1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002, 2003
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
36 @c !!set GDB edit command default editor
39 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
41 @c This is a dir.info fragment to support semi-automated addition of
42 @c manuals to an info tree.
43 @dircategory Programming & development tools.
45 * Gdb: (gdb). The @sc{gnu} debugger.
49 This file documents the @sc{gnu} debugger @value{GDBN}.
52 This is the @value{EDITION} Edition, @value{DATE},
53 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
54 for @value{GDBN} Version @value{GDBVN}.
56 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,@*
57 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
59 Permission is granted to copy, distribute and/or modify this document
60 under the terms of the GNU Free Documentation License, Version 1.1 or
61 any later version published by the Free Software Foundation; with the
62 Invariant Sections being ``Free Software'' and ``Free Software Needs
63 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
64 and with the Back-Cover Texts as in (a) below.
66 (a) The Free Software Foundation's Back-Cover Text is: ``You have
67 freedom to copy and modify this GNU Manual, like GNU software. Copies
68 published by the Free Software Foundation raise funds for GNU
73 @title Debugging with @value{GDBN}
74 @subtitle The @sc{gnu} Source-Level Debugger
76 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
77 @subtitle @value{DATE}
78 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
82 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
83 \hfill {\it Debugging with @value{GDBN}}\par
84 \hfill \TeX{}info \texinfoversion\par
88 @vskip 0pt plus 1filll
89 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
90 1996, 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
92 Published by the Free Software Foundation @*
93 59 Temple Place - Suite 330, @*
94 Boston, MA 02111-1307 USA @*
97 Permission is granted to copy, distribute and/or modify this document
98 under the terms of the GNU Free Documentation License, Version 1.1 or
99 any later version published by the Free Software Foundation; with the
100 Invariant Sections being ``Free Software'' and ``Free Software Needs
101 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
102 and with the Back-Cover Texts as in (a) below.
104 (a) The Free Software Foundation's Back-Cover Text is: ``You have
105 freedom to copy and modify this GNU Manual, like GNU software. Copies
106 published by the Free Software Foundation raise funds for GNU
112 @node Top, Summary, (dir), (dir)
114 @top Debugging with @value{GDBN}
116 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
118 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
121 Copyright (C) 1988-2003 Free Software Foundation, Inc.
124 * Summary:: Summary of @value{GDBN}
125 * Sample Session:: A sample @value{GDBN} session
127 * Invocation:: Getting in and out of @value{GDBN}
128 * Commands:: @value{GDBN} commands
129 * Running:: Running programs under @value{GDBN}
130 * Stopping:: Stopping and continuing
131 * Stack:: Examining the stack
132 * Source:: Examining source files
133 * Data:: Examining data
134 * Macros:: Preprocessor Macros
135 * Tracepoints:: Debugging remote targets non-intrusively
136 * Overlays:: Debugging programs that use overlays
138 * Languages:: Using @value{GDBN} with different languages
140 * Symbols:: Examining the symbol table
141 * Altering:: Altering execution
142 * GDB Files:: @value{GDBN} files
143 * Targets:: Specifying a debugging target
144 * Remote Debugging:: Debugging remote programs
145 * Configurations:: Configuration-specific information
146 * Controlling GDB:: Controlling @value{GDBN}
147 * Sequences:: Canned sequences of commands
148 * TUI:: @value{GDBN} Text User Interface
149 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
150 * Annotations:: @value{GDBN}'s annotation interface.
151 * GDB/MI:: @value{GDBN}'s Machine Interface.
153 * GDB Bugs:: Reporting bugs in @value{GDBN}
154 * Formatting Documentation:: How to format and print @value{GDBN} documentation
156 * Command Line Editing:: Command Line Editing
157 * Using History Interactively:: Using History Interactively
158 * Installing GDB:: Installing GDB
159 * Maintenance Commands:: Maintenance Commands
160 * Remote Protocol:: GDB Remote Serial Protocol
161 * Copying:: GNU General Public License says
162 how you can copy and share GDB
163 * GNU Free Documentation License:: The license for this documentation
172 @unnumbered Summary of @value{GDBN}
174 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
175 going on ``inside'' another program while it executes---or what another
176 program was doing at the moment it crashed.
178 @value{GDBN} can do four main kinds of things (plus other things in support of
179 these) to help you catch bugs in the act:
183 Start your program, specifying anything that might affect its behavior.
186 Make your program stop on specified conditions.
189 Examine what has happened, when your program has stopped.
192 Change things in your program, so you can experiment with correcting the
193 effects of one bug and go on to learn about another.
196 You can use @value{GDBN} to debug programs written in C and C++.
197 For more information, see @ref{Support,,Supported languages}.
198 For more information, see @ref{C,,C and C++}.
201 Support for Modula-2 is partial. For information on Modula-2, see
202 @ref{Modula-2,,Modula-2}.
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.
394 Marko Mlinar contributed OpenRISC 1000 support.
396 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
398 Rich Schaefer and Peter Schauer helped with support of SunOS shared
401 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
402 about several machine instruction sets.
404 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
405 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
406 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
407 and RDI targets, respectively.
409 Brian Fox is the author of the readline libraries providing
410 command-line editing and command history.
412 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
413 Modula-2 support, and contributed the Languages chapter of this manual.
415 Fred Fish wrote most of the support for Unix System Vr4.
416 He also enhanced the command-completion support to cover C@t{++} overloaded
419 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
422 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
424 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
426 Toshiba sponsored the support for the TX39 Mips processor.
428 Matsushita sponsored the support for the MN10200 and MN10300 processors.
430 Fujitsu sponsored the support for SPARClite and FR30 processors.
432 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
435 Michael Snyder added support for tracepoints.
437 Stu Grossman wrote gdbserver.
439 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
440 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
442 The following people at the Hewlett-Packard Company contributed
443 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
444 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
445 compiler, and the terminal user interface: Ben Krepp, Richard Title,
446 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
447 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
448 information in this manual.
450 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
451 Robert Hoehne made significant contributions to the DJGPP port.
453 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
454 development since 1991. Cygnus engineers who have worked on @value{GDBN}
455 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
456 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
457 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
458 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
459 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
460 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
461 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
462 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
463 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
464 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
465 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
466 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
467 Zuhn have made contributions both large and small.
469 Jim Blandy added support for preprocessor macros, while working for Red
473 @chapter A Sample @value{GDBN} Session
475 You can use this manual at your leisure to read all about @value{GDBN}.
476 However, a handful of commands are enough to get started using the
477 debugger. This chapter illustrates those commands.
480 In this sample session, we emphasize user input like this: @b{input},
481 to make it easier to pick out from the surrounding output.
484 @c FIXME: this example may not be appropriate for some configs, where
485 @c FIXME...primary interest is in remote use.
487 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
488 processor) exhibits the following bug: sometimes, when we change its
489 quote strings from the default, the commands used to capture one macro
490 definition within another stop working. In the following short @code{m4}
491 session, we define a macro @code{foo} which expands to @code{0000}; we
492 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
493 same thing. However, when we change the open quote string to
494 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
495 procedure fails to define a new synonym @code{baz}:
504 @b{define(bar,defn(`foo'))}
508 @b{changequote(<QUOTE>,<UNQUOTE>)}
510 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
513 m4: End of input: 0: fatal error: EOF in string
517 Let us use @value{GDBN} to try to see what is going on.
520 $ @b{@value{GDBP} m4}
521 @c FIXME: this falsifies the exact text played out, to permit smallbook
522 @c FIXME... format to come out better.
523 @value{GDBN} is free software and you are welcome to distribute copies
524 of it under certain conditions; type "show copying" to see
526 There is absolutely no warranty for @value{GDBN}; type "show warranty"
529 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
534 @value{GDBN} reads only enough symbol data to know where to find the
535 rest when needed; as a result, the first prompt comes up very quickly.
536 We now tell @value{GDBN} to use a narrower display width than usual, so
537 that examples fit in this manual.
540 (@value{GDBP}) @b{set width 70}
544 We need to see how the @code{m4} built-in @code{changequote} works.
545 Having looked at the source, we know the relevant subroutine is
546 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
547 @code{break} command.
550 (@value{GDBP}) @b{break m4_changequote}
551 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
555 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
556 control; as long as control does not reach the @code{m4_changequote}
557 subroutine, the program runs as usual:
560 (@value{GDBP}) @b{run}
561 Starting program: /work/Editorial/gdb/gnu/m4/m4
569 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
570 suspends execution of @code{m4}, displaying information about the
571 context where it stops.
574 @b{changequote(<QUOTE>,<UNQUOTE>)}
576 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
578 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
582 Now we use the command @code{n} (@code{next}) to advance execution to
583 the next line of the current function.
587 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
592 @code{set_quotes} looks like a promising subroutine. We can go into it
593 by using the command @code{s} (@code{step}) instead of @code{next}.
594 @code{step} goes to the next line to be executed in @emph{any}
595 subroutine, so it steps into @code{set_quotes}.
599 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
601 530 if (lquote != def_lquote)
605 The display that shows the subroutine where @code{m4} is now
606 suspended (and its arguments) is called a stack frame display. It
607 shows a summary of the stack. We can use the @code{backtrace}
608 command (which can also be spelled @code{bt}), to see where we are
609 in the stack as a whole: the @code{backtrace} command displays a
610 stack frame for each active subroutine.
613 (@value{GDBP}) @b{bt}
614 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
616 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
618 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
619 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
621 #4 0x79dc in expand_input () at macro.c:40
622 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
626 We step through a few more lines to see what happens. The first two
627 times, we can use @samp{s}; the next two times we use @code{n} to avoid
628 falling into the @code{xstrdup} subroutine.
632 0x3b5c 532 if (rquote != def_rquote)
634 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
635 def_lquote : xstrdup(lq);
637 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
640 538 len_lquote = strlen(rquote);
644 The last line displayed looks a little odd; we can examine the variables
645 @code{lquote} and @code{rquote} to see if they are in fact the new left
646 and right quotes we specified. We use the command @code{p}
647 (@code{print}) to see their values.
650 (@value{GDBP}) @b{p lquote}
651 $1 = 0x35d40 "<QUOTE>"
652 (@value{GDBP}) @b{p rquote}
653 $2 = 0x35d50 "<UNQUOTE>"
657 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
658 To look at some context, we can display ten lines of source
659 surrounding the current line with the @code{l} (@code{list}) command.
665 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
667 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
670 538 len_lquote = strlen(rquote);
671 539 len_rquote = strlen(lquote);
678 Let us step past the two lines that set @code{len_lquote} and
679 @code{len_rquote}, and then examine the values of those variables.
683 539 len_rquote = strlen(lquote);
686 (@value{GDBP}) @b{p len_lquote}
688 (@value{GDBP}) @b{p len_rquote}
693 That certainly looks wrong, assuming @code{len_lquote} and
694 @code{len_rquote} are meant to be the lengths of @code{lquote} and
695 @code{rquote} respectively. We can set them to better values using
696 the @code{p} command, since it can print the value of
697 any expression---and that expression can include subroutine calls and
701 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
703 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
708 Is that enough to fix the problem of using the new quotes with the
709 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
710 executing with the @code{c} (@code{continue}) command, and then try the
711 example that caused trouble initially:
717 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
724 Success! The new quotes now work just as well as the default ones. The
725 problem seems to have been just the two typos defining the wrong
726 lengths. We allow @code{m4} exit by giving it an EOF as input:
730 Program exited normally.
734 The message @samp{Program exited normally.} is from @value{GDBN}; it
735 indicates @code{m4} has finished executing. We can end our @value{GDBN}
736 session with the @value{GDBN} @code{quit} command.
739 (@value{GDBP}) @b{quit}
743 @chapter Getting In and Out of @value{GDBN}
745 This chapter discusses how to start @value{GDBN}, and how to get out of it.
749 type @samp{@value{GDBP}} to start @value{GDBN}.
751 type @kbd{quit} or @kbd{C-d} to exit.
755 * Invoking GDB:: How to start @value{GDBN}
756 * Quitting GDB:: How to quit @value{GDBN}
757 * Shell Commands:: How to use shell commands inside @value{GDBN}
761 @section Invoking @value{GDBN}
763 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
764 @value{GDBN} reads commands from the terminal until you tell it to exit.
766 You can also run @code{@value{GDBP}} with a variety of arguments and options,
767 to specify more of your debugging environment at the outset.
769 The command-line options described here are designed
770 to cover a variety of situations; in some environments, some of these
771 options may effectively be unavailable.
773 The most usual way to start @value{GDBN} is with one argument,
774 specifying an executable program:
777 @value{GDBP} @var{program}
781 You can also start with both an executable program and a core file
785 @value{GDBP} @var{program} @var{core}
788 You can, instead, specify a process ID as a second argument, if you want
789 to debug a running process:
792 @value{GDBP} @var{program} 1234
796 would attach @value{GDBN} to process @code{1234} (unless you also have a file
797 named @file{1234}; @value{GDBN} does check for a core file first).
799 Taking advantage of the second command-line argument requires a fairly
800 complete operating system; when you use @value{GDBN} as a remote
801 debugger attached to a bare board, there may not be any notion of
802 ``process'', and there is often no way to get a core dump. @value{GDBN}
803 will warn you if it is unable to attach or to read core dumps.
805 You can optionally have @code{@value{GDBP}} pass any arguments after the
806 executable file to the inferior using @code{--args}. This option stops
809 gdb --args gcc -O2 -c foo.c
811 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
812 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
814 You can run @code{@value{GDBP}} without printing the front material, which describes
815 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
822 You can further control how @value{GDBN} starts up by using command-line
823 options. @value{GDBN} itself can remind you of the options available.
833 to display all available options and briefly describe their use
834 (@samp{@value{GDBP} -h} is a shorter equivalent).
836 All options and command line arguments you give are processed
837 in sequential order. The order makes a difference when the
838 @samp{-x} option is used.
842 * File Options:: Choosing files
843 * Mode Options:: Choosing modes
847 @subsection Choosing files
849 When @value{GDBN} starts, it reads any arguments other than options as
850 specifying an executable file and core file (or process ID). This is
851 the same as if the arguments were specified by the @samp{-se} and
852 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
853 first argument that does not have an associated option flag as
854 equivalent to the @samp{-se} option followed by that argument; and the
855 second argument that does not have an associated option flag, if any, as
856 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
857 If the second argument begins with a decimal digit, @value{GDBN} will
858 first attempt to attach to it as a process, and if that fails, attempt
859 to open it as a corefile. If you have a corefile whose name begins with
860 a digit, you can prevent @value{GDBN} from treating it as a pid by
861 prefixing it with @file{./}, eg. @file{./12345}.
863 If @value{GDBN} has not been configured to included core file support,
864 such as for most embedded targets, then it will complain about a second
865 argument and ignore it.
867 Many options have both long and short forms; both are shown in the
868 following list. @value{GDBN} also recognizes the long forms if you truncate
869 them, so long as enough of the option is present to be unambiguous.
870 (If you prefer, you can flag option arguments with @samp{--} rather
871 than @samp{-}, though we illustrate the more usual convention.)
873 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
874 @c way, both those who look for -foo and --foo in the index, will find
878 @item -symbols @var{file}
880 @cindex @code{--symbols}
882 Read symbol table from file @var{file}.
884 @item -exec @var{file}
886 @cindex @code{--exec}
888 Use file @var{file} as the executable file to execute when appropriate,
889 and for examining pure data in conjunction with a core dump.
893 Read symbol table from file @var{file} and use it as the executable
896 @item -core @var{file}
898 @cindex @code{--core}
900 Use file @var{file} as a core dump to examine.
902 @item -c @var{number}
903 @item -pid @var{number}
904 @itemx -p @var{number}
907 Connect to process ID @var{number}, as with the @code{attach} command.
908 If there is no such process, @value{GDBN} will attempt to open a core
909 file named @var{number}.
911 @item -command @var{file}
913 @cindex @code{--command}
915 Execute @value{GDBN} commands from file @var{file}. @xref{Command
916 Files,, Command files}.
918 @item -directory @var{directory}
919 @itemx -d @var{directory}
920 @cindex @code{--directory}
922 Add @var{directory} to the path to search for source files.
926 @cindex @code{--mapped}
928 @emph{Warning: this option depends on operating system facilities that are not
929 supported on all systems.}@*
930 If memory-mapped files are available on your system through the @code{mmap}
931 system call, you can use this option
932 to have @value{GDBN} write the symbols from your
933 program into a reusable file in the current directory. If the program you are debugging is
934 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
935 Future @value{GDBN} debugging sessions notice the presence of this file,
936 and can quickly map in symbol information from it, rather than reading
937 the symbol table from the executable program.
939 The @file{.syms} file is specific to the host machine where @value{GDBN}
940 is run. It holds an exact image of the internal @value{GDBN} symbol
941 table. It cannot be shared across multiple host platforms.
945 @cindex @code{--readnow}
947 Read each symbol file's entire symbol table immediately, rather than
948 the default, which is to read it incrementally as it is needed.
949 This makes startup slower, but makes future operations faster.
953 You typically combine the @code{-mapped} and @code{-readnow} options in
954 order to build a @file{.syms} file that contains complete symbol
955 information. (@xref{Files,,Commands to specify files}, for information
956 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
957 but build a @file{.syms} file for future use is:
960 gdb -batch -nx -mapped -readnow programname
964 @subsection Choosing modes
966 You can run @value{GDBN} in various alternative modes---for example, in
967 batch mode or quiet mode.
974 Do not execute commands found in any initialization files. Normally,
975 @value{GDBN} executes the commands in these files after all the command
976 options and arguments have been processed. @xref{Command Files,,Command
982 @cindex @code{--quiet}
983 @cindex @code{--silent}
985 ``Quiet''. Do not print the introductory and copyright messages. These
986 messages are also suppressed in batch mode.
989 @cindex @code{--batch}
990 Run in batch mode. Exit with status @code{0} after processing all the
991 command files specified with @samp{-x} (and all commands from
992 initialization files, if not inhibited with @samp{-n}). Exit with
993 nonzero status if an error occurs in executing the @value{GDBN} commands
994 in the command files.
996 Batch mode may be useful for running @value{GDBN} as a filter, for
997 example to download and run a program on another computer; in order to
998 make this more useful, the message
1001 Program exited normally.
1005 (which is ordinarily issued whenever a program running under
1006 @value{GDBN} control terminates) is not issued when running in batch
1011 @cindex @code{--nowindows}
1013 ``No windows''. If @value{GDBN} comes with a graphical user interface
1014 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1015 interface. If no GUI is available, this option has no effect.
1019 @cindex @code{--windows}
1021 If @value{GDBN} includes a GUI, then this option requires it to be
1024 @item -cd @var{directory}
1026 Run @value{GDBN} using @var{directory} as its working directory,
1027 instead of the current directory.
1031 @cindex @code{--fullname}
1033 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1034 subprocess. It tells @value{GDBN} to output the full file name and line
1035 number in a standard, recognizable fashion each time a stack frame is
1036 displayed (which includes each time your program stops). This
1037 recognizable format looks like two @samp{\032} characters, followed by
1038 the file name, line number and character position separated by colons,
1039 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1040 @samp{\032} characters as a signal to display the source code for the
1044 @cindex @code{--epoch}
1045 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1046 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1047 routines so as to allow Epoch to display values of expressions in a
1050 @item -annotate @var{level}
1051 @cindex @code{--annotate}
1052 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1053 effect is identical to using @samp{set annotate @var{level}}
1054 (@pxref{Annotations}).
1055 Annotation level controls how much information does @value{GDBN} print
1056 together with its prompt, values of expressions, source lines, and other
1057 types of output. Level 0 is the normal, level 1 is for use when
1058 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1059 maximum annotation suitable for programs that control @value{GDBN}.
1062 @cindex @code{--async}
1063 Use the asynchronous event loop for the command-line interface.
1064 @value{GDBN} processes all events, such as user keyboard input, via a
1065 special event loop. This allows @value{GDBN} to accept and process user
1066 commands in parallel with the debugged process being
1067 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1068 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1069 suspended when the debuggee runs.}, so you don't need to wait for
1070 control to return to @value{GDBN} before you type the next command.
1071 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1072 operation is not yet in place, so @samp{-async} does not work fully
1074 @c FIXME: when the target side of the event loop is done, the above NOTE
1075 @c should be removed.
1077 When the standard input is connected to a terminal device, @value{GDBN}
1078 uses the asynchronous event loop by default, unless disabled by the
1079 @samp{-noasync} option.
1082 @cindex @code{--noasync}
1083 Disable the asynchronous event loop for the command-line interface.
1086 @cindex @code{--args}
1087 Change interpretation of command line so that arguments following the
1088 executable file are passed as command line arguments to the inferior.
1089 This option stops option processing.
1091 @item -baud @var{bps}
1093 @cindex @code{--baud}
1095 Set the line speed (baud rate or bits per second) of any serial
1096 interface used by @value{GDBN} for remote debugging.
1098 @item -tty @var{device}
1099 @itemx -t @var{device}
1100 @cindex @code{--tty}
1102 Run using @var{device} for your program's standard input and output.
1103 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1105 @c resolve the situation of these eventually
1107 @cindex @code{--tui}
1108 Activate the Terminal User Interface when starting.
1109 The Terminal User Interface manages several text windows on the terminal,
1110 showing source, assembly, registers and @value{GDBN} command outputs
1111 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1112 Do not use this option if you run @value{GDBN} from Emacs
1113 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1116 @c @cindex @code{--xdb}
1117 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1118 @c For information, see the file @file{xdb_trans.html}, which is usually
1119 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1122 @item -interpreter @var{interp}
1123 @cindex @code{--interpreter}
1124 Use the interpreter @var{interp} for interface with the controlling
1125 program or device. This option is meant to be set by programs which
1126 communicate with @value{GDBN} using it as a back end.
1128 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1129 @value{GDBN} to use the current @dfn{@sc{gdb/mi} interface}
1130 (@pxref{GDB/MI, , The @sc{gdb/mi} Interface}). The previous @sc{gdb/mi}
1131 interface, included in @value{GDBN} version 5.3, can be selected with
1132 @samp{--interpreter=mi1}. Earlier @sc{gdb/mi} interfaces
1136 @cindex @code{--write}
1137 Open the executable and core files for both reading and writing. This
1138 is equivalent to the @samp{set write on} command inside @value{GDBN}
1142 @cindex @code{--statistics}
1143 This option causes @value{GDBN} to print statistics about time and
1144 memory usage after it completes each command and returns to the prompt.
1147 @cindex @code{--version}
1148 This option causes @value{GDBN} to print its version number and
1149 no-warranty blurb, and exit.
1154 @section Quitting @value{GDBN}
1155 @cindex exiting @value{GDBN}
1156 @cindex leaving @value{GDBN}
1159 @kindex quit @r{[}@var{expression}@r{]}
1160 @kindex q @r{(@code{quit})}
1161 @item quit @r{[}@var{expression}@r{]}
1163 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1164 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1165 do not supply @var{expression}, @value{GDBN} will terminate normally;
1166 otherwise it will terminate using the result of @var{expression} as the
1171 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1172 terminates the action of any @value{GDBN} command that is in progress and
1173 returns to @value{GDBN} command level. It is safe to type the interrupt
1174 character at any time because @value{GDBN} does not allow it to take effect
1175 until a time when it is safe.
1177 If you have been using @value{GDBN} to control an attached process or
1178 device, you can release it with the @code{detach} command
1179 (@pxref{Attach, ,Debugging an already-running process}).
1181 @node Shell Commands
1182 @section Shell commands
1184 If you need to execute occasional shell commands during your
1185 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1186 just use the @code{shell} command.
1190 @cindex shell escape
1191 @item shell @var{command string}
1192 Invoke a standard shell to execute @var{command string}.
1193 If it exists, the environment variable @code{SHELL} determines which
1194 shell to run. Otherwise @value{GDBN} uses the default shell
1195 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1198 The utility @code{make} is often needed in development environments.
1199 You do not have to use the @code{shell} command for this purpose in
1204 @cindex calling make
1205 @item make @var{make-args}
1206 Execute the @code{make} program with the specified
1207 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1211 @chapter @value{GDBN} Commands
1213 You can abbreviate a @value{GDBN} command to the first few letters of the command
1214 name, if that abbreviation is unambiguous; and you can repeat certain
1215 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1216 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1217 show you the alternatives available, if there is more than one possibility).
1220 * Command Syntax:: How to give commands to @value{GDBN}
1221 * Completion:: Command completion
1222 * Help:: How to ask @value{GDBN} for help
1225 @node Command Syntax
1226 @section Command syntax
1228 A @value{GDBN} command is a single line of input. There is no limit on
1229 how long it can be. It starts with a command name, which is followed by
1230 arguments whose meaning depends on the command name. For example, the
1231 command @code{step} accepts an argument which is the number of times to
1232 step, as in @samp{step 5}. You can also use the @code{step} command
1233 with no arguments. Some commands do not allow any arguments.
1235 @cindex abbreviation
1236 @value{GDBN} command names may always be truncated if that abbreviation is
1237 unambiguous. Other possible command abbreviations are listed in the
1238 documentation for individual commands. In some cases, even ambiguous
1239 abbreviations are allowed; for example, @code{s} is specially defined as
1240 equivalent to @code{step} even though there are other commands whose
1241 names start with @code{s}. You can test abbreviations by using them as
1242 arguments to the @code{help} command.
1244 @cindex repeating commands
1245 @kindex RET @r{(repeat last command)}
1246 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1247 repeat the previous command. Certain commands (for example, @code{run})
1248 will not repeat this way; these are commands whose unintentional
1249 repetition might cause trouble and which you are unlikely to want to
1252 The @code{list} and @code{x} commands, when you repeat them with
1253 @key{RET}, construct new arguments rather than repeating
1254 exactly as typed. This permits easy scanning of source or memory.
1256 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1257 output, in a way similar to the common utility @code{more}
1258 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1259 @key{RET} too many in this situation, @value{GDBN} disables command
1260 repetition after any command that generates this sort of display.
1262 @kindex # @r{(a comment)}
1264 Any text from a @kbd{#} to the end of the line is a comment; it does
1265 nothing. This is useful mainly in command files (@pxref{Command
1266 Files,,Command files}).
1268 @cindex repeating command sequences
1269 @kindex C-o @r{(operate-and-get-next)}
1270 The @kbd{C-o} binding is useful for repeating a complex sequence of
1271 commands. This command accepts the current line, like @kbd{RET}, and
1272 then fetches the next line relative to the current line from the history
1276 @section Command completion
1279 @cindex word completion
1280 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1281 only one possibility; it can also show you what the valid possibilities
1282 are for the next word in a command, at any time. This works for @value{GDBN}
1283 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1285 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1286 of a word. If there is only one possibility, @value{GDBN} fills in the
1287 word, and waits for you to finish the command (or press @key{RET} to
1288 enter it). For example, if you type
1290 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1291 @c complete accuracy in these examples; space introduced for clarity.
1292 @c If texinfo enhancements make it unnecessary, it would be nice to
1293 @c replace " @key" by "@key" in the following...
1295 (@value{GDBP}) info bre @key{TAB}
1299 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1300 the only @code{info} subcommand beginning with @samp{bre}:
1303 (@value{GDBP}) info breakpoints
1307 You can either press @key{RET} at this point, to run the @code{info
1308 breakpoints} command, or backspace and enter something else, if
1309 @samp{breakpoints} does not look like the command you expected. (If you
1310 were sure you wanted @code{info breakpoints} in the first place, you
1311 might as well just type @key{RET} immediately after @samp{info bre},
1312 to exploit command abbreviations rather than command completion).
1314 If there is more than one possibility for the next word when you press
1315 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1316 characters and try again, or just press @key{TAB} a second time;
1317 @value{GDBN} displays all the possible completions for that word. For
1318 example, you might want to set a breakpoint on a subroutine whose name
1319 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1320 just sounds the bell. Typing @key{TAB} again displays all the
1321 function names in your program that begin with those characters, for
1325 (@value{GDBP}) b make_ @key{TAB}
1326 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1327 make_a_section_from_file make_environ
1328 make_abs_section make_function_type
1329 make_blockvector make_pointer_type
1330 make_cleanup make_reference_type
1331 make_command make_symbol_completion_list
1332 (@value{GDBP}) b make_
1336 After displaying the available possibilities, @value{GDBN} copies your
1337 partial input (@samp{b make_} in the example) so you can finish the
1340 If you just want to see the list of alternatives in the first place, you
1341 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1342 means @kbd{@key{META} ?}. You can type this either by holding down a
1343 key designated as the @key{META} shift on your keyboard (if there is
1344 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1346 @cindex quotes in commands
1347 @cindex completion of quoted strings
1348 Sometimes the string you need, while logically a ``word'', may contain
1349 parentheses or other characters that @value{GDBN} normally excludes from
1350 its notion of a word. To permit word completion to work in this
1351 situation, you may enclose words in @code{'} (single quote marks) in
1352 @value{GDBN} commands.
1354 The most likely situation where you might need this is in typing the
1355 name of a C@t{++} function. This is because C@t{++} allows function
1356 overloading (multiple definitions of the same function, distinguished
1357 by argument type). For example, when you want to set a breakpoint you
1358 may need to distinguish whether you mean the version of @code{name}
1359 that takes an @code{int} parameter, @code{name(int)}, or the version
1360 that takes a @code{float} parameter, @code{name(float)}. To use the
1361 word-completion facilities in this situation, type a single quote
1362 @code{'} at the beginning of the function name. This alerts
1363 @value{GDBN} that it may need to consider more information than usual
1364 when you press @key{TAB} or @kbd{M-?} to request word completion:
1367 (@value{GDBP}) b 'bubble( @kbd{M-?}
1368 bubble(double,double) bubble(int,int)
1369 (@value{GDBP}) b 'bubble(
1372 In some cases, @value{GDBN} can tell that completing a name requires using
1373 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1374 completing as much as it can) if you do not type the quote in the first
1378 (@value{GDBP}) b bub @key{TAB}
1379 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1380 (@value{GDBP}) b 'bubble(
1384 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1385 you have not yet started typing the argument list when you ask for
1386 completion on an overloaded symbol.
1388 For more information about overloaded functions, see @ref{C plus plus
1389 expressions, ,C@t{++} expressions}. You can use the command @code{set
1390 overload-resolution off} to disable overload resolution;
1391 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1395 @section Getting help
1396 @cindex online documentation
1399 You can always ask @value{GDBN} itself for information on its commands,
1400 using the command @code{help}.
1403 @kindex h @r{(@code{help})}
1406 You can use @code{help} (abbreviated @code{h}) with no arguments to
1407 display a short list of named classes of commands:
1411 List of classes of commands:
1413 aliases -- Aliases of other commands
1414 breakpoints -- Making program stop at certain points
1415 data -- Examining data
1416 files -- Specifying and examining files
1417 internals -- Maintenance commands
1418 obscure -- Obscure features
1419 running -- Running the program
1420 stack -- Examining the stack
1421 status -- Status inquiries
1422 support -- Support facilities
1423 tracepoints -- Tracing of program execution without@*
1424 stopping the program
1425 user-defined -- User-defined commands
1427 Type "help" followed by a class name for a list of
1428 commands in that class.
1429 Type "help" followed by command name for full
1431 Command name abbreviations are allowed if unambiguous.
1434 @c the above line break eliminates huge line overfull...
1436 @item help @var{class}
1437 Using one of the general help classes as an argument, you can get a
1438 list of the individual commands in that class. For example, here is the
1439 help display for the class @code{status}:
1442 (@value{GDBP}) help status
1447 @c Line break in "show" line falsifies real output, but needed
1448 @c to fit in smallbook page size.
1449 info -- Generic command for showing things
1450 about the program being debugged
1451 show -- Generic command for showing things
1454 Type "help" followed by command name for full
1456 Command name abbreviations are allowed if unambiguous.
1460 @item help @var{command}
1461 With a command name as @code{help} argument, @value{GDBN} displays a
1462 short paragraph on how to use that command.
1465 @item apropos @var{args}
1466 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1467 commands, and their documentation, for the regular expression specified in
1468 @var{args}. It prints out all matches found. For example:
1479 set symbol-reloading -- Set dynamic symbol table reloading
1480 multiple times in one run
1481 show symbol-reloading -- Show dynamic symbol table reloading
1482 multiple times in one run
1487 @item complete @var{args}
1488 The @code{complete @var{args}} command lists all the possible completions
1489 for the beginning of a command. Use @var{args} to specify the beginning of the
1490 command you want completed. For example:
1496 @noindent results in:
1507 @noindent This is intended for use by @sc{gnu} Emacs.
1510 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1511 and @code{show} to inquire about the state of your program, or the state
1512 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1513 manual introduces each of them in the appropriate context. The listings
1514 under @code{info} and under @code{show} in the Index point to
1515 all the sub-commands. @xref{Index}.
1520 @kindex i @r{(@code{info})}
1522 This command (abbreviated @code{i}) is for describing the state of your
1523 program. For example, you can list the arguments given to your program
1524 with @code{info args}, list the registers currently in use with @code{info
1525 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1526 You can get a complete list of the @code{info} sub-commands with
1527 @w{@code{help info}}.
1531 You can assign the result of an expression to an environment variable with
1532 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1533 @code{set prompt $}.
1537 In contrast to @code{info}, @code{show} is for describing the state of
1538 @value{GDBN} itself.
1539 You can change most of the things you can @code{show}, by using the
1540 related command @code{set}; for example, you can control what number
1541 system is used for displays with @code{set radix}, or simply inquire
1542 which is currently in use with @code{show radix}.
1545 To display all the settable parameters and their current
1546 values, you can use @code{show} with no arguments; you may also use
1547 @code{info set}. Both commands produce the same display.
1548 @c FIXME: "info set" violates the rule that "info" is for state of
1549 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1550 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1554 Here are three miscellaneous @code{show} subcommands, all of which are
1555 exceptional in lacking corresponding @code{set} commands:
1558 @kindex show version
1559 @cindex version number
1561 Show what version of @value{GDBN} is running. You should include this
1562 information in @value{GDBN} bug-reports. If multiple versions of
1563 @value{GDBN} are in use at your site, you may need to determine which
1564 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1565 commands are introduced, and old ones may wither away. Also, many
1566 system vendors ship variant versions of @value{GDBN}, and there are
1567 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1568 The version number is the same as the one announced when you start
1571 @kindex show copying
1573 Display information about permission for copying @value{GDBN}.
1575 @kindex show warranty
1577 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1578 if your version of @value{GDBN} comes with one.
1583 @chapter Running Programs Under @value{GDBN}
1585 When you run a program under @value{GDBN}, you must first generate
1586 debugging information when you compile it.
1588 You may start @value{GDBN} with its arguments, if any, in an environment
1589 of your choice. If you are doing native debugging, you may redirect
1590 your program's input and output, debug an already running process, or
1591 kill a child process.
1594 * Compilation:: Compiling for debugging
1595 * Starting:: Starting your program
1596 * Arguments:: Your program's arguments
1597 * Environment:: Your program's environment
1599 * Working Directory:: Your program's working directory
1600 * Input/Output:: Your program's input and output
1601 * Attach:: Debugging an already-running process
1602 * Kill Process:: Killing the child process
1604 * Threads:: Debugging programs with multiple threads
1605 * Processes:: Debugging programs with multiple processes
1609 @section Compiling for debugging
1611 In order to debug a program effectively, you need to generate
1612 debugging information when you compile it. This debugging information
1613 is stored in the object file; it describes the data type of each
1614 variable or function and the correspondence between source line numbers
1615 and addresses in the executable code.
1617 To request debugging information, specify the @samp{-g} option when you run
1620 Most compilers do not include information about preprocessor macros in
1621 the debugging information if you specify the @option{-g} flag alone,
1622 because this information is rather large. Version 3.1 of @value{NGCC},
1623 the @sc{gnu} C compiler, provides macro information if you specify the
1624 options @option{-gdwarf-2} and @option{-g3}; the former option requests
1625 debugging information in the Dwarf 2 format, and the latter requests
1626 ``extra information''. In the future, we hope to find more compact ways
1627 to represent macro information, so that it can be included with
1630 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1631 options together. Using those compilers, you cannot generate optimized
1632 executables containing debugging information.
1634 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1635 without @samp{-O}, making it possible to debug optimized code. We
1636 recommend that you @emph{always} use @samp{-g} whenever you compile a
1637 program. You may think your program is correct, but there is no sense
1638 in pushing your luck.
1640 @cindex optimized code, debugging
1641 @cindex debugging optimized code
1642 When you debug a program compiled with @samp{-g -O}, remember that the
1643 optimizer is rearranging your code; the debugger shows you what is
1644 really there. Do not be too surprised when the execution path does not
1645 exactly match your source file! An extreme example: if you define a
1646 variable, but never use it, @value{GDBN} never sees that
1647 variable---because the compiler optimizes it out of existence.
1649 Some things do not work as well with @samp{-g -O} as with just
1650 @samp{-g}, particularly on machines with instruction scheduling. If in
1651 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1652 please report it to us as a bug (including a test case!).
1654 Older versions of the @sc{gnu} C compiler permitted a variant option
1655 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1656 format; if your @sc{gnu} C compiler has this option, do not use it.
1660 @section Starting your program
1666 @kindex r @r{(@code{run})}
1669 Use the @code{run} command to start your program under @value{GDBN}.
1670 You must first specify the program name (except on VxWorks) with an
1671 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1672 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1673 (@pxref{Files, ,Commands to specify files}).
1677 If you are running your program in an execution environment that
1678 supports processes, @code{run} creates an inferior process and makes
1679 that process run your program. (In environments without processes,
1680 @code{run} jumps to the start of your program.)
1682 The execution of a program is affected by certain information it
1683 receives from its superior. @value{GDBN} provides ways to specify this
1684 information, which you must do @emph{before} starting your program. (You
1685 can change it after starting your program, but such changes only affect
1686 your program the next time you start it.) This information may be
1687 divided into four categories:
1690 @item The @emph{arguments.}
1691 Specify the arguments to give your program as the arguments of the
1692 @code{run} command. If a shell is available on your target, the shell
1693 is used to pass the arguments, so that you may use normal conventions
1694 (such as wildcard expansion or variable substitution) in describing
1696 In Unix systems, you can control which shell is used with the
1697 @code{SHELL} environment variable.
1698 @xref{Arguments, ,Your program's arguments}.
1700 @item The @emph{environment.}
1701 Your program normally inherits its environment from @value{GDBN}, but you can
1702 use the @value{GDBN} commands @code{set environment} and @code{unset
1703 environment} to change parts of the environment that affect
1704 your program. @xref{Environment, ,Your program's environment}.
1706 @item The @emph{working directory.}
1707 Your program inherits its working directory from @value{GDBN}. You can set
1708 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1709 @xref{Working Directory, ,Your program's working directory}.
1711 @item The @emph{standard input and output.}
1712 Your program normally uses the same device for standard input and
1713 standard output as @value{GDBN} is using. You can redirect input and output
1714 in the @code{run} command line, or you can use the @code{tty} command to
1715 set a different device for your program.
1716 @xref{Input/Output, ,Your program's input and output}.
1719 @emph{Warning:} While input and output redirection work, you cannot use
1720 pipes to pass the output of the program you are debugging to another
1721 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1725 When you issue the @code{run} command, your program begins to execute
1726 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1727 of how to arrange for your program to stop. Once your program has
1728 stopped, you may call functions in your program, using the @code{print}
1729 or @code{call} commands. @xref{Data, ,Examining Data}.
1731 If the modification time of your symbol file has changed since the last
1732 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1733 table, and reads it again. When it does this, @value{GDBN} tries to retain
1734 your current breakpoints.
1737 @section Your program's arguments
1739 @cindex arguments (to your program)
1740 The arguments to your program can be specified by the arguments of the
1742 They are passed to a shell, which expands wildcard characters and
1743 performs redirection of I/O, and thence to your program. Your
1744 @code{SHELL} environment variable (if it exists) specifies what shell
1745 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1746 the default shell (@file{/bin/sh} on Unix).
1748 On non-Unix systems, the program is usually invoked directly by
1749 @value{GDBN}, which emulates I/O redirection via the appropriate system
1750 calls, and the wildcard characters are expanded by the startup code of
1751 the program, not by the shell.
1753 @code{run} with no arguments uses the same arguments used by the previous
1754 @code{run}, or those set by the @code{set args} command.
1759 Specify the arguments to be used the next time your program is run. If
1760 @code{set args} has no arguments, @code{run} executes your program
1761 with no arguments. Once you have run your program with arguments,
1762 using @code{set args} before the next @code{run} is the only way to run
1763 it again without arguments.
1767 Show the arguments to give your program when it is started.
1771 @section Your program's environment
1773 @cindex environment (of your program)
1774 The @dfn{environment} consists of a set of environment variables and
1775 their values. Environment variables conventionally record such things as
1776 your user name, your home directory, your terminal type, and your search
1777 path for programs to run. Usually you set up environment variables with
1778 the shell and they are inherited by all the other programs you run. When
1779 debugging, it can be useful to try running your program with a modified
1780 environment without having to start @value{GDBN} over again.
1784 @item path @var{directory}
1785 Add @var{directory} to the front of the @code{PATH} environment variable
1786 (the search path for executables) that will be passed to your program.
1787 The value of @code{PATH} used by @value{GDBN} does not change.
1788 You may specify several directory names, separated by whitespace or by a
1789 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1790 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1791 is moved to the front, so it is searched sooner.
1793 You can use the string @samp{$cwd} to refer to whatever is the current
1794 working directory at the time @value{GDBN} searches the path. If you
1795 use @samp{.} instead, it refers to the directory where you executed the
1796 @code{path} command. @value{GDBN} replaces @samp{.} in the
1797 @var{directory} argument (with the current path) before adding
1798 @var{directory} to the search path.
1799 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1800 @c document that, since repeating it would be a no-op.
1804 Display the list of search paths for executables (the @code{PATH}
1805 environment variable).
1807 @kindex show environment
1808 @item show environment @r{[}@var{varname}@r{]}
1809 Print the value of environment variable @var{varname} to be given to
1810 your program when it starts. If you do not supply @var{varname},
1811 print the names and values of all environment variables to be given to
1812 your program. You can abbreviate @code{environment} as @code{env}.
1814 @kindex set environment
1815 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1816 Set environment variable @var{varname} to @var{value}. The value
1817 changes for your program only, not for @value{GDBN} itself. @var{value} may
1818 be any string; the values of environment variables are just strings, and
1819 any interpretation is supplied by your program itself. The @var{value}
1820 parameter is optional; if it is eliminated, the variable is set to a
1822 @c "any string" here does not include leading, trailing
1823 @c blanks. Gnu asks: does anyone care?
1825 For example, this command:
1832 tells the debugged program, when subsequently run, that its user is named
1833 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1834 are not actually required.)
1836 @kindex unset environment
1837 @item unset environment @var{varname}
1838 Remove variable @var{varname} from the environment to be passed to your
1839 program. This is different from @samp{set env @var{varname} =};
1840 @code{unset environment} removes the variable from the environment,
1841 rather than assigning it an empty value.
1844 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1846 by your @code{SHELL} environment variable if it exists (or
1847 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1848 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1849 @file{.bashrc} for BASH---any variables you set in that file affect
1850 your program. You may wish to move setting of environment variables to
1851 files that are only run when you sign on, such as @file{.login} or
1854 @node Working Directory
1855 @section Your program's working directory
1857 @cindex working directory (of your program)
1858 Each time you start your program with @code{run}, it inherits its
1859 working directory from the current working directory of @value{GDBN}.
1860 The @value{GDBN} working directory is initially whatever it inherited
1861 from its parent process (typically the shell), but you can specify a new
1862 working directory in @value{GDBN} with the @code{cd} command.
1864 The @value{GDBN} working directory also serves as a default for the commands
1865 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1870 @item cd @var{directory}
1871 Set the @value{GDBN} working directory to @var{directory}.
1875 Print the @value{GDBN} working directory.
1879 @section Your program's input and output
1884 By default, the program you run under @value{GDBN} does input and output to
1885 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1886 to its own terminal modes to interact with you, but it records the terminal
1887 modes your program was using and switches back to them when you continue
1888 running your program.
1891 @kindex info terminal
1893 Displays information recorded by @value{GDBN} about the terminal modes your
1897 You can redirect your program's input and/or output using shell
1898 redirection with the @code{run} command. For example,
1905 starts your program, diverting its output to the file @file{outfile}.
1908 @cindex controlling terminal
1909 Another way to specify where your program should do input and output is
1910 with the @code{tty} command. This command accepts a file name as
1911 argument, and causes this file to be the default for future @code{run}
1912 commands. It also resets the controlling terminal for the child
1913 process, for future @code{run} commands. For example,
1920 directs that processes started with subsequent @code{run} commands
1921 default to do input and output on the terminal @file{/dev/ttyb} and have
1922 that as their controlling terminal.
1924 An explicit redirection in @code{run} overrides the @code{tty} command's
1925 effect on the input/output device, but not its effect on the controlling
1928 When you use the @code{tty} command or redirect input in the @code{run}
1929 command, only the input @emph{for your program} is affected. The input
1930 for @value{GDBN} still comes from your terminal.
1933 @section Debugging an already-running process
1938 @item attach @var{process-id}
1939 This command attaches to a running process---one that was started
1940 outside @value{GDBN}. (@code{info files} shows your active
1941 targets.) The command takes as argument a process ID. The usual way to
1942 find out the process-id of a Unix process is with the @code{ps} utility,
1943 or with the @samp{jobs -l} shell command.
1945 @code{attach} does not repeat if you press @key{RET} a second time after
1946 executing the command.
1949 To use @code{attach}, your program must be running in an environment
1950 which supports processes; for example, @code{attach} does not work for
1951 programs on bare-board targets that lack an operating system. You must
1952 also have permission to send the process a signal.
1954 When you use @code{attach}, the debugger finds the program running in
1955 the process first by looking in the current working directory, then (if
1956 the program is not found) by using the source file search path
1957 (@pxref{Source Path, ,Specifying source directories}). You can also use
1958 the @code{file} command to load the program. @xref{Files, ,Commands to
1961 The first thing @value{GDBN} does after arranging to debug the specified
1962 process is to stop it. You can examine and modify an attached process
1963 with all the @value{GDBN} commands that are ordinarily available when
1964 you start processes with @code{run}. You can insert breakpoints; you
1965 can step and continue; you can modify storage. If you would rather the
1966 process continue running, you may use the @code{continue} command after
1967 attaching @value{GDBN} to the process.
1972 When you have finished debugging the attached process, you can use the
1973 @code{detach} command to release it from @value{GDBN} control. Detaching
1974 the process continues its execution. After the @code{detach} command,
1975 that process and @value{GDBN} become completely independent once more, and you
1976 are ready to @code{attach} another process or start one with @code{run}.
1977 @code{detach} does not repeat if you press @key{RET} again after
1978 executing the command.
1981 If you exit @value{GDBN} or use the @code{run} command while you have an
1982 attached process, you kill that process. By default, @value{GDBN} asks
1983 for confirmation if you try to do either of these things; you can
1984 control whether or not you need to confirm by using the @code{set
1985 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1989 @section Killing the child process
1994 Kill the child process in which your program is running under @value{GDBN}.
1997 This command is useful if you wish to debug a core dump instead of a
1998 running process. @value{GDBN} ignores any core dump file while your program
2001 On some operating systems, a program cannot be executed outside @value{GDBN}
2002 while you have breakpoints set on it inside @value{GDBN}. You can use the
2003 @code{kill} command in this situation to permit running your program
2004 outside the debugger.
2006 The @code{kill} command is also useful if you wish to recompile and
2007 relink your program, since on many systems it is impossible to modify an
2008 executable file while it is running in a process. In this case, when you
2009 next type @code{run}, @value{GDBN} notices that the file has changed, and
2010 reads the symbol table again (while trying to preserve your current
2011 breakpoint settings).
2014 @section Debugging programs with multiple threads
2016 @cindex threads of execution
2017 @cindex multiple threads
2018 @cindex switching threads
2019 In some operating systems, such as HP-UX and Solaris, a single program
2020 may have more than one @dfn{thread} of execution. The precise semantics
2021 of threads differ from one operating system to another, but in general
2022 the threads of a single program are akin to multiple processes---except
2023 that they share one address space (that is, they can all examine and
2024 modify the same variables). On the other hand, each thread has its own
2025 registers and execution stack, and perhaps private memory.
2027 @value{GDBN} provides these facilities for debugging multi-thread
2031 @item automatic notification of new threads
2032 @item @samp{thread @var{threadno}}, a command to switch among threads
2033 @item @samp{info threads}, a command to inquire about existing threads
2034 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2035 a command to apply a command to a list of threads
2036 @item thread-specific breakpoints
2040 @emph{Warning:} These facilities are not yet available on every
2041 @value{GDBN} configuration where the operating system supports threads.
2042 If your @value{GDBN} does not support threads, these commands have no
2043 effect. For example, a system without thread support shows no output
2044 from @samp{info threads}, and always rejects the @code{thread} command,
2048 (@value{GDBP}) info threads
2049 (@value{GDBP}) thread 1
2050 Thread ID 1 not known. Use the "info threads" command to
2051 see the IDs of currently known threads.
2053 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2054 @c doesn't support threads"?
2057 @cindex focus of debugging
2058 @cindex current thread
2059 The @value{GDBN} thread debugging facility allows you to observe all
2060 threads while your program runs---but whenever @value{GDBN} takes
2061 control, one thread in particular is always the focus of debugging.
2062 This thread is called the @dfn{current thread}. Debugging commands show
2063 program information from the perspective of the current thread.
2065 @cindex @code{New} @var{systag} message
2066 @cindex thread identifier (system)
2067 @c FIXME-implementors!! It would be more helpful if the [New...] message
2068 @c included GDB's numeric thread handle, so you could just go to that
2069 @c thread without first checking `info threads'.
2070 Whenever @value{GDBN} detects a new thread in your program, it displays
2071 the target system's identification for the thread with a message in the
2072 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2073 whose form varies depending on the particular system. For example, on
2074 LynxOS, you might see
2077 [New process 35 thread 27]
2081 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2082 the @var{systag} is simply something like @samp{process 368}, with no
2085 @c FIXME!! (1) Does the [New...] message appear even for the very first
2086 @c thread of a program, or does it only appear for the
2087 @c second---i.e.@: when it becomes obvious we have a multithread
2089 @c (2) *Is* there necessarily a first thread always? Or do some
2090 @c multithread systems permit starting a program with multiple
2091 @c threads ab initio?
2093 @cindex thread number
2094 @cindex thread identifier (GDB)
2095 For debugging purposes, @value{GDBN} associates its own thread
2096 number---always a single integer---with each thread in your program.
2099 @kindex info threads
2101 Display a summary of all threads currently in your
2102 program. @value{GDBN} displays for each thread (in this order):
2105 @item the thread number assigned by @value{GDBN}
2107 @item the target system's thread identifier (@var{systag})
2109 @item the current stack frame summary for that thread
2113 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2114 indicates the current thread.
2118 @c end table here to get a little more width for example
2121 (@value{GDBP}) info threads
2122 3 process 35 thread 27 0x34e5 in sigpause ()
2123 2 process 35 thread 23 0x34e5 in sigpause ()
2124 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2130 @cindex thread number
2131 @cindex thread identifier (GDB)
2132 For debugging purposes, @value{GDBN} associates its own thread
2133 number---a small integer assigned in thread-creation order---with each
2134 thread in your program.
2136 @cindex @code{New} @var{systag} message, on HP-UX
2137 @cindex thread identifier (system), on HP-UX
2138 @c FIXME-implementors!! It would be more helpful if the [New...] message
2139 @c included GDB's numeric thread handle, so you could just go to that
2140 @c thread without first checking `info threads'.
2141 Whenever @value{GDBN} detects a new thread in your program, it displays
2142 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2143 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2144 whose form varies depending on the particular system. For example, on
2148 [New thread 2 (system thread 26594)]
2152 when @value{GDBN} notices a new thread.
2155 @kindex info threads
2157 Display a summary of all threads currently in your
2158 program. @value{GDBN} displays for each thread (in this order):
2161 @item the thread number assigned by @value{GDBN}
2163 @item the target system's thread identifier (@var{systag})
2165 @item the current stack frame summary for that thread
2169 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2170 indicates the current thread.
2174 @c end table here to get a little more width for example
2177 (@value{GDBP}) info threads
2178 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2180 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2181 from /usr/lib/libc.2
2182 1 system thread 27905 0x7b003498 in _brk () \@*
2183 from /usr/lib/libc.2
2187 @kindex thread @var{threadno}
2188 @item thread @var{threadno}
2189 Make thread number @var{threadno} the current thread. The command
2190 argument @var{threadno} is the internal @value{GDBN} thread number, as
2191 shown in the first field of the @samp{info threads} display.
2192 @value{GDBN} responds by displaying the system identifier of the thread
2193 you selected, and its current stack frame summary:
2196 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2197 (@value{GDBP}) thread 2
2198 [Switching to process 35 thread 23]
2199 0x34e5 in sigpause ()
2203 As with the @samp{[New @dots{}]} message, the form of the text after
2204 @samp{Switching to} depends on your system's conventions for identifying
2207 @kindex thread apply
2208 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2209 The @code{thread apply} command allows you to apply a command to one or
2210 more threads. Specify the numbers of the threads that you want affected
2211 with the command argument @var{threadno}. @var{threadno} is the internal
2212 @value{GDBN} thread number, as shown in the first field of the @samp{info
2213 threads} display. To apply a command to all threads, use
2214 @code{thread apply all} @var{args}.
2217 @cindex automatic thread selection
2218 @cindex switching threads automatically
2219 @cindex threads, automatic switching
2220 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2221 signal, it automatically selects the thread where that breakpoint or
2222 signal happened. @value{GDBN} alerts you to the context switch with a
2223 message of the form @samp{[Switching to @var{systag}]} to identify the
2226 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2227 more information about how @value{GDBN} behaves when you stop and start
2228 programs with multiple threads.
2230 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2231 watchpoints in programs with multiple threads.
2234 @section Debugging programs with multiple processes
2236 @cindex fork, debugging programs which call
2237 @cindex multiple processes
2238 @cindex processes, multiple
2239 On most systems, @value{GDBN} has no special support for debugging
2240 programs which create additional processes using the @code{fork}
2241 function. When a program forks, @value{GDBN} will continue to debug the
2242 parent process and the child process will run unimpeded. If you have
2243 set a breakpoint in any code which the child then executes, the child
2244 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2245 will cause it to terminate.
2247 However, if you want to debug the child process there is a workaround
2248 which isn't too painful. Put a call to @code{sleep} in the code which
2249 the child process executes after the fork. It may be useful to sleep
2250 only if a certain environment variable is set, or a certain file exists,
2251 so that the delay need not occur when you don't want to run @value{GDBN}
2252 on the child. While the child is sleeping, use the @code{ps} program to
2253 get its process ID. Then tell @value{GDBN} (a new invocation of
2254 @value{GDBN} if you are also debugging the parent process) to attach to
2255 the child process (@pxref{Attach}). From that point on you can debug
2256 the child process just like any other process which you attached to.
2258 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2259 debugging programs that create additional processes using the
2260 @code{fork} or @code{vfork} function.
2262 By default, when a program forks, @value{GDBN} will continue to debug
2263 the parent process and the child process will run unimpeded.
2265 If you want to follow the child process instead of the parent process,
2266 use the command @w{@code{set follow-fork-mode}}.
2269 @kindex set follow-fork-mode
2270 @item set follow-fork-mode @var{mode}
2271 Set the debugger response to a program call of @code{fork} or
2272 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2273 process. The @var{mode} can be:
2277 The original process is debugged after a fork. The child process runs
2278 unimpeded. This is the default.
2281 The new process is debugged after a fork. The parent process runs
2285 The debugger will ask for one of the above choices.
2288 @item show follow-fork-mode
2289 Display the current debugger response to a @code{fork} or @code{vfork} call.
2292 If you ask to debug a child process and a @code{vfork} is followed by an
2293 @code{exec}, @value{GDBN} executes the new target up to the first
2294 breakpoint in the new target. If you have a breakpoint set on
2295 @code{main} in your original program, the breakpoint will also be set on
2296 the child process's @code{main}.
2298 When a child process is spawned by @code{vfork}, you cannot debug the
2299 child or parent until an @code{exec} call completes.
2301 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2302 call executes, the new target restarts. To restart the parent process,
2303 use the @code{file} command with the parent executable name as its
2306 You can use the @code{catch} command to make @value{GDBN} stop whenever
2307 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2308 Catchpoints, ,Setting catchpoints}.
2311 @chapter Stopping and Continuing
2313 The principal purposes of using a debugger are so that you can stop your
2314 program before it terminates; or so that, if your program runs into
2315 trouble, you can investigate and find out why.
2317 Inside @value{GDBN}, your program may stop for any of several reasons,
2318 such as a signal, a breakpoint, or reaching a new line after a
2319 @value{GDBN} command such as @code{step}. You may then examine and
2320 change variables, set new breakpoints or remove old ones, and then
2321 continue execution. Usually, the messages shown by @value{GDBN} provide
2322 ample explanation of the status of your program---but you can also
2323 explicitly request this information at any time.
2326 @kindex info program
2328 Display information about the status of your program: whether it is
2329 running or not, what process it is, and why it stopped.
2333 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2334 * Continuing and Stepping:: Resuming execution
2336 * Thread Stops:: Stopping and starting multi-thread programs
2340 @section Breakpoints, watchpoints, and catchpoints
2343 A @dfn{breakpoint} makes your program stop whenever a certain point in
2344 the program is reached. For each breakpoint, you can add conditions to
2345 control in finer detail whether your program stops. You can set
2346 breakpoints with the @code{break} command and its variants (@pxref{Set
2347 Breaks, ,Setting breakpoints}), to specify the place where your program
2348 should stop by line number, function name or exact address in the
2351 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2352 breakpoints in shared libraries before the executable is run. There is
2353 a minor limitation on HP-UX systems: you must wait until the executable
2354 is run in order to set breakpoints in shared library routines that are
2355 not called directly by the program (for example, routines that are
2356 arguments in a @code{pthread_create} call).
2359 @cindex memory tracing
2360 @cindex breakpoint on memory address
2361 @cindex breakpoint on variable modification
2362 A @dfn{watchpoint} is a special breakpoint that stops your program
2363 when the value of an expression changes. You must use a different
2364 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2365 watchpoints}), but aside from that, you can manage a watchpoint like
2366 any other breakpoint: you enable, disable, and delete both breakpoints
2367 and watchpoints using the same commands.
2369 You can arrange to have values from your program displayed automatically
2370 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2374 @cindex breakpoint on events
2375 A @dfn{catchpoint} is another special breakpoint that stops your program
2376 when a certain kind of event occurs, such as the throwing of a C@t{++}
2377 exception or the loading of a library. As with watchpoints, you use a
2378 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2379 catchpoints}), but aside from that, you can manage a catchpoint like any
2380 other breakpoint. (To stop when your program receives a signal, use the
2381 @code{handle} command; see @ref{Signals, ,Signals}.)
2383 @cindex breakpoint numbers
2384 @cindex numbers for breakpoints
2385 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2386 catchpoint when you create it; these numbers are successive integers
2387 starting with one. In many of the commands for controlling various
2388 features of breakpoints you use the breakpoint number to say which
2389 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2390 @dfn{disabled}; if disabled, it has no effect on your program until you
2393 @cindex breakpoint ranges
2394 @cindex ranges of breakpoints
2395 Some @value{GDBN} commands accept a range of breakpoints on which to
2396 operate. A breakpoint range is either a single breakpoint number, like
2397 @samp{5}, or two such numbers, in increasing order, separated by a
2398 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2399 all breakpoint in that range are operated on.
2402 * Set Breaks:: Setting breakpoints
2403 * Set Watchpoints:: Setting watchpoints
2404 * Set Catchpoints:: Setting catchpoints
2405 * Delete Breaks:: Deleting breakpoints
2406 * Disabling:: Disabling breakpoints
2407 * Conditions:: Break conditions
2408 * Break Commands:: Breakpoint command lists
2409 * Breakpoint Menus:: Breakpoint menus
2410 * Error in Breakpoints:: ``Cannot insert breakpoints''
2414 @subsection Setting breakpoints
2416 @c FIXME LMB what does GDB do if no code on line of breakpt?
2417 @c consider in particular declaration with/without initialization.
2419 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2422 @kindex b @r{(@code{break})}
2423 @vindex $bpnum@r{, convenience variable}
2424 @cindex latest breakpoint
2425 Breakpoints are set with the @code{break} command (abbreviated
2426 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2427 number of the breakpoint you've set most recently; see @ref{Convenience
2428 Vars,, Convenience variables}, for a discussion of what you can do with
2429 convenience variables.
2431 You have several ways to say where the breakpoint should go.
2434 @item break @var{function}
2435 Set a breakpoint at entry to function @var{function}.
2436 When using source languages that permit overloading of symbols, such as
2437 C@t{++}, @var{function} may refer to more than one possible place to break.
2438 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2440 @item break +@var{offset}
2441 @itemx break -@var{offset}
2442 Set a breakpoint some number of lines forward or back from the position
2443 at which execution stopped in the currently selected @dfn{stack frame}.
2444 (@xref{Frames, ,Frames}, for a description of stack frames.)
2446 @item break @var{linenum}
2447 Set a breakpoint at line @var{linenum} in the current source file.
2448 The current source file is the last file whose source text was printed.
2449 The breakpoint will stop your program just before it executes any of the
2452 @item break @var{filename}:@var{linenum}
2453 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2455 @item break @var{filename}:@var{function}
2456 Set a breakpoint at entry to function @var{function} found in file
2457 @var{filename}. Specifying a file name as well as a function name is
2458 superfluous except when multiple files contain similarly named
2461 @item break *@var{address}
2462 Set a breakpoint at address @var{address}. You can use this to set
2463 breakpoints in parts of your program which do not have debugging
2464 information or source files.
2467 When called without any arguments, @code{break} sets a breakpoint at
2468 the next instruction to be executed in the selected stack frame
2469 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2470 innermost, this makes your program stop as soon as control
2471 returns to that frame. This is similar to the effect of a
2472 @code{finish} command in the frame inside the selected frame---except
2473 that @code{finish} does not leave an active breakpoint. If you use
2474 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2475 the next time it reaches the current location; this may be useful
2478 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2479 least one instruction has been executed. If it did not do this, you
2480 would be unable to proceed past a breakpoint without first disabling the
2481 breakpoint. This rule applies whether or not the breakpoint already
2482 existed when your program stopped.
2484 @item break @dots{} if @var{cond}
2485 Set a breakpoint with condition @var{cond}; evaluate the expression
2486 @var{cond} each time the breakpoint is reached, and stop only if the
2487 value is nonzero---that is, if @var{cond} evaluates as true.
2488 @samp{@dots{}} stands for one of the possible arguments described
2489 above (or no argument) specifying where to break. @xref{Conditions,
2490 ,Break conditions}, for more information on breakpoint conditions.
2493 @item tbreak @var{args}
2494 Set a breakpoint enabled only for one stop. @var{args} are the
2495 same as for the @code{break} command, and the breakpoint is set in the same
2496 way, but the breakpoint is automatically deleted after the first time your
2497 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2500 @item hbreak @var{args}
2501 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2502 @code{break} command and the breakpoint is set in the same way, but the
2503 breakpoint requires hardware support and some target hardware may not
2504 have this support. The main purpose of this is EPROM/ROM code
2505 debugging, so you can set a breakpoint at an instruction without
2506 changing the instruction. This can be used with the new trap-generation
2507 provided by SPARClite DSU and some x86-based targets. These targets
2508 will generate traps when a program accesses some data or instruction
2509 address that is assigned to the debug registers. However the hardware
2510 breakpoint registers can take a limited number of breakpoints. For
2511 example, on the DSU, only two data breakpoints can be set at a time, and
2512 @value{GDBN} will reject this command if more than two are used. Delete
2513 or disable unused hardware breakpoints before setting new ones
2514 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2517 @item thbreak @var{args}
2518 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2519 are the same as for the @code{hbreak} command and the breakpoint is set in
2520 the same way. However, like the @code{tbreak} command,
2521 the breakpoint is automatically deleted after the
2522 first time your program stops there. Also, like the @code{hbreak}
2523 command, the breakpoint requires hardware support and some target hardware
2524 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2525 See also @ref{Conditions, ,Break conditions}.
2528 @cindex regular expression
2529 @item rbreak @var{regex}
2530 Set breakpoints on all functions matching the regular expression
2531 @var{regex}. This command sets an unconditional breakpoint on all
2532 matches, printing a list of all breakpoints it set. Once these
2533 breakpoints are set, they are treated just like the breakpoints set with
2534 the @code{break} command. You can delete them, disable them, or make
2535 them conditional the same way as any other breakpoint.
2537 The syntax of the regular expression is the standard one used with tools
2538 like @file{grep}. Note that this is different from the syntax used by
2539 shells, so for instance @code{foo*} matches all functions that include
2540 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2541 @code{.*} leading and trailing the regular expression you supply, so to
2542 match only functions that begin with @code{foo}, use @code{^foo}.
2544 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2545 breakpoints on overloaded functions that are not members of any special
2548 @kindex info breakpoints
2549 @cindex @code{$_} and @code{info breakpoints}
2550 @item info breakpoints @r{[}@var{n}@r{]}
2551 @itemx info break @r{[}@var{n}@r{]}
2552 @itemx info watchpoints @r{[}@var{n}@r{]}
2553 Print a table of all breakpoints, watchpoints, and catchpoints set and
2554 not deleted, with the following columns for each breakpoint:
2557 @item Breakpoint Numbers
2559 Breakpoint, watchpoint, or catchpoint.
2561 Whether the breakpoint is marked to be disabled or deleted when hit.
2562 @item Enabled or Disabled
2563 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2564 that are not enabled.
2566 Where the breakpoint is in your program, as a memory address.
2568 Where the breakpoint is in the source for your program, as a file and
2573 If a breakpoint is conditional, @code{info break} shows the condition on
2574 the line following the affected breakpoint; breakpoint commands, if any,
2575 are listed after that.
2578 @code{info break} with a breakpoint
2579 number @var{n} as argument lists only that breakpoint. The
2580 convenience variable @code{$_} and the default examining-address for
2581 the @code{x} command are set to the address of the last breakpoint
2582 listed (@pxref{Memory, ,Examining memory}).
2585 @code{info break} displays a count of the number of times the breakpoint
2586 has been hit. This is especially useful in conjunction with the
2587 @code{ignore} command. You can ignore a large number of breakpoint
2588 hits, look at the breakpoint info to see how many times the breakpoint
2589 was hit, and then run again, ignoring one less than that number. This
2590 will get you quickly to the last hit of that breakpoint.
2593 @value{GDBN} allows you to set any number of breakpoints at the same place in
2594 your program. There is nothing silly or meaningless about this. When
2595 the breakpoints are conditional, this is even useful
2596 (@pxref{Conditions, ,Break conditions}).
2598 @cindex negative breakpoint numbers
2599 @cindex internal @value{GDBN} breakpoints
2600 @value{GDBN} itself sometimes sets breakpoints in your program for
2601 special purposes, such as proper handling of @code{longjmp} (in C
2602 programs). These internal breakpoints are assigned negative numbers,
2603 starting with @code{-1}; @samp{info breakpoints} does not display them.
2604 You can see these breakpoints with the @value{GDBN} maintenance command
2605 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
2608 @node Set Watchpoints
2609 @subsection Setting watchpoints
2611 @cindex setting watchpoints
2612 @cindex software watchpoints
2613 @cindex hardware watchpoints
2614 You can use a watchpoint to stop execution whenever the value of an
2615 expression changes, without having to predict a particular place where
2618 Depending on your system, watchpoints may be implemented in software or
2619 hardware. @value{GDBN} does software watchpointing by single-stepping your
2620 program and testing the variable's value each time, which is hundreds of
2621 times slower than normal execution. (But this may still be worth it, to
2622 catch errors where you have no clue what part of your program is the
2625 On some systems, such as HP-UX, @sc{gnu}/Linux and some other x86-based targets,
2626 @value{GDBN} includes support for
2627 hardware watchpoints, which do not slow down the running of your
2632 @item watch @var{expr}
2633 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2634 is written into by the program and its value changes.
2637 @item rwatch @var{expr}
2638 Set a watchpoint that will break when watch @var{expr} is read by the program.
2641 @item awatch @var{expr}
2642 Set a watchpoint that will break when @var{expr} is either read or written into
2645 @kindex info watchpoints
2646 @item info watchpoints
2647 This command prints a list of watchpoints, breakpoints, and catchpoints;
2648 it is the same as @code{info break}.
2651 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2652 watchpoints execute very quickly, and the debugger reports a change in
2653 value at the exact instruction where the change occurs. If @value{GDBN}
2654 cannot set a hardware watchpoint, it sets a software watchpoint, which
2655 executes more slowly and reports the change in value at the next
2656 statement, not the instruction, after the change occurs.
2658 When you issue the @code{watch} command, @value{GDBN} reports
2661 Hardware watchpoint @var{num}: @var{expr}
2665 if it was able to set a hardware watchpoint.
2667 Currently, the @code{awatch} and @code{rwatch} commands can only set
2668 hardware watchpoints, because accesses to data that don't change the
2669 value of the watched expression cannot be detected without examining
2670 every instruction as it is being executed, and @value{GDBN} does not do
2671 that currently. If @value{GDBN} finds that it is unable to set a
2672 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2673 will print a message like this:
2676 Expression cannot be implemented with read/access watchpoint.
2679 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2680 data type of the watched expression is wider than what a hardware
2681 watchpoint on the target machine can handle. For example, some systems
2682 can only watch regions that are up to 4 bytes wide; on such systems you
2683 cannot set hardware watchpoints for an expression that yields a
2684 double-precision floating-point number (which is typically 8 bytes
2685 wide). As a work-around, it might be possible to break the large region
2686 into a series of smaller ones and watch them with separate watchpoints.
2688 If you set too many hardware watchpoints, @value{GDBN} might be unable
2689 to insert all of them when you resume the execution of your program.
2690 Since the precise number of active watchpoints is unknown until such
2691 time as the program is about to be resumed, @value{GDBN} might not be
2692 able to warn you about this when you set the watchpoints, and the
2693 warning will be printed only when the program is resumed:
2696 Hardware watchpoint @var{num}: Could not insert watchpoint
2700 If this happens, delete or disable some of the watchpoints.
2702 The SPARClite DSU will generate traps when a program accesses some data
2703 or instruction address that is assigned to the debug registers. For the
2704 data addresses, DSU facilitates the @code{watch} command. However the
2705 hardware breakpoint registers can only take two data watchpoints, and
2706 both watchpoints must be the same kind. For example, you can set two
2707 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2708 @strong{or} two with @code{awatch} commands, but you cannot set one
2709 watchpoint with one command and the other with a different command.
2710 @value{GDBN} will reject the command if you try to mix watchpoints.
2711 Delete or disable unused watchpoint commands before setting new ones.
2713 If you call a function interactively using @code{print} or @code{call},
2714 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2715 kind of breakpoint or the call completes.
2717 @value{GDBN} automatically deletes watchpoints that watch local
2718 (automatic) variables, or expressions that involve such variables, when
2719 they go out of scope, that is, when the execution leaves the block in
2720 which these variables were defined. In particular, when the program
2721 being debugged terminates, @emph{all} local variables go out of scope,
2722 and so only watchpoints that watch global variables remain set. If you
2723 rerun the program, you will need to set all such watchpoints again. One
2724 way of doing that would be to set a code breakpoint at the entry to the
2725 @code{main} function and when it breaks, set all the watchpoints.
2728 @cindex watchpoints and threads
2729 @cindex threads and watchpoints
2730 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2731 usefulness. With the current watchpoint implementation, @value{GDBN}
2732 can only watch the value of an expression @emph{in a single thread}. If
2733 you are confident that the expression can only change due to the current
2734 thread's activity (and if you are also confident that no other thread
2735 can become current), then you can use watchpoints as usual. However,
2736 @value{GDBN} may not notice when a non-current thread's activity changes
2739 @c FIXME: this is almost identical to the previous paragraph.
2740 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2741 have only limited usefulness. If @value{GDBN} creates a software
2742 watchpoint, it can only watch the value of an expression @emph{in a
2743 single thread}. If you are confident that the expression can only
2744 change due to the current thread's activity (and if you are also
2745 confident that no other thread can become current), then you can use
2746 software watchpoints as usual. However, @value{GDBN} may not notice
2747 when a non-current thread's activity changes the expression. (Hardware
2748 watchpoints, in contrast, watch an expression in all threads.)
2751 @node Set Catchpoints
2752 @subsection Setting catchpoints
2753 @cindex catchpoints, setting
2754 @cindex exception handlers
2755 @cindex event handling
2757 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2758 kinds of program events, such as C@t{++} exceptions or the loading of a
2759 shared library. Use the @code{catch} command to set a catchpoint.
2763 @item catch @var{event}
2764 Stop when @var{event} occurs. @var{event} can be any of the following:
2768 The throwing of a C@t{++} exception.
2772 The catching of a C@t{++} exception.
2776 A call to @code{exec}. This is currently only available for HP-UX.
2780 A call to @code{fork}. This is currently only available for HP-UX.
2784 A call to @code{vfork}. This is currently only available for HP-UX.
2787 @itemx load @var{libname}
2789 The dynamic loading of any shared library, or the loading of the library
2790 @var{libname}. This is currently only available for HP-UX.
2793 @itemx unload @var{libname}
2794 @kindex catch unload
2795 The unloading of any dynamically loaded shared library, or the unloading
2796 of the library @var{libname}. This is currently only available for HP-UX.
2799 @item tcatch @var{event}
2800 Set a catchpoint that is enabled only for one stop. The catchpoint is
2801 automatically deleted after the first time the event is caught.
2805 Use the @code{info break} command to list the current catchpoints.
2807 There are currently some limitations to C@t{++} exception handling
2808 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2812 If you call a function interactively, @value{GDBN} normally returns
2813 control to you when the function has finished executing. If the call
2814 raises an exception, however, the call may bypass the mechanism that
2815 returns control to you and cause your program either to abort or to
2816 simply continue running until it hits a breakpoint, catches a signal
2817 that @value{GDBN} is listening for, or exits. This is the case even if
2818 you set a catchpoint for the exception; catchpoints on exceptions are
2819 disabled within interactive calls.
2822 You cannot raise an exception interactively.
2825 You cannot install an exception handler interactively.
2828 @cindex raise exceptions
2829 Sometimes @code{catch} is not the best way to debug exception handling:
2830 if you need to know exactly where an exception is raised, it is better to
2831 stop @emph{before} the exception handler is called, since that way you
2832 can see the stack before any unwinding takes place. If you set a
2833 breakpoint in an exception handler instead, it may not be easy to find
2834 out where the exception was raised.
2836 To stop just before an exception handler is called, you need some
2837 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2838 raised by calling a library function named @code{__raise_exception}
2839 which has the following ANSI C interface:
2842 /* @var{addr} is where the exception identifier is stored.
2843 @var{id} is the exception identifier. */
2844 void __raise_exception (void **addr, void *id);
2848 To make the debugger catch all exceptions before any stack
2849 unwinding takes place, set a breakpoint on @code{__raise_exception}
2850 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2852 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2853 that depends on the value of @var{id}, you can stop your program when
2854 a specific exception is raised. You can use multiple conditional
2855 breakpoints to stop your program when any of a number of exceptions are
2860 @subsection Deleting breakpoints
2862 @cindex clearing breakpoints, watchpoints, catchpoints
2863 @cindex deleting breakpoints, watchpoints, catchpoints
2864 It is often necessary to eliminate a breakpoint, watchpoint, or
2865 catchpoint once it has done its job and you no longer want your program
2866 to stop there. This is called @dfn{deleting} the breakpoint. A
2867 breakpoint that has been deleted no longer exists; it is forgotten.
2869 With the @code{clear} command you can delete breakpoints according to
2870 where they are in your program. With the @code{delete} command you can
2871 delete individual breakpoints, watchpoints, or catchpoints by specifying
2872 their breakpoint numbers.
2874 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2875 automatically ignores breakpoints on the first instruction to be executed
2876 when you continue execution without changing the execution address.
2881 Delete any breakpoints at the next instruction to be executed in the
2882 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2883 the innermost frame is selected, this is a good way to delete a
2884 breakpoint where your program just stopped.
2886 @item clear @var{function}
2887 @itemx clear @var{filename}:@var{function}
2888 Delete any breakpoints set at entry to the function @var{function}.
2890 @item clear @var{linenum}
2891 @itemx clear @var{filename}:@var{linenum}
2892 Delete any breakpoints set at or within the code of the specified line.
2894 @cindex delete breakpoints
2896 @kindex d @r{(@code{delete})}
2897 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2898 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2899 ranges specified as arguments. If no argument is specified, delete all
2900 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2901 confirm off}). You can abbreviate this command as @code{d}.
2905 @subsection Disabling breakpoints
2907 @kindex disable breakpoints
2908 @kindex enable breakpoints
2909 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2910 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2911 it had been deleted, but remembers the information on the breakpoint so
2912 that you can @dfn{enable} it again later.
2914 You disable and enable breakpoints, watchpoints, and catchpoints with
2915 the @code{enable} and @code{disable} commands, optionally specifying one
2916 or more breakpoint numbers as arguments. Use @code{info break} or
2917 @code{info watch} to print a list of breakpoints, watchpoints, and
2918 catchpoints if you do not know which numbers to use.
2920 A breakpoint, watchpoint, or catchpoint can have any of four different
2921 states of enablement:
2925 Enabled. The breakpoint stops your program. A breakpoint set
2926 with the @code{break} command starts out in this state.
2928 Disabled. The breakpoint has no effect on your program.
2930 Enabled once. The breakpoint stops your program, but then becomes
2933 Enabled for deletion. The breakpoint stops your program, but
2934 immediately after it does so it is deleted permanently. A breakpoint
2935 set with the @code{tbreak} command starts out in this state.
2938 You can use the following commands to enable or disable breakpoints,
2939 watchpoints, and catchpoints:
2942 @kindex disable breakpoints
2944 @kindex dis @r{(@code{disable})}
2945 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2946 Disable the specified breakpoints---or all breakpoints, if none are
2947 listed. A disabled breakpoint has no effect but is not forgotten. All
2948 options such as ignore-counts, conditions and commands are remembered in
2949 case the breakpoint is enabled again later. You may abbreviate
2950 @code{disable} as @code{dis}.
2952 @kindex enable breakpoints
2954 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2955 Enable the specified breakpoints (or all defined breakpoints). They
2956 become effective once again in stopping your program.
2958 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2959 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2960 of these breakpoints immediately after stopping your program.
2962 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2963 Enable the specified breakpoints to work once, then die. @value{GDBN}
2964 deletes any of these breakpoints as soon as your program stops there.
2967 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2968 @c confusing: tbreak is also initially enabled.
2969 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2970 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2971 subsequently, they become disabled or enabled only when you use one of
2972 the commands above. (The command @code{until} can set and delete a
2973 breakpoint of its own, but it does not change the state of your other
2974 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2978 @subsection Break conditions
2979 @cindex conditional breakpoints
2980 @cindex breakpoint conditions
2982 @c FIXME what is scope of break condition expr? Context where wanted?
2983 @c in particular for a watchpoint?
2984 The simplest sort of breakpoint breaks every time your program reaches a
2985 specified place. You can also specify a @dfn{condition} for a
2986 breakpoint. A condition is just a Boolean expression in your
2987 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2988 a condition evaluates the expression each time your program reaches it,
2989 and your program stops only if the condition is @emph{true}.
2991 This is the converse of using assertions for program validation; in that
2992 situation, you want to stop when the assertion is violated---that is,
2993 when the condition is false. In C, if you want to test an assertion expressed
2994 by the condition @var{assert}, you should set the condition
2995 @samp{! @var{assert}} on the appropriate breakpoint.
2997 Conditions are also accepted for watchpoints; you may not need them,
2998 since a watchpoint is inspecting the value of an expression anyhow---but
2999 it might be simpler, say, to just set a watchpoint on a variable name,
3000 and specify a condition that tests whether the new value is an interesting
3003 Break conditions can have side effects, and may even call functions in
3004 your program. This can be useful, for example, to activate functions
3005 that log program progress, or to use your own print functions to
3006 format special data structures. The effects are completely predictable
3007 unless there is another enabled breakpoint at the same address. (In
3008 that case, @value{GDBN} might see the other breakpoint first and stop your
3009 program without checking the condition of this one.) Note that
3010 breakpoint commands are usually more convenient and flexible than break
3012 purpose of performing side effects when a breakpoint is reached
3013 (@pxref{Break Commands, ,Breakpoint command lists}).
3015 Break conditions can be specified when a breakpoint is set, by using
3016 @samp{if} in the arguments to the @code{break} command. @xref{Set
3017 Breaks, ,Setting breakpoints}. They can also be changed at any time
3018 with the @code{condition} command.
3020 You can also use the @code{if} keyword with the @code{watch} command.
3021 The @code{catch} command does not recognize the @code{if} keyword;
3022 @code{condition} is the only way to impose a further condition on a
3027 @item condition @var{bnum} @var{expression}
3028 Specify @var{expression} as the break condition for breakpoint,
3029 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3030 breakpoint @var{bnum} stops your program only if the value of
3031 @var{expression} is true (nonzero, in C). When you use
3032 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3033 syntactic correctness, and to determine whether symbols in it have
3034 referents in the context of your breakpoint. If @var{expression} uses
3035 symbols not referenced in the context of the breakpoint, @value{GDBN}
3036 prints an error message:
3039 No symbol "foo" in current context.
3044 not actually evaluate @var{expression} at the time the @code{condition}
3045 command (or a command that sets a breakpoint with a condition, like
3046 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3048 @item condition @var{bnum}
3049 Remove the condition from breakpoint number @var{bnum}. It becomes
3050 an ordinary unconditional breakpoint.
3053 @cindex ignore count (of breakpoint)
3054 A special case of a breakpoint condition is to stop only when the
3055 breakpoint has been reached a certain number of times. This is so
3056 useful that there is a special way to do it, using the @dfn{ignore
3057 count} of the breakpoint. Every breakpoint has an ignore count, which
3058 is an integer. Most of the time, the ignore count is zero, and
3059 therefore has no effect. But if your program reaches a breakpoint whose
3060 ignore count is positive, then instead of stopping, it just decrements
3061 the ignore count by one and continues. As a result, if the ignore count
3062 value is @var{n}, the breakpoint does not stop the next @var{n} times
3063 your program reaches it.
3067 @item ignore @var{bnum} @var{count}
3068 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3069 The next @var{count} times the breakpoint is reached, your program's
3070 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3073 To make the breakpoint stop the next time it is reached, specify
3076 When you use @code{continue} to resume execution of your program from a
3077 breakpoint, you can specify an ignore count directly as an argument to
3078 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3079 Stepping,,Continuing and stepping}.
3081 If a breakpoint has a positive ignore count and a condition, the
3082 condition is not checked. Once the ignore count reaches zero,
3083 @value{GDBN} resumes checking the condition.
3085 You could achieve the effect of the ignore count with a condition such
3086 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3087 is decremented each time. @xref{Convenience Vars, ,Convenience
3091 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3094 @node Break Commands
3095 @subsection Breakpoint command lists
3097 @cindex breakpoint commands
3098 You can give any breakpoint (or watchpoint or catchpoint) a series of
3099 commands to execute when your program stops due to that breakpoint. For
3100 example, you might want to print the values of certain expressions, or
3101 enable other breakpoints.
3106 @item commands @r{[}@var{bnum}@r{]}
3107 @itemx @dots{} @var{command-list} @dots{}
3109 Specify a list of commands for breakpoint number @var{bnum}. The commands
3110 themselves appear on the following lines. Type a line containing just
3111 @code{end} to terminate the commands.
3113 To remove all commands from a breakpoint, type @code{commands} and
3114 follow it immediately with @code{end}; that is, give no commands.
3116 With no @var{bnum} argument, @code{commands} refers to the last
3117 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3118 recently encountered).
3121 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3122 disabled within a @var{command-list}.
3124 You can use breakpoint commands to start your program up again. Simply
3125 use the @code{continue} command, or @code{step}, or any other command
3126 that resumes execution.
3128 Any other commands in the command list, after a command that resumes
3129 execution, are ignored. This is because any time you resume execution
3130 (even with a simple @code{next} or @code{step}), you may encounter
3131 another breakpoint---which could have its own command list, leading to
3132 ambiguities about which list to execute.
3135 If the first command you specify in a command list is @code{silent}, the
3136 usual message about stopping at a breakpoint is not printed. This may
3137 be desirable for breakpoints that are to print a specific message and
3138 then continue. If none of the remaining commands print anything, you
3139 see no sign that the breakpoint was reached. @code{silent} is
3140 meaningful only at the beginning of a breakpoint command list.
3142 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3143 print precisely controlled output, and are often useful in silent
3144 breakpoints. @xref{Output, ,Commands for controlled output}.
3146 For example, here is how you could use breakpoint commands to print the
3147 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3153 printf "x is %d\n",x
3158 One application for breakpoint commands is to compensate for one bug so
3159 you can test for another. Put a breakpoint just after the erroneous line
3160 of code, give it a condition to detect the case in which something
3161 erroneous has been done, and give it commands to assign correct values
3162 to any variables that need them. End with the @code{continue} command
3163 so that your program does not stop, and start with the @code{silent}
3164 command so that no output is produced. Here is an example:
3175 @node Breakpoint Menus
3176 @subsection Breakpoint menus
3178 @cindex symbol overloading
3180 Some programming languages (notably C@t{++}) permit a single function name
3181 to be defined several times, for application in different contexts.
3182 This is called @dfn{overloading}. When a function name is overloaded,
3183 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3184 a breakpoint. If you realize this is a problem, you can use
3185 something like @samp{break @var{function}(@var{types})} to specify which
3186 particular version of the function you want. Otherwise, @value{GDBN} offers
3187 you a menu of numbered choices for different possible breakpoints, and
3188 waits for your selection with the prompt @samp{>}. The first two
3189 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3190 sets a breakpoint at each definition of @var{function}, and typing
3191 @kbd{0} aborts the @code{break} command without setting any new
3194 For example, the following session excerpt shows an attempt to set a
3195 breakpoint at the overloaded symbol @code{String::after}.
3196 We choose three particular definitions of that function name:
3198 @c FIXME! This is likely to change to show arg type lists, at least
3201 (@value{GDBP}) b String::after
3204 [2] file:String.cc; line number:867
3205 [3] file:String.cc; line number:860
3206 [4] file:String.cc; line number:875
3207 [5] file:String.cc; line number:853
3208 [6] file:String.cc; line number:846
3209 [7] file:String.cc; line number:735
3211 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3212 Breakpoint 2 at 0xb344: file String.cc, line 875.
3213 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3214 Multiple breakpoints were set.
3215 Use the "delete" command to delete unwanted
3221 @c @ifclear BARETARGET
3222 @node Error in Breakpoints
3223 @subsection ``Cannot insert breakpoints''
3225 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3227 Under some operating systems, breakpoints cannot be used in a program if
3228 any other process is running that program. In this situation,
3229 attempting to run or continue a program with a breakpoint causes
3230 @value{GDBN} to print an error message:
3233 Cannot insert breakpoints.
3234 The same program may be running in another process.
3237 When this happens, you have three ways to proceed:
3241 Remove or disable the breakpoints, then continue.
3244 Suspend @value{GDBN}, and copy the file containing your program to a new
3245 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3246 that @value{GDBN} should run your program under that name.
3247 Then start your program again.
3250 Relink your program so that the text segment is nonsharable, using the
3251 linker option @samp{-N}. The operating system limitation may not apply
3252 to nonsharable executables.
3256 A similar message can be printed if you request too many active
3257 hardware-assisted breakpoints and watchpoints:
3259 @c FIXME: the precise wording of this message may change; the relevant
3260 @c source change is not committed yet (Sep 3, 1999).
3262 Stopped; cannot insert breakpoints.
3263 You may have requested too many hardware breakpoints and watchpoints.
3267 This message is printed when you attempt to resume the program, since
3268 only then @value{GDBN} knows exactly how many hardware breakpoints and
3269 watchpoints it needs to insert.
3271 When this message is printed, you need to disable or remove some of the
3272 hardware-assisted breakpoints and watchpoints, and then continue.
3275 @node Continuing and Stepping
3276 @section Continuing and stepping
3280 @cindex resuming execution
3281 @dfn{Continuing} means resuming program execution until your program
3282 completes normally. In contrast, @dfn{stepping} means executing just
3283 one more ``step'' of your program, where ``step'' may mean either one
3284 line of source code, or one machine instruction (depending on what
3285 particular command you use). Either when continuing or when stepping,
3286 your program may stop even sooner, due to a breakpoint or a signal. (If
3287 it stops due to a signal, you may want to use @code{handle}, or use
3288 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3292 @kindex c @r{(@code{continue})}
3293 @kindex fg @r{(resume foreground execution)}
3294 @item continue @r{[}@var{ignore-count}@r{]}
3295 @itemx c @r{[}@var{ignore-count}@r{]}
3296 @itemx fg @r{[}@var{ignore-count}@r{]}
3297 Resume program execution, at the address where your program last stopped;
3298 any breakpoints set at that address are bypassed. The optional argument
3299 @var{ignore-count} allows you to specify a further number of times to
3300 ignore a breakpoint at this location; its effect is like that of
3301 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3303 The argument @var{ignore-count} is meaningful only when your program
3304 stopped due to a breakpoint. At other times, the argument to
3305 @code{continue} is ignored.
3307 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3308 debugged program is deemed to be the foreground program) are provided
3309 purely for convenience, and have exactly the same behavior as
3313 To resume execution at a different place, you can use @code{return}
3314 (@pxref{Returning, ,Returning from a function}) to go back to the
3315 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3316 different address}) to go to an arbitrary location in your program.
3318 A typical technique for using stepping is to set a breakpoint
3319 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3320 beginning of the function or the section of your program where a problem
3321 is believed to lie, run your program until it stops at that breakpoint,
3322 and then step through the suspect area, examining the variables that are
3323 interesting, until you see the problem happen.
3327 @kindex s @r{(@code{step})}
3329 Continue running your program until control reaches a different source
3330 line, then stop it and return control to @value{GDBN}. This command is
3331 abbreviated @code{s}.
3334 @c "without debugging information" is imprecise; actually "without line
3335 @c numbers in the debugging information". (gcc -g1 has debugging info but
3336 @c not line numbers). But it seems complex to try to make that
3337 @c distinction here.
3338 @emph{Warning:} If you use the @code{step} command while control is
3339 within a function that was compiled without debugging information,
3340 execution proceeds until control reaches a function that does have
3341 debugging information. Likewise, it will not step into a function which
3342 is compiled without debugging information. To step through functions
3343 without debugging information, use the @code{stepi} command, described
3347 The @code{step} command only stops at the first instruction of a source
3348 line. This prevents the multiple stops that could otherwise occur in
3349 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3350 to stop if a function that has debugging information is called within
3351 the line. In other words, @code{step} @emph{steps inside} any functions
3352 called within the line.
3354 Also, the @code{step} command only enters a function if there is line
3355 number information for the function. Otherwise it acts like the
3356 @code{next} command. This avoids problems when using @code{cc -gl}
3357 on MIPS machines. Previously, @code{step} entered subroutines if there
3358 was any debugging information about the routine.
3360 @item step @var{count}
3361 Continue running as in @code{step}, but do so @var{count} times. If a
3362 breakpoint is reached, or a signal not related to stepping occurs before
3363 @var{count} steps, stepping stops right away.
3366 @kindex n @r{(@code{next})}
3367 @item next @r{[}@var{count}@r{]}
3368 Continue to the next source line in the current (innermost) stack frame.
3369 This is similar to @code{step}, but function calls that appear within
3370 the line of code are executed without stopping. Execution stops when
3371 control reaches a different line of code at the original stack level
3372 that was executing when you gave the @code{next} command. This command
3373 is abbreviated @code{n}.
3375 An argument @var{count} is a repeat count, as for @code{step}.
3378 @c FIX ME!! Do we delete this, or is there a way it fits in with
3379 @c the following paragraph? --- Vctoria
3381 @c @code{next} within a function that lacks debugging information acts like
3382 @c @code{step}, but any function calls appearing within the code of the
3383 @c function are executed without stopping.
3385 The @code{next} command only stops at the first instruction of a
3386 source line. This prevents multiple stops that could otherwise occur in
3387 @code{switch} statements, @code{for} loops, etc.
3389 @kindex set step-mode
3391 @cindex functions without line info, and stepping
3392 @cindex stepping into functions with no line info
3393 @itemx set step-mode on
3394 The @code{set step-mode on} command causes the @code{step} command to
3395 stop at the first instruction of a function which contains no debug line
3396 information rather than stepping over it.
3398 This is useful in cases where you may be interested in inspecting the
3399 machine instructions of a function which has no symbolic info and do not
3400 want @value{GDBN} to automatically skip over this function.
3402 @item set step-mode off
3403 Causes the @code{step} command to step over any functions which contains no
3404 debug information. This is the default.
3408 Continue running until just after function in the selected stack frame
3409 returns. Print the returned value (if any).
3411 Contrast this with the @code{return} command (@pxref{Returning,
3412 ,Returning from a function}).
3415 @kindex u @r{(@code{until})}
3418 Continue running until a source line past the current line, in the
3419 current stack frame, is reached. This command is used to avoid single
3420 stepping through a loop more than once. It is like the @code{next}
3421 command, except that when @code{until} encounters a jump, it
3422 automatically continues execution until the program counter is greater
3423 than the address of the jump.
3425 This means that when you reach the end of a loop after single stepping
3426 though it, @code{until} makes your program continue execution until it
3427 exits the loop. In contrast, a @code{next} command at the end of a loop
3428 simply steps back to the beginning of the loop, which forces you to step
3429 through the next iteration.
3431 @code{until} always stops your program if it attempts to exit the current
3434 @code{until} may produce somewhat counterintuitive results if the order
3435 of machine code does not match the order of the source lines. For
3436 example, in the following excerpt from a debugging session, the @code{f}
3437 (@code{frame}) command shows that execution is stopped at line
3438 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3442 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3444 (@value{GDBP}) until
3445 195 for ( ; argc > 0; NEXTARG) @{
3448 This happened because, for execution efficiency, the compiler had
3449 generated code for the loop closure test at the end, rather than the
3450 start, of the loop---even though the test in a C @code{for}-loop is
3451 written before the body of the loop. The @code{until} command appeared
3452 to step back to the beginning of the loop when it advanced to this
3453 expression; however, it has not really gone to an earlier
3454 statement---not in terms of the actual machine code.
3456 @code{until} with no argument works by means of single
3457 instruction stepping, and hence is slower than @code{until} with an
3460 @item until @var{location}
3461 @itemx u @var{location}
3462 Continue running your program until either the specified location is
3463 reached, or the current stack frame returns. @var{location} is any of
3464 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3465 ,Setting breakpoints}). This form of the command uses breakpoints, and
3466 hence is quicker than @code{until} without an argument. The specified
3467 location is actually reached only if it is in the current frame. This
3468 implies that @code{until} can be used to skip over recursive function
3469 invocations. For instance in the code below, if the current location is
3470 line @code{96}, issuing @code{until 99} will execute the program up to
3471 line @code{99} in the same invocation of factorial, i.e. after the inner
3472 invocations have returned.
3475 94 int factorial (int value)
3477 96 if (value > 1) @{
3478 97 value *= factorial (value - 1);
3485 @kindex advance @var{location}
3486 @itemx advance @var{location}
3487 Continue running the program up to the given location. An argument is
3488 required, anything of the same form as arguments for the @code{break}
3489 command. Execution will also stop upon exit from the current stack
3490 frame. This command is similar to @code{until}, but @code{advance} will
3491 not skip over recursive function calls, and the target location doesn't
3492 have to be in the same frame as the current one.
3496 @kindex si @r{(@code{stepi})}
3498 @itemx stepi @var{arg}
3500 Execute one machine instruction, then stop and return to the debugger.
3502 It is often useful to do @samp{display/i $pc} when stepping by machine
3503 instructions. This makes @value{GDBN} automatically display the next
3504 instruction to be executed, each time your program stops. @xref{Auto
3505 Display,, Automatic display}.
3507 An argument is a repeat count, as in @code{step}.
3511 @kindex ni @r{(@code{nexti})}
3513 @itemx nexti @var{arg}
3515 Execute one machine instruction, but if it is a function call,
3516 proceed until the function returns.
3518 An argument is a repeat count, as in @code{next}.
3525 A signal is an asynchronous event that can happen in a program. The
3526 operating system defines the possible kinds of signals, and gives each
3527 kind a name and a number. For example, in Unix @code{SIGINT} is the
3528 signal a program gets when you type an interrupt character (often @kbd{C-c});
3529 @code{SIGSEGV} is the signal a program gets from referencing a place in
3530 memory far away from all the areas in use; @code{SIGALRM} occurs when
3531 the alarm clock timer goes off (which happens only if your program has
3532 requested an alarm).
3534 @cindex fatal signals
3535 Some signals, including @code{SIGALRM}, are a normal part of the
3536 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3537 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3538 program has not specified in advance some other way to handle the signal.
3539 @code{SIGINT} does not indicate an error in your program, but it is normally
3540 fatal so it can carry out the purpose of the interrupt: to kill the program.
3542 @value{GDBN} has the ability to detect any occurrence of a signal in your
3543 program. You can tell @value{GDBN} in advance what to do for each kind of
3546 @cindex handling signals
3547 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3548 @code{SIGALRM} be silently passed to your program
3549 (so as not to interfere with their role in the program's functioning)
3550 but to stop your program immediately whenever an error signal happens.
3551 You can change these settings with the @code{handle} command.
3554 @kindex info signals
3557 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3558 handle each one. You can use this to see the signal numbers of all
3559 the defined types of signals.
3561 @code{info handle} is an alias for @code{info signals}.
3564 @item handle @var{signal} @var{keywords}@dots{}
3565 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3566 can be the number of a signal or its name (with or without the
3567 @samp{SIG} at the beginning); a list of signal numbers of the form
3568 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3569 known signals. The @var{keywords} say what change to make.
3573 The keywords allowed by the @code{handle} command can be abbreviated.
3574 Their full names are:
3578 @value{GDBN} should not stop your program when this signal happens. It may
3579 still print a message telling you that the signal has come in.
3582 @value{GDBN} should stop your program when this signal happens. This implies
3583 the @code{print} keyword as well.
3586 @value{GDBN} should print a message when this signal happens.
3589 @value{GDBN} should not mention the occurrence of the signal at all. This
3590 implies the @code{nostop} keyword as well.
3594 @value{GDBN} should allow your program to see this signal; your program
3595 can handle the signal, or else it may terminate if the signal is fatal
3596 and not handled. @code{pass} and @code{noignore} are synonyms.
3600 @value{GDBN} should not allow your program to see this signal.
3601 @code{nopass} and @code{ignore} are synonyms.
3605 When a signal stops your program, the signal is not visible to the
3607 continue. Your program sees the signal then, if @code{pass} is in
3608 effect for the signal in question @emph{at that time}. In other words,
3609 after @value{GDBN} reports a signal, you can use the @code{handle}
3610 command with @code{pass} or @code{nopass} to control whether your
3611 program sees that signal when you continue.
3613 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3614 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3615 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3618 You can also use the @code{signal} command to prevent your program from
3619 seeing a signal, or cause it to see a signal it normally would not see,
3620 or to give it any signal at any time. For example, if your program stopped
3621 due to some sort of memory reference error, you might store correct
3622 values into the erroneous variables and continue, hoping to see more
3623 execution; but your program would probably terminate immediately as
3624 a result of the fatal signal once it saw the signal. To prevent this,
3625 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3629 @section Stopping and starting multi-thread programs
3631 When your program has multiple threads (@pxref{Threads,, Debugging
3632 programs with multiple threads}), you can choose whether to set
3633 breakpoints on all threads, or on a particular thread.
3636 @cindex breakpoints and threads
3637 @cindex thread breakpoints
3638 @kindex break @dots{} thread @var{threadno}
3639 @item break @var{linespec} thread @var{threadno}
3640 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3641 @var{linespec} specifies source lines; there are several ways of
3642 writing them, but the effect is always to specify some source line.
3644 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3645 to specify that you only want @value{GDBN} to stop the program when a
3646 particular thread reaches this breakpoint. @var{threadno} is one of the
3647 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3648 column of the @samp{info threads} display.
3650 If you do not specify @samp{thread @var{threadno}} when you set a
3651 breakpoint, the breakpoint applies to @emph{all} threads of your
3654 You can use the @code{thread} qualifier on conditional breakpoints as
3655 well; in this case, place @samp{thread @var{threadno}} before the
3656 breakpoint condition, like this:
3659 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3664 @cindex stopped threads
3665 @cindex threads, stopped
3666 Whenever your program stops under @value{GDBN} for any reason,
3667 @emph{all} threads of execution stop, not just the current thread. This
3668 allows you to examine the overall state of the program, including
3669 switching between threads, without worrying that things may change
3672 @cindex continuing threads
3673 @cindex threads, continuing
3674 Conversely, whenever you restart the program, @emph{all} threads start
3675 executing. @emph{This is true even when single-stepping} with commands
3676 like @code{step} or @code{next}.
3678 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3679 Since thread scheduling is up to your debugging target's operating
3680 system (not controlled by @value{GDBN}), other threads may
3681 execute more than one statement while the current thread completes a
3682 single step. Moreover, in general other threads stop in the middle of a
3683 statement, rather than at a clean statement boundary, when the program
3686 You might even find your program stopped in another thread after
3687 continuing or even single-stepping. This happens whenever some other
3688 thread runs into a breakpoint, a signal, or an exception before the
3689 first thread completes whatever you requested.
3691 On some OSes, you can lock the OS scheduler and thus allow only a single
3695 @item set scheduler-locking @var{mode}
3696 Set the scheduler locking mode. If it is @code{off}, then there is no
3697 locking and any thread may run at any time. If @code{on}, then only the
3698 current thread may run when the inferior is resumed. The @code{step}
3699 mode optimizes for single-stepping. It stops other threads from
3700 ``seizing the prompt'' by preempting the current thread while you are
3701 stepping. Other threads will only rarely (or never) get a chance to run
3702 when you step. They are more likely to run when you @samp{next} over a
3703 function call, and they are completely free to run when you use commands
3704 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3705 thread hits a breakpoint during its timeslice, they will never steal the
3706 @value{GDBN} prompt away from the thread that you are debugging.
3708 @item show scheduler-locking
3709 Display the current scheduler locking mode.
3714 @chapter Examining the Stack
3716 When your program has stopped, the first thing you need to know is where it
3717 stopped and how it got there.
3720 Each time your program performs a function call, information about the call
3722 That information includes the location of the call in your program,
3723 the arguments of the call,
3724 and the local variables of the function being called.
3725 The information is saved in a block of data called a @dfn{stack frame}.
3726 The stack frames are allocated in a region of memory called the @dfn{call
3729 When your program stops, the @value{GDBN} commands for examining the
3730 stack allow you to see all of this information.
3732 @cindex selected frame
3733 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3734 @value{GDBN} commands refer implicitly to the selected frame. In
3735 particular, whenever you ask @value{GDBN} for the value of a variable in
3736 your program, the value is found in the selected frame. There are
3737 special @value{GDBN} commands to select whichever frame you are
3738 interested in. @xref{Selection, ,Selecting a frame}.
3740 When your program stops, @value{GDBN} automatically selects the
3741 currently executing frame and describes it briefly, similar to the
3742 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3745 * Frames:: Stack frames
3746 * Backtrace:: Backtraces
3747 * Selection:: Selecting a frame
3748 * Frame Info:: Information on a frame
3753 @section Stack frames
3755 @cindex frame, definition
3757 The call stack is divided up into contiguous pieces called @dfn{stack
3758 frames}, or @dfn{frames} for short; each frame is the data associated
3759 with one call to one function. The frame contains the arguments given
3760 to the function, the function's local variables, and the address at
3761 which the function is executing.
3763 @cindex initial frame
3764 @cindex outermost frame
3765 @cindex innermost frame
3766 When your program is started, the stack has only one frame, that of the
3767 function @code{main}. This is called the @dfn{initial} frame or the
3768 @dfn{outermost} frame. Each time a function is called, a new frame is
3769 made. Each time a function returns, the frame for that function invocation
3770 is eliminated. If a function is recursive, there can be many frames for
3771 the same function. The frame for the function in which execution is
3772 actually occurring is called the @dfn{innermost} frame. This is the most
3773 recently created of all the stack frames that still exist.
3775 @cindex frame pointer
3776 Inside your program, stack frames are identified by their addresses. A
3777 stack frame consists of many bytes, each of which has its own address; each
3778 kind of computer has a convention for choosing one byte whose
3779 address serves as the address of the frame. Usually this address is kept
3780 in a register called the @dfn{frame pointer register} while execution is
3781 going on in that frame.
3783 @cindex frame number
3784 @value{GDBN} assigns numbers to all existing stack frames, starting with
3785 zero for the innermost frame, one for the frame that called it,
3786 and so on upward. These numbers do not really exist in your program;
3787 they are assigned by @value{GDBN} to give you a way of designating stack
3788 frames in @value{GDBN} commands.
3790 @c The -fomit-frame-pointer below perennially causes hbox overflow
3791 @c underflow problems.
3792 @cindex frameless execution
3793 Some compilers provide a way to compile functions so that they operate
3794 without stack frames. (For example, the @value{GCC} option
3796 @samp{-fomit-frame-pointer}
3798 generates functions without a frame.)
3799 This is occasionally done with heavily used library functions to save
3800 the frame setup time. @value{GDBN} has limited facilities for dealing
3801 with these function invocations. If the innermost function invocation
3802 has no stack frame, @value{GDBN} nevertheless regards it as though
3803 it had a separate frame, which is numbered zero as usual, allowing
3804 correct tracing of the function call chain. However, @value{GDBN} has
3805 no provision for frameless functions elsewhere in the stack.
3808 @kindex frame@r{, command}
3809 @cindex current stack frame
3810 @item frame @var{args}
3811 The @code{frame} command allows you to move from one stack frame to another,
3812 and to print the stack frame you select. @var{args} may be either the
3813 address of the frame or the stack frame number. Without an argument,
3814 @code{frame} prints the current stack frame.
3816 @kindex select-frame
3817 @cindex selecting frame silently
3819 The @code{select-frame} command allows you to move from one stack frame
3820 to another without printing the frame. This is the silent version of
3829 @cindex stack traces
3830 A backtrace is a summary of how your program got where it is. It shows one
3831 line per frame, for many frames, starting with the currently executing
3832 frame (frame zero), followed by its caller (frame one), and on up the
3837 @kindex bt @r{(@code{backtrace})}
3840 Print a backtrace of the entire stack: one line per frame for all
3841 frames in the stack.
3843 You can stop the backtrace at any time by typing the system interrupt
3844 character, normally @kbd{C-c}.
3846 @item backtrace @var{n}
3848 Similar, but print only the innermost @var{n} frames.
3850 @item backtrace -@var{n}
3852 Similar, but print only the outermost @var{n} frames.
3857 @kindex info s @r{(@code{info stack})}
3858 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3859 are additional aliases for @code{backtrace}.
3861 Each line in the backtrace shows the frame number and the function name.
3862 The program counter value is also shown---unless you use @code{set
3863 print address off}. The backtrace also shows the source file name and
3864 line number, as well as the arguments to the function. The program
3865 counter value is omitted if it is at the beginning of the code for that
3868 Here is an example of a backtrace. It was made with the command
3869 @samp{bt 3}, so it shows the innermost three frames.
3873 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3875 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3876 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3878 (More stack frames follow...)
3883 The display for frame zero does not begin with a program counter
3884 value, indicating that your program has stopped at the beginning of the
3885 code for line @code{993} of @code{builtin.c}.
3887 @kindex set backtrace-below-main
3888 @kindex show backtrace-below-main
3890 Most programs have a standard entry point---a place where system libraries
3891 and startup code transition into user code. For C this is @code{main}.
3892 When @value{GDBN} finds the entry function in a backtrace it will terminate
3893 the backtrace, to avoid tracing into highly system-specific (and generally
3894 uninteresting) code. If you need to examine the startup code, then you can
3895 change this behavior.
3898 @item set backtrace-below-main off
3899 Backtraces will stop when they encounter the user entry point. This is the
3902 @item set backtrace-below-main
3903 @itemx set backtrace-below-main on
3904 Backtraces will continue past the user entry point to the top of the stack.
3906 @item show backtrace-below-main
3907 Display the current backtrace policy.
3911 @section Selecting a frame
3913 Most commands for examining the stack and other data in your program work on
3914 whichever stack frame is selected at the moment. Here are the commands for
3915 selecting a stack frame; all of them finish by printing a brief description
3916 of the stack frame just selected.
3919 @kindex frame@r{, selecting}
3920 @kindex f @r{(@code{frame})}
3923 Select frame number @var{n}. Recall that frame zero is the innermost
3924 (currently executing) frame, frame one is the frame that called the
3925 innermost one, and so on. The highest-numbered frame is the one for
3928 @item frame @var{addr}
3930 Select the frame at address @var{addr}. This is useful mainly if the
3931 chaining of stack frames has been damaged by a bug, making it
3932 impossible for @value{GDBN} to assign numbers properly to all frames. In
3933 addition, this can be useful when your program has multiple stacks and
3934 switches between them.
3936 On the SPARC architecture, @code{frame} needs two addresses to
3937 select an arbitrary frame: a frame pointer and a stack pointer.
3939 On the MIPS and Alpha architecture, it needs two addresses: a stack
3940 pointer and a program counter.
3942 On the 29k architecture, it needs three addresses: a register stack
3943 pointer, a program counter, and a memory stack pointer.
3944 @c note to future updaters: this is conditioned on a flag
3945 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3946 @c as of 27 Jan 1994.
3950 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3951 advances toward the outermost frame, to higher frame numbers, to frames
3952 that have existed longer. @var{n} defaults to one.
3955 @kindex do @r{(@code{down})}
3957 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3958 advances toward the innermost frame, to lower frame numbers, to frames
3959 that were created more recently. @var{n} defaults to one. You may
3960 abbreviate @code{down} as @code{do}.
3963 All of these commands end by printing two lines of output describing the
3964 frame. The first line shows the frame number, the function name, the
3965 arguments, and the source file and line number of execution in that
3966 frame. The second line shows the text of that source line.
3974 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3976 10 read_input_file (argv[i]);
3980 After such a printout, the @code{list} command with no arguments
3981 prints ten lines centered on the point of execution in the frame.
3982 You can also edit the program at the point of execution with your favorite
3983 editing program by typing @code{edit}.
3984 @xref{List, ,Printing source lines},
3988 @kindex down-silently
3990 @item up-silently @var{n}
3991 @itemx down-silently @var{n}
3992 These two commands are variants of @code{up} and @code{down},
3993 respectively; they differ in that they do their work silently, without
3994 causing display of the new frame. They are intended primarily for use
3995 in @value{GDBN} command scripts, where the output might be unnecessary and
4000 @section Information about a frame
4002 There are several other commands to print information about the selected
4008 When used without any argument, this command does not change which
4009 frame is selected, but prints a brief description of the currently
4010 selected stack frame. It can be abbreviated @code{f}. With an
4011 argument, this command is used to select a stack frame.
4012 @xref{Selection, ,Selecting a frame}.
4015 @kindex info f @r{(@code{info frame})}
4018 This command prints a verbose description of the selected stack frame,
4023 the address of the frame
4025 the address of the next frame down (called by this frame)
4027 the address of the next frame up (caller of this frame)
4029 the language in which the source code corresponding to this frame is written
4031 the address of the frame's arguments
4033 the address of the frame's local variables
4035 the program counter saved in it (the address of execution in the caller frame)
4037 which registers were saved in the frame
4040 @noindent The verbose description is useful when
4041 something has gone wrong that has made the stack format fail to fit
4042 the usual conventions.
4044 @item info frame @var{addr}
4045 @itemx info f @var{addr}
4046 Print a verbose description of the frame at address @var{addr}, without
4047 selecting that frame. The selected frame remains unchanged by this
4048 command. This requires the same kind of address (more than one for some
4049 architectures) that you specify in the @code{frame} command.
4050 @xref{Selection, ,Selecting a frame}.
4054 Print the arguments of the selected frame, each on a separate line.
4058 Print the local variables of the selected frame, each on a separate
4059 line. These are all variables (declared either static or automatic)
4060 accessible at the point of execution of the selected frame.
4063 @cindex catch exceptions, list active handlers
4064 @cindex exception handlers, how to list
4066 Print a list of all the exception handlers that are active in the
4067 current stack frame at the current point of execution. To see other
4068 exception handlers, visit the associated frame (using the @code{up},
4069 @code{down}, or @code{frame} commands); then type @code{info catch}.
4070 @xref{Set Catchpoints, , Setting catchpoints}.
4076 @chapter Examining Source Files
4078 @value{GDBN} can print parts of your program's source, since the debugging
4079 information recorded in the program tells @value{GDBN} what source files were
4080 used to build it. When your program stops, @value{GDBN} spontaneously prints
4081 the line where it stopped. Likewise, when you select a stack frame
4082 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4083 execution in that frame has stopped. You can print other portions of
4084 source files by explicit command.
4086 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4087 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4088 @value{GDBN} under @sc{gnu} Emacs}.
4091 * List:: Printing source lines
4092 * Edit:: Editing source files
4093 * Search:: Searching source files
4094 * Source Path:: Specifying source directories
4095 * Machine Code:: Source and machine code
4099 @section Printing source lines
4102 @kindex l @r{(@code{list})}
4103 To print lines from a source file, use the @code{list} command
4104 (abbreviated @code{l}). By default, ten lines are printed.
4105 There are several ways to specify what part of the file you want to print.
4107 Here are the forms of the @code{list} command most commonly used:
4110 @item list @var{linenum}
4111 Print lines centered around line number @var{linenum} in the
4112 current source file.
4114 @item list @var{function}
4115 Print lines centered around the beginning of function
4119 Print more lines. If the last lines printed were printed with a
4120 @code{list} command, this prints lines following the last lines
4121 printed; however, if the last line printed was a solitary line printed
4122 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4123 Stack}), this prints lines centered around that line.
4126 Print lines just before the lines last printed.
4129 By default, @value{GDBN} prints ten source lines with any of these forms of
4130 the @code{list} command. You can change this using @code{set listsize}:
4133 @kindex set listsize
4134 @item set listsize @var{count}
4135 Make the @code{list} command display @var{count} source lines (unless
4136 the @code{list} argument explicitly specifies some other number).
4138 @kindex show listsize
4140 Display the number of lines that @code{list} prints.
4143 Repeating a @code{list} command with @key{RET} discards the argument,
4144 so it is equivalent to typing just @code{list}. This is more useful
4145 than listing the same lines again. An exception is made for an
4146 argument of @samp{-}; that argument is preserved in repetition so that
4147 each repetition moves up in the source file.
4150 In general, the @code{list} command expects you to supply zero, one or two
4151 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4152 of writing them, but the effect is always to specify some source line.
4153 Here is a complete description of the possible arguments for @code{list}:
4156 @item list @var{linespec}
4157 Print lines centered around the line specified by @var{linespec}.
4159 @item list @var{first},@var{last}
4160 Print lines from @var{first} to @var{last}. Both arguments are
4163 @item list ,@var{last}
4164 Print lines ending with @var{last}.
4166 @item list @var{first},
4167 Print lines starting with @var{first}.
4170 Print lines just after the lines last printed.
4173 Print lines just before the lines last printed.
4176 As described in the preceding table.
4179 Here are the ways of specifying a single source line---all the
4184 Specifies line @var{number} of the current source file.
4185 When a @code{list} command has two linespecs, this refers to
4186 the same source file as the first linespec.
4189 Specifies the line @var{offset} lines after the last line printed.
4190 When used as the second linespec in a @code{list} command that has
4191 two, this specifies the line @var{offset} lines down from the
4195 Specifies the line @var{offset} lines before the last line printed.
4197 @item @var{filename}:@var{number}
4198 Specifies line @var{number} in the source file @var{filename}.
4200 @item @var{function}
4201 Specifies the line that begins the body of the function @var{function}.
4202 For example: in C, this is the line with the open brace.
4204 @item @var{filename}:@var{function}
4205 Specifies the line of the open-brace that begins the body of the
4206 function @var{function} in the file @var{filename}. You only need the
4207 file name with a function name to avoid ambiguity when there are
4208 identically named functions in different source files.
4210 @item *@var{address}
4211 Specifies the line containing the program address @var{address}.
4212 @var{address} may be any expression.
4216 @section Editing source files
4217 @cindex editing source files
4220 @kindex e @r{(@code{edit})}
4221 To edit the lines in a source file, use the @code{edit} command.
4222 The editing program of your choice
4223 is invoked with the current line set to
4224 the active line in the program.
4225 Alternatively, there are several ways to specify what part of the file you
4226 want to print if you want to see other parts of the program.
4228 Here are the forms of the @code{edit} command most commonly used:
4232 Edit the current source file at the active line number in the program.
4234 @item edit @var{number}
4235 Edit the current source file with @var{number} as the active line number.
4237 @item edit @var{function}
4238 Edit the file containing @var{function} at the beginning of its definition.
4240 @item edit @var{filename}:@var{number}
4241 Specifies line @var{number} in the source file @var{filename}.
4243 @item edit @var{filename}:@var{function}
4244 Specifies the line that begins the body of the
4245 function @var{function} in the file @var{filename}. You only need the
4246 file name with a function name to avoid ambiguity when there are
4247 identically named functions in different source files.
4249 @item edit *@var{address}
4250 Specifies the line containing the program address @var{address}.
4251 @var{address} may be any expression.
4254 @subsection Choosing your editor
4255 You can customize @value{GDBN} to use any editor you want
4257 The only restriction is that your editor (say @code{ex}), recognizes the
4258 following command-line syntax:
4260 ex +@var{number} file
4262 The optional numeric value +@var{number} designates the active line in
4263 the file.}. By default, it is @value{EDITOR}, but you can change this
4264 by setting the environment variable @code{EDITOR} before using
4265 @value{GDBN}. For example, to configure @value{GDBN} to use the
4266 @code{vi} editor, you could use these commands with the @code{sh} shell:
4272 or in the @code{csh} shell,
4274 setenv EDITOR /usr/bin/vi
4279 @section Searching source files
4281 @kindex reverse-search
4283 There are two commands for searching through the current source file for a
4288 @kindex forward-search
4289 @item forward-search @var{regexp}
4290 @itemx search @var{regexp}
4291 The command @samp{forward-search @var{regexp}} checks each line,
4292 starting with the one following the last line listed, for a match for
4293 @var{regexp}. It lists the line that is found. You can use the
4294 synonym @samp{search @var{regexp}} or abbreviate the command name as
4297 @item reverse-search @var{regexp}
4298 The command @samp{reverse-search @var{regexp}} checks each line, starting
4299 with the one before the last line listed and going backward, for a match
4300 for @var{regexp}. It lists the line that is found. You can abbreviate
4301 this command as @code{rev}.
4305 @section Specifying source directories
4308 @cindex directories for source files
4309 Executable programs sometimes do not record the directories of the source
4310 files from which they were compiled, just the names. Even when they do,
4311 the directories could be moved between the compilation and your debugging
4312 session. @value{GDBN} has a list of directories to search for source files;
4313 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4314 it tries all the directories in the list, in the order they are present
4315 in the list, until it finds a file with the desired name. Note that
4316 the executable search path is @emph{not} used for this purpose. Neither is
4317 the current working directory, unless it happens to be in the source
4320 If @value{GDBN} cannot find a source file in the source path, and the
4321 object program records a directory, @value{GDBN} tries that directory
4322 too. If the source path is empty, and there is no record of the
4323 compilation directory, @value{GDBN} looks in the current directory as a
4326 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4327 any information it has cached about where source files are found and where
4328 each line is in the file.
4332 When you start @value{GDBN}, its source path includes only @samp{cdir}
4333 and @samp{cwd}, in that order.
4334 To add other directories, use the @code{directory} command.
4337 @item directory @var{dirname} @dots{}
4338 @item dir @var{dirname} @dots{}
4339 Add directory @var{dirname} to the front of the source path. Several
4340 directory names may be given to this command, separated by @samp{:}
4341 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4342 part of absolute file names) or
4343 whitespace. You may specify a directory that is already in the source
4344 path; this moves it forward, so @value{GDBN} searches it sooner.
4348 @vindex $cdir@r{, convenience variable}
4349 @vindex $cwdr@r{, convenience variable}
4350 @cindex compilation directory
4351 @cindex current directory
4352 @cindex working directory
4353 @cindex directory, current
4354 @cindex directory, compilation
4355 You can use the string @samp{$cdir} to refer to the compilation
4356 directory (if one is recorded), and @samp{$cwd} to refer to the current
4357 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4358 tracks the current working directory as it changes during your @value{GDBN}
4359 session, while the latter is immediately expanded to the current
4360 directory at the time you add an entry to the source path.
4363 Reset the source path to empty again. This requires confirmation.
4365 @c RET-repeat for @code{directory} is explicitly disabled, but since
4366 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4368 @item show directories
4369 @kindex show directories
4370 Print the source path: show which directories it contains.
4373 If your source path is cluttered with directories that are no longer of
4374 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4375 versions of source. You can correct the situation as follows:
4379 Use @code{directory} with no argument to reset the source path to empty.
4382 Use @code{directory} with suitable arguments to reinstall the
4383 directories you want in the source path. You can add all the
4384 directories in one command.
4388 @section Source and machine code
4390 You can use the command @code{info line} to map source lines to program
4391 addresses (and vice versa), and the command @code{disassemble} to display
4392 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4393 mode, the @code{info line} command causes the arrow to point to the
4394 line specified. Also, @code{info line} prints addresses in symbolic form as
4399 @item info line @var{linespec}
4400 Print the starting and ending addresses of the compiled code for
4401 source line @var{linespec}. You can specify source lines in any of
4402 the ways understood by the @code{list} command (@pxref{List, ,Printing
4406 For example, we can use @code{info line} to discover the location of
4407 the object code for the first line of function
4408 @code{m4_changequote}:
4410 @c FIXME: I think this example should also show the addresses in
4411 @c symbolic form, as they usually would be displayed.
4413 (@value{GDBP}) info line m4_changequote
4414 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4418 We can also inquire (using @code{*@var{addr}} as the form for
4419 @var{linespec}) what source line covers a particular address:
4421 (@value{GDBP}) info line *0x63ff
4422 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4425 @cindex @code{$_} and @code{info line}
4426 @kindex x@r{(examine), and} info line
4427 After @code{info line}, the default address for the @code{x} command
4428 is changed to the starting address of the line, so that @samp{x/i} is
4429 sufficient to begin examining the machine code (@pxref{Memory,
4430 ,Examining memory}). Also, this address is saved as the value of the
4431 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4436 @cindex assembly instructions
4437 @cindex instructions, assembly
4438 @cindex machine instructions
4439 @cindex listing machine instructions
4441 This specialized command dumps a range of memory as machine
4442 instructions. The default memory range is the function surrounding the
4443 program counter of the selected frame. A single argument to this
4444 command is a program counter value; @value{GDBN} dumps the function
4445 surrounding this value. Two arguments specify a range of addresses
4446 (first inclusive, second exclusive) to dump.
4449 The following example shows the disassembly of a range of addresses of
4450 HP PA-RISC 2.0 code:
4453 (@value{GDBP}) disas 0x32c4 0x32e4
4454 Dump of assembler code from 0x32c4 to 0x32e4:
4455 0x32c4 <main+204>: addil 0,dp
4456 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4457 0x32cc <main+212>: ldil 0x3000,r31
4458 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4459 0x32d4 <main+220>: ldo 0(r31),rp
4460 0x32d8 <main+224>: addil -0x800,dp
4461 0x32dc <main+228>: ldo 0x588(r1),r26
4462 0x32e0 <main+232>: ldil 0x3000,r31
4463 End of assembler dump.
4466 Some architectures have more than one commonly-used set of instruction
4467 mnemonics or other syntax.
4470 @kindex set disassembly-flavor
4471 @cindex assembly instructions
4472 @cindex instructions, assembly
4473 @cindex machine instructions
4474 @cindex listing machine instructions
4475 @cindex Intel disassembly flavor
4476 @cindex AT&T disassembly flavor
4477 @item set disassembly-flavor @var{instruction-set}
4478 Select the instruction set to use when disassembling the
4479 program via the @code{disassemble} or @code{x/i} commands.
4481 Currently this command is only defined for the Intel x86 family. You
4482 can set @var{instruction-set} to either @code{intel} or @code{att}.
4483 The default is @code{att}, the AT&T flavor used by default by Unix
4484 assemblers for x86-based targets.
4489 @chapter Examining Data
4491 @cindex printing data
4492 @cindex examining data
4495 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4496 @c document because it is nonstandard... Under Epoch it displays in a
4497 @c different window or something like that.
4498 The usual way to examine data in your program is with the @code{print}
4499 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4500 evaluates and prints the value of an expression of the language your
4501 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4502 Different Languages}).
4505 @item print @var{expr}
4506 @itemx print /@var{f} @var{expr}
4507 @var{expr} is an expression (in the source language). By default the
4508 value of @var{expr} is printed in a format appropriate to its data type;
4509 you can choose a different format by specifying @samp{/@var{f}}, where
4510 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4514 @itemx print /@var{f}
4515 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4516 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4517 conveniently inspect the same value in an alternative format.
4520 A more low-level way of examining data is with the @code{x} command.
4521 It examines data in memory at a specified address and prints it in a
4522 specified format. @xref{Memory, ,Examining memory}.
4524 If you are interested in information about types, or about how the
4525 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4526 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4530 * Expressions:: Expressions
4531 * Variables:: Program variables
4532 * Arrays:: Artificial arrays
4533 * Output Formats:: Output formats
4534 * Memory:: Examining memory
4535 * Auto Display:: Automatic display
4536 * Print Settings:: Print settings
4537 * Value History:: Value history
4538 * Convenience Vars:: Convenience variables
4539 * Registers:: Registers
4540 * Floating Point Hardware:: Floating point hardware
4541 * Vector Unit:: Vector Unit
4542 * Memory Region Attributes:: Memory region attributes
4543 * Dump/Restore Files:: Copy between memory and a file
4544 * Character Sets:: Debugging programs that use a different
4545 character set than GDB does
4549 @section Expressions
4552 @code{print} and many other @value{GDBN} commands accept an expression and
4553 compute its value. Any kind of constant, variable or operator defined
4554 by the programming language you are using is valid in an expression in
4555 @value{GDBN}. This includes conditional expressions, function calls,
4556 casts, and string constants. It also includes preprocessor macros, if
4557 you compiled your program to include this information; see
4560 @value{GDBN} supports array constants in expressions input by
4561 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4562 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4563 memory that is @code{malloc}ed in the target program.
4565 Because C is so widespread, most of the expressions shown in examples in
4566 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4567 Languages}, for information on how to use expressions in other
4570 In this section, we discuss operators that you can use in @value{GDBN}
4571 expressions regardless of your programming language.
4573 Casts are supported in all languages, not just in C, because it is so
4574 useful to cast a number into a pointer in order to examine a structure
4575 at that address in memory.
4576 @c FIXME: casts supported---Mod2 true?
4578 @value{GDBN} supports these operators, in addition to those common
4579 to programming languages:
4583 @samp{@@} is a binary operator for treating parts of memory as arrays.
4584 @xref{Arrays, ,Artificial arrays}, for more information.
4587 @samp{::} allows you to specify a variable in terms of the file or
4588 function where it is defined. @xref{Variables, ,Program variables}.
4590 @cindex @{@var{type}@}
4591 @cindex type casting memory
4592 @cindex memory, viewing as typed object
4593 @cindex casts, to view memory
4594 @item @{@var{type}@} @var{addr}
4595 Refers to an object of type @var{type} stored at address @var{addr} in
4596 memory. @var{addr} may be any expression whose value is an integer or
4597 pointer (but parentheses are required around binary operators, just as in
4598 a cast). This construct is allowed regardless of what kind of data is
4599 normally supposed to reside at @var{addr}.
4603 @section Program variables
4605 The most common kind of expression to use is the name of a variable
4608 Variables in expressions are understood in the selected stack frame
4609 (@pxref{Selection, ,Selecting a frame}); they must be either:
4613 global (or file-static)
4620 visible according to the scope rules of the
4621 programming language from the point of execution in that frame
4624 @noindent This means that in the function
4639 you can examine and use the variable @code{a} whenever your program is
4640 executing within the function @code{foo}, but you can only use or
4641 examine the variable @code{b} while your program is executing inside
4642 the block where @code{b} is declared.
4644 @cindex variable name conflict
4645 There is an exception: you can refer to a variable or function whose
4646 scope is a single source file even if the current execution point is not
4647 in this file. But it is possible to have more than one such variable or
4648 function with the same name (in different source files). If that
4649 happens, referring to that name has unpredictable effects. If you wish,
4650 you can specify a static variable in a particular function or file,
4651 using the colon-colon notation:
4653 @cindex colon-colon, context for variables/functions
4655 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4656 @cindex @code{::}, context for variables/functions
4659 @var{file}::@var{variable}
4660 @var{function}::@var{variable}
4664 Here @var{file} or @var{function} is the name of the context for the
4665 static @var{variable}. In the case of file names, you can use quotes to
4666 make sure @value{GDBN} parses the file name as a single word---for example,
4667 to print a global value of @code{x} defined in @file{f2.c}:
4670 (@value{GDBP}) p 'f2.c'::x
4673 @cindex C@t{++} scope resolution
4674 This use of @samp{::} is very rarely in conflict with the very similar
4675 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4676 scope resolution operator in @value{GDBN} expressions.
4677 @c FIXME: Um, so what happens in one of those rare cases where it's in
4680 @cindex wrong values
4681 @cindex variable values, wrong
4683 @emph{Warning:} Occasionally, a local variable may appear to have the
4684 wrong value at certain points in a function---just after entry to a new
4685 scope, and just before exit.
4687 You may see this problem when you are stepping by machine instructions.
4688 This is because, on most machines, it takes more than one instruction to
4689 set up a stack frame (including local variable definitions); if you are
4690 stepping by machine instructions, variables may appear to have the wrong
4691 values until the stack frame is completely built. On exit, it usually
4692 also takes more than one machine instruction to destroy a stack frame;
4693 after you begin stepping through that group of instructions, local
4694 variable definitions may be gone.
4696 This may also happen when the compiler does significant optimizations.
4697 To be sure of always seeing accurate values, turn off all optimization
4700 @cindex ``No symbol "foo" in current context''
4701 Another possible effect of compiler optimizations is to optimize
4702 unused variables out of existence, or assign variables to registers (as
4703 opposed to memory addresses). Depending on the support for such cases
4704 offered by the debug info format used by the compiler, @value{GDBN}
4705 might not be able to display values for such local variables. If that
4706 happens, @value{GDBN} will print a message like this:
4709 No symbol "foo" in current context.
4712 To solve such problems, either recompile without optimizations, or use a
4713 different debug info format, if the compiler supports several such
4714 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4715 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4716 in a format that is superior to formats such as COFF. You may be able
4717 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4718 debug info. See @ref{Debugging Options,,Options for Debugging Your
4719 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4724 @section Artificial arrays
4726 @cindex artificial array
4727 @kindex @@@r{, referencing memory as an array}
4728 It is often useful to print out several successive objects of the
4729 same type in memory; a section of an array, or an array of
4730 dynamically determined size for which only a pointer exists in the
4733 You can do this by referring to a contiguous span of memory as an
4734 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4735 operand of @samp{@@} should be the first element of the desired array
4736 and be an individual object. The right operand should be the desired length
4737 of the array. The result is an array value whose elements are all of
4738 the type of the left argument. The first element is actually the left
4739 argument; the second element comes from bytes of memory immediately
4740 following those that hold the first element, and so on. Here is an
4741 example. If a program says
4744 int *array = (int *) malloc (len * sizeof (int));
4748 you can print the contents of @code{array} with
4754 The left operand of @samp{@@} must reside in memory. Array values made
4755 with @samp{@@} in this way behave just like other arrays in terms of
4756 subscripting, and are coerced to pointers when used in expressions.
4757 Artificial arrays most often appear in expressions via the value history
4758 (@pxref{Value History, ,Value history}), after printing one out.
4760 Another way to create an artificial array is to use a cast.
4761 This re-interprets a value as if it were an array.
4762 The value need not be in memory:
4764 (@value{GDBP}) p/x (short[2])0x12345678
4765 $1 = @{0x1234, 0x5678@}
4768 As a convenience, if you leave the array length out (as in
4769 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4770 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4772 (@value{GDBP}) p/x (short[])0x12345678
4773 $2 = @{0x1234, 0x5678@}
4776 Sometimes the artificial array mechanism is not quite enough; in
4777 moderately complex data structures, the elements of interest may not
4778 actually be adjacent---for example, if you are interested in the values
4779 of pointers in an array. One useful work-around in this situation is
4780 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4781 variables}) as a counter in an expression that prints the first
4782 interesting value, and then repeat that expression via @key{RET}. For
4783 instance, suppose you have an array @code{dtab} of pointers to
4784 structures, and you are interested in the values of a field @code{fv}
4785 in each structure. Here is an example of what you might type:
4795 @node Output Formats
4796 @section Output formats
4798 @cindex formatted output
4799 @cindex output formats
4800 By default, @value{GDBN} prints a value according to its data type. Sometimes
4801 this is not what you want. For example, you might want to print a number
4802 in hex, or a pointer in decimal. Or you might want to view data in memory
4803 at a certain address as a character string or as an instruction. To do
4804 these things, specify an @dfn{output format} when you print a value.
4806 The simplest use of output formats is to say how to print a value
4807 already computed. This is done by starting the arguments of the
4808 @code{print} command with a slash and a format letter. The format
4809 letters supported are:
4813 Regard the bits of the value as an integer, and print the integer in
4817 Print as integer in signed decimal.
4820 Print as integer in unsigned decimal.
4823 Print as integer in octal.
4826 Print as integer in binary. The letter @samp{t} stands for ``two''.
4827 @footnote{@samp{b} cannot be used because these format letters are also
4828 used with the @code{x} command, where @samp{b} stands for ``byte'';
4829 see @ref{Memory,,Examining memory}.}
4832 @cindex unknown address, locating
4833 @cindex locate address
4834 Print as an address, both absolute in hexadecimal and as an offset from
4835 the nearest preceding symbol. You can use this format used to discover
4836 where (in what function) an unknown address is located:
4839 (@value{GDBP}) p/a 0x54320
4840 $3 = 0x54320 <_initialize_vx+396>
4844 The command @code{info symbol 0x54320} yields similar results.
4845 @xref{Symbols, info symbol}.
4848 Regard as an integer and print it as a character constant.
4851 Regard the bits of the value as a floating point number and print
4852 using typical floating point syntax.
4855 For example, to print the program counter in hex (@pxref{Registers}), type
4862 Note that no space is required before the slash; this is because command
4863 names in @value{GDBN} cannot contain a slash.
4865 To reprint the last value in the value history with a different format,
4866 you can use the @code{print} command with just a format and no
4867 expression. For example, @samp{p/x} reprints the last value in hex.
4870 @section Examining memory
4872 You can use the command @code{x} (for ``examine'') to examine memory in
4873 any of several formats, independently of your program's data types.
4875 @cindex examining memory
4877 @kindex x @r{(examine memory)}
4878 @item x/@var{nfu} @var{addr}
4881 Use the @code{x} command to examine memory.
4884 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4885 much memory to display and how to format it; @var{addr} is an
4886 expression giving the address where you want to start displaying memory.
4887 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4888 Several commands set convenient defaults for @var{addr}.
4891 @item @var{n}, the repeat count
4892 The repeat count is a decimal integer; the default is 1. It specifies
4893 how much memory (counting by units @var{u}) to display.
4894 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4897 @item @var{f}, the display format
4898 The display format is one of the formats used by @code{print},
4899 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4900 The default is @samp{x} (hexadecimal) initially.
4901 The default changes each time you use either @code{x} or @code{print}.
4903 @item @var{u}, the unit size
4904 The unit size is any of
4910 Halfwords (two bytes).
4912 Words (four bytes). This is the initial default.
4914 Giant words (eight bytes).
4917 Each time you specify a unit size with @code{x}, that size becomes the
4918 default unit the next time you use @code{x}. (For the @samp{s} and
4919 @samp{i} formats, the unit size is ignored and is normally not written.)
4921 @item @var{addr}, starting display address
4922 @var{addr} is the address where you want @value{GDBN} to begin displaying
4923 memory. The expression need not have a pointer value (though it may);
4924 it is always interpreted as an integer address of a byte of memory.
4925 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4926 @var{addr} is usually just after the last address examined---but several
4927 other commands also set the default address: @code{info breakpoints} (to
4928 the address of the last breakpoint listed), @code{info line} (to the
4929 starting address of a line), and @code{print} (if you use it to display
4930 a value from memory).
4933 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4934 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4935 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4936 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4937 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4939 Since the letters indicating unit sizes are all distinct from the
4940 letters specifying output formats, you do not have to remember whether
4941 unit size or format comes first; either order works. The output
4942 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4943 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4945 Even though the unit size @var{u} is ignored for the formats @samp{s}
4946 and @samp{i}, you might still want to use a count @var{n}; for example,
4947 @samp{3i} specifies that you want to see three machine instructions,
4948 including any operands. The command @code{disassemble} gives an
4949 alternative way of inspecting machine instructions; see @ref{Machine
4950 Code,,Source and machine code}.
4952 All the defaults for the arguments to @code{x} are designed to make it
4953 easy to continue scanning memory with minimal specifications each time
4954 you use @code{x}. For example, after you have inspected three machine
4955 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4956 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4957 the repeat count @var{n} is used again; the other arguments default as
4958 for successive uses of @code{x}.
4960 @cindex @code{$_}, @code{$__}, and value history
4961 The addresses and contents printed by the @code{x} command are not saved
4962 in the value history because there is often too much of them and they
4963 would get in the way. Instead, @value{GDBN} makes these values available for
4964 subsequent use in expressions as values of the convenience variables
4965 @code{$_} and @code{$__}. After an @code{x} command, the last address
4966 examined is available for use in expressions in the convenience variable
4967 @code{$_}. The contents of that address, as examined, are available in
4968 the convenience variable @code{$__}.
4970 If the @code{x} command has a repeat count, the address and contents saved
4971 are from the last memory unit printed; this is not the same as the last
4972 address printed if several units were printed on the last line of output.
4975 @section Automatic display
4976 @cindex automatic display
4977 @cindex display of expressions
4979 If you find that you want to print the value of an expression frequently
4980 (to see how it changes), you might want to add it to the @dfn{automatic
4981 display list} so that @value{GDBN} prints its value each time your program stops.
4982 Each expression added to the list is given a number to identify it;
4983 to remove an expression from the list, you specify that number.
4984 The automatic display looks like this:
4988 3: bar[5] = (struct hack *) 0x3804
4992 This display shows item numbers, expressions and their current values. As with
4993 displays you request manually using @code{x} or @code{print}, you can
4994 specify the output format you prefer; in fact, @code{display} decides
4995 whether to use @code{print} or @code{x} depending on how elaborate your
4996 format specification is---it uses @code{x} if you specify a unit size,
4997 or one of the two formats (@samp{i} and @samp{s}) that are only
4998 supported by @code{x}; otherwise it uses @code{print}.
5002 @item display @var{expr}
5003 Add the expression @var{expr} to the list of expressions to display
5004 each time your program stops. @xref{Expressions, ,Expressions}.
5006 @code{display} does not repeat if you press @key{RET} again after using it.
5008 @item display/@var{fmt} @var{expr}
5009 For @var{fmt} specifying only a display format and not a size or
5010 count, add the expression @var{expr} to the auto-display list but
5011 arrange to display it each time in the specified format @var{fmt}.
5012 @xref{Output Formats,,Output formats}.
5014 @item display/@var{fmt} @var{addr}
5015 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
5016 number of units, add the expression @var{addr} as a memory address to
5017 be examined each time your program stops. Examining means in effect
5018 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
5021 For example, @samp{display/i $pc} can be helpful, to see the machine
5022 instruction about to be executed each time execution stops (@samp{$pc}
5023 is a common name for the program counter; @pxref{Registers, ,Registers}).
5026 @kindex delete display
5028 @item undisplay @var{dnums}@dots{}
5029 @itemx delete display @var{dnums}@dots{}
5030 Remove item numbers @var{dnums} from the list of expressions to display.
5032 @code{undisplay} does not repeat if you press @key{RET} after using it.
5033 (Otherwise you would just get the error @samp{No display number @dots{}}.)
5035 @kindex disable display
5036 @item disable display @var{dnums}@dots{}
5037 Disable the display of item numbers @var{dnums}. A disabled display
5038 item is not printed automatically, but is not forgotten. It may be
5039 enabled again later.
5041 @kindex enable display
5042 @item enable display @var{dnums}@dots{}
5043 Enable display of item numbers @var{dnums}. It becomes effective once
5044 again in auto display of its expression, until you specify otherwise.
5047 Display the current values of the expressions on the list, just as is
5048 done when your program stops.
5050 @kindex info display
5052 Print the list of expressions previously set up to display
5053 automatically, each one with its item number, but without showing the
5054 values. This includes disabled expressions, which are marked as such.
5055 It also includes expressions which would not be displayed right now
5056 because they refer to automatic variables not currently available.
5059 If a display expression refers to local variables, then it does not make
5060 sense outside the lexical context for which it was set up. Such an
5061 expression is disabled when execution enters a context where one of its
5062 variables is not defined. For example, if you give the command
5063 @code{display last_char} while inside a function with an argument
5064 @code{last_char}, @value{GDBN} displays this argument while your program
5065 continues to stop inside that function. When it stops elsewhere---where
5066 there is no variable @code{last_char}---the display is disabled
5067 automatically. The next time your program stops where @code{last_char}
5068 is meaningful, you can enable the display expression once again.
5070 @node Print Settings
5071 @section Print settings
5073 @cindex format options
5074 @cindex print settings
5075 @value{GDBN} provides the following ways to control how arrays, structures,
5076 and symbols are printed.
5079 These settings are useful for debugging programs in any language:
5082 @kindex set print address
5083 @item set print address
5084 @itemx set print address on
5085 @value{GDBN} prints memory addresses showing the location of stack
5086 traces, structure values, pointer values, breakpoints, and so forth,
5087 even when it also displays the contents of those addresses. The default
5088 is @code{on}. For example, this is what a stack frame display looks like with
5089 @code{set print address on}:
5094 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
5096 530 if (lquote != def_lquote)
5100 @item set print address off
5101 Do not print addresses when displaying their contents. For example,
5102 this is the same stack frame displayed with @code{set print address off}:
5106 (@value{GDBP}) set print addr off
5108 #0 set_quotes (lq="<<", rq=">>") at input.c:530
5109 530 if (lquote != def_lquote)
5113 You can use @samp{set print address off} to eliminate all machine
5114 dependent displays from the @value{GDBN} interface. For example, with
5115 @code{print address off}, you should get the same text for backtraces on
5116 all machines---whether or not they involve pointer arguments.
5118 @kindex show print address
5119 @item show print address
5120 Show whether or not addresses are to be printed.
5123 When @value{GDBN} prints a symbolic address, it normally prints the
5124 closest earlier symbol plus an offset. If that symbol does not uniquely
5125 identify the address (for example, it is a name whose scope is a single
5126 source file), you may need to clarify. One way to do this is with
5127 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5128 you can set @value{GDBN} to print the source file and line number when
5129 it prints a symbolic address:
5132 @kindex set print symbol-filename
5133 @item set print symbol-filename on
5134 Tell @value{GDBN} to print the source file name and line number of a
5135 symbol in the symbolic form of an address.
5137 @item set print symbol-filename off
5138 Do not print source file name and line number of a symbol. This is the
5141 @kindex show print symbol-filename
5142 @item show print symbol-filename
5143 Show whether or not @value{GDBN} will print the source file name and
5144 line number of a symbol in the symbolic form of an address.
5147 Another situation where it is helpful to show symbol filenames and line
5148 numbers is when disassembling code; @value{GDBN} shows you the line
5149 number and source file that corresponds to each instruction.
5151 Also, you may wish to see the symbolic form only if the address being
5152 printed is reasonably close to the closest earlier symbol:
5155 @kindex set print max-symbolic-offset
5156 @item set print max-symbolic-offset @var{max-offset}
5157 Tell @value{GDBN} to only display the symbolic form of an address if the
5158 offset between the closest earlier symbol and the address is less than
5159 @var{max-offset}. The default is 0, which tells @value{GDBN}
5160 to always print the symbolic form of an address if any symbol precedes it.
5162 @kindex show print max-symbolic-offset
5163 @item show print max-symbolic-offset
5164 Ask how large the maximum offset is that @value{GDBN} prints in a
5168 @cindex wild pointer, interpreting
5169 @cindex pointer, finding referent
5170 If you have a pointer and you are not sure where it points, try
5171 @samp{set print symbol-filename on}. Then you can determine the name
5172 and source file location of the variable where it points, using
5173 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5174 For example, here @value{GDBN} shows that a variable @code{ptt} points
5175 at another variable @code{t}, defined in @file{hi2.c}:
5178 (@value{GDBP}) set print symbol-filename on
5179 (@value{GDBP}) p/a ptt
5180 $4 = 0xe008 <t in hi2.c>
5184 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5185 does not show the symbol name and filename of the referent, even with
5186 the appropriate @code{set print} options turned on.
5189 Other settings control how different kinds of objects are printed:
5192 @kindex set print array
5193 @item set print array
5194 @itemx set print array on
5195 Pretty print arrays. This format is more convenient to read,
5196 but uses more space. The default is off.
5198 @item set print array off
5199 Return to compressed format for arrays.
5201 @kindex show print array
5202 @item show print array
5203 Show whether compressed or pretty format is selected for displaying
5206 @kindex set print elements
5207 @item set print elements @var{number-of-elements}
5208 Set a limit on how many elements of an array @value{GDBN} will print.
5209 If @value{GDBN} is printing a large array, it stops printing after it has
5210 printed the number of elements set by the @code{set print elements} command.
5211 This limit also applies to the display of strings.
5212 When @value{GDBN} starts, this limit is set to 200.
5213 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5215 @kindex show print elements
5216 @item show print elements
5217 Display the number of elements of a large array that @value{GDBN} will print.
5218 If the number is 0, then the printing is unlimited.
5220 @kindex set print null-stop
5221 @item set print null-stop
5222 Cause @value{GDBN} to stop printing the characters of an array when the first
5223 @sc{null} is encountered. This is useful when large arrays actually
5224 contain only short strings.
5227 @kindex set print pretty
5228 @item set print pretty on
5229 Cause @value{GDBN} to print structures in an indented format with one member
5230 per line, like this:
5245 @item set print pretty off
5246 Cause @value{GDBN} to print structures in a compact format, like this:
5250 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5251 meat = 0x54 "Pork"@}
5256 This is the default format.
5258 @kindex show print pretty
5259 @item show print pretty
5260 Show which format @value{GDBN} is using to print structures.
5262 @kindex set print sevenbit-strings
5263 @item set print sevenbit-strings on
5264 Print using only seven-bit characters; if this option is set,
5265 @value{GDBN} displays any eight-bit characters (in strings or
5266 character values) using the notation @code{\}@var{nnn}. This setting is
5267 best if you are working in English (@sc{ascii}) and you use the
5268 high-order bit of characters as a marker or ``meta'' bit.
5270 @item set print sevenbit-strings off
5271 Print full eight-bit characters. This allows the use of more
5272 international character sets, and is the default.
5274 @kindex show print sevenbit-strings
5275 @item show print sevenbit-strings
5276 Show whether or not @value{GDBN} is printing only seven-bit characters.
5278 @kindex set print union
5279 @item set print union on
5280 Tell @value{GDBN} to print unions which are contained in structures. This
5281 is the default setting.
5283 @item set print union off
5284 Tell @value{GDBN} not to print unions which are contained in structures.
5286 @kindex show print union
5287 @item show print union
5288 Ask @value{GDBN} whether or not it will print unions which are contained in
5291 For example, given the declarations
5294 typedef enum @{Tree, Bug@} Species;
5295 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5296 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5307 struct thing foo = @{Tree, @{Acorn@}@};
5311 with @code{set print union on} in effect @samp{p foo} would print
5314 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5318 and with @code{set print union off} in effect it would print
5321 $1 = @{it = Tree, form = @{...@}@}
5327 These settings are of interest when debugging C@t{++} programs:
5331 @kindex set print demangle
5332 @item set print demangle
5333 @itemx set print demangle on
5334 Print C@t{++} names in their source form rather than in the encoded
5335 (``mangled'') form passed to the assembler and linker for type-safe
5336 linkage. The default is on.
5338 @kindex show print demangle
5339 @item show print demangle
5340 Show whether C@t{++} names are printed in mangled or demangled form.
5342 @kindex set print asm-demangle
5343 @item set print asm-demangle
5344 @itemx set print asm-demangle on
5345 Print C@t{++} names in their source form rather than their mangled form, even
5346 in assembler code printouts such as instruction disassemblies.
5349 @kindex show print asm-demangle
5350 @item show print asm-demangle
5351 Show whether C@t{++} names in assembly listings are printed in mangled
5354 @kindex set demangle-style
5355 @cindex C@t{++} symbol decoding style
5356 @cindex symbol decoding style, C@t{++}
5357 @item set demangle-style @var{style}
5358 Choose among several encoding schemes used by different compilers to
5359 represent C@t{++} names. The choices for @var{style} are currently:
5363 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5366 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5367 This is the default.
5370 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5373 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5376 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5377 @strong{Warning:} this setting alone is not sufficient to allow
5378 debugging @code{cfront}-generated executables. @value{GDBN} would
5379 require further enhancement to permit that.
5382 If you omit @var{style}, you will see a list of possible formats.
5384 @kindex show demangle-style
5385 @item show demangle-style
5386 Display the encoding style currently in use for decoding C@t{++} symbols.
5388 @kindex set print object
5389 @item set print object
5390 @itemx set print object on
5391 When displaying a pointer to an object, identify the @emph{actual}
5392 (derived) type of the object rather than the @emph{declared} type, using
5393 the virtual function table.
5395 @item set print object off
5396 Display only the declared type of objects, without reference to the
5397 virtual function table. This is the default setting.
5399 @kindex show print object
5400 @item show print object
5401 Show whether actual, or declared, object types are displayed.
5403 @kindex set print static-members
5404 @item set print static-members
5405 @itemx set print static-members on
5406 Print static members when displaying a C@t{++} object. The default is on.
5408 @item set print static-members off
5409 Do not print static members when displaying a C@t{++} object.
5411 @kindex show print static-members
5412 @item show print static-members
5413 Show whether C@t{++} static members are printed, or not.
5415 @c These don't work with HP ANSI C++ yet.
5416 @kindex set print vtbl
5417 @item set print vtbl
5418 @itemx set print vtbl on
5419 Pretty print C@t{++} virtual function tables. The default is off.
5420 (The @code{vtbl} commands do not work on programs compiled with the HP
5421 ANSI C@t{++} compiler (@code{aCC}).)
5423 @item set print vtbl off
5424 Do not pretty print C@t{++} virtual function tables.
5426 @kindex show print vtbl
5427 @item show print vtbl
5428 Show whether C@t{++} virtual function tables are pretty printed, or not.
5432 @section Value history
5434 @cindex value history
5435 Values printed by the @code{print} command are saved in the @value{GDBN}
5436 @dfn{value history}. This allows you to refer to them in other expressions.
5437 Values are kept until the symbol table is re-read or discarded
5438 (for example with the @code{file} or @code{symbol-file} commands).
5439 When the symbol table changes, the value history is discarded,
5440 since the values may contain pointers back to the types defined in the
5445 @cindex history number
5446 The values printed are given @dfn{history numbers} by which you can
5447 refer to them. These are successive integers starting with one.
5448 @code{print} shows you the history number assigned to a value by
5449 printing @samp{$@var{num} = } before the value; here @var{num} is the
5452 To refer to any previous value, use @samp{$} followed by the value's
5453 history number. The way @code{print} labels its output is designed to
5454 remind you of this. Just @code{$} refers to the most recent value in
5455 the history, and @code{$$} refers to the value before that.
5456 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5457 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5458 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5460 For example, suppose you have just printed a pointer to a structure and
5461 want to see the contents of the structure. It suffices to type
5467 If you have a chain of structures where the component @code{next} points
5468 to the next one, you can print the contents of the next one with this:
5475 You can print successive links in the chain by repeating this
5476 command---which you can do by just typing @key{RET}.
5478 Note that the history records values, not expressions. If the value of
5479 @code{x} is 4 and you type these commands:
5487 then the value recorded in the value history by the @code{print} command
5488 remains 4 even though the value of @code{x} has changed.
5493 Print the last ten values in the value history, with their item numbers.
5494 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5495 values} does not change the history.
5497 @item show values @var{n}
5498 Print ten history values centered on history item number @var{n}.
5501 Print ten history values just after the values last printed. If no more
5502 values are available, @code{show values +} produces no display.
5505 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5506 same effect as @samp{show values +}.
5508 @node Convenience Vars
5509 @section Convenience variables
5511 @cindex convenience variables
5512 @value{GDBN} provides @dfn{convenience variables} that you can use within
5513 @value{GDBN} to hold on to a value and refer to it later. These variables
5514 exist entirely within @value{GDBN}; they are not part of your program, and
5515 setting a convenience variable has no direct effect on further execution
5516 of your program. That is why you can use them freely.
5518 Convenience variables are prefixed with @samp{$}. Any name preceded by
5519 @samp{$} can be used for a convenience variable, unless it is one of
5520 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5521 (Value history references, in contrast, are @emph{numbers} preceded
5522 by @samp{$}. @xref{Value History, ,Value history}.)
5524 You can save a value in a convenience variable with an assignment
5525 expression, just as you would set a variable in your program.
5529 set $foo = *object_ptr
5533 would save in @code{$foo} the value contained in the object pointed to by
5536 Using a convenience variable for the first time creates it, but its
5537 value is @code{void} until you assign a new value. You can alter the
5538 value with another assignment at any time.
5540 Convenience variables have no fixed types. You can assign a convenience
5541 variable any type of value, including structures and arrays, even if
5542 that variable already has a value of a different type. The convenience
5543 variable, when used as an expression, has the type of its current value.
5546 @kindex show convenience
5547 @item show convenience
5548 Print a list of convenience variables used so far, and their values.
5549 Abbreviated @code{show conv}.
5552 One of the ways to use a convenience variable is as a counter to be
5553 incremented or a pointer to be advanced. For example, to print
5554 a field from successive elements of an array of structures:
5558 print bar[$i++]->contents
5562 Repeat that command by typing @key{RET}.
5564 Some convenience variables are created automatically by @value{GDBN} and given
5565 values likely to be useful.
5568 @vindex $_@r{, convenience variable}
5570 The variable @code{$_} is automatically set by the @code{x} command to
5571 the last address examined (@pxref{Memory, ,Examining memory}). Other
5572 commands which provide a default address for @code{x} to examine also
5573 set @code{$_} to that address; these commands include @code{info line}
5574 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5575 except when set by the @code{x} command, in which case it is a pointer
5576 to the type of @code{$__}.
5578 @vindex $__@r{, convenience variable}
5580 The variable @code{$__} is automatically set by the @code{x} command
5581 to the value found in the last address examined. Its type is chosen
5582 to match the format in which the data was printed.
5585 @vindex $_exitcode@r{, convenience variable}
5586 The variable @code{$_exitcode} is automatically set to the exit code when
5587 the program being debugged terminates.
5590 On HP-UX systems, if you refer to a function or variable name that
5591 begins with a dollar sign, @value{GDBN} searches for a user or system
5592 name first, before it searches for a convenience variable.
5598 You can refer to machine register contents, in expressions, as variables
5599 with names starting with @samp{$}. The names of registers are different
5600 for each machine; use @code{info registers} to see the names used on
5604 @kindex info registers
5605 @item info registers
5606 Print the names and values of all registers except floating-point
5607 and vector registers (in the selected stack frame).
5609 @kindex info all-registers
5610 @cindex floating point registers
5611 @item info all-registers
5612 Print the names and values of all registers, including floating-point
5613 and vector registers (in the selected stack frame).
5615 @item info registers @var{regname} @dots{}
5616 Print the @dfn{relativized} value of each specified register @var{regname}.
5617 As discussed in detail below, register values are normally relative to
5618 the selected stack frame. @var{regname} may be any register name valid on
5619 the machine you are using, with or without the initial @samp{$}.
5622 @value{GDBN} has four ``standard'' register names that are available (in
5623 expressions) on most machines---whenever they do not conflict with an
5624 architecture's canonical mnemonics for registers. The register names
5625 @code{$pc} and @code{$sp} are used for the program counter register and
5626 the stack pointer. @code{$fp} is used for a register that contains a
5627 pointer to the current stack frame, and @code{$ps} is used for a
5628 register that contains the processor status. For example,
5629 you could print the program counter in hex with
5636 or print the instruction to be executed next with
5643 or add four to the stack pointer@footnote{This is a way of removing
5644 one word from the stack, on machines where stacks grow downward in
5645 memory (most machines, nowadays). This assumes that the innermost
5646 stack frame is selected; setting @code{$sp} is not allowed when other
5647 stack frames are selected. To pop entire frames off the stack,
5648 regardless of machine architecture, use @code{return};
5649 see @ref{Returning, ,Returning from a function}.} with
5655 Whenever possible, these four standard register names are available on
5656 your machine even though the machine has different canonical mnemonics,
5657 so long as there is no conflict. The @code{info registers} command
5658 shows the canonical names. For example, on the SPARC, @code{info
5659 registers} displays the processor status register as @code{$psr} but you
5660 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5661 is an alias for the @sc{eflags} register.
5663 @value{GDBN} always considers the contents of an ordinary register as an
5664 integer when the register is examined in this way. Some machines have
5665 special registers which can hold nothing but floating point; these
5666 registers are considered to have floating point values. There is no way
5667 to refer to the contents of an ordinary register as floating point value
5668 (although you can @emph{print} it as a floating point value with
5669 @samp{print/f $@var{regname}}).
5671 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5672 means that the data format in which the register contents are saved by
5673 the operating system is not the same one that your program normally
5674 sees. For example, the registers of the 68881 floating point
5675 coprocessor are always saved in ``extended'' (raw) format, but all C
5676 programs expect to work with ``double'' (virtual) format. In such
5677 cases, @value{GDBN} normally works with the virtual format only (the format
5678 that makes sense for your program), but the @code{info registers} command
5679 prints the data in both formats.
5681 Normally, register values are relative to the selected stack frame
5682 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5683 value that the register would contain if all stack frames farther in
5684 were exited and their saved registers restored. In order to see the
5685 true contents of hardware registers, you must select the innermost
5686 frame (with @samp{frame 0}).
5688 However, @value{GDBN} must deduce where registers are saved, from the machine
5689 code generated by your compiler. If some registers are not saved, or if
5690 @value{GDBN} is unable to locate the saved registers, the selected stack
5691 frame makes no difference.
5693 @node Floating Point Hardware
5694 @section Floating point hardware
5695 @cindex floating point
5697 Depending on the configuration, @value{GDBN} may be able to give
5698 you more information about the status of the floating point hardware.
5703 Display hardware-dependent information about the floating
5704 point unit. The exact contents and layout vary depending on the
5705 floating point chip. Currently, @samp{info float} is supported on
5706 the ARM and x86 machines.
5710 @section Vector Unit
5713 Depending on the configuration, @value{GDBN} may be able to give you
5714 more information about the status of the vector unit.
5719 Display information about the vector unit. The exact contents and
5720 layout vary depending on the hardware.
5723 @node Memory Region Attributes
5724 @section Memory region attributes
5725 @cindex memory region attributes
5727 @dfn{Memory region attributes} allow you to describe special handling
5728 required by regions of your target's memory. @value{GDBN} uses attributes
5729 to determine whether to allow certain types of memory accesses; whether to
5730 use specific width accesses; and whether to cache target memory.
5732 Defined memory regions can be individually enabled and disabled. When a
5733 memory region is disabled, @value{GDBN} uses the default attributes when
5734 accessing memory in that region. Similarly, if no memory regions have
5735 been defined, @value{GDBN} uses the default attributes when accessing
5738 When a memory region is defined, it is given a number to identify it;
5739 to enable, disable, or remove a memory region, you specify that number.
5743 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
5744 Define memory region bounded by @var{lower} and @var{upper} with
5745 attributes @var{attributes}@dots{}. Note that @var{upper} == 0 is a
5746 special case: it is treated as the the target's maximum memory address.
5747 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
5750 @item delete mem @var{nums}@dots{}
5751 Remove memory regions @var{nums}@dots{}.
5754 @item disable mem @var{nums}@dots{}
5755 Disable memory regions @var{nums}@dots{}.
5756 A disabled memory region is not forgotten.
5757 It may be enabled again later.
5760 @item enable mem @var{nums}@dots{}
5761 Enable memory regions @var{nums}@dots{}.
5765 Print a table of all defined memory regions, with the following columns
5769 @item Memory Region Number
5770 @item Enabled or Disabled.
5771 Enabled memory regions are marked with @samp{y}.
5772 Disabled memory regions are marked with @samp{n}.
5775 The address defining the inclusive lower bound of the memory region.
5778 The address defining the exclusive upper bound of the memory region.
5781 The list of attributes set for this memory region.
5786 @subsection Attributes
5788 @subsubsection Memory Access Mode
5789 The access mode attributes set whether @value{GDBN} may make read or
5790 write accesses to a memory region.
5792 While these attributes prevent @value{GDBN} from performing invalid
5793 memory accesses, they do nothing to prevent the target system, I/O DMA,
5794 etc. from accessing memory.
5798 Memory is read only.
5800 Memory is write only.
5802 Memory is read/write. This is the default.
5805 @subsubsection Memory Access Size
5806 The acccess size attributes tells @value{GDBN} to use specific sized
5807 accesses in the memory region. Often memory mapped device registers
5808 require specific sized accesses. If no access size attribute is
5809 specified, @value{GDBN} may use accesses of any size.
5813 Use 8 bit memory accesses.
5815 Use 16 bit memory accesses.
5817 Use 32 bit memory accesses.
5819 Use 64 bit memory accesses.
5822 @c @subsubsection Hardware/Software Breakpoints
5823 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5824 @c will use hardware or software breakpoints for the internal breakpoints
5825 @c used by the step, next, finish, until, etc. commands.
5829 @c Always use hardware breakpoints
5830 @c @item swbreak (default)
5833 @subsubsection Data Cache
5834 The data cache attributes set whether @value{GDBN} will cache target
5835 memory. While this generally improves performance by reducing debug
5836 protocol overhead, it can lead to incorrect results because @value{GDBN}
5837 does not know about volatile variables or memory mapped device
5842 Enable @value{GDBN} to cache target memory.
5844 Disable @value{GDBN} from caching target memory. This is the default.
5847 @c @subsubsection Memory Write Verification
5848 @c The memory write verification attributes set whether @value{GDBN}
5849 @c will re-reads data after each write to verify the write was successful.
5853 @c @item noverify (default)
5856 @node Dump/Restore Files
5857 @section Copy between memory and a file
5858 @cindex dump/restore files
5859 @cindex append data to a file
5860 @cindex dump data to a file
5861 @cindex restore data from a file
5866 The commands @code{dump}, @code{append}, and @code{restore} are used
5867 for copying data between target memory and a file. Data is written
5868 into a file using @code{dump} or @code{append}, and restored from a
5869 file into memory by using @code{restore}. Files may be binary, srec,
5870 intel hex, or tekhex (but only binary files can be appended).
5874 @kindex append binary
5875 @item dump binary memory @var{filename} @var{start_addr} @var{end_addr}
5876 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5877 raw binary format file @var{filename}.
5879 @item append binary memory @var{filename} @var{start_addr} @var{end_addr}
5880 Append contents of memory from @var{start_addr} to @var{end_addr} to
5881 raw binary format file @var{filename}.
5883 @item dump binary value @var{filename} @var{expression}
5884 Dump value of @var{expression} into raw binary format file @var{filename}.
5886 @item append binary memory @var{filename} @var{expression}
5887 Append value of @var{expression} to raw binary format file @var{filename}.
5890 @item dump ihex memory @var{filename} @var{start_addr} @var{end_addr}
5891 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5892 intel hex format file @var{filename}.
5894 @item dump ihex value @var{filename} @var{expression}
5895 Dump value of @var{expression} into intel hex format file @var{filename}.
5898 @item dump srec memory @var{filename} @var{start_addr} @var{end_addr}
5899 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5900 srec format file @var{filename}.
5902 @item dump srec value @var{filename} @var{expression}
5903 Dump value of @var{expression} into srec format file @var{filename}.
5906 @item dump tekhex memory @var{filename} @var{start_addr} @var{end_addr}
5907 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5908 tekhex format file @var{filename}.
5910 @item dump tekhex value @var{filename} @var{expression}
5911 Dump value of @var{expression} into tekhex format file @var{filename}.
5913 @item restore @var{filename} [@var{binary}] @var{bias} @var{start} @var{end}
5914 Restore the contents of file @var{filename} into memory. The @code{restore}
5915 command can automatically recognize any known bfd file format, except for
5916 raw binary. To restore a raw binary file you must use the optional argument
5917 @var{binary} after the filename.
5919 If @var{bias} is non-zero, its value will be added to the addresses
5920 contained in the file. Binary files always start at address zero, so
5921 they will be restored at address @var{bias}. Other bfd files have
5922 a built-in location; they will be restored at offset @var{bias}
5925 If @var{start} and/or @var{end} are non-zero, then only data between
5926 file offset @var{start} and file offset @var{end} will be restored.
5927 These offsets are relative to the addresses in the file, before
5928 the @var{bias} argument is applied.
5932 @node Character Sets
5933 @section Character Sets
5934 @cindex character sets
5936 @cindex translating between character sets
5937 @cindex host character set
5938 @cindex target character set
5940 If the program you are debugging uses a different character set to
5941 represent characters and strings than the one @value{GDBN} uses itself,
5942 @value{GDBN} can automatically translate between the character sets for
5943 you. The character set @value{GDBN} uses we call the @dfn{host
5944 character set}; the one the inferior program uses we call the
5945 @dfn{target character set}.
5947 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
5948 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
5949 remote protocol (@pxref{Remote,Remote Debugging}) to debug a program
5950 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
5951 then the host character set is Latin-1, and the target character set is
5952 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
5953 target-charset ebcdic-us}, then @value{GDBN} translates between
5954 @sc{ebcdic} and Latin 1 as you print character or string values, or use
5955 character and string literals in expressions.
5957 @value{GDBN} has no way to automatically recognize which character set
5958 the inferior program uses; you must tell it, using the @code{set
5959 target-charset} command, described below.
5961 Here are the commands for controlling @value{GDBN}'s character set
5965 @item set target-charset @var{charset}
5966 @kindex set target-charset
5967 Set the current target character set to @var{charset}. We list the
5968 character set names @value{GDBN} recognizes below, but if you invoke the
5969 @code{set target-charset} command with no argument, @value{GDBN} lists
5970 the character sets it supports.
5974 @item set host-charset @var{charset}
5975 @kindex set host-charset
5976 Set the current host character set to @var{charset}.
5978 By default, @value{GDBN} uses a host character set appropriate to the
5979 system it is running on; you can override that default using the
5980 @code{set host-charset} command.
5982 @value{GDBN} can only use certain character sets as its host character
5983 set. We list the character set names @value{GDBN} recognizes below, and
5984 indicate which can be host character sets, but if you invoke the
5985 @code{set host-charset} command with no argument, @value{GDBN} lists the
5986 character sets it supports, placing an asterisk (@samp{*}) after those
5987 it can use as a host character set.
5989 @item set charset @var{charset}
5991 Set the current host and target character sets to @var{charset}. If you
5992 invoke the @code{set charset} command with no argument, it lists the
5993 character sets it supports. @value{GDBN} can only use certain character
5994 sets as its host character set; it marks those in the list with an
5995 asterisk (@samp{*}).
5998 @itemx show host-charset
5999 @itemx show target-charset
6000 @kindex show charset
6001 @kindex show host-charset
6002 @kindex show target-charset
6003 Show the current host and target charsets. The @code{show host-charset}
6004 and @code{show target-charset} commands are synonyms for @code{show
6009 @value{GDBN} currently includes support for the following character
6015 @cindex ASCII character set
6016 Seven-bit U.S. @sc{ascii}. @value{GDBN} can use this as its host
6020 @cindex ISO 8859-1 character set
6021 @cindex ISO Latin 1 character set
6022 The ISO Latin 1 character set. This extends ASCII with accented
6023 characters needed for French, German, and Spanish. @value{GDBN} can use
6024 this as its host character set.
6028 @cindex EBCDIC character set
6029 @cindex IBM1047 character set
6030 Variants of the @sc{ebcdic} character set, used on some of IBM's
6031 mainframe operating systems. (@sc{gnu}/Linux on the S/390 uses U.S. @sc{ascii}.)
6032 @value{GDBN} cannot use these as its host character set.
6036 Note that these are all single-byte character sets. More work inside
6037 GDB is needed to support multi-byte or variable-width character
6038 encodings, like the UTF-8 and UCS-2 encodings of Unicode.
6040 Here is an example of @value{GDBN}'s character set support in action.
6041 Assume that the following source code has been placed in the file
6042 @file{charset-test.c}:
6048 = @{72, 101, 108, 108, 111, 44, 32, 119,
6049 111, 114, 108, 100, 33, 10, 0@};
6050 char ibm1047_hello[]
6051 = @{200, 133, 147, 147, 150, 107, 64, 166,
6052 150, 153, 147, 132, 90, 37, 0@};
6056 printf ("Hello, world!\n");
6060 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
6061 containing the string @samp{Hello, world!} followed by a newline,
6062 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
6064 We compile the program, and invoke the debugger on it:
6067 $ gcc -g charset-test.c -o charset-test
6068 $ gdb -nw charset-test
6069 GNU gdb 2001-12-19-cvs
6070 Copyright 2001 Free Software Foundation, Inc.
6075 We can use the @code{show charset} command to see what character sets
6076 @value{GDBN} is currently using to interpret and display characters and
6081 The current host and target character set is `iso-8859-1'.
6085 For the sake of printing this manual, let's use @sc{ascii} as our
6086 initial character set:
6088 (gdb) set charset ascii
6090 The current host and target character set is `ascii'.
6094 Let's assume that @sc{ascii} is indeed the correct character set for our
6095 host system --- in other words, let's assume that if @value{GDBN} prints
6096 characters using the @sc{ascii} character set, our terminal will display
6097 them properly. Since our current target character set is also
6098 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
6101 (gdb) print ascii_hello
6102 $1 = 0x401698 "Hello, world!\n"
6103 (gdb) print ascii_hello[0]
6108 @value{GDBN} uses the target character set for character and string
6109 literals you use in expressions:
6117 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
6120 @value{GDBN} relies on the user to tell it which character set the
6121 target program uses. If we print @code{ibm1047_hello} while our target
6122 character set is still @sc{ascii}, we get jibberish:
6125 (gdb) print ibm1047_hello
6126 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
6127 (gdb) print ibm1047_hello[0]
6132 If we invoke the @code{set target-charset} command without an argument,
6133 @value{GDBN} tells us the character sets it supports:
6136 (gdb) set target-charset
6137 Valid character sets are:
6142 * - can be used as a host character set
6145 We can select @sc{ibm1047} as our target character set, and examine the
6146 program's strings again. Now the @sc{ascii} string is wrong, but
6147 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
6148 target character set, @sc{ibm1047}, to the host character set,
6149 @sc{ascii}, and they display correctly:
6152 (gdb) set target-charset ibm1047
6154 The current host character set is `ascii'.
6155 The current target character set is `ibm1047'.
6156 (gdb) print ascii_hello
6157 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
6158 (gdb) print ascii_hello[0]
6160 (gdb) print ibm1047_hello
6161 $8 = 0x4016a8 "Hello, world!\n"
6162 (gdb) print ibm1047_hello[0]
6167 As above, @value{GDBN} uses the target character set for character and
6168 string literals you use in expressions:
6176 The IBM1047 character set uses the number 78 to encode the @samp{+}
6181 @chapter C Preprocessor Macros
6183 Some languages, such as C and C++, provide a way to define and invoke
6184 ``preprocessor macros'' which expand into strings of tokens.
6185 @value{GDBN} can evaluate expressions containing macro invocations, show
6186 the result of macro expansion, and show a macro's definition, including
6187 where it was defined.
6189 You may need to compile your program specially to provide @value{GDBN}
6190 with information about preprocessor macros. Most compilers do not
6191 include macros in their debugging information, even when you compile
6192 with the @option{-g} flag. @xref{Compilation}.
6194 A program may define a macro at one point, remove that definition later,
6195 and then provide a different definition after that. Thus, at different
6196 points in the program, a macro may have different definitions, or have
6197 no definition at all. If there is a current stack frame, @value{GDBN}
6198 uses the macros in scope at that frame's source code line. Otherwise,
6199 @value{GDBN} uses the macros in scope at the current listing location;
6202 At the moment, @value{GDBN} does not support the @code{##}
6203 token-splicing operator, the @code{#} stringification operator, or
6204 variable-arity macros.
6206 Whenever @value{GDBN} evaluates an expression, it always expands any
6207 macro invocations present in the expression. @value{GDBN} also provides
6208 the following commands for working with macros explicitly.
6212 @kindex macro expand
6213 @cindex macro expansion, showing the results of preprocessor
6214 @cindex preprocessor macro expansion, showing the results of
6215 @cindex expanding preprocessor macros
6216 @item macro expand @var{expression}
6217 @itemx macro exp @var{expression}
6218 Show the results of expanding all preprocessor macro invocations in
6219 @var{expression}. Since @value{GDBN} simply expands macros, but does
6220 not parse the result, @var{expression} need not be a valid expression;
6221 it can be any string of tokens.
6223 @kindex macro expand-once
6224 @item macro expand-once @var{expression}
6225 @itemx macro exp1 @var{expression}
6226 @i{(This command is not yet implemented.)} Show the results of
6227 expanding those preprocessor macro invocations that appear explicitly in
6228 @var{expression}. Macro invocations appearing in that expansion are
6229 left unchanged. This command allows you to see the effect of a
6230 particular macro more clearly, without being confused by further
6231 expansions. Since @value{GDBN} simply expands macros, but does not
6232 parse the result, @var{expression} need not be a valid expression; it
6233 can be any string of tokens.
6236 @cindex macro definition, showing
6237 @cindex definition, showing a macro's
6238 @item info macro @var{macro}
6239 Show the definition of the macro named @var{macro}, and describe the
6240 source location where that definition was established.
6242 @kindex macro define
6243 @cindex user-defined macros
6244 @cindex defining macros interactively
6245 @cindex macros, user-defined
6246 @item macro define @var{macro} @var{replacement-list}
6247 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
6248 @i{(This command is not yet implemented.)} Introduce a definition for a
6249 preprocessor macro named @var{macro}, invocations of which are replaced
6250 by the tokens given in @var{replacement-list}. The first form of this
6251 command defines an ``object-like'' macro, which takes no arguments; the
6252 second form defines a ``function-like'' macro, which takes the arguments
6253 given in @var{arglist}.
6255 A definition introduced by this command is in scope in every expression
6256 evaluated in @value{GDBN}, until it is removed with the @command{macro
6257 undef} command, described below. The definition overrides all
6258 definitions for @var{macro} present in the program being debugged, as
6259 well as any previous user-supplied definition.
6262 @item macro undef @var{macro}
6263 @i{(This command is not yet implemented.)} Remove any user-supplied
6264 definition for the macro named @var{macro}. This command only affects
6265 definitions provided with the @command{macro define} command, described
6266 above; it cannot remove definitions present in the program being
6271 @cindex macros, example of debugging with
6272 Here is a transcript showing the above commands in action. First, we
6273 show our source files:
6281 #define ADD(x) (M + x)
6286 printf ("Hello, world!\n");
6288 printf ("We're so creative.\n");
6290 printf ("Goodbye, world!\n");
6297 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
6298 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
6299 compiler includes information about preprocessor macros in the debugging
6303 $ gcc -gdwarf-2 -g3 sample.c -o sample
6307 Now, we start @value{GDBN} on our sample program:
6311 GNU gdb 2002-05-06-cvs
6312 Copyright 2002 Free Software Foundation, Inc.
6313 GDB is free software, @dots{}
6317 We can expand macros and examine their definitions, even when the
6318 program is not running. @value{GDBN} uses the current listing position
6319 to decide which macro definitions are in scope:
6325 5 #define ADD(x) (M + x)
6330 10 printf ("Hello, world!\n");
6332 12 printf ("We're so creative.\n");
6333 (gdb) info macro ADD
6334 Defined at /home/jimb/gdb/macros/play/sample.c:5
6335 #define ADD(x) (M + x)
6337 Defined at /home/jimb/gdb/macros/play/sample.h:1
6338 included at /home/jimb/gdb/macros/play/sample.c:2
6340 (gdb) macro expand ADD(1)
6341 expands to: (42 + 1)
6342 (gdb) macro expand-once ADD(1)
6343 expands to: once (M + 1)
6347 In the example above, note that @command{macro expand-once} expands only
6348 the macro invocation explicit in the original text --- the invocation of
6349 @code{ADD} --- but does not expand the invocation of the macro @code{M},
6350 which was introduced by @code{ADD}.
6352 Once the program is running, GDB uses the macro definitions in force at
6353 the source line of the current stack frame:
6357 Breakpoint 1 at 0x8048370: file sample.c, line 10.
6359 Starting program: /home/jimb/gdb/macros/play/sample
6361 Breakpoint 1, main () at sample.c:10
6362 10 printf ("Hello, world!\n");
6366 At line 10, the definition of the macro @code{N} at line 9 is in force:
6370 Defined at /home/jimb/gdb/macros/play/sample.c:9
6372 (gdb) macro expand N Q M
6379 As we step over directives that remove @code{N}'s definition, and then
6380 give it a new definition, @value{GDBN} finds the definition (or lack
6381 thereof) in force at each point:
6386 12 printf ("We're so creative.\n");
6388 The symbol `N' has no definition as a C/C++ preprocessor macro
6389 at /home/jimb/gdb/macros/play/sample.c:12
6392 14 printf ("Goodbye, world!\n");
6394 Defined at /home/jimb/gdb/macros/play/sample.c:13
6396 (gdb) macro expand N Q M
6397 expands to: 1729 < 42
6405 @chapter Tracepoints
6406 @c This chapter is based on the documentation written by Michael
6407 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
6410 In some applications, it is not feasible for the debugger to interrupt
6411 the program's execution long enough for the developer to learn
6412 anything helpful about its behavior. If the program's correctness
6413 depends on its real-time behavior, delays introduced by a debugger
6414 might cause the program to change its behavior drastically, or perhaps
6415 fail, even when the code itself is correct. It is useful to be able
6416 to observe the program's behavior without interrupting it.
6418 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
6419 specify locations in the program, called @dfn{tracepoints}, and
6420 arbitrary expressions to evaluate when those tracepoints are reached.
6421 Later, using the @code{tfind} command, you can examine the values
6422 those expressions had when the program hit the tracepoints. The
6423 expressions may also denote objects in memory---structures or arrays,
6424 for example---whose values @value{GDBN} should record; while visiting
6425 a particular tracepoint, you may inspect those objects as if they were
6426 in memory at that moment. However, because @value{GDBN} records these
6427 values without interacting with you, it can do so quickly and
6428 unobtrusively, hopefully not disturbing the program's behavior.
6430 The tracepoint facility is currently available only for remote
6431 targets. @xref{Targets}. In addition, your remote target must know how
6432 to collect trace data. This functionality is implemented in the remote
6433 stub; however, none of the stubs distributed with @value{GDBN} support
6434 tracepoints as of this writing.
6436 This chapter describes the tracepoint commands and features.
6440 * Analyze Collected Data::
6441 * Tracepoint Variables::
6444 @node Set Tracepoints
6445 @section Commands to Set Tracepoints
6447 Before running such a @dfn{trace experiment}, an arbitrary number of
6448 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
6449 tracepoint has a number assigned to it by @value{GDBN}. Like with
6450 breakpoints, tracepoint numbers are successive integers starting from
6451 one. Many of the commands associated with tracepoints take the
6452 tracepoint number as their argument, to identify which tracepoint to
6455 For each tracepoint, you can specify, in advance, some arbitrary set
6456 of data that you want the target to collect in the trace buffer when
6457 it hits that tracepoint. The collected data can include registers,
6458 local variables, or global data. Later, you can use @value{GDBN}
6459 commands to examine the values these data had at the time the
6462 This section describes commands to set tracepoints and associated
6463 conditions and actions.
6466 * Create and Delete Tracepoints::
6467 * Enable and Disable Tracepoints::
6468 * Tracepoint Passcounts::
6469 * Tracepoint Actions::
6470 * Listing Tracepoints::
6471 * Starting and Stopping Trace Experiment::
6474 @node Create and Delete Tracepoints
6475 @subsection Create and Delete Tracepoints
6478 @cindex set tracepoint
6481 The @code{trace} command is very similar to the @code{break} command.
6482 Its argument can be a source line, a function name, or an address in
6483 the target program. @xref{Set Breaks}. The @code{trace} command
6484 defines a tracepoint, which is a point in the target program where the
6485 debugger will briefly stop, collect some data, and then allow the
6486 program to continue. Setting a tracepoint or changing its commands
6487 doesn't take effect until the next @code{tstart} command; thus, you
6488 cannot change the tracepoint attributes once a trace experiment is
6491 Here are some examples of using the @code{trace} command:
6494 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
6496 (@value{GDBP}) @b{trace +2} // 2 lines forward
6498 (@value{GDBP}) @b{trace my_function} // first source line of function
6500 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
6502 (@value{GDBP}) @b{trace *0x2117c4} // an address
6506 You can abbreviate @code{trace} as @code{tr}.
6509 @cindex last tracepoint number
6510 @cindex recent tracepoint number
6511 @cindex tracepoint number
6512 The convenience variable @code{$tpnum} records the tracepoint number
6513 of the most recently set tracepoint.
6515 @kindex delete tracepoint
6516 @cindex tracepoint deletion
6517 @item delete tracepoint @r{[}@var{num}@r{]}
6518 Permanently delete one or more tracepoints. With no argument, the
6519 default is to delete all tracepoints.
6524 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
6526 (@value{GDBP}) @b{delete trace} // remove all tracepoints
6530 You can abbreviate this command as @code{del tr}.
6533 @node Enable and Disable Tracepoints
6534 @subsection Enable and Disable Tracepoints
6537 @kindex disable tracepoint
6538 @item disable tracepoint @r{[}@var{num}@r{]}
6539 Disable tracepoint @var{num}, or all tracepoints if no argument
6540 @var{num} is given. A disabled tracepoint will have no effect during
6541 the next trace experiment, but it is not forgotten. You can re-enable
6542 a disabled tracepoint using the @code{enable tracepoint} command.
6544 @kindex enable tracepoint
6545 @item enable tracepoint @r{[}@var{num}@r{]}
6546 Enable tracepoint @var{num}, or all tracepoints. The enabled
6547 tracepoints will become effective the next time a trace experiment is
6551 @node Tracepoint Passcounts
6552 @subsection Tracepoint Passcounts
6556 @cindex tracepoint pass count
6557 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
6558 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
6559 automatically stop a trace experiment. If a tracepoint's passcount is
6560 @var{n}, then the trace experiment will be automatically stopped on
6561 the @var{n}'th time that tracepoint is hit. If the tracepoint number
6562 @var{num} is not specified, the @code{passcount} command sets the
6563 passcount of the most recently defined tracepoint. If no passcount is
6564 given, the trace experiment will run until stopped explicitly by the
6570 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
6571 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
6573 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
6574 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
6575 (@value{GDBP}) @b{trace foo}
6576 (@value{GDBP}) @b{pass 3}
6577 (@value{GDBP}) @b{trace bar}
6578 (@value{GDBP}) @b{pass 2}
6579 (@value{GDBP}) @b{trace baz}
6580 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
6581 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
6582 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
6583 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
6587 @node Tracepoint Actions
6588 @subsection Tracepoint Action Lists
6592 @cindex tracepoint actions
6593 @item actions @r{[}@var{num}@r{]}
6594 This command will prompt for a list of actions to be taken when the
6595 tracepoint is hit. If the tracepoint number @var{num} is not
6596 specified, this command sets the actions for the one that was most
6597 recently defined (so that you can define a tracepoint and then say
6598 @code{actions} without bothering about its number). You specify the
6599 actions themselves on the following lines, one action at a time, and
6600 terminate the actions list with a line containing just @code{end}. So
6601 far, the only defined actions are @code{collect} and
6602 @code{while-stepping}.
6604 @cindex remove actions from a tracepoint
6605 To remove all actions from a tracepoint, type @samp{actions @var{num}}
6606 and follow it immediately with @samp{end}.
6609 (@value{GDBP}) @b{collect @var{data}} // collect some data
6611 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
6613 (@value{GDBP}) @b{end} // signals the end of actions.
6616 In the following example, the action list begins with @code{collect}
6617 commands indicating the things to be collected when the tracepoint is
6618 hit. Then, in order to single-step and collect additional data
6619 following the tracepoint, a @code{while-stepping} command is used,
6620 followed by the list of things to be collected while stepping. The
6621 @code{while-stepping} command is terminated by its own separate
6622 @code{end} command. Lastly, the action list is terminated by an
6626 (@value{GDBP}) @b{trace foo}
6627 (@value{GDBP}) @b{actions}
6628 Enter actions for tracepoint 1, one per line:
6637 @kindex collect @r{(tracepoints)}
6638 @item collect @var{expr1}, @var{expr2}, @dots{}
6639 Collect values of the given expressions when the tracepoint is hit.
6640 This command accepts a comma-separated list of any valid expressions.
6641 In addition to global, static, or local variables, the following
6642 special arguments are supported:
6646 collect all registers
6649 collect all function arguments
6652 collect all local variables.
6655 You can give several consecutive @code{collect} commands, each one
6656 with a single argument, or one @code{collect} command with several
6657 arguments separated by commas: the effect is the same.
6659 The command @code{info scope} (@pxref{Symbols, info scope}) is
6660 particularly useful for figuring out what data to collect.
6662 @kindex while-stepping @r{(tracepoints)}
6663 @item while-stepping @var{n}
6664 Perform @var{n} single-step traces after the tracepoint, collecting
6665 new data at each step. The @code{while-stepping} command is
6666 followed by the list of what to collect while stepping (followed by
6667 its own @code{end} command):
6671 > collect $regs, myglobal
6677 You may abbreviate @code{while-stepping} as @code{ws} or
6681 @node Listing Tracepoints
6682 @subsection Listing Tracepoints
6685 @kindex info tracepoints
6686 @cindex information about tracepoints
6687 @item info tracepoints @r{[}@var{num}@r{]}
6688 Display information about the tracepoint @var{num}. If you don't specify
6689 a tracepoint number, displays information about all the tracepoints
6690 defined so far. For each tracepoint, the following information is
6697 whether it is enabled or disabled
6701 its passcount as given by the @code{passcount @var{n}} command
6703 its step count as given by the @code{while-stepping @var{n}} command
6705 where in the source files is the tracepoint set
6707 its action list as given by the @code{actions} command
6711 (@value{GDBP}) @b{info trace}
6712 Num Enb Address PassC StepC What
6713 1 y 0x002117c4 0 0 <gdb_asm>
6714 2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
6715 3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
6720 This command can be abbreviated @code{info tp}.
6723 @node Starting and Stopping Trace Experiment
6724 @subsection Starting and Stopping Trace Experiment
6728 @cindex start a new trace experiment
6729 @cindex collected data discarded
6731 This command takes no arguments. It starts the trace experiment, and
6732 begins collecting data. This has the side effect of discarding all
6733 the data collected in the trace buffer during the previous trace
6737 @cindex stop a running trace experiment
6739 This command takes no arguments. It ends the trace experiment, and
6740 stops collecting data.
6742 @strong{Note:} a trace experiment and data collection may stop
6743 automatically if any tracepoint's passcount is reached
6744 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6747 @cindex status of trace data collection
6748 @cindex trace experiment, status of
6750 This command displays the status of the current trace data
6754 Here is an example of the commands we described so far:
6757 (@value{GDBP}) @b{trace gdb_c_test}
6758 (@value{GDBP}) @b{actions}
6759 Enter actions for tracepoint #1, one per line.
6760 > collect $regs,$locals,$args
6765 (@value{GDBP}) @b{tstart}
6766 [time passes @dots{}]
6767 (@value{GDBP}) @b{tstop}
6771 @node Analyze Collected Data
6772 @section Using the collected data
6774 After the tracepoint experiment ends, you use @value{GDBN} commands
6775 for examining the trace data. The basic idea is that each tracepoint
6776 collects a trace @dfn{snapshot} every time it is hit and another
6777 snapshot every time it single-steps. All these snapshots are
6778 consecutively numbered from zero and go into a buffer, and you can
6779 examine them later. The way you examine them is to @dfn{focus} on a
6780 specific trace snapshot. When the remote stub is focused on a trace
6781 snapshot, it will respond to all @value{GDBN} requests for memory and
6782 registers by reading from the buffer which belongs to that snapshot,
6783 rather than from @emph{real} memory or registers of the program being
6784 debugged. This means that @strong{all} @value{GDBN} commands
6785 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6786 behave as if we were currently debugging the program state as it was
6787 when the tracepoint occurred. Any requests for data that are not in
6788 the buffer will fail.
6791 * tfind:: How to select a trace snapshot
6792 * tdump:: How to display all data for a snapshot
6793 * save-tracepoints:: How to save tracepoints for a future run
6797 @subsection @code{tfind @var{n}}
6800 @cindex select trace snapshot
6801 @cindex find trace snapshot
6802 The basic command for selecting a trace snapshot from the buffer is
6803 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6804 counting from zero. If no argument @var{n} is given, the next
6805 snapshot is selected.
6807 Here are the various forms of using the @code{tfind} command.
6811 Find the first snapshot in the buffer. This is a synonym for
6812 @code{tfind 0} (since 0 is the number of the first snapshot).
6815 Stop debugging trace snapshots, resume @emph{live} debugging.
6818 Same as @samp{tfind none}.
6821 No argument means find the next trace snapshot.
6824 Find the previous trace snapshot before the current one. This permits
6825 retracing earlier steps.
6827 @item tfind tracepoint @var{num}
6828 Find the next snapshot associated with tracepoint @var{num}. Search
6829 proceeds forward from the last examined trace snapshot. If no
6830 argument @var{num} is given, it means find the next snapshot collected
6831 for the same tracepoint as the current snapshot.
6833 @item tfind pc @var{addr}
6834 Find the next snapshot associated with the value @var{addr} of the
6835 program counter. Search proceeds forward from the last examined trace
6836 snapshot. If no argument @var{addr} is given, it means find the next
6837 snapshot with the same value of PC as the current snapshot.
6839 @item tfind outside @var{addr1}, @var{addr2}
6840 Find the next snapshot whose PC is outside the given range of
6843 @item tfind range @var{addr1}, @var{addr2}
6844 Find the next snapshot whose PC is between @var{addr1} and
6845 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6847 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6848 Find the next snapshot associated with the source line @var{n}. If
6849 the optional argument @var{file} is given, refer to line @var{n} in
6850 that source file. Search proceeds forward from the last examined
6851 trace snapshot. If no argument @var{n} is given, it means find the
6852 next line other than the one currently being examined; thus saying
6853 @code{tfind line} repeatedly can appear to have the same effect as
6854 stepping from line to line in a @emph{live} debugging session.
6857 The default arguments for the @code{tfind} commands are specifically
6858 designed to make it easy to scan through the trace buffer. For
6859 instance, @code{tfind} with no argument selects the next trace
6860 snapshot, and @code{tfind -} with no argument selects the previous
6861 trace snapshot. So, by giving one @code{tfind} command, and then
6862 simply hitting @key{RET} repeatedly you can examine all the trace
6863 snapshots in order. Or, by saying @code{tfind -} and then hitting
6864 @key{RET} repeatedly you can examine the snapshots in reverse order.
6865 The @code{tfind line} command with no argument selects the snapshot
6866 for the next source line executed. The @code{tfind pc} command with
6867 no argument selects the next snapshot with the same program counter
6868 (PC) as the current frame. The @code{tfind tracepoint} command with
6869 no argument selects the next trace snapshot collected by the same
6870 tracepoint as the current one.
6872 In addition to letting you scan through the trace buffer manually,
6873 these commands make it easy to construct @value{GDBN} scripts that
6874 scan through the trace buffer and print out whatever collected data
6875 you are interested in. Thus, if we want to examine the PC, FP, and SP
6876 registers from each trace frame in the buffer, we can say this:
6879 (@value{GDBP}) @b{tfind start}
6880 (@value{GDBP}) @b{while ($trace_frame != -1)}
6881 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6882 $trace_frame, $pc, $sp, $fp
6886 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6887 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6888 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6889 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6890 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6891 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6892 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6893 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6894 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6895 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6896 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6899 Or, if we want to examine the variable @code{X} at each source line in
6903 (@value{GDBP}) @b{tfind start}
6904 (@value{GDBP}) @b{while ($trace_frame != -1)}
6905 > printf "Frame %d, X == %d\n", $trace_frame, X
6915 @subsection @code{tdump}
6917 @cindex dump all data collected at tracepoint
6918 @cindex tracepoint data, display
6920 This command takes no arguments. It prints all the data collected at
6921 the current trace snapshot.
6924 (@value{GDBP}) @b{trace 444}
6925 (@value{GDBP}) @b{actions}
6926 Enter actions for tracepoint #2, one per line:
6927 > collect $regs, $locals, $args, gdb_long_test
6930 (@value{GDBP}) @b{tstart}
6932 (@value{GDBP}) @b{tfind line 444}
6933 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6935 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6937 (@value{GDBP}) @b{tdump}
6938 Data collected at tracepoint 2, trace frame 1:
6939 d0 0xc4aa0085 -995491707
6943 d4 0x71aea3d 119204413
6948 a1 0x3000668 50333288
6951 a4 0x3000698 50333336
6953 fp 0x30bf3c 0x30bf3c
6954 sp 0x30bf34 0x30bf34
6956 pc 0x20b2c8 0x20b2c8
6960 p = 0x20e5b4 "gdb-test"
6967 gdb_long_test = 17 '\021'
6972 @node save-tracepoints
6973 @subsection @code{save-tracepoints @var{filename}}
6974 @kindex save-tracepoints
6975 @cindex save tracepoints for future sessions
6977 This command saves all current tracepoint definitions together with
6978 their actions and passcounts, into a file @file{@var{filename}}
6979 suitable for use in a later debugging session. To read the saved
6980 tracepoint definitions, use the @code{source} command (@pxref{Command
6983 @node Tracepoint Variables
6984 @section Convenience Variables for Tracepoints
6985 @cindex tracepoint variables
6986 @cindex convenience variables for tracepoints
6989 @vindex $trace_frame
6990 @item (int) $trace_frame
6991 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6992 snapshot is selected.
6995 @item (int) $tracepoint
6996 The tracepoint for the current trace snapshot.
6999 @item (int) $trace_line
7000 The line number for the current trace snapshot.
7003 @item (char []) $trace_file
7004 The source file for the current trace snapshot.
7007 @item (char []) $trace_func
7008 The name of the function containing @code{$tracepoint}.
7011 Note: @code{$trace_file} is not suitable for use in @code{printf},
7012 use @code{output} instead.
7014 Here's a simple example of using these convenience variables for
7015 stepping through all the trace snapshots and printing some of their
7019 (@value{GDBP}) @b{tfind start}
7021 (@value{GDBP}) @b{while $trace_frame != -1}
7022 > output $trace_file
7023 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
7029 @chapter Debugging Programs That Use Overlays
7032 If your program is too large to fit completely in your target system's
7033 memory, you can sometimes use @dfn{overlays} to work around this
7034 problem. @value{GDBN} provides some support for debugging programs that
7038 * How Overlays Work:: A general explanation of overlays.
7039 * Overlay Commands:: Managing overlays in @value{GDBN}.
7040 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
7041 mapped by asking the inferior.
7042 * Overlay Sample Program:: A sample program using overlays.
7045 @node How Overlays Work
7046 @section How Overlays Work
7047 @cindex mapped overlays
7048 @cindex unmapped overlays
7049 @cindex load address, overlay's
7050 @cindex mapped address
7051 @cindex overlay area
7053 Suppose you have a computer whose instruction address space is only 64
7054 kilobytes long, but which has much more memory which can be accessed by
7055 other means: special instructions, segment registers, or memory
7056 management hardware, for example. Suppose further that you want to
7057 adapt a program which is larger than 64 kilobytes to run on this system.
7059 One solution is to identify modules of your program which are relatively
7060 independent, and need not call each other directly; call these modules
7061 @dfn{overlays}. Separate the overlays from the main program, and place
7062 their machine code in the larger memory. Place your main program in
7063 instruction memory, but leave at least enough space there to hold the
7064 largest overlay as well.
7066 Now, to call a function located in an overlay, you must first copy that
7067 overlay's machine code from the large memory into the space set aside
7068 for it in the instruction memory, and then jump to its entry point
7071 @c NB: In the below the mapped area's size is greater or equal to the
7072 @c size of all overlays. This is intentional to remind the developer
7073 @c that overlays don't necessarily need to be the same size.
7077 Data Instruction Larger
7078 Address Space Address Space Address Space
7079 +-----------+ +-----------+ +-----------+
7081 +-----------+ +-----------+ +-----------+<-- overlay 1
7082 | program | | main | .----| overlay 1 | load address
7083 | variables | | program | | +-----------+
7084 | and heap | | | | | |
7085 +-----------+ | | | +-----------+<-- overlay 2
7086 | | +-----------+ | | | load address
7087 +-----------+ | | | .-| overlay 2 |
7089 mapped --->+-----------+ | | +-----------+
7091 | overlay | <-' | | |
7092 | area | <---' +-----------+<-- overlay 3
7093 | | <---. | | load address
7094 +-----------+ `--| overlay 3 |
7101 @anchor{A code overlay}A code overlay
7105 The diagram (@pxref{A code overlay}) shows a system with separate data
7106 and instruction address spaces. To map an overlay, the program copies
7107 its code from the larger address space to the instruction address space.
7108 Since the overlays shown here all use the same mapped address, only one
7109 may be mapped at a time. For a system with a single address space for
7110 data and instructions, the diagram would be similar, except that the
7111 program variables and heap would share an address space with the main
7112 program and the overlay area.
7114 An overlay loaded into instruction memory and ready for use is called a
7115 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
7116 instruction memory. An overlay not present (or only partially present)
7117 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
7118 is its address in the larger memory. The mapped address is also called
7119 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
7120 called the @dfn{load memory address}, or @dfn{LMA}.
7122 Unfortunately, overlays are not a completely transparent way to adapt a
7123 program to limited instruction memory. They introduce a new set of
7124 global constraints you must keep in mind as you design your program:
7129 Before calling or returning to a function in an overlay, your program
7130 must make sure that overlay is actually mapped. Otherwise, the call or
7131 return will transfer control to the right address, but in the wrong
7132 overlay, and your program will probably crash.
7135 If the process of mapping an overlay is expensive on your system, you
7136 will need to choose your overlays carefully to minimize their effect on
7137 your program's performance.
7140 The executable file you load onto your system must contain each
7141 overlay's instructions, appearing at the overlay's load address, not its
7142 mapped address. However, each overlay's instructions must be relocated
7143 and its symbols defined as if the overlay were at its mapped address.
7144 You can use GNU linker scripts to specify different load and relocation
7145 addresses for pieces of your program; see @ref{Overlay Description,,,
7146 ld.info, Using ld: the GNU linker}.
7149 The procedure for loading executable files onto your system must be able
7150 to load their contents into the larger address space as well as the
7151 instruction and data spaces.
7155 The overlay system described above is rather simple, and could be
7156 improved in many ways:
7161 If your system has suitable bank switch registers or memory management
7162 hardware, you could use those facilities to make an overlay's load area
7163 contents simply appear at their mapped address in instruction space.
7164 This would probably be faster than copying the overlay to its mapped
7165 area in the usual way.
7168 If your overlays are small enough, you could set aside more than one
7169 overlay area, and have more than one overlay mapped at a time.
7172 You can use overlays to manage data, as well as instructions. In
7173 general, data overlays are even less transparent to your design than
7174 code overlays: whereas code overlays only require care when you call or
7175 return to functions, data overlays require care every time you access
7176 the data. Also, if you change the contents of a data overlay, you
7177 must copy its contents back out to its load address before you can copy a
7178 different data overlay into the same mapped area.
7183 @node Overlay Commands
7184 @section Overlay Commands
7186 To use @value{GDBN}'s overlay support, each overlay in your program must
7187 correspond to a separate section of the executable file. The section's
7188 virtual memory address and load memory address must be the overlay's
7189 mapped and load addresses. Identifying overlays with sections allows
7190 @value{GDBN} to determine the appropriate address of a function or
7191 variable, depending on whether the overlay is mapped or not.
7193 @value{GDBN}'s overlay commands all start with the word @code{overlay};
7194 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
7199 Disable @value{GDBN}'s overlay support. When overlay support is
7200 disabled, @value{GDBN} assumes that all functions and variables are
7201 always present at their mapped addresses. By default, @value{GDBN}'s
7202 overlay support is disabled.
7204 @item overlay manual
7205 @kindex overlay manual
7206 @cindex manual overlay debugging
7207 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
7208 relies on you to tell it which overlays are mapped, and which are not,
7209 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
7210 commands described below.
7212 @item overlay map-overlay @var{overlay}
7213 @itemx overlay map @var{overlay}
7214 @kindex overlay map-overlay
7215 @cindex map an overlay
7216 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
7217 be the name of the object file section containing the overlay. When an
7218 overlay is mapped, @value{GDBN} assumes it can find the overlay's
7219 functions and variables at their mapped addresses. @value{GDBN} assumes
7220 that any other overlays whose mapped ranges overlap that of
7221 @var{overlay} are now unmapped.
7223 @item overlay unmap-overlay @var{overlay}
7224 @itemx overlay unmap @var{overlay}
7225 @kindex overlay unmap-overlay
7226 @cindex unmap an overlay
7227 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
7228 must be the name of the object file section containing the overlay.
7229 When an overlay is unmapped, @value{GDBN} assumes it can find the
7230 overlay's functions and variables at their load addresses.
7233 @kindex overlay auto
7234 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
7235 consults a data structure the overlay manager maintains in the inferior
7236 to see which overlays are mapped. For details, see @ref{Automatic
7239 @item overlay load-target
7241 @kindex overlay load-target
7242 @cindex reloading the overlay table
7243 Re-read the overlay table from the inferior. Normally, @value{GDBN}
7244 re-reads the table @value{GDBN} automatically each time the inferior
7245 stops, so this command should only be necessary if you have changed the
7246 overlay mapping yourself using @value{GDBN}. This command is only
7247 useful when using automatic overlay debugging.
7249 @item overlay list-overlays
7251 @cindex listing mapped overlays
7252 Display a list of the overlays currently mapped, along with their mapped
7253 addresses, load addresses, and sizes.
7257 Normally, when @value{GDBN} prints a code address, it includes the name
7258 of the function the address falls in:
7262 $3 = @{int ()@} 0x11a0 <main>
7265 When overlay debugging is enabled, @value{GDBN} recognizes code in
7266 unmapped overlays, and prints the names of unmapped functions with
7267 asterisks around them. For example, if @code{foo} is a function in an
7268 unmapped overlay, @value{GDBN} prints it this way:
7272 No sections are mapped.
7274 $5 = @{int (int)@} 0x100000 <*foo*>
7277 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
7282 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
7283 mapped at 0x1016 - 0x104a
7285 $6 = @{int (int)@} 0x1016 <foo>
7288 When overlay debugging is enabled, @value{GDBN} can find the correct
7289 address for functions and variables in an overlay, whether or not the
7290 overlay is mapped. This allows most @value{GDBN} commands, like
7291 @code{break} and @code{disassemble}, to work normally, even on unmapped
7292 code. However, @value{GDBN}'s breakpoint support has some limitations:
7296 @cindex breakpoints in overlays
7297 @cindex overlays, setting breakpoints in
7298 You can set breakpoints in functions in unmapped overlays, as long as
7299 @value{GDBN} can write to the overlay at its load address.
7301 @value{GDBN} can not set hardware or simulator-based breakpoints in
7302 unmapped overlays. However, if you set a breakpoint at the end of your
7303 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
7304 you are using manual overlay management), @value{GDBN} will re-set its
7305 breakpoints properly.
7309 @node Automatic Overlay Debugging
7310 @section Automatic Overlay Debugging
7311 @cindex automatic overlay debugging
7313 @value{GDBN} can automatically track which overlays are mapped and which
7314 are not, given some simple co-operation from the overlay manager in the
7315 inferior. If you enable automatic overlay debugging with the
7316 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
7317 looks in the inferior's memory for certain variables describing the
7318 current state of the overlays.
7320 Here are the variables your overlay manager must define to support
7321 @value{GDBN}'s automatic overlay debugging:
7325 @item @code{_ovly_table}:
7326 This variable must be an array of the following structures:
7331 /* The overlay's mapped address. */
7334 /* The size of the overlay, in bytes. */
7337 /* The overlay's load address. */
7340 /* Non-zero if the overlay is currently mapped;
7342 unsigned long mapped;
7346 @item @code{_novlys}:
7347 This variable must be a four-byte signed integer, holding the total
7348 number of elements in @code{_ovly_table}.
7352 To decide whether a particular overlay is mapped or not, @value{GDBN}
7353 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
7354 @code{lma} members equal the VMA and LMA of the overlay's section in the
7355 executable file. When @value{GDBN} finds a matching entry, it consults
7356 the entry's @code{mapped} member to determine whether the overlay is
7359 In addition, your overlay manager may define a function called
7360 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
7361 will silently set a breakpoint there. If the overlay manager then
7362 calls this function whenever it has changed the overlay table, this
7363 will enable @value{GDBN} to accurately keep track of which overlays
7364 are in program memory, and update any breakpoints that may be set
7365 in overlays. This will allow breakpoints to work even if the
7366 overlays are kept in ROM or other non-writable memory while they
7367 are not being executed.
7369 @node Overlay Sample Program
7370 @section Overlay Sample Program
7371 @cindex overlay example program
7373 When linking a program which uses overlays, you must place the overlays
7374 at their load addresses, while relocating them to run at their mapped
7375 addresses. To do this, you must write a linker script (@pxref{Overlay
7376 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
7377 since linker scripts are specific to a particular host system, target
7378 architecture, and target memory layout, this manual cannot provide
7379 portable sample code demonstrating @value{GDBN}'s overlay support.
7381 However, the @value{GDBN} source distribution does contain an overlaid
7382 program, with linker scripts for a few systems, as part of its test
7383 suite. The program consists of the following files from
7384 @file{gdb/testsuite/gdb.base}:
7388 The main program file.
7390 A simple overlay manager, used by @file{overlays.c}.
7395 Overlay modules, loaded and used by @file{overlays.c}.
7398 Linker scripts for linking the test program on the @code{d10v-elf}
7399 and @code{m32r-elf} targets.
7402 You can build the test program using the @code{d10v-elf} GCC
7403 cross-compiler like this:
7406 $ d10v-elf-gcc -g -c overlays.c
7407 $ d10v-elf-gcc -g -c ovlymgr.c
7408 $ d10v-elf-gcc -g -c foo.c
7409 $ d10v-elf-gcc -g -c bar.c
7410 $ d10v-elf-gcc -g -c baz.c
7411 $ d10v-elf-gcc -g -c grbx.c
7412 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
7413 baz.o grbx.o -Wl,-Td10v.ld -o overlays
7416 The build process is identical for any other architecture, except that
7417 you must substitute the appropriate compiler and linker script for the
7418 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
7422 @chapter Using @value{GDBN} with Different Languages
7425 Although programming languages generally have common aspects, they are
7426 rarely expressed in the same manner. For instance, in ANSI C,
7427 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
7428 Modula-2, it is accomplished by @code{p^}. Values can also be
7429 represented (and displayed) differently. Hex numbers in C appear as
7430 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
7432 @cindex working language
7433 Language-specific information is built into @value{GDBN} for some languages,
7434 allowing you to express operations like the above in your program's
7435 native language, and allowing @value{GDBN} to output values in a manner
7436 consistent with the syntax of your program's native language. The
7437 language you use to build expressions is called the @dfn{working
7441 * Setting:: Switching between source languages
7442 * Show:: Displaying the language
7443 * Checks:: Type and range checks
7444 * Support:: Supported languages
7448 @section Switching between source languages
7450 There are two ways to control the working language---either have @value{GDBN}
7451 set it automatically, or select it manually yourself. You can use the
7452 @code{set language} command for either purpose. On startup, @value{GDBN}
7453 defaults to setting the language automatically. The working language is
7454 used to determine how expressions you type are interpreted, how values
7457 In addition to the working language, every source file that
7458 @value{GDBN} knows about has its own working language. For some object
7459 file formats, the compiler might indicate which language a particular
7460 source file is in. However, most of the time @value{GDBN} infers the
7461 language from the name of the file. The language of a source file
7462 controls whether C@t{++} names are demangled---this way @code{backtrace} can
7463 show each frame appropriately for its own language. There is no way to
7464 set the language of a source file from within @value{GDBN}, but you can
7465 set the language associated with a filename extension. @xref{Show, ,
7466 Displaying the language}.
7468 This is most commonly a problem when you use a program, such
7469 as @code{cfront} or @code{f2c}, that generates C but is written in
7470 another language. In that case, make the
7471 program use @code{#line} directives in its C output; that way
7472 @value{GDBN} will know the correct language of the source code of the original
7473 program, and will display that source code, not the generated C code.
7476 * Filenames:: Filename extensions and languages.
7477 * Manually:: Setting the working language manually
7478 * Automatically:: Having @value{GDBN} infer the source language
7482 @subsection List of filename extensions and languages
7484 If a source file name ends in one of the following extensions, then
7485 @value{GDBN} infers that its language is the one indicated.
7505 Modula-2 source file
7509 Assembler source file. This actually behaves almost like C, but
7510 @value{GDBN} does not skip over function prologues when stepping.
7513 In addition, you may set the language associated with a filename
7514 extension. @xref{Show, , Displaying the language}.
7517 @subsection Setting the working language
7519 If you allow @value{GDBN} to set the language automatically,
7520 expressions are interpreted the same way in your debugging session and
7523 @kindex set language
7524 If you wish, you may set the language manually. To do this, issue the
7525 command @samp{set language @var{lang}}, where @var{lang} is the name of
7527 @code{c} or @code{modula-2}.
7528 For a list of the supported languages, type @samp{set language}.
7530 Setting the language manually prevents @value{GDBN} from updating the working
7531 language automatically. This can lead to confusion if you try
7532 to debug a program when the working language is not the same as the
7533 source language, when an expression is acceptable to both
7534 languages---but means different things. For instance, if the current
7535 source file were written in C, and @value{GDBN} was parsing Modula-2, a
7543 might not have the effect you intended. In C, this means to add
7544 @code{b} and @code{c} and place the result in @code{a}. The result
7545 printed would be the value of @code{a}. In Modula-2, this means to compare
7546 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
7549 @subsection Having @value{GDBN} infer the source language
7551 To have @value{GDBN} set the working language automatically, use
7552 @samp{set language local} or @samp{set language auto}. @value{GDBN}
7553 then infers the working language. That is, when your program stops in a
7554 frame (usually by encountering a breakpoint), @value{GDBN} sets the
7555 working language to the language recorded for the function in that
7556 frame. If the language for a frame is unknown (that is, if the function
7557 or block corresponding to the frame was defined in a source file that
7558 does not have a recognized extension), the current working language is
7559 not changed, and @value{GDBN} issues a warning.
7561 This may not seem necessary for most programs, which are written
7562 entirely in one source language. However, program modules and libraries
7563 written in one source language can be used by a main program written in
7564 a different source language. Using @samp{set language auto} in this
7565 case frees you from having to set the working language manually.
7568 @section Displaying the language
7570 The following commands help you find out which language is the
7571 working language, and also what language source files were written in.
7573 @kindex show language
7574 @kindex info frame@r{, show the source language}
7575 @kindex info source@r{, show the source language}
7578 Display the current working language. This is the
7579 language you can use with commands such as @code{print} to
7580 build and compute expressions that may involve variables in your program.
7583 Display the source language for this frame. This language becomes the
7584 working language if you use an identifier from this frame.
7585 @xref{Frame Info, ,Information about a frame}, to identify the other
7586 information listed here.
7589 Display the source language of this source file.
7590 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
7591 information listed here.
7594 In unusual circumstances, you may have source files with extensions
7595 not in the standard list. You can then set the extension associated
7596 with a language explicitly:
7598 @kindex set extension-language
7599 @kindex info extensions
7601 @item set extension-language @var{.ext} @var{language}
7602 Set source files with extension @var{.ext} to be assumed to be in
7603 the source language @var{language}.
7605 @item info extensions
7606 List all the filename extensions and the associated languages.
7610 @section Type and range checking
7613 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
7614 checking are included, but they do not yet have any effect. This
7615 section documents the intended facilities.
7617 @c FIXME remove warning when type/range code added
7619 Some languages are designed to guard you against making seemingly common
7620 errors through a series of compile- and run-time checks. These include
7621 checking the type of arguments to functions and operators, and making
7622 sure mathematical overflows are caught at run time. Checks such as
7623 these help to ensure a program's correctness once it has been compiled
7624 by eliminating type mismatches, and providing active checks for range
7625 errors when your program is running.
7627 @value{GDBN} can check for conditions like the above if you wish.
7628 Although @value{GDBN} does not check the statements in your program, it
7629 can check expressions entered directly into @value{GDBN} for evaluation via
7630 the @code{print} command, for example. As with the working language,
7631 @value{GDBN} can also decide whether or not to check automatically based on
7632 your program's source language. @xref{Support, ,Supported languages},
7633 for the default settings of supported languages.
7636 * Type Checking:: An overview of type checking
7637 * Range Checking:: An overview of range checking
7640 @cindex type checking
7641 @cindex checks, type
7643 @subsection An overview of type checking
7645 Some languages, such as Modula-2, are strongly typed, meaning that the
7646 arguments to operators and functions have to be of the correct type,
7647 otherwise an error occurs. These checks prevent type mismatch
7648 errors from ever causing any run-time problems. For example,
7656 The second example fails because the @code{CARDINAL} 1 is not
7657 type-compatible with the @code{REAL} 2.3.
7659 For the expressions you use in @value{GDBN} commands, you can tell the
7660 @value{GDBN} type checker to skip checking;
7661 to treat any mismatches as errors and abandon the expression;
7662 or to only issue warnings when type mismatches occur,
7663 but evaluate the expression anyway. When you choose the last of
7664 these, @value{GDBN} evaluates expressions like the second example above, but
7665 also issues a warning.
7667 Even if you turn type checking off, there may be other reasons
7668 related to type that prevent @value{GDBN} from evaluating an expression.
7669 For instance, @value{GDBN} does not know how to add an @code{int} and
7670 a @code{struct foo}. These particular type errors have nothing to do
7671 with the language in use, and usually arise from expressions, such as
7672 the one described above, which make little sense to evaluate anyway.
7674 Each language defines to what degree it is strict about type. For
7675 instance, both Modula-2 and C require the arguments to arithmetical
7676 operators to be numbers. In C, enumerated types and pointers can be
7677 represented as numbers, so that they are valid arguments to mathematical
7678 operators. @xref{Support, ,Supported languages}, for further
7679 details on specific languages.
7681 @value{GDBN} provides some additional commands for controlling the type checker:
7683 @kindex set check@r{, type}
7684 @kindex set check type
7685 @kindex show check type
7687 @item set check type auto
7688 Set type checking on or off based on the current working language.
7689 @xref{Support, ,Supported languages}, for the default settings for
7692 @item set check type on
7693 @itemx set check type off
7694 Set type checking on or off, overriding the default setting for the
7695 current working language. Issue a warning if the setting does not
7696 match the language default. If any type mismatches occur in
7697 evaluating an expression while type checking is on, @value{GDBN} prints a
7698 message and aborts evaluation of the expression.
7700 @item set check type warn
7701 Cause the type checker to issue warnings, but to always attempt to
7702 evaluate the expression. Evaluating the expression may still
7703 be impossible for other reasons. For example, @value{GDBN} cannot add
7704 numbers and structures.
7707 Show the current setting of the type checker, and whether or not @value{GDBN}
7708 is setting it automatically.
7711 @cindex range checking
7712 @cindex checks, range
7713 @node Range Checking
7714 @subsection An overview of range checking
7716 In some languages (such as Modula-2), it is an error to exceed the
7717 bounds of a type; this is enforced with run-time checks. Such range
7718 checking is meant to ensure program correctness by making sure
7719 computations do not overflow, or indices on an array element access do
7720 not exceed the bounds of the array.
7722 For expressions you use in @value{GDBN} commands, you can tell
7723 @value{GDBN} to treat range errors in one of three ways: ignore them,
7724 always treat them as errors and abandon the expression, or issue
7725 warnings but evaluate the expression anyway.
7727 A range error can result from numerical overflow, from exceeding an
7728 array index bound, or when you type a constant that is not a member
7729 of any type. Some languages, however, do not treat overflows as an
7730 error. In many implementations of C, mathematical overflow causes the
7731 result to ``wrap around'' to lower values---for example, if @var{m} is
7732 the largest integer value, and @var{s} is the smallest, then
7735 @var{m} + 1 @result{} @var{s}
7738 This, too, is specific to individual languages, and in some cases
7739 specific to individual compilers or machines. @xref{Support, ,
7740 Supported languages}, for further details on specific languages.
7742 @value{GDBN} provides some additional commands for controlling the range checker:
7744 @kindex set check@r{, range}
7745 @kindex set check range
7746 @kindex show check range
7748 @item set check range auto
7749 Set range checking on or off based on the current working language.
7750 @xref{Support, ,Supported languages}, for the default settings for
7753 @item set check range on
7754 @itemx set check range off
7755 Set range checking on or off, overriding the default setting for the
7756 current working language. A warning is issued if the setting does not
7757 match the language default. If a range error occurs and range checking is on,
7758 then a message is printed and evaluation of the expression is aborted.
7760 @item set check range warn
7761 Output messages when the @value{GDBN} range checker detects a range error,
7762 but attempt to evaluate the expression anyway. Evaluating the
7763 expression may still be impossible for other reasons, such as accessing
7764 memory that the process does not own (a typical example from many Unix
7768 Show the current setting of the range checker, and whether or not it is
7769 being set automatically by @value{GDBN}.
7773 @section Supported languages
7775 @value{GDBN} supports C, C@t{++}, Fortran, Java, assembly, and Modula-2.
7776 @c This is false ...
7777 Some @value{GDBN} features may be used in expressions regardless of the
7778 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7779 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7780 ,Expressions}) can be used with the constructs of any supported
7783 The following sections detail to what degree each source language is
7784 supported by @value{GDBN}. These sections are not meant to be language
7785 tutorials or references, but serve only as a reference guide to what the
7786 @value{GDBN} expression parser accepts, and what input and output
7787 formats should look like for different languages. There are many good
7788 books written on each of these languages; please look to these for a
7789 language reference or tutorial.
7793 * Modula-2:: Modula-2
7797 @subsection C and C@t{++}
7799 @cindex C and C@t{++}
7800 @cindex expressions in C or C@t{++}
7802 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7803 to both languages. Whenever this is the case, we discuss those languages
7807 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7808 @cindex @sc{gnu} C@t{++}
7809 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7810 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7811 effectively, you must compile your C@t{++} programs with a supported
7812 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7813 compiler (@code{aCC}).
7815 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7816 format. You can select that format explicitly with the @code{g++}
7817 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7818 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7819 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7822 * C Operators:: C and C@t{++} operators
7823 * C Constants:: C and C@t{++} constants
7824 * C plus plus expressions:: C@t{++} expressions
7825 * C Defaults:: Default settings for C and C@t{++}
7826 * C Checks:: C and C@t{++} type and range checks
7827 * Debugging C:: @value{GDBN} and C
7828 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7832 @subsubsection C and C@t{++} operators
7834 @cindex C and C@t{++} operators
7836 Operators must be defined on values of specific types. For instance,
7837 @code{+} is defined on numbers, but not on structures. Operators are
7838 often defined on groups of types.
7840 For the purposes of C and C@t{++}, the following definitions hold:
7845 @emph{Integral types} include @code{int} with any of its storage-class
7846 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7849 @emph{Floating-point types} include @code{float}, @code{double}, and
7850 @code{long double} (if supported by the target platform).
7853 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7856 @emph{Scalar types} include all of the above.
7861 The following operators are supported. They are listed here
7862 in order of increasing precedence:
7866 The comma or sequencing operator. Expressions in a comma-separated list
7867 are evaluated from left to right, with the result of the entire
7868 expression being the last expression evaluated.
7871 Assignment. The value of an assignment expression is the value
7872 assigned. Defined on scalar types.
7875 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7876 and translated to @w{@code{@var{a} = @var{a op b}}}.
7877 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7878 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7879 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7882 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7883 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7887 Logical @sc{or}. Defined on integral types.
7890 Logical @sc{and}. Defined on integral types.
7893 Bitwise @sc{or}. Defined on integral types.
7896 Bitwise exclusive-@sc{or}. Defined on integral types.
7899 Bitwise @sc{and}. Defined on integral types.
7902 Equality and inequality. Defined on scalar types. The value of these
7903 expressions is 0 for false and non-zero for true.
7905 @item <@r{, }>@r{, }<=@r{, }>=
7906 Less than, greater than, less than or equal, greater than or equal.
7907 Defined on scalar types. The value of these expressions is 0 for false
7908 and non-zero for true.
7911 left shift, and right shift. Defined on integral types.
7914 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7917 Addition and subtraction. Defined on integral types, floating-point types and
7920 @item *@r{, }/@r{, }%
7921 Multiplication, division, and modulus. Multiplication and division are
7922 defined on integral and floating-point types. Modulus is defined on
7926 Increment and decrement. When appearing before a variable, the
7927 operation is performed before the variable is used in an expression;
7928 when appearing after it, the variable's value is used before the
7929 operation takes place.
7932 Pointer dereferencing. Defined on pointer types. Same precedence as
7936 Address operator. Defined on variables. Same precedence as @code{++}.
7938 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7939 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7940 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7941 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7945 Negative. Defined on integral and floating-point types. Same
7946 precedence as @code{++}.
7949 Logical negation. Defined on integral types. Same precedence as
7953 Bitwise complement operator. Defined on integral types. Same precedence as
7958 Structure member, and pointer-to-structure member. For convenience,
7959 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7960 pointer based on the stored type information.
7961 Defined on @code{struct} and @code{union} data.
7964 Dereferences of pointers to members.
7967 Array indexing. @code{@var{a}[@var{i}]} is defined as
7968 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7971 Function parameter list. Same precedence as @code{->}.
7974 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7975 and @code{class} types.
7978 Doubled colons also represent the @value{GDBN} scope operator
7979 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7983 If an operator is redefined in the user code, @value{GDBN} usually
7984 attempts to invoke the redefined version instead of using the operator's
7992 @subsubsection C and C@t{++} constants
7994 @cindex C and C@t{++} constants
7996 @value{GDBN} allows you to express the constants of C and C@t{++} in the
8001 Integer constants are a sequence of digits. Octal constants are
8002 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
8003 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
8004 @samp{l}, specifying that the constant should be treated as a
8008 Floating point constants are a sequence of digits, followed by a decimal
8009 point, followed by a sequence of digits, and optionally followed by an
8010 exponent. An exponent is of the form:
8011 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
8012 sequence of digits. The @samp{+} is optional for positive exponents.
8013 A floating-point constant may also end with a letter @samp{f} or
8014 @samp{F}, specifying that the constant should be treated as being of
8015 the @code{float} (as opposed to the default @code{double}) type; or with
8016 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
8020 Enumerated constants consist of enumerated identifiers, or their
8021 integral equivalents.
8024 Character constants are a single character surrounded by single quotes
8025 (@code{'}), or a number---the ordinal value of the corresponding character
8026 (usually its @sc{ascii} value). Within quotes, the single character may
8027 be represented by a letter or by @dfn{escape sequences}, which are of
8028 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
8029 of the character's ordinal value; or of the form @samp{\@var{x}}, where
8030 @samp{@var{x}} is a predefined special character---for example,
8031 @samp{\n} for newline.
8034 String constants are a sequence of character constants surrounded by
8035 double quotes (@code{"}). Any valid character constant (as described
8036 above) may appear. Double quotes within the string must be preceded by
8037 a backslash, so for instance @samp{"a\"b'c"} is a string of five
8041 Pointer constants are an integral value. You can also write pointers
8042 to constants using the C operator @samp{&}.
8045 Array constants are comma-separated lists surrounded by braces @samp{@{}
8046 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
8047 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
8048 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
8052 * C plus plus expressions::
8059 @node C plus plus expressions
8060 @subsubsection C@t{++} expressions
8062 @cindex expressions in C@t{++}
8063 @value{GDBN} expression handling can interpret most C@t{++} expressions.
8065 @cindex C@t{++} support, not in @sc{coff}
8066 @cindex @sc{coff} versus C@t{++}
8067 @cindex C@t{++} and object formats
8068 @cindex object formats and C@t{++}
8069 @cindex a.out and C@t{++}
8070 @cindex @sc{ecoff} and C@t{++}
8071 @cindex @sc{xcoff} and C@t{++}
8072 @cindex @sc{elf}/stabs and C@t{++}
8073 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
8074 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
8075 @c periodically whether this has happened...
8077 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
8078 proper compiler. Typically, C@t{++} debugging depends on the use of
8079 additional debugging information in the symbol table, and thus requires
8080 special support. In particular, if your compiler generates a.out, MIPS
8081 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
8082 symbol table, these facilities are all available. (With @sc{gnu} CC,
8083 you can use the @samp{-gstabs} option to request stabs debugging
8084 extensions explicitly.) Where the object code format is standard
8085 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
8086 support in @value{GDBN} does @emph{not} work.
8091 @cindex member functions
8093 Member function calls are allowed; you can use expressions like
8096 count = aml->GetOriginal(x, y)
8099 @vindex this@r{, inside C@t{++} member functions}
8100 @cindex namespace in C@t{++}
8102 While a member function is active (in the selected stack frame), your
8103 expressions have the same namespace available as the member function;
8104 that is, @value{GDBN} allows implicit references to the class instance
8105 pointer @code{this} following the same rules as C@t{++}.
8107 @cindex call overloaded functions
8108 @cindex overloaded functions, calling
8109 @cindex type conversions in C@t{++}
8111 You can call overloaded functions; @value{GDBN} resolves the function
8112 call to the right definition, with some restrictions. @value{GDBN} does not
8113 perform overload resolution involving user-defined type conversions,
8114 calls to constructors, or instantiations of templates that do not exist
8115 in the program. It also cannot handle ellipsis argument lists or
8118 It does perform integral conversions and promotions, floating-point
8119 promotions, arithmetic conversions, pointer conversions, conversions of
8120 class objects to base classes, and standard conversions such as those of
8121 functions or arrays to pointers; it requires an exact match on the
8122 number of function arguments.
8124 Overload resolution is always performed, unless you have specified
8125 @code{set overload-resolution off}. @xref{Debugging C plus plus,
8126 ,@value{GDBN} features for C@t{++}}.
8128 You must specify @code{set overload-resolution off} in order to use an
8129 explicit function signature to call an overloaded function, as in
8131 p 'foo(char,int)'('x', 13)
8134 The @value{GDBN} command-completion facility can simplify this;
8135 see @ref{Completion, ,Command completion}.
8137 @cindex reference declarations
8139 @value{GDBN} understands variables declared as C@t{++} references; you can use
8140 them in expressions just as you do in C@t{++} source---they are automatically
8143 In the parameter list shown when @value{GDBN} displays a frame, the values of
8144 reference variables are not displayed (unlike other variables); this
8145 avoids clutter, since references are often used for large structures.
8146 The @emph{address} of a reference variable is always shown, unless
8147 you have specified @samp{set print address off}.
8150 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
8151 expressions can use it just as expressions in your program do. Since
8152 one scope may be defined in another, you can use @code{::} repeatedly if
8153 necessary, for example in an expression like
8154 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
8155 resolving name scope by reference to source files, in both C and C@t{++}
8156 debugging (@pxref{Variables, ,Program variables}).
8159 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
8160 calling virtual functions correctly, printing out virtual bases of
8161 objects, calling functions in a base subobject, casting objects, and
8162 invoking user-defined operators.
8165 @subsubsection C and C@t{++} defaults
8167 @cindex C and C@t{++} defaults
8169 If you allow @value{GDBN} to set type and range checking automatically, they
8170 both default to @code{off} whenever the working language changes to
8171 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
8172 selects the working language.
8174 If you allow @value{GDBN} to set the language automatically, it
8175 recognizes source files whose names end with @file{.c}, @file{.C}, or
8176 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
8177 these files, it sets the working language to C or C@t{++}.
8178 @xref{Automatically, ,Having @value{GDBN} infer the source language},
8179 for further details.
8181 @c Type checking is (a) primarily motivated by Modula-2, and (b)
8182 @c unimplemented. If (b) changes, it might make sense to let this node
8183 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
8186 @subsubsection C and C@t{++} type and range checks
8188 @cindex C and C@t{++} checks
8190 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
8191 is not used. However, if you turn type checking on, @value{GDBN}
8192 considers two variables type equivalent if:
8196 The two variables are structured and have the same structure, union, or
8200 The two variables have the same type name, or types that have been
8201 declared equivalent through @code{typedef}.
8204 @c leaving this out because neither J Gilmore nor R Pesch understand it.
8207 The two @code{struct}, @code{union}, or @code{enum} variables are
8208 declared in the same declaration. (Note: this may not be true for all C
8213 Range checking, if turned on, is done on mathematical operations. Array
8214 indices are not checked, since they are often used to index a pointer
8215 that is not itself an array.
8218 @subsubsection @value{GDBN} and C
8220 The @code{set print union} and @code{show print union} commands apply to
8221 the @code{union} type. When set to @samp{on}, any @code{union} that is
8222 inside a @code{struct} or @code{class} is also printed. Otherwise, it
8223 appears as @samp{@{...@}}.
8225 The @code{@@} operator aids in the debugging of dynamic arrays, formed
8226 with pointers and a memory allocation function. @xref{Expressions,
8230 * Debugging C plus plus::
8233 @node Debugging C plus plus
8234 @subsubsection @value{GDBN} features for C@t{++}
8236 @cindex commands for C@t{++}
8238 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
8239 designed specifically for use with C@t{++}. Here is a summary:
8242 @cindex break in overloaded functions
8243 @item @r{breakpoint menus}
8244 When you want a breakpoint in a function whose name is overloaded,
8245 @value{GDBN} breakpoint menus help you specify which function definition
8246 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
8248 @cindex overloading in C@t{++}
8249 @item rbreak @var{regex}
8250 Setting breakpoints using regular expressions is helpful for setting
8251 breakpoints on overloaded functions that are not members of any special
8253 @xref{Set Breaks, ,Setting breakpoints}.
8255 @cindex C@t{++} exception handling
8258 Debug C@t{++} exception handling using these commands. @xref{Set
8259 Catchpoints, , Setting catchpoints}.
8262 @item ptype @var{typename}
8263 Print inheritance relationships as well as other information for type
8265 @xref{Symbols, ,Examining the Symbol Table}.
8267 @cindex C@t{++} symbol display
8268 @item set print demangle
8269 @itemx show print demangle
8270 @itemx set print asm-demangle
8271 @itemx show print asm-demangle
8272 Control whether C@t{++} symbols display in their source form, both when
8273 displaying code as C@t{++} source and when displaying disassemblies.
8274 @xref{Print Settings, ,Print settings}.
8276 @item set print object
8277 @itemx show print object
8278 Choose whether to print derived (actual) or declared types of objects.
8279 @xref{Print Settings, ,Print settings}.
8281 @item set print vtbl
8282 @itemx show print vtbl
8283 Control the format for printing virtual function tables.
8284 @xref{Print Settings, ,Print settings}.
8285 (The @code{vtbl} commands do not work on programs compiled with the HP
8286 ANSI C@t{++} compiler (@code{aCC}).)
8288 @kindex set overload-resolution
8289 @cindex overloaded functions, overload resolution
8290 @item set overload-resolution on
8291 Enable overload resolution for C@t{++} expression evaluation. The default
8292 is on. For overloaded functions, @value{GDBN} evaluates the arguments
8293 and searches for a function whose signature matches the argument types,
8294 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
8295 expressions}, for details). If it cannot find a match, it emits a
8298 @item set overload-resolution off
8299 Disable overload resolution for C@t{++} expression evaluation. For
8300 overloaded functions that are not class member functions, @value{GDBN}
8301 chooses the first function of the specified name that it finds in the
8302 symbol table, whether or not its arguments are of the correct type. For
8303 overloaded functions that are class member functions, @value{GDBN}
8304 searches for a function whose signature @emph{exactly} matches the
8307 @item @r{Overloaded symbol names}
8308 You can specify a particular definition of an overloaded symbol, using
8309 the same notation that is used to declare such symbols in C@t{++}: type
8310 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
8311 also use the @value{GDBN} command-line word completion facilities to list the
8312 available choices, or to finish the type list for you.
8313 @xref{Completion,, Command completion}, for details on how to do this.
8317 @subsection Modula-2
8319 @cindex Modula-2, @value{GDBN} support
8321 The extensions made to @value{GDBN} to support Modula-2 only support
8322 output from the @sc{gnu} Modula-2 compiler (which is currently being
8323 developed). Other Modula-2 compilers are not currently supported, and
8324 attempting to debug executables produced by them is most likely
8325 to give an error as @value{GDBN} reads in the executable's symbol
8328 @cindex expressions in Modula-2
8330 * M2 Operators:: Built-in operators
8331 * Built-In Func/Proc:: Built-in functions and procedures
8332 * M2 Constants:: Modula-2 constants
8333 * M2 Defaults:: Default settings for Modula-2
8334 * Deviations:: Deviations from standard Modula-2
8335 * M2 Checks:: Modula-2 type and range checks
8336 * M2 Scope:: The scope operators @code{::} and @code{.}
8337 * GDB/M2:: @value{GDBN} and Modula-2
8341 @subsubsection Operators
8342 @cindex Modula-2 operators
8344 Operators must be defined on values of specific types. For instance,
8345 @code{+} is defined on numbers, but not on structures. Operators are
8346 often defined on groups of types. For the purposes of Modula-2, the
8347 following definitions hold:
8352 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
8356 @emph{Character types} consist of @code{CHAR} and its subranges.
8359 @emph{Floating-point types} consist of @code{REAL}.
8362 @emph{Pointer types} consist of anything declared as @code{POINTER TO
8366 @emph{Scalar types} consist of all of the above.
8369 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
8372 @emph{Boolean types} consist of @code{BOOLEAN}.
8376 The following operators are supported, and appear in order of
8377 increasing precedence:
8381 Function argument or array index separator.
8384 Assignment. The value of @var{var} @code{:=} @var{value} is
8388 Less than, greater than on integral, floating-point, or enumerated
8392 Less than or equal to, greater than or equal to
8393 on integral, floating-point and enumerated types, or set inclusion on
8394 set types. Same precedence as @code{<}.
8396 @item =@r{, }<>@r{, }#
8397 Equality and two ways of expressing inequality, valid on scalar types.
8398 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
8399 available for inequality, since @code{#} conflicts with the script
8403 Set membership. Defined on set types and the types of their members.
8404 Same precedence as @code{<}.
8407 Boolean disjunction. Defined on boolean types.
8410 Boolean conjunction. Defined on boolean types.
8413 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
8416 Addition and subtraction on integral and floating-point types, or union
8417 and difference on set types.
8420 Multiplication on integral and floating-point types, or set intersection
8424 Division on floating-point types, or symmetric set difference on set
8425 types. Same precedence as @code{*}.
8428 Integer division and remainder. Defined on integral types. Same
8429 precedence as @code{*}.
8432 Negative. Defined on @code{INTEGER} and @code{REAL} data.
8435 Pointer dereferencing. Defined on pointer types.
8438 Boolean negation. Defined on boolean types. Same precedence as
8442 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
8443 precedence as @code{^}.
8446 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
8449 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
8453 @value{GDBN} and Modula-2 scope operators.
8457 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
8458 treats the use of the operator @code{IN}, or the use of operators
8459 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
8460 @code{<=}, and @code{>=} on sets as an error.
8464 @node Built-In Func/Proc
8465 @subsubsection Built-in functions and procedures
8466 @cindex Modula-2 built-ins
8468 Modula-2 also makes available several built-in procedures and functions.
8469 In describing these, the following metavariables are used:
8474 represents an @code{ARRAY} variable.
8477 represents a @code{CHAR} constant or variable.
8480 represents a variable or constant of integral type.
8483 represents an identifier that belongs to a set. Generally used in the
8484 same function with the metavariable @var{s}. The type of @var{s} should
8485 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
8488 represents a variable or constant of integral or floating-point type.
8491 represents a variable or constant of floating-point type.
8497 represents a variable.
8500 represents a variable or constant of one of many types. See the
8501 explanation of the function for details.
8504 All Modula-2 built-in procedures also return a result, described below.
8508 Returns the absolute value of @var{n}.
8511 If @var{c} is a lower case letter, it returns its upper case
8512 equivalent, otherwise it returns its argument.
8515 Returns the character whose ordinal value is @var{i}.
8518 Decrements the value in the variable @var{v} by one. Returns the new value.
8520 @item DEC(@var{v},@var{i})
8521 Decrements the value in the variable @var{v} by @var{i}. Returns the
8524 @item EXCL(@var{m},@var{s})
8525 Removes the element @var{m} from the set @var{s}. Returns the new
8528 @item FLOAT(@var{i})
8529 Returns the floating point equivalent of the integer @var{i}.
8532 Returns the index of the last member of @var{a}.
8535 Increments the value in the variable @var{v} by one. Returns the new value.
8537 @item INC(@var{v},@var{i})
8538 Increments the value in the variable @var{v} by @var{i}. Returns the
8541 @item INCL(@var{m},@var{s})
8542 Adds the element @var{m} to the set @var{s} if it is not already
8543 there. Returns the new set.
8546 Returns the maximum value of the type @var{t}.
8549 Returns the minimum value of the type @var{t}.
8552 Returns boolean TRUE if @var{i} is an odd number.
8555 Returns the ordinal value of its argument. For example, the ordinal
8556 value of a character is its @sc{ascii} value (on machines supporting the
8557 @sc{ascii} character set). @var{x} must be of an ordered type, which include
8558 integral, character and enumerated types.
8561 Returns the size of its argument. @var{x} can be a variable or a type.
8563 @item TRUNC(@var{r})
8564 Returns the integral part of @var{r}.
8566 @item VAL(@var{t},@var{i})
8567 Returns the member of the type @var{t} whose ordinal value is @var{i}.
8571 @emph{Warning:} Sets and their operations are not yet supported, so
8572 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
8576 @cindex Modula-2 constants
8578 @subsubsection Constants
8580 @value{GDBN} allows you to express the constants of Modula-2 in the following
8586 Integer constants are simply a sequence of digits. When used in an
8587 expression, a constant is interpreted to be type-compatible with the
8588 rest of the expression. Hexadecimal integers are specified by a
8589 trailing @samp{H}, and octal integers by a trailing @samp{B}.
8592 Floating point constants appear as a sequence of digits, followed by a
8593 decimal point and another sequence of digits. An optional exponent can
8594 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
8595 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
8596 digits of the floating point constant must be valid decimal (base 10)
8600 Character constants consist of a single character enclosed by a pair of
8601 like quotes, either single (@code{'}) or double (@code{"}). They may
8602 also be expressed by their ordinal value (their @sc{ascii} value, usually)
8603 followed by a @samp{C}.
8606 String constants consist of a sequence of characters enclosed by a
8607 pair of like quotes, either single (@code{'}) or double (@code{"}).
8608 Escape sequences in the style of C are also allowed. @xref{C
8609 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
8613 Enumerated constants consist of an enumerated identifier.
8616 Boolean constants consist of the identifiers @code{TRUE} and
8620 Pointer constants consist of integral values only.
8623 Set constants are not yet supported.
8627 @subsubsection Modula-2 defaults
8628 @cindex Modula-2 defaults
8630 If type and range checking are set automatically by @value{GDBN}, they
8631 both default to @code{on} whenever the working language changes to
8632 Modula-2. This happens regardless of whether you or @value{GDBN}
8633 selected the working language.
8635 If you allow @value{GDBN} to set the language automatically, then entering
8636 code compiled from a file whose name ends with @file{.mod} sets the
8637 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8638 the language automatically}, for further details.
8641 @subsubsection Deviations from standard Modula-2
8642 @cindex Modula-2, deviations from
8644 A few changes have been made to make Modula-2 programs easier to debug.
8645 This is done primarily via loosening its type strictness:
8649 Unlike in standard Modula-2, pointer constants can be formed by
8650 integers. This allows you to modify pointer variables during
8651 debugging. (In standard Modula-2, the actual address contained in a
8652 pointer variable is hidden from you; it can only be modified
8653 through direct assignment to another pointer variable or expression that
8654 returned a pointer.)
8657 C escape sequences can be used in strings and characters to represent
8658 non-printable characters. @value{GDBN} prints out strings with these
8659 escape sequences embedded. Single non-printable characters are
8660 printed using the @samp{CHR(@var{nnn})} format.
8663 The assignment operator (@code{:=}) returns the value of its right-hand
8667 All built-in procedures both modify @emph{and} return their argument.
8671 @subsubsection Modula-2 type and range checks
8672 @cindex Modula-2 checks
8675 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8678 @c FIXME remove warning when type/range checks added
8680 @value{GDBN} considers two Modula-2 variables type equivalent if:
8684 They are of types that have been declared equivalent via a @code{TYPE
8685 @var{t1} = @var{t2}} statement
8688 They have been declared on the same line. (Note: This is true of the
8689 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8692 As long as type checking is enabled, any attempt to combine variables
8693 whose types are not equivalent is an error.
8695 Range checking is done on all mathematical operations, assignment, array
8696 index bounds, and all built-in functions and procedures.
8699 @subsubsection The scope operators @code{::} and @code{.}
8701 @cindex @code{.}, Modula-2 scope operator
8702 @cindex colon, doubled as scope operator
8704 @vindex colon-colon@r{, in Modula-2}
8705 @c Info cannot handle :: but TeX can.
8708 @vindex ::@r{, in Modula-2}
8711 There are a few subtle differences between the Modula-2 scope operator
8712 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8717 @var{module} . @var{id}
8718 @var{scope} :: @var{id}
8722 where @var{scope} is the name of a module or a procedure,
8723 @var{module} the name of a module, and @var{id} is any declared
8724 identifier within your program, except another module.
8726 Using the @code{::} operator makes @value{GDBN} search the scope
8727 specified by @var{scope} for the identifier @var{id}. If it is not
8728 found in the specified scope, then @value{GDBN} searches all scopes
8729 enclosing the one specified by @var{scope}.
8731 Using the @code{.} operator makes @value{GDBN} search the current scope for
8732 the identifier specified by @var{id} that was imported from the
8733 definition module specified by @var{module}. With this operator, it is
8734 an error if the identifier @var{id} was not imported from definition
8735 module @var{module}, or if @var{id} is not an identifier in
8739 @subsubsection @value{GDBN} and Modula-2
8741 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8742 Five subcommands of @code{set print} and @code{show print} apply
8743 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8744 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8745 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8746 analogue in Modula-2.
8748 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8749 with any language, is not useful with Modula-2. Its
8750 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8751 created in Modula-2 as they can in C or C@t{++}. However, because an
8752 address can be specified by an integral constant, the construct
8753 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8755 @cindex @code{#} in Modula-2
8756 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8757 interpreted as the beginning of a comment. Use @code{<>} instead.
8760 @chapter Examining the Symbol Table
8762 The commands described in this chapter allow you to inquire about the
8763 symbols (names of variables, functions and types) defined in your
8764 program. This information is inherent in the text of your program and
8765 does not change as your program executes. @value{GDBN} finds it in your
8766 program's symbol table, in the file indicated when you started @value{GDBN}
8767 (@pxref{File Options, ,Choosing files}), or by one of the
8768 file-management commands (@pxref{Files, ,Commands to specify files}).
8770 @cindex symbol names
8771 @cindex names of symbols
8772 @cindex quoting names
8773 Occasionally, you may need to refer to symbols that contain unusual
8774 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8775 most frequent case is in referring to static variables in other
8776 source files (@pxref{Variables,,Program variables}). File names
8777 are recorded in object files as debugging symbols, but @value{GDBN} would
8778 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8779 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8780 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8787 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8790 @kindex info address
8791 @cindex address of a symbol
8792 @item info address @var{symbol}
8793 Describe where the data for @var{symbol} is stored. For a register
8794 variable, this says which register it is kept in. For a non-register
8795 local variable, this prints the stack-frame offset at which the variable
8798 Note the contrast with @samp{print &@var{symbol}}, which does not work
8799 at all for a register variable, and for a stack local variable prints
8800 the exact address of the current instantiation of the variable.
8803 @cindex symbol from address
8804 @item info symbol @var{addr}
8805 Print the name of a symbol which is stored at the address @var{addr}.
8806 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8807 nearest symbol and an offset from it:
8810 (@value{GDBP}) info symbol 0x54320
8811 _initialize_vx + 396 in section .text
8815 This is the opposite of the @code{info address} command. You can use
8816 it to find out the name of a variable or a function given its address.
8819 @item whatis @var{expr}
8820 Print the data type of expression @var{expr}. @var{expr} is not
8821 actually evaluated, and any side-effecting operations (such as
8822 assignments or function calls) inside it do not take place.
8823 @xref{Expressions, ,Expressions}.
8826 Print the data type of @code{$}, the last value in the value history.
8829 @item ptype @var{typename}
8830 Print a description of data type @var{typename}. @var{typename} may be
8831 the name of a type, or for C code it may have the form @samp{class
8832 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8833 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8835 @item ptype @var{expr}
8837 Print a description of the type of expression @var{expr}. @code{ptype}
8838 differs from @code{whatis} by printing a detailed description, instead
8839 of just the name of the type.
8841 For example, for this variable declaration:
8844 struct complex @{double real; double imag;@} v;
8848 the two commands give this output:
8852 (@value{GDBP}) whatis v
8853 type = struct complex
8854 (@value{GDBP}) ptype v
8855 type = struct complex @{
8863 As with @code{whatis}, using @code{ptype} without an argument refers to
8864 the type of @code{$}, the last value in the value history.
8867 @item info types @var{regexp}
8869 Print a brief description of all types whose names match @var{regexp}
8870 (or all types in your program, if you supply no argument). Each
8871 complete typename is matched as though it were a complete line; thus,
8872 @samp{i type value} gives information on all types in your program whose
8873 names include the string @code{value}, but @samp{i type ^value$} gives
8874 information only on types whose complete name is @code{value}.
8876 This command differs from @code{ptype} in two ways: first, like
8877 @code{whatis}, it does not print a detailed description; second, it
8878 lists all source files where a type is defined.
8881 @cindex local variables
8882 @item info scope @var{addr}
8883 List all the variables local to a particular scope. This command
8884 accepts a location---a function name, a source line, or an address
8885 preceded by a @samp{*}, and prints all the variables local to the
8886 scope defined by that location. For example:
8889 (@value{GDBP}) @b{info scope command_line_handler}
8890 Scope for command_line_handler:
8891 Symbol rl is an argument at stack/frame offset 8, length 4.
8892 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8893 Symbol linelength is in static storage at address 0x150a1c, length 4.
8894 Symbol p is a local variable in register $esi, length 4.
8895 Symbol p1 is a local variable in register $ebx, length 4.
8896 Symbol nline is a local variable in register $edx, length 4.
8897 Symbol repeat is a local variable at frame offset -8, length 4.
8901 This command is especially useful for determining what data to collect
8902 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8907 Show information about the current source file---that is, the source file for
8908 the function containing the current point of execution:
8911 the name of the source file, and the directory containing it,
8913 the directory it was compiled in,
8915 its length, in lines,
8917 which programming language it is written in,
8919 whether the executable includes debugging information for that file, and
8920 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
8922 whether the debugging information includes information about
8923 preprocessor macros.
8927 @kindex info sources
8929 Print the names of all source files in your program for which there is
8930 debugging information, organized into two lists: files whose symbols
8931 have already been read, and files whose symbols will be read when needed.
8933 @kindex info functions
8934 @item info functions
8935 Print the names and data types of all defined functions.
8937 @item info functions @var{regexp}
8938 Print the names and data types of all defined functions
8939 whose names contain a match for regular expression @var{regexp}.
8940 Thus, @samp{info fun step} finds all functions whose names
8941 include @code{step}; @samp{info fun ^step} finds those whose names
8942 start with @code{step}. If a function name contains characters
8943 that conflict with the regular expression language (eg.
8944 @samp{operator*()}), they may be quoted with a backslash.
8946 @kindex info variables
8947 @item info variables
8948 Print the names and data types of all variables that are declared
8949 outside of functions (i.e.@: excluding local variables).
8951 @item info variables @var{regexp}
8952 Print the names and data types of all variables (except for local
8953 variables) whose names contain a match for regular expression
8957 This was never implemented.
8958 @kindex info methods
8960 @itemx info methods @var{regexp}
8961 The @code{info methods} command permits the user to examine all defined
8962 methods within C@t{++} program, or (with the @var{regexp} argument) a
8963 specific set of methods found in the various C@t{++} classes. Many
8964 C@t{++} classes provide a large number of methods. Thus, the output
8965 from the @code{ptype} command can be overwhelming and hard to use. The
8966 @code{info-methods} command filters the methods, printing only those
8967 which match the regular-expression @var{regexp}.
8970 @cindex reloading symbols
8971 Some systems allow individual object files that make up your program to
8972 be replaced without stopping and restarting your program. For example,
8973 in VxWorks you can simply recompile a defective object file and keep on
8974 running. If you are running on one of these systems, you can allow
8975 @value{GDBN} to reload the symbols for automatically relinked modules:
8978 @kindex set symbol-reloading
8979 @item set symbol-reloading on
8980 Replace symbol definitions for the corresponding source file when an
8981 object file with a particular name is seen again.
8983 @item set symbol-reloading off
8984 Do not replace symbol definitions when encountering object files of the
8985 same name more than once. This is the default state; if you are not
8986 running on a system that permits automatic relinking of modules, you
8987 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8988 may discard symbols when linking large programs, that may contain
8989 several modules (from different directories or libraries) with the same
8992 @kindex show symbol-reloading
8993 @item show symbol-reloading
8994 Show the current @code{on} or @code{off} setting.
8997 @kindex set opaque-type-resolution
8998 @item set opaque-type-resolution on
8999 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
9000 declared as a pointer to a @code{struct}, @code{class}, or
9001 @code{union}---for example, @code{struct MyType *}---that is used in one
9002 source file although the full declaration of @code{struct MyType} is in
9003 another source file. The default is on.
9005 A change in the setting of this subcommand will not take effect until
9006 the next time symbols for a file are loaded.
9008 @item set opaque-type-resolution off
9009 Tell @value{GDBN} not to resolve opaque types. In this case, the type
9010 is printed as follows:
9012 @{<no data fields>@}
9015 @kindex show opaque-type-resolution
9016 @item show opaque-type-resolution
9017 Show whether opaque types are resolved or not.
9019 @kindex maint print symbols
9021 @kindex maint print psymbols
9022 @cindex partial symbol dump
9023 @item maint print symbols @var{filename}
9024 @itemx maint print psymbols @var{filename}
9025 @itemx maint print msymbols @var{filename}
9026 Write a dump of debugging symbol data into the file @var{filename}.
9027 These commands are used to debug the @value{GDBN} symbol-reading code. Only
9028 symbols with debugging data are included. If you use @samp{maint print
9029 symbols}, @value{GDBN} includes all the symbols for which it has already
9030 collected full details: that is, @var{filename} reflects symbols for
9031 only those files whose symbols @value{GDBN} has read. You can use the
9032 command @code{info sources} to find out which files these are. If you
9033 use @samp{maint print psymbols} instead, the dump shows information about
9034 symbols that @value{GDBN} only knows partially---that is, symbols defined in
9035 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
9036 @samp{maint print msymbols} dumps just the minimal symbol information
9037 required for each object file from which @value{GDBN} has read some symbols.
9038 @xref{Files, ,Commands to specify files}, for a discussion of how
9039 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
9043 @chapter Altering Execution
9045 Once you think you have found an error in your program, you might want to
9046 find out for certain whether correcting the apparent error would lead to
9047 correct results in the rest of the run. You can find the answer by
9048 experiment, using the @value{GDBN} features for altering execution of the
9051 For example, you can store new values into variables or memory
9052 locations, give your program a signal, restart it at a different
9053 address, or even return prematurely from a function.
9056 * Assignment:: Assignment to variables
9057 * Jumping:: Continuing at a different address
9058 * Signaling:: Giving your program a signal
9059 * Returning:: Returning from a function
9060 * Calling:: Calling your program's functions
9061 * Patching:: Patching your program
9065 @section Assignment to variables
9068 @cindex setting variables
9069 To alter the value of a variable, evaluate an assignment expression.
9070 @xref{Expressions, ,Expressions}. For example,
9077 stores the value 4 into the variable @code{x}, and then prints the
9078 value of the assignment expression (which is 4).
9079 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
9080 information on operators in supported languages.
9082 @kindex set variable
9083 @cindex variables, setting
9084 If you are not interested in seeing the value of the assignment, use the
9085 @code{set} command instead of the @code{print} command. @code{set} is
9086 really the same as @code{print} except that the expression's value is
9087 not printed and is not put in the value history (@pxref{Value History,
9088 ,Value history}). The expression is evaluated only for its effects.
9090 If the beginning of the argument string of the @code{set} command
9091 appears identical to a @code{set} subcommand, use the @code{set
9092 variable} command instead of just @code{set}. This command is identical
9093 to @code{set} except for its lack of subcommands. For example, if your
9094 program has a variable @code{width}, you get an error if you try to set
9095 a new value with just @samp{set width=13}, because @value{GDBN} has the
9096 command @code{set width}:
9099 (@value{GDBP}) whatis width
9101 (@value{GDBP}) p width
9103 (@value{GDBP}) set width=47
9104 Invalid syntax in expression.
9108 The invalid expression, of course, is @samp{=47}. In
9109 order to actually set the program's variable @code{width}, use
9112 (@value{GDBP}) set var width=47
9115 Because the @code{set} command has many subcommands that can conflict
9116 with the names of program variables, it is a good idea to use the
9117 @code{set variable} command instead of just @code{set}. For example, if
9118 your program has a variable @code{g}, you run into problems if you try
9119 to set a new value with just @samp{set g=4}, because @value{GDBN} has
9120 the command @code{set gnutarget}, abbreviated @code{set g}:
9124 (@value{GDBP}) whatis g
9128 (@value{GDBP}) set g=4
9132 The program being debugged has been started already.
9133 Start it from the beginning? (y or n) y
9134 Starting program: /home/smith/cc_progs/a.out
9135 "/home/smith/cc_progs/a.out": can't open to read symbols:
9137 (@value{GDBP}) show g
9138 The current BFD target is "=4".
9143 The program variable @code{g} did not change, and you silently set the
9144 @code{gnutarget} to an invalid value. In order to set the variable
9148 (@value{GDBP}) set var g=4
9151 @value{GDBN} allows more implicit conversions in assignments than C; you can
9152 freely store an integer value into a pointer variable or vice versa,
9153 and you can convert any structure to any other structure that is the
9154 same length or shorter.
9155 @comment FIXME: how do structs align/pad in these conversions?
9156 @comment /doc@cygnus.com 18dec1990
9158 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9159 construct to generate a value of specified type at a specified address
9160 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9161 to memory location @code{0x83040} as an integer (which implies a certain size
9162 and representation in memory), and
9165 set @{int@}0x83040 = 4
9169 stores the value 4 into that memory location.
9172 @section Continuing at a different address
9174 Ordinarily, when you continue your program, you do so at the place where
9175 it stopped, with the @code{continue} command. You can instead continue at
9176 an address of your own choosing, with the following commands:
9180 @item jump @var{linespec}
9181 Resume execution at line @var{linespec}. Execution stops again
9182 immediately if there is a breakpoint there. @xref{List, ,Printing
9183 source lines}, for a description of the different forms of
9184 @var{linespec}. It is common practice to use the @code{tbreak} command
9185 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9188 The @code{jump} command does not change the current stack frame, or
9189 the stack pointer, or the contents of any memory location or any
9190 register other than the program counter. If line @var{linespec} is in
9191 a different function from the one currently executing, the results may
9192 be bizarre if the two functions expect different patterns of arguments or
9193 of local variables. For this reason, the @code{jump} command requests
9194 confirmation if the specified line is not in the function currently
9195 executing. However, even bizarre results are predictable if you are
9196 well acquainted with the machine-language code of your program.
9198 @item jump *@var{address}
9199 Resume execution at the instruction at address @var{address}.
9202 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9203 On many systems, you can get much the same effect as the @code{jump}
9204 command by storing a new value into the register @code{$pc}. The
9205 difference is that this does not start your program running; it only
9206 changes the address of where it @emph{will} run when you continue. For
9214 makes the next @code{continue} command or stepping command execute at
9215 address @code{0x485}, rather than at the address where your program stopped.
9216 @xref{Continuing and Stepping, ,Continuing and stepping}.
9218 The most common occasion to use the @code{jump} command is to back
9219 up---perhaps with more breakpoints set---over a portion of a program
9220 that has already executed, in order to examine its execution in more
9225 @section Giving your program a signal
9229 @item signal @var{signal}
9230 Resume execution where your program stopped, but immediately give it the
9231 signal @var{signal}. @var{signal} can be the name or the number of a
9232 signal. For example, on many systems @code{signal 2} and @code{signal
9233 SIGINT} are both ways of sending an interrupt signal.
9235 Alternatively, if @var{signal} is zero, continue execution without
9236 giving a signal. This is useful when your program stopped on account of
9237 a signal and would ordinary see the signal when resumed with the
9238 @code{continue} command; @samp{signal 0} causes it to resume without a
9241 @code{signal} does not repeat when you press @key{RET} a second time
9242 after executing the command.
9246 Invoking the @code{signal} command is not the same as invoking the
9247 @code{kill} utility from the shell. Sending a signal with @code{kill}
9248 causes @value{GDBN} to decide what to do with the signal depending on
9249 the signal handling tables (@pxref{Signals}). The @code{signal} command
9250 passes the signal directly to your program.
9254 @section Returning from a function
9257 @cindex returning from a function
9260 @itemx return @var{expression}
9261 You can cancel execution of a function call with the @code{return}
9262 command. If you give an
9263 @var{expression} argument, its value is used as the function's return
9267 When you use @code{return}, @value{GDBN} discards the selected stack frame
9268 (and all frames within it). You can think of this as making the
9269 discarded frame return prematurely. If you wish to specify a value to
9270 be returned, give that value as the argument to @code{return}.
9272 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9273 frame}), and any other frames inside of it, leaving its caller as the
9274 innermost remaining frame. That frame becomes selected. The
9275 specified value is stored in the registers used for returning values
9278 The @code{return} command does not resume execution; it leaves the
9279 program stopped in the state that would exist if the function had just
9280 returned. In contrast, the @code{finish} command (@pxref{Continuing
9281 and Stepping, ,Continuing and stepping}) resumes execution until the
9282 selected stack frame returns naturally.
9285 @section Calling program functions
9287 @cindex calling functions
9290 @item call @var{expr}
9291 Evaluate the expression @var{expr} without displaying @code{void}
9295 You can use this variant of the @code{print} command if you want to
9296 execute a function from your program, but without cluttering the output
9297 with @code{void} returned values. If the result is not void, it
9298 is printed and saved in the value history.
9301 @section Patching programs
9303 @cindex patching binaries
9304 @cindex writing into executables
9305 @cindex writing into corefiles
9307 By default, @value{GDBN} opens the file containing your program's
9308 executable code (or the corefile) read-only. This prevents accidental
9309 alterations to machine code; but it also prevents you from intentionally
9310 patching your program's binary.
9312 If you'd like to be able to patch the binary, you can specify that
9313 explicitly with the @code{set write} command. For example, you might
9314 want to turn on internal debugging flags, or even to make emergency
9320 @itemx set write off
9321 If you specify @samp{set write on}, @value{GDBN} opens executable and
9322 core files for both reading and writing; if you specify @samp{set write
9323 off} (the default), @value{GDBN} opens them read-only.
9325 If you have already loaded a file, you must load it again (using the
9326 @code{exec-file} or @code{core-file} command) after changing @code{set
9327 write}, for your new setting to take effect.
9331 Display whether executable files and core files are opened for writing
9336 @chapter @value{GDBN} Files
9338 @value{GDBN} needs to know the file name of the program to be debugged,
9339 both in order to read its symbol table and in order to start your
9340 program. To debug a core dump of a previous run, you must also tell
9341 @value{GDBN} the name of the core dump file.
9344 * Files:: Commands to specify files
9345 * Symbol Errors:: Errors reading symbol files
9349 @section Commands to specify files
9351 @cindex symbol table
9352 @cindex core dump file
9354 You may want to specify executable and core dump file names. The usual
9355 way to do this is at start-up time, using the arguments to
9356 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9357 Out of @value{GDBN}}).
9359 Occasionally it is necessary to change to a different file during a
9360 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9361 a file you want to use. In these situations the @value{GDBN} commands
9362 to specify new files are useful.
9365 @cindex executable file
9367 @item file @var{filename}
9368 Use @var{filename} as the program to be debugged. It is read for its
9369 symbols and for the contents of pure memory. It is also the program
9370 executed when you use the @code{run} command. If you do not specify a
9371 directory and the file is not found in the @value{GDBN} working directory,
9372 @value{GDBN} uses the environment variable @code{PATH} as a list of
9373 directories to search, just as the shell does when looking for a program
9374 to run. You can change the value of this variable, for both @value{GDBN}
9375 and your program, using the @code{path} command.
9377 On systems with memory-mapped files, an auxiliary file named
9378 @file{@var{filename}.syms} may hold symbol table information for
9379 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9380 @file{@var{filename}.syms}, starting up more quickly. See the
9381 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9382 (available on the command line, and with the commands @code{file},
9383 @code{symbol-file}, or @code{add-symbol-file}, described below),
9384 for more information.
9387 @code{file} with no argument makes @value{GDBN} discard any information it
9388 has on both executable file and the symbol table.
9391 @item exec-file @r{[} @var{filename} @r{]}
9392 Specify that the program to be run (but not the symbol table) is found
9393 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9394 if necessary to locate your program. Omitting @var{filename} means to
9395 discard information on the executable file.
9398 @item symbol-file @r{[} @var{filename} @r{]}
9399 Read symbol table information from file @var{filename}. @code{PATH} is
9400 searched when necessary. Use the @code{file} command to get both symbol
9401 table and program to run from the same file.
9403 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9404 program's symbol table.
9406 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9407 of its convenience variables, the value history, and all breakpoints and
9408 auto-display expressions. This is because they may contain pointers to
9409 the internal data recording symbols and data types, which are part of
9410 the old symbol table data being discarded inside @value{GDBN}.
9412 @code{symbol-file} does not repeat if you press @key{RET} again after
9415 When @value{GDBN} is configured for a particular environment, it
9416 understands debugging information in whatever format is the standard
9417 generated for that environment; you may use either a @sc{gnu} compiler, or
9418 other compilers that adhere to the local conventions.
9419 Best results are usually obtained from @sc{gnu} compilers; for example,
9420 using @code{@value{GCC}} you can generate debugging information for
9423 For most kinds of object files, with the exception of old SVR3 systems
9424 using COFF, the @code{symbol-file} command does not normally read the
9425 symbol table in full right away. Instead, it scans the symbol table
9426 quickly to find which source files and which symbols are present. The
9427 details are read later, one source file at a time, as they are needed.
9429 The purpose of this two-stage reading strategy is to make @value{GDBN}
9430 start up faster. For the most part, it is invisible except for
9431 occasional pauses while the symbol table details for a particular source
9432 file are being read. (The @code{set verbose} command can turn these
9433 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9434 warnings and messages}.)
9436 We have not implemented the two-stage strategy for COFF yet. When the
9437 symbol table is stored in COFF format, @code{symbol-file} reads the
9438 symbol table data in full right away. Note that ``stabs-in-COFF''
9439 still does the two-stage strategy, since the debug info is actually
9443 @cindex reading symbols immediately
9444 @cindex symbols, reading immediately
9446 @cindex memory-mapped symbol file
9447 @cindex saving symbol table
9448 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9449 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9450 You can override the @value{GDBN} two-stage strategy for reading symbol
9451 tables by using the @samp{-readnow} option with any of the commands that
9452 load symbol table information, if you want to be sure @value{GDBN} has the
9453 entire symbol table available.
9455 If memory-mapped files are available on your system through the
9456 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9457 cause @value{GDBN} to write the symbols for your program into a reusable
9458 file. Future @value{GDBN} debugging sessions map in symbol information
9459 from this auxiliary symbol file (if the program has not changed), rather
9460 than spending time reading the symbol table from the executable
9461 program. Using the @samp{-mapped} option has the same effect as
9462 starting @value{GDBN} with the @samp{-mapped} command-line option.
9464 You can use both options together, to make sure the auxiliary symbol
9465 file has all the symbol information for your program.
9467 The auxiliary symbol file for a program called @var{myprog} is called
9468 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9469 than the corresponding executable), @value{GDBN} always attempts to use
9470 it when you debug @var{myprog}; no special options or commands are
9473 The @file{.syms} file is specific to the host machine where you run
9474 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9475 symbol table. It cannot be shared across multiple host platforms.
9477 @c FIXME: for now no mention of directories, since this seems to be in
9478 @c flux. 13mar1992 status is that in theory GDB would look either in
9479 @c current dir or in same dir as myprog; but issues like competing
9480 @c GDB's, or clutter in system dirs, mean that in practice right now
9481 @c only current dir is used. FFish says maybe a special GDB hierarchy
9482 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9487 @item core-file @r{[} @var{filename} @r{]}
9488 Specify the whereabouts of a core dump file to be used as the ``contents
9489 of memory''. Traditionally, core files contain only some parts of the
9490 address space of the process that generated them; @value{GDBN} can access the
9491 executable file itself for other parts.
9493 @code{core-file} with no argument specifies that no core file is
9496 Note that the core file is ignored when your program is actually running
9497 under @value{GDBN}. So, if you have been running your program and you
9498 wish to debug a core file instead, you must kill the subprocess in which
9499 the program is running. To do this, use the @code{kill} command
9500 (@pxref{Kill Process, ,Killing the child process}).
9502 @kindex add-symbol-file
9503 @cindex dynamic linking
9504 @item add-symbol-file @var{filename} @var{address}
9505 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9506 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9507 The @code{add-symbol-file} command reads additional symbol table
9508 information from the file @var{filename}. You would use this command
9509 when @var{filename} has been dynamically loaded (by some other means)
9510 into the program that is running. @var{address} should be the memory
9511 address at which the file has been loaded; @value{GDBN} cannot figure
9512 this out for itself. You can additionally specify an arbitrary number
9513 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9514 section name and base address for that section. You can specify any
9515 @var{address} as an expression.
9517 The symbol table of the file @var{filename} is added to the symbol table
9518 originally read with the @code{symbol-file} command. You can use the
9519 @code{add-symbol-file} command any number of times; the new symbol data
9520 thus read keeps adding to the old. To discard all old symbol data
9521 instead, use the @code{symbol-file} command without any arguments.
9523 @cindex relocatable object files, reading symbols from
9524 @cindex object files, relocatable, reading symbols from
9525 @cindex reading symbols from relocatable object files
9526 @cindex symbols, reading from relocatable object files
9527 @cindex @file{.o} files, reading symbols from
9528 Although @var{filename} is typically a shared library file, an
9529 executable file, or some other object file which has been fully
9530 relocated for loading into a process, you can also load symbolic
9531 information from relocatable @file{.o} files, as long as:
9535 the file's symbolic information refers only to linker symbols defined in
9536 that file, not to symbols defined by other object files,
9538 every section the file's symbolic information refers to has actually
9539 been loaded into the inferior, as it appears in the file, and
9541 you can determine the address at which every section was loaded, and
9542 provide these to the @code{add-symbol-file} command.
9546 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9547 relocatable files into an already running program; such systems
9548 typically make the requirements above easy to meet. However, it's
9549 important to recognize that many native systems use complex link
9550 procedures (@code{.linkonce} section factoring and C++ constructor table
9551 assembly, for example) that make the requirements difficult to meet. In
9552 general, one cannot assume that using @code{add-symbol-file} to read a
9553 relocatable object file's symbolic information will have the same effect
9554 as linking the relocatable object file into the program in the normal
9557 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9559 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9560 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9561 table information for @var{filename}.
9563 @kindex add-shared-symbol-file
9564 @item add-shared-symbol-file
9565 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9566 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9567 shared libraries, however if @value{GDBN} does not find yours, you can run
9568 @code{add-shared-symbol-file}. It takes no arguments.
9572 The @code{section} command changes the base address of section SECTION of
9573 the exec file to ADDR. This can be used if the exec file does not contain
9574 section addresses, (such as in the a.out format), or when the addresses
9575 specified in the file itself are wrong. Each section must be changed
9576 separately. The @code{info files} command, described below, lists all
9577 the sections and their addresses.
9583 @code{info files} and @code{info target} are synonymous; both print the
9584 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9585 including the names of the executable and core dump files currently in
9586 use by @value{GDBN}, and the files from which symbols were loaded. The
9587 command @code{help target} lists all possible targets rather than
9590 @kindex maint info sections
9591 @item maint info sections
9592 Another command that can give you extra information about program sections
9593 is @code{maint info sections}. In addition to the section information
9594 displayed by @code{info files}, this command displays the flags and file
9595 offset of each section in the executable and core dump files. In addition,
9596 @code{maint info sections} provides the following command options (which
9597 may be arbitrarily combined):
9601 Display sections for all loaded object files, including shared libraries.
9602 @item @var{sections}
9603 Display info only for named @var{sections}.
9604 @item @var{section-flags}
9605 Display info only for sections for which @var{section-flags} are true.
9606 The section flags that @value{GDBN} currently knows about are:
9609 Section will have space allocated in the process when loaded.
9610 Set for all sections except those containing debug information.
9612 Section will be loaded from the file into the child process memory.
9613 Set for pre-initialized code and data, clear for @code{.bss} sections.
9615 Section needs to be relocated before loading.
9617 Section cannot be modified by the child process.
9619 Section contains executable code only.
9621 Section contains data only (no executable code).
9623 Section will reside in ROM.
9625 Section contains data for constructor/destructor lists.
9627 Section is not empty.
9629 An instruction to the linker to not output the section.
9630 @item COFF_SHARED_LIBRARY
9631 A notification to the linker that the section contains
9632 COFF shared library information.
9634 Section contains common symbols.
9637 @kindex set trust-readonly-sections
9638 @item set trust-readonly-sections on
9639 Tell @value{GDBN} that readonly sections in your object file
9640 really are read-only (i.e.@: that their contents will not change).
9641 In that case, @value{GDBN} can fetch values from these sections
9642 out of the object file, rather than from the target program.
9643 For some targets (notably embedded ones), this can be a significant
9644 enhancement to debugging performance.
9648 @item set trust-readonly-sections off
9649 Tell @value{GDBN} not to trust readonly sections. This means that
9650 the contents of the section might change while the program is running,
9651 and must therefore be fetched from the target when needed.
9654 All file-specifying commands allow both absolute and relative file names
9655 as arguments. @value{GDBN} always converts the file name to an absolute file
9656 name and remembers it that way.
9658 @cindex shared libraries
9659 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9662 @value{GDBN} automatically loads symbol definitions from shared libraries
9663 when you use the @code{run} command, or when you examine a core file.
9664 (Before you issue the @code{run} command, @value{GDBN} does not understand
9665 references to a function in a shared library, however---unless you are
9666 debugging a core file).
9668 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9669 automatically loads the symbols at the time of the @code{shl_load} call.
9671 @c FIXME: some @value{GDBN} release may permit some refs to undef
9672 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9673 @c FIXME...lib; check this from time to time when updating manual
9675 There are times, however, when you may wish to not automatically load
9676 symbol definitions from shared libraries, such as when they are
9677 particularly large or there are many of them.
9679 To control the automatic loading of shared library symbols, use the
9683 @kindex set auto-solib-add
9684 @item set auto-solib-add @var{mode}
9685 If @var{mode} is @code{on}, symbols from all shared object libraries
9686 will be loaded automatically when the inferior begins execution, you
9687 attach to an independently started inferior, or when the dynamic linker
9688 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9689 is @code{off}, symbols must be loaded manually, using the
9690 @code{sharedlibrary} command. The default value is @code{on}.
9692 @kindex show auto-solib-add
9693 @item show auto-solib-add
9694 Display the current autoloading mode.
9697 To explicitly load shared library symbols, use the @code{sharedlibrary}
9701 @kindex info sharedlibrary
9704 @itemx info sharedlibrary
9705 Print the names of the shared libraries which are currently loaded.
9707 @kindex sharedlibrary
9709 @item sharedlibrary @var{regex}
9710 @itemx share @var{regex}
9711 Load shared object library symbols for files matching a
9712 Unix regular expression.
9713 As with files loaded automatically, it only loads shared libraries
9714 required by your program for a core file or after typing @code{run}. If
9715 @var{regex} is omitted all shared libraries required by your program are
9719 On some systems, such as HP-UX systems, @value{GDBN} supports
9720 autoloading shared library symbols until a limiting threshold size is
9721 reached. This provides the benefit of allowing autoloading to remain on
9722 by default, but avoids autoloading excessively large shared libraries,
9723 up to a threshold that is initially set, but which you can modify if you
9726 Beyond that threshold, symbols from shared libraries must be explicitly
9727 loaded. To load these symbols, use the command @code{sharedlibrary
9728 @var{filename}}. The base address of the shared library is determined
9729 automatically by @value{GDBN} and need not be specified.
9731 To display or set the threshold, use the commands:
9734 @kindex set auto-solib-limit
9735 @item set auto-solib-limit @var{threshold}
9736 Set the autoloading size threshold, in an integral number of megabytes.
9737 If @var{threshold} is nonzero and shared library autoloading is enabled,
9738 symbols from all shared object libraries will be loaded until the total
9739 size of the loaded shared library symbols exceeds this threshold.
9740 Otherwise, symbols must be loaded manually, using the
9741 @code{sharedlibrary} command. The default threshold is 100 (i.e.@: 100
9744 @kindex show auto-solib-limit
9745 @item show auto-solib-limit
9746 Display the current autoloading size threshold, in megabytes.
9749 Shared libraries are also supported in many cross or remote debugging
9750 configurations. A copy of the target's libraries need to be present on the
9751 host system; they need to be the same as the target libraries, although the
9752 copies on the target can be stripped as long as the copies on the host are
9755 You need to tell @value{GDBN} where the target libraries are, so that it can
9756 load the correct copies---otherwise, it may try to load the host's libraries.
9757 @value{GDBN} has two variables to specify the search directories for target
9761 @kindex set solib-absolute-prefix
9762 @item set solib-absolute-prefix @var{path}
9763 If this variable is set, @var{path} will be used as a prefix for any
9764 absolute shared library paths; many runtime loaders store the absolute
9765 paths to the shared library in the target program's memory. If you use
9766 @samp{solib-absolute-prefix} to find shared libraries, they need to be laid
9767 out in the same way that they are on the target, with e.g.@: a
9768 @file{/usr/lib} hierarchy under @var{path}.
9770 You can set the default value of @samp{solib-absolute-prefix} by using the
9771 configure-time @samp{--with-sysroot} option.
9773 @kindex show solib-absolute-prefix
9774 @item show solib-absolute-prefix
9775 Display the current shared library prefix.
9777 @kindex set solib-search-path
9778 @item set solib-search-path @var{path}
9779 If this variable is set, @var{path} is a colon-separated list of directories
9780 to search for shared libraries. @samp{solib-search-path} is used after
9781 @samp{solib-absolute-prefix} fails to locate the library, or if the path to
9782 the library is relative instead of absolute. If you want to use
9783 @samp{solib-search-path} instead of @samp{solib-absolute-prefix}, be sure to
9784 set @samp{solib-absolute-prefix} to a nonexistant directory to prevent
9785 @value{GDBN} from finding your host's libraries.
9787 @kindex show solib-search-path
9788 @item show solib-search-path
9789 Display the current shared library search path.
9793 @section Errors reading symbol files
9795 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9796 such as symbol types it does not recognize, or known bugs in compiler
9797 output. By default, @value{GDBN} does not notify you of such problems, since
9798 they are relatively common and primarily of interest to people
9799 debugging compilers. If you are interested in seeing information
9800 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9801 only one message about each such type of problem, no matter how many
9802 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9803 to see how many times the problems occur, with the @code{set
9804 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9807 The messages currently printed, and their meanings, include:
9810 @item inner block not inside outer block in @var{symbol}
9812 The symbol information shows where symbol scopes begin and end
9813 (such as at the start of a function or a block of statements). This
9814 error indicates that an inner scope block is not fully contained
9815 in its outer scope blocks.
9817 @value{GDBN} circumvents the problem by treating the inner block as if it had
9818 the same scope as the outer block. In the error message, @var{symbol}
9819 may be shown as ``@code{(don't know)}'' if the outer block is not a
9822 @item block at @var{address} out of order
9824 The symbol information for symbol scope blocks should occur in
9825 order of increasing addresses. This error indicates that it does not
9828 @value{GDBN} does not circumvent this problem, and has trouble
9829 locating symbols in the source file whose symbols it is reading. (You
9830 can often determine what source file is affected by specifying
9831 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9834 @item bad block start address patched
9836 The symbol information for a symbol scope block has a start address
9837 smaller than the address of the preceding source line. This is known
9838 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9840 @value{GDBN} circumvents the problem by treating the symbol scope block as
9841 starting on the previous source line.
9843 @item bad string table offset in symbol @var{n}
9846 Symbol number @var{n} contains a pointer into the string table which is
9847 larger than the size of the string table.
9849 @value{GDBN} circumvents the problem by considering the symbol to have the
9850 name @code{foo}, which may cause other problems if many symbols end up
9853 @item unknown symbol type @code{0x@var{nn}}
9855 The symbol information contains new data types that @value{GDBN} does
9856 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9857 uncomprehended information, in hexadecimal.
9859 @value{GDBN} circumvents the error by ignoring this symbol information.
9860 This usually allows you to debug your program, though certain symbols
9861 are not accessible. If you encounter such a problem and feel like
9862 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9863 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9864 and examine @code{*bufp} to see the symbol.
9866 @item stub type has NULL name
9868 @value{GDBN} could not find the full definition for a struct or class.
9870 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9871 The symbol information for a C@t{++} member function is missing some
9872 information that recent versions of the compiler should have output for
9875 @item info mismatch between compiler and debugger
9877 @value{GDBN} could not parse a type specification output by the compiler.
9882 @chapter Specifying a Debugging Target
9884 @cindex debugging target
9887 A @dfn{target} is the execution environment occupied by your program.
9889 Often, @value{GDBN} runs in the same host environment as your program;
9890 in that case, the debugging target is specified as a side effect when
9891 you use the @code{file} or @code{core} commands. When you need more
9892 flexibility---for example, running @value{GDBN} on a physically separate
9893 host, or controlling a standalone system over a serial port or a
9894 realtime system over a TCP/IP connection---you can use the @code{target}
9895 command to specify one of the target types configured for @value{GDBN}
9896 (@pxref{Target Commands, ,Commands for managing targets}).
9899 * Active Targets:: Active targets
9900 * Target Commands:: Commands for managing targets
9901 * Byte Order:: Choosing target byte order
9902 * Remote:: Remote debugging
9903 * KOD:: Kernel Object Display
9907 @node Active Targets
9908 @section Active targets
9910 @cindex stacking targets
9911 @cindex active targets
9912 @cindex multiple targets
9914 There are three classes of targets: processes, core files, and
9915 executable files. @value{GDBN} can work concurrently on up to three
9916 active targets, one in each class. This allows you to (for example)
9917 start a process and inspect its activity without abandoning your work on
9920 For example, if you execute @samp{gdb a.out}, then the executable file
9921 @code{a.out} is the only active target. If you designate a core file as
9922 well---presumably from a prior run that crashed and coredumped---then
9923 @value{GDBN} has two active targets and uses them in tandem, looking
9924 first in the corefile target, then in the executable file, to satisfy
9925 requests for memory addresses. (Typically, these two classes of target
9926 are complementary, since core files contain only a program's
9927 read-write memory---variables and so on---plus machine status, while
9928 executable files contain only the program text and initialized data.)
9930 When you type @code{run}, your executable file becomes an active process
9931 target as well. When a process target is active, all @value{GDBN}
9932 commands requesting memory addresses refer to that target; addresses in
9933 an active core file or executable file target are obscured while the
9934 process target is active.
9936 Use the @code{core-file} and @code{exec-file} commands to select a new
9937 core file or executable target (@pxref{Files, ,Commands to specify
9938 files}). To specify as a target a process that is already running, use
9939 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9942 @node Target Commands
9943 @section Commands for managing targets
9946 @item target @var{type} @var{parameters}
9947 Connects the @value{GDBN} host environment to a target machine or
9948 process. A target is typically a protocol for talking to debugging
9949 facilities. You use the argument @var{type} to specify the type or
9950 protocol of the target machine.
9952 Further @var{parameters} are interpreted by the target protocol, but
9953 typically include things like device names or host names to connect
9954 with, process numbers, and baud rates.
9956 The @code{target} command does not repeat if you press @key{RET} again
9957 after executing the command.
9961 Displays the names of all targets available. To display targets
9962 currently selected, use either @code{info target} or @code{info files}
9963 (@pxref{Files, ,Commands to specify files}).
9965 @item help target @var{name}
9966 Describe a particular target, including any parameters necessary to
9969 @kindex set gnutarget
9970 @item set gnutarget @var{args}
9971 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9972 knows whether it is reading an @dfn{executable},
9973 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9974 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9975 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9978 @emph{Warning:} To specify a file format with @code{set gnutarget},
9979 you must know the actual BFD name.
9983 @xref{Files, , Commands to specify files}.
9985 @kindex show gnutarget
9986 @item show gnutarget
9987 Use the @code{show gnutarget} command to display what file format
9988 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9989 @value{GDBN} will determine the file format for each file automatically,
9990 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9993 Here are some common targets (available, or not, depending on the GDB
9998 @item target exec @var{program}
9999 An executable file. @samp{target exec @var{program}} is the same as
10000 @samp{exec-file @var{program}}.
10002 @kindex target core
10003 @item target core @var{filename}
10004 A core dump file. @samp{target core @var{filename}} is the same as
10005 @samp{core-file @var{filename}}.
10007 @kindex target remote
10008 @item target remote @var{dev}
10009 Remote serial target in GDB-specific protocol. The argument @var{dev}
10010 specifies what serial device to use for the connection (e.g.
10011 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
10012 supports the @code{load} command. This is only useful if you have
10013 some other way of getting the stub to the target system, and you can put
10014 it somewhere in memory where it won't get clobbered by the download.
10018 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
10026 works; however, you cannot assume that a specific memory map, device
10027 drivers, or even basic I/O is available, although some simulators do
10028 provide these. For info about any processor-specific simulator details,
10029 see the appropriate section in @ref{Embedded Processors, ,Embedded
10034 Some configurations may include these targets as well:
10038 @kindex target nrom
10039 @item target nrom @var{dev}
10040 NetROM ROM emulator. This target only supports downloading.
10044 Different targets are available on different configurations of @value{GDBN};
10045 your configuration may have more or fewer targets.
10047 Many remote targets require you to download the executable's code
10048 once you've successfully established a connection.
10052 @kindex load @var{filename}
10053 @item load @var{filename}
10054 Depending on what remote debugging facilities are configured into
10055 @value{GDBN}, the @code{load} command may be available. Where it exists, it
10056 is meant to make @var{filename} (an executable) available for debugging
10057 on the remote system---by downloading, or dynamic linking, for example.
10058 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
10059 the @code{add-symbol-file} command.
10061 If your @value{GDBN} does not have a @code{load} command, attempting to
10062 execute it gets the error message ``@code{You can't do that when your
10063 target is @dots{}}''
10065 The file is loaded at whatever address is specified in the executable.
10066 For some object file formats, you can specify the load address when you
10067 link the program; for other formats, like a.out, the object file format
10068 specifies a fixed address.
10069 @c FIXME! This would be a good place for an xref to the GNU linker doc.
10071 @code{load} does not repeat if you press @key{RET} again after using it.
10075 @section Choosing target byte order
10077 @cindex choosing target byte order
10078 @cindex target byte order
10080 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
10081 offer the ability to run either big-endian or little-endian byte
10082 orders. Usually the executable or symbol will include a bit to
10083 designate the endian-ness, and you will not need to worry about
10084 which to use. However, you may still find it useful to adjust
10085 @value{GDBN}'s idea of processor endian-ness manually.
10088 @kindex set endian big
10089 @item set endian big
10090 Instruct @value{GDBN} to assume the target is big-endian.
10092 @kindex set endian little
10093 @item set endian little
10094 Instruct @value{GDBN} to assume the target is little-endian.
10096 @kindex set endian auto
10097 @item set endian auto
10098 Instruct @value{GDBN} to use the byte order associated with the
10102 Display @value{GDBN}'s current idea of the target byte order.
10106 Note that these commands merely adjust interpretation of symbolic
10107 data on the host, and that they have absolutely no effect on the
10111 @section Remote debugging
10112 @cindex remote debugging
10114 If you are trying to debug a program running on a machine that cannot run
10115 @value{GDBN} in the usual way, it is often useful to use remote debugging.
10116 For example, you might use remote debugging on an operating system kernel,
10117 or on a small system which does not have a general purpose operating system
10118 powerful enough to run a full-featured debugger.
10120 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
10121 to make this work with particular debugging targets. In addition,
10122 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
10123 but not specific to any particular target system) which you can use if you
10124 write the remote stubs---the code that runs on the remote system to
10125 communicate with @value{GDBN}.
10127 Other remote targets may be available in your
10128 configuration of @value{GDBN}; use @code{help target} to list them.
10131 @section Kernel Object Display
10133 @cindex kernel object display
10134 @cindex kernel object
10137 Some targets support kernel object display. Using this facility,
10138 @value{GDBN} communicates specially with the underlying operating system
10139 and can display information about operating system-level objects such as
10140 mutexes and other synchronization objects. Exactly which objects can be
10141 displayed is determined on a per-OS basis.
10143 Use the @code{set os} command to set the operating system. This tells
10144 @value{GDBN} which kernel object display module to initialize:
10147 (@value{GDBP}) set os cisco
10150 If @code{set os} succeeds, @value{GDBN} will display some information
10151 about the operating system, and will create a new @code{info} command
10152 which can be used to query the target. The @code{info} command is named
10153 after the operating system:
10156 (@value{GDBP}) info cisco
10157 List of Cisco Kernel Objects
10159 any Any and all objects
10162 Further subcommands can be used to query about particular objects known
10165 There is currently no way to determine whether a given operating system
10166 is supported other than to try it.
10169 @node Remote Debugging
10170 @chapter Debugging remote programs
10173 * Server:: Using the gdbserver program
10174 * NetWare:: Using the gdbserve.nlm program
10175 * remote stub:: Implementing a remote stub
10179 @section Using the @code{gdbserver} program
10182 @cindex remote connection without stubs
10183 @code{gdbserver} is a control program for Unix-like systems, which
10184 allows you to connect your program with a remote @value{GDBN} via
10185 @code{target remote}---but without linking in the usual debugging stub.
10187 @code{gdbserver} is not a complete replacement for the debugging stubs,
10188 because it requires essentially the same operating-system facilities
10189 that @value{GDBN} itself does. In fact, a system that can run
10190 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10191 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10192 because it is a much smaller program than @value{GDBN} itself. It is
10193 also easier to port than all of @value{GDBN}, so you may be able to get
10194 started more quickly on a new system by using @code{gdbserver}.
10195 Finally, if you develop code for real-time systems, you may find that
10196 the tradeoffs involved in real-time operation make it more convenient to
10197 do as much development work as possible on another system, for example
10198 by cross-compiling. You can use @code{gdbserver} to make a similar
10199 choice for debugging.
10201 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10202 or a TCP connection, using the standard @value{GDBN} remote serial
10206 @item On the target machine,
10207 you need to have a copy of the program you want to debug.
10208 @code{gdbserver} does not need your program's symbol table, so you can
10209 strip the program if necessary to save space. @value{GDBN} on the host
10210 system does all the symbol handling.
10212 To use the server, you must tell it how to communicate with @value{GDBN};
10213 the name of your program; and the arguments for your program. The usual
10217 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10220 @var{comm} is either a device name (to use a serial line) or a TCP
10221 hostname and portnumber. For example, to debug Emacs with the argument
10222 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10226 target> gdbserver /dev/com1 emacs foo.txt
10229 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10232 To use a TCP connection instead of a serial line:
10235 target> gdbserver host:2345 emacs foo.txt
10238 The only difference from the previous example is the first argument,
10239 specifying that you are communicating with the host @value{GDBN} via
10240 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10241 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10242 (Currently, the @samp{host} part is ignored.) You can choose any number
10243 you want for the port number as long as it does not conflict with any
10244 TCP ports already in use on the target system (for example, @code{23} is
10245 reserved for @code{telnet}).@footnote{If you choose a port number that
10246 conflicts with another service, @code{gdbserver} prints an error message
10247 and exits.} You must use the same port number with the host @value{GDBN}
10248 @code{target remote} command.
10250 On some targets, @code{gdbserver} can also attach to running programs.
10251 This is accomplished via the @code{--attach} argument. The syntax is:
10254 target> gdbserver @var{comm} --attach @var{pid}
10257 @var{pid} is the process ID of a currently running process. It isn't necessary
10258 to point @code{gdbserver} at a binary for the running process.
10260 @item On the @value{GDBN} host machine,
10261 you need an unstripped copy of your program, since @value{GDBN} needs
10262 symbols and debugging information. Start up @value{GDBN} as usual,
10263 using the name of the local copy of your program as the first argument.
10264 (You may also need the @w{@samp{--baud}} option if the serial line is
10265 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10266 remote} to establish communications with @code{gdbserver}. Its argument
10267 is either a device name (usually a serial device, like
10268 @file{/dev/ttyb}), or a TCP port descriptor in the form
10269 @code{@var{host}:@var{PORT}}. For example:
10272 (@value{GDBP}) target remote /dev/ttyb
10276 communicates with the server via serial line @file{/dev/ttyb}, and
10279 (@value{GDBP}) target remote the-target:2345
10283 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10284 For TCP connections, you must start up @code{gdbserver} prior to using
10285 the @code{target remote} command. Otherwise you may get an error whose
10286 text depends on the host system, but which usually looks something like
10287 @samp{Connection refused}.
10291 @section Using the @code{gdbserve.nlm} program
10293 @kindex gdbserve.nlm
10294 @code{gdbserve.nlm} is a control program for NetWare systems, which
10295 allows you to connect your program with a remote @value{GDBN} via
10296 @code{target remote}.
10298 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10299 using the standard @value{GDBN} remote serial protocol.
10302 @item On the target machine,
10303 you need to have a copy of the program you want to debug.
10304 @code{gdbserve.nlm} does not need your program's symbol table, so you
10305 can strip the program if necessary to save space. @value{GDBN} on the
10306 host system does all the symbol handling.
10308 To use the server, you must tell it how to communicate with
10309 @value{GDBN}; the name of your program; and the arguments for your
10310 program. The syntax is:
10313 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10314 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10317 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10318 the baud rate used by the connection. @var{port} and @var{node} default
10319 to 0, @var{baud} defaults to 9600@dmn{bps}.
10321 For example, to debug Emacs with the argument @samp{foo.txt}and
10322 communicate with @value{GDBN} over serial port number 2 or board 1
10323 using a 19200@dmn{bps} connection:
10326 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10329 @item On the @value{GDBN} host machine,
10330 you need an unstripped copy of your program, since @value{GDBN} needs
10331 symbols and debugging information. Start up @value{GDBN} as usual,
10332 using the name of the local copy of your program as the first argument.
10333 (You may also need the @w{@samp{--baud}} option if the serial line is
10334 running at anything other than 9600@dmn{bps}. After that, use @code{target
10335 remote} to establish communications with @code{gdbserve.nlm}. Its
10336 argument is a device name (usually a serial device, like
10337 @file{/dev/ttyb}). For example:
10340 (@value{GDBP}) target remote /dev/ttyb
10344 communications with the server via serial line @file{/dev/ttyb}.
10348 @section Implementing a remote stub
10350 @cindex debugging stub, example
10351 @cindex remote stub, example
10352 @cindex stub example, remote debugging
10353 The stub files provided with @value{GDBN} implement the target side of the
10354 communication protocol, and the @value{GDBN} side is implemented in the
10355 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10356 these subroutines to communicate, and ignore the details. (If you're
10357 implementing your own stub file, you can still ignore the details: start
10358 with one of the existing stub files. @file{sparc-stub.c} is the best
10359 organized, and therefore the easiest to read.)
10361 @cindex remote serial debugging, overview
10362 To debug a program running on another machine (the debugging
10363 @dfn{target} machine), you must first arrange for all the usual
10364 prerequisites for the program to run by itself. For example, for a C
10369 A startup routine to set up the C runtime environment; these usually
10370 have a name like @file{crt0}. The startup routine may be supplied by
10371 your hardware supplier, or you may have to write your own.
10374 A C subroutine library to support your program's
10375 subroutine calls, notably managing input and output.
10378 A way of getting your program to the other machine---for example, a
10379 download program. These are often supplied by the hardware
10380 manufacturer, but you may have to write your own from hardware
10384 The next step is to arrange for your program to use a serial port to
10385 communicate with the machine where @value{GDBN} is running (the @dfn{host}
10386 machine). In general terms, the scheme looks like this:
10390 @value{GDBN} already understands how to use this protocol; when everything
10391 else is set up, you can simply use the @samp{target remote} command
10392 (@pxref{Targets,,Specifying a Debugging Target}).
10394 @item On the target,
10395 you must link with your program a few special-purpose subroutines that
10396 implement the @value{GDBN} remote serial protocol. The file containing these
10397 subroutines is called a @dfn{debugging stub}.
10399 On certain remote targets, you can use an auxiliary program
10400 @code{gdbserver} instead of linking a stub into your program.
10401 @xref{Server,,Using the @code{gdbserver} program}, for details.
10404 The debugging stub is specific to the architecture of the remote
10405 machine; for example, use @file{sparc-stub.c} to debug programs on
10408 @cindex remote serial stub list
10409 These working remote stubs are distributed with @value{GDBN}:
10414 @cindex @file{i386-stub.c}
10417 For Intel 386 and compatible architectures.
10420 @cindex @file{m68k-stub.c}
10421 @cindex Motorola 680x0
10423 For Motorola 680x0 architectures.
10426 @cindex @file{sh-stub.c}
10429 For Hitachi SH architectures.
10432 @cindex @file{sparc-stub.c}
10434 For @sc{sparc} architectures.
10436 @item sparcl-stub.c
10437 @cindex @file{sparcl-stub.c}
10440 For Fujitsu @sc{sparclite} architectures.
10444 The @file{README} file in the @value{GDBN} distribution may list other
10445 recently added stubs.
10448 * Stub Contents:: What the stub can do for you
10449 * Bootstrapping:: What you must do for the stub
10450 * Debug Session:: Putting it all together
10453 @node Stub Contents
10454 @subsection What the stub can do for you
10456 @cindex remote serial stub
10457 The debugging stub for your architecture supplies these three
10461 @item set_debug_traps
10462 @kindex set_debug_traps
10463 @cindex remote serial stub, initialization
10464 This routine arranges for @code{handle_exception} to run when your
10465 program stops. You must call this subroutine explicitly near the
10466 beginning of your program.
10468 @item handle_exception
10469 @kindex handle_exception
10470 @cindex remote serial stub, main routine
10471 This is the central workhorse, but your program never calls it
10472 explicitly---the setup code arranges for @code{handle_exception} to
10473 run when a trap is triggered.
10475 @code{handle_exception} takes control when your program stops during
10476 execution (for example, on a breakpoint), and mediates communications
10477 with @value{GDBN} on the host machine. This is where the communications
10478 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10479 representative on the target machine. It begins by sending summary
10480 information on the state of your program, then continues to execute,
10481 retrieving and transmitting any information @value{GDBN} needs, until you
10482 execute a @value{GDBN} command that makes your program resume; at that point,
10483 @code{handle_exception} returns control to your own code on the target
10487 @cindex @code{breakpoint} subroutine, remote
10488 Use this auxiliary subroutine to make your program contain a
10489 breakpoint. Depending on the particular situation, this may be the only
10490 way for @value{GDBN} to get control. For instance, if your target
10491 machine has some sort of interrupt button, you won't need to call this;
10492 pressing the interrupt button transfers control to
10493 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10494 simply receiving characters on the serial port may also trigger a trap;
10495 again, in that situation, you don't need to call @code{breakpoint} from
10496 your own program---simply running @samp{target remote} from the host
10497 @value{GDBN} session gets control.
10499 Call @code{breakpoint} if none of these is true, or if you simply want
10500 to make certain your program stops at a predetermined point for the
10501 start of your debugging session.
10504 @node Bootstrapping
10505 @subsection What you must do for the stub
10507 @cindex remote stub, support routines
10508 The debugging stubs that come with @value{GDBN} are set up for a particular
10509 chip architecture, but they have no information about the rest of your
10510 debugging target machine.
10512 First of all you need to tell the stub how to communicate with the
10516 @item int getDebugChar()
10517 @kindex getDebugChar
10518 Write this subroutine to read a single character from the serial port.
10519 It may be identical to @code{getchar} for your target system; a
10520 different name is used to allow you to distinguish the two if you wish.
10522 @item void putDebugChar(int)
10523 @kindex putDebugChar
10524 Write this subroutine to write a single character to the serial port.
10525 It may be identical to @code{putchar} for your target system; a
10526 different name is used to allow you to distinguish the two if you wish.
10529 @cindex control C, and remote debugging
10530 @cindex interrupting remote targets
10531 If you want @value{GDBN} to be able to stop your program while it is
10532 running, you need to use an interrupt-driven serial driver, and arrange
10533 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10534 character). That is the character which @value{GDBN} uses to tell the
10535 remote system to stop.
10537 Getting the debugging target to return the proper status to @value{GDBN}
10538 probably requires changes to the standard stub; one quick and dirty way
10539 is to just execute a breakpoint instruction (the ``dirty'' part is that
10540 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10542 Other routines you need to supply are:
10545 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10546 @kindex exceptionHandler
10547 Write this function to install @var{exception_address} in the exception
10548 handling tables. You need to do this because the stub does not have any
10549 way of knowing what the exception handling tables on your target system
10550 are like (for example, the processor's table might be in @sc{rom},
10551 containing entries which point to a table in @sc{ram}).
10552 @var{exception_number} is the exception number which should be changed;
10553 its meaning is architecture-dependent (for example, different numbers
10554 might represent divide by zero, misaligned access, etc). When this
10555 exception occurs, control should be transferred directly to
10556 @var{exception_address}, and the processor state (stack, registers,
10557 and so on) should be just as it is when a processor exception occurs. So if
10558 you want to use a jump instruction to reach @var{exception_address}, it
10559 should be a simple jump, not a jump to subroutine.
10561 For the 386, @var{exception_address} should be installed as an interrupt
10562 gate so that interrupts are masked while the handler runs. The gate
10563 should be at privilege level 0 (the most privileged level). The
10564 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10565 help from @code{exceptionHandler}.
10567 @item void flush_i_cache()
10568 @kindex flush_i_cache
10569 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10570 instruction cache, if any, on your target machine. If there is no
10571 instruction cache, this subroutine may be a no-op.
10573 On target machines that have instruction caches, @value{GDBN} requires this
10574 function to make certain that the state of your program is stable.
10578 You must also make sure this library routine is available:
10581 @item void *memset(void *, int, int)
10583 This is the standard library function @code{memset} that sets an area of
10584 memory to a known value. If you have one of the free versions of
10585 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10586 either obtain it from your hardware manufacturer, or write your own.
10589 If you do not use the GNU C compiler, you may need other standard
10590 library subroutines as well; this varies from one stub to another,
10591 but in general the stubs are likely to use any of the common library
10592 subroutines which @code{@value{GCC}} generates as inline code.
10595 @node Debug Session
10596 @subsection Putting it all together
10598 @cindex remote serial debugging summary
10599 In summary, when your program is ready to debug, you must follow these
10604 Make sure you have defined the supporting low-level routines
10605 (@pxref{Bootstrapping,,What you must do for the stub}):
10607 @code{getDebugChar}, @code{putDebugChar},
10608 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10612 Insert these lines near the top of your program:
10620 For the 680x0 stub only, you need to provide a variable called
10621 @code{exceptionHook}. Normally you just use:
10624 void (*exceptionHook)() = 0;
10628 but if before calling @code{set_debug_traps}, you set it to point to a
10629 function in your program, that function is called when
10630 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10631 error). The function indicated by @code{exceptionHook} is called with
10632 one parameter: an @code{int} which is the exception number.
10635 Compile and link together: your program, the @value{GDBN} debugging stub for
10636 your target architecture, and the supporting subroutines.
10639 Make sure you have a serial connection between your target machine and
10640 the @value{GDBN} host, and identify the serial port on the host.
10643 @c The "remote" target now provides a `load' command, so we should
10644 @c document that. FIXME.
10645 Download your program to your target machine (or get it there by
10646 whatever means the manufacturer provides), and start it.
10649 To start remote debugging, run @value{GDBN} on the host machine, and specify
10650 as an executable file the program that is running in the remote machine.
10651 This tells @value{GDBN} how to find your program's symbols and the contents
10655 @cindex serial line, @code{target remote}
10656 Establish communication using the @code{target remote} command.
10657 Its argument specifies how to communicate with the target
10658 machine---either via a devicename attached to a direct serial line, or a
10659 TCP or UDP port (usually to a terminal server which in turn has a serial line
10660 to the target). For example, to use a serial line connected to the
10661 device named @file{/dev/ttyb}:
10664 target remote /dev/ttyb
10667 @cindex TCP port, @code{target remote}
10668 To use a TCP connection, use an argument of the form
10669 @code{@var{host}:@var{port}} or @code{tcp:@var{host}:@var{port}}.
10670 For example, to connect to port 2828 on a
10671 terminal server named @code{manyfarms}:
10674 target remote manyfarms:2828
10677 If your remote target is actually running on the same machine as
10678 your debugger session (e.g.@: a simulator of your target running on
10679 the same host), you can omit the hostname. For example, to connect
10680 to port 1234 on your local machine:
10683 target remote :1234
10687 Note that the colon is still required here.
10689 @cindex UDP port, @code{target remote}
10690 To use a UDP connection, use an argument of the form
10691 @code{udp:@var{host}:@var{port}}. For example, to connect to UDP port 2828
10692 on a terminal server named @code{manyfarms}:
10695 target remote udp:manyfarms:2828
10698 When using a UDP connection for remote debugging, you should keep in mind
10699 that the `U' stands for ``Unreliable''. UDP can silently drop packets on
10700 busy or unreliable networks, which will cause havoc with your debugging
10705 Now you can use all the usual commands to examine and change data and to
10706 step and continue the remote program.
10708 To resume the remote program and stop debugging it, use the @code{detach}
10711 @cindex interrupting remote programs
10712 @cindex remote programs, interrupting
10713 Whenever @value{GDBN} is waiting for the remote program, if you type the
10714 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10715 program. This may or may not succeed, depending in part on the hardware
10716 and the serial drivers the remote system uses. If you type the
10717 interrupt character once again, @value{GDBN} displays this prompt:
10720 Interrupted while waiting for the program.
10721 Give up (and stop debugging it)? (y or n)
10724 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10725 (If you decide you want to try again later, you can use @samp{target
10726 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10727 goes back to waiting.
10730 @node Configurations
10731 @chapter Configuration-Specific Information
10733 While nearly all @value{GDBN} commands are available for all native and
10734 cross versions of the debugger, there are some exceptions. This chapter
10735 describes things that are only available in certain configurations.
10737 There are three major categories of configurations: native
10738 configurations, where the host and target are the same, embedded
10739 operating system configurations, which are usually the same for several
10740 different processor architectures, and bare embedded processors, which
10741 are quite different from each other.
10746 * Embedded Processors::
10753 This section describes details specific to particular native
10758 * SVR4 Process Information:: SVR4 process information
10759 * DJGPP Native:: Features specific to the DJGPP port
10760 * Cygwin Native:: Features specific to the Cygwin port
10766 On HP-UX systems, if you refer to a function or variable name that
10767 begins with a dollar sign, @value{GDBN} searches for a user or system
10768 name first, before it searches for a convenience variable.
10770 @node SVR4 Process Information
10771 @subsection SVR4 process information
10774 @cindex process image
10776 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10777 used to examine the image of a running process using file-system
10778 subroutines. If @value{GDBN} is configured for an operating system with
10779 this facility, the command @code{info proc} is available to report on
10780 several kinds of information about the process running your program.
10781 @code{info proc} works only on SVR4 systems that include the
10782 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10783 and Unixware, but not HP-UX or @sc{gnu}/Linux, for example.
10788 Summarize available information about the process.
10790 @kindex info proc mappings
10791 @item info proc mappings
10792 Report on the address ranges accessible in the program, with information
10793 on whether your program may read, write, or execute each range.
10795 @comment These sub-options of 'info proc' were not included when
10796 @comment procfs.c was re-written. Keep their descriptions around
10797 @comment against the day when someone finds the time to put them back in.
10798 @kindex info proc times
10799 @item info proc times
10800 Starting time, user CPU time, and system CPU time for your program and
10803 @kindex info proc id
10805 Report on the process IDs related to your program: its own process ID,
10806 the ID of its parent, the process group ID, and the session ID.
10808 @kindex info proc status
10809 @item info proc status
10810 General information on the state of the process. If the process is
10811 stopped, this report includes the reason for stopping, and any signal
10814 @item info proc all
10815 Show all the above information about the process.
10820 @subsection Features for Debugging @sc{djgpp} Programs
10821 @cindex @sc{djgpp} debugging
10822 @cindex native @sc{djgpp} debugging
10823 @cindex MS-DOS-specific commands
10825 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10826 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10827 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10828 top of real-mode DOS systems and their emulations.
10830 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10831 defines a few commands specific to the @sc{djgpp} port. This
10832 subsection describes those commands.
10837 This is a prefix of @sc{djgpp}-specific commands which print
10838 information about the target system and important OS structures.
10841 @cindex MS-DOS system info
10842 @cindex free memory information (MS-DOS)
10843 @item info dos sysinfo
10844 This command displays assorted information about the underlying
10845 platform: the CPU type and features, the OS version and flavor, the
10846 DPMI version, and the available conventional and DPMI memory.
10851 @cindex segment descriptor tables
10852 @cindex descriptor tables display
10854 @itemx info dos ldt
10855 @itemx info dos idt
10856 These 3 commands display entries from, respectively, Global, Local,
10857 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10858 tables are data structures which store a descriptor for each segment
10859 that is currently in use. The segment's selector is an index into a
10860 descriptor table; the table entry for that index holds the
10861 descriptor's base address and limit, and its attributes and access
10864 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10865 segment (used for both data and the stack), and a DOS segment (which
10866 allows access to DOS/BIOS data structures and absolute addresses in
10867 conventional memory). However, the DPMI host will usually define
10868 additional segments in order to support the DPMI environment.
10870 @cindex garbled pointers
10871 These commands allow to display entries from the descriptor tables.
10872 Without an argument, all entries from the specified table are
10873 displayed. An argument, which should be an integer expression, means
10874 display a single entry whose index is given by the argument. For
10875 example, here's a convenient way to display information about the
10876 debugged program's data segment:
10879 @exdent @code{(@value{GDBP}) info dos ldt $ds}
10880 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
10884 This comes in handy when you want to see whether a pointer is outside
10885 the data segment's limit (i.e.@: @dfn{garbled}).
10887 @cindex page tables display (MS-DOS)
10889 @itemx info dos pte
10890 These two commands display entries from, respectively, the Page
10891 Directory and the Page Tables. Page Directories and Page Tables are
10892 data structures which control how virtual memory addresses are mapped
10893 into physical addresses. A Page Table includes an entry for every
10894 page of memory that is mapped into the program's address space; there
10895 may be several Page Tables, each one holding up to 4096 entries. A
10896 Page Directory has up to 4096 entries, one each for every Page Table
10897 that is currently in use.
10899 Without an argument, @kbd{info dos pde} displays the entire Page
10900 Directory, and @kbd{info dos pte} displays all the entries in all of
10901 the Page Tables. An argument, an integer expression, given to the
10902 @kbd{info dos pde} command means display only that entry from the Page
10903 Directory table. An argument given to the @kbd{info dos pte} command
10904 means display entries from a single Page Table, the one pointed to by
10905 the specified entry in the Page Directory.
10907 @cindex direct memory access (DMA) on MS-DOS
10908 These commands are useful when your program uses @dfn{DMA} (Direct
10909 Memory Access), which needs physical addresses to program the DMA
10912 These commands are supported only with some DPMI servers.
10914 @cindex physical address from linear address
10915 @item info dos address-pte @var{addr}
10916 This command displays the Page Table entry for a specified linear
10917 address. The argument linear address @var{addr} should already have the
10918 appropriate segment's base address added to it, because this command
10919 accepts addresses which may belong to @emph{any} segment. For
10920 example, here's how to display the Page Table entry for the page where
10921 the variable @code{i} is stored:
10924 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
10925 @exdent @code{Page Table entry for address 0x11a00d30:}
10926 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
10930 This says that @code{i} is stored at offset @code{0xd30} from the page
10931 whose physical base address is @code{0x02698000}, and prints all the
10932 attributes of that page.
10934 Note that you must cast the addresses of variables to a @code{char *},
10935 since otherwise the value of @code{__djgpp_base_address}, the base
10936 address of all variables and functions in a @sc{djgpp} program, will
10937 be added using the rules of C pointer arithmetics: if @code{i} is
10938 declared an @code{int}, @value{GDBN} will add 4 times the value of
10939 @code{__djgpp_base_address} to the address of @code{i}.
10941 Here's another example, it displays the Page Table entry for the
10945 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
10946 @exdent @code{Page Table entry for address 0x29110:}
10947 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
10951 (The @code{+ 3} offset is because the transfer buffer's address is the
10952 3rd member of the @code{_go32_info_block} structure.) The output of
10953 this command clearly shows that addresses in conventional memory are
10954 mapped 1:1, i.e.@: the physical and linear addresses are identical.
10956 This command is supported only with some DPMI servers.
10959 @node Cygwin Native
10960 @subsection Features for Debugging MS Windows PE executables
10961 @cindex MS Windows debugging
10962 @cindex native Cygwin debugging
10963 @cindex Cygwin-specific commands
10965 @value{GDBN} supports native debugging of MS Windows programs, and
10966 defines a few commands specific to the Cygwin port. This
10967 subsection describes those commands.
10972 This is a prefix of MS Windows specific commands which print
10973 information about the target system and important OS structures.
10975 @item info w32 selector
10976 This command displays information returned by
10977 the Win32 API @code{GetThreadSelectorEntry} function.
10978 It takes an optional argument that is evaluated to
10979 a long value to give the information about this given selector.
10980 Without argument, this command displays information
10981 about the the six segment registers.
10985 This is a Cygwin specific alias of info shared.
10987 @kindex dll-symbols
10989 This command loads symbols from a dll similarly to
10990 add-sym command but without the need to specify a base address.
10992 @kindex set new-console
10993 @item set new-console @var{mode}
10994 If @var{mode} is @code{on} the debuggee will
10995 be started in a new console on next start.
10996 If @var{mode} is @code{off}i, the debuggee will
10997 be started in the same console as the debugger.
10999 @kindex show new-console
11000 @item show new-console
11001 Displays whether a new console is used
11002 when the debuggee is started.
11004 @kindex set new-group
11005 @item set new-group @var{mode}
11006 This boolean value controls whether the debuggee should
11007 start a new group or stay in the same group as the debugger.
11008 This affects the way the Windows OS handles
11011 @kindex show new-group
11012 @item show new-group
11013 Displays current value of new-group boolean.
11015 @kindex set debugevents
11016 @item set debugevents
11017 This boolean value adds debug output concerning events seen by the debugger.
11019 @kindex set debugexec
11020 @item set debugexec
11021 This boolean value adds debug output concerning execute events
11022 seen by the debugger.
11024 @kindex set debugexceptions
11025 @item set debugexceptions
11026 This boolean value adds debug ouptut concerning exception events
11027 seen by the debugger.
11029 @kindex set debugmemory
11030 @item set debugmemory
11031 This boolean value adds debug ouptut concerning memory events
11032 seen by the debugger.
11036 This boolean values specifies whether the debuggee is called
11037 via a shell or directly (default value is on).
11041 Displays if the debuggee will be started with a shell.
11046 @section Embedded Operating Systems
11048 This section describes configurations involving the debugging of
11049 embedded operating systems that are available for several different
11053 * VxWorks:: Using @value{GDBN} with VxWorks
11056 @value{GDBN} includes the ability to debug programs running on
11057 various real-time operating systems.
11060 @subsection Using @value{GDBN} with VxWorks
11066 @kindex target vxworks
11067 @item target vxworks @var{machinename}
11068 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11069 is the target system's machine name or IP address.
11073 On VxWorks, @code{load} links @var{filename} dynamically on the
11074 current target system as well as adding its symbols in @value{GDBN}.
11076 @value{GDBN} enables developers to spawn and debug tasks running on networked
11077 VxWorks targets from a Unix host. Already-running tasks spawned from
11078 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11079 both the Unix host and on the VxWorks target. The program
11080 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11081 installed with the name @code{vxgdb}, to distinguish it from a
11082 @value{GDBN} for debugging programs on the host itself.)
11085 @item VxWorks-timeout @var{args}
11086 @kindex vxworks-timeout
11087 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11088 This option is set by the user, and @var{args} represents the number of
11089 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11090 your VxWorks target is a slow software simulator or is on the far side
11091 of a thin network line.
11094 The following information on connecting to VxWorks was current when
11095 this manual was produced; newer releases of VxWorks may use revised
11098 @kindex INCLUDE_RDB
11099 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11100 to include the remote debugging interface routines in the VxWorks
11101 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11102 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11103 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11104 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11105 information on configuring and remaking VxWorks, see the manufacturer's
11107 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11109 Once you have included @file{rdb.a} in your VxWorks system image and set
11110 your Unix execution search path to find @value{GDBN}, you are ready to
11111 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11112 @code{vxgdb}, depending on your installation).
11114 @value{GDBN} comes up showing the prompt:
11121 * VxWorks Connection:: Connecting to VxWorks
11122 * VxWorks Download:: VxWorks download
11123 * VxWorks Attach:: Running tasks
11126 @node VxWorks Connection
11127 @subsubsection Connecting to VxWorks
11129 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11130 network. To connect to a target whose host name is ``@code{tt}'', type:
11133 (vxgdb) target vxworks tt
11137 @value{GDBN} displays messages like these:
11140 Attaching remote machine across net...
11145 @value{GDBN} then attempts to read the symbol tables of any object modules
11146 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11147 these files by searching the directories listed in the command search
11148 path (@pxref{Environment, ,Your program's environment}); if it fails
11149 to find an object file, it displays a message such as:
11152 prog.o: No such file or directory.
11155 When this happens, add the appropriate directory to the search path with
11156 the @value{GDBN} command @code{path}, and execute the @code{target}
11159 @node VxWorks Download
11160 @subsubsection VxWorks download
11162 @cindex download to VxWorks
11163 If you have connected to the VxWorks target and you want to debug an
11164 object that has not yet been loaded, you can use the @value{GDBN}
11165 @code{load} command to download a file from Unix to VxWorks
11166 incrementally. The object file given as an argument to the @code{load}
11167 command is actually opened twice: first by the VxWorks target in order
11168 to download the code, then by @value{GDBN} in order to read the symbol
11169 table. This can lead to problems if the current working directories on
11170 the two systems differ. If both systems have NFS mounted the same
11171 filesystems, you can avoid these problems by using absolute paths.
11172 Otherwise, it is simplest to set the working directory on both systems
11173 to the directory in which the object file resides, and then to reference
11174 the file by its name, without any path. For instance, a program
11175 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11176 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11177 program, type this on VxWorks:
11180 -> cd "@var{vxpath}/vw/demo/rdb"
11184 Then, in @value{GDBN}, type:
11187 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11188 (vxgdb) load prog.o
11191 @value{GDBN} displays a response similar to this:
11194 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11197 You can also use the @code{load} command to reload an object module
11198 after editing and recompiling the corresponding source file. Note that
11199 this makes @value{GDBN} delete all currently-defined breakpoints,
11200 auto-displays, and convenience variables, and to clear the value
11201 history. (This is necessary in order to preserve the integrity of
11202 debugger's data structures that reference the target system's symbol
11205 @node VxWorks Attach
11206 @subsubsection Running tasks
11208 @cindex running VxWorks tasks
11209 You can also attach to an existing task using the @code{attach} command as
11213 (vxgdb) attach @var{task}
11217 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11218 or suspended when you attach to it. Running tasks are suspended at
11219 the time of attachment.
11221 @node Embedded Processors
11222 @section Embedded Processors
11224 This section goes into details specific to particular embedded
11230 * H8/300:: Hitachi H8/300
11231 * H8/500:: Hitachi H8/500
11232 * i960:: Intel i960
11233 * M32R/D:: Mitsubishi M32R/D
11234 * M68K:: Motorola M68K
11235 * MIPS Embedded:: MIPS Embedded
11236 * OpenRISC 1000:: OpenRisc 1000
11237 * PA:: HP PA Embedded
11240 * Sparclet:: Tsqware Sparclet
11241 * Sparclite:: Fujitsu Sparclite
11242 * ST2000:: Tandem ST2000
11243 * Z8000:: Zilog Z8000
11252 @item target rdi @var{dev}
11253 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11254 use this target to communicate with both boards running the Angel
11255 monitor, or with the EmbeddedICE JTAG debug device.
11258 @item target rdp @var{dev}
11264 @subsection Hitachi H8/300
11268 @kindex target hms@r{, with H8/300}
11269 @item target hms @var{dev}
11270 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11271 Use special commands @code{device} and @code{speed} to control the serial
11272 line and the communications speed used.
11274 @kindex target e7000@r{, with H8/300}
11275 @item target e7000 @var{dev}
11276 E7000 emulator for Hitachi H8 and SH.
11278 @kindex target sh3@r{, with H8/300}
11279 @kindex target sh3e@r{, with H8/300}
11280 @item target sh3 @var{dev}
11281 @itemx target sh3e @var{dev}
11282 Hitachi SH-3 and SH-3E target systems.
11286 @cindex download to H8/300 or H8/500
11287 @cindex H8/300 or H8/500 download
11288 @cindex download to Hitachi SH
11289 @cindex Hitachi SH download
11290 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11291 board, the @code{load} command downloads your program to the Hitachi
11292 board and also opens it as the current executable target for
11293 @value{GDBN} on your host (like the @code{file} command).
11295 @value{GDBN} needs to know these things to talk to your
11296 Hitachi SH, H8/300, or H8/500:
11300 that you want to use @samp{target hms}, the remote debugging interface
11301 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11302 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11303 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11304 H8/300, or H8/500.)
11307 what serial device connects your host to your Hitachi board (the first
11308 serial device available on your host is the default).
11311 what speed to use over the serial device.
11315 * Hitachi Boards:: Connecting to Hitachi boards.
11316 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11317 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11320 @node Hitachi Boards
11321 @subsubsection Connecting to Hitachi boards
11323 @c only for Unix hosts
11325 @cindex serial device, Hitachi micros
11326 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11327 need to explicitly set the serial device. The default @var{port} is the
11328 first available port on your host. This is only necessary on Unix
11329 hosts, where it is typically something like @file{/dev/ttya}.
11332 @cindex serial line speed, Hitachi micros
11333 @code{@value{GDBN}} has another special command to set the communications
11334 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11335 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11336 the DOS @code{mode} command (for instance,
11337 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11339 The @samp{device} and @samp{speed} commands are available only when you
11340 use a Unix host to debug your Hitachi microprocessor programs. If you
11342 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11343 called @code{asynctsr} to communicate with the development board
11344 through a PC serial port. You must also use the DOS @code{mode} command
11345 to set up the serial port on the DOS side.
11347 The following sample session illustrates the steps needed to start a
11348 program under @value{GDBN} control on an H8/300. The example uses a
11349 sample H8/300 program called @file{t.x}. The procedure is the same for
11350 the Hitachi SH and the H8/500.
11352 First hook up your development board. In this example, we use a
11353 board attached to serial port @code{COM2}; if you use a different serial
11354 port, substitute its name in the argument of the @code{mode} command.
11355 When you call @code{asynctsr}, the auxiliary comms program used by the
11356 debugger, you give it just the numeric part of the serial port's name;
11357 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11361 C:\H8300\TEST> asynctsr 2
11362 C:\H8300\TEST> mode com2:9600,n,8,1,p
11364 Resident portion of MODE loaded
11366 COM2: 9600, n, 8, 1, p
11371 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11372 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11373 disable it, or even boot without it, to use @code{asynctsr} to control
11374 your development board.
11377 @kindex target hms@r{, and serial protocol}
11378 Now that serial communications are set up, and the development board is
11379 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11380 the name of your program as the argument. @code{@value{GDBN}} prompts
11381 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11382 commands to begin your debugging session: @samp{target hms} to specify
11383 cross-debugging to the Hitachi board, and the @code{load} command to
11384 download your program to the board. @code{load} displays the names of
11385 the program's sections, and a @samp{*} for each 2K of data downloaded.
11386 (If you want to refresh @value{GDBN} data on symbols or on the
11387 executable file without downloading, use the @value{GDBN} commands
11388 @code{file} or @code{symbol-file}. These commands, and @code{load}
11389 itself, are described in @ref{Files,,Commands to specify files}.)
11392 (eg-C:\H8300\TEST) @value{GDBP} t.x
11393 @value{GDBN} is free software and you are welcome to distribute copies
11394 of it under certain conditions; type "show copying" to see
11396 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11398 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11399 (@value{GDBP}) target hms
11400 Connected to remote H8/300 HMS system.
11401 (@value{GDBP}) load t.x
11402 .text : 0x8000 .. 0xabde ***********
11403 .data : 0xabde .. 0xad30 *
11404 .stack : 0xf000 .. 0xf014 *
11407 At this point, you're ready to run or debug your program. From here on,
11408 you can use all the usual @value{GDBN} commands. The @code{break} command
11409 sets breakpoints; the @code{run} command starts your program;
11410 @code{print} or @code{x} display data; the @code{continue} command
11411 resumes execution after stopping at a breakpoint. You can use the
11412 @code{help} command at any time to find out more about @value{GDBN} commands.
11414 Remember, however, that @emph{operating system} facilities aren't
11415 available on your development board; for example, if your program hangs,
11416 you can't send an interrupt---but you can press the @sc{reset} switch!
11418 Use the @sc{reset} button on the development board
11421 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11422 no way to pass an interrupt signal to the development board); and
11425 to return to the @value{GDBN} command prompt after your program finishes
11426 normally. The communications protocol provides no other way for @value{GDBN}
11427 to detect program completion.
11430 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11431 development board as a ``normal exit'' of your program.
11434 @subsubsection Using the E7000 in-circuit emulator
11436 @kindex target e7000@r{, with Hitachi ICE}
11437 You can use the E7000 in-circuit emulator to develop code for either the
11438 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11439 e7000} command to connect @value{GDBN} to your E7000:
11442 @item target e7000 @var{port} @var{speed}
11443 Use this form if your E7000 is connected to a serial port. The
11444 @var{port} argument identifies what serial port to use (for example,
11445 @samp{com2}). The third argument is the line speed in bits per second
11446 (for example, @samp{9600}).
11448 @item target e7000 @var{hostname}
11449 If your E7000 is installed as a host on a TCP/IP network, you can just
11450 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11453 @node Hitachi Special
11454 @subsubsection Special @value{GDBN} commands for Hitachi micros
11456 Some @value{GDBN} commands are available only for the H8/300:
11460 @kindex set machine
11461 @kindex show machine
11462 @item set machine h8300
11463 @itemx set machine h8300h
11464 Condition @value{GDBN} for one of the two variants of the H8/300
11465 architecture with @samp{set machine}. You can use @samp{show machine}
11466 to check which variant is currently in effect.
11475 @kindex set memory @var{mod}
11476 @cindex memory models, H8/500
11477 @item set memory @var{mod}
11479 Specify which H8/500 memory model (@var{mod}) you are using with
11480 @samp{set memory}; check which memory model is in effect with @samp{show
11481 memory}. The accepted values for @var{mod} are @code{small},
11482 @code{big}, @code{medium}, and @code{compact}.
11487 @subsection Intel i960
11491 @kindex target mon960
11492 @item target mon960 @var{dev}
11493 MON960 monitor for Intel i960.
11495 @kindex target nindy
11496 @item target nindy @var{devicename}
11497 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11498 the name of the serial device to use for the connection, e.g.
11505 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11506 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11507 tell @value{GDBN} how to connect to the 960 in several ways:
11511 Through command line options specifying serial port, version of the
11512 Nindy protocol, and communications speed;
11515 By responding to a prompt on startup;
11518 By using the @code{target} command at any point during your @value{GDBN}
11519 session. @xref{Target Commands, ,Commands for managing targets}.
11523 @cindex download to Nindy-960
11524 With the Nindy interface to an Intel 960 board, @code{load}
11525 downloads @var{filename} to the 960 as well as adding its symbols in
11529 * Nindy Startup:: Startup with Nindy
11530 * Nindy Options:: Options for Nindy
11531 * Nindy Reset:: Nindy reset command
11534 @node Nindy Startup
11535 @subsubsection Startup with Nindy
11537 If you simply start @code{@value{GDBP}} without using any command-line
11538 options, you are prompted for what serial port to use, @emph{before} you
11539 reach the ordinary @value{GDBN} prompt:
11542 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11546 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11547 identifies the serial port you want to use. You can, if you choose,
11548 simply start up with no Nindy connection by responding to the prompt
11549 with an empty line. If you do this and later wish to attach to Nindy,
11550 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11552 @node Nindy Options
11553 @subsubsection Options for Nindy
11555 These are the startup options for beginning your @value{GDBN} session with a
11556 Nindy-960 board attached:
11559 @item -r @var{port}
11560 Specify the serial port name of a serial interface to be used to connect
11561 to the target system. This option is only available when @value{GDBN} is
11562 configured for the Intel 960 target architecture. You may specify
11563 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11564 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11565 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11568 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11569 the ``old'' Nindy monitor protocol to connect to the target system.
11570 This option is only available when @value{GDBN} is configured for the Intel 960
11571 target architecture.
11574 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11575 connect to a target system that expects the newer protocol, the connection
11576 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11577 attempts to reconnect at several different line speeds. You can abort
11578 this process with an interrupt.
11582 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11583 system, in an attempt to reset it, before connecting to a Nindy target.
11586 @emph{Warning:} Many target systems do not have the hardware that this
11587 requires; it only works with a few boards.
11591 The standard @samp{-b} option controls the line speed used on the serial
11596 @subsubsection Nindy reset command
11601 For a Nindy target, this command sends a ``break'' to the remote target
11602 system; this is only useful if the target has been equipped with a
11603 circuit to perform a hard reset (or some other interesting action) when
11604 a break is detected.
11609 @subsection Mitsubishi M32R/D
11613 @kindex target m32r
11614 @item target m32r @var{dev}
11615 Mitsubishi M32R/D ROM monitor.
11622 The Motorola m68k configuration includes ColdFire support, and
11623 target command for the following ROM monitors.
11627 @kindex target abug
11628 @item target abug @var{dev}
11629 ABug ROM monitor for M68K.
11631 @kindex target cpu32bug
11632 @item target cpu32bug @var{dev}
11633 CPU32BUG monitor, running on a CPU32 (M68K) board.
11635 @kindex target dbug
11636 @item target dbug @var{dev}
11637 dBUG ROM monitor for Motorola ColdFire.
11640 @item target est @var{dev}
11641 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11643 @kindex target rom68k
11644 @item target rom68k @var{dev}
11645 ROM 68K monitor, running on an M68K IDP board.
11649 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11650 instead have only a single special target command:
11654 @kindex target es1800
11655 @item target es1800 @var{dev}
11656 ES-1800 emulator for M68K.
11664 @kindex target rombug
11665 @item target rombug @var{dev}
11666 ROMBUG ROM monitor for OS/9000.
11670 @node MIPS Embedded
11671 @subsection MIPS Embedded
11673 @cindex MIPS boards
11674 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11675 MIPS board attached to a serial line. This is available when
11676 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11679 Use these @value{GDBN} commands to specify the connection to your target board:
11682 @item target mips @var{port}
11683 @kindex target mips @var{port}
11684 To run a program on the board, start up @code{@value{GDBP}} with the
11685 name of your program as the argument. To connect to the board, use the
11686 command @samp{target mips @var{port}}, where @var{port} is the name of
11687 the serial port connected to the board. If the program has not already
11688 been downloaded to the board, you may use the @code{load} command to
11689 download it. You can then use all the usual @value{GDBN} commands.
11691 For example, this sequence connects to the target board through a serial
11692 port, and loads and runs a program called @var{prog} through the
11696 host$ @value{GDBP} @var{prog}
11697 @value{GDBN} is free software and @dots{}
11698 (@value{GDBP}) target mips /dev/ttyb
11699 (@value{GDBP}) load @var{prog}
11703 @item target mips @var{hostname}:@var{portnumber}
11704 On some @value{GDBN} host configurations, you can specify a TCP
11705 connection (for instance, to a serial line managed by a terminal
11706 concentrator) instead of a serial port, using the syntax
11707 @samp{@var{hostname}:@var{portnumber}}.
11709 @item target pmon @var{port}
11710 @kindex target pmon @var{port}
11713 @item target ddb @var{port}
11714 @kindex target ddb @var{port}
11715 NEC's DDB variant of PMON for Vr4300.
11717 @item target lsi @var{port}
11718 @kindex target lsi @var{port}
11719 LSI variant of PMON.
11721 @kindex target r3900
11722 @item target r3900 @var{dev}
11723 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11725 @kindex target array
11726 @item target array @var{dev}
11727 Array Tech LSI33K RAID controller board.
11733 @value{GDBN} also supports these special commands for MIPS targets:
11736 @item set processor @var{args}
11737 @itemx show processor
11738 @kindex set processor @var{args}
11739 @kindex show processor
11740 Use the @code{set processor} command to set the type of MIPS
11741 processor when you want to access processor-type-specific registers.
11742 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11743 to use the CPU registers appropriate for the 3041 chip.
11744 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11745 is using. Use the @code{info reg} command to see what registers
11746 @value{GDBN} is using.
11748 @item set mipsfpu double
11749 @itemx set mipsfpu single
11750 @itemx set mipsfpu none
11751 @itemx show mipsfpu
11752 @kindex set mipsfpu
11753 @kindex show mipsfpu
11754 @cindex MIPS remote floating point
11755 @cindex floating point, MIPS remote
11756 If your target board does not support the MIPS floating point
11757 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11758 need this, you may wish to put the command in your @value{GDBN} init
11759 file). This tells @value{GDBN} how to find the return value of
11760 functions which return floating point values. It also allows
11761 @value{GDBN} to avoid saving the floating point registers when calling
11762 functions on the board. If you are using a floating point coprocessor
11763 with only single precision floating point support, as on the @sc{r4650}
11764 processor, use the command @samp{set mipsfpu single}. The default
11765 double precision floating point coprocessor may be selected using
11766 @samp{set mipsfpu double}.
11768 In previous versions the only choices were double precision or no
11769 floating point, so @samp{set mipsfpu on} will select double precision
11770 and @samp{set mipsfpu off} will select no floating point.
11772 As usual, you can inquire about the @code{mipsfpu} variable with
11773 @samp{show mipsfpu}.
11775 @item set remotedebug @var{n}
11776 @itemx show remotedebug
11777 @kindex set remotedebug@r{, MIPS protocol}
11778 @kindex show remotedebug@r{, MIPS protocol}
11779 @cindex @code{remotedebug}, MIPS protocol
11780 @cindex MIPS @code{remotedebug} protocol
11781 @c FIXME! For this to be useful, you must know something about the MIPS
11782 @c FIXME...protocol. Where is it described?
11783 You can see some debugging information about communications with the board
11784 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11785 @samp{set remotedebug 1}, every packet is displayed. If you set it
11786 to @code{2}, every character is displayed. You can check the current value
11787 at any time with the command @samp{show remotedebug}.
11789 @item set timeout @var{seconds}
11790 @itemx set retransmit-timeout @var{seconds}
11791 @itemx show timeout
11792 @itemx show retransmit-timeout
11793 @cindex @code{timeout}, MIPS protocol
11794 @cindex @code{retransmit-timeout}, MIPS protocol
11795 @kindex set timeout
11796 @kindex show timeout
11797 @kindex set retransmit-timeout
11798 @kindex show retransmit-timeout
11799 You can control the timeout used while waiting for a packet, in the MIPS
11800 remote protocol, with the @code{set timeout @var{seconds}} command. The
11801 default is 5 seconds. Similarly, you can control the timeout used while
11802 waiting for an acknowledgement of a packet with the @code{set
11803 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11804 You can inspect both values with @code{show timeout} and @code{show
11805 retransmit-timeout}. (These commands are @emph{only} available when
11806 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11808 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11809 is waiting for your program to stop. In that case, @value{GDBN} waits
11810 forever because it has no way of knowing how long the program is going
11811 to run before stopping.
11814 @node OpenRISC 1000
11815 @subsection OpenRISC 1000
11816 @cindex OpenRISC 1000
11818 @cindex or1k boards
11819 See OR1k Architecture document (@uref{www.opencores.org}) for more information
11820 about platform and commands.
11824 @kindex target jtag
11825 @item target jtag jtag://@var{host}:@var{port}
11827 Connects to remote JTAG server.
11828 JTAG remote server can be either an or1ksim or JTAG server,
11829 connected via parallel port to the board.
11831 Example: @code{target jtag jtag://localhost:9999}
11834 @item or1ksim @var{command}
11835 If connected to @code{or1ksim} OpenRISC 1000 Architectural
11836 Simulator, proprietary commands can be executed.
11838 @kindex info or1k spr
11839 @item info or1k spr
11840 Displays spr groups.
11842 @item info or1k spr @var{group}
11843 @itemx info or1k spr @var{groupno}
11844 Displays register names in selected group.
11846 @item info or1k spr @var{group} @var{register}
11847 @itemx info or1k spr @var{register}
11848 @itemx info or1k spr @var{groupno} @var{registerno}
11849 @itemx info or1k spr @var{registerno}
11850 Shows information about specified spr register.
11853 @item spr @var{group} @var{register} @var{value}
11854 @itemx spr @var{register @var{value}}
11855 @itemx spr @var{groupno} @var{registerno @var{value}}
11856 @itemx spr @var{registerno @var{value}}
11857 Writes @var{value} to specified spr register.
11860 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
11861 It is very similar to @value{GDBN} trace, except it does not interfere with normal
11862 program execution and is thus much faster. Hardware breakpoints/watchpoint
11863 triggers can be set using:
11866 Load effective address/data
11868 Store effective address/data
11870 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
11875 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
11876 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
11878 @code{htrace} commands:
11879 @cindex OpenRISC 1000 htrace
11882 @item hwatch @var{conditional}
11883 Set hardware watchpoint on combination of Load/Store Effecive Address(es)
11884 or Data. For example:
11886 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
11888 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
11890 @kindex htrace info
11892 Display information about current HW trace configuration.
11894 @kindex htrace trigger
11895 @item htrace trigger @var{conditional}
11896 Set starting criteria for HW trace.
11898 @kindex htrace qualifier
11899 @item htrace qualifier @var{conditional}
11900 Set acquisition qualifier for HW trace.
11902 @kindex htrace stop
11903 @item htrace stop @var{conditional}
11904 Set HW trace stopping criteria.
11906 @kindex htrace record
11907 @item htrace record @var{[data]*}
11908 Selects the data to be recorded, when qualifier is met and HW trace was
11911 @kindex htrace enable
11912 @item htrace enable
11913 @kindex htrace disable
11914 @itemx htrace disable
11915 Enables/disables the HW trace.
11917 @kindex htrace rewind
11918 @item htrace rewind @var{[filename]}
11919 Clears currently recorded trace data.
11921 If filename is specified, new trace file is made and any newly collected data
11922 will be written there.
11924 @kindex htrace print
11925 @item htrace print @var{[start [len]]}
11926 Prints trace buffer, using current record configuration.
11928 @kindex htrace mode continuous
11929 @item htrace mode continuous
11930 Set continuous trace mode.
11932 @kindex htrace mode suspend
11933 @item htrace mode suspend
11934 Set suspend trace mode.
11939 @subsection PowerPC
11943 @kindex target dink32
11944 @item target dink32 @var{dev}
11945 DINK32 ROM monitor.
11947 @kindex target ppcbug
11948 @item target ppcbug @var{dev}
11949 @kindex target ppcbug1
11950 @item target ppcbug1 @var{dev}
11951 PPCBUG ROM monitor for PowerPC.
11954 @item target sds @var{dev}
11955 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11960 @subsection HP PA Embedded
11964 @kindex target op50n
11965 @item target op50n @var{dev}
11966 OP50N monitor, running on an OKI HPPA board.
11968 @kindex target w89k
11969 @item target w89k @var{dev}
11970 W89K monitor, running on a Winbond HPPA board.
11975 @subsection Hitachi SH
11979 @kindex target hms@r{, with Hitachi SH}
11980 @item target hms @var{dev}
11981 A Hitachi SH board attached via serial line to your host. Use special
11982 commands @code{device} and @code{speed} to control the serial line and
11983 the communications speed used.
11985 @kindex target e7000@r{, with Hitachi SH}
11986 @item target e7000 @var{dev}
11987 E7000 emulator for Hitachi SH.
11989 @kindex target sh3@r{, with SH}
11990 @kindex target sh3e@r{, with SH}
11991 @item target sh3 @var{dev}
11992 @item target sh3e @var{dev}
11993 Hitachi SH-3 and SH-3E target systems.
11998 @subsection Tsqware Sparclet
12002 @value{GDBN} enables developers to debug tasks running on
12003 Sparclet targets from a Unix host.
12004 @value{GDBN} uses code that runs on
12005 both the Unix host and on the Sparclet target. The program
12006 @code{@value{GDBP}} is installed and executed on the Unix host.
12009 @item remotetimeout @var{args}
12010 @kindex remotetimeout
12011 @value{GDBN} supports the option @code{remotetimeout}.
12012 This option is set by the user, and @var{args} represents the number of
12013 seconds @value{GDBN} waits for responses.
12016 @cindex compiling, on Sparclet
12017 When compiling for debugging, include the options @samp{-g} to get debug
12018 information and @samp{-Ttext} to relocate the program to where you wish to
12019 load it on the target. You may also want to add the options @samp{-n} or
12020 @samp{-N} in order to reduce the size of the sections. Example:
12023 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12026 You can use @code{objdump} to verify that the addresses are what you intended:
12029 sparclet-aout-objdump --headers --syms prog
12032 @cindex running, on Sparclet
12034 your Unix execution search path to find @value{GDBN}, you are ready to
12035 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12036 (or @code{sparclet-aout-gdb}, depending on your installation).
12038 @value{GDBN} comes up showing the prompt:
12045 * Sparclet File:: Setting the file to debug
12046 * Sparclet Connection:: Connecting to Sparclet
12047 * Sparclet Download:: Sparclet download
12048 * Sparclet Execution:: Running and debugging
12051 @node Sparclet File
12052 @subsubsection Setting file to debug
12054 The @value{GDBN} command @code{file} lets you choose with program to debug.
12057 (gdbslet) file prog
12061 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12062 @value{GDBN} locates
12063 the file by searching the directories listed in the command search
12065 If the file was compiled with debug information (option "-g"), source
12066 files will be searched as well.
12067 @value{GDBN} locates
12068 the source files by searching the directories listed in the directory search
12069 path (@pxref{Environment, ,Your program's environment}).
12071 to find a file, it displays a message such as:
12074 prog: No such file or directory.
12077 When this happens, add the appropriate directories to the search paths with
12078 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12079 @code{target} command again.
12081 @node Sparclet Connection
12082 @subsubsection Connecting to Sparclet
12084 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12085 To connect to a target on serial port ``@code{ttya}'', type:
12088 (gdbslet) target sparclet /dev/ttya
12089 Remote target sparclet connected to /dev/ttya
12090 main () at ../prog.c:3
12094 @value{GDBN} displays messages like these:
12100 @node Sparclet Download
12101 @subsubsection Sparclet download
12103 @cindex download to Sparclet
12104 Once connected to the Sparclet target,
12105 you can use the @value{GDBN}
12106 @code{load} command to download the file from the host to the target.
12107 The file name and load offset should be given as arguments to the @code{load}
12109 Since the file format is aout, the program must be loaded to the starting
12110 address. You can use @code{objdump} to find out what this value is. The load
12111 offset is an offset which is added to the VMA (virtual memory address)
12112 of each of the file's sections.
12113 For instance, if the program
12114 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12115 and bss at 0x12010170, in @value{GDBN}, type:
12118 (gdbslet) load prog 0x12010000
12119 Loading section .text, size 0xdb0 vma 0x12010000
12122 If the code is loaded at a different address then what the program was linked
12123 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12124 to tell @value{GDBN} where to map the symbol table.
12126 @node Sparclet Execution
12127 @subsubsection Running and debugging
12129 @cindex running and debugging Sparclet programs
12130 You can now begin debugging the task using @value{GDBN}'s execution control
12131 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12132 manual for the list of commands.
12136 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12138 Starting program: prog
12139 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12140 3 char *symarg = 0;
12142 4 char *execarg = "hello!";
12147 @subsection Fujitsu Sparclite
12151 @kindex target sparclite
12152 @item target sparclite @var{dev}
12153 Fujitsu sparclite boards, used only for the purpose of loading.
12154 You must use an additional command to debug the program.
12155 For example: target remote @var{dev} using @value{GDBN} standard
12161 @subsection Tandem ST2000
12163 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12166 To connect your ST2000 to the host system, see the manufacturer's
12167 manual. Once the ST2000 is physically attached, you can run:
12170 target st2000 @var{dev} @var{speed}
12174 to establish it as your debugging environment. @var{dev} is normally
12175 the name of a serial device, such as @file{/dev/ttya}, connected to the
12176 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12177 connection (for example, to a serial line attached via a terminal
12178 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12180 The @code{load} and @code{attach} commands are @emph{not} defined for
12181 this target; you must load your program into the ST2000 as you normally
12182 would for standalone operation. @value{GDBN} reads debugging information
12183 (such as symbols) from a separate, debugging version of the program
12184 available on your host computer.
12185 @c FIXME!! This is terribly vague; what little content is here is
12186 @c basically hearsay.
12188 @cindex ST2000 auxiliary commands
12189 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12193 @item st2000 @var{command}
12194 @kindex st2000 @var{cmd}
12195 @cindex STDBUG commands (ST2000)
12196 @cindex commands to STDBUG (ST2000)
12197 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12198 manual for available commands.
12201 @cindex connect (to STDBUG)
12202 Connect the controlling terminal to the STDBUG command monitor. When
12203 you are done interacting with STDBUG, typing either of two character
12204 sequences gets you back to the @value{GDBN} command prompt:
12205 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12206 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12210 @subsection Zilog Z8000
12213 @cindex simulator, Z8000
12214 @cindex Zilog Z8000 simulator
12216 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12219 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12220 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12221 segmented variant). The simulator recognizes which architecture is
12222 appropriate by inspecting the object code.
12225 @item target sim @var{args}
12227 @kindex target sim@r{, with Z8000}
12228 Debug programs on a simulated CPU. If the simulator supports setup
12229 options, specify them via @var{args}.
12233 After specifying this target, you can debug programs for the simulated
12234 CPU in the same style as programs for your host computer; use the
12235 @code{file} command to load a new program image, the @code{run} command
12236 to run your program, and so on.
12238 As well as making available all the usual machine registers
12239 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12240 additional items of information as specially named registers:
12245 Counts clock-ticks in the simulator.
12248 Counts instructions run in the simulator.
12251 Execution time in 60ths of a second.
12255 You can refer to these values in @value{GDBN} expressions with the usual
12256 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12257 conditional breakpoint that suspends only after at least 5000
12258 simulated clock ticks.
12260 @node Architectures
12261 @section Architectures
12263 This section describes characteristics of architectures that affect
12264 all uses of @value{GDBN} with the architecture, both native and cross.
12277 @kindex set rstack_high_address
12278 @cindex AMD 29K register stack
12279 @cindex register stack, AMD29K
12280 @item set rstack_high_address @var{address}
12281 On AMD 29000 family processors, registers are saved in a separate
12282 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12283 extent of this stack. Normally, @value{GDBN} just assumes that the
12284 stack is ``large enough''. This may result in @value{GDBN} referencing
12285 memory locations that do not exist. If necessary, you can get around
12286 this problem by specifying the ending address of the register stack with
12287 the @code{set rstack_high_address} command. The argument should be an
12288 address, which you probably want to precede with @samp{0x} to specify in
12291 @kindex show rstack_high_address
12292 @item show rstack_high_address
12293 Display the current limit of the register stack, on AMD 29000 family
12301 See the following section.
12306 @cindex stack on Alpha
12307 @cindex stack on MIPS
12308 @cindex Alpha stack
12310 Alpha- and MIPS-based computers use an unusual stack frame, which
12311 sometimes requires @value{GDBN} to search backward in the object code to
12312 find the beginning of a function.
12314 @cindex response time, MIPS debugging
12315 To improve response time (especially for embedded applications, where
12316 @value{GDBN} may be restricted to a slow serial line for this search)
12317 you may want to limit the size of this search, using one of these
12321 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12322 @item set heuristic-fence-post @var{limit}
12323 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12324 search for the beginning of a function. A value of @var{0} (the
12325 default) means there is no limit. However, except for @var{0}, the
12326 larger the limit the more bytes @code{heuristic-fence-post} must search
12327 and therefore the longer it takes to run.
12329 @item show heuristic-fence-post
12330 Display the current limit.
12334 These commands are available @emph{only} when @value{GDBN} is configured
12335 for debugging programs on Alpha or MIPS processors.
12338 @node Controlling GDB
12339 @chapter Controlling @value{GDBN}
12341 You can alter the way @value{GDBN} interacts with you by using the
12342 @code{set} command. For commands controlling how @value{GDBN} displays
12343 data, see @ref{Print Settings, ,Print settings}. Other settings are
12348 * Editing:: Command editing
12349 * History:: Command history
12350 * Screen Size:: Screen size
12351 * Numbers:: Numbers
12352 * ABI:: Configuring the current ABI
12353 * Messages/Warnings:: Optional warnings and messages
12354 * Debugging Output:: Optional messages about internal happenings
12362 @value{GDBN} indicates its readiness to read a command by printing a string
12363 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12364 can change the prompt string with the @code{set prompt} command. For
12365 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12366 the prompt in one of the @value{GDBN} sessions so that you can always tell
12367 which one you are talking to.
12369 @emph{Note:} @code{set prompt} does not add a space for you after the
12370 prompt you set. This allows you to set a prompt which ends in a space
12371 or a prompt that does not.
12375 @item set prompt @var{newprompt}
12376 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12378 @kindex show prompt
12380 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12384 @section Command editing
12386 @cindex command line editing
12388 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12389 @sc{gnu} library provides consistent behavior for programs which provide a
12390 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12391 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12392 substitution, and a storage and recall of command history across
12393 debugging sessions.
12395 You may control the behavior of command line editing in @value{GDBN} with the
12396 command @code{set}.
12399 @kindex set editing
12402 @itemx set editing on
12403 Enable command line editing (enabled by default).
12405 @item set editing off
12406 Disable command line editing.
12408 @kindex show editing
12410 Show whether command line editing is enabled.
12414 @section Command history
12416 @value{GDBN} can keep track of the commands you type during your
12417 debugging sessions, so that you can be certain of precisely what
12418 happened. Use these commands to manage the @value{GDBN} command
12422 @cindex history substitution
12423 @cindex history file
12424 @kindex set history filename
12425 @kindex GDBHISTFILE
12426 @item set history filename @var{fname}
12427 Set the name of the @value{GDBN} command history file to @var{fname}.
12428 This is the file where @value{GDBN} reads an initial command history
12429 list, and where it writes the command history from this session when it
12430 exits. You can access this list through history expansion or through
12431 the history command editing characters listed below. This file defaults
12432 to the value of the environment variable @code{GDBHISTFILE}, or to
12433 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12436 @cindex history save
12437 @kindex set history save
12438 @item set history save
12439 @itemx set history save on
12440 Record command history in a file, whose name may be specified with the
12441 @code{set history filename} command. By default, this option is disabled.
12443 @item set history save off
12444 Stop recording command history in a file.
12446 @cindex history size
12447 @kindex set history size
12448 @item set history size @var{size}
12449 Set the number of commands which @value{GDBN} keeps in its history list.
12450 This defaults to the value of the environment variable
12451 @code{HISTSIZE}, or to 256 if this variable is not set.
12454 @cindex history expansion
12455 History expansion assigns special meaning to the character @kbd{!}.
12456 @ifset have-readline-appendices
12457 @xref{Event Designators}.
12460 Since @kbd{!} is also the logical not operator in C, history expansion
12461 is off by default. If you decide to enable history expansion with the
12462 @code{set history expansion on} command, you may sometimes need to
12463 follow @kbd{!} (when it is used as logical not, in an expression) with
12464 a space or a tab to prevent it from being expanded. The readline
12465 history facilities do not attempt substitution on the strings
12466 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12468 The commands to control history expansion are:
12471 @kindex set history expansion
12472 @item set history expansion on
12473 @itemx set history expansion
12474 Enable history expansion. History expansion is off by default.
12476 @item set history expansion off
12477 Disable history expansion.
12479 The readline code comes with more complete documentation of
12480 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12481 or @code{vi} may wish to read it.
12482 @ifset have-readline-appendices
12483 @xref{Command Line Editing}.
12487 @kindex show history
12489 @itemx show history filename
12490 @itemx show history save
12491 @itemx show history size
12492 @itemx show history expansion
12493 These commands display the state of the @value{GDBN} history parameters.
12494 @code{show history} by itself displays all four states.
12500 @item show commands
12501 Display the last ten commands in the command history.
12503 @item show commands @var{n}
12504 Print ten commands centered on command number @var{n}.
12506 @item show commands +
12507 Print ten commands just after the commands last printed.
12511 @section Screen size
12512 @cindex size of screen
12513 @cindex pauses in output
12515 Certain commands to @value{GDBN} may produce large amounts of
12516 information output to the screen. To help you read all of it,
12517 @value{GDBN} pauses and asks you for input at the end of each page of
12518 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12519 to discard the remaining output. Also, the screen width setting
12520 determines when to wrap lines of output. Depending on what is being
12521 printed, @value{GDBN} tries to break the line at a readable place,
12522 rather than simply letting it overflow onto the following line.
12524 Normally @value{GDBN} knows the size of the screen from the terminal
12525 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12526 together with the value of the @code{TERM} environment variable and the
12527 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12528 you can override it with the @code{set height} and @code{set
12535 @kindex show height
12536 @item set height @var{lpp}
12538 @itemx set width @var{cpl}
12540 These @code{set} commands specify a screen height of @var{lpp} lines and
12541 a screen width of @var{cpl} characters. The associated @code{show}
12542 commands display the current settings.
12544 If you specify a height of zero lines, @value{GDBN} does not pause during
12545 output no matter how long the output is. This is useful if output is to a
12546 file or to an editor buffer.
12548 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12549 from wrapping its output.
12554 @cindex number representation
12555 @cindex entering numbers
12557 You can always enter numbers in octal, decimal, or hexadecimal in
12558 @value{GDBN} by the usual conventions: octal numbers begin with
12559 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12560 begin with @samp{0x}. Numbers that begin with none of these are, by
12561 default, entered in base 10; likewise, the default display for
12562 numbers---when no particular format is specified---is base 10. You can
12563 change the default base for both input and output with the @code{set
12567 @kindex set input-radix
12568 @item set input-radix @var{base}
12569 Set the default base for numeric input. Supported choices
12570 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12571 specified either unambiguously or using the current default radix; for
12581 sets the base to decimal. On the other hand, @samp{set radix 10}
12582 leaves the radix unchanged no matter what it was.
12584 @kindex set output-radix
12585 @item set output-radix @var{base}
12586 Set the default base for numeric display. Supported choices
12587 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12588 specified either unambiguously or using the current default radix.
12590 @kindex show input-radix
12591 @item show input-radix
12592 Display the current default base for numeric input.
12594 @kindex show output-radix
12595 @item show output-radix
12596 Display the current default base for numeric display.
12600 @section Configuring the current ABI
12602 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
12603 application automatically. However, sometimes you need to override its
12604 conclusions. Use these commands to manage @value{GDBN}'s view of the
12611 One @value{GDBN} configuration can debug binaries for multiple operating
12612 system targets, either via remote debugging or native emulation.
12613 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
12614 but you can override its conclusion using the @code{set osabi} command.
12615 One example where this is useful is in debugging of binaries which use
12616 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
12617 not have the same identifying marks that the standard C library for your
12622 Show the OS ABI currently in use.
12625 With no argument, show the list of registered available OS ABI's.
12627 @item set osabi @var{abi}
12628 Set the current OS ABI to @var{abi}.
12631 @cindex float promotion
12632 @kindex set coerce-float-to-double
12634 Generally, the way that an argument of type @code{float} is passed to a
12635 function depends on whether the function is prototyped. For a prototyped
12636 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
12637 according to the architecture's convention for @code{float}. For unprototyped
12638 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
12639 @code{double} and then passed.
12641 Unfortunately, some forms of debug information do not reliably indicate whether
12642 a function is prototyped. If @value{GDBN} calls a function that is not marked
12643 as prototyped, it consults @kbd{set coerce-float-to-double}.
12646 @item set coerce-float-to-double
12647 @itemx set coerce-float-to-double on
12648 Arguments of type @code{float} will be promoted to @code{double} when passed
12649 to an unprototyped function. This is the default setting.
12651 @item set coerce-float-to-double off
12652 Arguments of type @code{float} will be passed directly to unprototyped
12656 @node Messages/Warnings
12657 @section Optional warnings and messages
12659 By default, @value{GDBN} is silent about its inner workings. If you are
12660 running on a slow machine, you may want to use the @code{set verbose}
12661 command. This makes @value{GDBN} tell you when it does a lengthy
12662 internal operation, so you will not think it has crashed.
12664 Currently, the messages controlled by @code{set verbose} are those
12665 which announce that the symbol table for a source file is being read;
12666 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12669 @kindex set verbose
12670 @item set verbose on
12671 Enables @value{GDBN} output of certain informational messages.
12673 @item set verbose off
12674 Disables @value{GDBN} output of certain informational messages.
12676 @kindex show verbose
12678 Displays whether @code{set verbose} is on or off.
12681 By default, if @value{GDBN} encounters bugs in the symbol table of an
12682 object file, it is silent; but if you are debugging a compiler, you may
12683 find this information useful (@pxref{Symbol Errors, ,Errors reading
12688 @kindex set complaints
12689 @item set complaints @var{limit}
12690 Permits @value{GDBN} to output @var{limit} complaints about each type of
12691 unusual symbols before becoming silent about the problem. Set
12692 @var{limit} to zero to suppress all complaints; set it to a large number
12693 to prevent complaints from being suppressed.
12695 @kindex show complaints
12696 @item show complaints
12697 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12701 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12702 lot of stupid questions to confirm certain commands. For example, if
12703 you try to run a program which is already running:
12707 The program being debugged has been started already.
12708 Start it from the beginning? (y or n)
12711 If you are willing to unflinchingly face the consequences of your own
12712 commands, you can disable this ``feature'':
12716 @kindex set confirm
12718 @cindex confirmation
12719 @cindex stupid questions
12720 @item set confirm off
12721 Disables confirmation requests.
12723 @item set confirm on
12724 Enables confirmation requests (the default).
12726 @kindex show confirm
12728 Displays state of confirmation requests.
12732 @node Debugging Output
12733 @section Optional messages about internal happenings
12735 @kindex set debug arch
12736 @item set debug arch
12737 Turns on or off display of gdbarch debugging info. The default is off
12738 @kindex show debug arch
12739 @item show debug arch
12740 Displays the current state of displaying gdbarch debugging info.
12741 @kindex set debug event
12742 @item set debug event
12743 Turns on or off display of @value{GDBN} event debugging info. The
12745 @kindex show debug event
12746 @item show debug event
12747 Displays the current state of displaying @value{GDBN} event debugging
12749 @kindex set debug expression
12750 @item set debug expression
12751 Turns on or off display of @value{GDBN} expression debugging info. The
12753 @kindex show debug expression
12754 @item show debug expression
12755 Displays the current state of displaying @value{GDBN} expression
12757 @kindex set debug overload
12758 @item set debug overload
12759 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12760 info. This includes info such as ranking of functions, etc. The default
12762 @kindex show debug overload
12763 @item show debug overload
12764 Displays the current state of displaying @value{GDBN} C@t{++} overload
12766 @kindex set debug remote
12767 @cindex packets, reporting on stdout
12768 @cindex serial connections, debugging
12769 @item set debug remote
12770 Turns on or off display of reports on all packets sent back and forth across
12771 the serial line to the remote machine. The info is printed on the
12772 @value{GDBN} standard output stream. The default is off.
12773 @kindex show debug remote
12774 @item show debug remote
12775 Displays the state of display of remote packets.
12776 @kindex set debug serial
12777 @item set debug serial
12778 Turns on or off display of @value{GDBN} serial debugging info. The
12780 @kindex show debug serial
12781 @item show debug serial
12782 Displays the current state of displaying @value{GDBN} serial debugging
12784 @kindex set debug target
12785 @item set debug target
12786 Turns on or off display of @value{GDBN} target debugging info. This info
12787 includes what is going on at the target level of GDB, as it happens. The
12789 @kindex show debug target
12790 @item show debug target
12791 Displays the current state of displaying @value{GDBN} target debugging
12793 @kindex set debug varobj
12794 @item set debug varobj
12795 Turns on or off display of @value{GDBN} variable object debugging
12796 info. The default is off.
12797 @kindex show debug varobj
12798 @item show debug varobj
12799 Displays the current state of displaying @value{GDBN} variable object
12804 @chapter Canned Sequences of Commands
12806 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12807 command lists}), @value{GDBN} provides two ways to store sequences of
12808 commands for execution as a unit: user-defined commands and command
12812 * Define:: User-defined commands
12813 * Hooks:: User-defined command hooks
12814 * Command Files:: Command files
12815 * Output:: Commands for controlled output
12819 @section User-defined commands
12821 @cindex user-defined command
12822 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12823 which you assign a new name as a command. This is done with the
12824 @code{define} command. User commands may accept up to 10 arguments
12825 separated by whitespace. Arguments are accessed within the user command
12826 via @var{$arg0@dots{}$arg9}. A trivial example:
12830 print $arg0 + $arg1 + $arg2
12834 To execute the command use:
12841 This defines the command @code{adder}, which prints the sum of
12842 its three arguments. Note the arguments are text substitutions, so they may
12843 reference variables, use complex expressions, or even perform inferior
12849 @item define @var{commandname}
12850 Define a command named @var{commandname}. If there is already a command
12851 by that name, you are asked to confirm that you want to redefine it.
12853 The definition of the command is made up of other @value{GDBN} command lines,
12854 which are given following the @code{define} command. The end of these
12855 commands is marked by a line containing @code{end}.
12860 Takes a single argument, which is an expression to evaluate.
12861 It is followed by a series of commands that are executed
12862 only if the expression is true (nonzero).
12863 There can then optionally be a line @code{else}, followed
12864 by a series of commands that are only executed if the expression
12865 was false. The end of the list is marked by a line containing @code{end}.
12869 The syntax is similar to @code{if}: the command takes a single argument,
12870 which is an expression to evaluate, and must be followed by the commands to
12871 execute, one per line, terminated by an @code{end}.
12872 The commands are executed repeatedly as long as the expression
12876 @item document @var{commandname}
12877 Document the user-defined command @var{commandname}, so that it can be
12878 accessed by @code{help}. The command @var{commandname} must already be
12879 defined. This command reads lines of documentation just as @code{define}
12880 reads the lines of the command definition, ending with @code{end}.
12881 After the @code{document} command is finished, @code{help} on command
12882 @var{commandname} displays the documentation you have written.
12884 You may use the @code{document} command again to change the
12885 documentation of a command. Redefining the command with @code{define}
12886 does not change the documentation.
12888 @kindex help user-defined
12889 @item help user-defined
12890 List all user-defined commands, with the first line of the documentation
12895 @itemx show user @var{commandname}
12896 Display the @value{GDBN} commands used to define @var{commandname} (but
12897 not its documentation). If no @var{commandname} is given, display the
12898 definitions for all user-defined commands.
12900 @kindex show max-user-call-depth
12901 @kindex set max-user-call-depth
12902 @item show max-user-call-depth
12903 @itemx set max-user-call-depth
12904 The value of @code{max-user-call-depth} controls how many recursion
12905 levels are allowed in user-defined commands before GDB suspects an
12906 infinite recursion and aborts the command.
12910 When user-defined commands are executed, the
12911 commands of the definition are not printed. An error in any command
12912 stops execution of the user-defined command.
12914 If used interactively, commands that would ask for confirmation proceed
12915 without asking when used inside a user-defined command. Many @value{GDBN}
12916 commands that normally print messages to say what they are doing omit the
12917 messages when used in a user-defined command.
12920 @section User-defined command hooks
12921 @cindex command hooks
12922 @cindex hooks, for commands
12923 @cindex hooks, pre-command
12927 You may define @dfn{hooks}, which are a special kind of user-defined
12928 command. Whenever you run the command @samp{foo}, if the user-defined
12929 command @samp{hook-foo} exists, it is executed (with no arguments)
12930 before that command.
12932 @cindex hooks, post-command
12935 A hook may also be defined which is run after the command you executed.
12936 Whenever you run the command @samp{foo}, if the user-defined command
12937 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12938 that command. Post-execution hooks may exist simultaneously with
12939 pre-execution hooks, for the same command.
12941 It is valid for a hook to call the command which it hooks. If this
12942 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12944 @c It would be nice if hookpost could be passed a parameter indicating
12945 @c if the command it hooks executed properly or not. FIXME!
12947 @kindex stop@r{, a pseudo-command}
12948 In addition, a pseudo-command, @samp{stop} exists. Defining
12949 (@samp{hook-stop}) makes the associated commands execute every time
12950 execution stops in your program: before breakpoint commands are run,
12951 displays are printed, or the stack frame is printed.
12953 For example, to ignore @code{SIGALRM} signals while
12954 single-stepping, but treat them normally during normal execution,
12959 handle SIGALRM nopass
12963 handle SIGALRM pass
12966 define hook-continue
12967 handle SIGLARM pass
12971 As a further example, to hook at the begining and end of the @code{echo}
12972 command, and to add extra text to the beginning and end of the message,
12980 define hookpost-echo
12984 (@value{GDBP}) echo Hello World
12985 <<<---Hello World--->>>
12990 You can define a hook for any single-word command in @value{GDBN}, but
12991 not for command aliases; you should define a hook for the basic command
12992 name, e.g. @code{backtrace} rather than @code{bt}.
12993 @c FIXME! So how does Joe User discover whether a command is an alias
12995 If an error occurs during the execution of your hook, execution of
12996 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12997 (before the command that you actually typed had a chance to run).
12999 If you try to define a hook which does not match any known command, you
13000 get a warning from the @code{define} command.
13002 @node Command Files
13003 @section Command files
13005 @cindex command files
13006 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
13007 commands. Comments (lines starting with @kbd{#}) may also be included.
13008 An empty line in a command file does nothing; it does not mean to repeat
13009 the last command, as it would from the terminal.
13012 @cindex @file{.gdbinit}
13013 @cindex @file{gdb.ini}
13014 When you start @value{GDBN}, it automatically executes commands from its
13015 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
13016 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
13017 limitations of file names imposed by DOS filesystems.}.
13018 During startup, @value{GDBN} does the following:
13022 Reads the init file (if any) in your home directory@footnote{On
13023 DOS/Windows systems, the home directory is the one pointed to by the
13024 @code{HOME} environment variable.}.
13027 Processes command line options and operands.
13030 Reads the init file (if any) in the current working directory.
13033 Reads command files specified by the @samp{-x} option.
13036 The init file in your home directory can set options (such as @samp{set
13037 complaints}) that affect subsequent processing of command line options
13038 and operands. Init files are not executed if you use the @samp{-nx}
13039 option (@pxref{Mode Options, ,Choosing modes}).
13041 @cindex init file name
13042 On some configurations of @value{GDBN}, the init file is known by a
13043 different name (these are typically environments where a specialized
13044 form of @value{GDBN} may need to coexist with other forms, hence a
13045 different name for the specialized version's init file). These are the
13046 environments with special init file names:
13048 @cindex @file{.vxgdbinit}
13051 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13053 @cindex @file{.os68gdbinit}
13055 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13057 @cindex @file{.esgdbinit}
13059 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13062 You can also request the execution of a command file with the
13063 @code{source} command:
13067 @item source @var{filename}
13068 Execute the command file @var{filename}.
13071 The lines in a command file are executed sequentially. They are not
13072 printed as they are executed. An error in any command terminates
13073 execution of the command file and control is returned to the console.
13075 Commands that would ask for confirmation if used interactively proceed
13076 without asking when used in a command file. Many @value{GDBN} commands that
13077 normally print messages to say what they are doing omit the messages
13078 when called from command files.
13080 @value{GDBN} also accepts command input from standard input. In this
13081 mode, normal output goes to standard output and error output goes to
13082 standard error. Errors in a command file supplied on standard input do
13083 not terminate execution of the command file --- execution continues with
13087 gdb < cmds > log 2>&1
13090 (The syntax above will vary depending on the shell used.) This example
13091 will execute commands from the file @file{cmds}. All output and errors
13092 would be directed to @file{log}.
13095 @section Commands for controlled output
13097 During the execution of a command file or a user-defined command, normal
13098 @value{GDBN} output is suppressed; the only output that appears is what is
13099 explicitly printed by the commands in the definition. This section
13100 describes three commands useful for generating exactly the output you
13105 @item echo @var{text}
13106 @c I do not consider backslash-space a standard C escape sequence
13107 @c because it is not in ANSI.
13108 Print @var{text}. Nonprinting characters can be included in
13109 @var{text} using C escape sequences, such as @samp{\n} to print a
13110 newline. @strong{No newline is printed unless you specify one.}
13111 In addition to the standard C escape sequences, a backslash followed
13112 by a space stands for a space. This is useful for displaying a
13113 string with spaces at the beginning or the end, since leading and
13114 trailing spaces are otherwise trimmed from all arguments.
13115 To print @samp{@w{ }and foo =@w{ }}, use the command
13116 @samp{echo \@w{ }and foo = \@w{ }}.
13118 A backslash at the end of @var{text} can be used, as in C, to continue
13119 the command onto subsequent lines. For example,
13122 echo This is some text\n\
13123 which is continued\n\
13124 onto several lines.\n
13127 produces the same output as
13130 echo This is some text\n
13131 echo which is continued\n
13132 echo onto several lines.\n
13136 @item output @var{expression}
13137 Print the value of @var{expression} and nothing but that value: no
13138 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13139 value history either. @xref{Expressions, ,Expressions}, for more information
13142 @item output/@var{fmt} @var{expression}
13143 Print the value of @var{expression} in format @var{fmt}. You can use
13144 the same formats as for @code{print}. @xref{Output Formats,,Output
13145 formats}, for more information.
13148 @item printf @var{string}, @var{expressions}@dots{}
13149 Print the values of the @var{expressions} under the control of
13150 @var{string}. The @var{expressions} are separated by commas and may be
13151 either numbers or pointers. Their values are printed as specified by
13152 @var{string}, exactly as if your program were to execute the C
13154 @c FIXME: the above implies that at least all ANSI C formats are
13155 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13156 @c Either this is a bug, or the manual should document what formats are
13160 printf (@var{string}, @var{expressions}@dots{});
13163 For example, you can print two values in hex like this:
13166 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13169 The only backslash-escape sequences that you can use in the format
13170 string are the simple ones that consist of backslash followed by a
13175 @chapter @value{GDBN} Text User Interface
13179 * TUI Overview:: TUI overview
13180 * TUI Keys:: TUI key bindings
13181 * TUI Single Key Mode:: TUI single key mode
13182 * TUI Commands:: TUI specific commands
13183 * TUI Configuration:: TUI configuration variables
13186 The @value{GDBN} Text User Interface, TUI in short,
13187 is a terminal interface which uses the @code{curses} library
13188 to show the source file, the assembly output, the program registers
13189 and @value{GDBN} commands in separate text windows.
13190 The TUI is available only when @value{GDBN} is configured
13191 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13194 @section TUI overview
13196 The TUI has two display modes that can be switched while
13201 A curses (or TUI) mode in which it displays several text
13202 windows on the terminal.
13205 A standard mode which corresponds to the @value{GDBN} configured without
13209 In the TUI mode, @value{GDBN} can display several text window
13214 This window is the @value{GDBN} command window with the @value{GDBN}
13215 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13216 managed using readline but through the TUI. The @emph{command}
13217 window is always visible.
13220 The source window shows the source file of the program. The current
13221 line as well as active breakpoints are displayed in this window.
13224 The assembly window shows the disassembly output of the program.
13227 This window shows the processor registers. It detects when
13228 a register is changed and when this is the case, registers that have
13229 changed are highlighted.
13233 The source and assembly windows show the current program position
13234 by highlighting the current line and marking them with the @samp{>} marker.
13235 Breakpoints are also indicated with two markers. A first one
13236 indicates the breakpoint type:
13240 Breakpoint which was hit at least once.
13243 Breakpoint which was never hit.
13246 Hardware breakpoint which was hit at least once.
13249 Hardware breakpoint which was never hit.
13253 The second marker indicates whether the breakpoint is enabled or not:
13257 Breakpoint is enabled.
13260 Breakpoint is disabled.
13264 The source, assembly and register windows are attached to the thread
13265 and the frame position. They are updated when the current thread
13266 changes, when the frame changes or when the program counter changes.
13267 These three windows are arranged by the TUI according to several
13268 layouts. The layout defines which of these three windows are visible.
13269 The following layouts are available:
13279 source and assembly
13282 source and registers
13285 assembly and registers
13289 On top of the command window a status line gives various information
13290 concerning the current process begin debugged. The status line is
13291 updated when the information it shows changes. The following fields
13296 Indicates the current gdb target
13297 (@pxref{Targets, ,Specifying a Debugging Target}).
13300 Gives information about the current process or thread number.
13301 When no process is being debugged, this field is set to @code{No process}.
13304 Gives the current function name for the selected frame.
13305 The name is demangled if demangling is turned on (@pxref{Print Settings}).
13306 When there is no symbol corresponding to the current program counter
13307 the string @code{??} is displayed.
13310 Indicates the current line number for the selected frame.
13311 When the current line number is not known the string @code{??} is displayed.
13314 Indicates the current program counter address.
13319 @section TUI Key Bindings
13320 @cindex TUI key bindings
13322 The TUI installs several key bindings in the readline keymaps
13323 (@pxref{Command Line Editing}).
13324 They allow to leave or enter in the TUI mode or they operate
13325 directly on the TUI layout and windows. The TUI also provides
13326 a @emph{SingleKey} keymap which binds several keys directly to
13327 @value{GDBN} commands. The following key bindings
13328 are installed for both TUI mode and the @value{GDBN} standard mode.
13337 Enter or leave the TUI mode. When the TUI mode is left,
13338 the curses window management is left and @value{GDBN} operates using
13339 its standard mode writing on the terminal directly. When the TUI
13340 mode is entered, the control is given back to the curses windows.
13341 The screen is then refreshed.
13345 Use a TUI layout with only one window. The layout will
13346 either be @samp{source} or @samp{assembly}. When the TUI mode
13347 is not active, it will switch to the TUI mode.
13349 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13353 Use a TUI layout with at least two windows. When the current
13354 layout shows already two windows, a next layout with two windows is used.
13355 When a new layout is chosen, one window will always be common to the
13356 previous layout and the new one.
13358 Think of it as the Emacs @kbd{C-x 2} binding.
13362 Use the TUI @emph{SingleKey} keymap that binds single key to gdb commands
13363 (@pxref{TUI Single Key Mode}).
13367 The following key bindings are handled only by the TUI mode:
13372 Scroll the active window one page up.
13376 Scroll the active window one page down.
13380 Scroll the active window one line up.
13384 Scroll the active window one line down.
13388 Scroll the active window one column left.
13392 Scroll the active window one column right.
13396 Refresh the screen.
13400 In the TUI mode, the arrow keys are used by the active window
13401 for scrolling. This means they are not available for readline. It is
13402 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13403 @key{C-b} and @key{C-f}.
13405 @node TUI Single Key Mode
13406 @section TUI Single Key Mode
13407 @cindex TUI single key mode
13409 The TUI provides a @emph{SingleKey} mode in which it installs a particular
13410 key binding in the readline keymaps to connect single keys to
13414 @kindex c @r{(SingleKey TUI key)}
13418 @kindex d @r{(SingleKey TUI key)}
13422 @kindex f @r{(SingleKey TUI key)}
13426 @kindex n @r{(SingleKey TUI key)}
13430 @kindex q @r{(SingleKey TUI key)}
13432 exit the @emph{SingleKey} mode.
13434 @kindex r @r{(SingleKey TUI key)}
13438 @kindex s @r{(SingleKey TUI key)}
13442 @kindex u @r{(SingleKey TUI key)}
13446 @kindex v @r{(SingleKey TUI key)}
13450 @kindex w @r{(SingleKey TUI key)}
13456 Other keys temporarily switch to the @value{GDBN} command prompt.
13457 The key that was pressed is inserted in the editing buffer so that
13458 it is possible to type most @value{GDBN} commands without interaction
13459 with the TUI @emph{SingleKey} mode. Once the command is entered the TUI
13460 @emph{SingleKey} mode is restored. The only way to permanently leave
13461 this mode is by hitting @key{q} or @samp{@key{C-x} @key{s}}.
13465 @section TUI specific commands
13466 @cindex TUI commands
13468 The TUI has specific commands to control the text windows.
13469 These commands are always available, that is they do not depend on
13470 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13471 is in the standard mode, using these commands will automatically switch
13477 List and give the size of all displayed windows.
13480 @kindex layout next
13481 Display the next layout.
13484 @kindex layout prev
13485 Display the previous layout.
13489 Display the source window only.
13493 Display the assembly window only.
13496 @kindex layout split
13497 Display the source and assembly window.
13500 @kindex layout regs
13501 Display the register window together with the source or assembly window.
13503 @item focus next | prev | src | asm | regs | split
13505 Set the focus to the named window.
13506 This command allows to change the active window so that scrolling keys
13507 can be affected to another window.
13511 Refresh the screen. This is similar to using @key{C-L} key.
13515 Update the source window and the current execution point.
13517 @item winheight @var{name} +@var{count}
13518 @itemx winheight @var{name} -@var{count}
13520 Change the height of the window @var{name} by @var{count}
13521 lines. Positive counts increase the height, while negative counts
13526 @node TUI Configuration
13527 @section TUI configuration variables
13528 @cindex TUI configuration variables
13530 The TUI has several configuration variables that control the
13531 appearance of windows on the terminal.
13534 @item set tui border-kind @var{kind}
13535 @kindex set tui border-kind
13536 Select the border appearance for the source, assembly and register windows.
13537 The possible values are the following:
13540 Use a space character to draw the border.
13543 Use ascii characters + - and | to draw the border.
13546 Use the Alternate Character Set to draw the border. The border is
13547 drawn using character line graphics if the terminal supports them.
13551 @item set tui active-border-mode @var{mode}
13552 @kindex set tui active-border-mode
13553 Select the attributes to display the border of the active window.
13554 The possible values are @code{normal}, @code{standout}, @code{reverse},
13555 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13557 @item set tui border-mode @var{mode}
13558 @kindex set tui border-mode
13559 Select the attributes to display the border of other windows.
13560 The @var{mode} can be one of the following:
13563 Use normal attributes to display the border.
13569 Use reverse video mode.
13572 Use half bright mode.
13574 @item half-standout
13575 Use half bright and standout mode.
13578 Use extra bright or bold mode.
13580 @item bold-standout
13581 Use extra bright or bold and standout mode.
13588 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13591 @cindex @sc{gnu} Emacs
13592 A special interface allows you to use @sc{gnu} Emacs to view (and
13593 edit) the source files for the program you are debugging with
13596 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13597 executable file you want to debug as an argument. This command starts
13598 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13599 created Emacs buffer.
13600 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13602 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13607 All ``terminal'' input and output goes through the Emacs buffer.
13610 This applies both to @value{GDBN} commands and their output, and to the input
13611 and output done by the program you are debugging.
13613 This is useful because it means that you can copy the text of previous
13614 commands and input them again; you can even use parts of the output
13617 All the facilities of Emacs' Shell mode are available for interacting
13618 with your program. In particular, you can send signals the usual
13619 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13624 @value{GDBN} displays source code through Emacs.
13627 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13628 source file for that frame and puts an arrow (@samp{=>}) at the
13629 left margin of the current line. Emacs uses a separate buffer for
13630 source display, and splits the screen to show both your @value{GDBN} session
13633 Explicit @value{GDBN} @code{list} or search commands still produce output as
13634 usual, but you probably have no reason to use them from Emacs.
13637 @emph{Warning:} If the directory where your program resides is not your
13638 current directory, it can be easy to confuse Emacs about the location of
13639 the source files, in which case the auxiliary display buffer does not
13640 appear to show your source. @value{GDBN} can find programs by searching your
13641 environment's @code{PATH} variable, so the @value{GDBN} input and output
13642 session proceeds normally; but Emacs does not get enough information
13643 back from @value{GDBN} to locate the source files in this situation. To
13644 avoid this problem, either start @value{GDBN} mode from the directory where
13645 your program resides, or specify an absolute file name when prompted for the
13646 @kbd{M-x gdb} argument.
13648 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13649 switch to debugging a program in some other location, from an existing
13650 @value{GDBN} buffer in Emacs.
13653 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13654 you need to call @value{GDBN} by a different name (for example, if you keep
13655 several configurations around, with different names) you can set the
13656 Emacs variable @code{gdb-command-name}; for example,
13659 (setq gdb-command-name "mygdb")
13663 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13664 in your @file{.emacs} file) makes Emacs call the program named
13665 ``@code{mygdb}'' instead.
13667 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13668 addition to the standard Shell mode commands:
13672 Describe the features of Emacs' @value{GDBN} Mode.
13675 Execute to another source line, like the @value{GDBN} @code{step} command; also
13676 update the display window to show the current file and location.
13679 Execute to next source line in this function, skipping all function
13680 calls, like the @value{GDBN} @code{next} command. Then update the display window
13681 to show the current file and location.
13684 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13685 display window accordingly.
13687 @item M-x gdb-nexti
13688 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13689 display window accordingly.
13692 Execute until exit from the selected stack frame, like the @value{GDBN}
13693 @code{finish} command.
13696 Continue execution of your program, like the @value{GDBN} @code{continue}
13699 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13702 Go up the number of frames indicated by the numeric argument
13703 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13704 like the @value{GDBN} @code{up} command.
13706 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13709 Go down the number of frames indicated by the numeric argument, like the
13710 @value{GDBN} @code{down} command.
13712 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13715 Read the number where the cursor is positioned, and insert it at the end
13716 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13717 around an address that was displayed earlier, type @kbd{disassemble};
13718 then move the cursor to the address display, and pick up the
13719 argument for @code{disassemble} by typing @kbd{C-x &}.
13721 You can customize this further by defining elements of the list
13722 @code{gdb-print-command}; once it is defined, you can format or
13723 otherwise process numbers picked up by @kbd{C-x &} before they are
13724 inserted. A numeric argument to @kbd{C-x &} indicates that you
13725 wish special formatting, and also acts as an index to pick an element of the
13726 list. If the list element is a string, the number to be inserted is
13727 formatted using the Emacs function @code{format}; otherwise the number
13728 is passed as an argument to the corresponding list element.
13731 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13732 tells @value{GDBN} to set a breakpoint on the source line point is on.
13734 If you accidentally delete the source-display buffer, an easy way to get
13735 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13736 request a frame display; when you run under Emacs, this recreates
13737 the source buffer if necessary to show you the context of the current
13740 The source files displayed in Emacs are in ordinary Emacs buffers
13741 which are visiting the source files in the usual way. You can edit
13742 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13743 communicates with Emacs in terms of line numbers. If you add or
13744 delete lines from the text, the line numbers that @value{GDBN} knows cease
13745 to correspond properly with the code.
13747 @c The following dropped because Epoch is nonstandard. Reactivate
13748 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13750 @kindex Emacs Epoch environment
13754 Version 18 of @sc{gnu} Emacs has a built-in window system
13755 called the @code{epoch}
13756 environment. Users of this environment can use a new command,
13757 @code{inspect} which performs identically to @code{print} except that
13758 each value is printed in its own window.
13761 @include annotate.texi
13762 @include gdbmi.texinfo
13765 @chapter Reporting Bugs in @value{GDBN}
13766 @cindex bugs in @value{GDBN}
13767 @cindex reporting bugs in @value{GDBN}
13769 Your bug reports play an essential role in making @value{GDBN} reliable.
13771 Reporting a bug may help you by bringing a solution to your problem, or it
13772 may not. But in any case the principal function of a bug report is to help
13773 the entire community by making the next version of @value{GDBN} work better. Bug
13774 reports are your contribution to the maintenance of @value{GDBN}.
13776 In order for a bug report to serve its purpose, you must include the
13777 information that enables us to fix the bug.
13780 * Bug Criteria:: Have you found a bug?
13781 * Bug Reporting:: How to report bugs
13785 @section Have you found a bug?
13786 @cindex bug criteria
13788 If you are not sure whether you have found a bug, here are some guidelines:
13791 @cindex fatal signal
13792 @cindex debugger crash
13793 @cindex crash of debugger
13795 If the debugger gets a fatal signal, for any input whatever, that is a
13796 @value{GDBN} bug. Reliable debuggers never crash.
13798 @cindex error on valid input
13800 If @value{GDBN} produces an error message for valid input, that is a
13801 bug. (Note that if you're cross debugging, the problem may also be
13802 somewhere in the connection to the target.)
13804 @cindex invalid input
13806 If @value{GDBN} does not produce an error message for invalid input,
13807 that is a bug. However, you should note that your idea of
13808 ``invalid input'' might be our idea of ``an extension'' or ``support
13809 for traditional practice''.
13812 If you are an experienced user of debugging tools, your suggestions
13813 for improvement of @value{GDBN} are welcome in any case.
13816 @node Bug Reporting
13817 @section How to report bugs
13818 @cindex bug reports
13819 @cindex @value{GDBN} bugs, reporting
13821 A number of companies and individuals offer support for @sc{gnu} products.
13822 If you obtained @value{GDBN} from a support organization, we recommend you
13823 contact that organization first.
13825 You can find contact information for many support companies and
13826 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13828 @c should add a web page ref...
13830 In any event, we also recommend that you submit bug reports for
13831 @value{GDBN}. The prefered method is to submit them directly using
13832 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
13833 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
13836 @strong{Do not send bug reports to @samp{info-gdb}, or to
13837 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13838 not want to receive bug reports. Those that do have arranged to receive
13841 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13842 serves as a repeater. The mailing list and the newsgroup carry exactly
13843 the same messages. Often people think of posting bug reports to the
13844 newsgroup instead of mailing them. This appears to work, but it has one
13845 problem which can be crucial: a newsgroup posting often lacks a mail
13846 path back to the sender. Thus, if we need to ask for more information,
13847 we may be unable to reach you. For this reason, it is better to send
13848 bug reports to the mailing list.
13850 The fundamental principle of reporting bugs usefully is this:
13851 @strong{report all the facts}. If you are not sure whether to state a
13852 fact or leave it out, state it!
13854 Often people omit facts because they think they know what causes the
13855 problem and assume that some details do not matter. Thus, you might
13856 assume that the name of the variable you use in an example does not matter.
13857 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13858 stray memory reference which happens to fetch from the location where that
13859 name is stored in memory; perhaps, if the name were different, the contents
13860 of that location would fool the debugger into doing the right thing despite
13861 the bug. Play it safe and give a specific, complete example. That is the
13862 easiest thing for you to do, and the most helpful.
13864 Keep in mind that the purpose of a bug report is to enable us to fix the
13865 bug. It may be that the bug has been reported previously, but neither
13866 you nor we can know that unless your bug report is complete and
13869 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13870 bell?'' Those bug reports are useless, and we urge everyone to
13871 @emph{refuse to respond to them} except to chide the sender to report
13874 To enable us to fix the bug, you should include all these things:
13878 The version of @value{GDBN}. @value{GDBN} announces it if you start
13879 with no arguments; you can also print it at any time using @code{show
13882 Without this, we will not know whether there is any point in looking for
13883 the bug in the current version of @value{GDBN}.
13886 The type of machine you are using, and the operating system name and
13890 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13891 ``@value{GCC}--2.8.1''.
13894 What compiler (and its version) was used to compile the program you are
13895 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13896 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13897 information; for other compilers, see the documentation for those
13901 The command arguments you gave the compiler to compile your example and
13902 observe the bug. For example, did you use @samp{-O}? To guarantee
13903 you will not omit something important, list them all. A copy of the
13904 Makefile (or the output from make) is sufficient.
13906 If we were to try to guess the arguments, we would probably guess wrong
13907 and then we might not encounter the bug.
13910 A complete input script, and all necessary source files, that will
13914 A description of what behavior you observe that you believe is
13915 incorrect. For example, ``It gets a fatal signal.''
13917 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13918 will certainly notice it. But if the bug is incorrect output, we might
13919 not notice unless it is glaringly wrong. You might as well not give us
13920 a chance to make a mistake.
13922 Even if the problem you experience is a fatal signal, you should still
13923 say so explicitly. Suppose something strange is going on, such as, your
13924 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13925 the C library on your system. (This has happened!) Your copy might
13926 crash and ours would not. If you told us to expect a crash, then when
13927 ours fails to crash, we would know that the bug was not happening for
13928 us. If you had not told us to expect a crash, then we would not be able
13929 to draw any conclusion from our observations.
13932 If you wish to suggest changes to the @value{GDBN} source, send us context
13933 diffs. If you even discuss something in the @value{GDBN} source, refer to
13934 it by context, not by line number.
13936 The line numbers in our development sources will not match those in your
13937 sources. Your line numbers would convey no useful information to us.
13941 Here are some things that are not necessary:
13945 A description of the envelope of the bug.
13947 Often people who encounter a bug spend a lot of time investigating
13948 which changes to the input file will make the bug go away and which
13949 changes will not affect it.
13951 This is often time consuming and not very useful, because the way we
13952 will find the bug is by running a single example under the debugger
13953 with breakpoints, not by pure deduction from a series of examples.
13954 We recommend that you save your time for something else.
13956 Of course, if you can find a simpler example to report @emph{instead}
13957 of the original one, that is a convenience for us. Errors in the
13958 output will be easier to spot, running under the debugger will take
13959 less time, and so on.
13961 However, simplification is not vital; if you do not want to do this,
13962 report the bug anyway and send us the entire test case you used.
13965 A patch for the bug.
13967 A patch for the bug does help us if it is a good one. But do not omit
13968 the necessary information, such as the test case, on the assumption that
13969 a patch is all we need. We might see problems with your patch and decide
13970 to fix the problem another way, or we might not understand it at all.
13972 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13973 construct an example that will make the program follow a certain path
13974 through the code. If you do not send us the example, we will not be able
13975 to construct one, so we will not be able to verify that the bug is fixed.
13977 And if we cannot understand what bug you are trying to fix, or why your
13978 patch should be an improvement, we will not install it. A test case will
13979 help us to understand.
13982 A guess about what the bug is or what it depends on.
13984 Such guesses are usually wrong. Even we cannot guess right about such
13985 things without first using the debugger to find the facts.
13988 @c The readline documentation is distributed with the readline code
13989 @c and consists of the two following files:
13991 @c inc-hist.texinfo
13992 @c Use -I with makeinfo to point to the appropriate directory,
13993 @c environment var TEXINPUTS with TeX.
13994 @include rluser.texinfo
13995 @include inc-hist.texinfo
13998 @node Formatting Documentation
13999 @appendix Formatting Documentation
14001 @cindex @value{GDBN} reference card
14002 @cindex reference card
14003 The @value{GDBN} 4 release includes an already-formatted reference card, ready
14004 for printing with PostScript or Ghostscript, in the @file{gdb}
14005 subdirectory of the main source directory@footnote{In
14006 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
14007 release.}. If you can use PostScript or Ghostscript with your printer,
14008 you can print the reference card immediately with @file{refcard.ps}.
14010 The release also includes the source for the reference card. You
14011 can format it, using @TeX{}, by typing:
14017 The @value{GDBN} reference card is designed to print in @dfn{landscape}
14018 mode on US ``letter'' size paper;
14019 that is, on a sheet 11 inches wide by 8.5 inches
14020 high. You will need to specify this form of printing as an option to
14021 your @sc{dvi} output program.
14023 @cindex documentation
14025 All the documentation for @value{GDBN} comes as part of the machine-readable
14026 distribution. The documentation is written in Texinfo format, which is
14027 a documentation system that uses a single source file to produce both
14028 on-line information and a printed manual. You can use one of the Info
14029 formatting commands to create the on-line version of the documentation
14030 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
14032 @value{GDBN} includes an already formatted copy of the on-line Info
14033 version of this manual in the @file{gdb} subdirectory. The main Info
14034 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
14035 subordinate files matching @samp{gdb.info*} in the same directory. If
14036 necessary, you can print out these files, or read them with any editor;
14037 but they are easier to read using the @code{info} subsystem in @sc{gnu}
14038 Emacs or the standalone @code{info} program, available as part of the
14039 @sc{gnu} Texinfo distribution.
14041 If you want to format these Info files yourself, you need one of the
14042 Info formatting programs, such as @code{texinfo-format-buffer} or
14045 If you have @code{makeinfo} installed, and are in the top level
14046 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
14047 version @value{GDBVN}), you can make the Info file by typing:
14054 If you want to typeset and print copies of this manual, you need @TeX{},
14055 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
14056 Texinfo definitions file.
14058 @TeX{} is a typesetting program; it does not print files directly, but
14059 produces output files called @sc{dvi} files. To print a typeset
14060 document, you need a program to print @sc{dvi} files. If your system
14061 has @TeX{} installed, chances are it has such a program. The precise
14062 command to use depends on your system; @kbd{lpr -d} is common; another
14063 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
14064 require a file name without any extension or a @samp{.dvi} extension.
14066 @TeX{} also requires a macro definitions file called
14067 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
14068 written in Texinfo format. On its own, @TeX{} cannot either read or
14069 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
14070 and is located in the @file{gdb-@var{version-number}/texinfo}
14073 If you have @TeX{} and a @sc{dvi} printer program installed, you can
14074 typeset and print this manual. First switch to the the @file{gdb}
14075 subdirectory of the main source directory (for example, to
14076 @file{gdb-@value{GDBVN}/gdb}) and type:
14082 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14084 @node Installing GDB
14085 @appendix Installing @value{GDBN}
14086 @cindex configuring @value{GDBN}
14087 @cindex installation
14089 @value{GDBN} comes with a @code{configure} script that automates the process
14090 of preparing @value{GDBN} for installation; you can then use @code{make} to
14091 build the @code{gdb} program.
14093 @c irrelevant in info file; it's as current as the code it lives with.
14094 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14095 look at the @file{README} file in the sources; we may have improved the
14096 installation procedures since publishing this manual.}
14099 The @value{GDBN} distribution includes all the source code you need for
14100 @value{GDBN} in a single directory, whose name is usually composed by
14101 appending the version number to @samp{gdb}.
14103 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14104 @file{gdb-@value{GDBVN}} directory. That directory contains:
14107 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14108 script for configuring @value{GDBN} and all its supporting libraries
14110 @item gdb-@value{GDBVN}/gdb
14111 the source specific to @value{GDBN} itself
14113 @item gdb-@value{GDBVN}/bfd
14114 source for the Binary File Descriptor library
14116 @item gdb-@value{GDBVN}/include
14117 @sc{gnu} include files
14119 @item gdb-@value{GDBVN}/libiberty
14120 source for the @samp{-liberty} free software library
14122 @item gdb-@value{GDBVN}/opcodes
14123 source for the library of opcode tables and disassemblers
14125 @item gdb-@value{GDBVN}/readline
14126 source for the @sc{gnu} command-line interface
14128 @item gdb-@value{GDBVN}/glob
14129 source for the @sc{gnu} filename pattern-matching subroutine
14131 @item gdb-@value{GDBVN}/mmalloc
14132 source for the @sc{gnu} memory-mapped malloc package
14135 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14136 from the @file{gdb-@var{version-number}} source directory, which in
14137 this example is the @file{gdb-@value{GDBVN}} directory.
14139 First switch to the @file{gdb-@var{version-number}} source directory
14140 if you are not already in it; then run @code{configure}. Pass the
14141 identifier for the platform on which @value{GDBN} will run as an
14147 cd gdb-@value{GDBVN}
14148 ./configure @var{host}
14153 where @var{host} is an identifier such as @samp{sun4} or
14154 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14155 (You can often leave off @var{host}; @code{configure} tries to guess the
14156 correct value by examining your system.)
14158 Running @samp{configure @var{host}} and then running @code{make} builds the
14159 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14160 libraries, then @code{gdb} itself. The configured source files, and the
14161 binaries, are left in the corresponding source directories.
14164 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14165 system does not recognize this automatically when you run a different
14166 shell, you may need to run @code{sh} on it explicitly:
14169 sh configure @var{host}
14172 If you run @code{configure} from a directory that contains source
14173 directories for multiple libraries or programs, such as the
14174 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14175 creates configuration files for every directory level underneath (unless
14176 you tell it not to, with the @samp{--norecursion} option).
14178 You can run the @code{configure} script from any of the
14179 subordinate directories in the @value{GDBN} distribution if you only want to
14180 configure that subdirectory, but be sure to specify a path to it.
14182 For example, with version @value{GDBVN}, type the following to configure only
14183 the @code{bfd} subdirectory:
14187 cd gdb-@value{GDBVN}/bfd
14188 ../configure @var{host}
14192 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14193 However, you should make sure that the shell on your path (named by
14194 the @samp{SHELL} environment variable) is publicly readable. Remember
14195 that @value{GDBN} uses the shell to start your program---some systems refuse to
14196 let @value{GDBN} debug child processes whose programs are not readable.
14199 * Separate Objdir:: Compiling @value{GDBN} in another directory
14200 * Config Names:: Specifying names for hosts and targets
14201 * Configure Options:: Summary of options for configure
14204 @node Separate Objdir
14205 @section Compiling @value{GDBN} in another directory
14207 If you want to run @value{GDBN} versions for several host or target machines,
14208 you need a different @code{gdb} compiled for each combination of
14209 host and target. @code{configure} is designed to make this easy by
14210 allowing you to generate each configuration in a separate subdirectory,
14211 rather than in the source directory. If your @code{make} program
14212 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14213 @code{make} in each of these directories builds the @code{gdb}
14214 program specified there.
14216 To build @code{gdb} in a separate directory, run @code{configure}
14217 with the @samp{--srcdir} option to specify where to find the source.
14218 (You also need to specify a path to find @code{configure}
14219 itself from your working directory. If the path to @code{configure}
14220 would be the same as the argument to @samp{--srcdir}, you can leave out
14221 the @samp{--srcdir} option; it is assumed.)
14223 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14224 separate directory for a Sun 4 like this:
14228 cd gdb-@value{GDBVN}
14231 ../gdb-@value{GDBVN}/configure sun4
14236 When @code{configure} builds a configuration using a remote source
14237 directory, it creates a tree for the binaries with the same structure
14238 (and using the same names) as the tree under the source directory. In
14239 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14240 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14241 @file{gdb-sun4/gdb}.
14243 One popular reason to build several @value{GDBN} configurations in separate
14244 directories is to configure @value{GDBN} for cross-compiling (where
14245 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14246 programs that run on another machine---the @dfn{target}).
14247 You specify a cross-debugging target by
14248 giving the @samp{--target=@var{target}} option to @code{configure}.
14250 When you run @code{make} to build a program or library, you must run
14251 it in a configured directory---whatever directory you were in when you
14252 called @code{configure} (or one of its subdirectories).
14254 The @code{Makefile} that @code{configure} generates in each source
14255 directory also runs recursively. If you type @code{make} in a source
14256 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14257 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14258 will build all the required libraries, and then build GDB.
14260 When you have multiple hosts or targets configured in separate
14261 directories, you can run @code{make} on them in parallel (for example,
14262 if they are NFS-mounted on each of the hosts); they will not interfere
14266 @section Specifying names for hosts and targets
14268 The specifications used for hosts and targets in the @code{configure}
14269 script are based on a three-part naming scheme, but some short predefined
14270 aliases are also supported. The full naming scheme encodes three pieces
14271 of information in the following pattern:
14274 @var{architecture}-@var{vendor}-@var{os}
14277 For example, you can use the alias @code{sun4} as a @var{host} argument,
14278 or as the value for @var{target} in a @code{--target=@var{target}}
14279 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14281 The @code{configure} script accompanying @value{GDBN} does not provide
14282 any query facility to list all supported host and target names or
14283 aliases. @code{configure} calls the Bourne shell script
14284 @code{config.sub} to map abbreviations to full names; you can read the
14285 script, if you wish, or you can use it to test your guesses on
14286 abbreviations---for example:
14289 % sh config.sub i386-linux
14291 % sh config.sub alpha-linux
14292 alpha-unknown-linux-gnu
14293 % sh config.sub hp9k700
14295 % sh config.sub sun4
14296 sparc-sun-sunos4.1.1
14297 % sh config.sub sun3
14298 m68k-sun-sunos4.1.1
14299 % sh config.sub i986v
14300 Invalid configuration `i986v': machine `i986v' not recognized
14304 @code{config.sub} is also distributed in the @value{GDBN} source
14305 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14307 @node Configure Options
14308 @section @code{configure} options
14310 Here is a summary of the @code{configure} options and arguments that
14311 are most often useful for building @value{GDBN}. @code{configure} also has
14312 several other options not listed here. @inforef{What Configure
14313 Does,,configure.info}, for a full explanation of @code{configure}.
14316 configure @r{[}--help@r{]}
14317 @r{[}--prefix=@var{dir}@r{]}
14318 @r{[}--exec-prefix=@var{dir}@r{]}
14319 @r{[}--srcdir=@var{dirname}@r{]}
14320 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14321 @r{[}--target=@var{target}@r{]}
14326 You may introduce options with a single @samp{-} rather than
14327 @samp{--} if you prefer; but you may abbreviate option names if you use
14332 Display a quick summary of how to invoke @code{configure}.
14334 @item --prefix=@var{dir}
14335 Configure the source to install programs and files under directory
14338 @item --exec-prefix=@var{dir}
14339 Configure the source to install programs under directory
14342 @c avoid splitting the warning from the explanation:
14344 @item --srcdir=@var{dirname}
14345 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14346 @code{make} that implements the @code{VPATH} feature.}@*
14347 Use this option to make configurations in directories separate from the
14348 @value{GDBN} source directories. Among other things, you can use this to
14349 build (or maintain) several configurations simultaneously, in separate
14350 directories. @code{configure} writes configuration specific files in
14351 the current directory, but arranges for them to use the source in the
14352 directory @var{dirname}. @code{configure} creates directories under
14353 the working directory in parallel to the source directories below
14356 @item --norecursion
14357 Configure only the directory level where @code{configure} is executed; do not
14358 propagate configuration to subdirectories.
14360 @item --target=@var{target}
14361 Configure @value{GDBN} for cross-debugging programs running on the specified
14362 @var{target}. Without this option, @value{GDBN} is configured to debug
14363 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14365 There is no convenient way to generate a list of all available targets.
14367 @item @var{host} @dots{}
14368 Configure @value{GDBN} to run on the specified @var{host}.
14370 There is no convenient way to generate a list of all available hosts.
14373 There are many other options available as well, but they are generally
14374 needed for special purposes only.
14376 @node Maintenance Commands
14377 @appendix Maintenance Commands
14378 @cindex maintenance commands
14379 @cindex internal commands
14381 In addition to commands intended for @value{GDBN} users, @value{GDBN}
14382 includes a number of commands intended for @value{GDBN} developers.
14383 These commands are provided here for reference.
14386 @kindex maint info breakpoints
14387 @item @anchor{maint info breakpoints}maint info breakpoints
14388 Using the same format as @samp{info breakpoints}, display both the
14389 breakpoints you've set explicitly, and those @value{GDBN} is using for
14390 internal purposes. Internal breakpoints are shown with negative
14391 breakpoint numbers. The type column identifies what kind of breakpoint
14396 Normal, explicitly set breakpoint.
14399 Normal, explicitly set watchpoint.
14402 Internal breakpoint, used to handle correctly stepping through
14403 @code{longjmp} calls.
14405 @item longjmp resume
14406 Internal breakpoint at the target of a @code{longjmp}.
14409 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
14412 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
14415 Shared library events.
14419 @kindex maint internal-error
14420 @kindex maint internal-warning
14421 @item maint internal-error
14422 @itemx maint internal-warning
14423 Cause @value{GDBN} to call the internal function @code{internal_error}
14424 or @code{internal_warning} and hence behave as though an internal error
14425 or internal warning has been detected. In addition to reporting the
14426 internal problem, these functions give the user the opportunity to
14427 either quit @value{GDBN} or create a core file of the current
14428 @value{GDBN} session.
14431 (gdb) @kbd{maint internal-error testing, 1, 2}
14432 @dots{}/maint.c:121: internal-error: testing, 1, 2
14433 A problem internal to GDB has been detected. Further
14434 debugging may prove unreliable.
14435 Quit this debugging session? (y or n) @kbd{n}
14436 Create a core file? (y or n) @kbd{n}
14440 Takes an optional parameter that is used as the text of the error or
14443 @kindex maint print registers
14444 @kindex maint print raw-registers
14445 @kindex maint print cooked-registers
14446 @item maint print registers
14447 @itemx maint print raw-registers
14448 @itemx maint print cooked-registers
14449 Print @value{GDBN}'s internal register data structures.
14451 The command @samp{maint print raw-registers} includes the contents of
14452 the raw register cache; and the command @samp{maint print
14453 cooked-registers} includes the (cooked) value of all registers.
14454 @xref{Registers,, Registers, gdbint, @value{GDBN} Internals}.
14456 Takes an optional file parameter.
14461 @node Remote Protocol
14462 @appendix @value{GDBN} Remote Serial Protocol
14467 * Stop Reply Packets::
14468 * General Query Packets::
14469 * Register Packet Format::
14476 There may be occasions when you need to know something about the
14477 protocol---for example, if there is only one serial port to your target
14478 machine, you might want your program to do something special if it
14479 recognizes a packet meant for @value{GDBN}.
14481 In the examples below, @samp{->} and @samp{<-} are used to indicate
14482 transmitted and received data respectfully.
14484 @cindex protocol, @value{GDBN} remote serial
14485 @cindex serial protocol, @value{GDBN} remote
14486 @cindex remote serial protocol
14487 All @value{GDBN} commands and responses (other than acknowledgments) are
14488 sent as a @var{packet}. A @var{packet} is introduced with the character
14489 @samp{$}, the actual @var{packet-data}, and the terminating character
14490 @samp{#} followed by a two-digit @var{checksum}:
14493 @code{$}@var{packet-data}@code{#}@var{checksum}
14497 @cindex checksum, for @value{GDBN} remote
14499 The two-digit @var{checksum} is computed as the modulo 256 sum of all
14500 characters between the leading @samp{$} and the trailing @samp{#} (an
14501 eight bit unsigned checksum).
14503 Implementors should note that prior to @value{GDBN} 5.0 the protocol
14504 specification also included an optional two-digit @var{sequence-id}:
14507 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
14510 @cindex sequence-id, for @value{GDBN} remote
14512 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
14513 has never output @var{sequence-id}s. Stubs that handle packets added
14514 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
14516 @cindex acknowledgment, for @value{GDBN} remote
14517 When either the host or the target machine receives a packet, the first
14518 response expected is an acknowledgment: either @samp{+} (to indicate
14519 the package was received correctly) or @samp{-} (to request
14523 -> @code{$}@var{packet-data}@code{#}@var{checksum}
14528 The host (@value{GDBN}) sends @var{command}s, and the target (the
14529 debugging stub incorporated in your program) sends a @var{response}. In
14530 the case of step and continue @var{command}s, the response is only sent
14531 when the operation has completed (the target has again stopped).
14533 @var{packet-data} consists of a sequence of characters with the
14534 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
14537 Fields within the packet should be separated using @samp{,} @samp{;} or
14538 @cindex remote protocol, field separator
14539 @samp{:}. Except where otherwise noted all numbers are represented in
14540 @sc{hex} with leading zeros suppressed.
14542 Implementors should note that prior to @value{GDBN} 5.0, the character
14543 @samp{:} could not appear as the third character in a packet (as it
14544 would potentially conflict with the @var{sequence-id}).
14546 Response @var{data} can be run-length encoded to save space. A @samp{*}
14547 means that the next character is an @sc{ascii} encoding giving a repeat count
14548 which stands for that many repetitions of the character preceding the
14549 @samp{*}. The encoding is @code{n+29}, yielding a printable character
14550 where @code{n >=3} (which is where rle starts to win). The printable
14551 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
14552 value greater than 126 should not be used.
14554 Some remote systems have used a different run-length encoding mechanism
14555 loosely refered to as the cisco encoding. Following the @samp{*}
14556 character are two hex digits that indicate the size of the packet.
14563 means the same as "0000".
14565 The error response returned for some packets includes a two character
14566 error number. That number is not well defined.
14568 For any @var{command} not supported by the stub, an empty response
14569 (@samp{$#00}) should be returned. That way it is possible to extend the
14570 protocol. A newer @value{GDBN} can tell if a packet is supported based
14573 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
14574 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
14580 The following table provides a complete list of all currently defined
14581 @var{command}s and their corresponding response @var{data}.
14585 @item @code{!} --- extended mode
14586 @cindex @code{!} packet
14588 Enable extended mode. In extended mode, the remote server is made
14589 persistent. The @samp{R} packet is used to restart the program being
14595 The remote target both supports and has enabled extended mode.
14598 @item @code{?} --- last signal
14599 @cindex @code{?} packet
14601 Indicate the reason the target halted. The reply is the same as for
14605 @xref{Stop Reply Packets}, for the reply specifications.
14607 @item @code{a} --- reserved
14609 Reserved for future use.
14611 @item @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,@dots{}} --- set program arguments @strong{(reserved)}
14612 @cindex @code{A} packet
14614 Initialized @samp{argv[]} array passed into program. @var{arglen}
14615 specifies the number of bytes in the hex encoded byte stream @var{arg}.
14616 See @code{gdbserver} for more details.
14624 @item @code{b}@var{baud} --- set baud @strong{(deprecated)}
14625 @cindex @code{b} packet
14627 Change the serial line speed to @var{baud}.
14629 JTC: @emph{When does the transport layer state change? When it's
14630 received, or after the ACK is transmitted. In either case, there are
14631 problems if the command or the acknowledgment packet is dropped.}
14633 Stan: @emph{If people really wanted to add something like this, and get
14634 it working for the first time, they ought to modify ser-unix.c to send
14635 some kind of out-of-band message to a specially-setup stub and have the
14636 switch happen "in between" packets, so that from remote protocol's point
14637 of view, nothing actually happened.}
14639 @item @code{B}@var{addr},@var{mode} --- set breakpoint @strong{(deprecated)}
14640 @cindex @code{B} packet
14642 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
14643 breakpoint at @var{addr}.
14645 This packet has been replaced by the @samp{Z} and @samp{z} packets
14646 (@pxref{insert breakpoint or watchpoint packet}).
14648 @item @code{c}@var{addr} --- continue
14649 @cindex @code{c} packet
14651 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14655 @xref{Stop Reply Packets}, for the reply specifications.
14657 @item @code{C}@var{sig}@code{;}@var{addr} --- continue with signal
14658 @cindex @code{C} packet
14660 Continue with signal @var{sig} (hex signal number). If
14661 @code{;}@var{addr} is omitted, resume at same address.
14664 @xref{Stop Reply Packets}, for the reply specifications.
14666 @item @code{d} --- toggle debug @strong{(deprecated)}
14667 @cindex @code{d} packet
14671 @item @code{D} --- detach
14672 @cindex @code{D} packet
14674 Detach @value{GDBN} from the remote system. Sent to the remote target
14675 before @value{GDBN} disconnects.
14679 @item @emph{no response}
14680 @value{GDBN} does not check for any response after sending this packet.
14683 @item @code{e} --- reserved
14685 Reserved for future use.
14687 @item @code{E} --- reserved
14689 Reserved for future use.
14691 @item @code{f} --- reserved
14693 Reserved for future use.
14695 @item @code{F} --- reserved
14697 Reserved for future use.
14699 @item @code{g} --- read registers
14700 @anchor{read registers packet}
14701 @cindex @code{g} packet
14703 Read general registers.
14707 @item @var{XX@dots{}}
14708 Each byte of register data is described by two hex digits. The bytes
14709 with the register are transmitted in target byte order. The size of
14710 each register and their position within the @samp{g} @var{packet} are
14711 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE}
14712 and @var{REGISTER_NAME} macros. The specification of several standard
14713 @code{g} packets is specified below.
14718 @item @code{G}@var{XX@dots{}} --- write regs
14719 @cindex @code{G} packet
14721 @xref{read registers packet}, for a description of the @var{XX@dots{}}
14732 @item @code{h} --- reserved
14734 Reserved for future use.
14736 @item @code{H}@var{c}@var{t@dots{}} --- set thread
14737 @cindex @code{H} packet
14739 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
14740 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
14741 should be @samp{c} for step and continue operations, @samp{g} for other
14742 operations. The thread designator @var{t@dots{}} may be -1, meaning all
14743 the threads, a thread number, or zero which means pick any thread.
14754 @c 'H': How restrictive (or permissive) is the thread model. If a
14755 @c thread is selected and stopped, are other threads allowed
14756 @c to continue to execute? As I mentioned above, I think the
14757 @c semantics of each command when a thread is selected must be
14758 @c described. For example:
14760 @c 'g': If the stub supports threads and a specific thread is
14761 @c selected, returns the register block from that thread;
14762 @c otherwise returns current registers.
14764 @c 'G' If the stub supports threads and a specific thread is
14765 @c selected, sets the registers of the register block of
14766 @c that thread; otherwise sets current registers.
14768 @item @code{i}@var{addr}@code{,}@var{nnn} --- cycle step @strong{(draft)}
14769 @anchor{cycle step packet}
14770 @cindex @code{i} packet
14772 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
14773 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
14774 step starting at that address.
14776 @item @code{I} --- signal then cycle step @strong{(reserved)}
14777 @cindex @code{I} packet
14779 @xref{step with signal packet}. @xref{cycle step packet}.
14781 @item @code{j} --- reserved
14783 Reserved for future use.
14785 @item @code{J} --- reserved
14787 Reserved for future use.
14789 @item @code{k} --- kill request
14790 @cindex @code{k} packet
14792 FIXME: @emph{There is no description of how to operate when a specific
14793 thread context has been selected (i.e.@: does 'k' kill only that
14796 @item @code{K} --- reserved
14798 Reserved for future use.
14800 @item @code{l} --- reserved
14802 Reserved for future use.
14804 @item @code{L} --- reserved
14806 Reserved for future use.
14808 @item @code{m}@var{addr}@code{,}@var{length} --- read memory
14809 @cindex @code{m} packet
14811 Read @var{length} bytes of memory starting at address @var{addr}.
14812 Neither @value{GDBN} nor the stub assume that sized memory transfers are
14813 assumed using word aligned accesses. FIXME: @emph{A word aligned memory
14814 transfer mechanism is needed.}
14818 @item @var{XX@dots{}}
14819 @var{XX@dots{}} is mem contents. Can be fewer bytes than requested if able
14820 to read only part of the data. Neither @value{GDBN} nor the stub assume
14821 that sized memory transfers are assumed using word aligned
14822 accesses. FIXME: @emph{A word aligned memory transfer mechanism is
14828 @item @code{M}@var{addr},@var{length}@code{:}@var{XX@dots{}} --- write mem
14829 @cindex @code{M} packet
14831 Write @var{length} bytes of memory starting at address @var{addr}.
14832 @var{XX@dots{}} is the data.
14839 for an error (this includes the case where only part of the data was
14843 @item @code{n} --- reserved
14845 Reserved for future use.
14847 @item @code{N} --- reserved
14849 Reserved for future use.
14851 @item @code{o} --- reserved
14853 Reserved for future use.
14855 @item @code{O} --- reserved
14857 Reserved for future use.
14859 @item @code{p}@var{n@dots{}} --- read reg @strong{(reserved)}
14860 @cindex @code{p} packet
14862 @xref{write register packet}.
14866 @item @var{r@dots{}.}
14867 The hex encoded value of the register in target byte order.
14870 @item @code{P}@var{n@dots{}}@code{=}@var{r@dots{}} --- write register
14871 @anchor{write register packet}
14872 @cindex @code{P} packet
14874 Write register @var{n@dots{}} with value @var{r@dots{}}, which contains two hex
14875 digits for each byte in the register (target byte order).
14885 @item @code{q}@var{query} --- general query
14886 @anchor{general query packet}
14887 @cindex @code{q} packet
14889 Request info about @var{query}. In general @value{GDBN} queries have a
14890 leading upper case letter. Custom vendor queries should use a company
14891 prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may optionally
14892 be followed by a @samp{,} or @samp{;} separated list. Stubs must ensure
14893 that they match the full @var{query} name.
14897 @item @var{XX@dots{}}
14898 Hex encoded data from query. The reply can not be empty.
14902 Indicating an unrecognized @var{query}.
14905 @item @code{Q}@var{var}@code{=}@var{val} --- general set
14906 @cindex @code{Q} packet
14908 Set value of @var{var} to @var{val}.
14910 @xref{general query packet}, for a discussion of naming conventions.
14912 @item @code{r} --- reset @strong{(deprecated)}
14913 @cindex @code{r} packet
14915 Reset the entire system.
14917 @item @code{R}@var{XX} --- remote restart
14918 @cindex @code{R} packet
14920 Restart the program being debugged. @var{XX}, while needed, is ignored.
14921 This packet is only available in extended mode.
14925 @item @emph{no reply}
14926 The @samp{R} packet has no reply.
14929 @item @code{s}@var{addr} --- step
14930 @cindex @code{s} packet
14932 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14936 @xref{Stop Reply Packets}, for the reply specifications.
14938 @item @code{S}@var{sig}@code{;}@var{addr} --- step with signal
14939 @anchor{step with signal packet}
14940 @cindex @code{S} packet
14942 Like @samp{C} but step not continue.
14945 @xref{Stop Reply Packets}, for the reply specifications.
14947 @item @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM} --- search
14948 @cindex @code{t} packet
14950 Search backwards starting at address @var{addr} for a match with pattern
14951 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
14952 @var{addr} must be at least 3 digits.
14954 @item @code{T}@var{XX} --- thread alive
14955 @cindex @code{T} packet
14957 Find out if the thread XX is alive.
14962 thread is still alive
14967 @item @code{u} --- reserved
14969 Reserved for future use.
14971 @item @code{U} --- reserved
14973 Reserved for future use.
14975 @item @code{v} --- reserved
14977 Reserved for future use.
14979 @item @code{V} --- reserved
14981 Reserved for future use.
14983 @item @code{w} --- reserved
14985 Reserved for future use.
14987 @item @code{W} --- reserved
14989 Reserved for future use.
14991 @item @code{x} --- reserved
14993 Reserved for future use.
14995 @item @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX@dots{}} --- write mem (binary)
14996 @cindex @code{X} packet
14998 @var{addr} is address, @var{length} is number of bytes, @var{XX@dots{}}
14999 is binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
15000 escaped using @code{0x7d}.
15010 @item @code{y} --- reserved
15012 Reserved for future use.
15014 @item @code{Y} reserved
15016 Reserved for future use.
15018 @item @code{z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- remove breakpoint or watchpoint @strong{(draft)}
15019 @itemx @code{Z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- insert breakpoint or watchpoint @strong{(draft)}
15020 @anchor{insert breakpoint or watchpoint packet}
15021 @cindex @code{z} packet
15022 @cindex @code{Z} packets
15024 Insert (@code{Z}) or remove (@code{z}) a @var{type} breakpoint or
15025 watchpoint starting at address @var{address} and covering the next
15026 @var{length} bytes.
15028 Each breakpoint and watchpoint packet @var{type} is documented
15031 @emph{Implementation notes: A remote target shall return an empty string
15032 for an unrecognized breakpoint or watchpoint packet @var{type}. A
15033 remote target shall support either both or neither of a given
15034 @code{Z}@var{type}@dots{} and @code{z}@var{type}@dots{} packet pair. To
15035 avoid potential problems with duplicate packets, the operations should
15036 be implemented in an idempotent way.}
15038 @item @code{z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- remove memory breakpoint @strong{(draft)}
15039 @item @code{Z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- insert memory breakpoint @strong{(draft)}
15040 @cindex @code{z0} packet
15041 @cindex @code{Z0} packet
15043 Insert (@code{Z0}) or remove (@code{z0}) a memory breakpoint at address
15044 @code{addr} of size @code{length}.
15046 A memory breakpoint is implemented by replacing the instruction at
15047 @var{addr} with a software breakpoint or trap instruction. The
15048 @code{length} is used by targets that indicates the size of the
15049 breakpoint (in bytes) that should be inserted (e.g., the @sc{arm} and
15050 @sc{mips} can insert either a 2 or 4 byte breakpoint).
15052 @emph{Implementation note: It is possible for a target to copy or move
15053 code that contains memory breakpoints (e.g., when implementing
15054 overlays). The behavior of this packet, in the presence of such a
15055 target, is not defined.}
15067 @item @code{z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- remove hardware breakpoint @strong{(draft)}
15068 @item @code{Z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- insert hardware breakpoint @strong{(draft)}
15069 @cindex @code{z1} packet
15070 @cindex @code{Z1} packet
15072 Insert (@code{Z1}) or remove (@code{z1}) a hardware breakpoint at
15073 address @code{addr} of size @code{length}.
15075 A hardware breakpoint is implemented using a mechanism that is not
15076 dependant on being able to modify the target's memory.
15078 @emph{Implementation note: A hardware breakpoint is not affected by code
15091 @item @code{z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- remove write watchpoint @strong{(draft)}
15092 @item @code{Z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- insert write watchpoint @strong{(draft)}
15093 @cindex @code{z2} packet
15094 @cindex @code{Z2} packet
15096 Insert (@code{Z2}) or remove (@code{z2}) a write watchpoint.
15108 @item @code{z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- remove read watchpoint @strong{(draft)}
15109 @item @code{Z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- insert read watchpoint @strong{(draft)}
15110 @cindex @code{z3} packet
15111 @cindex @code{Z3} packet
15113 Insert (@code{Z3}) or remove (@code{z3}) a read watchpoint.
15125 @item @code{z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- remove access watchpoint @strong{(draft)}
15126 @item @code{Z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- insert access watchpoint @strong{(draft)}
15127 @cindex @code{z4} packet
15128 @cindex @code{Z4} packet
15130 Insert (@code{Z4}) or remove (@code{z4}) an access watchpoint.
15144 @node Stop Reply Packets
15145 @section Stop Reply Packets
15146 @cindex stop reply packets
15148 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
15149 receive any of the below as a reply. In the case of the @samp{C},
15150 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
15151 when the target halts. In the below the exact meaning of @samp{signal
15152 number} is poorly defined. In general one of the UNIX signal numbering
15153 conventions is used.
15158 @var{AA} is the signal number
15160 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
15161 @cindex @code{T} packet reply
15163 @var{AA} = two hex digit signal number; @var{n...} = register number
15164 (hex), @var{r...} = target byte ordered register contents, size defined
15165 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
15166 thread process ID, this is a hex integer; @var{n...} = (@samp{watch} |
15167 @samp{rwatch} | @samp{awatch}, @var{r...} = data address, this is a hex
15168 integer; @var{n...} = other string not starting with valid hex digit.
15169 @value{GDBN} should ignore this @var{n...}, @var{r...} pair and go on
15170 to the next. This way we can extend the protocol.
15174 The process exited, and @var{AA} is the exit status. This is only
15175 applicable to certain targets.
15179 The process terminated with signal @var{AA}.
15181 @item N@var{AA};@var{t@dots{}};@var{d@dots{}};@var{b@dots{}} @strong{(obsolete)}
15183 @var{AA} = signal number; @var{t@dots{}} = address of symbol
15184 @code{_start}; @var{d@dots{}} = base of data section; @var{b@dots{}} =
15185 base of bss section. @emph{Note: only used by Cisco Systems targets.
15186 The difference between this reply and the @samp{qOffsets} query is that
15187 the @samp{N} packet may arrive spontaneously whereas the @samp{qOffsets}
15188 is a query initiated by the host debugger.}
15190 @item O@var{XX@dots{}}
15192 @var{XX@dots{}} is hex encoding of @sc{ascii} data. This can happen at
15193 any time while the program is running and the debugger should continue
15194 to wait for @samp{W}, @samp{T}, etc.
15198 @node General Query Packets
15199 @section General Query Packets
15201 The following set and query packets have already been defined.
15205 @item @code{q}@code{C} --- current thread
15207 Return the current thread id.
15211 @item @code{QC}@var{pid}
15212 Where @var{pid} is a HEX encoded 16 bit process id.
15214 Any other reply implies the old pid.
15217 @item @code{q}@code{fThreadInfo} -- all thread ids
15219 @code{q}@code{sThreadInfo}
15221 Obtain a list of active thread ids from the target (OS). Since there
15222 may be too many active threads to fit into one reply packet, this query
15223 works iteratively: it may require more than one query/reply sequence to
15224 obtain the entire list of threads. The first query of the sequence will
15225 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
15226 sequence will be the @code{qs}@code{ThreadInfo} query.
15228 NOTE: replaces the @code{qL} query (see below).
15232 @item @code{m}@var{id}
15234 @item @code{m}@var{id},@var{id}@dots{}
15235 a comma-separated list of thread ids
15237 (lower case 'el') denotes end of list.
15240 In response to each query, the target will reply with a list of one or
15241 more thread ids, in big-endian hex, separated by commas. @value{GDBN}
15242 will respond to each reply with a request for more thread ids (using the
15243 @code{qs} form of the query), until the target responds with @code{l}
15244 (lower-case el, for @code{'last'}).
15246 @item @code{q}@code{ThreadExtraInfo}@code{,}@var{id} --- extra thread info
15248 Where @var{id} is a thread-id in big-endian hex. Obtain a printable
15249 string description of a thread's attributes from the target OS. This
15250 string may contain anything that the target OS thinks is interesting for
15251 @value{GDBN} to tell the user about the thread. The string is displayed
15252 in @value{GDBN}'s @samp{info threads} display. Some examples of
15253 possible thread extra info strings are ``Runnable'', or ``Blocked on
15258 @item @var{XX@dots{}}
15259 Where @var{XX@dots{}} is a hex encoding of @sc{ascii} data, comprising
15260 the printable string containing the extra information about the thread's
15264 @item @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread} --- query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
15266 Obtain thread information from RTOS. Where: @var{startflag} (one hex
15267 digit) is one to indicate the first query and zero to indicate a
15268 subsequent query; @var{threadcount} (two hex digits) is the maximum
15269 number of threads the response packet can contain; and @var{nextthread}
15270 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
15271 returned in the response as @var{argthread}.
15273 NOTE: this query is replaced by the @code{q}@code{fThreadInfo} query
15278 @item @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread@dots{}}
15279 Where: @var{count} (two hex digits) is the number of threads being
15280 returned; @var{done} (one hex digit) is zero to indicate more threads
15281 and one indicates no further threads; @var{argthreadid} (eight hex
15282 digits) is @var{nextthread} from the request packet; @var{thread@dots{}}
15283 is a sequence of thread IDs from the target. @var{threadid} (eight hex
15284 digits). See @code{remote.c:parse_threadlist_response()}.
15287 @item @code{q}@code{CRC:}@var{addr}@code{,}@var{length} --- compute CRC of memory block
15291 @item @code{E}@var{NN}
15292 An error (such as memory fault)
15293 @item @code{C}@var{CRC32}
15294 A 32 bit cyclic redundancy check of the specified memory region.
15297 @item @code{q}@code{Offsets} --- query sect offs
15299 Get section offsets that the target used when re-locating the downloaded
15300 image. @emph{Note: while a @code{Bss} offset is included in the
15301 response, @value{GDBN} ignores this and instead applies the @code{Data}
15302 offset to the @code{Bss} section.}
15306 @item @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
15309 @item @code{q}@code{P}@var{mode}@var{threadid} --- thread info request
15311 Returns information on @var{threadid}. Where: @var{mode} is a hex
15312 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
15319 See @code{remote.c:remote_unpack_thread_info_response()}.
15321 @item @code{q}@code{Rcmd,}@var{command} --- remote command
15323 @var{command} (hex encoded) is passed to the local interpreter for
15324 execution. Invalid commands should be reported using the output string.
15325 Before the final result packet, the target may also respond with a
15326 number of intermediate @code{O}@var{output} console output packets.
15327 @emph{Implementors should note that providing access to a stubs's
15328 interpreter may have security implications}.
15333 A command response with no output.
15335 A command response with the hex encoded output string @var{OUTPUT}.
15336 @item @code{E}@var{NN}
15337 Indicate a badly formed request.
15339 When @samp{q}@samp{Rcmd} is not recognized.
15342 @item @code{qSymbol::} --- symbol lookup
15344 Notify the target that @value{GDBN} is prepared to serve symbol lookup
15345 requests. Accept requests from the target for the values of symbols.
15350 The target does not need to look up any (more) symbols.
15351 @item @code{qSymbol:}@var{sym_name}
15352 The target requests the value of symbol @var{sym_name} (hex encoded).
15353 @value{GDBN} may provide the value by using the
15354 @code{qSymbol:}@var{sym_value}:@var{sym_name} message, described below.
15357 @item @code{qSymbol:}@var{sym_value}:@var{sym_name} --- symbol value
15359 Set the value of @var{sym_name} to @var{sym_value}.
15361 @var{sym_name} (hex encoded) is the name of a symbol whose value the
15362 target has previously requested.
15364 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
15365 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
15371 The target does not need to look up any (more) symbols.
15372 @item @code{qSymbol:}@var{sym_name}
15373 The target requests the value of a new symbol @var{sym_name} (hex
15374 encoded). @value{GDBN} will continue to supply the values of symbols
15375 (if available), until the target ceases to request them.
15380 @node Register Packet Format
15381 @section Register Packet Format
15383 The following @samp{g}/@samp{G} packets have previously been defined.
15384 In the below, some thirty-two bit registers are transferred as
15385 sixty-four bits. Those registers should be zero/sign extended (which?)
15386 to fill the space allocated. Register bytes are transfered in target
15387 byte order. The two nibbles within a register byte are transfered
15388 most-significant - least-significant.
15394 All registers are transfered as thirty-two bit quantities in the order:
15395 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
15396 registers; fsr; fir; fp.
15400 All registers are transfered as sixty-four bit quantities (including
15401 thirty-two bit registers such as @code{sr}). The ordering is the same
15409 Example sequence of a target being re-started. Notice how the restart
15410 does not get any direct output:
15415 @emph{target restarts}
15418 <- @code{T001:1234123412341234}
15422 Example sequence of a target being stepped by a single instruction:
15425 -> @code{G1445@dots{}}
15430 <- @code{T001:1234123412341234}
15434 <- @code{1455@dots{}}
15448 % I think something like @colophon should be in texinfo. In the
15450 \long\def\colophon{\hbox to0pt{}\vfill
15451 \centerline{The body of this manual is set in}
15452 \centerline{\fontname\tenrm,}
15453 \centerline{with headings in {\bf\fontname\tenbf}}
15454 \centerline{and examples in {\tt\fontname\tentt}.}
15455 \centerline{{\it\fontname\tenit\/},}
15456 \centerline{{\bf\fontname\tenbf}, and}
15457 \centerline{{\sl\fontname\tensl\/}}
15458 \centerline{are used for emphasis.}\vfill}
15460 % Blame: doc@cygnus.com, 1991.