
10178 which to use. However, you may still find it useful to adjust
10179 @value{GDBN}'s idea of processor endian-ness manually.
10182 @kindex set endian big
10183 @item set endian big
10184 Instruct @value{GDBN} to assume the target is big-endian.
10186 @kindex set endian little
10187 @item set endian little
10188 Instruct @value{GDBN} to assume the target is little-endian.
10190 @kindex set endian auto
10191 @item set endian auto
10192 Instruct @value{GDBN} to use the byte order associated with the
10196 Display @value{GDBN}'s current idea of the target byte order.
10200 Note that these commands merely adjust interpretation of symbolic
10201 data on the host, and that they have absolutely no effect on the
10205 @section Remote debugging
10206 @cindex remote debugging
10208 If you are trying to debug a program running on a machine that cannot run
10209 @value{GDBN} in the usual way, it is often useful to use remote debugging.
10210 For example, you might use remote debugging on an operating system kernel,
10211 or on a small system which does not have a general purpose operating system
10212 powerful enough to run a full-featured debugger.
10214 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
10215 to make this work with particular debugging targets. In addition,
10216 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
10217 but not specific to any particular target system) which you can use if you
10218 write the remote stubs---the code that runs on the remote system to
10219 communicate with @value{GDBN}.
10221 Other remote targets may be available in your
10222 configuration of @value{GDBN}; use @code{help target} to list them.
10225 @section Kernel Object Display
10227 @cindex kernel object display
10228 @cindex kernel object
10231 Some targets support kernel object display. Using this facility,
10232 @value{GDBN} communicates specially with the underlying operating system
10233 and can display information about operating system-level objects such as
10234 mutexes and other synchronization objects. Exactly which objects can be
10235 displayed is determined on a per-OS basis.
10237 Use the @code{set os} command to set the operating system. This tells
10238 @value{GDBN} which kernel object display module to initialize:
10241 (@value{GDBP}) set os cisco
10244 If @code{set os} succeeds, @value{GDBN} will display some information
10245 about the operating system, and will create a new @code{info} command
10246 which can be used to query the target. The @code{info} command is named
10247 after the operating system:
10250 (@value{GDBP}) info cisco
10251 List of Cisco Kernel Objects
10253 any Any and all objects
10256 Further subcommands can be used to query about particular objects known
10259 There is currently no way to determine whether a given operating system
10260 is supported other than to try it.
10263 @node Remote Debugging
10264 @chapter Debugging remote programs
10267 * Server:: Using the gdbserver program
10268 * NetWare:: Using the gdbserve.nlm program
10269 * remote stub:: Implementing a remote stub
10273 @section Using the @code{gdbserver} program
10276 @cindex remote connection without stubs
10277 @code{gdbserver} is a control program for Unix-like systems, which
10278 allows you to connect your program with a remote @value{GDBN} via
10279 @code{target remote}---but without linking in the usual debugging stub.
10281 @code{gdbserver} is not a complete replacement for the debugging stubs,
10282 because it requires essentially the same operating-system facilities
10283 that @value{GDBN} itself does. In fact, a system that can run
10284 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10285 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10286 because it is a much smaller program than @value{GDBN} itself. It is
10287 also easier to port than all of @value{GDBN}, so you may be able to get
10288 started more quickly on a new system by using @code{gdbserver}.
10289 Finally, if you develop code for real-time systems, you may find that
10290 the tradeoffs involved in real-time operation make it more convenient to
10291 do as much development work as possible on another system, for example
10292 by cross-compiling. You can use @code{gdbserver} to make a similar
10293 choice for debugging.
10295 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10296 or a TCP connection, using the standard @value{GDBN} remote serial
10300 @item On the target machine,
10301 you need to have a copy of the program you want to debug.
10302 @code{gdbserver} does not need your program's symbol table, so you can
10303 strip the program if necessary to save space. @value{GDBN} on the host
10304 system does all the symbol handling.
10306 To use the server, you must tell it how to communicate with @value{GDBN};
10307 the name of your program; and the arguments for your program. The usual
10311 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10314 @var{comm} is either a device name (to use a serial line) or a TCP
10315 hostname and portnumber. For example, to debug Emacs with the argument
10316 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10320 target> gdbserver /dev/com1 emacs foo.txt
10323 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10326 To use a TCP connection instead of a serial line:
10329 target> gdbserver host:2345 emacs foo.txt
10332 The only difference from the previous example is the first argument,
10333 specifying that you are communicating with the host @value{GDBN} via
10334 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10335 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10336 (Currently, the @samp{host} part is ignored.) You can choose any number
10337 you want for the port number as long as it does not conflict with any
10338 TCP ports already in use on the target system (for example, @code{23} is
10339 reserved for @code{telnet}).@footnote{If you choose a port number that
10340 conflicts with another service, @code{gdbserver} prints an error message
10341 and exits.} You must use the same port number with the host @value{GDBN}
10342 @code{target remote} command.
10344 On some targets, @code{gdbserver} can also attach to running programs.
10345 This is accomplished via the @code{--attach} argument. The syntax is:
10348 target> gdbserver @var{comm} --attach @var{pid}
10351 @var{pid} is the process ID of a currently running process. It isn't necessary
10352 to point @code{gdbserver} at a binary for the running process.
10354 @item On the @value{GDBN} host machine,
10355 you need an unstripped copy of your program, since @value{GDBN} needs
10356 symbols and debugging information. Start up @value{GDBN} as usual,
10357 using the name of the local copy of your program as the first argument.
10358 (You may also need the @w{@samp{--baud}} option if the serial line is
10359 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10360 remote} to establish communications with @code{gdbserver}. Its argument
10361 is either a device name (usually a serial device, like
10362 @file{/dev/ttyb}), or a TCP port descriptor in the form
10363 @code{@var{host}:@var{PORT}}. For example:
10366 (@value{GDBP}) target remote /dev/ttyb
10370 communicates with the server via serial line @file{/dev/ttyb}, and
10373 (@value{GDBP}) target remote the-target:2345
10377 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10378 For TCP connections, you must start up @code{gdbserver} prior to using
10379 the @code{target remote} command. Otherwise you may get an error whose
10380 text depends on the host system, but which usually looks something like
10381 @samp{Connection refused}.
10385 @section Using the @code{gdbserve.nlm} program
10387 @kindex gdbserve.nlm
10388 @code{gdbserve.nlm} is a control program for NetWare systems, which
10389 allows you to connect your program with a remote @value{GDBN} via
10390 @code{target remote}.
10392 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10393 using the standard @value{GDBN} remote serial protocol.
10396 @item On the target machine,
10397 you need to have a copy of the program you want to debug.
10398 @code{gdbserve.nlm} does not need your program's symbol table, so you
10399 can strip the program if necessary to save space. @value{GDBN} on the
10400 host system does all the symbol handling.
10402 To use the server, you must tell it how to communicate with
10403 @value{GDBN}; the name of your program; and the arguments for your
10404 program. The syntax is:
10407 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10408 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10411 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10412 the baud rate used by the connection. @var{port} and @var{node} default
10413 to 0, @var{baud} defaults to 9600@dmn{bps}.
10415 For example, to debug Emacs with the argument @samp{foo.txt}and
10416 communicate with @value{GDBN} over serial port number 2 or board 1
10417 using a 19200@dmn{bps} connection:
10420 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10423 @item On the @value{GDBN} host machine,
10424 you need an unstripped copy of your program, since @value{GDBN} needs
10425 symbols and debugging information. Start up @value{GDBN} as usual,
10426 using the name of the local copy of your program as the first argument.
10427 (You may also need the @w{@samp{--baud}} option if the serial line is
10428 running at anything other than 9600@dmn{bps}. After that, use @code{target
10429 remote} to establish communications with @code{gdbserve.nlm}. Its
10430 argument is a device name (usually a serial device, like
10431 @file{/dev/ttyb}). For example:
10434 (@value{GDBP}) target remote /dev/ttyb
10438 communications with the server via serial line @file{/dev/ttyb}.
10442 @section Implementing a remote stub
10444 @cindex debugging stub, example
10445 @cindex remote stub, example
10446 @cindex stub example, remote debugging
10447 The stub files provided with @value{GDBN} implement the target side of the
10448 communication protocol, and the @value{GDBN} side is implemented in the
10449 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10450 these subroutines to communicate, and ignore the details. (If you're
10451 implementing your own stub file, you can still ignore the details: start
10452 with one of the existing stub files. @file{sparc-stub.c} is the best
10453 organized, and therefore the easiest to read.)
10455 @cindex remote serial debugging, overview
10456 To debug a program running on another machine (the debugging
10457 @dfn{target} machine), you must first arrange for all the usual
10458 prerequisites for the program to run by itself. For example, for a C
10463 A startup routine to set up the C runtime environment; these usually
10464 have a name like @file{crt0}. The startup routine may be supplied by
10465 your hardware supplier, or you may have to write your own.
10468 A C subroutine library to support your program's
10469 subroutine calls, notably managing input and output.
10472 A way of getting your program to the other machine---for example, a
10473 download program. These are often supplied by the hardware
10474 manufacturer, but you may have to write your own from hardware
10478 The next step is to arrange for your program to use a serial port to
10479 communicate with the machine where @value{GDBN} is running (the @dfn{host}
10480 machine). In general terms, the scheme looks like this:
10484 @value{GDBN} already understands how to use this protocol; when everything
10485 else is set up, you can simply use the @samp{target remote} command
10486 (@pxref{Targets,,Specifying a Debugging Target}).
10488 @item On the target,
10489 you must link with your program a few special-purpose subroutines that
10490 implement the @value{GDBN} remote serial protocol. The file containing these
10491 subroutines is called a @dfn{debugging stub}.
10493 On certain remote targets, you can use an auxiliary program
10494 @code{gdbserver} instead of linking a stub into your program.
10495 @xref{Server,,Using the @code{gdbserver} program}, for details.
10498 The debugging stub is specific to the architecture of the remote
10499 machine; for example, use @file{sparc-stub.c} to debug programs on
10502 @cindex remote serial stub list
10503 These working remote stubs are distributed with @value{GDBN}:
10508 @cindex @file{i386-stub.c}
10511 For Intel 386 and compatible architectures.
10514 @cindex @file{m68k-stub.c}
10515 @cindex Motorola 680x0
10517 For Motorola 680x0 architectures.
10520 @cindex @file{sh-stub.c}
10523 For Hitachi SH architectures.
10526 @cindex @file{sparc-stub.c}
10528 For @sc{sparc} architectures.
10530 @item sparcl-stub.c
10531 @cindex @file{sparcl-stub.c}
10534 For Fujitsu @sc{sparclite} architectures.
10538 The @file{README} file in the @value{GDBN} distribution may list other
10539 recently added stubs.
10542 * Stub Contents:: What the stub can do for you
10543 * Bootstrapping:: What you must do for the stub
10544 * Debug Session:: Putting it all together
10547 @node Stub Contents
10548 @subsection What the stub can do for you
10550 @cindex remote serial stub
10551 The debugging stub for your architecture supplies these three
10555 @item set_debug_traps
10556 @kindex set_debug_traps
10557 @cindex remote serial stub, initialization
10558 This routine arranges for @code{handle_exception} to run when your
10559 program stops. You must call this subroutine explicitly near the
10560 beginning of your program.
10562 @item handle_exception
10563 @kindex handle_exception
10564 @cindex remote serial stub, main routine
10565 This is the central workhorse, but your program never calls it
10566 explicitly---the setup code arranges for @code{handle_exception} to
10567 run when a trap is triggered.
10569 @code{handle_exception} takes control when your program stops during
10570 execution (for example, on a breakpoint), and mediates communications
10571 with @value{GDBN} on the host machine. This is where the communications
10572 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10573 representative on the target machine. It begins by sending summary
10574 information on the state of your program, then continues to execute,
10575 retrieving and transmitting any information @value{GDBN} needs, until you
10576 execute a @value{GDBN} command that makes your program resume; at that point,
10577 @code{handle_exception} returns control to your own code on the target
10581 @cindex @code{breakpoint} subroutine, remote
10582 Use this auxiliary subroutine to make your program contain a
10583 breakpoint. Depending on the particular situation, this may be the only
10584 way for @value{GDBN} to get control. For instance, if your target
10585 machine has some sort of interrupt button, you won't need to call this;
10586 pressing the interrupt button transfers control to
10587 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10588 simply receiving characters on the serial port may also trigger a trap;
10589 again, in that situation, you don't need to call @code{breakpoint} from
10590 your own program---simply running @samp{target remote} from the host
10591 @value{GDBN} session gets control.
10593 Call @code{breakpoint} if none of these is true, or if you simply want
10594 to make certain your program stops at a predetermined point for the
10595 start of your debugging session.
10598 @node Bootstrapping
10599 @subsection What you must do for the stub
10601 @cindex remote stub, support routines
10602 The debugging stubs that come with @value{GDBN} are set up for a particular
10603 chip architecture, but they have no information about the rest of your
10604 debugging target machine.
10606 First of all you need to tell the stub how to communicate with the
10610 @item int getDebugChar()
10611 @kindex getDebugChar
10612 Write this subroutine to read a single character from the serial port.
10613 It may be identical to @code{getchar} for your target system; a
10614 different name is used to allow you to distinguish the two if you wish.
10616 @item void putDebugChar(int)
10617 @kindex putDebugChar
10618 Write this subroutine to write a single character to the serial port.
10619 It may be identical to @code{putchar} for your target system; a
10620 different name is used to allow you to distinguish the two if you wish.
10623 @cindex control C, and remote debugging
10624 @cindex interrupting remote targets
10625 If you want @value{GDBN} to be able to stop your program while it is
10626 running, you need to use an interrupt-driven serial driver, and arrange
10627 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10628 character). That is the character which @value{GDBN} uses to tell the
10629 remote system to stop.
10631 Getting the debugging target to return the proper status to @value{GDBN}
10632 probably requires changes to the standard stub; one quick and dirty way
10633 is to just execute a breakpoint instruction (the ``dirty'' part is that
10634 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10636 Other routines you need to supply are:
10639 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10640 @kindex exceptionHandler
10641 Write this function to install @var{exception_address} in the exception
10642 handling tables. You need to do this because the stub does not have any
10643 way of knowing what the exception handling tables on your target system
10644 are like (for example, the processor's table might be in @sc{rom},
10645 containing entries which point to a table in @sc{ram}).
10646 @var{exception_number} is the exception number which should be changed;
10647 its meaning is architecture-dependent (for example, different numbers
10648 might represent divide by zero, misaligned access, etc). When this
10649 exception occurs, control should be transferred directly to
10650 @var{exception_address}, and the processor state (stack, registers,
10651 and so on) should be just as it is when a processor exception occurs. So if
10652 you want to use a jump instruction to reach @var{exception_address}, it
10653 should be a simple jump, not a jump to subroutine.
10655 For the 386, @var{exception_address} should be installed as an interrupt
10656 gate so that interrupts are masked while the handler runs. The gate
10657 should be at privilege level 0 (the most privileged level). The
10658 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10659 help from @code{exceptionHandler}.
10661 @item void flush_i_cache()
10662 @kindex flush_i_cache
10663 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10664 instruction cache, if any, on your target machine. If there is no
10665 instruction cache, this subroutine may be a no-op.
10667 On target machines that have instruction caches, @value{GDBN} requires this
10668 function to make certain that the state of your program is stable.
10672 You must also make sure this library routine is available:
10675 @item void *memset(void *, int, int)
10677 This is the standard library function @code{memset} that sets an area of
10678 memory to a known value. If you have one of the free versions of
10679 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10680 either obtain it from your hardware manufacturer, or write your own.
10683 If you do not use the GNU C compiler, you may need other standard
10684 library subroutines as well; this varies from one stub to another,
10685 but in general the stubs are likely to use any of the common library
10686 subroutines which @code{@value{GCC}} generates as inline code.
10689 @node Debug Session
10690 @subsection Putting it all together
10692 @cindex remote serial debugging summary
10693 In summary, when your program is ready to debug, you must follow these
10698 Make sure you have defined the supporting low-level routines
10699 (@pxref{Bootstrapping,,What you must do for the stub}):
10701 @code{getDebugChar}, @code{putDebugChar},
10702 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10706 Insert these lines near the top of your program:
10714 For the 680x0 stub only, you need to provide a variable called
10715 @code{exceptionHook}. Normally you just use:
10718 void (*exceptionHook)() = 0;
10722 but if before calling @code{set_debug_traps}, you set it to point to a
10723 function in your program, that function is called when
10724 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10725 error). The function indicated by @code{exceptionHook} is called with
10726 one parameter: an @code{int} which is the exception number.
10729 Compile and link together: your program, the @value{GDBN} debugging stub for
10730 your target architecture, and the supporting subroutines.
10733 Make sure you have a serial connection between your target machine and
10734 the @value{GDBN} host, and identify the serial port on the host.
10737 @c The "remote" target now provides a `load' command, so we should
10738 @c document that. FIXME.
10739 Download your program to your target machine (or get it there by
10740 whatever means the manufacturer provides), and start it.
10743 To start remote debugging, run @value{GDBN} on the host machine, and specify
10744 as an executable file the program that is running in the remote machine.
10745 This tells @value{GDBN} how to find your program's symbols and the contents
10749 @cindex serial line, @code{target remote}
10750 Establish communication using the @code{target remote} command.
10751 Its argument specifies how to communicate with the target
10752 machine---either via a devicename attached to a direct serial line, or a
10753 TCP or UDP port (usually to a terminal server which in turn has a serial line
10754 to the target). For example, to use a serial line connected to the
10755 device named @file{/dev/ttyb}:
10758 target remote /dev/ttyb
10761 @cindex TCP port, @code{target remote}
10762 To use a TCP connection, use an argument of the form
10763 @code{@var{host}:@var{port}} or @code{tcp:@var{host}:@var{port}}.
10764 For example, to connect to port 2828 on a
10765 terminal server named @code{manyfarms}:
10768 target remote manyfarms:2828
10771 If your remote target is actually running on the same machine as
10772 your debugger session (e.g.@: a simulator of your target running on
10773 the same host), you can omit the hostname. For example, to connect
10774 to port 1234 on your local machine:
10777 target remote :1234
10781 Note that the colon is still required here.
10783 @cindex UDP port, @code{target remote}
10784 To use a UDP connection, use an argument of the form
10785 @code{udp:@var{host}:@var{port}}. For example, to connect to UDP port 2828
10786 on a terminal server named @code{manyfarms}:
10789 target remote udp:manyfarms:2828
10792 When using a UDP connection for remote debugging, you should keep in mind
10793 that the `U' stands for ``Unreliable''. UDP can silently drop packets on
10794 busy or unreliable networks, which will cause havoc with your debugging
10799 Now you can use all the usual commands to examine and change data and to
10800 step and continue the remote program.
10802 To resume the remote program and stop debugging it, use the @code{detach}
10805 @cindex interrupting remote programs
10806 @cindex remote programs, interrupting
10807 Whenever @value{GDBN} is waiting for the remote program, if you type the
10808 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10809 program. This may or may not succeed, depending in part on the hardware
10810 and the serial drivers the remote system uses. If you type the
10811 interrupt character once again, @value{GDBN} displays this prompt:
10814 Interrupted while waiting for the program.
10815 Give up (and stop debugging it)? (y or n)
10818 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10819 (If you decide you want to try again later, you can use @samp{target
10820 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10821 goes back to waiting.
10824 @node Configurations
10825 @chapter Configuration-Specific Information
10827 While nearly all @value{GDBN} commands are available for all native and
10828 cross versions of the debugger, there are some exceptions. This chapter
10829 describes things that are only available in certain configurations.
10831 There are three major categories of configurations: native
10832 configurations, where the host and target are the same, embedded
10833 operating system configurations, which are usually the same for several
10834 different processor architectures, and bare embedded processors, which
10835 are quite different from each other.
10840 * Embedded Processors::
10847 This section describes details specific to particular native
10852 * SVR4 Process Information:: SVR4 process information
10853 * DJGPP Native:: Features specific to the DJGPP port
10854 * Cygwin Native:: Features specific to the Cygwin port
10860 On HP-UX systems, if you refer to a function or variable name that
10861 begins with a dollar sign, @value{GDBN} searches for a user or system
10862 name first, before it searches for a convenience variable.
10864 @node SVR4 Process Information
10865 @subsection SVR4 process information
10868 @cindex process image
10870 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10871 used to examine the image of a running process using file-system
10872 subroutines. If @value{GDBN} is configured for an operating system with
10873 this facility, the command @code{info proc} is available to report on
10874 several kinds of information about the process running your program.
10875 @code{info proc} works only on SVR4 systems that include the
10876 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10877 and Unixware, but not HP-UX or Linux, for example.
10882 Summarize available information about the process.
10884 @kindex info proc mappings
10885 @item info proc mappings
10886 Report on the address ranges accessible in the program, with information
10887 on whether your program may read, write, or execute each range.
10889 @comment These sub-options of 'info proc' were not included when
10890 @comment procfs.c was re-written. Keep their descriptions around
10891 @comment against the day when someone finds the time to put them back in.
10892 @kindex info proc times
10893 @item info proc times
10894 Starting time, user CPU time, and system CPU time for your program and
10897 @kindex info proc id
10899 Report on the process IDs related to your program: its own process ID,
10900 the ID of its parent, the process group ID, and the session ID.
10902 @kindex info proc status
10903 @item info proc status
10904 General information on the state of the process. If the process is
10905 stopped, this report includes the reason for stopping, and any signal
10908 @item info proc all
10909 Show all the above information about the process.
10914 @subsection Features for Debugging @sc{djgpp} Programs
10915 @cindex @sc{djgpp} debugging
10916 @cindex native @sc{djgpp} debugging
10917 @cindex MS-DOS-specific commands
10919 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10920 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10921 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10922 top of real-mode DOS systems and their emulations.
10924 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10925 defines a few commands specific to the @sc{djgpp} port. This
10926 subsection describes those commands.
10931 This is a prefix of @sc{djgpp}-specific commands which print
10932 information about the target system and important OS structures.
10935 @cindex MS-DOS system info
10936 @cindex free memory information (MS-DOS)
10937 @item info dos sysinfo
10938 This command displays assorted information about the underlying
10939 platform: the CPU type and features, the OS version and flavor, the
10940 DPMI version, and the available conventional and DPMI memory.
10945 @cindex segment descriptor tables
10946 @cindex descriptor tables display
10948 @itemx info dos ldt
10949 @itemx info dos idt
10950 These 3 commands display entries from, respectively, Global, Local,
10951 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10952 tables are data structures which store a descriptor for each segment
10953 that is currently in use. The segment's selector is an index into a
10954 descriptor table; the table entry for that index holds the
10955 descriptor's base address and limit, and its attributes and access
10958 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10959 segment (used for both data and the stack), and a DOS segment (which
10960 allows access to DOS/BIOS data structures and absolute addresses in
10961 conventional memory). However, the DPMI host will usually define
10962 additional segments in order to support the DPMI environment.
10964 @cindex garbled pointers
10965 These commands allow to display entries from the descriptor tables.
10966 Without an argument, all entries from the specified table are
10967 displayed. An argument, which should be an integer expression, means
10968 display a single entry whose index is given by the argument. For
10969 example, here's a convenient way to display information about the
10970 debugged program's data segment:
10973 @exdent @code{(@value{GDBP}) info dos ldt $ds}
10974 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
10978 This comes in handy when you want to see whether a pointer is outside
10979 the data segment's limit (i.e.@: @dfn{garbled}).
10981 @cindex page tables display (MS-DOS)
10983 @itemx info dos pte
10984 These two commands display entries from, respectively, the Page
10985 Directory and the Page Tables. Page Directories and Page Tables are
10986 data structures which control how virtual memory addresses are mapped
10987 into physical addresses. A Page Table includes an entry for every
10988 page of memory that is mapped into the program's address space; there
10989 may be several Page Tables, each one holding up to 4096 entries. A
10990 Page Directory has up to 4096 entries, one each for every Page Table
10991 that is currently in use.
10993 Without an argument, @kbd{info dos pde} displays the entire Page
10994 Directory, and @kbd{info dos pte} displays all the entries in all of
10995 the Page Tables. An argument, an integer expression, given to the
10996 @kbd{info dos pde} command means display only that entry from the Page
10997 Directory table. An argument given to the @kbd{info dos pte} command
10998 means display entries from a single Page Table, the one pointed to by
10999 the specified entry in the Page Directory.
11001 @cindex direct memory access (DMA) on MS-DOS
11002 These commands are useful when your program uses @dfn{DMA} (Direct
11003 Memory Access), which needs physical addresses to program the DMA
11006 These commands are supported only with some DPMI servers.
11008 @cindex physical address from linear address
11009 @item info dos address-pte @var{addr}
11010 This command displays the Page Table entry for a specified linear
11011 address. The argument linear address @var{addr} should already have the
11012 appropriate segment's base address added to it, because this command
11013 accepts addresses which may belong to @emph{any} segment. For
11014 example, here's how to display the Page Table entry for the page where
11015 the variable @code{i} is stored:
11018 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
11019 @exdent @code{Page Table entry for address 0x11a00d30:}
11020 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
11024 This says that @code{i} is stored at offset @code{0xd30} from the page
11025 whose physical base address is @code{0x02698000}, and prints all the
11026 attributes of that page.
11028 Note that you must cast the addresses of variables to a @code{char *},
11029 since otherwise the value of @code{__djgpp_base_address}, the base
11030 address of all variables and functions in a @sc{djgpp} program, will
11031 be added using the rules of C pointer arithmetics: if @code{i} is
11032 declared an @code{int}, @value{GDBN} will add 4 times the value of
11033 @code{__djgpp_base_address} to the address of @code{i}.
11035 Here's another example, it displays the Page Table entry for the
11039 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
11040 @exdent @code{Page Table entry for address 0x29110:}
11041 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
11045 (The @code{+ 3} offset is because the transfer buffer's address is the
11046 3rd member of the @code{_go32_info_block} structure.) The output of
11047 this command clearly shows that addresses in conventional memory are
11048 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11050 This command is supported only with some DPMI servers.
11053 @node Cygwin Native
11054 @subsection Features for Debugging MS Windows PE executables
11055 @cindex MS Windows debugging
11056 @cindex native Cygwin debugging
11057 @cindex Cygwin-specific commands
11059 @value{GDBN} supports native debugging of MS Windows programs, and
11060 defines a few commands specific to the Cygwin port. This
11061 subsection describes those commands.
11066 This is a prefix of MS Windows specific commands which print
11067 information about the target system and important OS structures.
11069 @item info w32 selector
11070 This command displays information returned by
11071 the Win32 API @code{GetThreadSelectorEntry} function.
11072 It takes an optional argument that is evaluated to
11073 a long value to give the information about this given selector.
11074 Without argument, this command displays information
11075 about the the six segment registers.
11079 This is a Cygwin specific alias of info shared.
11081 @kindex dll-symbols
11083 This command loads symbols from a dll similarly to
11084 add-sym command but without the need to specify a base address.
11086 @kindex set new-console
11087 @item set new-console @var{mode}
11088 If @var{mode} is @code{on} the debuggee will
11089 be started in a new console on next start.
11090 If @var{mode} is @code{off}i, the debuggee will
11091 be started in the same console as the debugger.
11093 @kindex show new-console
11094 @item show new-console
11095 Displays whether a new console is used
11096 when the debuggee is started.
11098 @kindex set new-group
11099 @item set new-group @var{mode}
11100 This boolean value controls whether the debuggee should
11101 start a new group or stay in the same group as the debugger.
11102 This affects the way the Windows OS handles
11105 @kindex show new-group
11106 @item show new-group
11107 Displays current value of new-group boolean.
11109 @kindex set debugevents
11110 @item set debugevents
11111 This boolean value adds debug output concerning events seen by the debugger.
11113 @kindex set debugexec
11114 @item set debugexec
11115 This boolean value adds debug output concerning execute events
11116 seen by the debugger.
11118 @kindex set debugexceptions
11119 @item set debugexceptions
11120 This boolean value adds debug ouptut concerning exception events
11121 seen by the debugger.
11123 @kindex set debugmemory
11124 @item set debugmemory
11125 This boolean value adds debug ouptut concerning memory events
11126 seen by the debugger.
11130 This boolean values specifies whether the debuggee is called
11131 via a shell or directly (default value is on).
11135 Displays if the debuggee will be started with a shell.
11140 @section Embedded Operating Systems
11142 This section describes configurations involving the debugging of
11143 embedded operating systems that are available for several different
11147 * VxWorks:: Using @value{GDBN} with VxWorks
11150 @value{GDBN} includes the ability to debug programs running on
11151 various real-time operating systems.
11154 @subsection Using @value{GDBN} with VxWorks
11160 @kindex target vxworks
11161 @item target vxworks @var{machinename}
11162 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11163 is the target system's machine name or IP address.
11167 On VxWorks, @code{load} links @var{filename} dynamically on the
11168 current target system as well as adding its symbols in @value{GDBN}.
11170 @value{GDBN} enables developers to spawn and debug tasks running on networked
11171 VxWorks targets from a Unix host. Already-running tasks spawned from
11172 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11173 both the Unix host and on the VxWorks target. The program
11174 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11175 installed with the name @code{vxgdb}, to distinguish it from a
11176 @value{GDBN} for debugging programs on the host itself.)
11179 @item VxWorks-timeout @var{args}
11180 @kindex vxworks-timeout
11181 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11182 This option is set by the user, and @var{args} represents the number of
11183 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11184 your VxWorks target is a slow software simulator or is on the far side
11185 of a thin network line.
11188 The following information on connecting to VxWorks was current when
11189 this manual was produced; newer releases of VxWorks may use revised
11192 @kindex INCLUDE_RDB
11193 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11194 to include the remote debugging interface routines in the VxWorks
11195 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11196 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11197 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11198 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11199 information on configuring and remaking VxWorks, see the manufacturer's
11201 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11203 Once you have included @file{rdb.a} in your VxWorks system image and set
11204 your Unix execution search path to find @value{GDBN}, you are ready to
11205 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11206 @code{vxgdb}, depending on your installation).
11208 @value{GDBN} comes up showing the prompt:
11215 * VxWorks Connection:: Connecting to VxWorks
11216 * VxWorks Download:: VxWorks download
11217 * VxWorks Attach:: Running tasks
11220 @node VxWorks Connection
11221 @subsubsection Connecting to VxWorks
11223 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11224 network. To connect to a target whose host name is ``@code{tt}'', type:
11227 (vxgdb) target vxworks tt
11231 @value{GDBN} displays messages like these:
11234 Attaching remote machine across net...
11239 @value{GDBN} then attempts to read the symbol tables of any object modules
11240 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11241 these files by searching the directories listed in the command search
11242 path (@pxref{Environment, ,Your program's environment}); if it fails
11243 to find an object file, it displays a message such as:
11246 prog.o: No such file or directory.
11249 When this happens, add the appropriate directory to the search path with
11250 the @value{GDBN} command @code{path}, and execute the @code{target}
11253 @node VxWorks Download
11254 @subsubsection VxWorks download
11256 @cindex download to VxWorks
11257 If you have connected to the VxWorks target and you want to debug an
11258 object that has not yet been loaded, you can use the @value{GDBN}
11259 @code{load} command to download a file from Unix to VxWorks
11260 incrementally. The object file given as an argument to the @code{load}
11261 command is actually opened twice: first by the VxWorks target in order
11262 to download the code, then by @value{GDBN} in order to read the symbol
11263 table. This can lead to problems if the current working directories on
11264 the two systems differ. If both systems have NFS mounted the same
11265 filesystems, you can avoid these problems by using absolute paths.
11266 Otherwise, it is simplest to set the working directory on both systems
11267 to the directory in which the object file resides, and then to reference
11268 the file by its name, without any path. For instance, a program
11269 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11270 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11271 program, type this on VxWorks:
11274 -> cd "@var{vxpath}/vw/demo/rdb"
11278 Then, in @value{GDBN}, type:
11281 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11282 (vxgdb) load prog.o
11285 @value{GDBN} displays a response similar to this:
11288 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11291 You can also use the @code{load} command to reload an object module
11292 after editing and recompiling the corresponding source file. Note that
11293 this makes @value{GDBN} delete all currently-defined breakpoints,
11294 auto-displays, and convenience variables, and to clear the value
11295 history. (This is necessary in order to preserve the integrity of
11296 debugger's data structures that reference the target system's symbol
11299 @node VxWorks Attach
11300 @subsubsection Running tasks
11302 @cindex running VxWorks tasks
11303 You can also attach to an existing task using the @code{attach} command as
11307 (vxgdb) attach @var{task}
11311 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11312 or suspended when you attach to it. Running tasks are suspended at
11313 the time of attachment.
11315 @node Embedded Processors
11316 @section Embedded Processors
11318 This section goes into details specific to particular embedded
11324 * H8/300:: Hitachi H8/300
11325 * H8/500:: Hitachi H8/500
11326 * i960:: Intel i960
11327 * M32R/D:: Mitsubishi M32R/D
11328 * M68K:: Motorola M68K
11329 @c OBSOLETE * M88K:: Motorola M88K
11330 * MIPS Embedded:: MIPS Embedded
11331 * PA:: HP PA Embedded
11334 * Sparclet:: Tsqware Sparclet
11335 * Sparclite:: Fujitsu Sparclite
11336 * ST2000:: Tandem ST2000
11337 * Z8000:: Zilog Z8000
11346 @item target rdi @var{dev}
11347 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11348 use this target to communicate with both boards running the Angel
11349 monitor, or with the EmbeddedICE JTAG debug device.
11352 @item target rdp @var{dev}
11358 @subsection Hitachi H8/300
11362 @kindex target hms@r{, with H8/300}
11363 @item target hms @var{dev}
11364 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11365 Use special commands @code{device} and @code{speed} to control the serial
11366 line and the communications speed used.
11368 @kindex target e7000@r{, with H8/300}
11369 @item target e7000 @var{dev}
11370 E7000 emulator for Hitachi H8 and SH.
11372 @kindex target sh3@r{, with H8/300}
11373 @kindex target sh3e@r{, with H8/300}
11374 @item target sh3 @var{dev}
11375 @itemx target sh3e @var{dev}
11376 Hitachi SH-3 and SH-3E target systems.
11380 @cindex download to H8/300 or H8/500
11381 @cindex H8/300 or H8/500 download
11382 @cindex download to Hitachi SH
11383 @cindex Hitachi SH download
11384 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11385 board, the @code{load} command downloads your program to the Hitachi
11386 board and also opens it as the current executable target for
11387 @value{GDBN} on your host (like the @code{file} command).
11389 @value{GDBN} needs to know these things to talk to your
11390 Hitachi SH, H8/300, or H8/500:
11394 that you want to use @samp{target hms}, the remote debugging interface
11395 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11396 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11397 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11398 H8/300, or H8/500.)
11401 what serial device connects your host to your Hitachi board (the first
11402 serial device available on your host is the default).
11405 what speed to use over the serial device.
11409 * Hitachi Boards:: Connecting to Hitachi boards.
11410 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11411 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11414 @node Hitachi Boards
11415 @subsubsection Connecting to Hitachi boards
11417 @c only for Unix hosts
11419 @cindex serial device, Hitachi micros
11420 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11421 need to explicitly set the serial device. The default @var{port} is the
11422 first available port on your host. This is only necessary on Unix
11423 hosts, where it is typically something like @file{/dev/ttya}.
11426 @cindex serial line speed, Hitachi micros
11427 @code{@value{GDBN}} has another special command to set the communications
11428 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11429 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11430 the DOS @code{mode} command (for instance,
11431 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11433 The @samp{device} and @samp{speed} commands are available only when you
11434 use a Unix host to debug your Hitachi microprocessor programs. If you
11436 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11437 called @code{asynctsr} to communicate with the development board
11438 through a PC serial port. You must also use the DOS @code{mode} command
11439 to set up the serial port on the DOS side.
11441 The following sample session illustrates the steps needed to start a
11442 program under @value{GDBN} control on an H8/300. The example uses a
11443 sample H8/300 program called @file{t.x}. The procedure is the same for
11444 the Hitachi SH and the H8/500.
11446 First hook up your development board. In this example, we use a
11447 board attached to serial port @code{COM2}; if you use a different serial
11448 port, substitute its name in the argument of the @code{mode} command.
11449 When you call @code{asynctsr}, the auxiliary comms program used by the
11450 debugger, you give it just the numeric part of the serial port's name;
11451 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11455 C:\H8300\TEST> asynctsr 2
11456 C:\H8300\TEST> mode com2:9600,n,8,1,p
11458 Resident portion of MODE loaded
11460 COM2: 9600, n, 8, 1, p
11465 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11466 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11467 disable it, or even boot without it, to use @code{asynctsr} to control
11468 your development board.
11471 @kindex target hms@r{, and serial protocol}
11472 Now that serial communications are set up, and the development board is
11473 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11474 the name of your program as the argument. @code{@value{GDBN}} prompts
11475 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11476 commands to begin your debugging session: @samp{target hms} to specify
11477 cross-debugging to the Hitachi board, and the @code{load} command to
11478 download your program to the board. @code{load} displays the names of
11479 the program's sections, and a @samp{*} for each 2K of data downloaded.
11480 (If you want to refresh @value{GDBN} data on symbols or on the
11481 executable file without downloading, use the @value{GDBN} commands
11482 @code{file} or @code{symbol-file}. These commands, and @code{load}
11483 itself, are described in @ref{Files,,Commands to specify files}.)
11486 (eg-C:\H8300\TEST) @value{GDBP} t.x
11487 @value{GDBN} is free software and you are welcome to distribute copies
11488 of it under certain conditions; type "show copying" to see
11490 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11492 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11493 (@value{GDBP}) target hms
11494 Connected to remote H8/300 HMS system.
11495 (@value{GDBP}) load t.x
11496 .text : 0x8000 .. 0xabde ***********
11497 .data : 0xabde .. 0xad30 *
11498 .stack : 0xf000 .. 0xf014 *
11501 At this point, you're ready to run or debug your program. From here on,
11502 you can use all the usual @value{GDBN} commands. The @code{break} command
11503 sets breakpoints; the @code{run} command starts your program;
11504 @code{print} or @code{x} display data; the @code{continue} command
11505 resumes execution after stopping at a breakpoint. You can use the
11506 @code{help} command at any time to find out more about @value{GDBN} commands.
11508 Remember, however, that @emph{operating system} facilities aren't
11509 available on your development board; for example, if your program hangs,
11510 you can't send an interrupt---but you can press the @sc{reset} switch!
11512 Use the @sc{reset} button on the development board
11515 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11516 no way to pass an interrupt signal to the development board); and
11519 to return to the @value{GDBN} command prompt after your program finishes
11520 normally. The communications protocol provides no other way for @value{GDBN}
11521 to detect program completion.
11524 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11525 development board as a ``normal exit'' of your program.
11528 @subsubsection Using the E7000 in-circuit emulator
11530 @kindex target e7000@r{, with Hitachi ICE}
11531 You can use the E7000 in-circuit emulator to develop code for either the
11532 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11533 e7000} command to connect @value{GDBN} to your E7000:
11536 @item target e7000 @var{port} @var{speed}
11537 Use this form if your E7000 is connected to a serial port. The
11538 @var{port} argument identifies what serial port to use (for example,
11539 @samp{com2}). The third argument is the line speed in bits per second
11540 (for example, @samp{9600}).
11542 @item target e7000 @var{hostname}
11543 If your E7000 is installed as a host on a TCP/IP network, you can just
11544 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11547 @node Hitachi Special
11548 @subsubsection Special @value{GDBN} commands for Hitachi micros
11550 Some @value{GDBN} commands are available only for the H8/300:
11554 @kindex set machine
11555 @kindex show machine
11556 @item set machine h8300
11557 @itemx set machine h8300h
11558 Condition @value{GDBN} for one of the two variants of the H8/300
11559 architecture with @samp{set machine}. You can use @samp{show machine}
11560 to check which variant is currently in effect.
11569 @kindex set memory @var{mod}
11570 @cindex memory models, H8/500
11571 @item set memory @var{mod}
11573 Specify which H8/500 memory model (@var{mod}) you are using with
11574 @samp{set memory}; check which memory model is in effect with @samp{show
11575 memory}. The accepted values for @var{mod} are @code{small},
11576 @code{big}, @code{medium}, and @code{compact}.
11581 @subsection Intel i960
11585 @kindex target mon960
11586 @item target mon960 @var{dev}
11587 MON960 monitor for Intel i960.
11589 @kindex target nindy
11590 @item target nindy @var{devicename}
11591 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11592 the name of the serial device to use for the connection, e.g.
11599 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11600 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11601 tell @value{GDBN} how to connect to the 960 in several ways:
11605 Through command line options specifying serial port, version of the
11606 Nindy protocol, and communications speed;
11609 By responding to a prompt on startup;
11612 By using the @code{target} command at any point during your @value{GDBN}
11613 session. @xref{Target Commands, ,Commands for managing targets}.
11617 @cindex download to Nindy-960
11618 With the Nindy interface to an Intel 960 board, @code{load}
11619 downloads @var{filename} to the 960 as well as adding its symbols in
11623 * Nindy Startup:: Startup with Nindy
11624 * Nindy Options:: Options for Nindy
11625 * Nindy Reset:: Nindy reset command
11628 @node Nindy Startup
11629 @subsubsection Startup with Nindy
11631 If you simply start @code{@value{GDBP}} without using any command-line
11632 options, you are prompted for what serial port to use, @emph{before} you
11633 reach the ordinary @value{GDBN} prompt:
11636 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11640 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11641 identifies the serial port you want to use. You can, if you choose,
11642 simply start up with no Nindy connection by responding to the prompt
11643 with an empty line. If you do this and later wish to attach to Nindy,
11644 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11646 @node Nindy Options
11647 @subsubsection Options for Nindy
11649 These are the startup options for beginning your @value{GDBN} session with a
11650 Nindy-960 board attached:
11653 @item -r @var{port}
11654 Specify the serial port name of a serial interface to be used to connect
11655 to the target system. This option is only available when @value{GDBN} is
11656 configured for the Intel 960 target architecture. You may specify
11657 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11658 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11659 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11662 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11663 the ``old'' Nindy monitor protocol to connect to the target system.
11664 This option is only available when @value{GDBN} is configured for the Intel 960
11665 target architecture.
11668 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11669 connect to a target system that expects the newer protocol, the connection
11670 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11671 attempts to reconnect at several different line speeds. You can abort
11672 this process with an interrupt.
11676 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11677 system, in an attempt to reset it, before connecting to a Nindy target.
11680 @emph{Warning:} Many target systems do not have the hardware that this
11681 requires; it only works with a few boards.
11685 The standard @samp{-b} option controls the line speed used on the serial
11690 @subsubsection Nindy reset command
11695 For a Nindy target, this command sends a ``break'' to the remote target
11696 system; this is only useful if the target has been equipped with a
11697 circuit to perform a hard reset (or some other interesting action) when
11698 a break is detected.
11703 @subsection Mitsubishi M32R/D
11707 @kindex target m32r
11708 @item target m32r @var{dev}
11709 Mitsubishi M32R/D ROM monitor.
11716 The Motorola m68k configuration includes ColdFire support, and
11717 target command for the following ROM monitors.
11721 @kindex target abug
11722 @item target abug @var{dev}
11723 ABug ROM monitor for M68K.
11725 @kindex target cpu32bug
11726 @item target cpu32bug @var{dev}
11727 CPU32BUG monitor, running on a CPU32 (M68K) board.
11729 @kindex target dbug
11730 @item target dbug @var{dev}
11731 dBUG ROM monitor for Motorola ColdFire.
11734 @item target est @var{dev}
11735 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11737 @kindex target rom68k
11738 @item target rom68k @var{dev}
11739 ROM 68K monitor, running on an M68K IDP board.
11743 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11744 instead have only a single special target command:
11748 @kindex target es1800
11749 @item target es1800 @var{dev}
11750 ES-1800 emulator for M68K.
11758 @kindex target rombug
11759 @item target rombug @var{dev}
11760 ROMBUG ROM monitor for OS/9000.
11764 @c OBSOLETE @node M88K
11765 @c OBSOLETE @subsection M88K
11767 @c OBSOLETE @table @code
11769 @c OBSOLETE @kindex target bug
11770 @c OBSOLETE @item target bug @var{dev}
11771 @c OBSOLETE BUG monitor, running on a MVME187 (m88k) board.
11773 @c OBSOLETE @end table
11775 @node MIPS Embedded
11776 @subsection MIPS Embedded
11778 @cindex MIPS boards
11779 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11780 MIPS board attached to a serial line. This is available when
11781 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11784 Use these @value{GDBN} commands to specify the connection to your target board:
11787 @item target mips @var{port}
11788 @kindex target mips @var{port}
11789 To run a program on the board, start up @code{@value{GDBP}} with the
11790 name of your program as the argument. To connect to the board, use the
11791 command @samp{target mips @var{port}}, where @var{port} is the name of
11792 the serial port connected to the board. If the program has not already
11793 been downloaded to the board, you may use the @code{load} command to
11794 download it. You can then use all the usual @value{GDBN} commands.
11796 For example, this sequence connects to the target board through a serial
11797 port, and loads and runs a program called @var{prog} through the
11801 host$ @value{GDBP} @var{prog}
11802 @value{GDBN} is free software and @dots{}
11803 (@value{GDBP}) target mips /dev/ttyb
11804 (@value{GDBP}) load @var{prog}
11808 @item target mips @var{hostname}:@var{portnumber}
11809 On some @value{GDBN} host configurations, you can specify a TCP
11810 connection (for instance, to a serial line managed by a terminal
11811 concentrator) instead of a serial port, using the syntax
11812 @samp{@var{hostname}:@var{portnumber}}.
11814 @item target pmon @var{port}
11815 @kindex target pmon @var{port}
11818 @item target ddb @var{port}
11819 @kindex target ddb @var{port}
11820 NEC's DDB variant of PMON for Vr4300.
11822 @item target lsi @var{port}
11823 @kindex target lsi @var{port}
11824 LSI variant of PMON.
11826 @kindex target r3900
11827 @item target r3900 @var{dev}
11828 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11830 @kindex target array
11831 @item target array @var{dev}
11832 Array Tech LSI33K RAID controller board.
11838 @value{GDBN} also supports these special commands for MIPS targets:
11841 @item set processor @var{args}
11842 @itemx show processor
11843 @kindex set processor @var{args}
11844 @kindex show processor
11845 Use the @code{set processor} command to set the type of MIPS
11846 processor when you want to access processor-type-specific registers.
11847 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11848 to use the CPU registers appropriate for the 3041 chip.
11849 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11850 is using. Use the @code{info reg} command to see what registers
11851 @value{GDBN} is using.
11853 @item set mipsfpu double
11854 @itemx set mipsfpu single
11855 @itemx set mipsfpu none
11856 @itemx show mipsfpu
11857 @kindex set mipsfpu
11858 @kindex show mipsfpu
11859 @cindex MIPS remote floating point
11860 @cindex floating point, MIPS remote
11861 If your target board does not support the MIPS floating point
11862 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11863 need this, you may wish to put the command in your @value{GDBN} init
11864 file). This tells @value{GDBN} how to find the return value of
11865 functions which return floating point values. It also allows
11866 @value{GDBN} to avoid saving the floating point registers when calling
11867 functions on the board. If you are using a floating point coprocessor
11868 with only single precision floating point support, as on the @sc{r4650}
11869 processor, use the command @samp{set mipsfpu single}. The default
11870 double precision floating point coprocessor may be selected using
11871 @samp{set mipsfpu double}.
11873 In previous versions the only choices were double precision or no
11874 floating point, so @samp{set mipsfpu on} will select double precision
11875 and @samp{set mipsfpu off} will select no floating point.
11877 As usual, you can inquire about the @code{mipsfpu} variable with
11878 @samp{show mipsfpu}.
11880 @item set remotedebug @var{n}
11881 @itemx show remotedebug
11882 @kindex set remotedebug@r{, MIPS protocol}
11883 @kindex show remotedebug@r{, MIPS protocol}
11884 @cindex @code{remotedebug}, MIPS protocol
11885 @cindex MIPS @code{remotedebug} protocol
11886 @c FIXME! For this to be useful, you must know something about the MIPS
11887 @c FIXME...protocol. Where is it described?
11888 You can see some debugging information about communications with the board
11889 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11890 @samp{set remotedebug 1}, every packet is displayed. If you set it
11891 to @code{2}, every character is displayed. You can check the current value
11892 at any time with the command @samp{show remotedebug}.
11894 @item set timeout @var{seconds}
11895 @itemx set retransmit-timeout @var{seconds}
11896 @itemx show timeout
11897 @itemx show retransmit-timeout
11898 @cindex @code{timeout}, MIPS protocol
11899 @cindex @code{retransmit-timeout}, MIPS protocol
11900 @kindex set timeout
11901 @kindex show timeout
11902 @kindex set retransmit-timeout
11903 @kindex show retransmit-timeout
11904 You can control the timeout used while waiting for a packet, in the MIPS
11905 remote protocol, with the @code{set timeout @var{seconds}} command. The
11906 default is 5 seconds. Similarly, you can control the timeout used while
11907 waiting for an acknowledgement of a packet with the @code{set
11908 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11909 You can inspect both values with @code{show timeout} and @code{show
11910 retransmit-timeout}. (These commands are @emph{only} available when
11911 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11913 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11914 is waiting for your program to stop. In that case, @value{GDBN} waits
11915 forever because it has no way of knowing how long the program is going
11916 to run before stopping.
11920 @subsection PowerPC
11924 @kindex target dink32
11925 @item target dink32 @var{dev}
11926 DINK32 ROM monitor.
11928 @kindex target ppcbug
11929 @item target ppcbug @var{dev}
11930 @kindex target ppcbug1
11931 @item target ppcbug1 @var{dev}
11932 PPCBUG ROM monitor for PowerPC.
11935 @item target sds @var{dev}
11936 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11941 @subsection HP PA Embedded
11945 @kindex target op50n
11946 @item target op50n @var{dev}
11947 OP50N monitor, running on an OKI HPPA board.
11949 @kindex target w89k
11950 @item target w89k @var{dev}
11951 W89K monitor, running on a Winbond HPPA board.
11956 @subsection Hitachi SH
11960 @kindex target hms@r{, with Hitachi SH}
11961 @item target hms @var{dev}
11962 A Hitachi SH board attached via serial line to your host. Use special
11963 commands @code{device} and @code{speed} to control the serial line and
11964 the communications speed used.
11966 @kindex target e7000@r{, with Hitachi SH}
11967 @item target e7000 @var{dev}
11968 E7000 emulator for Hitachi SH.
11970 @kindex target sh3@r{, with SH}
11971 @kindex target sh3e@r{, with SH}
11972 @item target sh3 @var{dev}
11973 @item target sh3e @var{dev}
11974 Hitachi SH-3 and SH-3E target systems.
11979 @subsection Tsqware Sparclet
11983 @value{GDBN} enables developers to debug tasks running on
11984 Sparclet targets from a Unix host.
11985 @value{GDBN} uses code that runs on
11986 both the Unix host and on the Sparclet target. The program
11987 @code{@value{GDBP}} is installed and executed on the Unix host.
11990 @item remotetimeout @var{args}
11991 @kindex remotetimeout
11992 @value{GDBN} supports the option @code{remotetimeout}.
11993 This option is set by the user, and @var{args} represents the number of
11994 seconds @value{GDBN} waits for responses.
11997 @cindex compiling, on Sparclet
11998 When compiling for debugging, include the options @samp{-g} to get debug
11999 information and @samp{-Ttext} to relocate the program to where you wish to
12000 load it on the target. You may also want to add the options @samp{-n} or
12001 @samp{-N} in order to reduce the size of the sections. Example:
12004 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12007 You can use @code{objdump} to verify that the addresses are what you intended:
12010 sparclet-aout-objdump --headers --syms prog
12013 @cindex running, on Sparclet
12015 your Unix execution search path to find @value{GDBN}, you are ready to
12016 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12017 (or @code{sparclet-aout-gdb}, depending on your installation).
12019 @value{GDBN} comes up showing the prompt:
12026 * Sparclet File:: Setting the file to debug
12027 * Sparclet Connection:: Connecting to Sparclet
12028 * Sparclet Download:: Sparclet download
12029 * Sparclet Execution:: Running and debugging
12032 @node Sparclet File
12033 @subsubsection Setting file to debug
12035 The @value{GDBN} command @code{file} lets you choose with program to debug.
12038 (gdbslet) file prog
12042 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12043 @value{GDBN} locates
12044 the file by searching the directories listed in the command search
12046 If the file was compiled with debug information (option "-g"), source
12047 files will be searched as well.
12048 @value{GDBN} locates
12049 the source files by searching the directories listed in the directory search
12050 path (@pxref{Environment, ,Your program's environment}).
12052 to find a file, it displays a message such as:
12055 prog: No such file or directory.
12058 When this happens, add the appropriate directories to the search paths with
12059 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12060 @code{target} command again.
12062 @node Sparclet Connection
12063 @subsubsection Connecting to Sparclet
12065 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12066 To connect to a target on serial port ``@code{ttya}'', type:
12069 (gdbslet) target sparclet /dev/ttya
12070 Remote target sparclet connected to /dev/ttya
12071 main () at ../prog.c:3
12075 @value{GDBN} displays messages like these:
12081 @node Sparclet Download
12082 @subsubsection Sparclet download
12084 @cindex download to Sparclet
12085 Once connected to the Sparclet target,
12086 you can use the @value{GDBN}
12087 @code{load} command to download the file from the host to the target.
12088 The file name and load offset should be given as arguments to the @code{load}
12090 Since the file format is aout, the program must be loaded to the starting
12091 address. You can use @code{objdump} to find out what this value is. The load
12092 offset is an offset which is added to the VMA (virtual memory address)
12093 of each of the file's sections.
12094 For instance, if the program
12095 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12096 and bss at 0x12010170, in @value{GDBN}, type:
12099 (gdbslet) load prog 0x12010000
12100 Loading section .text, size 0xdb0 vma 0x12010000
12103 If the code is loaded at a different address then what the program was linked
12104 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12105 to tell @value{GDBN} where to map the symbol table.
12107 @node Sparclet Execution
12108 @subsubsection Running and debugging
12110 @cindex running and debugging Sparclet programs
12111 You can now begin debugging the task using @value{GDBN}'s execution control
12112 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12113 manual for the list of commands.
12117 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12119 Starting program: prog
12120 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12121 3 char *symarg = 0;
12123 4 char *execarg = "hello!";
12128 @subsection Fujitsu Sparclite
12132 @kindex target sparclite
12133 @item target sparclite @var{dev}
12134 Fujitsu sparclite boards, used only for the purpose of loading.
12135 You must use an additional command to debug the program.
12136 For example: target remote @var{dev} using @value{GDBN} standard
12142 @subsection Tandem ST2000
12144 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12147 To connect your ST2000 to the host system, see the manufacturer's
12148 manual. Once the ST2000 is physically attached, you can run:
12151 target st2000 @var{dev} @var{speed}
12155 to establish it as your debugging environment. @var{dev} is normally
12156 the name of a serial device, such as @file{/dev/ttya}, connected to the
12157 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12158 connection (for example, to a serial line attached via a terminal
12159 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12161 The @code{load} and @code{attach} commands are @emph{not} defined for
12162 this target; you must load your program into the ST2000 as you normally
12163 would for standalone operation. @value{GDBN} reads debugging information
12164 (such as symbols) from a separate, debugging version of the program
12165 available on your host computer.
12166 @c FIXME!! This is terribly vague; what little content is here is
12167 @c basically hearsay.
12169 @cindex ST2000 auxiliary commands
12170 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12174 @item st2000 @var{command}
12175 @kindex st2000 @var{cmd}
12176 @cindex STDBUG commands (ST2000)
12177 @cindex commands to STDBUG (ST2000)
12178 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12179 manual for available commands.
12182 @cindex connect (to STDBUG)
12183 Connect the controlling terminal to the STDBUG command monitor. When
12184 you are done interacting with STDBUG, typing either of two character
12185 sequences gets you back to the @value{GDBN} command prompt:
12186 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12187 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12191 @subsection Zilog Z8000
12194 @cindex simulator, Z8000
12195 @cindex Zilog Z8000 simulator
12197 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12200 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12201 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12202 segmented variant). The simulator recognizes which architecture is
12203 appropriate by inspecting the object code.
12206 @item target sim @var{args}
12208 @kindex target sim@r{, with Z8000}
12209 Debug programs on a simulated CPU. If the simulator supports setup
12210 options, specify them via @var{args}.
12214 After specifying this target, you can debug programs for the simulated
12215 CPU in the same style as programs for your host computer; use the
12216 @code{file} command to load a new program image, the @code{run} command
12217 to run your program, and so on.
12219 As well as making available all the usual machine registers
12220 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12221 additional items of information as specially named registers:
12226 Counts clock-ticks in the simulator.
12229 Counts instructions run in the simulator.
12232 Execution time in 60ths of a second.
12236 You can refer to these values in @value{GDBN} expressions with the usual
12237 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12238 conditional breakpoint that suspends only after at least 5000
12239 simulated clock ticks.
12241 @node Architectures
12242 @section Architectures
12244 This section describes characteristics of architectures that affect
12245 all uses of @value{GDBN} with the architecture, both native and cross.
12258 @kindex set rstack_high_address
12259 @cindex AMD 29K register stack
12260 @cindex register stack, AMD29K
12261 @item set rstack_high_address @var{address}
12262 On AMD 29000 family processors, registers are saved in a separate
12263 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12264 extent of this stack. Normally, @value{GDBN} just assumes that the
12265 stack is ``large enough''. This may result in @value{GDBN} referencing
12266 memory locations that do not exist. If necessary, you can get around
12267 this problem by specifying the ending address of the register stack with
12268 the @code{set rstack_high_address} command. The argument should be an
12269 address, which you probably want to precede with @samp{0x} to specify in
12272 @kindex show rstack_high_address
12273 @item show rstack_high_address
12274 Display the current limit of the register stack, on AMD 29000 family
12282 See the following section.
12287 @cindex stack on Alpha
12288 @cindex stack on MIPS
12289 @cindex Alpha stack
12291 Alpha- and MIPS-based computers use an unusual stack frame, which
12292 sometimes requires @value{GDBN} to search backward in the object code to
12293 find the beginning of a function.
12295 @cindex response time, MIPS debugging
12296 To improve response time (especially for embedded applications, where
12297 @value{GDBN} may be restricted to a slow serial line for this search)
12298 you may want to limit the size of this search, using one of these
12302 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12303 @item set heuristic-fence-post @var{limit}
12304 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12305 search for the beginning of a function. A value of @var{0} (the
12306 default) means there is no limit. However, except for @var{0}, the
12307 larger the limit the more bytes @code{heuristic-fence-post} must search
12308 and therefore the longer it takes to run.
12310 @item show heuristic-fence-post
12311 Display the current limit.
12315 These commands are available @emph{only} when @value{GDBN} is configured
12316 for debugging programs on Alpha or MIPS processors.
12319 @node Controlling GDB
12320 @chapter Controlling @value{GDBN}
12322 You can alter the way @value{GDBN} interacts with you by using the
12323 @code{set} command. For commands controlling how @value{GDBN} displays
12324 data, see @ref{Print Settings, ,Print settings}. Other settings are
12329 * Editing:: Command editing
12330 * History:: Command history
12331 * Screen Size:: Screen size
12332 * Numbers:: Numbers
12333 * Messages/Warnings:: Optional warnings and messages
12334 * Debugging Output:: Optional messages about internal happenings
12342 @value{GDBN} indicates its readiness to read a command by printing a string
12343 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12344 can change the prompt string with the @code{set prompt} command. For
12345 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12346 the prompt in one of the @value{GDBN} sessions so that you can always tell
12347 which one you are talking to.
12349 @emph{Note:} @code{set prompt} does not add a space for you after the
12350 prompt you set. This allows you to set a prompt which ends in a space
12351 or a prompt that does not.
12355 @item set prompt @var{newprompt}
12356 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12358 @kindex show prompt
12360 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12364 @section Command editing
12366 @cindex command line editing
12368 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12369 @sc{gnu} library provides consistent behavior for programs which provide a
12370 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12371 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12372 substitution, and a storage and recall of command history across
12373 debugging sessions.
12375 You may control the behavior of command line editing in @value{GDBN} with the
12376 command @code{set}.
12379 @kindex set editing
12382 @itemx set editing on
12383 Enable command line editing (enabled by default).
12385 @item set editing off
12386 Disable command line editing.
12388 @kindex show editing
12390 Show whether command line editing is enabled.
12394 @section Command history
12396 @value{GDBN} can keep track of the commands you type during your
12397 debugging sessions, so that you can be certain of precisely what
12398 happened. Use these commands to manage the @value{GDBN} command
12402 @cindex history substitution
12403 @cindex history file
12404 @kindex set history filename
12405 @kindex GDBHISTFILE
12406 @item set history filename @var{fname}
12407 Set the name of the @value{GDBN} command history file to @var{fname}.
12408 This is the file where @value{GDBN} reads an initial command history
12409 list, and where it writes the command history from this session when it
12410 exits. You can access this list through history expansion or through
12411 the history command editing characters listed below. This file defaults
12412 to the value of the environment variable @code{GDBHISTFILE}, or to
12413 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12416 @cindex history save
12417 @kindex set history save
12418 @item set history save
12419 @itemx set history save on
12420 Record command history in a file, whose name may be specified with the
12421 @code{set history filename} command. By default, this option is disabled.
12423 @item set history save off
12424 Stop recording command history in a file.
12426 @cindex history size
12427 @kindex set history size
12428 @item set history size @var{size}
12429 Set the number of commands which @value{GDBN} keeps in its history list.
12430 This defaults to the value of the environment variable
12431 @code{HISTSIZE}, or to 256 if this variable is not set.
12434 @cindex history expansion
12435 History expansion assigns special meaning to the character @kbd{!}.
12436 @ifset have-readline-appendices
12437 @xref{Event Designators}.
12440 Since @kbd{!} is also the logical not operator in C, history expansion
12441 is off by default. If you decide to enable history expansion with the
12442 @code{set history expansion on} command, you may sometimes need to
12443 follow @kbd{!} (when it is used as logical not, in an expression) with
12444 a space or a tab to prevent it from being expanded. The readline
12445 history facilities do not attempt substitution on the strings
12446 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12448 The commands to control history expansion are:
12451 @kindex set history expansion
12452 @item set history expansion on
12453 @itemx set history expansion
12454 Enable history expansion. History expansion is off by default.
12456 @item set history expansion off
12457 Disable history expansion.
12459 The readline code comes with more complete documentation of
12460 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12461 or @code{vi} may wish to read it.
12462 @ifset have-readline-appendices
12463 @xref{Command Line Editing}.
12467 @kindex show history
12469 @itemx show history filename
12470 @itemx show history save
12471 @itemx show history size
12472 @itemx show history expansion
12473 These commands display the state of the @value{GDBN} history parameters.
12474 @code{show history} by itself displays all four states.
12480 @item show commands
12481 Display the last ten commands in the command history.
12483 @item show commands @var{n}
12484 Print ten commands centered on command number @var{n}.
12486 @item show commands +
12487 Print ten commands just after the commands last printed.
12491 @section Screen size
12492 @cindex size of screen
12493 @cindex pauses in output
12495 Certain commands to @value{GDBN} may produce large amounts of
12496 information output to the screen. To help you read all of it,
12497 @value{GDBN} pauses and asks you for input at the end of each page of
12498 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12499 to discard the remaining output. Also, the screen width setting
12500 determines when to wrap lines of output. Depending on what is being
12501 printed, @value{GDBN} tries to break the line at a readable place,
12502 rather than simply letting it overflow onto the following line.
12504 Normally @value{GDBN} knows the size of the screen from the terminal
12505 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12506 together with the value of the @code{TERM} environment variable and the
12507 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12508 you can override it with the @code{set height} and @code{set
12515 @kindex show height
12516 @item set height @var{lpp}
12518 @itemx set width @var{cpl}
12520 These @code{set} commands specify a screen height of @var{lpp} lines and
12521 a screen width of @var{cpl} characters. The associated @code{show}
12522 commands display the current settings.
12524 If you specify a height of zero lines, @value{GDBN} does not pause during
12525 output no matter how long the output is. This is useful if output is to a
12526 file or to an editor buffer.
12528 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12529 from wrapping its output.
12534 @cindex number representation
12535 @cindex entering numbers
12537 You can always enter numbers in octal, decimal, or hexadecimal in
12538 @value{GDBN} by the usual conventions: octal numbers begin with
12539 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12540 begin with @samp{0x}. Numbers that begin with none of these are, by
12541 default, entered in base 10; likewise, the default display for
12542 numbers---when no particular format is specified---is base 10. You can
12543 change the default base for both input and output with the @code{set
12547 @kindex set input-radix
12548 @item set input-radix @var{base}
12549 Set the default base for numeric input. Supported choices
12550 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12551 specified either unambiguously or using the current default radix; for
12561 sets the base to decimal. On the other hand, @samp{set radix 10}
12562 leaves the radix unchanged no matter what it was.
12564 @kindex set output-radix
12565 @item set output-radix @var{base}
12566 Set the default base for numeric display. Supported choices
12567 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12568 specified either unambiguously or using the current default radix.
12570 @kindex show input-radix
12571 @item show input-radix
12572 Display the current default base for numeric input.
12574 @kindex show output-radix
12575 @item show output-radix
12576 Display the current default base for numeric display.
12579 @node Messages/Warnings
12580 @section Optional warnings and messages
12582 By default, @value{GDBN} is silent about its inner workings. If you are
12583 running on a slow machine, you may want to use the @code{set verbose}
12584 command. This makes @value{GDBN} tell you when it does a lengthy
12585 internal operation, so you will not think it has crashed.
12587 Currently, the messages controlled by @code{set verbose} are those
12588 which announce that the symbol table for a source file is being read;
12589 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12592 @kindex set verbose
12593 @item set verbose on
12594 Enables @value{GDBN} output of certain informational messages.
12596 @item set verbose off
12597 Disables @value{GDBN} output of certain informational messages.
12599 @kindex show verbose
12601 Displays whether @code{set verbose} is on or off.
12604 By default, if @value{GDBN} encounters bugs in the symbol table of an
12605 object file, it is silent; but if you are debugging a compiler, you may
12606 find this information useful (@pxref{Symbol Errors, ,Errors reading
12611 @kindex set complaints
12612 @item set complaints @var{limit}
12613 Permits @value{GDBN} to output @var{limit} complaints about each type of
12614 unusual symbols before becoming silent about the problem. Set
12615 @var{limit} to zero to suppress all complaints; set it to a large number
12616 to prevent complaints from being suppressed.
12618 @kindex show complaints
12619 @item show complaints
12620 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12624 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12625 lot of stupid questions to confirm certain commands. For example, if
12626 you try to run a program which is already running:
12630 The program being debugged has been started already.
12631 Start it from the beginning? (y or n)
12634 If you are willing to unflinchingly face the consequences of your own
12635 commands, you can disable this ``feature'':
12639 @kindex set confirm
12641 @cindex confirmation
12642 @cindex stupid questions
12643 @item set confirm off
12644 Disables confirmation requests.
12646 @item set confirm on
12647 Enables confirmation requests (the default).
12649 @kindex show confirm
12651 Displays state of confirmation requests.
12655 @node Debugging Output
12656 @section Optional messages about internal happenings
12658 @kindex set debug arch
12659 @item set debug arch
12660 Turns on or off display of gdbarch debugging info. The default is off
12661 @kindex show debug arch
12662 @item show debug arch
12663 Displays the current state of displaying gdbarch debugging info.
12664 @kindex set debug event
12665 @item set debug event
12666 Turns on or off display of @value{GDBN} event debugging info. The
12668 @kindex show debug event
12669 @item show debug event
12670 Displays the current state of displaying @value{GDBN} event debugging
12672 @kindex set debug expression
12673 @item set debug expression
12674 Turns on or off display of @value{GDBN} expression debugging info. The
12676 @kindex show debug expression
12677 @item show debug expression
12678 Displays the current state of displaying @value{GDBN} expression
12680 @kindex set debug overload
12681 @item set debug overload
12682 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12683 info. This includes info such as ranking of functions, etc. The default
12685 @kindex show debug overload
12686 @item show debug overload
12687 Displays the current state of displaying @value{GDBN} C@t{++} overload
12689 @kindex set debug remote
12690 @cindex packets, reporting on stdout
12691 @cindex serial connections, debugging
12692 @item set debug remote
12693 Turns on or off display of reports on all packets sent back and forth across
12694 the serial line to the remote machine. The info is printed on the
12695 @value{GDBN} standard output stream. The default is off.
12696 @kindex show debug remote
12697 @item show debug remote
12698 Displays the state of display of remote packets.
12699 @kindex set debug serial
12700 @item set debug serial
12701 Turns on or off display of @value{GDBN} serial debugging info. The
12703 @kindex show debug serial
12704 @item show debug serial
12705 Displays the current state of displaying @value{GDBN} serial debugging
12707 @kindex set debug target
12708 @item set debug target
12709 Turns on or off display of @value{GDBN} target debugging info. This info
12710 includes what is going on at the target level of GDB, as it happens. The
12712 @kindex show debug target
12713 @item show debug target
12714 Displays the current state of displaying @value{GDBN} target debugging
12716 @kindex set debug varobj
12717 @item set debug varobj
12718 Turns on or off display of @value{GDBN} variable object debugging
12719 info. The default is off.
12720 @kindex show debug varobj
12721 @item show debug varobj
12722 Displays the current state of displaying @value{GDBN} variable object
12727 @chapter Canned Sequences of Commands
12729 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12730 command lists}), @value{GDBN} provides two ways to store sequences of
12731 commands for execution as a unit: user-defined commands and command
12735 * Define:: User-defined commands
12736 * Hooks:: User-defined command hooks
12737 * Command Files:: Command files
12738 * Output:: Commands for controlled output
12742 @section User-defined commands
12744 @cindex user-defined command
12745 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12746 which you assign a new name as a command. This is done with the
12747 @code{define} command. User commands may accept up to 10 arguments
12748 separated by whitespace. Arguments are accessed within the user command
12749 via @var{$arg0@dots{}$arg9}. A trivial example:
12753 print $arg0 + $arg1 + $arg2
12757 To execute the command use:
12764 This defines the command @code{adder}, which prints the sum of
12765 its three arguments. Note the arguments are text substitutions, so they may
12766 reference variables, use complex expressions, or even perform inferior
12772 @item define @var{commandname}
12773 Define a command named @var{commandname}. If there is already a command
12774 by that name, you are asked to confirm that you want to redefine it.
12776 The definition of the command is made up of other @value{GDBN} command lines,
12777 which are given following the @code{define} command. The end of these
12778 commands is marked by a line containing @code{end}.
12783 Takes a single argument, which is an expression to evaluate.
12784 It is followed by a series of commands that are executed
12785 only if the expression is true (nonzero).
12786 There can then optionally be a line @code{else}, followed
12787 by a series of commands that are only executed if the expression
12788 was false. The end of the list is marked by a line containing @code{end}.
12792 The syntax is similar to @code{if}: the command takes a single argument,
12793 which is an expression to evaluate, and must be followed by the commands to
12794 execute, one per line, terminated by an @code{end}.
12795 The commands are executed repeatedly as long as the expression
12799 @item document @var{commandname}
12800 Document the user-defined command @var{commandname}, so that it can be
12801 accessed by @code{help}. The command @var{commandname} must already be
12802 defined. This command reads lines of documentation just as @code{define}
12803 reads the lines of the command definition, ending with @code{end}.
12804 After the @code{document} command is finished, @code{help} on command
12805 @var{commandname} displays the documentation you have written.
12807 You may use the @code{document} command again to change the
12808 documentation of a command. Redefining the command with @code{define}
12809 does not change the documentation.
12811 @kindex help user-defined
12812 @item help user-defined
12813 List all user-defined commands, with the first line of the documentation
12818 @itemx show user @var{commandname}
12819 Display the @value{GDBN} commands used to define @var{commandname} (but
12820 not its documentation). If no @var{commandname} is given, display the
12821 definitions for all user-defined commands.
12823 @kindex show max-user-call-depth
12824 @kindex set max-user-call-depth
12825 @item show max-user-call-depth
12826 @itemx set max-user-call-depth
12827 The value of @code{max-user-call-depth} controls how many recursion
12828 levels are allowed in user-defined commands before GDB suspects an
12829 infinite recursion and aborts the command.
12833 When user-defined commands are executed, the
12834 commands of the definition are not printed. An error in any command
12835 stops execution of the user-defined command.
12837 If used interactively, commands that would ask for confirmation proceed
12838 without asking when used inside a user-defined command. Many @value{GDBN}
12839 commands that normally print messages to say what they are doing omit the
12840 messages when used in a user-defined command.
12843 @section User-defined command hooks
12844 @cindex command hooks
12845 @cindex hooks, for commands
12846 @cindex hooks, pre-command
12850 You may define @dfn{hooks}, which are a special kind of user-defined
12851 command. Whenever you run the command @samp{foo}, if the user-defined
12852 command @samp{hook-foo} exists, it is executed (with no arguments)
12853 before that command.
12855 @cindex hooks, post-command
12858 A hook may also be defined which is run after the command you executed.
12859 Whenever you run the command @samp{foo}, if the user-defined command
12860 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12861 that command. Post-execution hooks may exist simultaneously with
12862 pre-execution hooks, for the same command.
12864 It is valid for a hook to call the command which it hooks. If this
12865 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12867 @c It would be nice if hookpost could be passed a parameter indicating
12868 @c if the command it hooks executed properly or not. FIXME!
12870 @kindex stop@r{, a pseudo-command}
12871 In addition, a pseudo-command, @samp{stop} exists. Defining
12872 (@samp{hook-stop}) makes the associated commands execute every time
12873 execution stops in your program: before breakpoint commands are run,
12874 displays are printed, or the stack frame is printed.
12876 For example, to ignore @code{SIGALRM} signals while
12877 single-stepping, but treat them normally during normal execution,
12882 handle SIGALRM nopass
12886 handle SIGALRM pass
12889 define hook-continue
12890 handle SIGLARM pass
12894 As a further example, to hook at the begining and end of the @code{echo}
12895 command, and to add extra text to the beginning and end of the message,
12903 define hookpost-echo
12907 (@value{GDBP}) echo Hello World
12908 <<<---Hello World--->>>
12913 You can define a hook for any single-word command in @value{GDBN}, but
12914 not for command aliases; you should define a hook for the basic command
12915 name, e.g. @code{backtrace} rather than @code{bt}.
12916 @c FIXME! So how does Joe User discover whether a command is an alias
12918 If an error occurs during the execution of your hook, execution of
12919 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12920 (before the command that you actually typed had a chance to run).
12922 If you try to define a hook which does not match any known command, you
12923 get a warning from the @code{define} command.
12925 @node Command Files
12926 @section Command files
12928 @cindex command files
12929 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12930 commands. Comments (lines starting with @kbd{#}) may also be included.
12931 An empty line in a command file does nothing; it does not mean to repeat
12932 the last command, as it would from the terminal.
12935 @cindex @file{.gdbinit}
12936 @cindex @file{gdb.ini}
12937 When you start @value{GDBN}, it automatically executes commands from its
12938 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
12939 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
12940 limitations of file names imposed by DOS filesystems.}.
12941 During startup, @value{GDBN} does the following:
12945 Reads the init file (if any) in your home directory@footnote{On
12946 DOS/Windows systems, the home directory is the one pointed to by the
12947 @code{HOME} environment variable.}.
12950 Processes command line options and operands.
12953 Reads the init file (if any) in the current working directory.
12956 Reads command files specified by the @samp{-x} option.
12959 The init file in your home directory can set options (such as @samp{set
12960 complaints}) that affect subsequent processing of command line options
12961 and operands. Init files are not executed if you use the @samp{-nx}
12962 option (@pxref{Mode Options, ,Choosing modes}).
12964 @cindex init file name
12965 On some configurations of @value{GDBN}, the init file is known by a
12966 different name (these are typically environments where a specialized
12967 form of @value{GDBN} may need to coexist with other forms, hence a
12968 different name for the specialized version's init file). These are the
12969 environments with special init file names:
12971 @cindex @file{.vxgdbinit}
12974 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12976 @cindex @file{.os68gdbinit}
12978 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12980 @cindex @file{.esgdbinit}
12982 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12985 You can also request the execution of a command file with the
12986 @code{source} command:
12990 @item source @var{filename}
12991 Execute the command file @var{filename}.
12994 The lines in a command file are executed sequentially. They are not
12995 printed as they are executed. An error in any command terminates
12996 execution of the command file and control is returned to the console.
12998 Commands that would ask for confirmation if used interactively proceed
12999 without asking when used in a command file. Many @value{GDBN} commands that
13000 normally print messages to say what they are doing omit the messages
13001 when called from command files.
13003 @value{GDBN} also accepts command input from standard input. In this
13004 mode, normal output goes to standard output and error output goes to
13005 standard error. Errors in a command file supplied on standard input do
13006 not terminate execution of the command file --- execution continues with
13010 gdb < cmds > log 2>&1
13013 (The syntax above will vary depending on the shell used.) This example
13014 will execute commands from the file @file{cmds}. All output and errors
13015 would be directed to @file{log}.
13018 @section Commands for controlled output
13020 During the execution of a command file or a user-defined command, normal
13021 @value{GDBN} output is suppressed; the only output that appears is what is
13022 explicitly printed by the commands in the definition. This section
13023 describes three commands useful for generating exactly the output you
13028 @item echo @var{text}
13029 @c I do not consider backslash-space a standard C escape sequence
13030 @c because it is not in ANSI.
13031 Print @var{text}. Nonprinting characters can be included in
13032 @var{text} using C escape sequences, such as @samp{\n} to print a
13033 newline. @strong{No newline is printed unless you specify one.}
13034 In addition to the standard C escape sequences, a backslash followed
13035 by a space stands for a space. This is useful for displaying a
13036 string with spaces at the beginning or the end, since leading and
13037 trailing spaces are otherwise trimmed from all arguments.
13038 To print @samp{@w{ }and foo =@w{ }}, use the command
13039 @samp{echo \@w{ }and foo = \@w{ }}.
13041 A backslash at the end of @var{text} can be used, as in C, to continue
13042 the command onto subsequent lines. For example,
13045 echo This is some text\n\
13046 which is continued\n\
13047 onto several lines.\n
13050 produces the same output as
13053 echo This is some text\n
13054 echo which is continued\n
13055 echo onto several lines.\n
13059 @item output @var{expression}
13060 Print the value of @var{expression} and nothing but that value: no
13061 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13062 value history either. @xref{Expressions, ,Expressions}, for more information
13065 @item output/@var{fmt} @var{expression}
13066 Print the value of @var{expression} in format @var{fmt}. You can use
13067 the same formats as for @code{print}. @xref{Output Formats,,Output
13068 formats}, for more information.
13071 @item printf @var{string}, @var{expressions}@dots{}
13072 Print the values of the @var{expressions} under the control of
13073 @var{string}. The @var{expressions} are separated by commas and may be
13074 either numbers or pointers. Their values are printed as specified by
13075 @var{string}, exactly as if your program were to execute the C
13077 @c FIXME: the above implies that at least all ANSI C formats are
13078 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13079 @c Either this is a bug, or the manual should document what formats are
13083 printf (@var{string}, @var{expressions}@dots{});
13086 For example, you can print two values in hex like this:
13089 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13092 The only backslash-escape sequences that you can use in the format
13093 string are the simple ones that consist of backslash followed by a
13098 @chapter @value{GDBN} Text User Interface
13102 * TUI Overview:: TUI overview
13103 * TUI Keys:: TUI key bindings
13104 * TUI Single Key Mode:: TUI single key mode
13105 * TUI Commands:: TUI specific commands
13106 * TUI Configuration:: TUI configuration variables
13109 The @value{GDBN} Text User Interface, TUI in short,
13110 is a terminal interface which uses the @code{curses} library
13111 to show the source file, the assembly output, the program registers
13112 and @value{GDBN} commands in separate text windows.
13113 The TUI is available only when @value{GDBN} is configured
13114 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13117 @section TUI overview
13119 The TUI has two display modes that can be switched while
13124 A curses (or TUI) mode in which it displays several text
13125 windows on the terminal.
13128 A standard mode which corresponds to the @value{GDBN} configured without
13132 In the TUI mode, @value{GDBN} can display several text window
13137 This window is the @value{GDBN} command window with the @value{GDBN}
13138 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13139 managed using readline but through the TUI. The @emph{command}
13140 window is always visible.
13143 The source window shows the source file of the program. The current
13144 line as well as active breakpoints are displayed in this window.
13147 The assembly window shows the disassembly output of the program.
13150 This window shows the processor registers. It detects when
13151 a register is changed and when this is the case, registers that have
13152 changed are highlighted.
13156 The source and assembly windows show the current program position
13157 by highlighting the current line and marking them with the @samp{>} marker.
13158 Breakpoints are also indicated with two markers. A first one
13159 indicates the breakpoint type:
13163 Breakpoint which was hit at least once.
13166 Breakpoint which was never hit.
13169 Hardware breakpoint which was hit at least once.
13172 Hardware breakpoint which was never hit.
13176 The second marker indicates whether the breakpoint is enabled or not:
13180 Breakpoint is enabled.
13183 Breakpoint is disabled.
13187 The source, assembly and register windows are attached to the thread
13188 and the frame position. They are updated when the current thread
13189 changes, when the frame changes or when the program counter changes.
13190 These three windows are arranged by the TUI according to several
13191 layouts. The layout defines which of these three windows are visible.
13192 The following layouts are available:
13202 source and assembly
13205 source and registers
13208 assembly and registers
13212 On top of the command window a status line gives various information
13213 concerning the current process begin debugged. The status line is
13214 updated when the information it shows changes. The following fields
13219 Indicates the current gdb target
13220 (@pxref{Targets, ,Specifying a Debugging Target}).
13223 Gives information about the current process or thread number.
13224 When no process is being debugged, this field is set to @code{No process}.
13227 Gives the current function name for the selected frame.
13228 The name is demangled if demangling is turned on (@pxref{Print Settings}).
13229 When there is no symbol corresponding to the current program counter
13230 the string @code{??} is displayed.
13233 Indicates the current line number for the selected frame.
13234 When the current line number is not known the string @code{??} is displayed.
13237 Indicates the current program counter address.
13242 @section TUI Key Bindings
13243 @cindex TUI key bindings
13245 The TUI installs several key bindings in the readline keymaps
13246 (@pxref{Command Line Editing}).
13247 They allow to leave or enter in the TUI mode or they operate
13248 directly on the TUI layout and windows. The TUI also provides
13249 a @emph{SingleKey} keymap which binds several keys directly to
13250 @value{GDBN} commands. The following key bindings
13251 are installed for both TUI mode and the @value{GDBN} standard mode.
13260 Enter or leave the TUI mode. When the TUI mode is left,
13261 the curses window management is left and @value{GDBN} operates using
13262 its standard mode writing on the terminal directly. When the TUI
13263 mode is entered, the control is given back to the curses windows.
13264 The screen is then refreshed.
13268 Use a TUI layout with only one window. The layout will
13269 either be @samp{source} or @samp{assembly}. When the TUI mode
13270 is not active, it will switch to the TUI mode.
13272 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13276 Use a TUI layout with at least two windows. When the current
13277 layout shows already two windows, a next layout with two windows is used.
13278 When a new layout is chosen, one window will always be common to the
13279 previous layout and the new one.
13281 Think of it as the Emacs @kbd{C-x 2} binding.
13285 Use the TUI @emph{SingleKey} keymap that binds single key to gdb commands
13286 (@pxref{TUI Single Key Mode}).
13290 The following key bindings are handled only by the TUI mode:
13295 Scroll the active window one page up.
13299 Scroll the active window one page down.
13303 Scroll the active window one line up.
13307 Scroll the active window one line down.
13311 Scroll the active window one column left.
13315 Scroll the active window one column right.
13319 Refresh the screen.
13323 In the TUI mode, the arrow keys are used by the active window
13324 for scrolling. This means they are not available for readline. It is
13325 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13326 @key{C-b} and @key{C-f}.
13328 @node TUI Single Key Mode
13329 @section TUI Single Key Mode
13330 @cindex TUI single key mode
13332 The TUI provides a @emph{SingleKey} mode in which it installs a particular
13333 key binding in the readline keymaps to connect single keys to
13337 @kindex c @r{(SingleKey TUI key)}
13341 @kindex d @r{(SingleKey TUI key)}
13345 @kindex f @r{(SingleKey TUI key)}
13349 @kindex n @r{(SingleKey TUI key)}
13353 @kindex q @r{(SingleKey TUI key)}
13355 exit the @emph{SingleKey} mode.
13357 @kindex r @r{(SingleKey TUI key)}
13361 @kindex s @r{(SingleKey TUI key)}
13365 @kindex u @r{(SingleKey TUI key)}
13369 @kindex v @r{(SingleKey TUI key)}
13373 @kindex w @r{(SingleKey TUI key)}
13379 Other keys temporarily switch to the @value{GDBN} command prompt.
13380 The key that was pressed is inserted in the editing buffer so that
13381 it is possible to type most @value{GDBN} commands without interaction
13382 with the TUI @emph{SingleKey} mode. Once the command is entered the TUI
13383 @emph{SingleKey} mode is restored. The only way to permanently leave
13384 this mode is by hitting @key{q} or @samp{@key{C-x} @key{s}}.
13388 @section TUI specific commands
13389 @cindex TUI commands
13391 The TUI has specific commands to control the text windows.
13392 These commands are always available, that is they do not depend on
13393 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13394 is in the standard mode, using these commands will automatically switch
13400 List and give the size of all displayed windows.
13403 @kindex layout next
13404 Display the next layout.
13407 @kindex layout prev
13408 Display the previous layout.
13412 Display the source window only.
13416 Display the assembly window only.
13419 @kindex layout split
13420 Display the source and assembly window.
13423 @kindex layout regs
13424 Display the register window together with the source or assembly window.
13426 @item focus next | prev | src | asm | regs | split
13428 Set the focus to the named window.
13429 This command allows to change the active window so that scrolling keys
13430 can be affected to another window.
13434 Refresh the screen. This is similar to using @key{C-L} key.
13438 Update the source window and the current execution point.
13440 @item winheight @var{name} +@var{count}
13441 @itemx winheight @var{name} -@var{count}
13443 Change the height of the window @var{name} by @var{count}
13444 lines. Positive counts increase the height, while negative counts
13449 @node TUI Configuration
13450 @section TUI configuration variables
13451 @cindex TUI configuration variables
13453 The TUI has several configuration variables that control the
13454 appearance of windows on the terminal.
13457 @item set tui border-kind @var{kind}
13458 @kindex set tui border-kind
13459 Select the border appearance for the source, assembly and register windows.
13460 The possible values are the following:
13463 Use a space character to draw the border.
13466 Use ascii characters + - and | to draw the border.
13469 Use the Alternate Character Set to draw the border. The border is
13470 drawn using character line graphics if the terminal supports them.
13474 @item set tui active-border-mode @var{mode}
13475 @kindex set tui active-border-mode
13476 Select the attributes to display the border of the active window.
13477 The possible values are @code{normal}, @code{standout}, @code{reverse},
13478 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13480 @item set tui border-mode @var{mode}
13481 @kindex set tui border-mode
13482 Select the attributes to display the border of other windows.
13483 The @var{mode} can be one of the following:
13486 Use normal attributes to display the border.
13492 Use reverse video mode.
13495 Use half bright mode.
13497 @item half-standout
13498 Use half bright and standout mode.
13501 Use extra bright or bold mode.
13503 @item bold-standout
13504 Use extra bright or bold and standout mode.
13511 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13514 @cindex @sc{gnu} Emacs
13515 A special interface allows you to use @sc{gnu} Emacs to view (and
13516 edit) the source files for the program you are debugging with
13519 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13520 executable file you want to debug as an argument. This command starts
13521 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13522 created Emacs buffer.
13523 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13525 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13530 All ``terminal'' input and output goes through the Emacs buffer.
13533 This applies both to @value{GDBN} commands and their output, and to the input
13534 and output done by the program you are debugging.
13536 This is useful because it means that you can copy the text of previous
13537 commands and input them again; you can even use parts of the output
13540 All the facilities of Emacs' Shell mode are available for interacting
13541 with your program. In particular, you can send signals the usual
13542 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13547 @value{GDBN} displays source code through Emacs.
13550 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13551 source file for that frame and puts an arrow (@samp{=>}) at the
13552 left margin of the current line. Emacs uses a separate buffer for
13553 source display, and splits the screen to show both your @value{GDBN} session
13556 Explicit @value{GDBN} @code{list} or search commands still produce output as
13557 usual, but you probably have no reason to use them from Emacs.
13560 @emph{Warning:} If the directory where your program resides is not your
13561 current directory, it can be easy to confuse Emacs about the location of
13562 the source files, in which case the auxiliary display buffer does not
13563 appear to show your source. @value{GDBN} can find programs by searching your
13564 environment's @code{PATH} variable, so the @value{GDBN} input and output
13565 session proceeds normally; but Emacs does not get enough information
13566 back from @value{GDBN} to locate the source files in this situation. To
13567 avoid this problem, either start @value{GDBN} mode from the directory where
13568 your program resides, or specify an absolute file name when prompted for the
13569 @kbd{M-x gdb} argument.
13571 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13572 switch to debugging a program in some other location, from an existing
13573 @value{GDBN} buffer in Emacs.
13576 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13577 you need to call @value{GDBN} by a different name (for example, if you keep
13578 several configurations around, with different names) you can set the
13579 Emacs variable @code{gdb-command-name}; for example,
13582 (setq gdb-command-name "mygdb")
13586 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13587 in your @file{.emacs} file) makes Emacs call the program named
13588 ``@code{mygdb}'' instead.
13590 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13591 addition to the standard Shell mode commands:
13595 Describe the features of Emacs' @value{GDBN} Mode.
13598 Execute to another source line, like the @value{GDBN} @code{step} command; also
13599 update the display window to show the current file and location.
13602 Execute to next source line in this function, skipping all function
13603 calls, like the @value{GDBN} @code{next} command. Then update the display window
13604 to show the current file and location.
13607 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13608 display window accordingly.
13610 @item M-x gdb-nexti
13611 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13612 display window accordingly.
13615 Execute until exit from the selected stack frame, like the @value{GDBN}
13616 @code{finish} command.
13619 Continue execution of your program, like the @value{GDBN} @code{continue}
13622 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13625 Go up the number of frames indicated by the numeric argument
13626 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13627 like the @value{GDBN} @code{up} command.
13629 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13632 Go down the number of frames indicated by the numeric argument, like the
13633 @value{GDBN} @code{down} command.
13635 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13638 Read the number where the cursor is positioned, and insert it at the end
13639 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13640 around an address that was displayed earlier, type @kbd{disassemble};
13641 then move the cursor to the address display, and pick up the
13642 argument for @code{disassemble} by typing @kbd{C-x &}.
13644 You can customize this further by defining elements of the list
13645 @code{gdb-print-command}; once it is defined, you can format or
13646 otherwise process numbers picked up by @kbd{C-x &} before they are
13647 inserted. A numeric argument to @kbd{C-x &} indicates that you
13648 wish special formatting, and also acts as an index to pick an element of the
13649 list. If the list element is a string, the number to be inserted is
13650 formatted using the Emacs function @code{format}; otherwise the number
13651 is passed as an argument to the corresponding list element.
13654 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13655 tells @value{GDBN} to set a breakpoint on the source line point is on.
13657 If you accidentally delete the source-display buffer, an easy way to get
13658 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13659 request a frame display; when you run under Emacs, this recreates
13660 the source buffer if necessary to show you the context of the current
13663 The source files displayed in Emacs are in ordinary Emacs buffers
13664 which are visiting the source files in the usual way. You can edit
13665 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13666 communicates with Emacs in terms of line numbers. If you add or
13667 delete lines from the text, the line numbers that @value{GDBN} knows cease
13668 to correspond properly with the code.
13670 @c The following dropped because Epoch is nonstandard. Reactivate
13671 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13673 @kindex Emacs Epoch environment
13677 Version 18 of @sc{gnu} Emacs has a built-in window system
13678 called the @code{epoch}
13679 environment. Users of this environment can use a new command,
13680 @code{inspect} which performs identically to @code{print} except that
13681 each value is printed in its own window.
13684 @include annotate.texi
13685 @include gdbmi.texinfo
13688 @chapter Reporting Bugs in @value{GDBN}
13689 @cindex bugs in @value{GDBN}
13690 @cindex reporting bugs in @value{GDBN}
13692 Your bug reports play an essential role in making @value{GDBN} reliable.
13694 Reporting a bug may help you by bringing a solution to your problem, or it
13695 may not. But in any case the principal function of a bug report is to help
13696 the entire community by making the next version of @value{GDBN} work better. Bug
13697 reports are your contribution to the maintenance of @value{GDBN}.
13699 In order for a bug report to serve its purpose, you must include the
13700 information that enables us to fix the bug.
13703 * Bug Criteria:: Have you found a bug?
13704 * Bug Reporting:: How to report bugs
13708 @section Have you found a bug?
13709 @cindex bug criteria
13711 If you are not sure whether you have found a bug, here are some guidelines:
13714 @cindex fatal signal
13715 @cindex debugger crash
13716 @cindex crash of debugger
13718 If the debugger gets a fatal signal, for any input whatever, that is a
13719 @value{GDBN} bug. Reliable debuggers never crash.
13721 @cindex error on valid input
13723 If @value{GDBN} produces an error message for valid input, that is a
13724 bug. (Note that if you're cross debugging, the problem may also be
13725 somewhere in the connection to the target.)
13727 @cindex invalid input
13729 If @value{GDBN} does not produce an error message for invalid input,
13730 that is a bug. However, you should note that your idea of
13731 ``invalid input'' might be our idea of ``an extension'' or ``support
13732 for traditional practice''.
13735 If you are an experienced user of debugging tools, your suggestions
13736 for improvement of @value{GDBN} are welcome in any case.
13739 @node Bug Reporting
13740 @section How to report bugs
13741 @cindex bug reports
13742 @cindex @value{GDBN} bugs, reporting
13744 A number of companies and individuals offer support for @sc{gnu} products.
13745 If you obtained @value{GDBN} from a support organization, we recommend you
13746 contact that organization first.
13748 You can find contact information for many support companies and
13749 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13751 @c should add a web page ref...
13753 In any event, we also recommend that you submit bug reports for
13754 @value{GDBN}. The prefered method is to submit them directly using
13755 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
13756 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
13759 @strong{Do not send bug reports to @samp{info-gdb}, or to
13760 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13761 not want to receive bug reports. Those that do have arranged to receive
13764 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13765 serves as a repeater. The mailing list and the newsgroup carry exactly
13766 the same messages. Often people think of posting bug reports to the
13767 newsgroup instead of mailing them. This appears to work, but it has one
13768 problem which can be crucial: a newsgroup posting often lacks a mail
13769 path back to the sender. Thus, if we need to ask for more information,
13770 we may be unable to reach you. For this reason, it is better to send
13771 bug reports to the mailing list.
13773 The fundamental principle of reporting bugs usefully is this:
13774 @strong{report all the facts}. If you are not sure whether to state a
13775 fact or leave it out, state it!
13777 Often people omit facts because they think they know what causes the
13778 problem and assume that some details do not matter. Thus, you might
13779 assume that the name of the variable you use in an example does not matter.
13780 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13781 stray memory reference which happens to fetch from the location where that
13782 name is stored in memory; perhaps, if the name were different, the contents
13783 of that location would fool the debugger into doing the right thing despite
13784 the bug. Play it safe and give a specific, complete example. That is the
13785 easiest thing for you to do, and the most helpful.
13787 Keep in mind that the purpose of a bug report is to enable us to fix the
13788 bug. It may be that the bug has been reported previously, but neither
13789 you nor we can know that unless your bug report is complete and
13792 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13793 bell?'' Those bug reports are useless, and we urge everyone to
13794 @emph{refuse to respond to them} except to chide the sender to report
13797 To enable us to fix the bug, you should include all these things:
13801 The version of @value{GDBN}. @value{GDBN} announces it if you start
13802 with no arguments; you can also print it at any time using @code{show
13805 Without this, we will not know whether there is any point in looking for
13806 the bug in the current version of @value{GDBN}.
13809 The type of machine you are using, and the operating system name and
13813 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13814 ``@value{GCC}--2.8.1''.
13817 What compiler (and its version) was used to compile the program you are
13818 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13819 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13820 information; for other compilers, see the documentation for those
13824 The command arguments you gave the compiler to compile your example and
13825 observe the bug. For example, did you use @samp{-O}? To guarantee
13826 you will not omit something important, list them all. A copy of the
13827 Makefile (or the output from make) is sufficient.
13829 If we were to try to guess the arguments, we would probably guess wrong
13830 and then we might not encounter the bug.
13833 A complete input script, and all necessary source files, that will
13837 A description of what behavior you observe that you believe is
13838 incorrect. For example, ``It gets a fatal signal.''
13840 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13841 will certainly notice it. But if the bug is incorrect output, we might
13842 not notice unless it is glaringly wrong. You might as well not give us
13843 a chance to make a mistake.
13845 Even if the problem you experience is a fatal signal, you should still
13846 say so explicitly. Suppose something strange is going on, such as, your
13847 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13848 the C library on your system. (This has happened!) Your copy might
13849 crash and ours would not. If you told us to expect a crash, then when
13850 ours fails to crash, we would know that the bug was not happening for
13851 us. If you had not told us to expect a crash, then we would not be able
13852 to draw any conclusion from our observations.
13855 If you wish to suggest changes to the @value{GDBN} source, send us context
13856 diffs. If you even discuss something in the @value{GDBN} source, refer to
13857 it by context, not by line number.
13859 The line numbers in our development sources will not match those in your
13860 sources. Your line numbers would convey no useful information to us.
13864 Here are some things that are not necessary:
13868 A description of the envelope of the bug.
13870 Often people who encounter a bug spend a lot of time investigating
13871 which changes to the input file will make the bug go away and which
13872 changes will not affect it.
13874 This is often time consuming and not very useful, because the way we
13875 will find the bug is by running a single example under the debugger
13876 with breakpoints, not by pure deduction from a series of examples.
13877 We recommend that you save your time for something else.
13879 Of course, if you can find a simpler example to report @emph{instead}
13880 of the original one, that is a convenience for us. Errors in the
13881 output will be easier to spot, running under the debugger will take
13882 less time, and so on.
13884 However, simplification is not vital; if you do not want to do this,
13885 report the bug anyway and send us the entire test case you used.
13888 A patch for the bug.
13890 A patch for the bug does help us if it is a good one. But do not omit
13891 the necessary information, such as the test case, on the assumption that
13892 a patch is all we need. We might see problems with your patch and decide
13893 to fix the problem another way, or we might not understand it at all.
13895 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13896 construct an example that will make the program follow a certain path
13897 through the code. If you do not send us the example, we will not be able
13898 to construct one, so we will not be able to verify that the bug is fixed.
13900 And if we cannot understand what bug you are trying to fix, or why your
13901 patch should be an improvement, we will not install it. A test case will
13902 help us to understand.
13905 A guess about what the bug is or what it depends on.
13907 Such guesses are usually wrong. Even we cannot guess right about such
13908 things without first using the debugger to find the facts.
13911 @c The readline documentation is distributed with the readline code
13912 @c and consists of the two following files:
13914 @c inc-hist.texinfo
13915 @c Use -I with makeinfo to point to the appropriate directory,
13916 @c environment var TEXINPUTS with TeX.
13917 @include rluser.texinfo
13918 @include inc-hist.texinfo
13921 @node Formatting Documentation
13922 @appendix Formatting Documentation
13924 @cindex @value{GDBN} reference card
13925 @cindex reference card
13926 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13927 for printing with PostScript or Ghostscript, in the @file{gdb}
13928 subdirectory of the main source directory@footnote{In
13929 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13930 release.}. If you can use PostScript or Ghostscript with your printer,
13931 you can print the reference card immediately with @file{refcard.ps}.
13933 The release also includes the source for the reference card. You
13934 can format it, using @TeX{}, by typing:
13940 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13941 mode on US ``letter'' size paper;
13942 that is, on a sheet 11 inches wide by 8.5 inches
13943 high. You will need to specify this form of printing as an option to
13944 your @sc{dvi} output program.
13946 @cindex documentation
13948 All the documentation for @value{GDBN} comes as part of the machine-readable
13949 distribution. The documentation is written in Texinfo format, which is
13950 a documentation system that uses a single source file to produce both
13951 on-line information and a printed manual. You can use one of the Info
13952 formatting commands to create the on-line version of the documentation
13953 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13955 @value{GDBN} includes an already formatted copy of the on-line Info
13956 version of this manual in the @file{gdb} subdirectory. The main Info
13957 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13958 subordinate files matching @samp{gdb.info*} in the same directory. If
13959 necessary, you can print out these files, or read them with any editor;
13960 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13961 Emacs or the standalone @code{info} program, available as part of the
13962 @sc{gnu} Texinfo distribution.
13964 If you want to format these Info files yourself, you need one of the
13965 Info formatting programs, such as @code{texinfo-format-buffer} or
13968 If you have @code{makeinfo} installed, and are in the top level
13969 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13970 version @value{GDBVN}), you can make the Info file by typing:
13977 If you want to typeset and print copies of this manual, you need @TeX{},
13978 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13979 Texinfo definitions file.
13981 @TeX{} is a typesetting program; it does not print files directly, but
13982 produces output files called @sc{dvi} files. To print a typeset
13983 document, you need a program to print @sc{dvi} files. If your system
13984 has @TeX{} installed, chances are it has such a program. The precise
13985 command to use depends on your system; @kbd{lpr -d} is common; another
13986 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
13987 require a file name without any extension or a @samp{.dvi} extension.
13989 @TeX{} also requires a macro definitions file called
13990 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
13991 written in Texinfo format. On its own, @TeX{} cannot either read or
13992 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
13993 and is located in the @file{gdb-@var{version-number}/texinfo}
13996 If you have @TeX{} and a @sc{dvi} printer program installed, you can
13997 typeset and print this manual. First switch to the the @file{gdb}
13998 subdirectory of the main source directory (for example, to
13999 @file{gdb-@value{GDBVN}/gdb}) and type:
14005 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14007 @node Installing GDB
14008 @appendix Installing @value{GDBN}
14009 @cindex configuring @value{GDBN}
14010 @cindex installation
14012 @value{GDBN} comes with a @code{configure} script that automates the process
14013 of preparing @value{GDBN} for installation; you can then use @code{make} to
14014 build the @code{gdb} program.
14016 @c irrelevant in info file; it's as current as the code it lives with.
14017 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14018 look at the @file{README} file in the sources; we may have improved the
14019 installation procedures since publishing this manual.}
14022 The @value{GDBN} distribution includes all the source code you need for
14023 @value{GDBN} in a single directory, whose name is usually composed by
14024 appending the version number to @samp{gdb}.
14026 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14027 @file{gdb-@value{GDBVN}} directory. That directory contains:
14030 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14031 script for configuring @value{GDBN} and all its supporting libraries
14033 @item gdb-@value{GDBVN}/gdb
14034 the source specific to @value{GDBN} itself
14036 @item gdb-@value{GDBVN}/bfd
14037 source for the Binary File Descriptor library
14039 @item gdb-@value{GDBVN}/include
14040 @sc{gnu} include files
14042 @item gdb-@value{GDBVN}/libiberty
14043 source for the @samp{-liberty} free software library
14045 @item gdb-@value{GDBVN}/opcodes
14046 source for the library of opcode tables and disassemblers
14048 @item gdb-@value{GDBVN}/readline
14049 source for the @sc{gnu} command-line interface
14051 @item gdb-@value{GDBVN}/glob
14052 source for the @sc{gnu} filename pattern-matching subroutine
14054 @item gdb-@value{GDBVN}/mmalloc
14055 source for the @sc{gnu} memory-mapped malloc package
14058 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14059 from the @file{gdb-@var{version-number}} source directory, which in
14060 this example is the @file{gdb-@value{GDBVN}} directory.
14062 First switch to the @file{gdb-@var{version-number}} source directory
14063 if you are not already in it; then run @code{configure}. Pass the
14064 identifier for the platform on which @value{GDBN} will run as an
14070 cd gdb-@value{GDBVN}
14071 ./configure @var{host}
14076 where @var{host} is an identifier such as @samp{sun4} or
14077 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14078 (You can often leave off @var{host}; @code{configure} tries to guess the
14079 correct value by examining your system.)
14081 Running @samp{configure @var{host}} and then running @code{make} builds the
14082 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14083 libraries, then @code{gdb} itself. The configured source files, and the
14084 binaries, are left in the corresponding source directories.
14087 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14088 system does not recognize this automatically when you run a different
14089 shell, you may need to run @code{sh} on it explicitly:
14092 sh configure @var{host}
14095 If you run @code{configure} from a directory that contains source
14096 directories for multiple libraries or programs, such as the
14097 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14098 creates configuration files for every directory level underneath (unless
14099 you tell it not to, with the @samp{--norecursion} option).
14101 You can run the @code{configure} script from any of the
14102 subordinate directories in the @value{GDBN} distribution if you only want to
14103 configure that subdirectory, but be sure to specify a path to it.
14105 For example, with version @value{GDBVN}, type the following to configure only
14106 the @code{bfd} subdirectory:
14110 cd gdb-@value{GDBVN}/bfd
14111 ../configure @var{host}
14115 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14116 However, you should make sure that the shell on your path (named by
14117 the @samp{SHELL} environment variable) is publicly readable. Remember
14118 that @value{GDBN} uses the shell to start your program---some systems refuse to
14119 let @value{GDBN} debug child processes whose programs are not readable.
14122 * Separate Objdir:: Compiling @value{GDBN} in another directory
14123 * Config Names:: Specifying names for hosts and targets
14124 * Configure Options:: Summary of options for configure
14127 @node Separate Objdir
14128 @section Compiling @value{GDBN} in another directory
14130 If you want to run @value{GDBN} versions for several host or target machines,
14131 you need a different @code{gdb} compiled for each combination of
14132 host and target. @code{configure} is designed to make this easy by
14133 allowing you to generate each configuration in a separate subdirectory,
14134 rather than in the source directory. If your @code{make} program
14135 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14136 @code{make} in each of these directories builds the @code{gdb}
14137 program specified there.
14139 To build @code{gdb} in a separate directory, run @code{configure}
14140 with the @samp{--srcdir} option to specify where to find the source.
14141 (You also need to specify a path to find @code{configure}
14142 itself from your working directory. If the path to @code{configure}
14143 would be the same as the argument to @samp{--srcdir}, you can leave out
14144 the @samp{--srcdir} option; it is assumed.)
14146 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14147 separate directory for a Sun 4 like this:
14151 cd gdb-@value{GDBVN}
14154 ../gdb-@value{GDBVN}/configure sun4
14159 When @code{configure} builds a configuration using a remote source
14160 directory, it creates a tree for the binaries with the same structure
14161 (and using the same names) as the tree under the source directory. In
14162 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14163 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14164 @file{gdb-sun4/gdb}.
14166 One popular reason to build several @value{GDBN} configurations in separate
14167 directories is to configure @value{GDBN} for cross-compiling (where
14168 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14169 programs that run on another machine---the @dfn{target}).
14170 You specify a cross-debugging target by
14171 giving the @samp{--target=@var{target}} option to @code{configure}.
14173 When you run @code{make} to build a program or library, you must run
14174 it in a configured directory---whatever directory you were in when you
14175 called @code{configure} (or one of its subdirectories).
14177 The @code{Makefile} that @code{configure} generates in each source
14178 directory also runs recursively. If you type @code{make} in a source
14179 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14180 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14181 will build all the required libraries, and then build GDB.
14183 When you have multiple hosts or targets configured in separate
14184 directories, you can run @code{make} on them in parallel (for example,
14185 if they are NFS-mounted on each of the hosts); they will not interfere
14189 @section Specifying names for hosts and targets
14191 The specifications used for hosts and targets in the @code{configure}
14192 script are based on a three-part naming scheme, but some short predefined
14193 aliases are also supported. The full naming scheme encodes three pieces
14194 of information in the following pattern:
14197 @var{architecture}-@var{vendor}-@var{os}
14200 For example, you can use the alias @code{sun4} as a @var{host} argument,
14201 or as the value for @var{target} in a @code{--target=@var{target}}
14202 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14204 The @code{configure} script accompanying @value{GDBN} does not provide
14205 any query facility to list all supported host and target names or
14206 aliases. @code{configure} calls the Bourne shell script
14207 @code{config.sub} to map abbreviations to full names; you can read the
14208 script, if you wish, or you can use it to test your guesses on
14209 abbreviations---for example:
14212 % sh config.sub i386-linux
14214 % sh config.sub alpha-linux
14215 alpha-unknown-linux-gnu
14216 % sh config.sub hp9k700
14218 % sh config.sub sun4
14219 sparc-sun-sunos4.1.1
14220 % sh config.sub sun3
14221 m68k-sun-sunos4.1.1
14222 % sh config.sub i986v
14223 Invalid configuration `i986v': machine `i986v' not recognized
14227 @code{config.sub} is also distributed in the @value{GDBN} source
14228 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14230 @node Configure Options
14231 @section @code{configure} options
14233 Here is a summary of the @code{configure} options and arguments that
14234 are most often useful for building @value{GDBN}. @code{configure} also has
14235 several other options not listed here. @inforef{What Configure
14236 Does,,configure.info}, for a full explanation of @code{configure}.
14239 configure @r{[}--help@r{]}
14240 @r{[}--prefix=@var{dir}@r{]}
14241 @r{[}--exec-prefix=@var{dir}@r{]}
14242 @r{[}--srcdir=@var{dirname}@r{]}
14243 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14244 @r{[}--target=@var{target}@r{]}
14249 You may introduce options with a single @samp{-} rather than
14250 @samp{--} if you prefer; but you may abbreviate option names if you use
14255 Display a quick summary of how to invoke @code{configure}.
14257 @item --prefix=@var{dir}
14258 Configure the source to install programs and files under directory
14261 @item --exec-prefix=@var{dir}
14262 Configure the source to install programs under directory
14265 @c avoid splitting the warning from the explanation:
14267 @item --srcdir=@var{dirname}
14268 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14269 @code{make} that implements the @code{VPATH} feature.}@*
14270 Use this option to make configurations in directories separate from the
14271 @value{GDBN} source directories. Among other things, you can use this to
14272 build (or maintain) several configurations simultaneously, in separate
14273 directories. @code{configure} writes configuration specific files in
14274 the current directory, but arranges for them to use the source in the
14275 directory @var{dirname}. @code{configure} creates directories under
14276 the working directory in parallel to the source directories below
14279 @item --norecursion
14280 Configure only the directory level where @code{configure} is executed; do not
14281 propagate configuration to subdirectories.
14283 @item --target=@var{target}
14284 Configure @value{GDBN} for cross-debugging programs running on the specified
14285 @var{target}. Without this option, @value{GDBN} is configured to debug
14286 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14288 There is no convenient way to generate a list of all available targets.
14290 @item @var{host} @dots{}
14291 Configure @value{GDBN} to run on the specified @var{host}.
14293 There is no convenient way to generate a list of all available hosts.
14296 There are many other options available as well, but they are generally
14297 needed for special purposes only.
14299 @node Maintenance Commands
14300 @appendix Maintenance Commands
14301 @cindex maintenance commands
14302 @cindex internal commands
14304 In addition to commands intended for @value{GDBN} users, @value{GDBN}
14305 includes a number of commands intended for @value{GDBN} developers.
14306 These commands are provided here for reference.
14309 @kindex maint info breakpoints
14310 @item @anchor{maint info breakpoints}maint info breakpoints
14311 Using the same format as @samp{info breakpoints}, display both the
14312 breakpoints you've set explicitly, and those @value{GDBN} is using for
14313 internal purposes. Internal breakpoints are shown with negative
14314 breakpoint numbers. The type column identifies what kind of breakpoint
14319 Normal, explicitly set breakpoint.
14322 Normal, explicitly set watchpoint.
14325 Internal breakpoint, used to handle correctly stepping through
14326 @code{longjmp} calls.
14328 @item longjmp resume
14329 Internal breakpoint at the target of a @code{longjmp}.
14332 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
14335 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
14338 Shared library events.
14342 @kindex maint internal-error
14343 @kindex maint internal-warning
14344 @item maint internal-error
14345 @itemx maint internal-warning
14346 Cause @value{GDBN} to call the internal function @code{internal_error}
14347 or @code{internal_warning} and hence behave as though an internal error
14348 or internal warning has been detected. In addition to reporting the
14349 internal problem, these functions give the user the opportunity to
14350 either quit @value{GDBN} or create a core file of the current
14351 @value{GDBN} session.
14354 (gdb) @kbd{maint internal-error testing, 1, 2}
14355 @dots{}/maint.c:121: internal-error: testing, 1, 2
14356 A problem internal to GDB has been detected. Further
14357 debugging may prove unreliable.
14358 Quit this debugging session? (y or n) @kbd{n}
14359 Create a core file? (y or n) @kbd{n}
14363 Takes an optional parameter that is used as the text of the error or
14366 @kindex maint print registers
14367 @kindex maint print raw-registers
14368 @kindex maint print cooked-registers
14369 @item maint print registers
14370 @itemx maint print raw-registers
14371 @itemx maint print cooked-registers
14372 Print @value{GDBN}'s internal register data structures.
14374 The command @samp{maint print raw-registers} includes the contents of
14375 the raw register cache; and the command @samp{maint print
14376 cooked-registers} includes the (cooked) value of all registers.
14377 @xref{Registers,, Registers, gdbint, @value{GDBN} Internals}.
14379 Takes an optional file parameter.
14384 @node Remote Protocol
14385 @appendix @value{GDBN} Remote Serial Protocol
14390 * Stop Reply Packets::
14391 * General Query Packets::
14392 * Register Packet Format::
14399 There may be occasions when you need to know something about the
14400 protocol---for example, if there is only one serial port to your target
14401 machine, you might want your program to do something special if it
14402 recognizes a packet meant for @value{GDBN}.
14404 In the examples below, @samp{->} and @samp{<-} are used to indicate
14405 transmitted and received data respectfully.
14407 @cindex protocol, @value{GDBN} remote serial
14408 @cindex serial protocol, @value{GDBN} remote
14409 @cindex remote serial protocol
14410 All @value{GDBN} commands and responses (other than acknowledgments) are
14411 sent as a @var{packet}. A @var{packet} is introduced with the character
14412 @samp{$}, the actual @var{packet-data}, and the terminating character
14413 @samp{#} followed by a two-digit @var{checksum}:
14416 @code{$}@var{packet-data}@code{#}@var{checksum}
14420 @cindex checksum, for @value{GDBN} remote
14422 The two-digit @var{checksum} is computed as the modulo 256 sum of all
14423 characters between the leading @samp{$} and the trailing @samp{#} (an
14424 eight bit unsigned checksum).
14426 Implementors should note that prior to @value{GDBN} 5.0 the protocol
14427 specification also included an optional two-digit @var{sequence-id}:
14430 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
14433 @cindex sequence-id, for @value{GDBN} remote
14435 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
14436 has never output @var{sequence-id}s. Stubs that handle packets added
14437 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
14439 @cindex acknowledgment, for @value{GDBN} remote
14440 When either the host or the target machine receives a packet, the first
14441 response expected is an acknowledgment: either @samp{+} (to indicate
14442 the package was received correctly) or @samp{-} (to request
14446 -> @code{$}@var{packet-data}@code{#}@var{checksum}
14451 The host (@value{GDBN}) sends @var{command}s, and the target (the
14452 debugging stub incorporated in your program) sends a @var{response}. In
14453 the case of step and continue @var{command}s, the response is only sent
14454 when the operation has completed (the target has again stopped).
14456 @var{packet-data} consists of a sequence of characters with the
14457 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
14460 Fields within the packet should be separated using @samp{,} @samp{;} or
14461 @cindex remote protocol, field separator
14462 @samp{:}. Except where otherwise noted all numbers are represented in
14463 @sc{hex} with leading zeros suppressed.
14465 Implementors should note that prior to @value{GDBN} 5.0, the character
14466 @samp{:} could not appear as the third character in a packet (as it
14467 would potentially conflict with the @var{sequence-id}).
14469 Response @var{data} can be run-length encoded to save space. A @samp{*}
14470 means that the next character is an @sc{ascii} encoding giving a repeat count
14471 which stands for that many repetitions of the character preceding the
14472 @samp{*}. The encoding is @code{n+29}, yielding a printable character
14473 where @code{n >=3} (which is where rle starts to win). The printable
14474 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
14475 value greater than 126 should not be used.
14477 Some remote systems have used a different run-length encoding mechanism
14478 loosely refered to as the cisco encoding. Following the @samp{*}
14479 character are two hex digits that indicate the size of the packet.
14486 means the same as "0000".
14488 The error response returned for some packets includes a two character
14489 error number. That number is not well defined.
14491 For any @var{command} not supported by the stub, an empty response
14492 (@samp{$#00}) should be returned. That way it is possible to extend the
14493 protocol. A newer @value{GDBN} can tell if a packet is supported based
14496 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
14497 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
14503 The following table provides a complete list of all currently defined
14504 @var{command}s and their corresponding response @var{data}.
14508 @item @code{!} --- extended mode
14509 @cindex @code{!} packet
14511 Enable extended mode. In extended mode, the remote server is made
14512 persistent. The @samp{R} packet is used to restart the program being
14518 The remote target both supports and has enabled extended mode.
14521 @item @code{?} --- last signal
14522 @cindex @code{?} packet
14524 Indicate the reason the target halted. The reply is the same as for
14528 @xref{Stop Reply Packets}, for the reply specifications.
14530 @item @code{a} --- reserved
14532 Reserved for future use.
14534 @item @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,@dots{}} --- set program arguments @strong{(reserved)}
14535 @cindex @code{A} packet
14537 Initialized @samp{argv[]} array passed into program. @var{arglen}
14538 specifies the number of bytes in the hex encoded byte stream @var{arg}.
14539 See @code{gdbserver} for more details.
14547 @item @code{b}@var{baud} --- set baud @strong{(deprecated)}
14548 @cindex @code{b} packet
14550 Change the serial line speed to @var{baud}.
14552 JTC: @emph{When does the transport layer state change? When it's
14553 received, or after the ACK is transmitted. In either case, there are
14554 problems if the command or the acknowledgment packet is dropped.}
14556 Stan: @emph{If people really wanted to add something like this, and get
14557 it working for the first time, they ought to modify ser-unix.c to send
14558 some kind of out-of-band message to a specially-setup stub and have the
14559 switch happen "in between" packets, so that from remote protocol's point
14560 of view, nothing actually happened.}
14562 @item @code{B}@var{addr},@var{mode} --- set breakpoint @strong{(deprecated)}
14563 @cindex @code{B} packet
14565 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
14566 breakpoint at @var{addr}.
14568 This packet has been replaced by the @samp{Z} and @samp{z} packets
14569 (@pxref{insert breakpoint or watchpoint packet}).
14571 @item @code{c}@var{addr} --- continue
14572 @cindex @code{c} packet
14574 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14578 @xref{Stop Reply Packets}, for the reply specifications.
14580 @item @code{C}@var{sig}@code{;}@var{addr} --- continue with signal
14581 @cindex @code{C} packet
14583 Continue with signal @var{sig} (hex signal number). If
14584 @code{;}@var{addr} is omitted, resume at same address.
14587 @xref{Stop Reply Packets}, for the reply specifications.
14589 @item @code{d} --- toggle debug @strong{(deprecated)}
14590 @cindex @code{d} packet
14594 @item @code{D} --- detach
14595 @cindex @code{D} packet
14597 Detach @value{GDBN} from the remote system. Sent to the remote target
14598 before @value{GDBN} disconnects.
14602 @item @emph{no response}
14603 @value{GDBN} does not check for any response after sending this packet.
14606 @item @code{e} --- reserved
14608 Reserved for future use.
14610 @item @code{E} --- reserved
14612 Reserved for future use.
14614 @item @code{f} --- reserved
14616 Reserved for future use.
14618 @item @code{F} --- reserved
14620 Reserved for future use.
14622 @item @code{g} --- read registers
14623 @anchor{read registers packet}
14624 @cindex @code{g} packet
14626 Read general registers.
14630 @item @var{XX@dots{}}
14631 Each byte of register data is described by two hex digits. The bytes
14632 with the register are transmitted in target byte order. The size of
14633 each register and their position within the @samp{g} @var{packet} are
14634 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE}
14635 and @var{REGISTER_NAME} macros. The specification of several standard
14636 @code{g} packets is specified below.
14641 @item @code{G}@var{XX@dots{}} --- write regs
14642 @cindex @code{G} packet
14644 @xref{read registers packet}, for a description of the @var{XX@dots{}}
14655 @item @code{h} --- reserved
14657 Reserved for future use.
14659 @item @code{H}@var{c}@var{t@dots{}} --- set thread
14660 @cindex @code{H} packet
14662 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
14663 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
14664 should be @samp{c} for step and continue operations, @samp{g} for other
14665 operations. The thread designator @var{t@dots{}} may be -1, meaning all
14666 the threads, a thread number, or zero which means pick any thread.
14677 @c 'H': How restrictive (or permissive) is the thread model. If a
14678 @c thread is selected and stopped, are other threads allowed
14679 @c to continue to execute? As I mentioned above, I think the
14680 @c semantics of each command when a thread is selected must be
14681 @c described. For example:
14683 @c 'g': If the stub supports threads and a specific thread is
14684 @c selected, returns the register block from that thread;
14685 @c otherwise returns current registers.
14687 @c 'G' If the stub supports threads and a specific thread is
14688 @c selected, sets the registers of the register block of
14689 @c that thread; otherwise sets current registers.
14691 @item @code{i}@var{addr}@code{,}@var{nnn} --- cycle step @strong{(draft)}
14692 @anchor{cycle step packet}
14693 @cindex @code{i} packet
14695 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
14696 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
14697 step starting at that address.
14699 @item @code{I} --- signal then cycle step @strong{(reserved)}
14700 @cindex @code{I} packet
14702 @xref{step with signal packet}. @xref{cycle step packet}.
14704 @item @code{j} --- reserved
14706 Reserved for future use.
14708 @item @code{J} --- reserved
14710 Reserved for future use.
14712 @item @code{k} --- kill request
14713 @cindex @code{k} packet
14715 FIXME: @emph{There is no description of how to operate when a specific
14716 thread context has been selected (i.e.@: does 'k' kill only that
14719 @item @code{K} --- reserved
14721 Reserved for future use.
14723 @item @code{l} --- reserved
14725 Reserved for future use.
14727 @item @code{L} --- reserved
14729 Reserved for future use.
14731 @item @code{m}@var{addr}@code{,}@var{length} --- read memory
14732 @cindex @code{m} packet
14734 Read @var{length} bytes of memory starting at address @var{addr}.
14735 Neither @value{GDBN} nor the stub assume that sized memory transfers are
14736 assumed using word alligned accesses. FIXME: @emph{A word aligned memory
14737 transfer mechanism is needed.}
14741 @item @var{XX@dots{}}
14742 @var{XX@dots{}} is mem contents. Can be fewer bytes than requested if able
14743 to read only part of the data. Neither @value{GDBN} nor the stub assume
14744 that sized memory transfers are assumed using word alligned
14745 accesses. FIXME: @emph{A word aligned memory transfer mechanism is
14751 @item @code{M}@var{addr},@var{length}@code{:}@var{XX@dots{}} --- write mem
14752 @cindex @code{M} packet
14754 Write @var{length} bytes of memory starting at address @var{addr}.
14755 @var{XX@dots{}} is the data.
14762 for an error (this includes the case where only part of the data was
14766 @item @code{n} --- reserved
14768 Reserved for future use.
14770 @item @code{N} --- reserved
14772 Reserved for future use.
14774 @item @code{o} --- reserved
14776 Reserved for future use.
14778 @item @code{O} --- reserved
14780 Reserved for future use.
14782 @item @code{p}@var{n@dots{}} --- read reg @strong{(reserved)}
14783 @cindex @code{p} packet
14785 @xref{write register packet}.
14789 @item @var{r@dots{}.}
14790 The hex encoded value of the register in target byte order.
14793 @item @code{P}@var{n@dots{}}@code{=}@var{r@dots{}} --- write register
14794 @anchor{write register packet}
14795 @cindex @code{P} packet
14797 Write register @var{n@dots{}} with value @var{r@dots{}}, which contains two hex
14798 digits for each byte in the register (target byte order).
14808 @item @code{q}@var{query} --- general query
14809 @anchor{general query packet}
14810 @cindex @code{q} packet
14812 Request info about @var{query}. In general @value{GDBN} queries have a
14813 leading upper case letter. Custom vendor queries should use a company
14814 prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may optionally
14815 be followed by a @samp{,} or @samp{;} separated list. Stubs must ensure
14816 that they match the full @var{query} name.
14820 @item @var{XX@dots{}}
14821 Hex encoded data from query. The reply can not be empty.
14825 Indicating an unrecognized @var{query}.
14828 @item @code{Q}@var{var}@code{=}@var{val} --- general set
14829 @cindex @code{Q} packet
14831 Set value of @var{var} to @var{val}.
14833 @xref{general query packet}, for a discussion of naming conventions.
14835 @item @code{r} --- reset @strong{(deprecated)}
14836 @cindex @code{r} packet
14838 Reset the entire system.
14840 @item @code{R}@var{XX} --- remote restart
14841 @cindex @code{R} packet
14843 Restart the program being debugged. @var{XX}, while needed, is ignored.
14844 This packet is only available in extended mode.
14848 @item @emph{no reply}
14849 The @samp{R} packet has no reply.
14852 @item @code{s}@var{addr} --- step
14853 @cindex @code{s} packet
14855 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14859 @xref{Stop Reply Packets}, for the reply specifications.
14861 @item @code{S}@var{sig}@code{;}@var{addr} --- step with signal
14862 @anchor{step with signal packet}
14863 @cindex @code{S} packet
14865 Like @samp{C} but step not continue.
14868 @xref{Stop Reply Packets}, for the reply specifications.
14870 @item @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM} --- search
14871 @cindex @code{t} packet
14873 Search backwards starting at address @var{addr} for a match with pattern
14874 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
14875 @var{addr} must be at least 3 digits.
14877 @item @code{T}@var{XX} --- thread alive
14878 @cindex @code{T} packet
14880 Find out if the thread XX is alive.
14885 thread is still alive
14890 @item @code{u} --- reserved
14892 Reserved for future use.
14894 @item @code{U} --- reserved
14896 Reserved for future use.
14898 @item @code{v} --- reserved
14900 Reserved for future use.
14902 @item @code{V} --- reserved
14904 Reserved for future use.
14906 @item @code{w} --- reserved
14908 Reserved for future use.
14910 @item @code{W} --- reserved
14912 Reserved for future use.
14914 @item @code{x} --- reserved
14916 Reserved for future use.
14918 @item @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX@dots{}} --- write mem (binary)
14919 @cindex @code{X} packet
14921 @var{addr} is address, @var{length} is number of bytes, @var{XX@dots{}}
14922 is binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
14923 escaped using @code{0x7d}.
14933 @item @code{y} --- reserved
14935 Reserved for future use.
14937 @item @code{Y} reserved
14939 Reserved for future use.
14941 @item @code{z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- remove breakpoint or watchpoint @strong{(draft)}
14942 @itemx @code{Z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- insert breakpoint or watchpoint @strong{(draft)}
14943 @anchor{insert breakpoint or watchpoint packet}
14944 @cindex @code{z} packet
14945 @cindex @code{Z} packets
14947 Insert (@code{Z}) or remove (@code{z}) a @var{type} breakpoint or
14948 watchpoint starting at address @var{address} and covering the next
14949 @var{length} bytes.
14951 Each breakpoint and watchpoint packet @var{type} is documented
14954 @emph{Implementation notes: A remote target shall return @samp{} for an
14955 unrecognized breakpoint or watchpoint packet @var{type}. A remote
14956 target shall support either both or neither of a given
14957 @code{Z}@var{type}@dots{} and @code{z}@var{type}@dots{} packet pair. To
14958 avoid potential problems with duplicate packets, the operations should
14959 be implemented in an idempotent way.}
14961 @item @code{z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- remove memory breakpoint @strong{(draft)}
14962 @item @code{Z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- insert memory breakpoint @strong{(draft)}
14963 @cindex @code{z0} packet
14964 @cindex @code{Z0} packet
14966 Insert (@code{Z0}) or remove (@code{z0}) a memory breakpoint at address
14967 @code{addr} of size @code{length}.
14969 A memory breakpoint is implemented by replacing the instruction at
14970 @var{addr} with a software breakpoint or trap instruction. The
14971 @code{length} is used by targets that indicates the size of the
14972 breakpoint (in bytes) that should be inserted (e.g., the @sc{arm} and
14973 @sc{mips} can insert either a 2 or 4 byte breakpoint).
14975 @emph{Implementation note: It is possible for a target to copy or move
14976 code that contains memory breakpoints (e.g., when implementing
14977 overlays). The behavior of this packet, in the presence of such a
14978 target, is not defined.}
14990 @item @code{z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- remove hardware breakpoint @strong{(draft)}
14991 @item @code{Z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- insert hardware breakpoint @strong{(draft)}
14992 @cindex @code{z1} packet
14993 @cindex @code{Z1} packet
14995 Insert (@code{Z1}) or remove (@code{z1}) a hardware breakpoint at
14996 address @code{addr} of size @code{length}.
14998 A hardware breakpoint is implemented using a mechanism that is not
14999 dependant on being able to modify the target's memory.
15001 @emph{Implementation note: A hardware breakpoint is not affected by code
15014 @item @code{z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- remove write watchpoint @strong{(draft)}
15015 @item @code{Z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- insert write watchpoint @strong{(draft)}
15016 @cindex @code{z2} packet
15017 @cindex @code{Z2} packet
15019 Insert (@code{Z2}) or remove (@code{z2}) a write watchpoint.
15031 @item @code{z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- remove read watchpoint @strong{(draft)}
15032 @item @code{Z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- insert read watchpoint @strong{(draft)}
15033 @cindex @code{z3} packet
15034 @cindex @code{Z3} packet
15036 Insert (@code{Z3}) or remove (@code{z3}) a write watchpoint.
15048 @item @code{z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- remove read watchpoint @strong{(draft)}
15049 @item @code{Z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- insert read watchpoint @strong{(draft)}
15050 @cindex @code{z4} packet
15051 @cindex @code{Z4} packet
15053 Insert (@code{Z4}) or remove (@code{z4}) an access watchpoint.
15067 @node Stop Reply Packets
15068 @section Stop Reply Packets
15069 @cindex stop reply packets
15071 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
15072 receive any of the below as a reply. In the case of the @samp{C},
15073 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
15074 when the target halts. In the below the exact meaning of @samp{signal
15075 number} is poorly defined. In general one of the UNIX signal numbering
15076 conventions is used.
15081 @var{AA} is the signal number
15083 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
15084 @cindex @code{T} packet reply
15086 @var{AA} = two hex digit signal number; @var{n...} = register number
15087 (hex), @var{r...} = target byte ordered register contents, size defined
15088 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
15089 thread process ID, this is a hex integer; @var{n...} = (@samp{watch} |
15090 @samp{rwatch} | @samp{awatch}, @var{r...} = data address, this is a hex
15091 integer; @var{n...} = other string not starting with valid hex digit.
15092 @value{GDBN} should ignore this @var{n...}, @var{r...} pair and go on
15093 to the next. This way we can extend the protocol.
15097 The process exited, and @var{AA} is the exit status. This is only
15098 applicable to certain targets.
15102 The process terminated with signal @var{AA}.
15104 @item N@var{AA};@var{t@dots{}};@var{d@dots{}};@var{b@dots{}} @strong{(obsolete)}
15106 @var{AA} = signal number; @var{t@dots{}} = address of symbol
15107 @code{_start}; @var{d@dots{}} = base of data section; @var{b@dots{}} =
15108 base of bss section. @emph{Note: only used by Cisco Systems targets.
15109 The difference between this reply and the @samp{qOffsets} query is that
15110 the @samp{N} packet may arrive spontaneously whereas the @samp{qOffsets}
15111 is a query initiated by the host debugger.}
15113 @item O@var{XX@dots{}}
15115 @var{XX@dots{}} is hex encoding of @sc{ascii} data. This can happen at
15116 any time while the program is running and the debugger should continue
15117 to wait for @samp{W}, @samp{T}, etc.
15121 @node General Query Packets
15122 @section General Query Packets
15124 The following set and query packets have already been defined.
15128 @item @code{q}@code{C} --- current thread
15130 Return the current thread id.
15134 @item @code{QC}@var{pid}
15135 Where @var{pid} is a HEX encoded 16 bit process id.
15137 Any other reply implies the old pid.
15140 @item @code{q}@code{fThreadInfo} -- all thread ids
15142 @code{q}@code{sThreadInfo}
15144 Obtain a list of active thread ids from the target (OS). Since there
15145 may be too many active threads to fit into one reply packet, this query
15146 works iteratively: it may require more than one query/reply sequence to
15147 obtain the entire list of threads. The first query of the sequence will
15148 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
15149 sequence will be the @code{qs}@code{ThreadInfo} query.
15151 NOTE: replaces the @code{qL} query (see below).
15155 @item @code{m}@var{id}
15157 @item @code{m}@var{id},@var{id}@dots{}
15158 a comma-separated list of thread ids
15160 (lower case 'el') denotes end of list.
15163 In response to each query, the target will reply with a list of one or
15164 more thread ids, in big-endian hex, separated by commas. @value{GDBN}
15165 will respond to each reply with a request for more thread ids (using the
15166 @code{qs} form of the query), until the target responds with @code{l}
15167 (lower-case el, for @code{'last'}).
15169 @item @code{q}@code{ThreadExtraInfo}@code{,}@var{id} --- extra thread info
15171 Where @var{id} is a thread-id in big-endian hex. Obtain a printable
15172 string description of a thread's attributes from the target OS. This
15173 string may contain anything that the target OS thinks is interesting for
15174 @value{GDBN} to tell the user about the thread. The string is displayed
15175 in @value{GDBN}'s @samp{info threads} display. Some examples of
15176 possible thread extra info strings are ``Runnable'', or ``Blocked on
15181 @item @var{XX@dots{}}
15182 Where @var{XX@dots{}} is a hex encoding of @sc{ascii} data, comprising
15183 the printable string containing the extra information about the thread's
15187 @item @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread} --- query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
15189 Obtain thread information from RTOS. Where: @var{startflag} (one hex
15190 digit) is one to indicate the first query and zero to indicate a
15191 subsequent query; @var{threadcount} (two hex digits) is the maximum
15192 number of threads the response packet can contain; and @var{nextthread}
15193 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
15194 returned in the response as @var{argthread}.
15196 NOTE: this query is replaced by the @code{q}@code{fThreadInfo} query
15201 @item @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread@dots{}}
15202 Where: @var{count} (two hex digits) is the number of threads being
15203 returned; @var{done} (one hex digit) is zero to indicate more threads
15204 and one indicates no further threads; @var{argthreadid} (eight hex
15205 digits) is @var{nextthread} from the request packet; @var{thread@dots{}}
15206 is a sequence of thread IDs from the target. @var{threadid} (eight hex
15207 digits). See @code{remote.c:parse_threadlist_response()}.
15210 @item @code{q}@code{CRC:}@var{addr}@code{,}@var{length} --- compute CRC of memory block
15214 @item @code{E}@var{NN}
15215 An error (such as memory fault)
15216 @item @code{C}@var{CRC32}
15217 A 32 bit cyclic redundancy check of the specified memory region.
15220 @item @code{q}@code{Offsets} --- query sect offs
15222 Get section offsets that the target used when re-locating the downloaded
15223 image. @emph{Note: while a @code{Bss} offset is included in the
15224 response, @value{GDBN} ignores this and instead applies the @code{Data}
15225 offset to the @code{Bss} section.}
15229 @item @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
15232 @item @code{q}@code{P}@var{mode}@var{threadid} --- thread info request
15234 Returns information on @var{threadid}. Where: @var{mode} is a hex
15235 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
15242 See @code{remote.c:remote_unpack_thread_info_response()}.
15244 @item @code{q}@code{Rcmd,}@var{command} --- remote command
15246 @var{command} (hex encoded) is passed to the local interpreter for
15247 execution. Invalid commands should be reported using the output string.
15248 Before the final result packet, the target may also respond with a
15249 number of intermediate @code{O}@var{output} console output packets.
15250 @emph{Implementors should note that providing access to a stubs's
15251 interpreter may have security implications}.
15256 A command response with no output.
15258 A command response with the hex encoded output string @var{OUTPUT}.
15259 @item @code{E}@var{NN}
15260 Indicate a badly formed request.
15262 When @samp{q}@samp{Rcmd} is not recognized.
15265 @item @code{qSymbol::} --- symbol lookup
15267 Notify the target that @value{GDBN} is prepared to serve symbol lookup
15268 requests. Accept requests from the target for the values of symbols.
15273 The target does not need to look up any (more) symbols.
15274 @item @code{qSymbol:}@var{sym_name}
15275 The target requests the value of symbol @var{sym_name} (hex encoded).
15276 @value{GDBN} may provide the value by using the
15277 @code{qSymbol:}@var{sym_value}:@var{sym_name} message, described below.
15280 @item @code{qSymbol:}@var{sym_value}:@var{sym_name} --- symbol value
15282 Set the value of @var{sym_name} to @var{sym_value}.
15284 @var{sym_name} (hex encoded) is the name of a symbol whose value the
15285 target has previously requested.
15287 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
15288 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
15294 The target does not need to look up any (more) symbols.
15295 @item @code{qSymbol:}@var{sym_name}
15296 The target requests the value of a new symbol @var{sym_name} (hex
15297 encoded). @value{GDBN} will continue to supply the values of symbols
15298 (if available), until the target ceases to request them.
15303 @node Register Packet Format
15304 @section Register Packet Format
15306 The following @samp{g}/@samp{G} packets have previously been defined.
15307 In the below, some thirty-two bit registers are transferred as
15308 sixty-four bits. Those registers should be zero/sign extended (which?)
15309 to fill the space allocated. Register bytes are transfered in target
15310 byte order. The two nibbles within a register byte are transfered
15311 most-significant - least-significant.
15317 All registers are transfered as thirty-two bit quantities in the order:
15318 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
15319 registers; fsr; fir; fp.
15323 All registers are transfered as sixty-four bit quantities (including
15324 thirty-two bit registers such as @code{sr}). The ordering is the same
15332 Example sequence of a target being re-started. Notice how the restart
15333 does not get any direct output:
15338 @emph{target restarts}
15341 <- @code{T001:1234123412341234}
15345 Example sequence of a target being stepped by a single instruction:
15348 -> @code{G1445@dots{}}
15353 <- @code{T001:1234123412341234}
15357 <- @code{1455@dots{}}
15371 % I think something like @colophon should be in texinfo. In the
15373 \long\def\colophon{\hbox to0pt{}\vfill
15374 \centerline{The body of this manual is set in}
15375 \centerline{\fontname\tenrm,}
15376 \centerline{with headings in {\bf\fontname\tenbf}}
15377 \centerline{and examples in {\tt\fontname\tentt}.}
15378 \centerline{{\it\fontname\tenit\/},}
15379 \centerline{{\bf\fontname\tenbf}, and}
15380 \centerline{{\sl\fontname\tensl\/}}
15381 \centerline{are used for emphasis.}\vfill}
15383 % Blame: doc@cygnus.com, 1991.