1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
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 THIS MANUAL REQUIRES TEXINFO 3.12 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Programming & development tools.
42 * Gdb: (gdb). The @sc{gnu} debugger.
46 This file documents the @sc{gnu} debugger @value{GDBN}.
49 This is the @value{EDITION} Edition, @value{DATE},
50 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
51 for @value{GDBN} Version @value{GDBVN}.
53 Copyright (C) 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
54 Free Software Foundation, Inc.
56 Permission is granted to copy, distribute and/or modify this document
57 under the terms of the GNU Free Documentation License, Version 1.1 or
58 any later version published by the Free Software Foundation; with the
59 Invariant Sections being ``A Sample GDB Session'' and ``Free
60 Software'', with the Front-Cover texts being ``A GNU Manual,'' and
61 with the Back-Cover Texts as in (a) below.
63 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
64 this GNU Manual, like GNU software. Copies published by the Free
65 Software Foundation raise funds for GNU development.''
69 @title Debugging with @value{GDBN}
70 @subtitle The @sc{gnu} Source-Level Debugger
72 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
73 @subtitle @value{DATE}
74 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
78 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
79 \hfill {\it Debugging with @value{GDBN}}\par
80 \hfill \TeX{}info \texinfoversion\par
84 @vskip 0pt plus 1filll
85 Copyright @copyright{} 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
86 Free Software Foundation, Inc.
88 Published by the Free Software Foundation @*
89 59 Temple Place - Suite 330, @*
90 Boston, MA 02111-1307 USA @*
93 Permission is granted to copy, distribute and/or modify this document
94 under the terms of the GNU Free Documentation License, Version 1.1 or
95 any later version published by the Free Software Foundation; with the
96 Invariant Sections being ``A Sample GDB Session'' and ``Free
97 Software'', with the Front-Cover texts being ``A GNU Manual,'' and
98 with the Back-Cover Texts as in (a) below.
100 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
101 this GNU Manual, like GNU software. Copies published by the Free
102 Software Foundation raise funds for GNU development.''
107 @node Top, Summary, (dir), (dir)
109 @top Debugging with @value{GDBN}
111 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
113 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
116 Copyright (C) 1988-2001 Free Software Foundation, Inc.
119 * Summary:: Summary of @value{GDBN}
120 * Sample Session:: A sample @value{GDBN} session
122 * Invocation:: Getting in and out of @value{GDBN}
123 * Commands:: @value{GDBN} commands
124 * Running:: Running programs under @value{GDBN}
125 * Stopping:: Stopping and continuing
126 * Stack:: Examining the stack
127 * Source:: Examining source files
128 * Data:: Examining data
129 * Tracepoints:: Debugging remote targets non-intrusively
131 * Languages:: Using @value{GDBN} with different languages
133 * Symbols:: Examining the symbol table
134 * Altering:: Altering execution
135 * GDB Files:: @value{GDBN} files
136 * Targets:: Specifying a debugging target
137 * Configurations:: Configuration-specific information
138 * Controlling GDB:: Controlling @value{GDBN}
139 * Sequences:: Canned sequences of commands
140 * TUI:: @value{GDBN} Text User Interface
141 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
142 * Annotations:: @value{GDBN}'s annotation interface.
143 * GDB/MI:: @value{GDBN}'s Machine Interface.
145 * GDB Bugs:: Reporting bugs in @value{GDBN}
146 * Formatting Documentation:: How to format and print @value{GDBN} documentation
148 * Command Line Editing:: Command Line Editing
149 * Using History Interactively:: Using History Interactively
150 * Installing GDB:: Installing GDB
156 @c the replication sucks, but this avoids a texinfo 3.12 lameness
161 @top Debugging with @value{GDBN}
163 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
165 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
168 Copyright (C) 1988-2000 Free Software Foundation, Inc.
171 * Summary:: Summary of @value{GDBN}
172 * Sample Session:: A sample @value{GDBN} session
174 * Invocation:: Getting in and out of @value{GDBN}
175 * Commands:: @value{GDBN} commands
176 * Running:: Running programs under @value{GDBN}
177 * Stopping:: Stopping and continuing
178 * Stack:: Examining the stack
179 * Source:: Examining source files
180 * Data:: Examining data
181 * Tracepoints:: Debugging remote targets non-intrusively
183 * Languages:: Using @value{GDBN} with different languages
185 * Symbols:: Examining the symbol table
186 * Altering:: Altering execution
187 * GDB Files:: @value{GDBN} files
188 * Targets:: Specifying a debugging target
189 * Configurations:: Configuration-specific information
190 * Controlling GDB:: Controlling @value{GDBN}
191 * Sequences:: Canned sequences of commands
192 * TUI:: @value{GDBN} Text User Interface
193 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
194 * Annotations:: @value{GDBN}'s annotation interface.
195 * GDB/MI:: @value{GDBN}'s Machine Interface.
197 * GDB Bugs:: Reporting bugs in @value{GDBN}
198 * Formatting Documentation:: How to format and print @value{GDBN} documentation
200 * Command Line Editing:: Command Line Editing
201 * Using History Interactively:: Using History Interactively
202 * Installing GDB:: Installing GDB
208 @c TeX can handle the contents at the start but makeinfo 3.12 can not
214 @unnumbered Summary of @value{GDBN}
216 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
217 going on ``inside'' another program while it executes---or what another
218 program was doing at the moment it crashed.
220 @value{GDBN} can do four main kinds of things (plus other things in support of
221 these) to help you catch bugs in the act:
225 Start your program, specifying anything that might affect its behavior.
228 Make your program stop on specified conditions.
231 Examine what has happened, when your program has stopped.
234 Change things in your program, so you can experiment with correcting the
235 effects of one bug and go on to learn about another.
238 You can use @value{GDBN} to debug programs written in C and C++.
239 For more information, see @ref{Support,,Supported languages}.
240 For more information, see @ref{C,,C and C++}.
244 Support for Modula-2 and Chill is partial. For information on Modula-2,
245 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
248 Debugging Pascal programs which use sets, subranges, file variables, or
249 nested functions does not currently work. @value{GDBN} does not support
250 entering expressions, printing values, or similar features using Pascal
254 @value{GDBN} can be used to debug programs written in Fortran, although
255 it may be necessary to refer to some variables with a trailing
259 * Free Software:: Freely redistributable software
260 * Contributors:: Contributors to GDB
264 @unnumberedsec Free software
266 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
267 General Public License
268 (GPL). The GPL gives you the freedom to copy or adapt a licensed
269 program---but every person getting a copy also gets with it the
270 freedom to modify that copy (which means that they must get access to
271 the source code), and the freedom to distribute further copies.
272 Typical software companies use copyrights to limit your freedoms; the
273 Free Software Foundation uses the GPL to preserve these freedoms.
275 Fundamentally, the General Public License is a license which says that
276 you have these freedoms and that you cannot take these freedoms away
280 @unnumberedsec Contributors to @value{GDBN}
282 Richard Stallman was the original author of @value{GDBN}, and of many
283 other @sc{gnu} programs. Many others have contributed to its
284 development. This section attempts to credit major contributors. One
285 of the virtues of free software is that everyone is free to contribute
286 to it; with regret, we cannot actually acknowledge everyone here. The
287 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
288 blow-by-blow account.
290 Changes much prior to version 2.0 are lost in the mists of time.
293 @emph{Plea:} Additions to this section are particularly welcome. If you
294 or your friends (or enemies, to be evenhanded) have been unfairly
295 omitted from this list, we would like to add your names!
298 So that they may not regard their many labors as thankless, we
299 particularly thank those who shepherded @value{GDBN} through major
301 Andrew Cagney (releases 5.0 and 5.1);
302 Jim Blandy (release 4.18);
303 Jason Molenda (release 4.17);
304 Stan Shebs (release 4.14);
305 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
306 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
307 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
308 Jim Kingdon (releases 3.5, 3.4, and 3.3);
309 and Randy Smith (releases 3.2, 3.1, and 3.0).
311 Richard Stallman, assisted at various times by Peter TerMaat, Chris
312 Hanson, and Richard Mlynarik, handled releases through 2.8.
314 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
315 in @value{GDBN}, with significant additional contributions from Per
316 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
317 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
318 much general update work leading to release 3.0).
320 @value{GDBN} uses the BFD subroutine library to examine multiple
321 object-file formats; BFD was a joint project of David V.
322 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
324 David Johnson wrote the original COFF support; Pace Willison did
325 the original support for encapsulated COFF.
327 Brent Benson of Harris Computer Systems contributed DWARF2 support.
329 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
330 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
332 Jean-Daniel Fekete contributed Sun 386i support.
333 Chris Hanson improved the HP9000 support.
334 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
335 David Johnson contributed Encore Umax support.
336 Jyrki Kuoppala contributed Altos 3068 support.
337 Jeff Law contributed HP PA and SOM support.
338 Keith Packard contributed NS32K support.
339 Doug Rabson contributed Acorn Risc Machine support.
340 Bob Rusk contributed Harris Nighthawk CX-UX support.
341 Chris Smith contributed Convex support (and Fortran debugging).
342 Jonathan Stone contributed Pyramid support.
343 Michael Tiemann contributed SPARC support.
344 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
345 Pace Willison contributed Intel 386 support.
346 Jay Vosburgh contributed Symmetry support.
348 Andreas Schwab contributed M68K Linux support.
350 Rich Schaefer and Peter Schauer helped with support of SunOS shared
353 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
354 about several machine instruction sets.
356 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
357 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
358 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
359 and RDI targets, respectively.
361 Brian Fox is the author of the readline libraries providing
362 command-line editing and command history.
364 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
365 Modula-2 support, and contributed the Languages chapter of this manual.
367 Fred Fish wrote most of the support for Unix System Vr4.
368 He also enhanced the command-completion support to cover C@t{++} overloaded
371 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
374 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
376 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
378 Toshiba sponsored the support for the TX39 Mips processor.
380 Matsushita sponsored the support for the MN10200 and MN10300 processors.
382 Fujitsu sponsored the support for SPARClite and FR30 processors.
384 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
387 Michael Snyder added support for tracepoints.
389 Stu Grossman wrote gdbserver.
391 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
392 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
394 The following people at the Hewlett-Packard Company contributed
395 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
396 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
397 compiler, and the terminal user interface: Ben Krepp, Richard Title,
398 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
399 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
400 information in this manual.
402 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
403 Robert Hoehne made significant contributions to the DJGPP port.
405 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
406 development since 1991. Cygnus engineers who have worked on @value{GDBN}
407 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
408 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
409 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
410 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
411 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
412 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
413 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
414 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
415 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
416 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
417 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
418 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
419 Zuhn have made contributions both large and small.
423 @chapter A Sample @value{GDBN} Session
425 You can use this manual at your leisure to read all about @value{GDBN}.
426 However, a handful of commands are enough to get started using the
427 debugger. This chapter illustrates those commands.
430 In this sample session, we emphasize user input like this: @b{input},
431 to make it easier to pick out from the surrounding output.
434 @c FIXME: this example may not be appropriate for some configs, where
435 @c FIXME...primary interest is in remote use.
437 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
438 processor) exhibits the following bug: sometimes, when we change its
439 quote strings from the default, the commands used to capture one macro
440 definition within another stop working. In the following short @code{m4}
441 session, we define a macro @code{foo} which expands to @code{0000}; we
442 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
443 same thing. However, when we change the open quote string to
444 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
445 procedure fails to define a new synonym @code{baz}:
454 @b{define(bar,defn(`foo'))}
458 @b{changequote(<QUOTE>,<UNQUOTE>)}
460 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
463 m4: End of input: 0: fatal error: EOF in string
467 Let us use @value{GDBN} to try to see what is going on.
470 $ @b{@value{GDBP} m4}
471 @c FIXME: this falsifies the exact text played out, to permit smallbook
472 @c FIXME... format to come out better.
473 @value{GDBN} is free software and you are welcome to distribute copies
474 of it under certain conditions; type "show copying" to see
476 There is absolutely no warranty for @value{GDBN}; type "show warranty"
479 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
484 @value{GDBN} reads only enough symbol data to know where to find the
485 rest when needed; as a result, the first prompt comes up very quickly.
486 We now tell @value{GDBN} to use a narrower display width than usual, so
487 that examples fit in this manual.
490 (@value{GDBP}) @b{set width 70}
494 We need to see how the @code{m4} built-in @code{changequote} works.
495 Having looked at the source, we know the relevant subroutine is
496 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
497 @code{break} command.
500 (@value{GDBP}) @b{break m4_changequote}
501 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
505 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
506 control; as long as control does not reach the @code{m4_changequote}
507 subroutine, the program runs as usual:
510 (@value{GDBP}) @b{run}
511 Starting program: /work/Editorial/gdb/gnu/m4/m4
519 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
520 suspends execution of @code{m4}, displaying information about the
521 context where it stops.
524 @b{changequote(<QUOTE>,<UNQUOTE>)}
526 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
528 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
532 Now we use the command @code{n} (@code{next}) to advance execution to
533 the next line of the current function.
537 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
542 @code{set_quotes} looks like a promising subroutine. We can go into it
543 by using the command @code{s} (@code{step}) instead of @code{next}.
544 @code{step} goes to the next line to be executed in @emph{any}
545 subroutine, so it steps into @code{set_quotes}.
549 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
551 530 if (lquote != def_lquote)
555 The display that shows the subroutine where @code{m4} is now
556 suspended (and its arguments) is called a stack frame display. It
557 shows a summary of the stack. We can use the @code{backtrace}
558 command (which can also be spelled @code{bt}), to see where we are
559 in the stack as a whole: the @code{backtrace} command displays a
560 stack frame for each active subroutine.
563 (@value{GDBP}) @b{bt}
564 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
566 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
568 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
569 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
571 #4 0x79dc in expand_input () at macro.c:40
572 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
576 We step through a few more lines to see what happens. The first two
577 times, we can use @samp{s}; the next two times we use @code{n} to avoid
578 falling into the @code{xstrdup} subroutine.
582 0x3b5c 532 if (rquote != def_rquote)
584 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
585 def_lquote : xstrdup(lq);
587 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
590 538 len_lquote = strlen(rquote);
594 The last line displayed looks a little odd; we can examine the variables
595 @code{lquote} and @code{rquote} to see if they are in fact the new left
596 and right quotes we specified. We use the command @code{p}
597 (@code{print}) to see their values.
600 (@value{GDBP}) @b{p lquote}
601 $1 = 0x35d40 "<QUOTE>"
602 (@value{GDBP}) @b{p rquote}
603 $2 = 0x35d50 "<UNQUOTE>"
607 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
608 To look at some context, we can display ten lines of source
609 surrounding the current line with the @code{l} (@code{list}) command.
615 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
617 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
620 538 len_lquote = strlen(rquote);
621 539 len_rquote = strlen(lquote);
628 Let us step past the two lines that set @code{len_lquote} and
629 @code{len_rquote}, and then examine the values of those variables.
633 539 len_rquote = strlen(lquote);
636 (@value{GDBP}) @b{p len_lquote}
638 (@value{GDBP}) @b{p len_rquote}
643 That certainly looks wrong, assuming @code{len_lquote} and
644 @code{len_rquote} are meant to be the lengths of @code{lquote} and
645 @code{rquote} respectively. We can set them to better values using
646 the @code{p} command, since it can print the value of
647 any expression---and that expression can include subroutine calls and
651 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
653 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
658 Is that enough to fix the problem of using the new quotes with the
659 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
660 executing with the @code{c} (@code{continue}) command, and then try the
661 example that caused trouble initially:
667 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
674 Success! The new quotes now work just as well as the default ones. The
675 problem seems to have been just the two typos defining the wrong
676 lengths. We allow @code{m4} exit by giving it an EOF as input:
680 Program exited normally.
684 The message @samp{Program exited normally.} is from @value{GDBN}; it
685 indicates @code{m4} has finished executing. We can end our @value{GDBN}
686 session with the @value{GDBN} @code{quit} command.
689 (@value{GDBP}) @b{quit}
693 @chapter Getting In and Out of @value{GDBN}
695 This chapter discusses how to start @value{GDBN}, and how to get out of it.
699 type @samp{@value{GDBP}} to start @value{GDBN}.
701 type @kbd{quit} or @kbd{C-d} to exit.
705 * Invoking GDB:: How to start @value{GDBN}
706 * Quitting GDB:: How to quit @value{GDBN}
707 * Shell Commands:: How to use shell commands inside @value{GDBN}
711 @section Invoking @value{GDBN}
713 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
714 @value{GDBN} reads commands from the terminal until you tell it to exit.
716 You can also run @code{@value{GDBP}} with a variety of arguments and options,
717 to specify more of your debugging environment at the outset.
719 The command-line options described here are designed
720 to cover a variety of situations; in some environments, some of these
721 options may effectively be unavailable.
723 The most usual way to start @value{GDBN} is with one argument,
724 specifying an executable program:
727 @value{GDBP} @var{program}
731 You can also start with both an executable program and a core file
735 @value{GDBP} @var{program} @var{core}
738 You can, instead, specify a process ID as a second argument, if you want
739 to debug a running process:
742 @value{GDBP} @var{program} 1234
746 would attach @value{GDBN} to process @code{1234} (unless you also have a file
747 named @file{1234}; @value{GDBN} does check for a core file first).
749 Taking advantage of the second command-line argument requires a fairly
750 complete operating system; when you use @value{GDBN} as a remote
751 debugger attached to a bare board, there may not be any notion of
752 ``process'', and there is often no way to get a core dump. @value{GDBN}
753 will warn you if it is unable to attach or to read core dumps.
755 You can run @code{@value{GDBP}} without printing the front material, which describes
756 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
763 You can further control how @value{GDBN} starts up by using command-line
764 options. @value{GDBN} itself can remind you of the options available.
774 to display all available options and briefly describe their use
775 (@samp{@value{GDBP} -h} is a shorter equivalent).
777 All options and command line arguments you give are processed
778 in sequential order. The order makes a difference when the
779 @samp{-x} option is used.
783 * File Options:: Choosing files
784 * Mode Options:: Choosing modes
788 @subsection Choosing files
790 When @value{GDBN} starts, it reads any arguments other than options as
791 specifying an executable file and core file (or process ID). This is
792 the same as if the arguments were specified by the @samp{-se} and
793 @samp{-c} options respectively. (@value{GDBN} reads the first argument
794 that does not have an associated option flag as equivalent to the
795 @samp{-se} option followed by that argument; and the second argument
796 that does not have an associated option flag, if any, as equivalent to
797 the @samp{-c} option followed by that argument.)
799 If @value{GDBN} has not been configured to included core file support,
800 such as for most embedded targets, then it will complain about a second
801 argument and ignore it.
803 Many options have both long and short forms; both are shown in the
804 following list. @value{GDBN} also recognizes the long forms if you truncate
805 them, so long as enough of the option is present to be unambiguous.
806 (If you prefer, you can flag option arguments with @samp{--} rather
807 than @samp{-}, though we illustrate the more usual convention.)
809 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
810 @c way, both those who look for -foo and --foo in the index, will find
814 @item -symbols @var{file}
816 @cindex @code{--symbols}
818 Read symbol table from file @var{file}.
820 @item -exec @var{file}
822 @cindex @code{--exec}
824 Use file @var{file} as the executable file to execute when appropriate,
825 and for examining pure data in conjunction with a core dump.
829 Read symbol table from file @var{file} and use it as the executable
832 @item -core @var{file}
834 @cindex @code{--core}
836 Use file @var{file} as a core dump to examine.
838 @item -c @var{number}
839 Connect to process ID @var{number}, as with the @code{attach} command
840 (unless there is a file in core-dump format named @var{number}, in which
841 case @samp{-c} specifies that file as a core dump to read).
843 @item -command @var{file}
845 @cindex @code{--command}
847 Execute @value{GDBN} commands from file @var{file}. @xref{Command
848 Files,, Command files}.
850 @item -directory @var{directory}
851 @itemx -d @var{directory}
852 @cindex @code{--directory}
854 Add @var{directory} to the path to search for source files.
858 @cindex @code{--mapped}
860 @emph{Warning: this option depends on operating system facilities that are not
861 supported on all systems.}@*
862 If memory-mapped files are available on your system through the @code{mmap}
863 system call, you can use this option
864 to have @value{GDBN} write the symbols from your
865 program into a reusable file in the current directory. If the program you are debugging is
866 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
867 Future @value{GDBN} debugging sessions notice the presence of this file,
868 and can quickly map in symbol information from it, rather than reading
869 the symbol table from the executable program.
871 The @file{.syms} file is specific to the host machine where @value{GDBN}
872 is run. It holds an exact image of the internal @value{GDBN} symbol
873 table. It cannot be shared across multiple host platforms.
877 @cindex @code{--readnow}
879 Read each symbol file's entire symbol table immediately, rather than
880 the default, which is to read it incrementally as it is needed.
881 This makes startup slower, but makes future operations faster.
885 You typically combine the @code{-mapped} and @code{-readnow} options in
886 order to build a @file{.syms} file that contains complete symbol
887 information. (@xref{Files,,Commands to specify files}, for information
888 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
889 but build a @file{.syms} file for future use is:
892 gdb -batch -nx -mapped -readnow programname
896 @subsection Choosing modes
898 You can run @value{GDBN} in various alternative modes---for example, in
899 batch mode or quiet mode.
906 Do not execute commands found in any initialization files (normally
907 called @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally,
908 @value{GDBN} executes the commands in these files after all the command
909 options and arguments have been processed. @xref{Command Files,,Command
915 @cindex @code{--quiet}
916 @cindex @code{--silent}
918 ``Quiet''. Do not print the introductory and copyright messages. These
919 messages are also suppressed in batch mode.
922 @cindex @code{--batch}
923 Run in batch mode. Exit with status @code{0} after processing all the
924 command files specified with @samp{-x} (and all commands from
925 initialization files, if not inhibited with @samp{-n}). Exit with
926 nonzero status if an error occurs in executing the @value{GDBN} commands
927 in the command files.
929 Batch mode may be useful for running @value{GDBN} as a filter, for
930 example to download and run a program on another computer; in order to
931 make this more useful, the message
934 Program exited normally.
938 (which is ordinarily issued whenever a program running under
939 @value{GDBN} control terminates) is not issued when running in batch
944 @cindex @code{--nowindows}
946 ``No windows''. If @value{GDBN} comes with a graphical user interface
947 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
948 interface. If no GUI is available, this option has no effect.
952 @cindex @code{--windows}
954 If @value{GDBN} includes a GUI, then this option requires it to be
957 @item -cd @var{directory}
959 Run @value{GDBN} using @var{directory} as its working directory,
960 instead of the current directory.
964 @cindex @code{--fullname}
966 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
967 subprocess. It tells @value{GDBN} to output the full file name and line
968 number in a standard, recognizable fashion each time a stack frame is
969 displayed (which includes each time your program stops). This
970 recognizable format looks like two @samp{\032} characters, followed by
971 the file name, line number and character position separated by colons,
972 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
973 @samp{\032} characters as a signal to display the source code for the
977 @cindex @code{--epoch}
978 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
979 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
980 routines so as to allow Epoch to display values of expressions in a
983 @item -annotate @var{level}
984 @cindex @code{--annotate}
985 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
986 effect is identical to using @samp{set annotate @var{level}}
987 (@pxref{Annotations}).
988 Annotation level controls how much information does @value{GDBN} print
989 together with its prompt, values of expressions, source lines, and other
990 types of output. Level 0 is the normal, level 1 is for use when
991 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
992 maximum annotation suitable for programs that control @value{GDBN}.
995 @cindex @code{--async}
996 Use the asynchronous event loop for the command-line interface.
997 @value{GDBN} processes all events, such as user keyboard input, via a
998 special event loop. This allows @value{GDBN} to accept and process user
999 commands in parallel with the debugged process being
1000 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1001 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1002 suspended when the debuggee runs.}, so you don't need to wait for
1003 control to return to @value{GDBN} before you type the next command.
1004 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1005 operation is not yet in place, so @samp{-async} does not work fully
1007 @c FIXME: when the target side of the event loop is done, the above NOTE
1008 @c should be removed.
1010 When the standard input is connected to a terminal device, @value{GDBN}
1011 uses the asynchronous event loop by default, unless disabled by the
1012 @samp{-noasync} option.
1015 @cindex @code{--noasync}
1016 Disable the asynchronous event loop for the command-line interface.
1018 @item -baud @var{bps}
1020 @cindex @code{--baud}
1022 Set the line speed (baud rate or bits per second) of any serial
1023 interface used by @value{GDBN} for remote debugging.
1025 @item -tty @var{device}
1026 @itemx -t @var{device}
1027 @cindex @code{--tty}
1029 Run using @var{device} for your program's standard input and output.
1030 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1032 @c resolve the situation of these eventually
1034 @cindex @code{--tui}
1035 Activate the Terminal User Interface when starting.
1036 The Terminal User Interface manages several text windows on the terminal,
1037 showing source, assembly, registers and @value{GDBN} command outputs
1038 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1039 Do not use this option if you run @value{GDBN} from Emacs
1040 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1043 @c @cindex @code{--xdb}
1044 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1045 @c For information, see the file @file{xdb_trans.html}, which is usually
1046 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1049 @item -interpreter @var{interp}
1050 @cindex @code{--interpreter}
1051 Use the interpreter @var{interp} for interface with the controlling
1052 program or device. This option is meant to be set by programs which
1053 communicate with @value{GDBN} using it as a back end.
1055 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1056 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1057 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1058 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1061 @cindex @code{--write}
1062 Open the executable and core files for both reading and writing. This
1063 is equivalent to the @samp{set write on} command inside @value{GDBN}
1067 @cindex @code{--statistics}
1068 This option causes @value{GDBN} to print statistics about time and
1069 memory usage after it completes each command and returns to the prompt.
1072 @cindex @code{--version}
1073 This option causes @value{GDBN} to print its version number and
1074 no-warranty blurb, and exit.
1079 @section Quitting @value{GDBN}
1080 @cindex exiting @value{GDBN}
1081 @cindex leaving @value{GDBN}
1084 @kindex quit @r{[}@var{expression}@r{]}
1085 @kindex q @r{(@code{quit})}
1086 @item quit @r{[}@var{expression}@r{]}
1088 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1089 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1090 do not supply @var{expression}, @value{GDBN} will terminate normally;
1091 otherwise it will terminate using the result of @var{expression} as the
1096 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1097 terminates the action of any @value{GDBN} command that is in progress and
1098 returns to @value{GDBN} command level. It is safe to type the interrupt
1099 character at any time because @value{GDBN} does not allow it to take effect
1100 until a time when it is safe.
1102 If you have been using @value{GDBN} to control an attached process or
1103 device, you can release it with the @code{detach} command
1104 (@pxref{Attach, ,Debugging an already-running process}).
1106 @node Shell Commands
1107 @section Shell commands
1109 If you need to execute occasional shell commands during your
1110 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1111 just use the @code{shell} command.
1115 @cindex shell escape
1116 @item shell @var{command string}
1117 Invoke a standard shell to execute @var{command string}.
1118 If it exists, the environment variable @code{SHELL} determines which
1119 shell to run. Otherwise @value{GDBN} uses the default shell
1120 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1123 The utility @code{make} is often needed in development environments.
1124 You do not have to use the @code{shell} command for this purpose in
1129 @cindex calling make
1130 @item make @var{make-args}
1131 Execute the @code{make} program with the specified
1132 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1136 @chapter @value{GDBN} Commands
1138 You can abbreviate a @value{GDBN} command to the first few letters of the command
1139 name, if that abbreviation is unambiguous; and you can repeat certain
1140 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1141 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1142 show you the alternatives available, if there is more than one possibility).
1145 * Command Syntax:: How to give commands to @value{GDBN}
1146 * Completion:: Command completion
1147 * Help:: How to ask @value{GDBN} for help
1150 @node Command Syntax
1151 @section Command syntax
1153 A @value{GDBN} command is a single line of input. There is no limit on
1154 how long it can be. It starts with a command name, which is followed by
1155 arguments whose meaning depends on the command name. For example, the
1156 command @code{step} accepts an argument which is the number of times to
1157 step, as in @samp{step 5}. You can also use the @code{step} command
1158 with no arguments. Some commands do not allow any arguments.
1160 @cindex abbreviation
1161 @value{GDBN} command names may always be truncated if that abbreviation is
1162 unambiguous. Other possible command abbreviations are listed in the
1163 documentation for individual commands. In some cases, even ambiguous
1164 abbreviations are allowed; for example, @code{s} is specially defined as
1165 equivalent to @code{step} even though there are other commands whose
1166 names start with @code{s}. You can test abbreviations by using them as
1167 arguments to the @code{help} command.
1169 @cindex repeating commands
1170 @kindex RET @r{(repeat last command)}
1171 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1172 repeat the previous command. Certain commands (for example, @code{run})
1173 will not repeat this way; these are commands whose unintentional
1174 repetition might cause trouble and which you are unlikely to want to
1177 The @code{list} and @code{x} commands, when you repeat them with
1178 @key{RET}, construct new arguments rather than repeating
1179 exactly as typed. This permits easy scanning of source or memory.
1181 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1182 output, in a way similar to the common utility @code{more}
1183 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1184 @key{RET} too many in this situation, @value{GDBN} disables command
1185 repetition after any command that generates this sort of display.
1187 @kindex # @r{(a comment)}
1189 Any text from a @kbd{#} to the end of the line is a comment; it does
1190 nothing. This is useful mainly in command files (@pxref{Command
1191 Files,,Command files}).
1194 @section Command completion
1197 @cindex word completion
1198 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1199 only one possibility; it can also show you what the valid possibilities
1200 are for the next word in a command, at any time. This works for @value{GDBN}
1201 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1203 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1204 of a word. If there is only one possibility, @value{GDBN} fills in the
1205 word, and waits for you to finish the command (or press @key{RET} to
1206 enter it). For example, if you type
1208 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1209 @c complete accuracy in these examples; space introduced for clarity.
1210 @c If texinfo enhancements make it unnecessary, it would be nice to
1211 @c replace " @key" by "@key" in the following...
1213 (@value{GDBP}) info bre @key{TAB}
1217 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1218 the only @code{info} subcommand beginning with @samp{bre}:
1221 (@value{GDBP}) info breakpoints
1225 You can either press @key{RET} at this point, to run the @code{info
1226 breakpoints} command, or backspace and enter something else, if
1227 @samp{breakpoints} does not look like the command you expected. (If you
1228 were sure you wanted @code{info breakpoints} in the first place, you
1229 might as well just type @key{RET} immediately after @samp{info bre},
1230 to exploit command abbreviations rather than command completion).
1232 If there is more than one possibility for the next word when you press
1233 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1234 characters and try again, or just press @key{TAB} a second time;
1235 @value{GDBN} displays all the possible completions for that word. For
1236 example, you might want to set a breakpoint on a subroutine whose name
1237 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1238 just sounds the bell. Typing @key{TAB} again displays all the
1239 function names in your program that begin with those characters, for
1243 (@value{GDBP}) b make_ @key{TAB}
1244 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1245 make_a_section_from_file make_environ
1246 make_abs_section make_function_type
1247 make_blockvector make_pointer_type
1248 make_cleanup make_reference_type
1249 make_command make_symbol_completion_list
1250 (@value{GDBP}) b make_
1254 After displaying the available possibilities, @value{GDBN} copies your
1255 partial input (@samp{b make_} in the example) so you can finish the
1258 If you just want to see the list of alternatives in the first place, you
1259 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1260 means @kbd{@key{META} ?}. You can type this either by holding down a
1261 key designated as the @key{META} shift on your keyboard (if there is
1262 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1264 @cindex quotes in commands
1265 @cindex completion of quoted strings
1266 Sometimes the string you need, while logically a ``word'', may contain
1267 parentheses or other characters that @value{GDBN} normally excludes from
1268 its notion of a word. To permit word completion to work in this
1269 situation, you may enclose words in @code{'} (single quote marks) in
1270 @value{GDBN} commands.
1272 The most likely situation where you might need this is in typing the
1273 name of a C@t{++} function. This is because C@t{++} allows function
1274 overloading (multiple definitions of the same function, distinguished
1275 by argument type). For example, when you want to set a breakpoint you
1276 may need to distinguish whether you mean the version of @code{name}
1277 that takes an @code{int} parameter, @code{name(int)}, or the version
1278 that takes a @code{float} parameter, @code{name(float)}. To use the
1279 word-completion facilities in this situation, type a single quote
1280 @code{'} at the beginning of the function name. This alerts
1281 @value{GDBN} that it may need to consider more information than usual
1282 when you press @key{TAB} or @kbd{M-?} to request word completion:
1285 (@value{GDBP}) b 'bubble( @kbd{M-?}
1286 bubble(double,double) bubble(int,int)
1287 (@value{GDBP}) b 'bubble(
1290 In some cases, @value{GDBN} can tell that completing a name requires using
1291 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1292 completing as much as it can) if you do not type the quote in the first
1296 (@value{GDBP}) b bub @key{TAB}
1297 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1298 (@value{GDBP}) b 'bubble(
1302 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1303 you have not yet started typing the argument list when you ask for
1304 completion on an overloaded symbol.
1306 For more information about overloaded functions, see @ref{C plus plus
1307 expressions, ,C@t{++} expressions}. You can use the command @code{set
1308 overload-resolution off} to disable overload resolution;
1309 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1313 @section Getting help
1314 @cindex online documentation
1317 You can always ask @value{GDBN} itself for information on its commands,
1318 using the command @code{help}.
1321 @kindex h @r{(@code{help})}
1324 You can use @code{help} (abbreviated @code{h}) with no arguments to
1325 display a short list of named classes of commands:
1329 List of classes of commands:
1331 aliases -- Aliases of other commands
1332 breakpoints -- Making program stop at certain points
1333 data -- Examining data
1334 files -- Specifying and examining files
1335 internals -- Maintenance commands
1336 obscure -- Obscure features
1337 running -- Running the program
1338 stack -- Examining the stack
1339 status -- Status inquiries
1340 support -- Support facilities
1341 tracepoints -- Tracing of program execution without@*
1342 stopping the program
1343 user-defined -- User-defined commands
1345 Type "help" followed by a class name for a list of
1346 commands in that class.
1347 Type "help" followed by command name for full
1349 Command name abbreviations are allowed if unambiguous.
1352 @c the above line break eliminates huge line overfull...
1354 @item help @var{class}
1355 Using one of the general help classes as an argument, you can get a
1356 list of the individual commands in that class. For example, here is the
1357 help display for the class @code{status}:
1360 (@value{GDBP}) help status
1365 @c Line break in "show" line falsifies real output, but needed
1366 @c to fit in smallbook page size.
1367 info -- Generic command for showing things
1368 about the program being debugged
1369 show -- Generic command for showing things
1372 Type "help" followed by command name for full
1374 Command name abbreviations are allowed if unambiguous.
1378 @item help @var{command}
1379 With a command name as @code{help} argument, @value{GDBN} displays a
1380 short paragraph on how to use that command.
1383 @item apropos @var{args}
1384 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1385 commands, and their documentation, for the regular expression specified in
1386 @var{args}. It prints out all matches found. For example:
1397 set symbol-reloading -- Set dynamic symbol table reloading
1398 multiple times in one run
1399 show symbol-reloading -- Show dynamic symbol table reloading
1400 multiple times in one run
1405 @item complete @var{args}
1406 The @code{complete @var{args}} command lists all the possible completions
1407 for the beginning of a command. Use @var{args} to specify the beginning of the
1408 command you want completed. For example:
1414 @noindent results in:
1425 @noindent This is intended for use by @sc{gnu} Emacs.
1428 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1429 and @code{show} to inquire about the state of your program, or the state
1430 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1431 manual introduces each of them in the appropriate context. The listings
1432 under @code{info} and under @code{show} in the Index point to
1433 all the sub-commands. @xref{Index}.
1438 @kindex i @r{(@code{info})}
1440 This command (abbreviated @code{i}) is for describing the state of your
1441 program. For example, you can list the arguments given to your program
1442 with @code{info args}, list the registers currently in use with @code{info
1443 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1444 You can get a complete list of the @code{info} sub-commands with
1445 @w{@code{help info}}.
1449 You can assign the result of an expression to an environment variable with
1450 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1451 @code{set prompt $}.
1455 In contrast to @code{info}, @code{show} is for describing the state of
1456 @value{GDBN} itself.
1457 You can change most of the things you can @code{show}, by using the
1458 related command @code{set}; for example, you can control what number
1459 system is used for displays with @code{set radix}, or simply inquire
1460 which is currently in use with @code{show radix}.
1463 To display all the settable parameters and their current
1464 values, you can use @code{show} with no arguments; you may also use
1465 @code{info set}. Both commands produce the same display.
1466 @c FIXME: "info set" violates the rule that "info" is for state of
1467 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1468 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1472 Here are three miscellaneous @code{show} subcommands, all of which are
1473 exceptional in lacking corresponding @code{set} commands:
1476 @kindex show version
1477 @cindex version number
1479 Show what version of @value{GDBN} is running. You should include this
1480 information in @value{GDBN} bug-reports. If multiple versions of
1481 @value{GDBN} are in use at your site, you may need to determine which
1482 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1483 commands are introduced, and old ones may wither away. Also, many
1484 system vendors ship variant versions of @value{GDBN}, and there are
1485 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1486 The version number is the same as the one announced when you start
1489 @kindex show copying
1491 Display information about permission for copying @value{GDBN}.
1493 @kindex show warranty
1495 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1496 if your version of @value{GDBN} comes with one.
1501 @chapter Running Programs Under @value{GDBN}
1503 When you run a program under @value{GDBN}, you must first generate
1504 debugging information when you compile it.
1506 You may start @value{GDBN} with its arguments, if any, in an environment
1507 of your choice. If you are doing native debugging, you may redirect
1508 your program's input and output, debug an already running process, or
1509 kill a child process.
1512 * Compilation:: Compiling for debugging
1513 * Starting:: Starting your program
1514 * Arguments:: Your program's arguments
1515 * Environment:: Your program's environment
1517 * Working Directory:: Your program's working directory
1518 * Input/Output:: Your program's input and output
1519 * Attach:: Debugging an already-running process
1520 * Kill Process:: Killing the child process
1522 * Threads:: Debugging programs with multiple threads
1523 * Processes:: Debugging programs with multiple processes
1527 @section Compiling for debugging
1529 In order to debug a program effectively, you need to generate
1530 debugging information when you compile it. This debugging information
1531 is stored in the object file; it describes the data type of each
1532 variable or function and the correspondence between source line numbers
1533 and addresses in the executable code.
1535 To request debugging information, specify the @samp{-g} option when you run
1538 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1539 options together. Using those compilers, you cannot generate optimized
1540 executables containing debugging information.
1542 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1543 without @samp{-O}, making it possible to debug optimized code. We
1544 recommend that you @emph{always} use @samp{-g} whenever you compile a
1545 program. You may think your program is correct, but there is no sense
1546 in pushing your luck.
1548 @cindex optimized code, debugging
1549 @cindex debugging optimized code
1550 When you debug a program compiled with @samp{-g -O}, remember that the
1551 optimizer is rearranging your code; the debugger shows you what is
1552 really there. Do not be too surprised when the execution path does not
1553 exactly match your source file! An extreme example: if you define a
1554 variable, but never use it, @value{GDBN} never sees that
1555 variable---because the compiler optimizes it out of existence.
1557 Some things do not work as well with @samp{-g -O} as with just
1558 @samp{-g}, particularly on machines with instruction scheduling. If in
1559 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1560 please report it to us as a bug (including a test case!).
1562 Older versions of the @sc{gnu} C compiler permitted a variant option
1563 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1564 format; if your @sc{gnu} C compiler has this option, do not use it.
1568 @section Starting your program
1574 @kindex r @r{(@code{run})}
1577 Use the @code{run} command to start your program under @value{GDBN}.
1578 You must first specify the program name (except on VxWorks) with an
1579 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1580 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1581 (@pxref{Files, ,Commands to specify files}).
1585 If you are running your program in an execution environment that
1586 supports processes, @code{run} creates an inferior process and makes
1587 that process run your program. (In environments without processes,
1588 @code{run} jumps to the start of your program.)
1590 The execution of a program is affected by certain information it
1591 receives from its superior. @value{GDBN} provides ways to specify this
1592 information, which you must do @emph{before} starting your program. (You
1593 can change it after starting your program, but such changes only affect
1594 your program the next time you start it.) This information may be
1595 divided into four categories:
1598 @item The @emph{arguments.}
1599 Specify the arguments to give your program as the arguments of the
1600 @code{run} command. If a shell is available on your target, the shell
1601 is used to pass the arguments, so that you may use normal conventions
1602 (such as wildcard expansion or variable substitution) in describing
1604 In Unix systems, you can control which shell is used with the
1605 @code{SHELL} environment variable.
1606 @xref{Arguments, ,Your program's arguments}.
1608 @item The @emph{environment.}
1609 Your program normally inherits its environment from @value{GDBN}, but you can
1610 use the @value{GDBN} commands @code{set environment} and @code{unset
1611 environment} to change parts of the environment that affect
1612 your program. @xref{Environment, ,Your program's environment}.
1614 @item The @emph{working directory.}
1615 Your program inherits its working directory from @value{GDBN}. You can set
1616 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1617 @xref{Working Directory, ,Your program's working directory}.
1619 @item The @emph{standard input and output.}
1620 Your program normally uses the same device for standard input and
1621 standard output as @value{GDBN} is using. You can redirect input and output
1622 in the @code{run} command line, or you can use the @code{tty} command to
1623 set a different device for your program.
1624 @xref{Input/Output, ,Your program's input and output}.
1627 @emph{Warning:} While input and output redirection work, you cannot use
1628 pipes to pass the output of the program you are debugging to another
1629 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1633 When you issue the @code{run} command, your program begins to execute
1634 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1635 of how to arrange for your program to stop. Once your program has
1636 stopped, you may call functions in your program, using the @code{print}
1637 or @code{call} commands. @xref{Data, ,Examining Data}.
1639 If the modification time of your symbol file has changed since the last
1640 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1641 table, and reads it again. When it does this, @value{GDBN} tries to retain
1642 your current breakpoints.
1645 @section Your program's arguments
1647 @cindex arguments (to your program)
1648 The arguments to your program can be specified by the arguments of the
1650 They are passed to a shell, which expands wildcard characters and
1651 performs redirection of I/O, and thence to your program. Your
1652 @code{SHELL} environment variable (if it exists) specifies what shell
1653 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1654 the default shell (@file{/bin/sh} on Unix).
1656 On non-Unix systems, the program is usually invoked directly by
1657 @value{GDBN}, which emulates I/O redirection via the appropriate system
1658 calls, and the wildcard characters are expanded by the startup code of
1659 the program, not by the shell.
1661 @code{run} with no arguments uses the same arguments used by the previous
1662 @code{run}, or those set by the @code{set args} command.
1667 Specify the arguments to be used the next time your program is run. If
1668 @code{set args} has no arguments, @code{run} executes your program
1669 with no arguments. Once you have run your program with arguments,
1670 using @code{set args} before the next @code{run} is the only way to run
1671 it again without arguments.
1675 Show the arguments to give your program when it is started.
1679 @section Your program's environment
1681 @cindex environment (of your program)
1682 The @dfn{environment} consists of a set of environment variables and
1683 their values. Environment variables conventionally record such things as
1684 your user name, your home directory, your terminal type, and your search
1685 path for programs to run. Usually you set up environment variables with
1686 the shell and they are inherited by all the other programs you run. When
1687 debugging, it can be useful to try running your program with a modified
1688 environment without having to start @value{GDBN} over again.
1692 @item path @var{directory}
1693 Add @var{directory} to the front of the @code{PATH} environment variable
1694 (the search path for executables) that will be passed to your program.
1695 The value of @code{PATH} used by @value{GDBN} does not change.
1696 You may specify several directory names, separated by whitespace or by a
1697 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1698 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1699 is moved to the front, so it is searched sooner.
1701 You can use the string @samp{$cwd} to refer to whatever is the current
1702 working directory at the time @value{GDBN} searches the path. If you
1703 use @samp{.} instead, it refers to the directory where you executed the
1704 @code{path} command. @value{GDBN} replaces @samp{.} in the
1705 @var{directory} argument (with the current path) before adding
1706 @var{directory} to the search path.
1707 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1708 @c document that, since repeating it would be a no-op.
1712 Display the list of search paths for executables (the @code{PATH}
1713 environment variable).
1715 @kindex show environment
1716 @item show environment @r{[}@var{varname}@r{]}
1717 Print the value of environment variable @var{varname} to be given to
1718 your program when it starts. If you do not supply @var{varname},
1719 print the names and values of all environment variables to be given to
1720 your program. You can abbreviate @code{environment} as @code{env}.
1722 @kindex set environment
1723 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1724 Set environment variable @var{varname} to @var{value}. The value
1725 changes for your program only, not for @value{GDBN} itself. @var{value} may
1726 be any string; the values of environment variables are just strings, and
1727 any interpretation is supplied by your program itself. The @var{value}
1728 parameter is optional; if it is eliminated, the variable is set to a
1730 @c "any string" here does not include leading, trailing
1731 @c blanks. Gnu asks: does anyone care?
1733 For example, this command:
1740 tells the debugged program, when subsequently run, that its user is named
1741 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1742 are not actually required.)
1744 @kindex unset environment
1745 @item unset environment @var{varname}
1746 Remove variable @var{varname} from the environment to be passed to your
1747 program. This is different from @samp{set env @var{varname} =};
1748 @code{unset environment} removes the variable from the environment,
1749 rather than assigning it an empty value.
1752 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1754 by your @code{SHELL} environment variable if it exists (or
1755 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1756 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1757 @file{.bashrc} for BASH---any variables you set in that file affect
1758 your program. You may wish to move setting of environment variables to
1759 files that are only run when you sign on, such as @file{.login} or
1762 @node Working Directory
1763 @section Your program's working directory
1765 @cindex working directory (of your program)
1766 Each time you start your program with @code{run}, it inherits its
1767 working directory from the current working directory of @value{GDBN}.
1768 The @value{GDBN} working directory is initially whatever it inherited
1769 from its parent process (typically the shell), but you can specify a new
1770 working directory in @value{GDBN} with the @code{cd} command.
1772 The @value{GDBN} working directory also serves as a default for the commands
1773 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1778 @item cd @var{directory}
1779 Set the @value{GDBN} working directory to @var{directory}.
1783 Print the @value{GDBN} working directory.
1787 @section Your program's input and output
1792 By default, the program you run under @value{GDBN} does input and output to
1793 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1794 to its own terminal modes to interact with you, but it records the terminal
1795 modes your program was using and switches back to them when you continue
1796 running your program.
1799 @kindex info terminal
1801 Displays information recorded by @value{GDBN} about the terminal modes your
1805 You can redirect your program's input and/or output using shell
1806 redirection with the @code{run} command. For example,
1813 starts your program, diverting its output to the file @file{outfile}.
1816 @cindex controlling terminal
1817 Another way to specify where your program should do input and output is
1818 with the @code{tty} command. This command accepts a file name as
1819 argument, and causes this file to be the default for future @code{run}
1820 commands. It also resets the controlling terminal for the child
1821 process, for future @code{run} commands. For example,
1828 directs that processes started with subsequent @code{run} commands
1829 default to do input and output on the terminal @file{/dev/ttyb} and have
1830 that as their controlling terminal.
1832 An explicit redirection in @code{run} overrides the @code{tty} command's
1833 effect on the input/output device, but not its effect on the controlling
1836 When you use the @code{tty} command or redirect input in the @code{run}
1837 command, only the input @emph{for your program} is affected. The input
1838 for @value{GDBN} still comes from your terminal.
1841 @section Debugging an already-running process
1846 @item attach @var{process-id}
1847 This command attaches to a running process---one that was started
1848 outside @value{GDBN}. (@code{info files} shows your active
1849 targets.) The command takes as argument a process ID. The usual way to
1850 find out the process-id of a Unix process is with the @code{ps} utility,
1851 or with the @samp{jobs -l} shell command.
1853 @code{attach} does not repeat if you press @key{RET} a second time after
1854 executing the command.
1857 To use @code{attach}, your program must be running in an environment
1858 which supports processes; for example, @code{attach} does not work for
1859 programs on bare-board targets that lack an operating system. You must
1860 also have permission to send the process a signal.
1862 When you use @code{attach}, the debugger finds the program running in
1863 the process first by looking in the current working directory, then (if
1864 the program is not found) by using the source file search path
1865 (@pxref{Source Path, ,Specifying source directories}). You can also use
1866 the @code{file} command to load the program. @xref{Files, ,Commands to
1869 The first thing @value{GDBN} does after arranging to debug the specified
1870 process is to stop it. You can examine and modify an attached process
1871 with all the @value{GDBN} commands that are ordinarily available when
1872 you start processes with @code{run}. You can insert breakpoints; you
1873 can step and continue; you can modify storage. If you would rather the
1874 process continue running, you may use the @code{continue} command after
1875 attaching @value{GDBN} to the process.
1880 When you have finished debugging the attached process, you can use the
1881 @code{detach} command to release it from @value{GDBN} control. Detaching
1882 the process continues its execution. After the @code{detach} command,
1883 that process and @value{GDBN} become completely independent once more, and you
1884 are ready to @code{attach} another process or start one with @code{run}.
1885 @code{detach} does not repeat if you press @key{RET} again after
1886 executing the command.
1889 If you exit @value{GDBN} or use the @code{run} command while you have an
1890 attached process, you kill that process. By default, @value{GDBN} asks
1891 for confirmation if you try to do either of these things; you can
1892 control whether or not you need to confirm by using the @code{set
1893 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1897 @section Killing the child process
1902 Kill the child process in which your program is running under @value{GDBN}.
1905 This command is useful if you wish to debug a core dump instead of a
1906 running process. @value{GDBN} ignores any core dump file while your program
1909 On some operating systems, a program cannot be executed outside @value{GDBN}
1910 while you have breakpoints set on it inside @value{GDBN}. You can use the
1911 @code{kill} command in this situation to permit running your program
1912 outside the debugger.
1914 The @code{kill} command is also useful if you wish to recompile and
1915 relink your program, since on many systems it is impossible to modify an
1916 executable file while it is running in a process. In this case, when you
1917 next type @code{run}, @value{GDBN} notices that the file has changed, and
1918 reads the symbol table again (while trying to preserve your current
1919 breakpoint settings).
1922 @section Debugging programs with multiple threads
1924 @cindex threads of execution
1925 @cindex multiple threads
1926 @cindex switching threads
1927 In some operating systems, such as HP-UX and Solaris, a single program
1928 may have more than one @dfn{thread} of execution. The precise semantics
1929 of threads differ from one operating system to another, but in general
1930 the threads of a single program are akin to multiple processes---except
1931 that they share one address space (that is, they can all examine and
1932 modify the same variables). On the other hand, each thread has its own
1933 registers and execution stack, and perhaps private memory.
1935 @value{GDBN} provides these facilities for debugging multi-thread
1939 @item automatic notification of new threads
1940 @item @samp{thread @var{threadno}}, a command to switch among threads
1941 @item @samp{info threads}, a command to inquire about existing threads
1942 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1943 a command to apply a command to a list of threads
1944 @item thread-specific breakpoints
1948 @emph{Warning:} These facilities are not yet available on every
1949 @value{GDBN} configuration where the operating system supports threads.
1950 If your @value{GDBN} does not support threads, these commands have no
1951 effect. For example, a system without thread support shows no output
1952 from @samp{info threads}, and always rejects the @code{thread} command,
1956 (@value{GDBP}) info threads
1957 (@value{GDBP}) thread 1
1958 Thread ID 1 not known. Use the "info threads" command to
1959 see the IDs of currently known threads.
1961 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1962 @c doesn't support threads"?
1965 @cindex focus of debugging
1966 @cindex current thread
1967 The @value{GDBN} thread debugging facility allows you to observe all
1968 threads while your program runs---but whenever @value{GDBN} takes
1969 control, one thread in particular is always the focus of debugging.
1970 This thread is called the @dfn{current thread}. Debugging commands show
1971 program information from the perspective of the current thread.
1973 @cindex @code{New} @var{systag} message
1974 @cindex thread identifier (system)
1975 @c FIXME-implementors!! It would be more helpful if the [New...] message
1976 @c included GDB's numeric thread handle, so you could just go to that
1977 @c thread without first checking `info threads'.
1978 Whenever @value{GDBN} detects a new thread in your program, it displays
1979 the target system's identification for the thread with a message in the
1980 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1981 whose form varies depending on the particular system. For example, on
1982 LynxOS, you might see
1985 [New process 35 thread 27]
1989 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1990 the @var{systag} is simply something like @samp{process 368}, with no
1993 @c FIXME!! (1) Does the [New...] message appear even for the very first
1994 @c thread of a program, or does it only appear for the
1995 @c second---i.e., when it becomes obvious we have a multithread
1997 @c (2) *Is* there necessarily a first thread always? Or do some
1998 @c multithread systems permit starting a program with multiple
1999 @c threads ab initio?
2001 @cindex thread number
2002 @cindex thread identifier (GDB)
2003 For debugging purposes, @value{GDBN} associates its own thread
2004 number---always a single integer---with each thread in your program.
2007 @kindex info threads
2009 Display a summary of all threads currently in your
2010 program. @value{GDBN} displays for each thread (in this order):
2013 @item the thread number assigned by @value{GDBN}
2015 @item the target system's thread identifier (@var{systag})
2017 @item the current stack frame summary for that thread
2021 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2022 indicates the current thread.
2026 @c end table here to get a little more width for example
2029 (@value{GDBP}) info threads
2030 3 process 35 thread 27 0x34e5 in sigpause ()
2031 2 process 35 thread 23 0x34e5 in sigpause ()
2032 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2038 @cindex thread number
2039 @cindex thread identifier (GDB)
2040 For debugging purposes, @value{GDBN} associates its own thread
2041 number---a small integer assigned in thread-creation order---with each
2042 thread in your program.
2044 @cindex @code{New} @var{systag} message, on HP-UX
2045 @cindex thread identifier (system), on HP-UX
2046 @c FIXME-implementors!! It would be more helpful if the [New...] message
2047 @c included GDB's numeric thread handle, so you could just go to that
2048 @c thread without first checking `info threads'.
2049 Whenever @value{GDBN} detects a new thread in your program, it displays
2050 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2051 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2052 whose form varies depending on the particular system. For example, on
2056 [New thread 2 (system thread 26594)]
2060 when @value{GDBN} notices a new thread.
2063 @kindex info threads
2065 Display a summary of all threads currently in your
2066 program. @value{GDBN} displays for each thread (in this order):
2069 @item the thread number assigned by @value{GDBN}
2071 @item the target system's thread identifier (@var{systag})
2073 @item the current stack frame summary for that thread
2077 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2078 indicates the current thread.
2082 @c end table here to get a little more width for example
2085 (@value{GDBP}) info threads
2086 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2088 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2089 from /usr/lib/libc.2
2090 1 system thread 27905 0x7b003498 in _brk () \@*
2091 from /usr/lib/libc.2
2095 @kindex thread @var{threadno}
2096 @item thread @var{threadno}
2097 Make thread number @var{threadno} the current thread. The command
2098 argument @var{threadno} is the internal @value{GDBN} thread number, as
2099 shown in the first field of the @samp{info threads} display.
2100 @value{GDBN} responds by displaying the system identifier of the thread
2101 you selected, and its current stack frame summary:
2104 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2105 (@value{GDBP}) thread 2
2106 [Switching to process 35 thread 23]
2107 0x34e5 in sigpause ()
2111 As with the @samp{[New @dots{}]} message, the form of the text after
2112 @samp{Switching to} depends on your system's conventions for identifying
2115 @kindex thread apply
2116 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2117 The @code{thread apply} command allows you to apply a command to one or
2118 more threads. Specify the numbers of the threads that you want affected
2119 with the command argument @var{threadno}. @var{threadno} is the internal
2120 @value{GDBN} thread number, as shown in the first field of the @samp{info
2121 threads} display. To apply a command to all threads, use
2122 @code{thread apply all} @var{args}.
2125 @cindex automatic thread selection
2126 @cindex switching threads automatically
2127 @cindex threads, automatic switching
2128 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2129 signal, it automatically selects the thread where that breakpoint or
2130 signal happened. @value{GDBN} alerts you to the context switch with a
2131 message of the form @samp{[Switching to @var{systag}]} to identify the
2134 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2135 more information about how @value{GDBN} behaves when you stop and start
2136 programs with multiple threads.
2138 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2139 watchpoints in programs with multiple threads.
2142 @section Debugging programs with multiple processes
2144 @cindex fork, debugging programs which call
2145 @cindex multiple processes
2146 @cindex processes, multiple
2147 On most systems, @value{GDBN} has no special support for debugging
2148 programs which create additional processes using the @code{fork}
2149 function. When a program forks, @value{GDBN} will continue to debug the
2150 parent process and the child process will run unimpeded. If you have
2151 set a breakpoint in any code which the child then executes, the child
2152 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2153 will cause it to terminate.
2155 However, if you want to debug the child process there is a workaround
2156 which isn't too painful. Put a call to @code{sleep} in the code which
2157 the child process executes after the fork. It may be useful to sleep
2158 only if a certain environment variable is set, or a certain file exists,
2159 so that the delay need not occur when you don't want to run @value{GDBN}
2160 on the child. While the child is sleeping, use the @code{ps} program to
2161 get its process ID. Then tell @value{GDBN} (a new invocation of
2162 @value{GDBN} if you are also debugging the parent process) to attach to
2163 the child process (@pxref{Attach}). From that point on you can debug
2164 the child process just like any other process which you attached to.
2166 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2167 debugging programs that create additional processes using the
2168 @code{fork} or @code{vfork} function.
2170 By default, when a program forks, @value{GDBN} will continue to debug
2171 the parent process and the child process will run unimpeded.
2173 If you want to follow the child process instead of the parent process,
2174 use the command @w{@code{set follow-fork-mode}}.
2177 @kindex set follow-fork-mode
2178 @item set follow-fork-mode @var{mode}
2179 Set the debugger response to a program call of @code{fork} or
2180 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2181 process. The @var{mode} can be:
2185 The original process is debugged after a fork. The child process runs
2186 unimpeded. This is the default.
2189 The new process is debugged after a fork. The parent process runs
2193 The debugger will ask for one of the above choices.
2196 @item show follow-fork-mode
2197 Display the current debugger response to a @code{fork} or @code{vfork} call.
2200 If you ask to debug a child process and a @code{vfork} is followed by an
2201 @code{exec}, @value{GDBN} executes the new target up to the first
2202 breakpoint in the new target. If you have a breakpoint set on
2203 @code{main} in your original program, the breakpoint will also be set on
2204 the child process's @code{main}.
2206 When a child process is spawned by @code{vfork}, you cannot debug the
2207 child or parent until an @code{exec} call completes.
2209 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2210 call executes, the new target restarts. To restart the parent process,
2211 use the @code{file} command with the parent executable name as its
2214 You can use the @code{catch} command to make @value{GDBN} stop whenever
2215 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2216 Catchpoints, ,Setting catchpoints}.
2219 @chapter Stopping and Continuing
2221 The principal purposes of using a debugger are so that you can stop your
2222 program before it terminates; or so that, if your program runs into
2223 trouble, you can investigate and find out why.
2225 Inside @value{GDBN}, your program may stop for any of several reasons,
2226 such as a signal, a breakpoint, or reaching a new line after a
2227 @value{GDBN} command such as @code{step}. You may then examine and
2228 change variables, set new breakpoints or remove old ones, and then
2229 continue execution. Usually, the messages shown by @value{GDBN} provide
2230 ample explanation of the status of your program---but you can also
2231 explicitly request this information at any time.
2234 @kindex info program
2236 Display information about the status of your program: whether it is
2237 running or not, what process it is, and why it stopped.
2241 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2242 * Continuing and Stepping:: Resuming execution
2244 * Thread Stops:: Stopping and starting multi-thread programs
2248 @section Breakpoints, watchpoints, and catchpoints
2251 A @dfn{breakpoint} makes your program stop whenever a certain point in
2252 the program is reached. For each breakpoint, you can add conditions to
2253 control in finer detail whether your program stops. You can set
2254 breakpoints with the @code{break} command and its variants (@pxref{Set
2255 Breaks, ,Setting breakpoints}), to specify the place where your program
2256 should stop by line number, function name or exact address in the
2259 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2260 breakpoints in shared libraries before the executable is run. There is
2261 a minor limitation on HP-UX systems: you must wait until the executable
2262 is run in order to set breakpoints in shared library routines that are
2263 not called directly by the program (for example, routines that are
2264 arguments in a @code{pthread_create} call).
2267 @cindex memory tracing
2268 @cindex breakpoint on memory address
2269 @cindex breakpoint on variable modification
2270 A @dfn{watchpoint} is a special breakpoint that stops your program
2271 when the value of an expression changes. You must use a different
2272 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2273 watchpoints}), but aside from that, you can manage a watchpoint like
2274 any other breakpoint: you enable, disable, and delete both breakpoints
2275 and watchpoints using the same commands.
2277 You can arrange to have values from your program displayed automatically
2278 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2282 @cindex breakpoint on events
2283 A @dfn{catchpoint} is another special breakpoint that stops your program
2284 when a certain kind of event occurs, such as the throwing of a C@t{++}
2285 exception or the loading of a library. As with watchpoints, you use a
2286 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2287 catchpoints}), but aside from that, you can manage a catchpoint like any
2288 other breakpoint. (To stop when your program receives a signal, use the
2289 @code{handle} command; see @ref{Signals, ,Signals}.)
2291 @cindex breakpoint numbers
2292 @cindex numbers for breakpoints
2293 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2294 catchpoint when you create it; these numbers are successive integers
2295 starting with one. In many of the commands for controlling various
2296 features of breakpoints you use the breakpoint number to say which
2297 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2298 @dfn{disabled}; if disabled, it has no effect on your program until you
2301 @cindex breakpoint ranges
2302 @cindex ranges of breakpoints
2303 Some @value{GDBN} commands accept a range of breakpoints on which to
2304 operate. A breakpoint range is either a single breakpoint number, like
2305 @samp{5}, or two such numbers, in increasing order, separated by a
2306 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2307 all breakpoint in that range are operated on.
2310 * Set Breaks:: Setting breakpoints
2311 * Set Watchpoints:: Setting watchpoints
2312 * Set Catchpoints:: Setting catchpoints
2313 * Delete Breaks:: Deleting breakpoints
2314 * Disabling:: Disabling breakpoints
2315 * Conditions:: Break conditions
2316 * Break Commands:: Breakpoint command lists
2317 * Breakpoint Menus:: Breakpoint menus
2318 * Error in Breakpoints:: ``Cannot insert breakpoints''
2322 @subsection Setting breakpoints
2324 @c FIXME LMB what does GDB do if no code on line of breakpt?
2325 @c consider in particular declaration with/without initialization.
2327 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2330 @kindex b @r{(@code{break})}
2331 @vindex $bpnum@r{, convenience variable}
2332 @cindex latest breakpoint
2333 Breakpoints are set with the @code{break} command (abbreviated
2334 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2335 number of the breakpoint you've set most recently; see @ref{Convenience
2336 Vars,, Convenience variables}, for a discussion of what you can do with
2337 convenience variables.
2339 You have several ways to say where the breakpoint should go.
2342 @item break @var{function}
2343 Set a breakpoint at entry to function @var{function}.
2344 When using source languages that permit overloading of symbols, such as
2345 C@t{++}, @var{function} may refer to more than one possible place to break.
2346 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2348 @item break +@var{offset}
2349 @itemx break -@var{offset}
2350 Set a breakpoint some number of lines forward or back from the position
2351 at which execution stopped in the currently selected @dfn{stack frame}.
2352 (@xref{Frames, ,Frames}, for a description of stack frames.)
2354 @item break @var{linenum}
2355 Set a breakpoint at line @var{linenum} in the current source file.
2356 The current source file is the last file whose source text was printed.
2357 The breakpoint will stop your program just before it executes any of the
2360 @item break @var{filename}:@var{linenum}
2361 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2363 @item break @var{filename}:@var{function}
2364 Set a breakpoint at entry to function @var{function} found in file
2365 @var{filename}. Specifying a file name as well as a function name is
2366 superfluous except when multiple files contain similarly named
2369 @item break *@var{address}
2370 Set a breakpoint at address @var{address}. You can use this to set
2371 breakpoints in parts of your program which do not have debugging
2372 information or source files.
2375 When called without any arguments, @code{break} sets a breakpoint at
2376 the next instruction to be executed in the selected stack frame
2377 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2378 innermost, this makes your program stop as soon as control
2379 returns to that frame. This is similar to the effect of a
2380 @code{finish} command in the frame inside the selected frame---except
2381 that @code{finish} does not leave an active breakpoint. If you use
2382 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2383 the next time it reaches the current location; this may be useful
2386 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2387 least one instruction has been executed. If it did not do this, you
2388 would be unable to proceed past a breakpoint without first disabling the
2389 breakpoint. This rule applies whether or not the breakpoint already
2390 existed when your program stopped.
2392 @item break @dots{} if @var{cond}
2393 Set a breakpoint with condition @var{cond}; evaluate the expression
2394 @var{cond} each time the breakpoint is reached, and stop only if the
2395 value is nonzero---that is, if @var{cond} evaluates as true.
2396 @samp{@dots{}} stands for one of the possible arguments described
2397 above (or no argument) specifying where to break. @xref{Conditions,
2398 ,Break conditions}, for more information on breakpoint conditions.
2401 @item tbreak @var{args}
2402 Set a breakpoint enabled only for one stop. @var{args} are the
2403 same as for the @code{break} command, and the breakpoint is set in the same
2404 way, but the breakpoint is automatically deleted after the first time your
2405 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2408 @item hbreak @var{args}
2409 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2410 @code{break} command and the breakpoint is set in the same way, but the
2411 breakpoint requires hardware support and some target hardware may not
2412 have this support. The main purpose of this is EPROM/ROM code
2413 debugging, so you can set a breakpoint at an instruction without
2414 changing the instruction. This can be used with the new trap-generation
2415 provided by SPARClite DSU and some x86-based targets. These targets
2416 will generate traps when a program accesses some data or instruction
2417 address that is assigned to the debug registers. However the hardware
2418 breakpoint registers can take a limited number of breakpoints. For
2419 example, on the DSU, only two data breakpoints can be set at a time, and
2420 @value{GDBN} will reject this command if more than two are used. Delete
2421 or disable unused hardware breakpoints before setting new ones
2422 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2425 @item thbreak @var{args}
2426 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2427 are the same as for the @code{hbreak} command and the breakpoint is set in
2428 the same way. However, like the @code{tbreak} command,
2429 the breakpoint is automatically deleted after the
2430 first time your program stops there. Also, like the @code{hbreak}
2431 command, the breakpoint requires hardware support and some target hardware
2432 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2433 See also @ref{Conditions, ,Break conditions}.
2436 @cindex regular expression
2437 @item rbreak @var{regex}
2438 Set breakpoints on all functions matching the regular expression
2439 @var{regex}. This command sets an unconditional breakpoint on all
2440 matches, printing a list of all breakpoints it set. Once these
2441 breakpoints are set, they are treated just like the breakpoints set with
2442 the @code{break} command. You can delete them, disable them, or make
2443 them conditional the same way as any other breakpoint.
2445 The syntax of the regular expression is the standard one used with tools
2446 like @file{grep}. Note that this is different from the syntax used by
2447 shells, so for instance @code{foo*} matches all functions that include
2448 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2449 @code{.*} leading and trailing the regular expression you supply, so to
2450 match only functions that begin with @code{foo}, use @code{^foo}.
2452 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2453 breakpoints on overloaded functions that are not members of any special
2456 @kindex info breakpoints
2457 @cindex @code{$_} and @code{info breakpoints}
2458 @item info breakpoints @r{[}@var{n}@r{]}
2459 @itemx info break @r{[}@var{n}@r{]}
2460 @itemx info watchpoints @r{[}@var{n}@r{]}
2461 Print a table of all breakpoints, watchpoints, and catchpoints set and
2462 not deleted, with the following columns for each breakpoint:
2465 @item Breakpoint Numbers
2467 Breakpoint, watchpoint, or catchpoint.
2469 Whether the breakpoint is marked to be disabled or deleted when hit.
2470 @item Enabled or Disabled
2471 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2472 that are not enabled.
2474 Where the breakpoint is in your program, as a memory address.
2476 Where the breakpoint is in the source for your program, as a file and
2481 If a breakpoint is conditional, @code{info break} shows the condition on
2482 the line following the affected breakpoint; breakpoint commands, if any,
2483 are listed after that.
2486 @code{info break} with a breakpoint
2487 number @var{n} as argument lists only that breakpoint. The
2488 convenience variable @code{$_} and the default examining-address for
2489 the @code{x} command are set to the address of the last breakpoint
2490 listed (@pxref{Memory, ,Examining memory}).
2493 @code{info break} displays a count of the number of times the breakpoint
2494 has been hit. This is especially useful in conjunction with the
2495 @code{ignore} command. You can ignore a large number of breakpoint
2496 hits, look at the breakpoint info to see how many times the breakpoint
2497 was hit, and then run again, ignoring one less than that number. This
2498 will get you quickly to the last hit of that breakpoint.
2501 @value{GDBN} allows you to set any number of breakpoints at the same place in
2502 your program. There is nothing silly or meaningless about this. When
2503 the breakpoints are conditional, this is even useful
2504 (@pxref{Conditions, ,Break conditions}).
2506 @cindex negative breakpoint numbers
2507 @cindex internal @value{GDBN} breakpoints
2508 @value{GDBN} itself sometimes sets breakpoints in your program for special
2509 purposes, such as proper handling of @code{longjmp} (in C programs).
2510 These internal breakpoints are assigned negative numbers, starting with
2511 @code{-1}; @samp{info breakpoints} does not display them.
2513 You can see these breakpoints with the @value{GDBN} maintenance command
2514 @samp{maint info breakpoints}.
2517 @kindex maint info breakpoints
2518 @item maint info breakpoints
2519 Using the same format as @samp{info breakpoints}, display both the
2520 breakpoints you've set explicitly, and those @value{GDBN} is using for
2521 internal purposes. Internal breakpoints are shown with negative
2522 breakpoint numbers. The type column identifies what kind of breakpoint
2527 Normal, explicitly set breakpoint.
2530 Normal, explicitly set watchpoint.
2533 Internal breakpoint, used to handle correctly stepping through
2534 @code{longjmp} calls.
2536 @item longjmp resume
2537 Internal breakpoint at the target of a @code{longjmp}.
2540 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2543 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2546 Shared library events.
2553 @node Set Watchpoints
2554 @subsection Setting watchpoints
2556 @cindex setting watchpoints
2557 @cindex software watchpoints
2558 @cindex hardware watchpoints
2559 You can use a watchpoint to stop execution whenever the value of an
2560 expression changes, without having to predict a particular place where
2563 Depending on your system, watchpoints may be implemented in software or
2564 hardware. @value{GDBN} does software watchpointing by single-stepping your
2565 program and testing the variable's value each time, which is hundreds of
2566 times slower than normal execution. (But this may still be worth it, to
2567 catch errors where you have no clue what part of your program is the
2570 On some systems, such as HP-UX, Linux and some other x86-based targets,
2571 @value{GDBN} includes support for
2572 hardware watchpoints, which do not slow down the running of your
2577 @item watch @var{expr}
2578 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2579 is written into by the program and its value changes.
2582 @item rwatch @var{expr}
2583 Set a watchpoint that will break when watch @var{expr} is read by the program.
2586 @item awatch @var{expr}
2587 Set a watchpoint that will break when @var{expr} is either read or written into
2590 @kindex info watchpoints
2591 @item info watchpoints
2592 This command prints a list of watchpoints, breakpoints, and catchpoints;
2593 it is the same as @code{info break}.
2596 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2597 watchpoints execute very quickly, and the debugger reports a change in
2598 value at the exact instruction where the change occurs. If @value{GDBN}
2599 cannot set a hardware watchpoint, it sets a software watchpoint, which
2600 executes more slowly and reports the change in value at the next
2601 statement, not the instruction, after the change occurs.
2603 When you issue the @code{watch} command, @value{GDBN} reports
2606 Hardware watchpoint @var{num}: @var{expr}
2610 if it was able to set a hardware watchpoint.
2612 Currently, the @code{awatch} and @code{rwatch} commands can only set
2613 hardware watchpoints, because accesses to data that don't change the
2614 value of the watched expression cannot be detected without examining
2615 every instruction as it is being executed, and @value{GDBN} does not do
2616 that currently. If @value{GDBN} finds that it is unable to set a
2617 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2618 will print a message like this:
2621 Expression cannot be implemented with read/access watchpoint.
2624 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2625 data type of the watched expression is wider than what a hardware
2626 watchpoint on the target machine can handle. For example, some systems
2627 can only watch regions that are up to 4 bytes wide; on such systems you
2628 cannot set hardware watchpoints for an expression that yields a
2629 double-precision floating-point number (which is typically 8 bytes
2630 wide). As a work-around, it might be possible to break the large region
2631 into a series of smaller ones and watch them with separate watchpoints.
2633 If you set too many hardware watchpoints, @value{GDBN} might be unable
2634 to insert all of them when you resume the execution of your program.
2635 Since the precise number of active watchpoints is unknown until such
2636 time as the program is about to be resumed, @value{GDBN} might not be
2637 able to warn you about this when you set the watchpoints, and the
2638 warning will be printed only when the program is resumed:
2641 Hardware watchpoint @var{num}: Could not insert watchpoint
2645 If this happens, delete or disable some of the watchpoints.
2647 The SPARClite DSU will generate traps when a program accesses some data
2648 or instruction address that is assigned to the debug registers. For the
2649 data addresses, DSU facilitates the @code{watch} command. However the
2650 hardware breakpoint registers can only take two data watchpoints, and
2651 both watchpoints must be the same kind. For example, you can set two
2652 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2653 @strong{or} two with @code{awatch} commands, but you cannot set one
2654 watchpoint with one command and the other with a different command.
2655 @value{GDBN} will reject the command if you try to mix watchpoints.
2656 Delete or disable unused watchpoint commands before setting new ones.
2658 If you call a function interactively using @code{print} or @code{call},
2659 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2660 kind of breakpoint or the call completes.
2662 @value{GDBN} automatically deletes watchpoints that watch local
2663 (automatic) variables, or expressions that involve such variables, when
2664 they go out of scope, that is, when the execution leaves the block in
2665 which these variables were defined. In particular, when the program
2666 being debugged terminates, @emph{all} local variables go out of scope,
2667 and so only watchpoints that watch global variables remain set. If you
2668 rerun the program, you will need to set all such watchpoints again. One
2669 way of doing that would be to set a code breakpoint at the entry to the
2670 @code{main} function and when it breaks, set all the watchpoints.
2673 @cindex watchpoints and threads
2674 @cindex threads and watchpoints
2675 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2676 usefulness. With the current watchpoint implementation, @value{GDBN}
2677 can only watch the value of an expression @emph{in a single thread}. If
2678 you are confident that the expression can only change due to the current
2679 thread's activity (and if you are also confident that no other thread
2680 can become current), then you can use watchpoints as usual. However,
2681 @value{GDBN} may not notice when a non-current thread's activity changes
2684 @c FIXME: this is almost identical to the previous paragraph.
2685 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2686 have only limited usefulness. If @value{GDBN} creates a software
2687 watchpoint, it can only watch the value of an expression @emph{in a
2688 single thread}. If you are confident that the expression can only
2689 change due to the current thread's activity (and if you are also
2690 confident that no other thread can become current), then you can use
2691 software watchpoints as usual. However, @value{GDBN} may not notice
2692 when a non-current thread's activity changes the expression. (Hardware
2693 watchpoints, in contrast, watch an expression in all threads.)
2696 @node Set Catchpoints
2697 @subsection Setting catchpoints
2698 @cindex catchpoints, setting
2699 @cindex exception handlers
2700 @cindex event handling
2702 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2703 kinds of program events, such as C@t{++} exceptions or the loading of a
2704 shared library. Use the @code{catch} command to set a catchpoint.
2708 @item catch @var{event}
2709 Stop when @var{event} occurs. @var{event} can be any of the following:
2713 The throwing of a C@t{++} exception.
2717 The catching of a C@t{++} exception.
2721 A call to @code{exec}. This is currently only available for HP-UX.
2725 A call to @code{fork}. This is currently only available for HP-UX.
2729 A call to @code{vfork}. This is currently only available for HP-UX.
2732 @itemx load @var{libname}
2734 The dynamic loading of any shared library, or the loading of the library
2735 @var{libname}. This is currently only available for HP-UX.
2738 @itemx unload @var{libname}
2739 @kindex catch unload
2740 The unloading of any dynamically loaded shared library, or the unloading
2741 of the library @var{libname}. This is currently only available for HP-UX.
2744 @item tcatch @var{event}
2745 Set a catchpoint that is enabled only for one stop. The catchpoint is
2746 automatically deleted after the first time the event is caught.
2750 Use the @code{info break} command to list the current catchpoints.
2752 There are currently some limitations to C@t{++} exception handling
2753 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2757 If you call a function interactively, @value{GDBN} normally returns
2758 control to you when the function has finished executing. If the call
2759 raises an exception, however, the call may bypass the mechanism that
2760 returns control to you and cause your program either to abort or to
2761 simply continue running until it hits a breakpoint, catches a signal
2762 that @value{GDBN} is listening for, or exits. This is the case even if
2763 you set a catchpoint for the exception; catchpoints on exceptions are
2764 disabled within interactive calls.
2767 You cannot raise an exception interactively.
2770 You cannot install an exception handler interactively.
2773 @cindex raise exceptions
2774 Sometimes @code{catch} is not the best way to debug exception handling:
2775 if you need to know exactly where an exception is raised, it is better to
2776 stop @emph{before} the exception handler is called, since that way you
2777 can see the stack before any unwinding takes place. If you set a
2778 breakpoint in an exception handler instead, it may not be easy to find
2779 out where the exception was raised.
2781 To stop just before an exception handler is called, you need some
2782 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2783 raised by calling a library function named @code{__raise_exception}
2784 which has the following ANSI C interface:
2787 /* @var{addr} is where the exception identifier is stored.
2788 @var{id} is the exception identifier. */
2789 void __raise_exception (void **addr, void *id);
2793 To make the debugger catch all exceptions before any stack
2794 unwinding takes place, set a breakpoint on @code{__raise_exception}
2795 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2797 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2798 that depends on the value of @var{id}, you can stop your program when
2799 a specific exception is raised. You can use multiple conditional
2800 breakpoints to stop your program when any of a number of exceptions are
2805 @subsection Deleting breakpoints
2807 @cindex clearing breakpoints, watchpoints, catchpoints
2808 @cindex deleting breakpoints, watchpoints, catchpoints
2809 It is often necessary to eliminate a breakpoint, watchpoint, or
2810 catchpoint once it has done its job and you no longer want your program
2811 to stop there. This is called @dfn{deleting} the breakpoint. A
2812 breakpoint that has been deleted no longer exists; it is forgotten.
2814 With the @code{clear} command you can delete breakpoints according to
2815 where they are in your program. With the @code{delete} command you can
2816 delete individual breakpoints, watchpoints, or catchpoints by specifying
2817 their breakpoint numbers.
2819 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2820 automatically ignores breakpoints on the first instruction to be executed
2821 when you continue execution without changing the execution address.
2826 Delete any breakpoints at the next instruction to be executed in the
2827 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2828 the innermost frame is selected, this is a good way to delete a
2829 breakpoint where your program just stopped.
2831 @item clear @var{function}
2832 @itemx clear @var{filename}:@var{function}
2833 Delete any breakpoints set at entry to the function @var{function}.
2835 @item clear @var{linenum}
2836 @itemx clear @var{filename}:@var{linenum}
2837 Delete any breakpoints set at or within the code of the specified line.
2839 @cindex delete breakpoints
2841 @kindex d @r{(@code{delete})}
2842 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2843 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2844 ranges specified as arguments. If no argument is specified, delete all
2845 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2846 confirm off}). You can abbreviate this command as @code{d}.
2850 @subsection Disabling breakpoints
2852 @kindex disable breakpoints
2853 @kindex enable breakpoints
2854 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2855 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2856 it had been deleted, but remembers the information on the breakpoint so
2857 that you can @dfn{enable} it again later.
2859 You disable and enable breakpoints, watchpoints, and catchpoints with
2860 the @code{enable} and @code{disable} commands, optionally specifying one
2861 or more breakpoint numbers as arguments. Use @code{info break} or
2862 @code{info watch} to print a list of breakpoints, watchpoints, and
2863 catchpoints if you do not know which numbers to use.
2865 A breakpoint, watchpoint, or catchpoint can have any of four different
2866 states of enablement:
2870 Enabled. The breakpoint stops your program. A breakpoint set
2871 with the @code{break} command starts out in this state.
2873 Disabled. The breakpoint has no effect on your program.
2875 Enabled once. The breakpoint stops your program, but then becomes
2878 Enabled for deletion. The breakpoint stops your program, but
2879 immediately after it does so it is deleted permanently. A breakpoint
2880 set with the @code{tbreak} command starts out in this state.
2883 You can use the following commands to enable or disable breakpoints,
2884 watchpoints, and catchpoints:
2887 @kindex disable breakpoints
2889 @kindex dis @r{(@code{disable})}
2890 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2891 Disable the specified breakpoints---or all breakpoints, if none are
2892 listed. A disabled breakpoint has no effect but is not forgotten. All
2893 options such as ignore-counts, conditions and commands are remembered in
2894 case the breakpoint is enabled again later. You may abbreviate
2895 @code{disable} as @code{dis}.
2897 @kindex enable breakpoints
2899 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2900 Enable the specified breakpoints (or all defined breakpoints). They
2901 become effective once again in stopping your program.
2903 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2904 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2905 of these breakpoints immediately after stopping your program.
2907 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2908 Enable the specified breakpoints to work once, then die. @value{GDBN}
2909 deletes any of these breakpoints as soon as your program stops there.
2912 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2913 @c confusing: tbreak is also initially enabled.
2914 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2915 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2916 subsequently, they become disabled or enabled only when you use one of
2917 the commands above. (The command @code{until} can set and delete a
2918 breakpoint of its own, but it does not change the state of your other
2919 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2923 @subsection Break conditions
2924 @cindex conditional breakpoints
2925 @cindex breakpoint conditions
2927 @c FIXME what is scope of break condition expr? Context where wanted?
2928 @c in particular for a watchpoint?
2929 The simplest sort of breakpoint breaks every time your program reaches a
2930 specified place. You can also specify a @dfn{condition} for a
2931 breakpoint. A condition is just a Boolean expression in your
2932 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2933 a condition evaluates the expression each time your program reaches it,
2934 and your program stops only if the condition is @emph{true}.
2936 This is the converse of using assertions for program validation; in that
2937 situation, you want to stop when the assertion is violated---that is,
2938 when the condition is false. In C, if you want to test an assertion expressed
2939 by the condition @var{assert}, you should set the condition
2940 @samp{! @var{assert}} on the appropriate breakpoint.
2942 Conditions are also accepted for watchpoints; you may not need them,
2943 since a watchpoint is inspecting the value of an expression anyhow---but
2944 it might be simpler, say, to just set a watchpoint on a variable name,
2945 and specify a condition that tests whether the new value is an interesting
2948 Break conditions can have side effects, and may even call functions in
2949 your program. This can be useful, for example, to activate functions
2950 that log program progress, or to use your own print functions to
2951 format special data structures. The effects are completely predictable
2952 unless there is another enabled breakpoint at the same address. (In
2953 that case, @value{GDBN} might see the other breakpoint first and stop your
2954 program without checking the condition of this one.) Note that
2955 breakpoint commands are usually more convenient and flexible than break
2957 purpose of performing side effects when a breakpoint is reached
2958 (@pxref{Break Commands, ,Breakpoint command lists}).
2960 Break conditions can be specified when a breakpoint is set, by using
2961 @samp{if} in the arguments to the @code{break} command. @xref{Set
2962 Breaks, ,Setting breakpoints}. They can also be changed at any time
2963 with the @code{condition} command.
2965 You can also use the @code{if} keyword with the @code{watch} command.
2966 The @code{catch} command does not recognize the @code{if} keyword;
2967 @code{condition} is the only way to impose a further condition on a
2972 @item condition @var{bnum} @var{expression}
2973 Specify @var{expression} as the break condition for breakpoint,
2974 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2975 breakpoint @var{bnum} stops your program only if the value of
2976 @var{expression} is true (nonzero, in C). When you use
2977 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2978 syntactic correctness, and to determine whether symbols in it have
2979 referents in the context of your breakpoint. If @var{expression} uses
2980 symbols not referenced in the context of the breakpoint, @value{GDBN}
2981 prints an error message:
2984 No symbol "foo" in current context.
2989 not actually evaluate @var{expression} at the time the @code{condition}
2990 command (or a command that sets a breakpoint with a condition, like
2991 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2993 @item condition @var{bnum}
2994 Remove the condition from breakpoint number @var{bnum}. It becomes
2995 an ordinary unconditional breakpoint.
2998 @cindex ignore count (of breakpoint)
2999 A special case of a breakpoint condition is to stop only when the
3000 breakpoint has been reached a certain number of times. This is so
3001 useful that there is a special way to do it, using the @dfn{ignore
3002 count} of the breakpoint. Every breakpoint has an ignore count, which
3003 is an integer. Most of the time, the ignore count is zero, and
3004 therefore has no effect. But if your program reaches a breakpoint whose
3005 ignore count is positive, then instead of stopping, it just decrements
3006 the ignore count by one and continues. As a result, if the ignore count
3007 value is @var{n}, the breakpoint does not stop the next @var{n} times
3008 your program reaches it.
3012 @item ignore @var{bnum} @var{count}
3013 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3014 The next @var{count} times the breakpoint is reached, your program's
3015 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3018 To make the breakpoint stop the next time it is reached, specify
3021 When you use @code{continue} to resume execution of your program from a
3022 breakpoint, you can specify an ignore count directly as an argument to
3023 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3024 Stepping,,Continuing and stepping}.
3026 If a breakpoint has a positive ignore count and a condition, the
3027 condition is not checked. Once the ignore count reaches zero,
3028 @value{GDBN} resumes checking the condition.
3030 You could achieve the effect of the ignore count with a condition such
3031 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3032 is decremented each time. @xref{Convenience Vars, ,Convenience
3036 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3039 @node Break Commands
3040 @subsection Breakpoint command lists
3042 @cindex breakpoint commands
3043 You can give any breakpoint (or watchpoint or catchpoint) a series of
3044 commands to execute when your program stops due to that breakpoint. For
3045 example, you might want to print the values of certain expressions, or
3046 enable other breakpoints.
3051 @item commands @r{[}@var{bnum}@r{]}
3052 @itemx @dots{} @var{command-list} @dots{}
3054 Specify a list of commands for breakpoint number @var{bnum}. The commands
3055 themselves appear on the following lines. Type a line containing just
3056 @code{end} to terminate the commands.
3058 To remove all commands from a breakpoint, type @code{commands} and
3059 follow it immediately with @code{end}; that is, give no commands.
3061 With no @var{bnum} argument, @code{commands} refers to the last
3062 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3063 recently encountered).
3066 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3067 disabled within a @var{command-list}.
3069 You can use breakpoint commands to start your program up again. Simply
3070 use the @code{continue} command, or @code{step}, or any other command
3071 that resumes execution.
3073 Any other commands in the command list, after a command that resumes
3074 execution, are ignored. This is because any time you resume execution
3075 (even with a simple @code{next} or @code{step}), you may encounter
3076 another breakpoint---which could have its own command list, leading to
3077 ambiguities about which list to execute.
3080 If the first command you specify in a command list is @code{silent}, the
3081 usual message about stopping at a breakpoint is not printed. This may
3082 be desirable for breakpoints that are to print a specific message and
3083 then continue. If none of the remaining commands print anything, you
3084 see no sign that the breakpoint was reached. @code{silent} is
3085 meaningful only at the beginning of a breakpoint command list.
3087 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3088 print precisely controlled output, and are often useful in silent
3089 breakpoints. @xref{Output, ,Commands for controlled output}.
3091 For example, here is how you could use breakpoint commands to print the
3092 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3098 printf "x is %d\n",x
3103 One application for breakpoint commands is to compensate for one bug so
3104 you can test for another. Put a breakpoint just after the erroneous line
3105 of code, give it a condition to detect the case in which something
3106 erroneous has been done, and give it commands to assign correct values
3107 to any variables that need them. End with the @code{continue} command
3108 so that your program does not stop, and start with the @code{silent}
3109 command so that no output is produced. Here is an example:
3120 @node Breakpoint Menus
3121 @subsection Breakpoint menus
3123 @cindex symbol overloading
3125 Some programming languages (notably C@t{++}) permit a single function name
3126 to be defined several times, for application in different contexts.
3127 This is called @dfn{overloading}. When a function name is overloaded,
3128 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3129 a breakpoint. If you realize this is a problem, you can use
3130 something like @samp{break @var{function}(@var{types})} to specify which
3131 particular version of the function you want. Otherwise, @value{GDBN} offers
3132 you a menu of numbered choices for different possible breakpoints, and
3133 waits for your selection with the prompt @samp{>}. The first two
3134 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3135 sets a breakpoint at each definition of @var{function}, and typing
3136 @kbd{0} aborts the @code{break} command without setting any new
3139 For example, the following session excerpt shows an attempt to set a
3140 breakpoint at the overloaded symbol @code{String::after}.
3141 We choose three particular definitions of that function name:
3143 @c FIXME! This is likely to change to show arg type lists, at least
3146 (@value{GDBP}) b String::after
3149 [2] file:String.cc; line number:867
3150 [3] file:String.cc; line number:860
3151 [4] file:String.cc; line number:875
3152 [5] file:String.cc; line number:853
3153 [6] file:String.cc; line number:846
3154 [7] file:String.cc; line number:735
3156 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3157 Breakpoint 2 at 0xb344: file String.cc, line 875.
3158 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3159 Multiple breakpoints were set.
3160 Use the "delete" command to delete unwanted
3166 @c @ifclear BARETARGET
3167 @node Error in Breakpoints
3168 @subsection ``Cannot insert breakpoints''
3170 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3172 Under some operating systems, breakpoints cannot be used in a program if
3173 any other process is running that program. In this situation,
3174 attempting to run or continue a program with a breakpoint causes
3175 @value{GDBN} to print an error message:
3178 Cannot insert breakpoints.
3179 The same program may be running in another process.
3182 When this happens, you have three ways to proceed:
3186 Remove or disable the breakpoints, then continue.
3189 Suspend @value{GDBN}, and copy the file containing your program to a new
3190 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3191 that @value{GDBN} should run your program under that name.
3192 Then start your program again.
3195 Relink your program so that the text segment is nonsharable, using the
3196 linker option @samp{-N}. The operating system limitation may not apply
3197 to nonsharable executables.
3201 A similar message can be printed if you request too many active
3202 hardware-assisted breakpoints and watchpoints:
3204 @c FIXME: the precise wording of this message may change; the relevant
3205 @c source change is not committed yet (Sep 3, 1999).
3207 Stopped; cannot insert breakpoints.
3208 You may have requested too many hardware breakpoints and watchpoints.
3212 This message is printed when you attempt to resume the program, since
3213 only then @value{GDBN} knows exactly how many hardware breakpoints and
3214 watchpoints it needs to insert.
3216 When this message is printed, you need to disable or remove some of the
3217 hardware-assisted breakpoints and watchpoints, and then continue.
3220 @node Continuing and Stepping
3221 @section Continuing and stepping
3225 @cindex resuming execution
3226 @dfn{Continuing} means resuming program execution until your program
3227 completes normally. In contrast, @dfn{stepping} means executing just
3228 one more ``step'' of your program, where ``step'' may mean either one
3229 line of source code, or one machine instruction (depending on what
3230 particular command you use). Either when continuing or when stepping,
3231 your program may stop even sooner, due to a breakpoint or a signal. (If
3232 it stops due to a signal, you may want to use @code{handle}, or use
3233 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3237 @kindex c @r{(@code{continue})}
3238 @kindex fg @r{(resume foreground execution)}
3239 @item continue @r{[}@var{ignore-count}@r{]}
3240 @itemx c @r{[}@var{ignore-count}@r{]}
3241 @itemx fg @r{[}@var{ignore-count}@r{]}
3242 Resume program execution, at the address where your program last stopped;
3243 any breakpoints set at that address are bypassed. The optional argument
3244 @var{ignore-count} allows you to specify a further number of times to
3245 ignore a breakpoint at this location; its effect is like that of
3246 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3248 The argument @var{ignore-count} is meaningful only when your program
3249 stopped due to a breakpoint. At other times, the argument to
3250 @code{continue} is ignored.
3252 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3253 debugged program is deemed to be the foreground program) are provided
3254 purely for convenience, and have exactly the same behavior as
3258 To resume execution at a different place, you can use @code{return}
3259 (@pxref{Returning, ,Returning from a function}) to go back to the
3260 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3261 different address}) to go to an arbitrary location in your program.
3263 A typical technique for using stepping is to set a breakpoint
3264 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3265 beginning of the function or the section of your program where a problem
3266 is believed to lie, run your program until it stops at that breakpoint,
3267 and then step through the suspect area, examining the variables that are
3268 interesting, until you see the problem happen.
3272 @kindex s @r{(@code{step})}
3274 Continue running your program until control reaches a different source
3275 line, then stop it and return control to @value{GDBN}. This command is
3276 abbreviated @code{s}.
3279 @c "without debugging information" is imprecise; actually "without line
3280 @c numbers in the debugging information". (gcc -g1 has debugging info but
3281 @c not line numbers). But it seems complex to try to make that
3282 @c distinction here.
3283 @emph{Warning:} If you use the @code{step} command while control is
3284 within a function that was compiled without debugging information,
3285 execution proceeds until control reaches a function that does have
3286 debugging information. Likewise, it will not step into a function which
3287 is compiled without debugging information. To step through functions
3288 without debugging information, use the @code{stepi} command, described
3292 The @code{step} command only stops at the first instruction of a source
3293 line. This prevents the multiple stops that could otherwise occur in
3294 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3295 to stop if a function that has debugging information is called within
3296 the line. In other words, @code{step} @emph{steps inside} any functions
3297 called within the line.
3299 Also, the @code{step} command only enters a function if there is line
3300 number information for the function. Otherwise it acts like the
3301 @code{next} command. This avoids problems when using @code{cc -gl}
3302 on MIPS machines. Previously, @code{step} entered subroutines if there
3303 was any debugging information about the routine.
3305 @item step @var{count}
3306 Continue running as in @code{step}, but do so @var{count} times. If a
3307 breakpoint is reached, or a signal not related to stepping occurs before
3308 @var{count} steps, stepping stops right away.
3311 @kindex n @r{(@code{next})}
3312 @item next @r{[}@var{count}@r{]}
3313 Continue to the next source line in the current (innermost) stack frame.
3314 This is similar to @code{step}, but function calls that appear within
3315 the line of code are executed without stopping. Execution stops when
3316 control reaches a different line of code at the original stack level
3317 that was executing when you gave the @code{next} command. This command
3318 is abbreviated @code{n}.
3320 An argument @var{count} is a repeat count, as for @code{step}.
3323 @c FIX ME!! Do we delete this, or is there a way it fits in with
3324 @c the following paragraph? --- Vctoria
3326 @c @code{next} within a function that lacks debugging information acts like
3327 @c @code{step}, but any function calls appearing within the code of the
3328 @c function are executed without stopping.
3330 The @code{next} command only stops at the first instruction of a
3331 source line. This prevents multiple stops that could otherwise occur in
3332 @code{switch} statements, @code{for} loops, etc.
3334 @kindex set step-mode
3336 @cindex functions without line info, and stepping
3337 @cindex stepping into functions with no line info
3338 @itemx set step-mode on
3339 The @code{set step-mode on} command causes the @code{step} command to
3340 stop at the first instruction of a function which contains no debug line
3341 information rather than stepping over it.
3343 This is useful in cases where you may be interested in inspecting the
3344 machine instructions of a function which has no symbolic info and do not
3345 want @value{GDBN} to automatically skip over this function.
3347 @item set step-mode off
3348 Causes the @code{step} command to step over any functions which contains no
3349 debug information. This is the default.
3353 Continue running until just after function in the selected stack frame
3354 returns. Print the returned value (if any).
3356 Contrast this with the @code{return} command (@pxref{Returning,
3357 ,Returning from a function}).
3360 @kindex u @r{(@code{until})}
3363 Continue running until a source line past the current line, in the
3364 current stack frame, is reached. This command is used to avoid single
3365 stepping through a loop more than once. It is like the @code{next}
3366 command, except that when @code{until} encounters a jump, it
3367 automatically continues execution until the program counter is greater
3368 than the address of the jump.
3370 This means that when you reach the end of a loop after single stepping
3371 though it, @code{until} makes your program continue execution until it
3372 exits the loop. In contrast, a @code{next} command at the end of a loop
3373 simply steps back to the beginning of the loop, which forces you to step
3374 through the next iteration.
3376 @code{until} always stops your program if it attempts to exit the current
3379 @code{until} may produce somewhat counterintuitive results if the order
3380 of machine code does not match the order of the source lines. For
3381 example, in the following excerpt from a debugging session, the @code{f}
3382 (@code{frame}) command shows that execution is stopped at line
3383 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3387 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3389 (@value{GDBP}) until
3390 195 for ( ; argc > 0; NEXTARG) @{
3393 This happened because, for execution efficiency, the compiler had
3394 generated code for the loop closure test at the end, rather than the
3395 start, of the loop---even though the test in a C @code{for}-loop is
3396 written before the body of the loop. The @code{until} command appeared
3397 to step back to the beginning of the loop when it advanced to this
3398 expression; however, it has not really gone to an earlier
3399 statement---not in terms of the actual machine code.
3401 @code{until} with no argument works by means of single
3402 instruction stepping, and hence is slower than @code{until} with an
3405 @item until @var{location}
3406 @itemx u @var{location}
3407 Continue running your program until either the specified location is
3408 reached, or the current stack frame returns. @var{location} is any of
3409 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3410 ,Setting breakpoints}). This form of the command uses breakpoints,
3411 and hence is quicker than @code{until} without an argument.
3414 @kindex si @r{(@code{stepi})}
3416 @itemx stepi @var{arg}
3418 Execute one machine instruction, then stop and return to the debugger.
3420 It is often useful to do @samp{display/i $pc} when stepping by machine
3421 instructions. This makes @value{GDBN} automatically display the next
3422 instruction to be executed, each time your program stops. @xref{Auto
3423 Display,, Automatic display}.
3425 An argument is a repeat count, as in @code{step}.
3429 @kindex ni @r{(@code{nexti})}
3431 @itemx nexti @var{arg}
3433 Execute one machine instruction, but if it is a function call,
3434 proceed until the function returns.
3436 An argument is a repeat count, as in @code{next}.
3443 A signal is an asynchronous event that can happen in a program. The
3444 operating system defines the possible kinds of signals, and gives each
3445 kind a name and a number. For example, in Unix @code{SIGINT} is the
3446 signal a program gets when you type an interrupt character (often @kbd{C-c});
3447 @code{SIGSEGV} is the signal a program gets from referencing a place in
3448 memory far away from all the areas in use; @code{SIGALRM} occurs when
3449 the alarm clock timer goes off (which happens only if your program has
3450 requested an alarm).
3452 @cindex fatal signals
3453 Some signals, including @code{SIGALRM}, are a normal part of the
3454 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3455 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3456 program has not specified in advance some other way to handle the signal.
3457 @code{SIGINT} does not indicate an error in your program, but it is normally
3458 fatal so it can carry out the purpose of the interrupt: to kill the program.
3460 @value{GDBN} has the ability to detect any occurrence of a signal in your
3461 program. You can tell @value{GDBN} in advance what to do for each kind of
3464 @cindex handling signals
3465 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3466 @code{SIGALRM} be silently passed to your program
3467 (so as not to interfere with their role in the program's functioning)
3468 but to stop your program immediately whenever an error signal happens.
3469 You can change these settings with the @code{handle} command.
3472 @kindex info signals
3475 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3476 handle each one. You can use this to see the signal numbers of all
3477 the defined types of signals.
3479 @code{info handle} is an alias for @code{info signals}.
3482 @item handle @var{signal} @var{keywords}@dots{}
3483 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3484 can be the number of a signal or its name (with or without the
3485 @samp{SIG} at the beginning); a list of signal numbers of the form
3486 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3487 known signals. The @var{keywords} say what change to make.
3491 The keywords allowed by the @code{handle} command can be abbreviated.
3492 Their full names are:
3496 @value{GDBN} should not stop your program when this signal happens. It may
3497 still print a message telling you that the signal has come in.
3500 @value{GDBN} should stop your program when this signal happens. This implies
3501 the @code{print} keyword as well.
3504 @value{GDBN} should print a message when this signal happens.
3507 @value{GDBN} should not mention the occurrence of the signal at all. This
3508 implies the @code{nostop} keyword as well.
3512 @value{GDBN} should allow your program to see this signal; your program
3513 can handle the signal, or else it may terminate if the signal is fatal
3514 and not handled. @code{pass} and @code{noignore} are synonyms.
3518 @value{GDBN} should not allow your program to see this signal.
3519 @code{nopass} and @code{ignore} are synonyms.
3523 When a signal stops your program, the signal is not visible to the
3525 continue. Your program sees the signal then, if @code{pass} is in
3526 effect for the signal in question @emph{at that time}. In other words,
3527 after @value{GDBN} reports a signal, you can use the @code{handle}
3528 command with @code{pass} or @code{nopass} to control whether your
3529 program sees that signal when you continue.
3531 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3532 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3533 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3536 You can also use the @code{signal} command to prevent your program from
3537 seeing a signal, or cause it to see a signal it normally would not see,
3538 or to give it any signal at any time. For example, if your program stopped
3539 due to some sort of memory reference error, you might store correct
3540 values into the erroneous variables and continue, hoping to see more
3541 execution; but your program would probably terminate immediately as
3542 a result of the fatal signal once it saw the signal. To prevent this,
3543 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3547 @section Stopping and starting multi-thread programs
3549 When your program has multiple threads (@pxref{Threads,, Debugging
3550 programs with multiple threads}), you can choose whether to set
3551 breakpoints on all threads, or on a particular thread.
3554 @cindex breakpoints and threads
3555 @cindex thread breakpoints
3556 @kindex break @dots{} thread @var{threadno}
3557 @item break @var{linespec} thread @var{threadno}
3558 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3559 @var{linespec} specifies source lines; there are several ways of
3560 writing them, but the effect is always to specify some source line.
3562 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3563 to specify that you only want @value{GDBN} to stop the program when a
3564 particular thread reaches this breakpoint. @var{threadno} is one of the
3565 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3566 column of the @samp{info threads} display.
3568 If you do not specify @samp{thread @var{threadno}} when you set a
3569 breakpoint, the breakpoint applies to @emph{all} threads of your
3572 You can use the @code{thread} qualifier on conditional breakpoints as
3573 well; in this case, place @samp{thread @var{threadno}} before the
3574 breakpoint condition, like this:
3577 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3582 @cindex stopped threads
3583 @cindex threads, stopped
3584 Whenever your program stops under @value{GDBN} for any reason,
3585 @emph{all} threads of execution stop, not just the current thread. This
3586 allows you to examine the overall state of the program, including
3587 switching between threads, without worrying that things may change
3590 @cindex continuing threads
3591 @cindex threads, continuing
3592 Conversely, whenever you restart the program, @emph{all} threads start
3593 executing. @emph{This is true even when single-stepping} with commands
3594 like @code{step} or @code{next}.
3596 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3597 Since thread scheduling is up to your debugging target's operating
3598 system (not controlled by @value{GDBN}), other threads may
3599 execute more than one statement while the current thread completes a
3600 single step. Moreover, in general other threads stop in the middle of a
3601 statement, rather than at a clean statement boundary, when the program
3604 You might even find your program stopped in another thread after
3605 continuing or even single-stepping. This happens whenever some other
3606 thread runs into a breakpoint, a signal, or an exception before the
3607 first thread completes whatever you requested.
3609 On some OSes, you can lock the OS scheduler and thus allow only a single
3613 @item set scheduler-locking @var{mode}
3614 Set the scheduler locking mode. If it is @code{off}, then there is no
3615 locking and any thread may run at any time. If @code{on}, then only the
3616 current thread may run when the inferior is resumed. The @code{step}
3617 mode optimizes for single-stepping. It stops other threads from
3618 ``seizing the prompt'' by preempting the current thread while you are
3619 stepping. Other threads will only rarely (or never) get a chance to run
3620 when you step. They are more likely to run when you @samp{next} over a
3621 function call, and they are completely free to run when you use commands
3622 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3623 thread hits a breakpoint during its timeslice, they will never steal the
3624 @value{GDBN} prompt away from the thread that you are debugging.
3626 @item show scheduler-locking
3627 Display the current scheduler locking mode.
3632 @chapter Examining the Stack
3634 When your program has stopped, the first thing you need to know is where it
3635 stopped and how it got there.
3638 Each time your program performs a function call, information about the call
3640 That information includes the location of the call in your program,
3641 the arguments of the call,
3642 and the local variables of the function being called.
3643 The information is saved in a block of data called a @dfn{stack frame}.
3644 The stack frames are allocated in a region of memory called the @dfn{call
3647 When your program stops, the @value{GDBN} commands for examining the
3648 stack allow you to see all of this information.
3650 @cindex selected frame
3651 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3652 @value{GDBN} commands refer implicitly to the selected frame. In
3653 particular, whenever you ask @value{GDBN} for the value of a variable in
3654 your program, the value is found in the selected frame. There are
3655 special @value{GDBN} commands to select whichever frame you are
3656 interested in. @xref{Selection, ,Selecting a frame}.
3658 When your program stops, @value{GDBN} automatically selects the
3659 currently executing frame and describes it briefly, similar to the
3660 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3663 * Frames:: Stack frames
3664 * Backtrace:: Backtraces
3665 * Selection:: Selecting a frame
3666 * Frame Info:: Information on a frame
3671 @section Stack frames
3673 @cindex frame, definition
3675 The call stack is divided up into contiguous pieces called @dfn{stack
3676 frames}, or @dfn{frames} for short; each frame is the data associated
3677 with one call to one function. The frame contains the arguments given
3678 to the function, the function's local variables, and the address at
3679 which the function is executing.
3681 @cindex initial frame
3682 @cindex outermost frame
3683 @cindex innermost frame
3684 When your program is started, the stack has only one frame, that of the
3685 function @code{main}. This is called the @dfn{initial} frame or the
3686 @dfn{outermost} frame. Each time a function is called, a new frame is
3687 made. Each time a function returns, the frame for that function invocation
3688 is eliminated. If a function is recursive, there can be many frames for
3689 the same function. The frame for the function in which execution is
3690 actually occurring is called the @dfn{innermost} frame. This is the most
3691 recently created of all the stack frames that still exist.
3693 @cindex frame pointer
3694 Inside your program, stack frames are identified by their addresses. A
3695 stack frame consists of many bytes, each of which has its own address; each
3696 kind of computer has a convention for choosing one byte whose
3697 address serves as the address of the frame. Usually this address is kept
3698 in a register called the @dfn{frame pointer register} while execution is
3699 going on in that frame.
3701 @cindex frame number
3702 @value{GDBN} assigns numbers to all existing stack frames, starting with
3703 zero for the innermost frame, one for the frame that called it,
3704 and so on upward. These numbers do not really exist in your program;
3705 they are assigned by @value{GDBN} to give you a way of designating stack
3706 frames in @value{GDBN} commands.
3708 @c The -fomit-frame-pointer below perennially causes hbox overflow
3709 @c underflow problems.
3710 @cindex frameless execution
3711 Some compilers provide a way to compile functions so that they operate
3712 without stack frames. (For example, the @value{GCC} option
3714 @samp{-fomit-frame-pointer}
3716 generates functions without a frame.)
3717 This is occasionally done with heavily used library functions to save
3718 the frame setup time. @value{GDBN} has limited facilities for dealing
3719 with these function invocations. If the innermost function invocation
3720 has no stack frame, @value{GDBN} nevertheless regards it as though
3721 it had a separate frame, which is numbered zero as usual, allowing
3722 correct tracing of the function call chain. However, @value{GDBN} has
3723 no provision for frameless functions elsewhere in the stack.
3726 @kindex frame@r{, command}
3727 @cindex current stack frame
3728 @item frame @var{args}
3729 The @code{frame} command allows you to move from one stack frame to another,
3730 and to print the stack frame you select. @var{args} may be either the
3731 address of the frame or the stack frame number. Without an argument,
3732 @code{frame} prints the current stack frame.
3734 @kindex select-frame
3735 @cindex selecting frame silently
3737 The @code{select-frame} command allows you to move from one stack frame
3738 to another without printing the frame. This is the silent version of
3747 @cindex stack traces
3748 A backtrace is a summary of how your program got where it is. It shows one
3749 line per frame, for many frames, starting with the currently executing
3750 frame (frame zero), followed by its caller (frame one), and on up the
3755 @kindex bt @r{(@code{backtrace})}
3758 Print a backtrace of the entire stack: one line per frame for all
3759 frames in the stack.
3761 You can stop the backtrace at any time by typing the system interrupt
3762 character, normally @kbd{C-c}.
3764 @item backtrace @var{n}
3766 Similar, but print only the innermost @var{n} frames.
3768 @item backtrace -@var{n}
3770 Similar, but print only the outermost @var{n} frames.
3775 @kindex info s @r{(@code{info stack})}
3776 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3777 are additional aliases for @code{backtrace}.
3779 Each line in the backtrace shows the frame number and the function name.
3780 The program counter value is also shown---unless you use @code{set
3781 print address off}. The backtrace also shows the source file name and
3782 line number, as well as the arguments to the function. The program
3783 counter value is omitted if it is at the beginning of the code for that
3786 Here is an example of a backtrace. It was made with the command
3787 @samp{bt 3}, so it shows the innermost three frames.
3791 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3793 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3794 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3796 (More stack frames follow...)
3801 The display for frame zero does not begin with a program counter
3802 value, indicating that your program has stopped at the beginning of the
3803 code for line @code{993} of @code{builtin.c}.
3806 @section Selecting a frame
3808 Most commands for examining the stack and other data in your program work on
3809 whichever stack frame is selected at the moment. Here are the commands for
3810 selecting a stack frame; all of them finish by printing a brief description
3811 of the stack frame just selected.
3814 @kindex frame@r{, selecting}
3815 @kindex f @r{(@code{frame})}
3818 Select frame number @var{n}. Recall that frame zero is the innermost
3819 (currently executing) frame, frame one is the frame that called the
3820 innermost one, and so on. The highest-numbered frame is the one for
3823 @item frame @var{addr}
3825 Select the frame at address @var{addr}. This is useful mainly if the
3826 chaining of stack frames has been damaged by a bug, making it
3827 impossible for @value{GDBN} to assign numbers properly to all frames. In
3828 addition, this can be useful when your program has multiple stacks and
3829 switches between them.
3831 On the SPARC architecture, @code{frame} needs two addresses to
3832 select an arbitrary frame: a frame pointer and a stack pointer.
3834 On the MIPS and Alpha architecture, it needs two addresses: a stack
3835 pointer and a program counter.
3837 On the 29k architecture, it needs three addresses: a register stack
3838 pointer, a program counter, and a memory stack pointer.
3839 @c note to future updaters: this is conditioned on a flag
3840 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3841 @c as of 27 Jan 1994.
3845 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3846 advances toward the outermost frame, to higher frame numbers, to frames
3847 that have existed longer. @var{n} defaults to one.
3850 @kindex do @r{(@code{down})}
3852 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3853 advances toward the innermost frame, to lower frame numbers, to frames
3854 that were created more recently. @var{n} defaults to one. You may
3855 abbreviate @code{down} as @code{do}.
3858 All of these commands end by printing two lines of output describing the
3859 frame. The first line shows the frame number, the function name, the
3860 arguments, and the source file and line number of execution in that
3861 frame. The second line shows the text of that source line.
3869 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3871 10 read_input_file (argv[i]);
3875 After such a printout, the @code{list} command with no arguments
3876 prints ten lines centered on the point of execution in the frame.
3877 @xref{List, ,Printing source lines}.
3880 @kindex down-silently
3882 @item up-silently @var{n}
3883 @itemx down-silently @var{n}
3884 These two commands are variants of @code{up} and @code{down},
3885 respectively; they differ in that they do their work silently, without
3886 causing display of the new frame. They are intended primarily for use
3887 in @value{GDBN} command scripts, where the output might be unnecessary and
3892 @section Information about a frame
3894 There are several other commands to print information about the selected
3900 When used without any argument, this command does not change which
3901 frame is selected, but prints a brief description of the currently
3902 selected stack frame. It can be abbreviated @code{f}. With an
3903 argument, this command is used to select a stack frame.
3904 @xref{Selection, ,Selecting a frame}.
3907 @kindex info f @r{(@code{info frame})}
3910 This command prints a verbose description of the selected stack frame,
3915 the address of the frame
3917 the address of the next frame down (called by this frame)
3919 the address of the next frame up (caller of this frame)
3921 the language in which the source code corresponding to this frame is written
3923 the address of the frame's arguments
3925 the address of the frame's local variables
3927 the program counter saved in it (the address of execution in the caller frame)
3929 which registers were saved in the frame
3932 @noindent The verbose description is useful when
3933 something has gone wrong that has made the stack format fail to fit
3934 the usual conventions.
3936 @item info frame @var{addr}
3937 @itemx info f @var{addr}
3938 Print a verbose description of the frame at address @var{addr}, without
3939 selecting that frame. The selected frame remains unchanged by this
3940 command. This requires the same kind of address (more than one for some
3941 architectures) that you specify in the @code{frame} command.
3942 @xref{Selection, ,Selecting a frame}.
3946 Print the arguments of the selected frame, each on a separate line.
3950 Print the local variables of the selected frame, each on a separate
3951 line. These are all variables (declared either static or automatic)
3952 accessible at the point of execution of the selected frame.
3955 @cindex catch exceptions, list active handlers
3956 @cindex exception handlers, how to list
3958 Print a list of all the exception handlers that are active in the
3959 current stack frame at the current point of execution. To see other
3960 exception handlers, visit the associated frame (using the @code{up},
3961 @code{down}, or @code{frame} commands); then type @code{info catch}.
3962 @xref{Set Catchpoints, , Setting catchpoints}.
3968 @chapter Examining Source Files
3970 @value{GDBN} can print parts of your program's source, since the debugging
3971 information recorded in the program tells @value{GDBN} what source files were
3972 used to build it. When your program stops, @value{GDBN} spontaneously prints
3973 the line where it stopped. Likewise, when you select a stack frame
3974 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3975 execution in that frame has stopped. You can print other portions of
3976 source files by explicit command.
3978 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3979 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3980 @value{GDBN} under @sc{gnu} Emacs}.
3983 * List:: Printing source lines
3984 * Search:: Searching source files
3985 * Source Path:: Specifying source directories
3986 * Machine Code:: Source and machine code
3990 @section Printing source lines
3993 @kindex l @r{(@code{list})}
3994 To print lines from a source file, use the @code{list} command
3995 (abbreviated @code{l}). By default, ten lines are printed.
3996 There are several ways to specify what part of the file you want to print.
3998 Here are the forms of the @code{list} command most commonly used:
4001 @item list @var{linenum}
4002 Print lines centered around line number @var{linenum} in the
4003 current source file.
4005 @item list @var{function}
4006 Print lines centered around the beginning of function
4010 Print more lines. If the last lines printed were printed with a
4011 @code{list} command, this prints lines following the last lines
4012 printed; however, if the last line printed was a solitary line printed
4013 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4014 Stack}), this prints lines centered around that line.
4017 Print lines just before the lines last printed.
4020 By default, @value{GDBN} prints ten source lines with any of these forms of
4021 the @code{list} command. You can change this using @code{set listsize}:
4024 @kindex set listsize
4025 @item set listsize @var{count}
4026 Make the @code{list} command display @var{count} source lines (unless
4027 the @code{list} argument explicitly specifies some other number).
4029 @kindex show listsize
4031 Display the number of lines that @code{list} prints.
4034 Repeating a @code{list} command with @key{RET} discards the argument,
4035 so it is equivalent to typing just @code{list}. This is more useful
4036 than listing the same lines again. An exception is made for an
4037 argument of @samp{-}; that argument is preserved in repetition so that
4038 each repetition moves up in the source file.
4041 In general, the @code{list} command expects you to supply zero, one or two
4042 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4043 of writing them, but the effect is always to specify some source line.
4044 Here is a complete description of the possible arguments for @code{list}:
4047 @item list @var{linespec}
4048 Print lines centered around the line specified by @var{linespec}.
4050 @item list @var{first},@var{last}
4051 Print lines from @var{first} to @var{last}. Both arguments are
4054 @item list ,@var{last}
4055 Print lines ending with @var{last}.
4057 @item list @var{first},
4058 Print lines starting with @var{first}.
4061 Print lines just after the lines last printed.
4064 Print lines just before the lines last printed.
4067 As described in the preceding table.
4070 Here are the ways of specifying a single source line---all the
4075 Specifies line @var{number} of the current source file.
4076 When a @code{list} command has two linespecs, this refers to
4077 the same source file as the first linespec.
4080 Specifies the line @var{offset} lines after the last line printed.
4081 When used as the second linespec in a @code{list} command that has
4082 two, this specifies the line @var{offset} lines down from the
4086 Specifies the line @var{offset} lines before the last line printed.
4088 @item @var{filename}:@var{number}
4089 Specifies line @var{number} in the source file @var{filename}.
4091 @item @var{function}
4092 Specifies the line that begins the body of the function @var{function}.
4093 For example: in C, this is the line with the open brace.
4095 @item @var{filename}:@var{function}
4096 Specifies the line of the open-brace that begins the body of the
4097 function @var{function} in the file @var{filename}. You only need the
4098 file name with a function name to avoid ambiguity when there are
4099 identically named functions in different source files.
4101 @item *@var{address}
4102 Specifies the line containing the program address @var{address}.
4103 @var{address} may be any expression.
4107 @section Searching source files
4109 @kindex reverse-search
4111 There are two commands for searching through the current source file for a
4116 @kindex forward-search
4117 @item forward-search @var{regexp}
4118 @itemx search @var{regexp}
4119 The command @samp{forward-search @var{regexp}} checks each line,
4120 starting with the one following the last line listed, for a match for
4121 @var{regexp}. It lists the line that is found. You can use the
4122 synonym @samp{search @var{regexp}} or abbreviate the command name as
4125 @item reverse-search @var{regexp}
4126 The command @samp{reverse-search @var{regexp}} checks each line, starting
4127 with the one before the last line listed and going backward, for a match
4128 for @var{regexp}. It lists the line that is found. You can abbreviate
4129 this command as @code{rev}.
4133 @section Specifying source directories
4136 @cindex directories for source files
4137 Executable programs sometimes do not record the directories of the source
4138 files from which they were compiled, just the names. Even when they do,
4139 the directories could be moved between the compilation and your debugging
4140 session. @value{GDBN} has a list of directories to search for source files;
4141 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4142 it tries all the directories in the list, in the order they are present
4143 in the list, until it finds a file with the desired name. Note that
4144 the executable search path is @emph{not} used for this purpose. Neither is
4145 the current working directory, unless it happens to be in the source
4148 If @value{GDBN} cannot find a source file in the source path, and the
4149 object program records a directory, @value{GDBN} tries that directory
4150 too. If the source path is empty, and there is no record of the
4151 compilation directory, @value{GDBN} looks in the current directory as a
4154 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4155 any information it has cached about where source files are found and where
4156 each line is in the file.
4160 When you start @value{GDBN}, its source path includes only @samp{cdir}
4161 and @samp{cwd}, in that order.
4162 To add other directories, use the @code{directory} command.
4165 @item directory @var{dirname} @dots{}
4166 @item dir @var{dirname} @dots{}
4167 Add directory @var{dirname} to the front of the source path. Several
4168 directory names may be given to this command, separated by @samp{:}
4169 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4170 part of absolute file names) or
4171 whitespace. You may specify a directory that is already in the source
4172 path; this moves it forward, so @value{GDBN} searches it sooner.
4176 @vindex $cdir@r{, convenience variable}
4177 @vindex $cwdr@r{, convenience variable}
4178 @cindex compilation directory
4179 @cindex current directory
4180 @cindex working directory
4181 @cindex directory, current
4182 @cindex directory, compilation
4183 You can use the string @samp{$cdir} to refer to the compilation
4184 directory (if one is recorded), and @samp{$cwd} to refer to the current
4185 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4186 tracks the current working directory as it changes during your @value{GDBN}
4187 session, while the latter is immediately expanded to the current
4188 directory at the time you add an entry to the source path.
4191 Reset the source path to empty again. This requires confirmation.
4193 @c RET-repeat for @code{directory} is explicitly disabled, but since
4194 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4196 @item show directories
4197 @kindex show directories
4198 Print the source path: show which directories it contains.
4201 If your source path is cluttered with directories that are no longer of
4202 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4203 versions of source. You can correct the situation as follows:
4207 Use @code{directory} with no argument to reset the source path to empty.
4210 Use @code{directory} with suitable arguments to reinstall the
4211 directories you want in the source path. You can add all the
4212 directories in one command.
4216 @section Source and machine code
4218 You can use the command @code{info line} to map source lines to program
4219 addresses (and vice versa), and the command @code{disassemble} to display
4220 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4221 mode, the @code{info line} command causes the arrow to point to the
4222 line specified. Also, @code{info line} prints addresses in symbolic form as
4227 @item info line @var{linespec}
4228 Print the starting and ending addresses of the compiled code for
4229 source line @var{linespec}. You can specify source lines in any of
4230 the ways understood by the @code{list} command (@pxref{List, ,Printing
4234 For example, we can use @code{info line} to discover the location of
4235 the object code for the first line of function
4236 @code{m4_changequote}:
4238 @c FIXME: I think this example should also show the addresses in
4239 @c symbolic form, as they usually would be displayed.
4241 (@value{GDBP}) info line m4_changequote
4242 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4246 We can also inquire (using @code{*@var{addr}} as the form for
4247 @var{linespec}) what source line covers a particular address:
4249 (@value{GDBP}) info line *0x63ff
4250 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4253 @cindex @code{$_} and @code{info line}
4254 @kindex x@r{(examine), and} info line
4255 After @code{info line}, the default address for the @code{x} command
4256 is changed to the starting address of the line, so that @samp{x/i} is
4257 sufficient to begin examining the machine code (@pxref{Memory,
4258 ,Examining memory}). Also, this address is saved as the value of the
4259 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4264 @cindex assembly instructions
4265 @cindex instructions, assembly
4266 @cindex machine instructions
4267 @cindex listing machine instructions
4269 This specialized command dumps a range of memory as machine
4270 instructions. The default memory range is the function surrounding the
4271 program counter of the selected frame. A single argument to this
4272 command is a program counter value; @value{GDBN} dumps the function
4273 surrounding this value. Two arguments specify a range of addresses
4274 (first inclusive, second exclusive) to dump.
4277 The following example shows the disassembly of a range of addresses of
4278 HP PA-RISC 2.0 code:
4281 (@value{GDBP}) disas 0x32c4 0x32e4
4282 Dump of assembler code from 0x32c4 to 0x32e4:
4283 0x32c4 <main+204>: addil 0,dp
4284 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4285 0x32cc <main+212>: ldil 0x3000,r31
4286 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4287 0x32d4 <main+220>: ldo 0(r31),rp
4288 0x32d8 <main+224>: addil -0x800,dp
4289 0x32dc <main+228>: ldo 0x588(r1),r26
4290 0x32e0 <main+232>: ldil 0x3000,r31
4291 End of assembler dump.
4294 Some architectures have more than one commonly-used set of instruction
4295 mnemonics or other syntax.
4298 @kindex set disassembly-flavor
4299 @cindex assembly instructions
4300 @cindex instructions, assembly
4301 @cindex machine instructions
4302 @cindex listing machine instructions
4303 @cindex Intel disassembly flavor
4304 @cindex AT&T disassembly flavor
4305 @item set disassembly-flavor @var{instruction-set}
4306 Select the instruction set to use when disassembling the
4307 program via the @code{disassemble} or @code{x/i} commands.
4309 Currently this command is only defined for the Intel x86 family. You
4310 can set @var{instruction-set} to either @code{intel} or @code{att}.
4311 The default is @code{att}, the AT&T flavor used by default by Unix
4312 assemblers for x86-based targets.
4317 @chapter Examining Data
4319 @cindex printing data
4320 @cindex examining data
4323 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4324 @c document because it is nonstandard... Under Epoch it displays in a
4325 @c different window or something like that.
4326 The usual way to examine data in your program is with the @code{print}
4327 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4328 evaluates and prints the value of an expression of the language your
4329 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4330 Different Languages}).
4333 @item print @var{expr}
4334 @itemx print /@var{f} @var{expr}
4335 @var{expr} is an expression (in the source language). By default the
4336 value of @var{expr} is printed in a format appropriate to its data type;
4337 you can choose a different format by specifying @samp{/@var{f}}, where
4338 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4342 @itemx print /@var{f}
4343 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4344 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4345 conveniently inspect the same value in an alternative format.
4348 A more low-level way of examining data is with the @code{x} command.
4349 It examines data in memory at a specified address and prints it in a
4350 specified format. @xref{Memory, ,Examining memory}.
4352 If you are interested in information about types, or about how the
4353 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4354 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4358 * Expressions:: Expressions
4359 * Variables:: Program variables
4360 * Arrays:: Artificial arrays
4361 * Output Formats:: Output formats
4362 * Memory:: Examining memory
4363 * Auto Display:: Automatic display
4364 * Print Settings:: Print settings
4365 * Value History:: Value history
4366 * Convenience Vars:: Convenience variables
4367 * Registers:: Registers
4368 * Floating Point Hardware:: Floating point hardware
4369 * Memory Region Attributes:: Memory region attributes
4373 @section Expressions
4376 @code{print} and many other @value{GDBN} commands accept an expression and
4377 compute its value. Any kind of constant, variable or operator defined
4378 by the programming language you are using is valid in an expression in
4379 @value{GDBN}. This includes conditional expressions, function calls, casts
4380 and string constants. It unfortunately does not include symbols defined
4381 by preprocessor @code{#define} commands.
4383 @value{GDBN} supports array constants in expressions input by
4384 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4385 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4386 memory that is @code{malloc}ed in the target program.
4388 Because C is so widespread, most of the expressions shown in examples in
4389 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4390 Languages}, for information on how to use expressions in other
4393 In this section, we discuss operators that you can use in @value{GDBN}
4394 expressions regardless of your programming language.
4396 Casts are supported in all languages, not just in C, because it is so
4397 useful to cast a number into a pointer in order to examine a structure
4398 at that address in memory.
4399 @c FIXME: casts supported---Mod2 true?
4401 @value{GDBN} supports these operators, in addition to those common
4402 to programming languages:
4406 @samp{@@} is a binary operator for treating parts of memory as arrays.
4407 @xref{Arrays, ,Artificial arrays}, for more information.
4410 @samp{::} allows you to specify a variable in terms of the file or
4411 function where it is defined. @xref{Variables, ,Program variables}.
4413 @cindex @{@var{type}@}
4414 @cindex type casting memory
4415 @cindex memory, viewing as typed object
4416 @cindex casts, to view memory
4417 @item @{@var{type}@} @var{addr}
4418 Refers to an object of type @var{type} stored at address @var{addr} in
4419 memory. @var{addr} may be any expression whose value is an integer or
4420 pointer (but parentheses are required around binary operators, just as in
4421 a cast). This construct is allowed regardless of what kind of data is
4422 normally supposed to reside at @var{addr}.
4426 @section Program variables
4428 The most common kind of expression to use is the name of a variable
4431 Variables in expressions are understood in the selected stack frame
4432 (@pxref{Selection, ,Selecting a frame}); they must be either:
4436 global (or file-static)
4443 visible according to the scope rules of the
4444 programming language from the point of execution in that frame
4447 @noindent This means that in the function
4462 you can examine and use the variable @code{a} whenever your program is
4463 executing within the function @code{foo}, but you can only use or
4464 examine the variable @code{b} while your program is executing inside
4465 the block where @code{b} is declared.
4467 @cindex variable name conflict
4468 There is an exception: you can refer to a variable or function whose
4469 scope is a single source file even if the current execution point is not
4470 in this file. But it is possible to have more than one such variable or
4471 function with the same name (in different source files). If that
4472 happens, referring to that name has unpredictable effects. If you wish,
4473 you can specify a static variable in a particular function or file,
4474 using the colon-colon notation:
4476 @cindex colon-colon, context for variables/functions
4478 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4479 @cindex @code{::}, context for variables/functions
4482 @var{file}::@var{variable}
4483 @var{function}::@var{variable}
4487 Here @var{file} or @var{function} is the name of the context for the
4488 static @var{variable}. In the case of file names, you can use quotes to
4489 make sure @value{GDBN} parses the file name as a single word---for example,
4490 to print a global value of @code{x} defined in @file{f2.c}:
4493 (@value{GDBP}) p 'f2.c'::x
4496 @cindex C@t{++} scope resolution
4497 This use of @samp{::} is very rarely in conflict with the very similar
4498 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4499 scope resolution operator in @value{GDBN} expressions.
4500 @c FIXME: Um, so what happens in one of those rare cases where it's in
4503 @cindex wrong values
4504 @cindex variable values, wrong
4506 @emph{Warning:} Occasionally, a local variable may appear to have the
4507 wrong value at certain points in a function---just after entry to a new
4508 scope, and just before exit.
4510 You may see this problem when you are stepping by machine instructions.
4511 This is because, on most machines, it takes more than one instruction to
4512 set up a stack frame (including local variable definitions); if you are
4513 stepping by machine instructions, variables may appear to have the wrong
4514 values until the stack frame is completely built. On exit, it usually
4515 also takes more than one machine instruction to destroy a stack frame;
4516 after you begin stepping through that group of instructions, local
4517 variable definitions may be gone.
4519 This may also happen when the compiler does significant optimizations.
4520 To be sure of always seeing accurate values, turn off all optimization
4523 @cindex ``No symbol "foo" in current context''
4524 Another possible effect of compiler optimizations is to optimize
4525 unused variables out of existence, or assign variables to registers (as
4526 opposed to memory addresses). Depending on the support for such cases
4527 offered by the debug info format used by the compiler, @value{GDBN}
4528 might not be able to display values for such local variables. If that
4529 happens, @value{GDBN} will print a message like this:
4532 No symbol "foo" in current context.
4535 To solve such problems, either recompile without optimizations, or use a
4536 different debug info format, if the compiler supports several such
4537 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4538 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4539 in a format that is superior to formats such as COFF. You may be able
4540 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4541 debug info. See @ref{Debugging Options,,Options for Debugging Your
4542 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4547 @section Artificial arrays
4549 @cindex artificial array
4550 @kindex @@@r{, referencing memory as an array}
4551 It is often useful to print out several successive objects of the
4552 same type in memory; a section of an array, or an array of
4553 dynamically determined size for which only a pointer exists in the
4556 You can do this by referring to a contiguous span of memory as an
4557 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4558 operand of @samp{@@} should be the first element of the desired array
4559 and be an individual object. The right operand should be the desired length
4560 of the array. The result is an array value whose elements are all of
4561 the type of the left argument. The first element is actually the left
4562 argument; the second element comes from bytes of memory immediately
4563 following those that hold the first element, and so on. Here is an
4564 example. If a program says
4567 int *array = (int *) malloc (len * sizeof (int));
4571 you can print the contents of @code{array} with
4577 The left operand of @samp{@@} must reside in memory. Array values made
4578 with @samp{@@} in this way behave just like other arrays in terms of
4579 subscripting, and are coerced to pointers when used in expressions.
4580 Artificial arrays most often appear in expressions via the value history
4581 (@pxref{Value History, ,Value history}), after printing one out.
4583 Another way to create an artificial array is to use a cast.
4584 This re-interprets a value as if it were an array.
4585 The value need not be in memory:
4587 (@value{GDBP}) p/x (short[2])0x12345678
4588 $1 = @{0x1234, 0x5678@}
4591 As a convenience, if you leave the array length out (as in
4592 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4593 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4595 (@value{GDBP}) p/x (short[])0x12345678
4596 $2 = @{0x1234, 0x5678@}
4599 Sometimes the artificial array mechanism is not quite enough; in
4600 moderately complex data structures, the elements of interest may not
4601 actually be adjacent---for example, if you are interested in the values
4602 of pointers in an array. One useful work-around in this situation is
4603 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4604 variables}) as a counter in an expression that prints the first
4605 interesting value, and then repeat that expression via @key{RET}. For
4606 instance, suppose you have an array @code{dtab} of pointers to
4607 structures, and you are interested in the values of a field @code{fv}
4608 in each structure. Here is an example of what you might type:
4618 @node Output Formats
4619 @section Output formats
4621 @cindex formatted output
4622 @cindex output formats
4623 By default, @value{GDBN} prints a value according to its data type. Sometimes
4624 this is not what you want. For example, you might want to print a number
4625 in hex, or a pointer in decimal. Or you might want to view data in memory
4626 at a certain address as a character string or as an instruction. To do
4627 these things, specify an @dfn{output format} when you print a value.
4629 The simplest use of output formats is to say how to print a value
4630 already computed. This is done by starting the arguments of the
4631 @code{print} command with a slash and a format letter. The format
4632 letters supported are:
4636 Regard the bits of the value as an integer, and print the integer in
4640 Print as integer in signed decimal.
4643 Print as integer in unsigned decimal.
4646 Print as integer in octal.
4649 Print as integer in binary. The letter @samp{t} stands for ``two''.
4650 @footnote{@samp{b} cannot be used because these format letters are also
4651 used with the @code{x} command, where @samp{b} stands for ``byte'';
4652 see @ref{Memory,,Examining memory}.}
4655 @cindex unknown address, locating
4656 @cindex locate address
4657 Print as an address, both absolute in hexadecimal and as an offset from
4658 the nearest preceding symbol. You can use this format used to discover
4659 where (in what function) an unknown address is located:
4662 (@value{GDBP}) p/a 0x54320
4663 $3 = 0x54320 <_initialize_vx+396>
4667 The command @code{info symbol 0x54320} yields similar results.
4668 @xref{Symbols, info symbol}.
4671 Regard as an integer and print it as a character constant.
4674 Regard the bits of the value as a floating point number and print
4675 using typical floating point syntax.
4678 For example, to print the program counter in hex (@pxref{Registers}), type
4685 Note that no space is required before the slash; this is because command
4686 names in @value{GDBN} cannot contain a slash.
4688 To reprint the last value in the value history with a different format,
4689 you can use the @code{print} command with just a format and no
4690 expression. For example, @samp{p/x} reprints the last value in hex.
4693 @section Examining memory
4695 You can use the command @code{x} (for ``examine'') to examine memory in
4696 any of several formats, independently of your program's data types.
4698 @cindex examining memory
4700 @kindex x @r{(examine memory)}
4701 @item x/@var{nfu} @var{addr}
4704 Use the @code{x} command to examine memory.
4707 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4708 much memory to display and how to format it; @var{addr} is an
4709 expression giving the address where you want to start displaying memory.
4710 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4711 Several commands set convenient defaults for @var{addr}.
4714 @item @var{n}, the repeat count
4715 The repeat count is a decimal integer; the default is 1. It specifies
4716 how much memory (counting by units @var{u}) to display.
4717 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4720 @item @var{f}, the display format
4721 The display format is one of the formats used by @code{print},
4722 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4723 The default is @samp{x} (hexadecimal) initially.
4724 The default changes each time you use either @code{x} or @code{print}.
4726 @item @var{u}, the unit size
4727 The unit size is any of
4733 Halfwords (two bytes).
4735 Words (four bytes). This is the initial default.
4737 Giant words (eight bytes).
4740 Each time you specify a unit size with @code{x}, that size becomes the
4741 default unit the next time you use @code{x}. (For the @samp{s} and
4742 @samp{i} formats, the unit size is ignored and is normally not written.)
4744 @item @var{addr}, starting display address
4745 @var{addr} is the address where you want @value{GDBN} to begin displaying
4746 memory. The expression need not have a pointer value (though it may);
4747 it is always interpreted as an integer address of a byte of memory.
4748 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4749 @var{addr} is usually just after the last address examined---but several
4750 other commands also set the default address: @code{info breakpoints} (to
4751 the address of the last breakpoint listed), @code{info line} (to the
4752 starting address of a line), and @code{print} (if you use it to display
4753 a value from memory).
4756 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4757 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4758 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4759 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4760 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4762 Since the letters indicating unit sizes are all distinct from the
4763 letters specifying output formats, you do not have to remember whether
4764 unit size or format comes first; either order works. The output
4765 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4766 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4768 Even though the unit size @var{u} is ignored for the formats @samp{s}
4769 and @samp{i}, you might still want to use a count @var{n}; for example,
4770 @samp{3i} specifies that you want to see three machine instructions,
4771 including any operands. The command @code{disassemble} gives an
4772 alternative way of inspecting machine instructions; see @ref{Machine
4773 Code,,Source and machine code}.
4775 All the defaults for the arguments to @code{x} are designed to make it
4776 easy to continue scanning memory with minimal specifications each time
4777 you use @code{x}. For example, after you have inspected three machine
4778 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4779 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4780 the repeat count @var{n} is used again; the other arguments default as
4781 for successive uses of @code{x}.
4783 @cindex @code{$_}, @code{$__}, and value history
4784 The addresses and contents printed by the @code{x} command are not saved
4785 in the value history because there is often too much of them and they
4786 would get in the way. Instead, @value{GDBN} makes these values available for
4787 subsequent use in expressions as values of the convenience variables
4788 @code{$_} and @code{$__}. After an @code{x} command, the last address
4789 examined is available for use in expressions in the convenience variable
4790 @code{$_}. The contents of that address, as examined, are available in
4791 the convenience variable @code{$__}.
4793 If the @code{x} command has a repeat count, the address and contents saved
4794 are from the last memory unit printed; this is not the same as the last
4795 address printed if several units were printed on the last line of output.
4798 @section Automatic display
4799 @cindex automatic display
4800 @cindex display of expressions
4802 If you find that you want to print the value of an expression frequently
4803 (to see how it changes), you might want to add it to the @dfn{automatic
4804 display list} so that @value{GDBN} prints its value each time your program stops.
4805 Each expression added to the list is given a number to identify it;
4806 to remove an expression from the list, you specify that number.
4807 The automatic display looks like this:
4811 3: bar[5] = (struct hack *) 0x3804
4815 This display shows item numbers, expressions and their current values. As with
4816 displays you request manually using @code{x} or @code{print}, you can
4817 specify the output format you prefer; in fact, @code{display} decides
4818 whether to use @code{print} or @code{x} depending on how elaborate your
4819 format specification is---it uses @code{x} if you specify a unit size,
4820 or one of the two formats (@samp{i} and @samp{s}) that are only
4821 supported by @code{x}; otherwise it uses @code{print}.
4825 @item display @var{expr}
4826 Add the expression @var{expr} to the list of expressions to display
4827 each time your program stops. @xref{Expressions, ,Expressions}.
4829 @code{display} does not repeat if you press @key{RET} again after using it.
4831 @item display/@var{fmt} @var{expr}
4832 For @var{fmt} specifying only a display format and not a size or
4833 count, add the expression @var{expr} to the auto-display list but
4834 arrange to display it each time in the specified format @var{fmt}.
4835 @xref{Output Formats,,Output formats}.
4837 @item display/@var{fmt} @var{addr}
4838 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4839 number of units, add the expression @var{addr} as a memory address to
4840 be examined each time your program stops. Examining means in effect
4841 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4844 For example, @samp{display/i $pc} can be helpful, to see the machine
4845 instruction about to be executed each time execution stops (@samp{$pc}
4846 is a common name for the program counter; @pxref{Registers, ,Registers}).
4849 @kindex delete display
4851 @item undisplay @var{dnums}@dots{}
4852 @itemx delete display @var{dnums}@dots{}
4853 Remove item numbers @var{dnums} from the list of expressions to display.
4855 @code{undisplay} does not repeat if you press @key{RET} after using it.
4856 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4858 @kindex disable display
4859 @item disable display @var{dnums}@dots{}
4860 Disable the display of item numbers @var{dnums}. A disabled display
4861 item is not printed automatically, but is not forgotten. It may be
4862 enabled again later.
4864 @kindex enable display
4865 @item enable display @var{dnums}@dots{}
4866 Enable display of item numbers @var{dnums}. It becomes effective once
4867 again in auto display of its expression, until you specify otherwise.
4870 Display the current values of the expressions on the list, just as is
4871 done when your program stops.
4873 @kindex info display
4875 Print the list of expressions previously set up to display
4876 automatically, each one with its item number, but without showing the
4877 values. This includes disabled expressions, which are marked as such.
4878 It also includes expressions which would not be displayed right now
4879 because they refer to automatic variables not currently available.
4882 If a display expression refers to local variables, then it does not make
4883 sense outside the lexical context for which it was set up. Such an
4884 expression is disabled when execution enters a context where one of its
4885 variables is not defined. For example, if you give the command
4886 @code{display last_char} while inside a function with an argument
4887 @code{last_char}, @value{GDBN} displays this argument while your program
4888 continues to stop inside that function. When it stops elsewhere---where
4889 there is no variable @code{last_char}---the display is disabled
4890 automatically. The next time your program stops where @code{last_char}
4891 is meaningful, you can enable the display expression once again.
4893 @node Print Settings
4894 @section Print settings
4896 @cindex format options
4897 @cindex print settings
4898 @value{GDBN} provides the following ways to control how arrays, structures,
4899 and symbols are printed.
4902 These settings are useful for debugging programs in any language:
4905 @kindex set print address
4906 @item set print address
4907 @itemx set print address on
4908 @value{GDBN} prints memory addresses showing the location of stack
4909 traces, structure values, pointer values, breakpoints, and so forth,
4910 even when it also displays the contents of those addresses. The default
4911 is @code{on}. For example, this is what a stack frame display looks like with
4912 @code{set print address on}:
4917 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4919 530 if (lquote != def_lquote)
4923 @item set print address off
4924 Do not print addresses when displaying their contents. For example,
4925 this is the same stack frame displayed with @code{set print address off}:
4929 (@value{GDBP}) set print addr off
4931 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4932 530 if (lquote != def_lquote)
4936 You can use @samp{set print address off} to eliminate all machine
4937 dependent displays from the @value{GDBN} interface. For example, with
4938 @code{print address off}, you should get the same text for backtraces on
4939 all machines---whether or not they involve pointer arguments.
4941 @kindex show print address
4942 @item show print address
4943 Show whether or not addresses are to be printed.
4946 When @value{GDBN} prints a symbolic address, it normally prints the
4947 closest earlier symbol plus an offset. If that symbol does not uniquely
4948 identify the address (for example, it is a name whose scope is a single
4949 source file), you may need to clarify. One way to do this is with
4950 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4951 you can set @value{GDBN} to print the source file and line number when
4952 it prints a symbolic address:
4955 @kindex set print symbol-filename
4956 @item set print symbol-filename on
4957 Tell @value{GDBN} to print the source file name and line number of a
4958 symbol in the symbolic form of an address.
4960 @item set print symbol-filename off
4961 Do not print source file name and line number of a symbol. This is the
4964 @kindex show print symbol-filename
4965 @item show print symbol-filename
4966 Show whether or not @value{GDBN} will print the source file name and
4967 line number of a symbol in the symbolic form of an address.
4970 Another situation where it is helpful to show symbol filenames and line
4971 numbers is when disassembling code; @value{GDBN} shows you the line
4972 number and source file that corresponds to each instruction.
4974 Also, you may wish to see the symbolic form only if the address being
4975 printed is reasonably close to the closest earlier symbol:
4978 @kindex set print max-symbolic-offset
4979 @item set print max-symbolic-offset @var{max-offset}
4980 Tell @value{GDBN} to only display the symbolic form of an address if the
4981 offset between the closest earlier symbol and the address is less than
4982 @var{max-offset}. The default is 0, which tells @value{GDBN}
4983 to always print the symbolic form of an address if any symbol precedes it.
4985 @kindex show print max-symbolic-offset
4986 @item show print max-symbolic-offset
4987 Ask how large the maximum offset is that @value{GDBN} prints in a
4991 @cindex wild pointer, interpreting
4992 @cindex pointer, finding referent
4993 If you have a pointer and you are not sure where it points, try
4994 @samp{set print symbol-filename on}. Then you can determine the name
4995 and source file location of the variable where it points, using
4996 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4997 For example, here @value{GDBN} shows that a variable @code{ptt} points
4998 at another variable @code{t}, defined in @file{hi2.c}:
5001 (@value{GDBP}) set print symbol-filename on
5002 (@value{GDBP}) p/a ptt
5003 $4 = 0xe008 <t in hi2.c>
5007 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5008 does not show the symbol name and filename of the referent, even with
5009 the appropriate @code{set print} options turned on.
5012 Other settings control how different kinds of objects are printed:
5015 @kindex set print array
5016 @item set print array
5017 @itemx set print array on
5018 Pretty print arrays. This format is more convenient to read,
5019 but uses more space. The default is off.
5021 @item set print array off
5022 Return to compressed format for arrays.
5024 @kindex show print array
5025 @item show print array
5026 Show whether compressed or pretty format is selected for displaying
5029 @kindex set print elements
5030 @item set print elements @var{number-of-elements}
5031 Set a limit on how many elements of an array @value{GDBN} will print.
5032 If @value{GDBN} is printing a large array, it stops printing after it has
5033 printed the number of elements set by the @code{set print elements} command.
5034 This limit also applies to the display of strings.
5035 When @value{GDBN} starts, this limit is set to 200.
5036 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5038 @kindex show print elements
5039 @item show print elements
5040 Display the number of elements of a large array that @value{GDBN} will print.
5041 If the number is 0, then the printing is unlimited.
5043 @kindex set print null-stop
5044 @item set print null-stop
5045 Cause @value{GDBN} to stop printing the characters of an array when the first
5046 @sc{null} is encountered. This is useful when large arrays actually
5047 contain only short strings.
5050 @kindex set print pretty
5051 @item set print pretty on
5052 Cause @value{GDBN} to print structures in an indented format with one member
5053 per line, like this:
5068 @item set print pretty off
5069 Cause @value{GDBN} to print structures in a compact format, like this:
5073 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5074 meat = 0x54 "Pork"@}
5079 This is the default format.
5081 @kindex show print pretty
5082 @item show print pretty
5083 Show which format @value{GDBN} is using to print structures.
5085 @kindex set print sevenbit-strings
5086 @item set print sevenbit-strings on
5087 Print using only seven-bit characters; if this option is set,
5088 @value{GDBN} displays any eight-bit characters (in strings or
5089 character values) using the notation @code{\}@var{nnn}. This setting is
5090 best if you are working in English (@sc{ascii}) and you use the
5091 high-order bit of characters as a marker or ``meta'' bit.
5093 @item set print sevenbit-strings off
5094 Print full eight-bit characters. This allows the use of more
5095 international character sets, and is the default.
5097 @kindex show print sevenbit-strings
5098 @item show print sevenbit-strings
5099 Show whether or not @value{GDBN} is printing only seven-bit characters.
5101 @kindex set print union
5102 @item set print union on
5103 Tell @value{GDBN} to print unions which are contained in structures. This
5104 is the default setting.
5106 @item set print union off
5107 Tell @value{GDBN} not to print unions which are contained in structures.
5109 @kindex show print union
5110 @item show print union
5111 Ask @value{GDBN} whether or not it will print unions which are contained in
5114 For example, given the declarations
5117 typedef enum @{Tree, Bug@} Species;
5118 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5119 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5130 struct thing foo = @{Tree, @{Acorn@}@};
5134 with @code{set print union on} in effect @samp{p foo} would print
5137 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5141 and with @code{set print union off} in effect it would print
5144 $1 = @{it = Tree, form = @{...@}@}
5150 These settings are of interest when debugging C@t{++} programs:
5154 @kindex set print demangle
5155 @item set print demangle
5156 @itemx set print demangle on
5157 Print C@t{++} names in their source form rather than in the encoded
5158 (``mangled'') form passed to the assembler and linker for type-safe
5159 linkage. The default is on.
5161 @kindex show print demangle
5162 @item show print demangle
5163 Show whether C@t{++} names are printed in mangled or demangled form.
5165 @kindex set print asm-demangle
5166 @item set print asm-demangle
5167 @itemx set print asm-demangle on
5168 Print C@t{++} names in their source form rather than their mangled form, even
5169 in assembler code printouts such as instruction disassemblies.
5172 @kindex show print asm-demangle
5173 @item show print asm-demangle
5174 Show whether C@t{++} names in assembly listings are printed in mangled
5177 @kindex set demangle-style
5178 @cindex C@t{++} symbol decoding style
5179 @cindex symbol decoding style, C@t{++}
5180 @item set demangle-style @var{style}
5181 Choose among several encoding schemes used by different compilers to
5182 represent C@t{++} names. The choices for @var{style} are currently:
5186 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5189 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5190 This is the default.
5193 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5196 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5199 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5200 @strong{Warning:} this setting alone is not sufficient to allow
5201 debugging @code{cfront}-generated executables. @value{GDBN} would
5202 require further enhancement to permit that.
5205 If you omit @var{style}, you will see a list of possible formats.
5207 @kindex show demangle-style
5208 @item show demangle-style
5209 Display the encoding style currently in use for decoding C@t{++} symbols.
5211 @kindex set print object
5212 @item set print object
5213 @itemx set print object on
5214 When displaying a pointer to an object, identify the @emph{actual}
5215 (derived) type of the object rather than the @emph{declared} type, using
5216 the virtual function table.
5218 @item set print object off
5219 Display only the declared type of objects, without reference to the
5220 virtual function table. This is the default setting.
5222 @kindex show print object
5223 @item show print object
5224 Show whether actual, or declared, object types are displayed.
5226 @kindex set print static-members
5227 @item set print static-members
5228 @itemx set print static-members on
5229 Print static members when displaying a C@t{++} object. The default is on.
5231 @item set print static-members off
5232 Do not print static members when displaying a C@t{++} object.
5234 @kindex show print static-members
5235 @item show print static-members
5236 Show whether C@t{++} static members are printed, or not.
5238 @c These don't work with HP ANSI C++ yet.
5239 @kindex set print vtbl
5240 @item set print vtbl
5241 @itemx set print vtbl on
5242 Pretty print C@t{++} virtual function tables. The default is off.
5243 (The @code{vtbl} commands do not work on programs compiled with the HP
5244 ANSI C@t{++} compiler (@code{aCC}).)
5246 @item set print vtbl off
5247 Do not pretty print C@t{++} virtual function tables.
5249 @kindex show print vtbl
5250 @item show print vtbl
5251 Show whether C@t{++} virtual function tables are pretty printed, or not.
5255 @section Value history
5257 @cindex value history
5258 Values printed by the @code{print} command are saved in the @value{GDBN}
5259 @dfn{value history}. This allows you to refer to them in other expressions.
5260 Values are kept until the symbol table is re-read or discarded
5261 (for example with the @code{file} or @code{symbol-file} commands).
5262 When the symbol table changes, the value history is discarded,
5263 since the values may contain pointers back to the types defined in the
5268 @cindex history number
5269 The values printed are given @dfn{history numbers} by which you can
5270 refer to them. These are successive integers starting with one.
5271 @code{print} shows you the history number assigned to a value by
5272 printing @samp{$@var{num} = } before the value; here @var{num} is the
5275 To refer to any previous value, use @samp{$} followed by the value's
5276 history number. The way @code{print} labels its output is designed to
5277 remind you of this. Just @code{$} refers to the most recent value in
5278 the history, and @code{$$} refers to the value before that.
5279 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5280 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5281 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5283 For example, suppose you have just printed a pointer to a structure and
5284 want to see the contents of the structure. It suffices to type
5290 If you have a chain of structures where the component @code{next} points
5291 to the next one, you can print the contents of the next one with this:
5298 You can print successive links in the chain by repeating this
5299 command---which you can do by just typing @key{RET}.
5301 Note that the history records values, not expressions. If the value of
5302 @code{x} is 4 and you type these commands:
5310 then the value recorded in the value history by the @code{print} command
5311 remains 4 even though the value of @code{x} has changed.
5316 Print the last ten values in the value history, with their item numbers.
5317 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5318 values} does not change the history.
5320 @item show values @var{n}
5321 Print ten history values centered on history item number @var{n}.
5324 Print ten history values just after the values last printed. If no more
5325 values are available, @code{show values +} produces no display.
5328 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5329 same effect as @samp{show values +}.
5331 @node Convenience Vars
5332 @section Convenience variables
5334 @cindex convenience variables
5335 @value{GDBN} provides @dfn{convenience variables} that you can use within
5336 @value{GDBN} to hold on to a value and refer to it later. These variables
5337 exist entirely within @value{GDBN}; they are not part of your program, and
5338 setting a convenience variable has no direct effect on further execution
5339 of your program. That is why you can use them freely.
5341 Convenience variables are prefixed with @samp{$}. Any name preceded by
5342 @samp{$} can be used for a convenience variable, unless it is one of
5343 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5344 (Value history references, in contrast, are @emph{numbers} preceded
5345 by @samp{$}. @xref{Value History, ,Value history}.)
5347 You can save a value in a convenience variable with an assignment
5348 expression, just as you would set a variable in your program.
5352 set $foo = *object_ptr
5356 would save in @code{$foo} the value contained in the object pointed to by
5359 Using a convenience variable for the first time creates it, but its
5360 value is @code{void} until you assign a new value. You can alter the
5361 value with another assignment at any time.
5363 Convenience variables have no fixed types. You can assign a convenience
5364 variable any type of value, including structures and arrays, even if
5365 that variable already has a value of a different type. The convenience
5366 variable, when used as an expression, has the type of its current value.
5369 @kindex show convenience
5370 @item show convenience
5371 Print a list of convenience variables used so far, and their values.
5372 Abbreviated @code{show conv}.
5375 One of the ways to use a convenience variable is as a counter to be
5376 incremented or a pointer to be advanced. For example, to print
5377 a field from successive elements of an array of structures:
5381 print bar[$i++]->contents
5385 Repeat that command by typing @key{RET}.
5387 Some convenience variables are created automatically by @value{GDBN} and given
5388 values likely to be useful.
5391 @vindex $_@r{, convenience variable}
5393 The variable @code{$_} is automatically set by the @code{x} command to
5394 the last address examined (@pxref{Memory, ,Examining memory}). Other
5395 commands which provide a default address for @code{x} to examine also
5396 set @code{$_} to that address; these commands include @code{info line}
5397 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5398 except when set by the @code{x} command, in which case it is a pointer
5399 to the type of @code{$__}.
5401 @vindex $__@r{, convenience variable}
5403 The variable @code{$__} is automatically set by the @code{x} command
5404 to the value found in the last address examined. Its type is chosen
5405 to match the format in which the data was printed.
5408 @vindex $_exitcode@r{, convenience variable}
5409 The variable @code{$_exitcode} is automatically set to the exit code when
5410 the program being debugged terminates.
5413 On HP-UX systems, if you refer to a function or variable name that
5414 begins with a dollar sign, @value{GDBN} searches for a user or system
5415 name first, before it searches for a convenience variable.
5421 You can refer to machine register contents, in expressions, as variables
5422 with names starting with @samp{$}. The names of registers are different
5423 for each machine; use @code{info registers} to see the names used on
5427 @kindex info registers
5428 @item info registers
5429 Print the names and values of all registers except floating-point
5430 registers (in the selected stack frame).
5432 @kindex info all-registers
5433 @cindex floating point registers
5434 @item info all-registers
5435 Print the names and values of all registers, including floating-point
5438 @item info registers @var{regname} @dots{}
5439 Print the @dfn{relativized} value of each specified register @var{regname}.
5440 As discussed in detail below, register values are normally relative to
5441 the selected stack frame. @var{regname} may be any register name valid on
5442 the machine you are using, with or without the initial @samp{$}.
5445 @value{GDBN} has four ``standard'' register names that are available (in
5446 expressions) on most machines---whenever they do not conflict with an
5447 architecture's canonical mnemonics for registers. The register names
5448 @code{$pc} and @code{$sp} are used for the program counter register and
5449 the stack pointer. @code{$fp} is used for a register that contains a
5450 pointer to the current stack frame, and @code{$ps} is used for a
5451 register that contains the processor status. For example,
5452 you could print the program counter in hex with
5459 or print the instruction to be executed next with
5466 or add four to the stack pointer@footnote{This is a way of removing
5467 one word from the stack, on machines where stacks grow downward in
5468 memory (most machines, nowadays). This assumes that the innermost
5469 stack frame is selected; setting @code{$sp} is not allowed when other
5470 stack frames are selected. To pop entire frames off the stack,
5471 regardless of machine architecture, use @code{return};
5472 see @ref{Returning, ,Returning from a function}.} with
5478 Whenever possible, these four standard register names are available on
5479 your machine even though the machine has different canonical mnemonics,
5480 so long as there is no conflict. The @code{info registers} command
5481 shows the canonical names. For example, on the SPARC, @code{info
5482 registers} displays the processor status register as @code{$psr} but you
5483 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5484 is an alias for the @sc{eflags} register.
5486 @value{GDBN} always considers the contents of an ordinary register as an
5487 integer when the register is examined in this way. Some machines have
5488 special registers which can hold nothing but floating point; these
5489 registers are considered to have floating point values. There is no way
5490 to refer to the contents of an ordinary register as floating point value
5491 (although you can @emph{print} it as a floating point value with
5492 @samp{print/f $@var{regname}}).
5494 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5495 means that the data format in which the register contents are saved by
5496 the operating system is not the same one that your program normally
5497 sees. For example, the registers of the 68881 floating point
5498 coprocessor are always saved in ``extended'' (raw) format, but all C
5499 programs expect to work with ``double'' (virtual) format. In such
5500 cases, @value{GDBN} normally works with the virtual format only (the format
5501 that makes sense for your program), but the @code{info registers} command
5502 prints the data in both formats.
5504 Normally, register values are relative to the selected stack frame
5505 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5506 value that the register would contain if all stack frames farther in
5507 were exited and their saved registers restored. In order to see the
5508 true contents of hardware registers, you must select the innermost
5509 frame (with @samp{frame 0}).
5511 However, @value{GDBN} must deduce where registers are saved, from the machine
5512 code generated by your compiler. If some registers are not saved, or if
5513 @value{GDBN} is unable to locate the saved registers, the selected stack
5514 frame makes no difference.
5516 @node Floating Point Hardware
5517 @section Floating point hardware
5518 @cindex floating point
5520 Depending on the configuration, @value{GDBN} may be able to give
5521 you more information about the status of the floating point hardware.
5526 Display hardware-dependent information about the floating
5527 point unit. The exact contents and layout vary depending on the
5528 floating point chip. Currently, @samp{info float} is supported on
5529 the ARM and x86 machines.
5532 @node Memory Region Attributes
5533 @section Memory Region Attributes
5534 @cindex memory region attributes
5536 @dfn{Memory region attributes} allow you to describe special handling
5537 required by regions of your target's memory. @value{GDBN} uses attributes
5538 to determine whether to allow certain types of memory accesses; whether to
5539 use specific width accesses; and whether to cache target memory.
5541 Defined memory regions can be individually enabled and disabled. When a
5542 memory region is disabled, @value{GDBN} uses the default attributes when
5543 accessing memory in that region. Similarly, if no memory regions have
5544 been defined, @value{GDBN} uses the default attributes when accessing
5547 When a memory region is defined, it is given a number to identify it;
5548 to enable, disable, or remove a memory region, you specify that number.
5552 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5553 Define memory region bounded by @var{address1} and @var{address2}
5554 with attributes @var{attributes}@dots{}.
5557 @item delete mem @var{nums}@dots{}
5558 Remove memory region numbers @var{nums}.
5561 @item disable mem @var{nums}@dots{}
5562 Disable memory region numbers @var{nums}.
5563 A disabled memory region is not forgotten.
5564 It may be enabled again later.
5567 @item enable mem @var{nums}@dots{}
5568 Enable memory region numbers @var{nums}.
5572 Print a table of all defined memory regions, with the following columns
5576 @item Memory Region Number
5577 @item Enabled or Disabled.
5578 Enabled memory regions are marked with @samp{y}.
5579 Disabled memory regions are marked with @samp{n}.
5582 The address defining the inclusive lower bound of the memory region.
5585 The address defining the exclusive upper bound of the memory region.
5588 The list of attributes set for this memory region.
5593 @subsection Attributes
5595 @subsubsection Memory Access Mode
5596 The access mode attributes set whether @value{GDBN} may make read or
5597 write accesses to a memory region.
5599 While these attributes prevent @value{GDBN} from performing invalid
5600 memory accesses, they do nothing to prevent the target system, I/O DMA,
5601 etc. from accessing memory.
5605 Memory is read only.
5607 Memory is write only.
5609 Memory is read/write (default).
5612 @subsubsection Memory Access Size
5613 The acccess size attributes tells @value{GDBN} to use specific sized
5614 accesses in the memory region. Often memory mapped device registers
5615 require specific sized accesses. If no access size attribute is
5616 specified, @value{GDBN} may use accesses of any size.
5620 Use 8 bit memory accesses.
5622 Use 16 bit memory accesses.
5624 Use 32 bit memory accesses.
5626 Use 64 bit memory accesses.
5629 @c @subsubsection Hardware/Software Breakpoints
5630 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5631 @c will use hardware or software breakpoints for the internal breakpoints
5632 @c used by the step, next, finish, until, etc. commands.
5636 @c Always use hardware breakpoints
5637 @c @item swbreak (default)
5640 @subsubsection Data Cache
5641 The data cache attributes set whether @value{GDBN} will cache target
5642 memory. While this generally improves performance by reducing debug
5643 protocol overhead, it can lead to incorrect results because @value{GDBN}
5644 does not know about volatile variables or memory mapped device
5649 Enable @value{GDBN} to cache target memory.
5650 @item nocache (default)
5651 Disable @value{GDBN} from caching target memory.
5654 @c @subsubsection Memory Write Verification
5655 @c The memory write verification attributes set whether @value{GDBN}
5656 @c will re-reads data after each write to verify the write was successful.
5660 @c @item noverify (default)
5664 @chapter Tracepoints
5665 @c This chapter is based on the documentation written by Michael
5666 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
5669 In some applications, it is not feasible for the debugger to interrupt
5670 the program's execution long enough for the developer to learn
5671 anything helpful about its behavior. If the program's correctness
5672 depends on its real-time behavior, delays introduced by a debugger
5673 might cause the program to change its behavior drastically, or perhaps
5674 fail, even when the code itself is correct. It is useful to be able
5675 to observe the program's behavior without interrupting it.
5677 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
5678 specify locations in the program, called @dfn{tracepoints}, and
5679 arbitrary expressions to evaluate when those tracepoints are reached.
5680 Later, using the @code{tfind} command, you can examine the values
5681 those expressions had when the program hit the tracepoints. The
5682 expressions may also denote objects in memory---structures or arrays,
5683 for example---whose values @value{GDBN} should record; while visiting
5684 a particular tracepoint, you may inspect those objects as if they were
5685 in memory at that moment. However, because @value{GDBN} records these
5686 values without interacting with you, it can do so quickly and
5687 unobtrusively, hopefully not disturbing the program's behavior.
5689 The tracepoint facility is currently available only for remote
5690 targets. @xref{Targets}.
5692 This chapter describes the tracepoint commands and features.
5696 * Analyze Collected Data::
5697 * Tracepoint Variables::
5700 @node Set Tracepoints
5701 @section Commands to Set Tracepoints
5703 Before running such a @dfn{trace experiment}, an arbitrary number of
5704 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
5705 tracepoint has a number assigned to it by @value{GDBN}. Like with
5706 breakpoints, tracepoint numbers are successive integers starting from
5707 one. Many of the commands associated with tracepoints take the
5708 tracepoint number as their argument, to identify which tracepoint to
5711 For each tracepoint, you can specify, in advance, some arbitrary set
5712 of data that you want the target to collect in the trace buffer when
5713 it hits that tracepoint. The collected data can include registers,
5714 local variables, or global data. Later, you can use @value{GDBN}
5715 commands to examine the values these data had at the time the
5718 This section describes commands to set tracepoints and associated
5719 conditions and actions.
5722 * Create and Delete Tracepoints::
5723 * Enable and Disable Tracepoints::
5724 * Tracepoint Passcounts::
5725 * Tracepoint Actions::
5726 * Listing Tracepoints::
5727 * Starting and Stopping Trace Experiment::
5730 @node Create and Delete Tracepoints
5731 @subsection Create and Delete Tracepoints
5734 @cindex set tracepoint
5737 The @code{trace} command is very similar to the @code{break} command.
5738 Its argument can be a source line, a function name, or an address in
5739 the target program. @xref{Set Breaks}. The @code{trace} command
5740 defines a tracepoint, which is a point in the target program where the
5741 debugger will briefly stop, collect some data, and then allow the
5742 program to continue. Setting a tracepoint or changing its commands
5743 doesn't take effect until the next @code{tstart} command; thus, you
5744 cannot change the tracepoint attributes once a trace experiment is
5747 Here are some examples of using the @code{trace} command:
5750 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
5752 (@value{GDBP}) @b{trace +2} // 2 lines forward
5754 (@value{GDBP}) @b{trace my_function} // first source line of function
5756 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
5758 (@value{GDBP}) @b{trace *0x2117c4} // an address
5762 You can abbreviate @code{trace} as @code{tr}.
5765 @cindex last tracepoint number
5766 @cindex recent tracepoint number
5767 @cindex tracepoint number
5768 The convenience variable @code{$tpnum} records the tracepoint number
5769 of the most recently set tracepoint.
5771 @kindex delete tracepoint
5772 @cindex tracepoint deletion
5773 @item delete tracepoint @r{[}@var{num}@r{]}
5774 Permanently delete one or more tracepoints. With no argument, the
5775 default is to delete all tracepoints.
5780 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
5782 (@value{GDBP}) @b{delete trace} // remove all tracepoints
5786 You can abbreviate this command as @code{del tr}.
5789 @node Enable and Disable Tracepoints
5790 @subsection Enable and Disable Tracepoints
5793 @kindex disable tracepoint
5794 @item disable tracepoint @r{[}@var{num}@r{]}
5795 Disable tracepoint @var{num}, or all tracepoints if no argument
5796 @var{num} is given. A disabled tracepoint will have no effect during
5797 the next trace experiment, but it is not forgotten. You can re-enable
5798 a disabled tracepoint using the @code{enable tracepoint} command.
5800 @kindex enable tracepoint
5801 @item enable tracepoint @r{[}@var{num}@r{]}
5802 Enable tracepoint @var{num}, or all tracepoints. The enabled
5803 tracepoints will become effective the next time a trace experiment is
5807 @node Tracepoint Passcounts
5808 @subsection Tracepoint Passcounts
5812 @cindex tracepoint pass count
5813 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
5814 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
5815 automatically stop a trace experiment. If a tracepoint's passcount is
5816 @var{n}, then the trace experiment will be automatically stopped on
5817 the @var{n}'th time that tracepoint is hit. If the tracepoint number
5818 @var{num} is not specified, the @code{passcount} command sets the
5819 passcount of the most recently defined tracepoint. If no passcount is
5820 given, the trace experiment will run until stopped explicitly by the
5826 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of tracepoint 2
5828 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
5829 // most recently defined tracepoint.
5830 (@value{GDBP}) @b{trace foo}
5831 (@value{GDBP}) @b{pass 3}
5832 (@value{GDBP}) @b{trace bar}
5833 (@value{GDBP}) @b{pass 2}
5834 (@value{GDBP}) @b{trace baz}
5835 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
5836 // executed 3 times OR when bar has
5837 // been executed 2 times
5838 // OR when baz has been executed 1 time.
5842 @node Tracepoint Actions
5843 @subsection Tracepoint Action Lists
5847 @cindex tracepoint actions
5848 @item actions @r{[}@var{num}@r{]}
5849 This command will prompt for a list of actions to be taken when the
5850 tracepoint is hit. If the tracepoint number @var{num} is not
5851 specified, this command sets the actions for the one that was most
5852 recently defined (so that you can define a tracepoint and then say
5853 @code{actions} without bothering about its number). You specify the
5854 actions themselves on the following lines, one action at a time, and
5855 terminate the actions list with a line containing just @code{end}. So
5856 far, the only defined actions are @code{collect} and
5857 @code{while-stepping}.
5859 @cindex remove actions from a tracepoint
5860 To remove all actions from a tracepoint, type @samp{actions @var{num}}
5861 and follow it immediately with @samp{end}.
5864 (@value{GDBP}) @b{collect @var{data}} // collect some data
5866 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times and collect data
5868 (@value{GDBP}) @b{end} // signals the end of actions.
5871 In the following example, the action list begins with @code{collect}
5872 commands indicating the things to be collected when the tracepoint is
5873 hit. Then, in order to single-step and collect additional data
5874 following the tracepoint, a @code{while-stepping} command is used,
5875 followed by the list of things to be collected while stepping. The
5876 @code{while-stepping} command is terminated by its own separate
5877 @code{end} command. Lastly, the action list is terminated by an
5881 (@value{GDBP}) @b{trace foo}
5882 (@value{GDBP}) @b{actions}
5883 Enter actions for tracepoint 1, one per line:
5892 @kindex collect @r{(tracepoints)}
5893 @item collect @var{expr1}, @var{expr2}, @dots{}
5894 Collect values of the given expressions when the tracepoint is hit.
5895 This command accepts a comma-separated list of any valid expressions.
5896 In addition to global, static, or local variables, the following
5897 special arguments are supported:
5901 collect all registers
5904 collect all function arguments
5907 collect all local variables.
5910 You can give several consecutive @code{collect} commands, each one
5911 with a single argument, or one @code{collect} command with several
5912 arguments separated by commas: the effect is the same.
5914 The command @code{info scope} (@pxref{Symbols, info scope}) is
5915 particularly useful for figuring out what data to collect.
5917 @kindex while-stepping @r{(tracepoints)}
5918 @item while-stepping @var{n}
5919 Perform @var{n} single-step traces after the tracepoint, collecting
5920 new data at each step. The @code{while-stepping} command is
5921 followed by the list of what to collect while stepping (followed by
5922 its own @code{end} command):
5926 > collect $regs, myglobal
5932 You may abbreviate @code{while-stepping} as @code{ws} or
5936 @node Listing Tracepoints
5937 @subsection Listing Tracepoints
5940 @kindex info tracepoints
5941 @cindex information about tracepoints
5942 @item info tracepoints @r{[}@var{num}@r{]}
5943 Display information the tracepoint @var{num}. If you don't specify a
5944 tracepoint number displays information about all the tracepoints
5945 defined so far. For each tracepoint, the following information is
5952 whether it is enabled or disabled
5956 its passcount as given by the @code{passcount @var{n}} command
5958 its step count as given by the @code{while-stepping @var{n}} command
5960 where in the source files is the tracepoint set
5962 its action list as given by the @code{actions} command
5966 (@value{GDBP}) @b{info trace}
5967 Num Enb Address PassC StepC What
5968 1 y 0x002117c4 0 0 <gdb_asm>
5969 2 y 0x0020dc64 0 0 in gdb_test at gdb_test.c:375
5970 3 y 0x0020b1f4 0 0 in collect_data at ../foo.c:1741
5975 This command can be abbreviated @code{info tp}.
5978 @node Starting and Stopping Trace Experiment
5979 @subsection Starting and Stopping Trace Experiment
5983 @cindex start a new trace experiment
5984 @cindex collected data discarded
5986 This command takes no arguments. It starts the trace experiment, and
5987 begins collecting data. This has the side effect of discarding all
5988 the data collected in the trace buffer during the previous trace
5992 @cindex stop a running trace experiment
5994 This command takes no arguments. It ends the trace experiment, and
5995 stops collecting data.
5997 @strong{Note:} a trace experiment and data collection may stop
5998 automatically if any tracepoint's passcount is reached
5999 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6002 @cindex status of trace data collection
6003 @cindex trace experiment, status of
6005 This command displays the status of the current trace data
6009 Here is an example of the commands we described so far:
6012 (@value{GDBP}) @b{trace gdb_c_test}
6013 (@value{GDBP}) @b{actions}
6014 Enter actions for tracepoint #1, one per line.
6015 > collect $regs,$locals,$args
6020 (@value{GDBP}) @b{tstart}
6021 [time passes @dots{}]
6022 (@value{GDBP}) @b{tstop}
6026 @node Analyze Collected Data
6027 @section Using the collected data
6029 After the tracepoint experiment ends, you use @value{GDBN} commands
6030 for examining the trace data. The basic idea is that each tracepoint
6031 collects a trace @dfn{snapshot} every time it is hit and another
6032 snapshot every time it single-steps. All these snapshots are
6033 consecutively numbered from zero and go into a buffer, and you can
6034 examine them later. The way you examine them is to @dfn{focus} on a
6035 specific trace snapshot. When the remote stub is focused on a trace
6036 snapshot, it will respond to all @value{GDBN} requests for memory and
6037 registers by reading from the buffer which belongs to that snapshot,
6038 rather than from @emph{real} memory or registers of the program being
6039 debugged. This means that @strong{all} @value{GDBN} commands
6040 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6041 behave as if we were currently debugging the program state as it was
6042 when the tracepoint occurred. Any requests for data that are not in
6043 the buffer will fail.
6046 * tfind:: How to select a trace snapshot
6047 * tdump:: How to display all data for a snapshot
6048 * save-tracepoints:: How to save tracepoints for a future run
6052 @subsection @code{tfind @var{n}}
6055 @cindex select trace snapshot
6056 @cindex find trace snapshot
6057 The basic command for selecting a trace snapshot from the buffer is
6058 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6059 counting from zero. If no argument @var{n} is given, the next
6060 snapshot is selected.
6062 Here are the various forms of using the @code{tfind} command.
6066 Find the first snapshot in the buffer. This is a synonym for
6067 @code{tfind 0} (since 0 is the number of the first snapshot).
6070 Stop debugging trace snapshots, resume @emph{live} debugging.
6073 Same as @samp{tfind none}.
6076 No argument means find the next trace snapshot.
6079 Find the previous trace snapshot before the current one. This permits
6080 retracing earlier steps.
6082 @item tfind tracepoint @var{num}
6083 Find the next snapshot associated with tracepoint @var{num}. Search
6084 proceeds forward from the last examined trace snapshot. If no
6085 argument @var{num} is given, it means find the next snapshot collected
6086 for the same tracepoint as the current snapshot.
6088 @item tfind pc @var{addr}
6089 Find the next snapshot associated with the value @var{addr} of the
6090 program counter. Search proceeds forward from the last examined trace
6091 snapshot. If no argument @var{addr} is given, it means find the next
6092 snapshot with the same value of PC as the current snapshot.
6094 @item tfind outside @var{addr1}, @var{addr2}
6095 Find the next snapshot whose PC is outside the given range of
6098 @item tfind range @var{addr1}, @var{addr2}
6099 Find the next snapshot whose PC is between @var{addr1} and
6100 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6102 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6103 Find the next snapshot associated with the source line @var{n}. If
6104 the optional argument @var{file} is given, refer to line @var{n} in
6105 that source file. Search proceeds forward from the last examined
6106 trace snapshot. If no argument @var{n} is given, it means find the
6107 next line other than the one currently being examined; thus saying
6108 @code{tfind line} repeatedly can appear to have the same effect as
6109 stepping from line to line in a @emph{live} debugging session.
6112 The default arguments for the @code{tfind} commands are specifically
6113 designed to make it easy to scan through the trace buffer. For
6114 instance, @code{tfind} with no argument selects the next trace
6115 snapshot, and @code{tfind -} with no argument selects the previous
6116 trace snapshot. So, by giving one @code{tfind} command, and then
6117 simply hitting @key{RET} repeatedly you can examine all the trace
6118 snapshots in order. Or, by saying @code{tfind -} and then hitting
6119 @key{RET} repeatedly you can examine the snapshots in reverse order.
6120 The @code{tfind line} command with no argument selects the snapshot
6121 for the next source line executed. The @code{tfind pc} command with
6122 no argument selects the next snapshot with the same program counter
6123 (PC) as the current frame. The @code{tfind tracepoint} command with
6124 no argument selects the next trace snapshot collected by the same
6125 tracepoint as the current one.
6127 In addition to letting you scan through the trace buffer manually,
6128 these commands make it easy to construct @value{GDBN} scripts that
6129 scan through the trace buffer and print out whatever collected data
6130 you are interested in. Thus, if we want to examine the PC, FP, and SP
6131 registers from each trace frame in the buffer, we can say this:
6134 (@value{GDBP}) @b{tfind start}
6135 (@value{GDBP}) @b{while ($trace_frame != -1)}
6136 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6137 $trace_frame, $pc, $sp, $fp
6141 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6142 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6143 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6144 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6145 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6146 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6147 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6148 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6149 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6150 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6151 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6154 Or, if we want to examine the variable @code{X} at each source line in
6158 (@value{GDBP}) @b{tfind start}
6159 (@value{GDBP}) @b{while ($trace_frame != -1)}
6160 > printf "Frame %d, X == %d\n", $trace_frame, X
6170 @subsection @code{tdump}
6172 @cindex dump all data collected at tracepoint
6173 @cindex tracepoint data, display
6175 This command takes no arguments. It prints all the data collected at
6176 the current trace snapshot.
6179 (@value{GDBP}) @b{trace 444}
6180 (@value{GDBP}) @b{actions}
6181 Enter actions for tracepoint #2, one per line:
6182 > collect $regs, $locals, $args, gdb_long_test
6185 (@value{GDBP}) @b{tstart}
6187 (@value{GDBP}) @b{tfind line 444}
6188 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6190 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6192 (@value{GDBP}) @b{tdump}
6193 Data collected at tracepoint 2, trace frame 1:
6194 d0 0xc4aa0085 -995491707
6198 d4 0x71aea3d 119204413
6203 a1 0x3000668 50333288
6206 a4 0x3000698 50333336
6208 fp 0x30bf3c 0x30bf3c
6209 sp 0x30bf34 0x30bf34
6211 pc 0x20b2c8 0x20b2c8
6215 p = 0x20e5b4 "gdb-test"
6222 gdb_long_test = 17 '\021'
6227 @node save-tracepoints
6228 @subsection @code{save-tracepoints @var{filename}}
6229 @kindex save-tracepoints
6230 @cindex save tracepoints for future sessions
6232 This command saves all current tracepoint definitions together with
6233 their actions and passcounts, into a file @file{@var{filename}}
6234 suitable for use in a later debugging session. To read the saved
6235 tracepoint definitions, use the @code{source} command (@pxref{Command
6238 @node Tracepoint Variables
6239 @section Convenience Variables for Tracepoints
6240 @cindex tracepoint variables
6241 @cindex convenience variables for tracepoints
6244 @vindex $trace_frame
6245 @item (int) $trace_frame
6246 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6247 snapshot is selected.
6250 @item (int) $tracepoint
6251 The tracepoint for the current trace snapshot.
6254 @item (int) $trace_line
6255 The line number for the current trace snapshot.
6258 @item (char []) $trace_file
6259 The source file for the current trace snapshot.
6262 @item (char []) $trace_func
6263 The name of the function containing @code{$tracepoint}.
6266 Note: @code{$trace_file} is not suitable for use in @code{printf},
6267 use @code{output} instead.
6269 Here's a simple example of using these convenience variables for
6270 stepping through all the trace snapshots and printing some of their
6274 (@value{GDBP}) @b{tfind start}
6276 (@value{GDBP}) @b{while $trace_frame != -1}
6277 > output $trace_file
6278 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6284 @chapter Using @value{GDBN} with Different Languages
6287 Although programming languages generally have common aspects, they are
6288 rarely expressed in the same manner. For instance, in ANSI C,
6289 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6290 Modula-2, it is accomplished by @code{p^}. Values can also be
6291 represented (and displayed) differently. Hex numbers in C appear as
6292 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6294 @cindex working language
6295 Language-specific information is built into @value{GDBN} for some languages,
6296 allowing you to express operations like the above in your program's
6297 native language, and allowing @value{GDBN} to output values in a manner
6298 consistent with the syntax of your program's native language. The
6299 language you use to build expressions is called the @dfn{working
6303 * Setting:: Switching between source languages
6304 * Show:: Displaying the language
6305 * Checks:: Type and range checks
6306 * Support:: Supported languages
6310 @section Switching between source languages
6312 There are two ways to control the working language---either have @value{GDBN}
6313 set it automatically, or select it manually yourself. You can use the
6314 @code{set language} command for either purpose. On startup, @value{GDBN}
6315 defaults to setting the language automatically. The working language is
6316 used to determine how expressions you type are interpreted, how values
6319 In addition to the working language, every source file that
6320 @value{GDBN} knows about has its own working language. For some object
6321 file formats, the compiler might indicate which language a particular
6322 source file is in. However, most of the time @value{GDBN} infers the
6323 language from the name of the file. The language of a source file
6324 controls whether C@t{++} names are demangled---this way @code{backtrace} can
6325 show each frame appropriately for its own language. There is no way to
6326 set the language of a source file from within @value{GDBN}, but you can
6327 set the language associated with a filename extension. @xref{Show, ,
6328 Displaying the language}.
6330 This is most commonly a problem when you use a program, such
6331 as @code{cfront} or @code{f2c}, that generates C but is written in
6332 another language. In that case, make the
6333 program use @code{#line} directives in its C output; that way
6334 @value{GDBN} will know the correct language of the source code of the original
6335 program, and will display that source code, not the generated C code.
6338 * Filenames:: Filename extensions and languages.
6339 * Manually:: Setting the working language manually
6340 * Automatically:: Having @value{GDBN} infer the source language
6344 @subsection List of filename extensions and languages
6346 If a source file name ends in one of the following extensions, then
6347 @value{GDBN} infers that its language is the one indicated.
6372 Modula-2 source file
6376 Assembler source file. This actually behaves almost like C, but
6377 @value{GDBN} does not skip over function prologues when stepping.
6380 In addition, you may set the language associated with a filename
6381 extension. @xref{Show, , Displaying the language}.
6384 @subsection Setting the working language
6386 If you allow @value{GDBN} to set the language automatically,
6387 expressions are interpreted the same way in your debugging session and
6390 @kindex set language
6391 If you wish, you may set the language manually. To do this, issue the
6392 command @samp{set language @var{lang}}, where @var{lang} is the name of
6394 @code{c} or @code{modula-2}.
6395 For a list of the supported languages, type @samp{set language}.
6397 Setting the language manually prevents @value{GDBN} from updating the working
6398 language automatically. This can lead to confusion if you try
6399 to debug a program when the working language is not the same as the
6400 source language, when an expression is acceptable to both
6401 languages---but means different things. For instance, if the current
6402 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6410 might not have the effect you intended. In C, this means to add
6411 @code{b} and @code{c} and place the result in @code{a}. The result
6412 printed would be the value of @code{a}. In Modula-2, this means to compare
6413 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6416 @subsection Having @value{GDBN} infer the source language
6418 To have @value{GDBN} set the working language automatically, use
6419 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6420 then infers the working language. That is, when your program stops in a
6421 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6422 working language to the language recorded for the function in that
6423 frame. If the language for a frame is unknown (that is, if the function
6424 or block corresponding to the frame was defined in a source file that
6425 does not have a recognized extension), the current working language is
6426 not changed, and @value{GDBN} issues a warning.
6428 This may not seem necessary for most programs, which are written
6429 entirely in one source language. However, program modules and libraries
6430 written in one source language can be used by a main program written in
6431 a different source language. Using @samp{set language auto} in this
6432 case frees you from having to set the working language manually.
6435 @section Displaying the language
6437 The following commands help you find out which language is the
6438 working language, and also what language source files were written in.
6440 @kindex show language
6441 @kindex info frame@r{, show the source language}
6442 @kindex info source@r{, show the source language}
6445 Display the current working language. This is the
6446 language you can use with commands such as @code{print} to
6447 build and compute expressions that may involve variables in your program.
6450 Display the source language for this frame. This language becomes the
6451 working language if you use an identifier from this frame.
6452 @xref{Frame Info, ,Information about a frame}, to identify the other
6453 information listed here.
6456 Display the source language of this source file.
6457 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6458 information listed here.
6461 In unusual circumstances, you may have source files with extensions
6462 not in the standard list. You can then set the extension associated
6463 with a language explicitly:
6465 @kindex set extension-language
6466 @kindex info extensions
6468 @item set extension-language @var{.ext} @var{language}
6469 Set source files with extension @var{.ext} to be assumed to be in
6470 the source language @var{language}.
6472 @item info extensions
6473 List all the filename extensions and the associated languages.
6477 @section Type and range checking
6480 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6481 checking are included, but they do not yet have any effect. This
6482 section documents the intended facilities.
6484 @c FIXME remove warning when type/range code added
6486 Some languages are designed to guard you against making seemingly common
6487 errors through a series of compile- and run-time checks. These include
6488 checking the type of arguments to functions and operators, and making
6489 sure mathematical overflows are caught at run time. Checks such as
6490 these help to ensure a program's correctness once it has been compiled
6491 by eliminating type mismatches, and providing active checks for range
6492 errors when your program is running.
6494 @value{GDBN} can check for conditions like the above if you wish.
6495 Although @value{GDBN} does not check the statements in your program, it
6496 can check expressions entered directly into @value{GDBN} for evaluation via
6497 the @code{print} command, for example. As with the working language,
6498 @value{GDBN} can also decide whether or not to check automatically based on
6499 your program's source language. @xref{Support, ,Supported languages},
6500 for the default settings of supported languages.
6503 * Type Checking:: An overview of type checking
6504 * Range Checking:: An overview of range checking
6507 @cindex type checking
6508 @cindex checks, type
6510 @subsection An overview of type checking
6512 Some languages, such as Modula-2, are strongly typed, meaning that the
6513 arguments to operators and functions have to be of the correct type,
6514 otherwise an error occurs. These checks prevent type mismatch
6515 errors from ever causing any run-time problems. For example,
6523 The second example fails because the @code{CARDINAL} 1 is not
6524 type-compatible with the @code{REAL} 2.3.
6526 For the expressions you use in @value{GDBN} commands, you can tell the
6527 @value{GDBN} type checker to skip checking;
6528 to treat any mismatches as errors and abandon the expression;
6529 or to only issue warnings when type mismatches occur,
6530 but evaluate the expression anyway. When you choose the last of
6531 these, @value{GDBN} evaluates expressions like the second example above, but
6532 also issues a warning.
6534 Even if you turn type checking off, there may be other reasons
6535 related to type that prevent @value{GDBN} from evaluating an expression.
6536 For instance, @value{GDBN} does not know how to add an @code{int} and
6537 a @code{struct foo}. These particular type errors have nothing to do
6538 with the language in use, and usually arise from expressions, such as
6539 the one described above, which make little sense to evaluate anyway.
6541 Each language defines to what degree it is strict about type. For
6542 instance, both Modula-2 and C require the arguments to arithmetical
6543 operators to be numbers. In C, enumerated types and pointers can be
6544 represented as numbers, so that they are valid arguments to mathematical
6545 operators. @xref{Support, ,Supported languages}, for further
6546 details on specific languages.
6548 @value{GDBN} provides some additional commands for controlling the type checker:
6550 @kindex set check@r{, type}
6551 @kindex set check type
6552 @kindex show check type
6554 @item set check type auto
6555 Set type checking on or off based on the current working language.
6556 @xref{Support, ,Supported languages}, for the default settings for
6559 @item set check type on
6560 @itemx set check type off
6561 Set type checking on or off, overriding the default setting for the
6562 current working language. Issue a warning if the setting does not
6563 match the language default. If any type mismatches occur in
6564 evaluating an expression while type checking is on, @value{GDBN} prints a
6565 message and aborts evaluation of the expression.
6567 @item set check type warn
6568 Cause the type checker to issue warnings, but to always attempt to
6569 evaluate the expression. Evaluating the expression may still
6570 be impossible for other reasons. For example, @value{GDBN} cannot add
6571 numbers and structures.
6574 Show the current setting of the type checker, and whether or not @value{GDBN}
6575 is setting it automatically.
6578 @cindex range checking
6579 @cindex checks, range
6580 @node Range Checking
6581 @subsection An overview of range checking
6583 In some languages (such as Modula-2), it is an error to exceed the
6584 bounds of a type; this is enforced with run-time checks. Such range
6585 checking is meant to ensure program correctness by making sure
6586 computations do not overflow, or indices on an array element access do
6587 not exceed the bounds of the array.
6589 For expressions you use in @value{GDBN} commands, you can tell
6590 @value{GDBN} to treat range errors in one of three ways: ignore them,
6591 always treat them as errors and abandon the expression, or issue
6592 warnings but evaluate the expression anyway.
6594 A range error can result from numerical overflow, from exceeding an
6595 array index bound, or when you type a constant that is not a member
6596 of any type. Some languages, however, do not treat overflows as an
6597 error. In many implementations of C, mathematical overflow causes the
6598 result to ``wrap around'' to lower values---for example, if @var{m} is
6599 the largest integer value, and @var{s} is the smallest, then
6602 @var{m} + 1 @result{} @var{s}
6605 This, too, is specific to individual languages, and in some cases
6606 specific to individual compilers or machines. @xref{Support, ,
6607 Supported languages}, for further details on specific languages.
6609 @value{GDBN} provides some additional commands for controlling the range checker:
6611 @kindex set check@r{, range}
6612 @kindex set check range
6613 @kindex show check range
6615 @item set check range auto
6616 Set range checking on or off based on the current working language.
6617 @xref{Support, ,Supported languages}, for the default settings for
6620 @item set check range on
6621 @itemx set check range off
6622 Set range checking on or off, overriding the default setting for the
6623 current working language. A warning is issued if the setting does not
6624 match the language default. If a range error occurs and range checking is on,
6625 then a message is printed and evaluation of the expression is aborted.
6627 @item set check range warn
6628 Output messages when the @value{GDBN} range checker detects a range error,
6629 but attempt to evaluate the expression anyway. Evaluating the
6630 expression may still be impossible for other reasons, such as accessing
6631 memory that the process does not own (a typical example from many Unix
6635 Show the current setting of the range checker, and whether or not it is
6636 being set automatically by @value{GDBN}.
6640 @section Supported languages
6642 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
6643 @c This is false ...
6644 Some @value{GDBN} features may be used in expressions regardless of the
6645 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6646 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6647 ,Expressions}) can be used with the constructs of any supported
6650 The following sections detail to what degree each source language is
6651 supported by @value{GDBN}. These sections are not meant to be language
6652 tutorials or references, but serve only as a reference guide to what the
6653 @value{GDBN} expression parser accepts, and what input and output
6654 formats should look like for different languages. There are many good
6655 books written on each of these languages; please look to these for a
6656 language reference or tutorial.
6660 * Modula-2:: Modula-2
6665 @subsection C and C@t{++}
6667 @cindex C and C@t{++}
6668 @cindex expressions in C or C@t{++}
6670 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
6671 to both languages. Whenever this is the case, we discuss those languages
6675 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
6676 @cindex @sc{gnu} C@t{++}
6677 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
6678 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
6679 effectively, you must compile your C@t{++} programs with a supported
6680 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
6681 compiler (@code{aCC}).
6683 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
6684 format. You can select that format explicitly with the @code{g++}
6685 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6686 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
6687 CC, gcc.info, Using @sc{gnu} CC}, for more information.
6690 * C Operators:: C and C@t{++} operators
6691 * C Constants:: C and C@t{++} constants
6692 * C plus plus expressions:: C@t{++} expressions
6693 * C Defaults:: Default settings for C and C@t{++}
6694 * C Checks:: C and C@t{++} type and range checks
6695 * Debugging C:: @value{GDBN} and C
6696 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
6700 @subsubsection C and C@t{++} operators
6702 @cindex C and C@t{++} operators
6704 Operators must be defined on values of specific types. For instance,
6705 @code{+} is defined on numbers, but not on structures. Operators are
6706 often defined on groups of types.
6708 For the purposes of C and C@t{++}, the following definitions hold:
6713 @emph{Integral types} include @code{int} with any of its storage-class
6714 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
6717 @emph{Floating-point types} include @code{float}, @code{double}, and
6718 @code{long double} (if supported by the target platform).
6721 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
6724 @emph{Scalar types} include all of the above.
6729 The following operators are supported. They are listed here
6730 in order of increasing precedence:
6734 The comma or sequencing operator. Expressions in a comma-separated list
6735 are evaluated from left to right, with the result of the entire
6736 expression being the last expression evaluated.
6739 Assignment. The value of an assignment expression is the value
6740 assigned. Defined on scalar types.
6743 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6744 and translated to @w{@code{@var{a} = @var{a op b}}}.
6745 @w{@code{@var{op}=}} and @code{=} have the same precedence.
6746 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6747 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6750 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6751 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6755 Logical @sc{or}. Defined on integral types.
6758 Logical @sc{and}. Defined on integral types.
6761 Bitwise @sc{or}. Defined on integral types.
6764 Bitwise exclusive-@sc{or}. Defined on integral types.
6767 Bitwise @sc{and}. Defined on integral types.
6770 Equality and inequality. Defined on scalar types. The value of these
6771 expressions is 0 for false and non-zero for true.
6773 @item <@r{, }>@r{, }<=@r{, }>=
6774 Less than, greater than, less than or equal, greater than or equal.
6775 Defined on scalar types. The value of these expressions is 0 for false
6776 and non-zero for true.
6779 left shift, and right shift. Defined on integral types.
6782 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6785 Addition and subtraction. Defined on integral types, floating-point types and
6788 @item *@r{, }/@r{, }%
6789 Multiplication, division, and modulus. Multiplication and division are
6790 defined on integral and floating-point types. Modulus is defined on
6794 Increment and decrement. When appearing before a variable, the
6795 operation is performed before the variable is used in an expression;
6796 when appearing after it, the variable's value is used before the
6797 operation takes place.
6800 Pointer dereferencing. Defined on pointer types. Same precedence as
6804 Address operator. Defined on variables. Same precedence as @code{++}.
6806 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
6807 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
6808 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6809 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
6813 Negative. Defined on integral and floating-point types. Same
6814 precedence as @code{++}.
6817 Logical negation. Defined on integral types. Same precedence as
6821 Bitwise complement operator. Defined on integral types. Same precedence as
6826 Structure member, and pointer-to-structure member. For convenience,
6827 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6828 pointer based on the stored type information.
6829 Defined on @code{struct} and @code{union} data.
6832 Dereferences of pointers to members.
6835 Array indexing. @code{@var{a}[@var{i}]} is defined as
6836 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6839 Function parameter list. Same precedence as @code{->}.
6842 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
6843 and @code{class} types.
6846 Doubled colons also represent the @value{GDBN} scope operator
6847 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6851 If an operator is redefined in the user code, @value{GDBN} usually
6852 attempts to invoke the redefined version instead of using the operator's
6860 @subsubsection C and C@t{++} constants
6862 @cindex C and C@t{++} constants
6864 @value{GDBN} allows you to express the constants of C and C@t{++} in the
6869 Integer constants are a sequence of digits. Octal constants are
6870 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6871 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6872 @samp{l}, specifying that the constant should be treated as a
6876 Floating point constants are a sequence of digits, followed by a decimal
6877 point, followed by a sequence of digits, and optionally followed by an
6878 exponent. An exponent is of the form:
6879 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6880 sequence of digits. The @samp{+} is optional for positive exponents.
6881 A floating-point constant may also end with a letter @samp{f} or
6882 @samp{F}, specifying that the constant should be treated as being of
6883 the @code{float} (as opposed to the default @code{double}) type; or with
6884 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6888 Enumerated constants consist of enumerated identifiers, or their
6889 integral equivalents.
6892 Character constants are a single character surrounded by single quotes
6893 (@code{'}), or a number---the ordinal value of the corresponding character
6894 (usually its @sc{ascii} value). Within quotes, the single character may
6895 be represented by a letter or by @dfn{escape sequences}, which are of
6896 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6897 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6898 @samp{@var{x}} is a predefined special character---for example,
6899 @samp{\n} for newline.
6902 String constants are a sequence of character constants surrounded by
6903 double quotes (@code{"}). Any valid character constant (as described
6904 above) may appear. Double quotes within the string must be preceded by
6905 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6909 Pointer constants are an integral value. You can also write pointers
6910 to constants using the C operator @samp{&}.
6913 Array constants are comma-separated lists surrounded by braces @samp{@{}
6914 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6915 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6916 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6920 * C plus plus expressions::
6927 @node C plus plus expressions
6928 @subsubsection C@t{++} expressions
6930 @cindex expressions in C@t{++}
6931 @value{GDBN} expression handling can interpret most C@t{++} expressions.
6933 @cindex C@t{++} support, not in @sc{coff}
6934 @cindex @sc{coff} versus C@t{++}
6935 @cindex C@t{++} and object formats
6936 @cindex object formats and C@t{++}
6937 @cindex a.out and C@t{++}
6938 @cindex @sc{ecoff} and C@t{++}
6939 @cindex @sc{xcoff} and C@t{++}
6940 @cindex @sc{elf}/stabs and C@t{++}
6941 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
6942 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6943 @c periodically whether this has happened...
6945 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
6946 proper compiler. Typically, C@t{++} debugging depends on the use of
6947 additional debugging information in the symbol table, and thus requires
6948 special support. In particular, if your compiler generates a.out, MIPS
6949 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6950 symbol table, these facilities are all available. (With @sc{gnu} CC,
6951 you can use the @samp{-gstabs} option to request stabs debugging
6952 extensions explicitly.) Where the object code format is standard
6953 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
6954 support in @value{GDBN} does @emph{not} work.
6959 @cindex member functions
6961 Member function calls are allowed; you can use expressions like
6964 count = aml->GetOriginal(x, y)
6967 @vindex this@r{, inside C@t{++} member functions}
6968 @cindex namespace in C@t{++}
6970 While a member function is active (in the selected stack frame), your
6971 expressions have the same namespace available as the member function;
6972 that is, @value{GDBN} allows implicit references to the class instance
6973 pointer @code{this} following the same rules as C@t{++}.
6975 @cindex call overloaded functions
6976 @cindex overloaded functions, calling
6977 @cindex type conversions in C@t{++}
6979 You can call overloaded functions; @value{GDBN} resolves the function
6980 call to the right definition, with some restrictions. @value{GDBN} does not
6981 perform overload resolution involving user-defined type conversions,
6982 calls to constructors, or instantiations of templates that do not exist
6983 in the program. It also cannot handle ellipsis argument lists or
6986 It does perform integral conversions and promotions, floating-point
6987 promotions, arithmetic conversions, pointer conversions, conversions of
6988 class objects to base classes, and standard conversions such as those of
6989 functions or arrays to pointers; it requires an exact match on the
6990 number of function arguments.
6992 Overload resolution is always performed, unless you have specified
6993 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6994 ,@value{GDBN} features for C@t{++}}.
6996 You must specify @code{set overload-resolution off} in order to use an
6997 explicit function signature to call an overloaded function, as in
6999 p 'foo(char,int)'('x', 13)
7002 The @value{GDBN} command-completion facility can simplify this;
7003 see @ref{Completion, ,Command completion}.
7005 @cindex reference declarations
7007 @value{GDBN} understands variables declared as C@t{++} references; you can use
7008 them in expressions just as you do in C@t{++} source---they are automatically
7011 In the parameter list shown when @value{GDBN} displays a frame, the values of
7012 reference variables are not displayed (unlike other variables); this
7013 avoids clutter, since references are often used for large structures.
7014 The @emph{address} of a reference variable is always shown, unless
7015 you have specified @samp{set print address off}.
7018 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7019 expressions can use it just as expressions in your program do. Since
7020 one scope may be defined in another, you can use @code{::} repeatedly if
7021 necessary, for example in an expression like
7022 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7023 resolving name scope by reference to source files, in both C and C@t{++}
7024 debugging (@pxref{Variables, ,Program variables}).
7027 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7028 calling virtual functions correctly, printing out virtual bases of
7029 objects, calling functions in a base subobject, casting objects, and
7030 invoking user-defined operators.
7033 @subsubsection C and C@t{++} defaults
7035 @cindex C and C@t{++} defaults
7037 If you allow @value{GDBN} to set type and range checking automatically, they
7038 both default to @code{off} whenever the working language changes to
7039 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7040 selects the working language.
7042 If you allow @value{GDBN} to set the language automatically, it
7043 recognizes source files whose names end with @file{.c}, @file{.C}, or
7044 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7045 these files, it sets the working language to C or C@t{++}.
7046 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7047 for further details.
7049 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7050 @c unimplemented. If (b) changes, it might make sense to let this node
7051 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7054 @subsubsection C and C@t{++} type and range checks
7056 @cindex C and C@t{++} checks
7058 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7059 is not used. However, if you turn type checking on, @value{GDBN}
7060 considers two variables type equivalent if:
7064 The two variables are structured and have the same structure, union, or
7068 The two variables have the same type name, or types that have been
7069 declared equivalent through @code{typedef}.
7072 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7075 The two @code{struct}, @code{union}, or @code{enum} variables are
7076 declared in the same declaration. (Note: this may not be true for all C
7081 Range checking, if turned on, is done on mathematical operations. Array
7082 indices are not checked, since they are often used to index a pointer
7083 that is not itself an array.
7086 @subsubsection @value{GDBN} and C
7088 The @code{set print union} and @code{show print union} commands apply to
7089 the @code{union} type. When set to @samp{on}, any @code{union} that is
7090 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7091 appears as @samp{@{...@}}.
7093 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7094 with pointers and a memory allocation function. @xref{Expressions,
7098 * Debugging C plus plus::
7101 @node Debugging C plus plus
7102 @subsubsection @value{GDBN} features for C@t{++}
7104 @cindex commands for C@t{++}
7106 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7107 designed specifically for use with C@t{++}. Here is a summary:
7110 @cindex break in overloaded functions
7111 @item @r{breakpoint menus}
7112 When you want a breakpoint in a function whose name is overloaded,
7113 @value{GDBN} breakpoint menus help you specify which function definition
7114 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7116 @cindex overloading in C@t{++}
7117 @item rbreak @var{regex}
7118 Setting breakpoints using regular expressions is helpful for setting
7119 breakpoints on overloaded functions that are not members of any special
7121 @xref{Set Breaks, ,Setting breakpoints}.
7123 @cindex C@t{++} exception handling
7126 Debug C@t{++} exception handling using these commands. @xref{Set
7127 Catchpoints, , Setting catchpoints}.
7130 @item ptype @var{typename}
7131 Print inheritance relationships as well as other information for type
7133 @xref{Symbols, ,Examining the Symbol Table}.
7135 @cindex C@t{++} symbol display
7136 @item set print demangle
7137 @itemx show print demangle
7138 @itemx set print asm-demangle
7139 @itemx show print asm-demangle
7140 Control whether C@t{++} symbols display in their source form, both when
7141 displaying code as C@t{++} source and when displaying disassemblies.
7142 @xref{Print Settings, ,Print settings}.
7144 @item set print object
7145 @itemx show print object
7146 Choose whether to print derived (actual) or declared types of objects.
7147 @xref{Print Settings, ,Print settings}.
7149 @item set print vtbl
7150 @itemx show print vtbl
7151 Control the format for printing virtual function tables.
7152 @xref{Print Settings, ,Print settings}.
7153 (The @code{vtbl} commands do not work on programs compiled with the HP
7154 ANSI C@t{++} compiler (@code{aCC}).)
7156 @kindex set overload-resolution
7157 @cindex overloaded functions, overload resolution
7158 @item set overload-resolution on
7159 Enable overload resolution for C@t{++} expression evaluation. The default
7160 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7161 and searches for a function whose signature matches the argument types,
7162 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7163 expressions}, for details). If it cannot find a match, it emits a
7166 @item set overload-resolution off
7167 Disable overload resolution for C@t{++} expression evaluation. For
7168 overloaded functions that are not class member functions, @value{GDBN}
7169 chooses the first function of the specified name that it finds in the
7170 symbol table, whether or not its arguments are of the correct type. For
7171 overloaded functions that are class member functions, @value{GDBN}
7172 searches for a function whose signature @emph{exactly} matches the
7175 @item @r{Overloaded symbol names}
7176 You can specify a particular definition of an overloaded symbol, using
7177 the same notation that is used to declare such symbols in C@t{++}: type
7178 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7179 also use the @value{GDBN} command-line word completion facilities to list the
7180 available choices, or to finish the type list for you.
7181 @xref{Completion,, Command completion}, for details on how to do this.
7185 @subsection Modula-2
7187 @cindex Modula-2, @value{GDBN} support
7189 The extensions made to @value{GDBN} to support Modula-2 only support
7190 output from the @sc{gnu} Modula-2 compiler (which is currently being
7191 developed). Other Modula-2 compilers are not currently supported, and
7192 attempting to debug executables produced by them is most likely
7193 to give an error as @value{GDBN} reads in the executable's symbol
7196 @cindex expressions in Modula-2
7198 * M2 Operators:: Built-in operators
7199 * Built-In Func/Proc:: Built-in functions and procedures
7200 * M2 Constants:: Modula-2 constants
7201 * M2 Defaults:: Default settings for Modula-2
7202 * Deviations:: Deviations from standard Modula-2
7203 * M2 Checks:: Modula-2 type and range checks
7204 * M2 Scope:: The scope operators @code{::} and @code{.}
7205 * GDB/M2:: @value{GDBN} and Modula-2
7209 @subsubsection Operators
7210 @cindex Modula-2 operators
7212 Operators must be defined on values of specific types. For instance,
7213 @code{+} is defined on numbers, but not on structures. Operators are
7214 often defined on groups of types. For the purposes of Modula-2, the
7215 following definitions hold:
7220 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7224 @emph{Character types} consist of @code{CHAR} and its subranges.
7227 @emph{Floating-point types} consist of @code{REAL}.
7230 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7234 @emph{Scalar types} consist of all of the above.
7237 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7240 @emph{Boolean types} consist of @code{BOOLEAN}.
7244 The following operators are supported, and appear in order of
7245 increasing precedence:
7249 Function argument or array index separator.
7252 Assignment. The value of @var{var} @code{:=} @var{value} is
7256 Less than, greater than on integral, floating-point, or enumerated
7260 Less than or equal to, greater than or equal to
7261 on integral, floating-point and enumerated types, or set inclusion on
7262 set types. Same precedence as @code{<}.
7264 @item =@r{, }<>@r{, }#
7265 Equality and two ways of expressing inequality, valid on scalar types.
7266 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7267 available for inequality, since @code{#} conflicts with the script
7271 Set membership. Defined on set types and the types of their members.
7272 Same precedence as @code{<}.
7275 Boolean disjunction. Defined on boolean types.
7278 Boolean conjunction. Defined on boolean types.
7281 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7284 Addition and subtraction on integral and floating-point types, or union
7285 and difference on set types.
7288 Multiplication on integral and floating-point types, or set intersection
7292 Division on floating-point types, or symmetric set difference on set
7293 types. Same precedence as @code{*}.
7296 Integer division and remainder. Defined on integral types. Same
7297 precedence as @code{*}.
7300 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7303 Pointer dereferencing. Defined on pointer types.
7306 Boolean negation. Defined on boolean types. Same precedence as
7310 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7311 precedence as @code{^}.
7314 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7317 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7321 @value{GDBN} and Modula-2 scope operators.
7325 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7326 treats the use of the operator @code{IN}, or the use of operators
7327 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7328 @code{<=}, and @code{>=} on sets as an error.
7332 @node Built-In Func/Proc
7333 @subsubsection Built-in functions and procedures
7334 @cindex Modula-2 built-ins
7336 Modula-2 also makes available several built-in procedures and functions.
7337 In describing these, the following metavariables are used:
7342 represents an @code{ARRAY} variable.
7345 represents a @code{CHAR} constant or variable.
7348 represents a variable or constant of integral type.
7351 represents an identifier that belongs to a set. Generally used in the
7352 same function with the metavariable @var{s}. The type of @var{s} should
7353 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7356 represents a variable or constant of integral or floating-point type.
7359 represents a variable or constant of floating-point type.
7365 represents a variable.
7368 represents a variable or constant of one of many types. See the
7369 explanation of the function for details.
7372 All Modula-2 built-in procedures also return a result, described below.
7376 Returns the absolute value of @var{n}.
7379 If @var{c} is a lower case letter, it returns its upper case
7380 equivalent, otherwise it returns its argument.
7383 Returns the character whose ordinal value is @var{i}.
7386 Decrements the value in the variable @var{v} by one. Returns the new value.
7388 @item DEC(@var{v},@var{i})
7389 Decrements the value in the variable @var{v} by @var{i}. Returns the
7392 @item EXCL(@var{m},@var{s})
7393 Removes the element @var{m} from the set @var{s}. Returns the new
7396 @item FLOAT(@var{i})
7397 Returns the floating point equivalent of the integer @var{i}.
7400 Returns the index of the last member of @var{a}.
7403 Increments the value in the variable @var{v} by one. Returns the new value.
7405 @item INC(@var{v},@var{i})
7406 Increments the value in the variable @var{v} by @var{i}. Returns the
7409 @item INCL(@var{m},@var{s})
7410 Adds the element @var{m} to the set @var{s} if it is not already
7411 there. Returns the new set.
7414 Returns the maximum value of the type @var{t}.
7417 Returns the minimum value of the type @var{t}.
7420 Returns boolean TRUE if @var{i} is an odd number.
7423 Returns the ordinal value of its argument. For example, the ordinal
7424 value of a character is its @sc{ascii} value (on machines supporting the
7425 @sc{ascii} character set). @var{x} must be of an ordered type, which include
7426 integral, character and enumerated types.
7429 Returns the size of its argument. @var{x} can be a variable or a type.
7431 @item TRUNC(@var{r})
7432 Returns the integral part of @var{r}.
7434 @item VAL(@var{t},@var{i})
7435 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7439 @emph{Warning:} Sets and their operations are not yet supported, so
7440 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7444 @cindex Modula-2 constants
7446 @subsubsection Constants
7448 @value{GDBN} allows you to express the constants of Modula-2 in the following
7454 Integer constants are simply a sequence of digits. When used in an
7455 expression, a constant is interpreted to be type-compatible with the
7456 rest of the expression. Hexadecimal integers are specified by a
7457 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7460 Floating point constants appear as a sequence of digits, followed by a
7461 decimal point and another sequence of digits. An optional exponent can
7462 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7463 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7464 digits of the floating point constant must be valid decimal (base 10)
7468 Character constants consist of a single character enclosed by a pair of
7469 like quotes, either single (@code{'}) or double (@code{"}). They may
7470 also be expressed by their ordinal value (their @sc{ascii} value, usually)
7471 followed by a @samp{C}.
7474 String constants consist of a sequence of characters enclosed by a
7475 pair of like quotes, either single (@code{'}) or double (@code{"}).
7476 Escape sequences in the style of C are also allowed. @xref{C
7477 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
7481 Enumerated constants consist of an enumerated identifier.
7484 Boolean constants consist of the identifiers @code{TRUE} and
7488 Pointer constants consist of integral values only.
7491 Set constants are not yet supported.
7495 @subsubsection Modula-2 defaults
7496 @cindex Modula-2 defaults
7498 If type and range checking are set automatically by @value{GDBN}, they
7499 both default to @code{on} whenever the working language changes to
7500 Modula-2. This happens regardless of whether you or @value{GDBN}
7501 selected the working language.
7503 If you allow @value{GDBN} to set the language automatically, then entering
7504 code compiled from a file whose name ends with @file{.mod} sets the
7505 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
7506 the language automatically}, for further details.
7509 @subsubsection Deviations from standard Modula-2
7510 @cindex Modula-2, deviations from
7512 A few changes have been made to make Modula-2 programs easier to debug.
7513 This is done primarily via loosening its type strictness:
7517 Unlike in standard Modula-2, pointer constants can be formed by
7518 integers. This allows you to modify pointer variables during
7519 debugging. (In standard Modula-2, the actual address contained in a
7520 pointer variable is hidden from you; it can only be modified
7521 through direct assignment to another pointer variable or expression that
7522 returned a pointer.)
7525 C escape sequences can be used in strings and characters to represent
7526 non-printable characters. @value{GDBN} prints out strings with these
7527 escape sequences embedded. Single non-printable characters are
7528 printed using the @samp{CHR(@var{nnn})} format.
7531 The assignment operator (@code{:=}) returns the value of its right-hand
7535 All built-in procedures both modify @emph{and} return their argument.
7539 @subsubsection Modula-2 type and range checks
7540 @cindex Modula-2 checks
7543 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
7546 @c FIXME remove warning when type/range checks added
7548 @value{GDBN} considers two Modula-2 variables type equivalent if:
7552 They are of types that have been declared equivalent via a @code{TYPE
7553 @var{t1} = @var{t2}} statement
7556 They have been declared on the same line. (Note: This is true of the
7557 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
7560 As long as type checking is enabled, any attempt to combine variables
7561 whose types are not equivalent is an error.
7563 Range checking is done on all mathematical operations, assignment, array
7564 index bounds, and all built-in functions and procedures.
7567 @subsubsection The scope operators @code{::} and @code{.}
7569 @cindex @code{.}, Modula-2 scope operator
7570 @cindex colon, doubled as scope operator
7572 @vindex colon-colon@r{, in Modula-2}
7573 @c Info cannot handle :: but TeX can.
7576 @vindex ::@r{, in Modula-2}
7579 There are a few subtle differences between the Modula-2 scope operator
7580 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
7585 @var{module} . @var{id}
7586 @var{scope} :: @var{id}
7590 where @var{scope} is the name of a module or a procedure,
7591 @var{module} the name of a module, and @var{id} is any declared
7592 identifier within your program, except another module.
7594 Using the @code{::} operator makes @value{GDBN} search the scope
7595 specified by @var{scope} for the identifier @var{id}. If it is not
7596 found in the specified scope, then @value{GDBN} searches all scopes
7597 enclosing the one specified by @var{scope}.
7599 Using the @code{.} operator makes @value{GDBN} search the current scope for
7600 the identifier specified by @var{id} that was imported from the
7601 definition module specified by @var{module}. With this operator, it is
7602 an error if the identifier @var{id} was not imported from definition
7603 module @var{module}, or if @var{id} is not an identifier in
7607 @subsubsection @value{GDBN} and Modula-2
7609 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
7610 Five subcommands of @code{set print} and @code{show print} apply
7611 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
7612 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
7613 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
7614 analogue in Modula-2.
7616 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
7617 with any language, is not useful with Modula-2. Its
7618 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
7619 created in Modula-2 as they can in C or C@t{++}. However, because an
7620 address can be specified by an integral constant, the construct
7621 @samp{@{@var{type}@}@var{adrexp}} is still useful.
7623 @cindex @code{#} in Modula-2
7624 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
7625 interpreted as the beginning of a comment. Use @code{<>} instead.
7630 The extensions made to @value{GDBN} to support Chill only support output
7631 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
7632 supported, and attempting to debug executables produced by them is most
7633 likely to give an error as @value{GDBN} reads in the executable's symbol
7636 @c This used to say "... following Chill related topics ...", but since
7637 @c menus are not shown in the printed manual, it would look awkward.
7638 This section covers the Chill related topics and the features
7639 of @value{GDBN} which support these topics.
7642 * How modes are displayed:: How modes are displayed
7643 * Locations:: Locations and their accesses
7644 * Values and their Operations:: Values and their Operations
7645 * Chill type and range checks::
7649 @node How modes are displayed
7650 @subsubsection How modes are displayed
7652 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
7653 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
7654 slightly from the standard specification of the Chill language. The
7657 @c FIXME: this @table's contents effectively disable @code by using @r
7658 @c on every @item. So why does it need @code?
7660 @item @r{@emph{Discrete modes:}}
7663 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
7666 @emph{Boolean Mode} which is predefined by @code{BOOL},
7668 @emph{Character Mode} which is predefined by @code{CHAR},
7670 @emph{Set Mode} which is displayed by the keyword @code{SET}.
7672 (@value{GDBP}) ptype x
7673 type = SET (karli = 10, susi = 20, fritzi = 100)
7675 If the type is an unnumbered set the set element values are omitted.
7677 @emph{Range Mode} which is displayed by
7679 @code{type = <basemode>(<lower bound> : <upper bound>)}
7681 where @code{<lower bound>, <upper bound>} can be of any discrete literal
7682 expression (e.g. set element names).
7685 @item @r{@emph{Powerset Mode:}}
7686 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7687 the member mode of the powerset. The member mode can be any discrete mode.
7689 (@value{GDBP}) ptype x
7690 type = POWERSET SET (egon, hugo, otto)
7693 @item @r{@emph{Reference Modes:}}
7696 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
7697 followed by the mode name to which the reference is bound.
7699 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7702 @item @r{@emph{Procedure mode}}
7703 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7704 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7705 list>} is a list of the parameter modes. @code{<return mode>} indicates
7706 the mode of the result of the procedure if any. The exceptionlist lists
7707 all possible exceptions which can be raised by the procedure.
7710 @item @r{@emph{Instance mode}}
7711 The instance mode is represented by a structure, which has a static
7712 type, and is therefore not really of interest.
7715 @item @r{@emph{Synchronization Modes:}}
7718 @emph{Event Mode} which is displayed by
7720 @code{EVENT (<event length>)}
7722 where @code{(<event length>)} is optional.
7724 @emph{Buffer Mode} which is displayed by
7726 @code{BUFFER (<buffer length>)<buffer element mode>}
7728 where @code{(<buffer length>)} is optional.
7731 @item @r{@emph{Timing Modes:}}
7734 @emph{Duration Mode} which is predefined by @code{DURATION}
7736 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7739 @item @r{@emph{Real Modes:}}
7740 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7742 @item @r{@emph{String Modes:}}
7745 @emph{Character String Mode} which is displayed by
7747 @code{CHARS(<string length>)}
7749 followed by the keyword @code{VARYING} if the String Mode is a varying
7752 @emph{Bit String Mode} which is displayed by
7759 @item @r{@emph{Array Mode:}}
7760 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7761 followed by the element mode (which may in turn be an array mode).
7763 (@value{GDBP}) ptype x
7766 SET (karli = 10, susi = 20, fritzi = 100)
7769 @item @r{@emph{Structure Mode}}
7770 The Structure mode is displayed by the keyword @code{STRUCT(<field
7771 list>)}. The @code{<field list>} consists of names and modes of fields
7772 of the structure. Variant structures have the keyword @code{CASE <field>
7773 OF <variant fields> ESAC} in their field list. Since the current version
7774 of the GNU Chill compiler doesn't implement tag processing (no runtime
7775 checks of variant fields, and therefore no debugging info), the output
7776 always displays all variant fields.
7778 (@value{GDBP}) ptype str
7793 @subsubsection Locations and their accesses
7795 A location in Chill is an object which can contain values.
7797 A value of a location is generally accessed by the (declared) name of
7798 the location. The output conforms to the specification of values in
7799 Chill programs. How values are specified
7800 is the topic of the next section, @ref{Values and their Operations}.
7802 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7803 display or change the result of a currently-active procedure:
7810 This does the same as the Chill action @code{RESULT EXPR} (which
7811 is not available in @value{GDBN}).
7813 Values of reference mode locations are printed by @code{PTR(<hex
7814 value>)} in case of a free reference mode, and by @code{(REF <reference
7815 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7816 represents the address where the reference points to. To access the
7817 value of the location referenced by the pointer, use the dereference
7820 Values of procedure mode locations are displayed by
7823 (<argument modes> ) <return mode> @} <address> <name of procedure
7826 @code{<argument modes>} is a list of modes according to the parameter
7827 specification of the procedure and @code{<address>} shows the address of
7831 Locations of instance modes are displayed just like a structure with two
7832 fields specifying the @emph{process type} and the @emph{copy number} of
7833 the investigated instance location@footnote{This comes from the current
7834 implementation of instances. They are implemented as a structure (no
7835 na). The output should be something like @code{[<name of the process>;
7836 <instance number>]}.}. The field names are @code{__proc_type} and
7839 Locations of synchronization modes are displayed like a structure with
7840 the field name @code{__event_data} in case of a event mode location, and
7841 like a structure with the field @code{__buffer_data} in case of a buffer
7842 mode location (refer to previous paragraph).
7844 Structure Mode locations are printed by @code{[.<field name>: <value>,
7845 ...]}. The @code{<field name>} corresponds to the structure mode
7846 definition and the layout of @code{<value>} varies depending of the mode
7847 of the field. If the investigated structure mode location is of variant
7848 structure mode, the variant parts of the structure are enclosed in curled
7849 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
7850 on the same memory location and represent the current values of the
7851 memory location in their specific modes. Since no tag processing is done
7852 all variants are displayed. A variant field is printed by
7853 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7856 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7857 [.cs: []], (susi) = [.ds: susi]}]
7861 Substructures of string mode-, array mode- or structure mode-values
7862 (e.g. array slices, fields of structure locations) are accessed using
7863 certain operations which are described in the next section, @ref{Values
7864 and their Operations}.
7866 A location value may be interpreted as having a different mode using the
7867 location conversion. This mode conversion is written as @code{<mode
7868 name>(<location>)}. The user has to consider that the sizes of the modes
7869 have to be equal otherwise an error occurs. Furthermore, no range
7870 checking of the location against the destination mode is performed, and
7871 therefore the result can be quite confusing.
7874 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7877 @node Values and their Operations
7878 @subsubsection Values and their Operations
7880 Values are used to alter locations, to investigate complex structures in
7881 more detail or to filter relevant information out of a large amount of
7882 data. There are several (mode dependent) operations defined which enable
7883 such investigations. These operations are not only applicable to
7884 constant values but also to locations, which can become quite useful
7885 when debugging complex structures. During parsing the command line
7886 (e.g. evaluating an expression) @value{GDBN} treats location names as
7887 the values behind these locations.
7889 This section describes how values have to be specified and which
7890 operations are legal to be used with such values.
7893 @item Literal Values
7894 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7895 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7897 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7898 @c be converted to a @ref.
7903 @emph{Integer Literals} are specified in the same manner as in Chill
7904 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7906 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7908 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7911 @emph{Set Literals} are defined by a name which was specified in a set
7912 mode. The value delivered by a Set Literal is the set value. This is
7913 comparable to an enumeration in C/C@t{++} language.
7915 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7916 emptiness literal delivers either the empty reference value, the empty
7917 procedure value or the empty instance value.
7920 @emph{Character String Literals} are defined by a sequence of characters
7921 enclosed in single- or double quotes. If a single- or double quote has
7922 to be part of the string literal it has to be stuffed (specified twice).
7924 @emph{Bitstring Literals} are specified in the same manner as in Chill
7925 programs (refer z200/88 chpt 5.2.4.8).
7927 @emph{Floating point literals} are specified in the same manner as in
7928 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7933 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7934 name>} can be omitted if the mode of the tuple is unambiguous. This
7935 unambiguity is derived from the context of a evaluated expression.
7936 @code{<tuple>} can be one of the following:
7939 @item @emph{Powerset Tuple}
7940 @item @emph{Array Tuple}
7941 @item @emph{Structure Tuple}
7942 Powerset tuples, array tuples and structure tuples are specified in the
7943 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7946 @item String Element Value
7947 A string element value is specified by
7949 @code{<string value>(<index>)}
7951 where @code{<index>} is a integer expression. It delivers a character
7952 value which is equivalent to the character indexed by @code{<index>} in
7955 @item String Slice Value
7956 A string slice value is specified by @code{<string value>(<slice
7957 spec>)}, where @code{<slice spec>} can be either a range of integer
7958 expressions or specified by @code{<start expr> up <size>}.
7959 @code{<size>} denotes the number of elements which the slice contains.
7960 The delivered value is a string value, which is part of the specified
7963 @item Array Element Values
7964 An array element value is specified by @code{<array value>(<expr>)} and
7965 delivers a array element value of the mode of the specified array.
7967 @item Array Slice Values
7968 An array slice is specified by @code{<array value>(<slice spec>)}, where
7969 @code{<slice spec>} can be either a range specified by expressions or by
7970 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7971 arrayelements the slice contains. The delivered value is an array value
7972 which is part of the specified array.
7974 @item Structure Field Values
7975 A structure field value is derived by @code{<structure value>.<field
7976 name>}, where @code{<field name>} indicates the name of a field specified
7977 in the mode definition of the structure. The mode of the delivered value
7978 corresponds to this mode definition in the structure definition.
7980 @item Procedure Call Value
7981 The procedure call value is derived from the return value of the
7982 procedure@footnote{If a procedure call is used for instance in an
7983 expression, then this procedure is called with all its side
7984 effects. This can lead to confusing results if used carelessly.}.
7986 Values of duration mode locations are represented by @code{ULONG} literals.
7988 Values of time mode locations appear as
7990 @code{TIME(<secs>:<nsecs>)}
7995 This is not implemented yet:
7996 @item Built-in Value
7998 The following built in functions are provided:
8010 @item @code{UPPER()}
8011 @item @code{LOWER()}
8012 @item @code{LENGTH()}
8016 @item @code{ARCSIN()}
8017 @item @code{ARCCOS()}
8018 @item @code{ARCTAN()}
8025 For a detailed description refer to the GNU Chill implementation manual
8029 @item Zero-adic Operator Value
8030 The zero-adic operator value is derived from the instance value for the
8031 current active process.
8033 @item Expression Values
8034 The value delivered by an expression is the result of the evaluation of
8035 the specified expression. If there are error conditions (mode
8036 incompatibility, etc.) the evaluation of expressions is aborted with a
8037 corresponding error message. Expressions may be parenthesised which
8038 causes the evaluation of this expression before any other expression
8039 which uses the result of the parenthesised expression. The following
8040 operators are supported by @value{GDBN}:
8043 @item @code{OR, ORIF, XOR}
8044 @itemx @code{AND, ANDIF}
8046 Logical operators defined over operands of boolean mode.
8049 Equality and inequality operators defined over all modes.
8053 Relational operators defined over predefined modes.
8056 @itemx @code{*, /, MOD, REM}
8057 Arithmetic operators defined over predefined modes.
8060 Change sign operator.
8063 String concatenation operator.
8066 String repetition operator.
8069 Referenced location operator which can be used either to take the
8070 address of a location (@code{->loc}), or to dereference a reference
8071 location (@code{loc->}).
8073 @item @code{OR, XOR}
8076 Powerset and bitstring operators.
8080 Powerset inclusion operators.
8083 Membership operator.
8087 @node Chill type and range checks
8088 @subsubsection Chill type and range checks
8090 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8091 of the two modes are equal. This rule applies recursively to more
8092 complex datatypes which means that complex modes are treated
8093 equivalent if all element modes (which also can be complex modes like
8094 structures, arrays, etc.) have the same size.
8096 Range checking is done on all mathematical operations, assignment, array
8097 index bounds and all built in procedures.
8099 Strong type checks are forced using the @value{GDBN} command @code{set
8100 check strong}. This enforces strong type and range checks on all
8101 operations where Chill constructs are used (expressions, built in
8102 functions, etc.) in respect to the semantics as defined in the z.200
8103 language specification.
8105 All checks can be disabled by the @value{GDBN} command @code{set check
8109 @c Deviations from the Chill Standard Z200/88
8110 see last paragraph ?
8113 @node Chill defaults
8114 @subsubsection Chill defaults
8116 If type and range checking are set automatically by @value{GDBN}, they
8117 both default to @code{on} whenever the working language changes to
8118 Chill. This happens regardless of whether you or @value{GDBN}
8119 selected the working language.
8121 If you allow @value{GDBN} to set the language automatically, then entering
8122 code compiled from a file whose name ends with @file{.ch} sets the
8123 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8124 the language automatically}, for further details.
8127 @chapter Examining the Symbol Table
8129 The commands described in this chapter allow you to inquire about the
8130 symbols (names of variables, functions and types) defined in your
8131 program. This information is inherent in the text of your program and
8132 does not change as your program executes. @value{GDBN} finds it in your
8133 program's symbol table, in the file indicated when you started @value{GDBN}
8134 (@pxref{File Options, ,Choosing files}), or by one of the
8135 file-management commands (@pxref{Files, ,Commands to specify files}).
8137 @cindex symbol names
8138 @cindex names of symbols
8139 @cindex quoting names
8140 Occasionally, you may need to refer to symbols that contain unusual
8141 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8142 most frequent case is in referring to static variables in other
8143 source files (@pxref{Variables,,Program variables}). File names
8144 are recorded in object files as debugging symbols, but @value{GDBN} would
8145 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8146 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8147 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8154 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8157 @kindex info address
8158 @cindex address of a symbol
8159 @item info address @var{symbol}
8160 Describe where the data for @var{symbol} is stored. For a register
8161 variable, this says which register it is kept in. For a non-register
8162 local variable, this prints the stack-frame offset at which the variable
8165 Note the contrast with @samp{print &@var{symbol}}, which does not work
8166 at all for a register variable, and for a stack local variable prints
8167 the exact address of the current instantiation of the variable.
8170 @cindex symbol from address
8171 @item info symbol @var{addr}
8172 Print the name of a symbol which is stored at the address @var{addr}.
8173 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8174 nearest symbol and an offset from it:
8177 (@value{GDBP}) info symbol 0x54320
8178 _initialize_vx + 396 in section .text
8182 This is the opposite of the @code{info address} command. You can use
8183 it to find out the name of a variable or a function given its address.
8186 @item whatis @var{expr}
8187 Print the data type of expression @var{expr}. @var{expr} is not
8188 actually evaluated, and any side-effecting operations (such as
8189 assignments or function calls) inside it do not take place.
8190 @xref{Expressions, ,Expressions}.
8193 Print the data type of @code{$}, the last value in the value history.
8196 @item ptype @var{typename}
8197 Print a description of data type @var{typename}. @var{typename} may be
8198 the name of a type, or for C code it may have the form @samp{class
8199 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8200 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8202 @item ptype @var{expr}
8204 Print a description of the type of expression @var{expr}. @code{ptype}
8205 differs from @code{whatis} by printing a detailed description, instead
8206 of just the name of the type.
8208 For example, for this variable declaration:
8211 struct complex @{double real; double imag;@} v;
8215 the two commands give this output:
8219 (@value{GDBP}) whatis v
8220 type = struct complex
8221 (@value{GDBP}) ptype v
8222 type = struct complex @{
8230 As with @code{whatis}, using @code{ptype} without an argument refers to
8231 the type of @code{$}, the last value in the value history.
8234 @item info types @var{regexp}
8236 Print a brief description of all types whose names match @var{regexp}
8237 (or all types in your program, if you supply no argument). Each
8238 complete typename is matched as though it were a complete line; thus,
8239 @samp{i type value} gives information on all types in your program whose
8240 names include the string @code{value}, but @samp{i type ^value$} gives
8241 information only on types whose complete name is @code{value}.
8243 This command differs from @code{ptype} in two ways: first, like
8244 @code{whatis}, it does not print a detailed description; second, it
8245 lists all source files where a type is defined.
8248 @cindex local variables
8249 @item info scope @var{addr}
8250 List all the variables local to a particular scope. This command
8251 accepts a location---a function name, a source line, or an address
8252 preceded by a @samp{*}, and prints all the variables local to the
8253 scope defined by that location. For example:
8256 (@value{GDBP}) @b{info scope command_line_handler}
8257 Scope for command_line_handler:
8258 Symbol rl is an argument at stack/frame offset 8, length 4.
8259 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8260 Symbol linelength is in static storage at address 0x150a1c, length 4.
8261 Symbol p is a local variable in register $esi, length 4.
8262 Symbol p1 is a local variable in register $ebx, length 4.
8263 Symbol nline is a local variable in register $edx, length 4.
8264 Symbol repeat is a local variable at frame offset -8, length 4.
8268 This command is especially useful for determining what data to collect
8269 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8274 Show the name of the current source file---that is, the source file for
8275 the function containing the current point of execution---and the language
8278 @kindex info sources
8280 Print the names of all source files in your program for which there is
8281 debugging information, organized into two lists: files whose symbols
8282 have already been read, and files whose symbols will be read when needed.
8284 @kindex info functions
8285 @item info functions
8286 Print the names and data types of all defined functions.
8288 @item info functions @var{regexp}
8289 Print the names and data types of all defined functions
8290 whose names contain a match for regular expression @var{regexp}.
8291 Thus, @samp{info fun step} finds all functions whose names
8292 include @code{step}; @samp{info fun ^step} finds those whose names
8293 start with @code{step}. If a function name contains characters
8294 that conflict with the regular expression language (eg.
8295 @samp{operator*()}), they may be quoted with a backslash.
8297 @kindex info variables
8298 @item info variables
8299 Print the names and data types of all variables that are declared
8300 outside of functions (i.e., excluding local variables).
8302 @item info variables @var{regexp}
8303 Print the names and data types of all variables (except for local
8304 variables) whose names contain a match for regular expression
8308 This was never implemented.
8309 @kindex info methods
8311 @itemx info methods @var{regexp}
8312 The @code{info methods} command permits the user to examine all defined
8313 methods within C@t{++} program, or (with the @var{regexp} argument) a
8314 specific set of methods found in the various C@t{++} classes. Many
8315 C@t{++} classes provide a large number of methods. Thus, the output
8316 from the @code{ptype} command can be overwhelming and hard to use. The
8317 @code{info-methods} command filters the methods, printing only those
8318 which match the regular-expression @var{regexp}.
8321 @cindex reloading symbols
8322 Some systems allow individual object files that make up your program to
8323 be replaced without stopping and restarting your program. For example,
8324 in VxWorks you can simply recompile a defective object file and keep on
8325 running. If you are running on one of these systems, you can allow
8326 @value{GDBN} to reload the symbols for automatically relinked modules:
8329 @kindex set symbol-reloading
8330 @item set symbol-reloading on
8331 Replace symbol definitions for the corresponding source file when an
8332 object file with a particular name is seen again.
8334 @item set symbol-reloading off
8335 Do not replace symbol definitions when encountering object files of the
8336 same name more than once. This is the default state; if you are not
8337 running on a system that permits automatic relinking of modules, you
8338 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8339 may discard symbols when linking large programs, that may contain
8340 several modules (from different directories or libraries) with the same
8343 @kindex show symbol-reloading
8344 @item show symbol-reloading
8345 Show the current @code{on} or @code{off} setting.
8348 @kindex set opaque-type-resolution
8349 @item set opaque-type-resolution on
8350 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8351 declared as a pointer to a @code{struct}, @code{class}, or
8352 @code{union}---for example, @code{struct MyType *}---that is used in one
8353 source file although the full declaration of @code{struct MyType} is in
8354 another source file. The default is on.
8356 A change in the setting of this subcommand will not take effect until
8357 the next time symbols for a file are loaded.
8359 @item set opaque-type-resolution off
8360 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8361 is printed as follows:
8363 @{<no data fields>@}
8366 @kindex show opaque-type-resolution
8367 @item show opaque-type-resolution
8368 Show whether opaque types are resolved or not.
8370 @kindex maint print symbols
8372 @kindex maint print psymbols
8373 @cindex partial symbol dump
8374 @item maint print symbols @var{filename}
8375 @itemx maint print psymbols @var{filename}
8376 @itemx maint print msymbols @var{filename}
8377 Write a dump of debugging symbol data into the file @var{filename}.
8378 These commands are used to debug the @value{GDBN} symbol-reading code. Only
8379 symbols with debugging data are included. If you use @samp{maint print
8380 symbols}, @value{GDBN} includes all the symbols for which it has already
8381 collected full details: that is, @var{filename} reflects symbols for
8382 only those files whose symbols @value{GDBN} has read. You can use the
8383 command @code{info sources} to find out which files these are. If you
8384 use @samp{maint print psymbols} instead, the dump shows information about
8385 symbols that @value{GDBN} only knows partially---that is, symbols defined in
8386 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
8387 @samp{maint print msymbols} dumps just the minimal symbol information
8388 required for each object file from which @value{GDBN} has read some symbols.
8389 @xref{Files, ,Commands to specify files}, for a discussion of how
8390 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
8394 @chapter Altering Execution
8396 Once you think you have found an error in your program, you might want to
8397 find out for certain whether correcting the apparent error would lead to
8398 correct results in the rest of the run. You can find the answer by
8399 experiment, using the @value{GDBN} features for altering execution of the
8402 For example, you can store new values into variables or memory
8403 locations, give your program a signal, restart it at a different
8404 address, or even return prematurely from a function.
8407 * Assignment:: Assignment to variables
8408 * Jumping:: Continuing at a different address
8409 * Signaling:: Giving your program a signal
8410 * Returning:: Returning from a function
8411 * Calling:: Calling your program's functions
8412 * Patching:: Patching your program
8416 @section Assignment to variables
8419 @cindex setting variables
8420 To alter the value of a variable, evaluate an assignment expression.
8421 @xref{Expressions, ,Expressions}. For example,
8428 stores the value 4 into the variable @code{x}, and then prints the
8429 value of the assignment expression (which is 4).
8430 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
8431 information on operators in supported languages.
8433 @kindex set variable
8434 @cindex variables, setting
8435 If you are not interested in seeing the value of the assignment, use the
8436 @code{set} command instead of the @code{print} command. @code{set} is
8437 really the same as @code{print} except that the expression's value is
8438 not printed and is not put in the value history (@pxref{Value History,
8439 ,Value history}). The expression is evaluated only for its effects.
8441 If the beginning of the argument string of the @code{set} command
8442 appears identical to a @code{set} subcommand, use the @code{set
8443 variable} command instead of just @code{set}. This command is identical
8444 to @code{set} except for its lack of subcommands. For example, if your
8445 program has a variable @code{width}, you get an error if you try to set
8446 a new value with just @samp{set width=13}, because @value{GDBN} has the
8447 command @code{set width}:
8450 (@value{GDBP}) whatis width
8452 (@value{GDBP}) p width
8454 (@value{GDBP}) set width=47
8455 Invalid syntax in expression.
8459 The invalid expression, of course, is @samp{=47}. In
8460 order to actually set the program's variable @code{width}, use
8463 (@value{GDBP}) set var width=47
8466 Because the @code{set} command has many subcommands that can conflict
8467 with the names of program variables, it is a good idea to use the
8468 @code{set variable} command instead of just @code{set}. For example, if
8469 your program has a variable @code{g}, you run into problems if you try
8470 to set a new value with just @samp{set g=4}, because @value{GDBN} has
8471 the command @code{set gnutarget}, abbreviated @code{set g}:
8475 (@value{GDBP}) whatis g
8479 (@value{GDBP}) set g=4
8483 The program being debugged has been started already.
8484 Start it from the beginning? (y or n) y
8485 Starting program: /home/smith/cc_progs/a.out
8486 "/home/smith/cc_progs/a.out": can't open to read symbols:
8488 (@value{GDBP}) show g
8489 The current BFD target is "=4".
8494 The program variable @code{g} did not change, and you silently set the
8495 @code{gnutarget} to an invalid value. In order to set the variable
8499 (@value{GDBP}) set var g=4
8502 @value{GDBN} allows more implicit conversions in assignments than C; you can
8503 freely store an integer value into a pointer variable or vice versa,
8504 and you can convert any structure to any other structure that is the
8505 same length or shorter.
8506 @comment FIXME: how do structs align/pad in these conversions?
8507 @comment /doc@cygnus.com 18dec1990
8509 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
8510 construct to generate a value of specified type at a specified address
8511 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
8512 to memory location @code{0x83040} as an integer (which implies a certain size
8513 and representation in memory), and
8516 set @{int@}0x83040 = 4
8520 stores the value 4 into that memory location.
8523 @section Continuing at a different address
8525 Ordinarily, when you continue your program, you do so at the place where
8526 it stopped, with the @code{continue} command. You can instead continue at
8527 an address of your own choosing, with the following commands:
8531 @item jump @var{linespec}
8532 Resume execution at line @var{linespec}. Execution stops again
8533 immediately if there is a breakpoint there. @xref{List, ,Printing
8534 source lines}, for a description of the different forms of
8535 @var{linespec}. It is common practice to use the @code{tbreak} command
8536 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
8539 The @code{jump} command does not change the current stack frame, or
8540 the stack pointer, or the contents of any memory location or any
8541 register other than the program counter. If line @var{linespec} is in
8542 a different function from the one currently executing, the results may
8543 be bizarre if the two functions expect different patterns of arguments or
8544 of local variables. For this reason, the @code{jump} command requests
8545 confirmation if the specified line is not in the function currently
8546 executing. However, even bizarre results are predictable if you are
8547 well acquainted with the machine-language code of your program.
8549 @item jump *@var{address}
8550 Resume execution at the instruction at address @var{address}.
8553 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
8554 On many systems, you can get much the same effect as the @code{jump}
8555 command by storing a new value into the register @code{$pc}. The
8556 difference is that this does not start your program running; it only
8557 changes the address of where it @emph{will} run when you continue. For
8565 makes the next @code{continue} command or stepping command execute at
8566 address @code{0x485}, rather than at the address where your program stopped.
8567 @xref{Continuing and Stepping, ,Continuing and stepping}.
8569 The most common occasion to use the @code{jump} command is to back
8570 up---perhaps with more breakpoints set---over a portion of a program
8571 that has already executed, in order to examine its execution in more
8576 @section Giving your program a signal
8580 @item signal @var{signal}
8581 Resume execution where your program stopped, but immediately give it the
8582 signal @var{signal}. @var{signal} can be the name or the number of a
8583 signal. For example, on many systems @code{signal 2} and @code{signal
8584 SIGINT} are both ways of sending an interrupt signal.
8586 Alternatively, if @var{signal} is zero, continue execution without
8587 giving a signal. This is useful when your program stopped on account of
8588 a signal and would ordinary see the signal when resumed with the
8589 @code{continue} command; @samp{signal 0} causes it to resume without a
8592 @code{signal} does not repeat when you press @key{RET} a second time
8593 after executing the command.
8597 Invoking the @code{signal} command is not the same as invoking the
8598 @code{kill} utility from the shell. Sending a signal with @code{kill}
8599 causes @value{GDBN} to decide what to do with the signal depending on
8600 the signal handling tables (@pxref{Signals}). The @code{signal} command
8601 passes the signal directly to your program.
8605 @section Returning from a function
8608 @cindex returning from a function
8611 @itemx return @var{expression}
8612 You can cancel execution of a function call with the @code{return}
8613 command. If you give an
8614 @var{expression} argument, its value is used as the function's return
8618 When you use @code{return}, @value{GDBN} discards the selected stack frame
8619 (and all frames within it). You can think of this as making the
8620 discarded frame return prematurely. If you wish to specify a value to
8621 be returned, give that value as the argument to @code{return}.
8623 This pops the selected stack frame (@pxref{Selection, ,Selecting a
8624 frame}), and any other frames inside of it, leaving its caller as the
8625 innermost remaining frame. That frame becomes selected. The
8626 specified value is stored in the registers used for returning values
8629 The @code{return} command does not resume execution; it leaves the
8630 program stopped in the state that would exist if the function had just
8631 returned. In contrast, the @code{finish} command (@pxref{Continuing
8632 and Stepping, ,Continuing and stepping}) resumes execution until the
8633 selected stack frame returns naturally.
8636 @section Calling program functions
8638 @cindex calling functions
8641 @item call @var{expr}
8642 Evaluate the expression @var{expr} without displaying @code{void}
8646 You can use this variant of the @code{print} command if you want to
8647 execute a function from your program, but without cluttering the output
8648 with @code{void} returned values. If the result is not void, it
8649 is printed and saved in the value history.
8651 For the A29K, a user-controlled variable @code{call_scratch_address},
8652 specifies the location of a scratch area to be used when @value{GDBN}
8653 calls a function in the target. This is necessary because the usual
8654 method of putting the scratch area on the stack does not work in systems
8655 that have separate instruction and data spaces.
8658 @section Patching programs
8660 @cindex patching binaries
8661 @cindex writing into executables
8662 @cindex writing into corefiles
8664 By default, @value{GDBN} opens the file containing your program's
8665 executable code (or the corefile) read-only. This prevents accidental
8666 alterations to machine code; but it also prevents you from intentionally
8667 patching your program's binary.
8669 If you'd like to be able to patch the binary, you can specify that
8670 explicitly with the @code{set write} command. For example, you might
8671 want to turn on internal debugging flags, or even to make emergency
8677 @itemx set write off
8678 If you specify @samp{set write on}, @value{GDBN} opens executable and
8679 core files for both reading and writing; if you specify @samp{set write
8680 off} (the default), @value{GDBN} opens them read-only.
8682 If you have already loaded a file, you must load it again (using the
8683 @code{exec-file} or @code{core-file} command) after changing @code{set
8684 write}, for your new setting to take effect.
8688 Display whether executable files and core files are opened for writing
8693 @chapter @value{GDBN} Files
8695 @value{GDBN} needs to know the file name of the program to be debugged,
8696 both in order to read its symbol table and in order to start your
8697 program. To debug a core dump of a previous run, you must also tell
8698 @value{GDBN} the name of the core dump file.
8701 * Files:: Commands to specify files
8702 * Symbol Errors:: Errors reading symbol files
8706 @section Commands to specify files
8708 @cindex symbol table
8709 @cindex core dump file
8711 You may want to specify executable and core dump file names. The usual
8712 way to do this is at start-up time, using the arguments to
8713 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
8714 Out of @value{GDBN}}).
8716 Occasionally it is necessary to change to a different file during a
8717 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8718 a file you want to use. In these situations the @value{GDBN} commands
8719 to specify new files are useful.
8722 @cindex executable file
8724 @item file @var{filename}
8725 Use @var{filename} as the program to be debugged. It is read for its
8726 symbols and for the contents of pure memory. It is also the program
8727 executed when you use the @code{run} command. If you do not specify a
8728 directory and the file is not found in the @value{GDBN} working directory,
8729 @value{GDBN} uses the environment variable @code{PATH} as a list of
8730 directories to search, just as the shell does when looking for a program
8731 to run. You can change the value of this variable, for both @value{GDBN}
8732 and your program, using the @code{path} command.
8734 On systems with memory-mapped files, an auxiliary file named
8735 @file{@var{filename}.syms} may hold symbol table information for
8736 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8737 @file{@var{filename}.syms}, starting up more quickly. See the
8738 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8739 (available on the command line, and with the commands @code{file},
8740 @code{symbol-file}, or @code{add-symbol-file}, described below),
8741 for more information.
8744 @code{file} with no argument makes @value{GDBN} discard any information it
8745 has on both executable file and the symbol table.
8748 @item exec-file @r{[} @var{filename} @r{]}
8749 Specify that the program to be run (but not the symbol table) is found
8750 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8751 if necessary to locate your program. Omitting @var{filename} means to
8752 discard information on the executable file.
8755 @item symbol-file @r{[} @var{filename} @r{]}
8756 Read symbol table information from file @var{filename}. @code{PATH} is
8757 searched when necessary. Use the @code{file} command to get both symbol
8758 table and program to run from the same file.
8760 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8761 program's symbol table.
8763 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8764 of its convenience variables, the value history, and all breakpoints and
8765 auto-display expressions. This is because they may contain pointers to
8766 the internal data recording symbols and data types, which are part of
8767 the old symbol table data being discarded inside @value{GDBN}.
8769 @code{symbol-file} does not repeat if you press @key{RET} again after
8772 When @value{GDBN} is configured for a particular environment, it
8773 understands debugging information in whatever format is the standard
8774 generated for that environment; you may use either a @sc{gnu} compiler, or
8775 other compilers that adhere to the local conventions.
8776 Best results are usually obtained from @sc{gnu} compilers; for example,
8777 using @code{@value{GCC}} you can generate debugging information for
8780 For most kinds of object files, with the exception of old SVR3 systems
8781 using COFF, the @code{symbol-file} command does not normally read the
8782 symbol table in full right away. Instead, it scans the symbol table
8783 quickly to find which source files and which symbols are present. The
8784 details are read later, one source file at a time, as they are needed.
8786 The purpose of this two-stage reading strategy is to make @value{GDBN}
8787 start up faster. For the most part, it is invisible except for
8788 occasional pauses while the symbol table details for a particular source
8789 file are being read. (The @code{set verbose} command can turn these
8790 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8791 warnings and messages}.)
8793 We have not implemented the two-stage strategy for COFF yet. When the
8794 symbol table is stored in COFF format, @code{symbol-file} reads the
8795 symbol table data in full right away. Note that ``stabs-in-COFF''
8796 still does the two-stage strategy, since the debug info is actually
8800 @cindex reading symbols immediately
8801 @cindex symbols, reading immediately
8803 @cindex memory-mapped symbol file
8804 @cindex saving symbol table
8805 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8806 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8807 You can override the @value{GDBN} two-stage strategy for reading symbol
8808 tables by using the @samp{-readnow} option with any of the commands that
8809 load symbol table information, if you want to be sure @value{GDBN} has the
8810 entire symbol table available.
8812 If memory-mapped files are available on your system through the
8813 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8814 cause @value{GDBN} to write the symbols for your program into a reusable
8815 file. Future @value{GDBN} debugging sessions map in symbol information
8816 from this auxiliary symbol file (if the program has not changed), rather
8817 than spending time reading the symbol table from the executable
8818 program. Using the @samp{-mapped} option has the same effect as
8819 starting @value{GDBN} with the @samp{-mapped} command-line option.
8821 You can use both options together, to make sure the auxiliary symbol
8822 file has all the symbol information for your program.
8824 The auxiliary symbol file for a program called @var{myprog} is called
8825 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8826 than the corresponding executable), @value{GDBN} always attempts to use
8827 it when you debug @var{myprog}; no special options or commands are
8830 The @file{.syms} file is specific to the host machine where you run
8831 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8832 symbol table. It cannot be shared across multiple host platforms.
8834 @c FIXME: for now no mention of directories, since this seems to be in
8835 @c flux. 13mar1992 status is that in theory GDB would look either in
8836 @c current dir or in same dir as myprog; but issues like competing
8837 @c GDB's, or clutter in system dirs, mean that in practice right now
8838 @c only current dir is used. FFish says maybe a special GDB hierarchy
8839 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8844 @item core-file @r{[} @var{filename} @r{]}
8845 Specify the whereabouts of a core dump file to be used as the ``contents
8846 of memory''. Traditionally, core files contain only some parts of the
8847 address space of the process that generated them; @value{GDBN} can access the
8848 executable file itself for other parts.
8850 @code{core-file} with no argument specifies that no core file is
8853 Note that the core file is ignored when your program is actually running
8854 under @value{GDBN}. So, if you have been running your program and you
8855 wish to debug a core file instead, you must kill the subprocess in which
8856 the program is running. To do this, use the @code{kill} command
8857 (@pxref{Kill Process, ,Killing the child process}).
8859 @kindex add-symbol-file
8860 @cindex dynamic linking
8861 @item add-symbol-file @var{filename} @var{address}
8862 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8863 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
8864 The @code{add-symbol-file} command reads additional symbol table
8865 information from the file @var{filename}. You would use this command
8866 when @var{filename} has been dynamically loaded (by some other means)
8867 into the program that is running. @var{address} should be the memory
8868 address at which the file has been loaded; @value{GDBN} cannot figure
8869 this out for itself. You can additionally specify an arbitrary number
8870 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
8871 section name and base address for that section. You can specify any
8872 @var{address} as an expression.
8874 The symbol table of the file @var{filename} is added to the symbol table
8875 originally read with the @code{symbol-file} command. You can use the
8876 @code{add-symbol-file} command any number of times; the new symbol data
8877 thus read keeps adding to the old. To discard all old symbol data
8878 instead, use the @code{symbol-file} command without any arguments.
8880 @cindex relocatable object files, reading symbols from
8881 @cindex object files, relocatable, reading symbols from
8882 @cindex reading symbols from relocatable object files
8883 @cindex symbols, reading from relocatable object files
8884 @cindex @file{.o} files, reading symbols from
8885 Although @var{filename} is typically a shared library file, an
8886 executable file, or some other object file which has been fully
8887 relocated for loading into a process, you can also load symbolic
8888 information from relocatable @file{.o} files, as long as:
8892 the file's symbolic information refers only to linker symbols defined in
8893 that file, not to symbols defined by other object files,
8895 every section the file's symbolic information refers to has actually
8896 been loaded into the inferior, as it appears in the file, and
8898 you can determine the address at which every section was loaded, and
8899 provide these to the @code{add-symbol-file} command.
8903 Some embedded operating systems, like Sun Chorus and VxWorks, can load
8904 relocatable files into an already running program; such systems
8905 typically make the requirements above easy to meet. However, it's
8906 important to recognize that many native systems use complex link
8907 procedures (@code{.linkonce} section factoring and C++ constructor table
8908 assembly, for example) that make the requirements difficult to meet. In
8909 general, one cannot assume that using @code{add-symbol-file} to read a
8910 relocatable object file's symbolic information will have the same effect
8911 as linking the relocatable object file into the program in the normal
8914 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8916 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8917 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8918 table information for @var{filename}.
8920 @kindex add-shared-symbol-file
8921 @item add-shared-symbol-file
8922 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8923 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8924 shared libraries, however if @value{GDBN} does not find yours, you can run
8925 @code{add-shared-symbol-file}. It takes no arguments.
8929 The @code{section} command changes the base address of section SECTION of
8930 the exec file to ADDR. This can be used if the exec file does not contain
8931 section addresses, (such as in the a.out format), or when the addresses
8932 specified in the file itself are wrong. Each section must be changed
8933 separately. The @code{info files} command, described below, lists all
8934 the sections and their addresses.
8940 @code{info files} and @code{info target} are synonymous; both print the
8941 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8942 including the names of the executable and core dump files currently in
8943 use by @value{GDBN}, and the files from which symbols were loaded. The
8944 command @code{help target} lists all possible targets rather than
8949 All file-specifying commands allow both absolute and relative file names
8950 as arguments. @value{GDBN} always converts the file name to an absolute file
8951 name and remembers it that way.
8953 @cindex shared libraries
8954 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8957 @value{GDBN} automatically loads symbol definitions from shared libraries
8958 when you use the @code{run} command, or when you examine a core file.
8959 (Before you issue the @code{run} command, @value{GDBN} does not understand
8960 references to a function in a shared library, however---unless you are
8961 debugging a core file).
8963 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8964 automatically loads the symbols at the time of the @code{shl_load} call.
8966 @c FIXME: some @value{GDBN} release may permit some refs to undef
8967 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8968 @c FIXME...lib; check this from time to time when updating manual
8970 There are times, however, when you may wish to not automatically load
8971 symbol definitions from shared libraries, such as when they are
8972 particularly large or there are many of them.
8974 To control the automatic loading of shared library symbols, use the
8978 @kindex set auto-solib-add
8979 @item set auto-solib-add @var{mode}
8980 If @var{mode} is @code{on}, symbols from all shared object libraries
8981 will be loaded automatically when the inferior begins execution, you
8982 attach to an independently started inferior, or when the dynamic linker
8983 informs @value{GDBN} that a new library has been loaded. If @var{mode}
8984 is @code{off}, symbols must be loaded manually, using the
8985 @code{sharedlibrary} command. The default value is @code{on}.
8987 @kindex show auto-solib-add
8988 @item show auto-solib-add
8989 Display the current autoloading mode.
8992 To explicitly load shared library symbols, use the @code{sharedlibrary}
8996 @kindex info sharedlibrary
8999 @itemx info sharedlibrary
9000 Print the names of the shared libraries which are currently loaded.
9002 @kindex sharedlibrary
9004 @item sharedlibrary @var{regex}
9005 @itemx share @var{regex}
9006 Load shared object library symbols for files matching a
9007 Unix regular expression.
9008 As with files loaded automatically, it only loads shared libraries
9009 required by your program for a core file or after typing @code{run}. If
9010 @var{regex} is omitted all shared libraries required by your program are
9014 On some systems, such as HP-UX systems, @value{GDBN} supports
9015 autoloading shared library symbols until a limiting threshold size is
9016 reached. This provides the benefit of allowing autoloading to remain on
9017 by default, but avoids autoloading excessively large shared libraries,
9018 up to a threshold that is initially set, but which you can modify if you
9021 Beyond that threshold, symbols from shared libraries must be explicitly
9022 loaded. To load these symbols, use the command @code{sharedlibrary
9023 @var{filename}}. The base address of the shared library is determined
9024 automatically by @value{GDBN} and need not be specified.
9026 To display or set the threshold, use the commands:
9029 @kindex set auto-solib-limit
9030 @item set auto-solib-limit @var{threshold}
9031 Set the autoloading size threshold, in an integral number of megabytes.
9032 If @var{threshold} is nonzero and shared library autoloading is enabled,
9033 symbols from all shared object libraries will be loaded until the total
9034 size of the loaded shared library symbols exceeds this threshold.
9035 Otherwise, symbols must be loaded manually, using the
9036 @code{sharedlibrary} command. The default threshold is 100 (i.e. 100
9039 @kindex show auto-solib-limit
9040 @item show auto-solib-limit
9041 Display the current autoloading size threshold, in megabytes.
9045 @section Errors reading symbol files
9047 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9048 such as symbol types it does not recognize, or known bugs in compiler
9049 output. By default, @value{GDBN} does not notify you of such problems, since
9050 they are relatively common and primarily of interest to people
9051 debugging compilers. If you are interested in seeing information
9052 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9053 only one message about each such type of problem, no matter how many
9054 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9055 to see how many times the problems occur, with the @code{set
9056 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9059 The messages currently printed, and their meanings, include:
9062 @item inner block not inside outer block in @var{symbol}
9064 The symbol information shows where symbol scopes begin and end
9065 (such as at the start of a function or a block of statements). This
9066 error indicates that an inner scope block is not fully contained
9067 in its outer scope blocks.
9069 @value{GDBN} circumvents the problem by treating the inner block as if it had
9070 the same scope as the outer block. In the error message, @var{symbol}
9071 may be shown as ``@code{(don't know)}'' if the outer block is not a
9074 @item block at @var{address} out of order
9076 The symbol information for symbol scope blocks should occur in
9077 order of increasing addresses. This error indicates that it does not
9080 @value{GDBN} does not circumvent this problem, and has trouble
9081 locating symbols in the source file whose symbols it is reading. (You
9082 can often determine what source file is affected by specifying
9083 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9086 @item bad block start address patched
9088 The symbol information for a symbol scope block has a start address
9089 smaller than the address of the preceding source line. This is known
9090 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9092 @value{GDBN} circumvents the problem by treating the symbol scope block as
9093 starting on the previous source line.
9095 @item bad string table offset in symbol @var{n}
9098 Symbol number @var{n} contains a pointer into the string table which is
9099 larger than the size of the string table.
9101 @value{GDBN} circumvents the problem by considering the symbol to have the
9102 name @code{foo}, which may cause other problems if many symbols end up
9105 @item unknown symbol type @code{0x@var{nn}}
9107 The symbol information contains new data types that @value{GDBN} does
9108 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9109 uncomprehended information, in hexadecimal.
9111 @value{GDBN} circumvents the error by ignoring this symbol information.
9112 This usually allows you to debug your program, though certain symbols
9113 are not accessible. If you encounter such a problem and feel like
9114 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9115 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9116 and examine @code{*bufp} to see the symbol.
9118 @item stub type has NULL name
9120 @value{GDBN} could not find the full definition for a struct or class.
9122 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9123 The symbol information for a C@t{++} member function is missing some
9124 information that recent versions of the compiler should have output for
9127 @item info mismatch between compiler and debugger
9129 @value{GDBN} could not parse a type specification output by the compiler.
9134 @chapter Specifying a Debugging Target
9136 @cindex debugging target
9139 A @dfn{target} is the execution environment occupied by your program.
9141 Often, @value{GDBN} runs in the same host environment as your program;
9142 in that case, the debugging target is specified as a side effect when
9143 you use the @code{file} or @code{core} commands. When you need more
9144 flexibility---for example, running @value{GDBN} on a physically separate
9145 host, or controlling a standalone system over a serial port or a
9146 realtime system over a TCP/IP connection---you can use the @code{target}
9147 command to specify one of the target types configured for @value{GDBN}
9148 (@pxref{Target Commands, ,Commands for managing targets}).
9151 * Active Targets:: Active targets
9152 * Target Commands:: Commands for managing targets
9153 * Byte Order:: Choosing target byte order
9154 * Remote:: Remote debugging
9155 * KOD:: Kernel Object Display
9159 @node Active Targets
9160 @section Active targets
9162 @cindex stacking targets
9163 @cindex active targets
9164 @cindex multiple targets
9166 There are three classes of targets: processes, core files, and
9167 executable files. @value{GDBN} can work concurrently on up to three
9168 active targets, one in each class. This allows you to (for example)
9169 start a process and inspect its activity without abandoning your work on
9172 For example, if you execute @samp{gdb a.out}, then the executable file
9173 @code{a.out} is the only active target. If you designate a core file as
9174 well---presumably from a prior run that crashed and coredumped---then
9175 @value{GDBN} has two active targets and uses them in tandem, looking
9176 first in the corefile target, then in the executable file, to satisfy
9177 requests for memory addresses. (Typically, these two classes of target
9178 are complementary, since core files contain only a program's
9179 read-write memory---variables and so on---plus machine status, while
9180 executable files contain only the program text and initialized data.)
9182 When you type @code{run}, your executable file becomes an active process
9183 target as well. When a process target is active, all @value{GDBN}
9184 commands requesting memory addresses refer to that target; addresses in
9185 an active core file or executable file target are obscured while the
9186 process target is active.
9188 Use the @code{core-file} and @code{exec-file} commands to select a new
9189 core file or executable target (@pxref{Files, ,Commands to specify
9190 files}). To specify as a target a process that is already running, use
9191 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9194 @node Target Commands
9195 @section Commands for managing targets
9198 @item target @var{type} @var{parameters}
9199 Connects the @value{GDBN} host environment to a target machine or
9200 process. A target is typically a protocol for talking to debugging
9201 facilities. You use the argument @var{type} to specify the type or
9202 protocol of the target machine.
9204 Further @var{parameters} are interpreted by the target protocol, but
9205 typically include things like device names or host names to connect
9206 with, process numbers, and baud rates.
9208 The @code{target} command does not repeat if you press @key{RET} again
9209 after executing the command.
9213 Displays the names of all targets available. To display targets
9214 currently selected, use either @code{info target} or @code{info files}
9215 (@pxref{Files, ,Commands to specify files}).
9217 @item help target @var{name}
9218 Describe a particular target, including any parameters necessary to
9221 @kindex set gnutarget
9222 @item set gnutarget @var{args}
9223 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9224 knows whether it is reading an @dfn{executable},
9225 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9226 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9227 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9230 @emph{Warning:} To specify a file format with @code{set gnutarget},
9231 you must know the actual BFD name.
9235 @xref{Files, , Commands to specify files}.
9237 @kindex show gnutarget
9238 @item show gnutarget
9239 Use the @code{show gnutarget} command to display what file format
9240 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9241 @value{GDBN} will determine the file format for each file automatically,
9242 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9245 Here are some common targets (available, or not, depending on the GDB
9250 @item target exec @var{program}
9251 An executable file. @samp{target exec @var{program}} is the same as
9252 @samp{exec-file @var{program}}.
9255 @item target core @var{filename}
9256 A core dump file. @samp{target core @var{filename}} is the same as
9257 @samp{core-file @var{filename}}.
9259 @kindex target remote
9260 @item target remote @var{dev}
9261 Remote serial target in GDB-specific protocol. The argument @var{dev}
9262 specifies what serial device to use for the connection (e.g.
9263 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9264 supports the @code{load} command. This is only useful if you have
9265 some other way of getting the stub to the target system, and you can put
9266 it somewhere in memory where it won't get clobbered by the download.
9270 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9278 works; however, you cannot assume that a specific memory map, device
9279 drivers, or even basic I/O is available, although some simulators do
9280 provide these. For info about any processor-specific simulator details,
9281 see the appropriate section in @ref{Embedded Processors, ,Embedded
9286 Some configurations may include these targets as well:
9291 @item target nrom @var{dev}
9292 NetROM ROM emulator. This target only supports downloading.
9296 Different targets are available on different configurations of @value{GDBN};
9297 your configuration may have more or fewer targets.
9299 Many remote targets require you to download the executable's code
9300 once you've successfully established a connection.
9304 @kindex load @var{filename}
9305 @item load @var{filename}
9306 Depending on what remote debugging facilities are configured into
9307 @value{GDBN}, the @code{load} command may be available. Where it exists, it
9308 is meant to make @var{filename} (an executable) available for debugging
9309 on the remote system---by downloading, or dynamic linking, for example.
9310 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
9311 the @code{add-symbol-file} command.
9313 If your @value{GDBN} does not have a @code{load} command, attempting to
9314 execute it gets the error message ``@code{You can't do that when your
9315 target is @dots{}}''
9317 The file is loaded at whatever address is specified in the executable.
9318 For some object file formats, you can specify the load address when you
9319 link the program; for other formats, like a.out, the object file format
9320 specifies a fixed address.
9321 @c FIXME! This would be a good place for an xref to the GNU linker doc.
9323 @code{load} does not repeat if you press @key{RET} again after using it.
9327 @section Choosing target byte order
9329 @cindex choosing target byte order
9330 @cindex target byte order
9332 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
9333 offer the ability to run either big-endian or little-endian byte
9334 orders. Usually the executable or symbol will include a bit to
9335 designate the endian-ness, and you will not need to worry about
9336 which to use. However, you may still find it useful to adjust
9337 @value{GDBN}'s idea of processor endian-ness manually.
9340 @kindex set endian big
9341 @item set endian big
9342 Instruct @value{GDBN} to assume the target is big-endian.
9344 @kindex set endian little
9345 @item set endian little
9346 Instruct @value{GDBN} to assume the target is little-endian.
9348 @kindex set endian auto
9349 @item set endian auto
9350 Instruct @value{GDBN} to use the byte order associated with the
9354 Display @value{GDBN}'s current idea of the target byte order.
9358 Note that these commands merely adjust interpretation of symbolic
9359 data on the host, and that they have absolutely no effect on the
9363 @section Remote debugging
9364 @cindex remote debugging
9366 If you are trying to debug a program running on a machine that cannot run
9367 @value{GDBN} in the usual way, it is often useful to use remote debugging.
9368 For example, you might use remote debugging on an operating system kernel,
9369 or on a small system which does not have a general purpose operating system
9370 powerful enough to run a full-featured debugger.
9372 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
9373 to make this work with particular debugging targets. In addition,
9374 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
9375 but not specific to any particular target system) which you can use if you
9376 write the remote stubs---the code that runs on the remote system to
9377 communicate with @value{GDBN}.
9379 Other remote targets may be available in your
9380 configuration of @value{GDBN}; use @code{help target} to list them.
9383 * Remote Serial:: @value{GDBN} remote serial protocol
9387 @subsection The @value{GDBN} remote serial protocol
9389 @cindex remote serial debugging, overview
9390 To debug a program running on another machine (the debugging
9391 @dfn{target} machine), you must first arrange for all the usual
9392 prerequisites for the program to run by itself. For example, for a C
9397 A startup routine to set up the C runtime environment; these usually
9398 have a name like @file{crt0}. The startup routine may be supplied by
9399 your hardware supplier, or you may have to write your own.
9402 A C subroutine library to support your program's
9403 subroutine calls, notably managing input and output.
9406 A way of getting your program to the other machine---for example, a
9407 download program. These are often supplied by the hardware
9408 manufacturer, but you may have to write your own from hardware
9412 The next step is to arrange for your program to use a serial port to
9413 communicate with the machine where @value{GDBN} is running (the @dfn{host}
9414 machine). In general terms, the scheme looks like this:
9418 @value{GDBN} already understands how to use this protocol; when everything
9419 else is set up, you can simply use the @samp{target remote} command
9420 (@pxref{Targets,,Specifying a Debugging Target}).
9422 @item On the target,
9423 you must link with your program a few special-purpose subroutines that
9424 implement the @value{GDBN} remote serial protocol. The file containing these
9425 subroutines is called a @dfn{debugging stub}.
9427 On certain remote targets, you can use an auxiliary program
9428 @code{gdbserver} instead of linking a stub into your program.
9429 @xref{Server,,Using the @code{gdbserver} program}, for details.
9432 The debugging stub is specific to the architecture of the remote
9433 machine; for example, use @file{sparc-stub.c} to debug programs on
9436 @cindex remote serial stub list
9437 These working remote stubs are distributed with @value{GDBN}:
9442 @cindex @file{i386-stub.c}
9445 For Intel 386 and compatible architectures.
9448 @cindex @file{m68k-stub.c}
9449 @cindex Motorola 680x0
9451 For Motorola 680x0 architectures.
9454 @cindex @file{sh-stub.c}
9457 For Hitachi SH architectures.
9460 @cindex @file{sparc-stub.c}
9462 For @sc{sparc} architectures.
9465 @cindex @file{sparcl-stub.c}
9468 For Fujitsu @sc{sparclite} architectures.
9472 The @file{README} file in the @value{GDBN} distribution may list other
9473 recently added stubs.
9476 * Stub Contents:: What the stub can do for you
9477 * Bootstrapping:: What you must do for the stub
9478 * Debug Session:: Putting it all together
9479 * Protocol:: Definition of the communication protocol
9480 * Server:: Using the `gdbserver' program
9481 * NetWare:: Using the `gdbserve.nlm' program
9485 @subsubsection What the stub can do for you
9487 @cindex remote serial stub
9488 The debugging stub for your architecture supplies these three
9492 @item set_debug_traps
9493 @kindex set_debug_traps
9494 @cindex remote serial stub, initialization
9495 This routine arranges for @code{handle_exception} to run when your
9496 program stops. You must call this subroutine explicitly near the
9497 beginning of your program.
9499 @item handle_exception
9500 @kindex handle_exception
9501 @cindex remote serial stub, main routine
9502 This is the central workhorse, but your program never calls it
9503 explicitly---the setup code arranges for @code{handle_exception} to
9504 run when a trap is triggered.
9506 @code{handle_exception} takes control when your program stops during
9507 execution (for example, on a breakpoint), and mediates communications
9508 with @value{GDBN} on the host machine. This is where the communications
9509 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
9510 representative on the target machine. It begins by sending summary
9511 information on the state of your program, then continues to execute,
9512 retrieving and transmitting any information @value{GDBN} needs, until you
9513 execute a @value{GDBN} command that makes your program resume; at that point,
9514 @code{handle_exception} returns control to your own code on the target
9518 @cindex @code{breakpoint} subroutine, remote
9519 Use this auxiliary subroutine to make your program contain a
9520 breakpoint. Depending on the particular situation, this may be the only
9521 way for @value{GDBN} to get control. For instance, if your target
9522 machine has some sort of interrupt button, you won't need to call this;
9523 pressing the interrupt button transfers control to
9524 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
9525 simply receiving characters on the serial port may also trigger a trap;
9526 again, in that situation, you don't need to call @code{breakpoint} from
9527 your own program---simply running @samp{target remote} from the host
9528 @value{GDBN} session gets control.
9530 Call @code{breakpoint} if none of these is true, or if you simply want
9531 to make certain your program stops at a predetermined point for the
9532 start of your debugging session.
9536 @subsubsection What you must do for the stub
9538 @cindex remote stub, support routines
9539 The debugging stubs that come with @value{GDBN} are set up for a particular
9540 chip architecture, but they have no information about the rest of your
9541 debugging target machine.
9543 First of all you need to tell the stub how to communicate with the
9547 @item int getDebugChar()
9548 @kindex getDebugChar
9549 Write this subroutine to read a single character from the serial port.
9550 It may be identical to @code{getchar} for your target system; a
9551 different name is used to allow you to distinguish the two if you wish.
9553 @item void putDebugChar(int)
9554 @kindex putDebugChar
9555 Write this subroutine to write a single character to the serial port.
9556 It may be identical to @code{putchar} for your target system; a
9557 different name is used to allow you to distinguish the two if you wish.
9560 @cindex control C, and remote debugging
9561 @cindex interrupting remote targets
9562 If you want @value{GDBN} to be able to stop your program while it is
9563 running, you need to use an interrupt-driven serial driver, and arrange
9564 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
9565 character). That is the character which @value{GDBN} uses to tell the
9566 remote system to stop.
9568 Getting the debugging target to return the proper status to @value{GDBN}
9569 probably requires changes to the standard stub; one quick and dirty way
9570 is to just execute a breakpoint instruction (the ``dirty'' part is that
9571 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
9573 Other routines you need to supply are:
9576 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
9577 @kindex exceptionHandler
9578 Write this function to install @var{exception_address} in the exception
9579 handling tables. You need to do this because the stub does not have any
9580 way of knowing what the exception handling tables on your target system
9581 are like (for example, the processor's table might be in @sc{rom},
9582 containing entries which point to a table in @sc{ram}).
9583 @var{exception_number} is the exception number which should be changed;
9584 its meaning is architecture-dependent (for example, different numbers
9585 might represent divide by zero, misaligned access, etc). When this
9586 exception occurs, control should be transferred directly to
9587 @var{exception_address}, and the processor state (stack, registers,
9588 and so on) should be just as it is when a processor exception occurs. So if
9589 you want to use a jump instruction to reach @var{exception_address}, it
9590 should be a simple jump, not a jump to subroutine.
9592 For the 386, @var{exception_address} should be installed as an interrupt
9593 gate so that interrupts are masked while the handler runs. The gate
9594 should be at privilege level 0 (the most privileged level). The
9595 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
9596 help from @code{exceptionHandler}.
9598 @item void flush_i_cache()
9599 @kindex flush_i_cache
9600 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
9601 instruction cache, if any, on your target machine. If there is no
9602 instruction cache, this subroutine may be a no-op.
9604 On target machines that have instruction caches, @value{GDBN} requires this
9605 function to make certain that the state of your program is stable.
9609 You must also make sure this library routine is available:
9612 @item void *memset(void *, int, int)
9614 This is the standard library function @code{memset} that sets an area of
9615 memory to a known value. If you have one of the free versions of
9616 @code{libc.a}, @code{memset} can be found there; otherwise, you must
9617 either obtain it from your hardware manufacturer, or write your own.
9620 If you do not use the GNU C compiler, you may need other standard
9621 library subroutines as well; this varies from one stub to another,
9622 but in general the stubs are likely to use any of the common library
9623 subroutines which @code{@value{GCC}} generates as inline code.
9627 @subsubsection Putting it all together
9629 @cindex remote serial debugging summary
9630 In summary, when your program is ready to debug, you must follow these
9635 Make sure you have defined the supporting low-level routines
9636 (@pxref{Bootstrapping,,What you must do for the stub}):
9638 @code{getDebugChar}, @code{putDebugChar},
9639 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
9643 Insert these lines near the top of your program:
9651 For the 680x0 stub only, you need to provide a variable called
9652 @code{exceptionHook}. Normally you just use:
9655 void (*exceptionHook)() = 0;
9659 but if before calling @code{set_debug_traps}, you set it to point to a
9660 function in your program, that function is called when
9661 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
9662 error). The function indicated by @code{exceptionHook} is called with
9663 one parameter: an @code{int} which is the exception number.
9666 Compile and link together: your program, the @value{GDBN} debugging stub for
9667 your target architecture, and the supporting subroutines.
9670 Make sure you have a serial connection between your target machine and
9671 the @value{GDBN} host, and identify the serial port on the host.
9674 @c The "remote" target now provides a `load' command, so we should
9675 @c document that. FIXME.
9676 Download your program to your target machine (or get it there by
9677 whatever means the manufacturer provides), and start it.
9680 To start remote debugging, run @value{GDBN} on the host machine, and specify
9681 as an executable file the program that is running in the remote machine.
9682 This tells @value{GDBN} how to find your program's symbols and the contents
9686 @cindex serial line, @code{target remote}
9687 Establish communication using the @code{target remote} command.
9688 Its argument specifies how to communicate with the target
9689 machine---either via a devicename attached to a direct serial line, or a
9690 TCP port (usually to a terminal server which in turn has a serial line
9691 to the target). For example, to use a serial line connected to the
9692 device named @file{/dev/ttyb}:
9695 target remote /dev/ttyb
9698 @cindex TCP port, @code{target remote}
9699 To use a TCP connection, use an argument of the form
9700 @code{@var{host}:port}. For example, to connect to port 2828 on a
9701 terminal server named @code{manyfarms}:
9704 target remote manyfarms:2828
9707 If your remote target is actually running on the same machine as
9708 your debugger session (e.g.@: a simulator of your target running on
9709 the same host), you can omit the hostname. For example, to connect
9710 to port 1234 on your local machine:
9717 Note that the colon is still required here.
9720 Now you can use all the usual commands to examine and change data and to
9721 step and continue the remote program.
9723 To resume the remote program and stop debugging it, use the @code{detach}
9726 @cindex interrupting remote programs
9727 @cindex remote programs, interrupting
9728 Whenever @value{GDBN} is waiting for the remote program, if you type the
9729 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
9730 program. This may or may not succeed, depending in part on the hardware
9731 and the serial drivers the remote system uses. If you type the
9732 interrupt character once again, @value{GDBN} displays this prompt:
9735 Interrupted while waiting for the program.
9736 Give up (and stop debugging it)? (y or n)
9739 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
9740 (If you decide you want to try again later, you can use @samp{target
9741 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
9742 goes back to waiting.
9745 @subsubsection Communication protocol
9747 @cindex debugging stub, example
9748 @cindex remote stub, example
9749 @cindex stub example, remote debugging
9750 The stub files provided with @value{GDBN} implement the target side of the
9751 communication protocol, and the @value{GDBN} side is implemented in the
9752 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
9753 these subroutines to communicate, and ignore the details. (If you're
9754 implementing your own stub file, you can still ignore the details: start
9755 with one of the existing stub files. @file{sparc-stub.c} is the best
9756 organized, and therefore the easiest to read.)
9758 However, there may be occasions when you need to know something about
9759 the protocol---for example, if there is only one serial port to your
9760 target machine, you might want your program to do something special if
9761 it recognizes a packet meant for @value{GDBN}.
9763 In the examples below, @samp{<-} and @samp{->} are used to indicate
9764 transmitted and received data respectfully.
9766 @cindex protocol, @value{GDBN} remote serial
9767 @cindex serial protocol, @value{GDBN} remote
9768 @cindex remote serial protocol
9769 All @value{GDBN} commands and responses (other than acknowledgments) are
9770 sent as a @var{packet}. A @var{packet} is introduced with the character
9771 @samp{$}, the actual @var{packet-data}, and the terminating character
9772 @samp{#} followed by a two-digit @var{checksum}:
9775 @code{$}@var{packet-data}@code{#}@var{checksum}
9779 @cindex checksum, for @value{GDBN} remote
9781 The two-digit @var{checksum} is computed as the modulo 256 sum of all
9782 characters between the leading @samp{$} and the trailing @samp{#} (an
9783 eight bit unsigned checksum).
9785 Implementors should note that prior to @value{GDBN} 5.0 the protocol
9786 specification also included an optional two-digit @var{sequence-id}:
9789 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
9792 @cindex sequence-id, for @value{GDBN} remote
9794 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
9795 has never output @var{sequence-id}s. Stubs that handle packets added
9796 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
9798 @cindex acknowledgment, for @value{GDBN} remote
9799 When either the host or the target machine receives a packet, the first
9800 response expected is an acknowledgment: either @samp{+} (to indicate
9801 the package was received correctly) or @samp{-} (to request
9805 <- @code{$}@var{packet-data}@code{#}@var{checksum}
9810 The host (@value{GDBN}) sends @var{command}s, and the target (the
9811 debugging stub incorporated in your program) sends a @var{response}. In
9812 the case of step and continue @var{command}s, the response is only sent
9813 when the operation has completed (the target has again stopped).
9815 @var{packet-data} consists of a sequence of characters with the
9816 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
9819 Fields within the packet should be separated using @samp{,} @samp{;} or
9820 @samp{:}. Except where otherwise noted all numbers are represented in
9821 HEX with leading zeros suppressed.
9823 Implementors should note that prior to @value{GDBN} 5.0, the character
9824 @samp{:} could not appear as the third character in a packet (as it
9825 would potentially conflict with the @var{sequence-id}).
9827 Response @var{data} can be run-length encoded to save space. A @samp{*}
9828 means that the next character is an @sc{ascii} encoding giving a repeat count
9829 which stands for that many repetitions of the character preceding the
9830 @samp{*}. The encoding is @code{n+29}, yielding a printable character
9831 where @code{n >=3} (which is where rle starts to win). The printable
9832 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
9833 value greater than 126 should not be used.
9835 Some remote systems have used a different run-length encoding mechanism
9836 loosely refered to as the cisco encoding. Following the @samp{*}
9837 character are two hex digits that indicate the size of the packet.
9844 means the same as "0000".
9846 The error response returned for some packets includes a two character
9847 error number. That number is not well defined.
9849 For any @var{command} not supported by the stub, an empty response
9850 (@samp{$#00}) should be returned. That way it is possible to extend the
9851 protocol. A newer @value{GDBN} can tell if a packet is supported based
9854 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
9855 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
9858 Below is a complete list of all currently defined @var{command}s and
9859 their corresponding response @var{data}:
9861 @multitable @columnfractions .30 .30 .40
9869 Enable extended mode. In extended mode, the remote server is made
9870 persistent. The @samp{R} packet is used to restart the program being
9873 @tab reply @samp{OK}
9875 The remote target both supports and has enabled extended mode.
9880 Indicate the reason the target halted. The reply is the same as for step
9889 @tab Reserved for future use
9891 @item set program arguments @strong{(reserved)}
9892 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
9897 Initialized @samp{argv[]} array passed into program. @var{arglen}
9898 specifies the number of bytes in the hex encoded byte stream @var{arg}.
9899 See @file{gdbserver} for more details.
9901 @tab reply @code{OK}
9903 @tab reply @code{E}@var{NN}
9905 @item set baud @strong{(deprecated)}
9906 @tab @code{b}@var{baud}
9908 Change the serial line speed to @var{baud}. JTC: @emph{When does the
9909 transport layer state change? When it's received, or after the ACK is
9910 transmitted. In either case, there are problems if the command or the
9911 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
9912 to add something like this, and get it working for the first time, they
9913 ought to modify ser-unix.c to send some kind of out-of-band message to a
9914 specially-setup stub and have the switch happen "in between" packets, so
9915 that from remote protocol's point of view, nothing actually
9918 @item set breakpoint @strong{(deprecated)}
9919 @tab @code{B}@var{addr},@var{mode}
9921 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
9922 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
9926 @tab @code{c}@var{addr}
9928 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9934 @item continue with signal
9935 @tab @code{C}@var{sig}@code{;}@var{addr}
9937 Continue with signal @var{sig} (hex signal number). If
9938 @code{;}@var{addr} is omitted, resume at same address.
9943 @item toggle debug @strong{(deprecated)}
9951 Detach @value{GDBN} from the remote system. Sent to the remote target before
9952 @value{GDBN} disconnects.
9954 @tab reply @emph{no response}
9956 @value{GDBN} does not check for any response after sending this packet.
9960 @tab Reserved for future use
9964 @tab Reserved for future use
9968 @tab Reserved for future use
9972 @tab Reserved for future use
9974 @item read registers
9976 @tab Read general registers.
9978 @tab reply @var{XX...}
9980 Each byte of register data is described by two hex digits. The bytes
9981 with the register are transmitted in target byte order. The size of
9982 each register and their position within the @samp{g} @var{packet} are
9983 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
9984 @var{REGISTER_NAME} macros. The specification of several standard
9985 @code{g} packets is specified below.
9987 @tab @code{E}@var{NN}
9991 @tab @code{G}@var{XX...}
9993 See @samp{g} for a description of the @var{XX...} data.
9995 @tab reply @code{OK}
9998 @tab reply @code{E}@var{NN}
10003 @tab Reserved for future use
10006 @tab @code{H}@var{c}@var{t...}
10008 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
10009 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
10010 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
10011 thread used in other operations. If zero, pick a thread, any thread.
10013 @tab reply @code{OK}
10016 @tab reply @code{E}@var{NN}
10020 @c 'H': How restrictive (or permissive) is the thread model. If a
10021 @c thread is selected and stopped, are other threads allowed
10022 @c to continue to execute? As I mentioned above, I think the
10023 @c semantics of each command when a thread is selected must be
10024 @c described. For example:
10026 @c 'g': If the stub supports threads and a specific thread is
10027 @c selected, returns the register block from that thread;
10028 @c otherwise returns current registers.
10030 @c 'G' If the stub supports threads and a specific thread is
10031 @c selected, sets the registers of the register block of
10032 @c that thread; otherwise sets current registers.
10034 @item cycle step @strong{(draft)}
10035 @tab @code{i}@var{addr}@code{,}@var{nnn}
10037 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
10038 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
10039 step starting at that address.
10041 @item signal then cycle step @strong{(reserved)}
10044 See @samp{i} and @samp{S} for likely syntax and semantics.
10048 @tab Reserved for future use
10052 @tab Reserved for future use
10057 FIXME: @emph{There is no description of how operate when a specific
10058 thread context has been selected (ie. does 'k' kill only that thread?)}.
10062 @tab Reserved for future use
10066 @tab Reserved for future use
10069 @tab @code{m}@var{addr}@code{,}@var{length}
10071 Read @var{length} bytes of memory starting at address @var{addr}.
10072 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
10073 using word alligned accesses. FIXME: @emph{A word aligned memory
10074 transfer mechanism is needed.}
10076 @tab reply @var{XX...}
10078 @var{XX...} is mem contents. Can be fewer bytes than requested if able
10079 to read only part of the data. Neither @value{GDBN} nor the stub assume that
10080 sized memory transfers are assumed using word alligned accesses. FIXME:
10081 @emph{A word aligned memory transfer mechanism is needed.}
10083 @tab reply @code{E}@var{NN}
10084 @tab @var{NN} is errno
10087 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
10089 Write @var{length} bytes of memory starting at address @var{addr}.
10090 @var{XX...} is the data.
10092 @tab reply @code{OK}
10095 @tab reply @code{E}@var{NN}
10097 for an error (this includes the case where only part of the data was
10102 @tab Reserved for future use
10106 @tab Reserved for future use
10110 @tab Reserved for future use
10114 @tab Reserved for future use
10116 @item read reg @strong{(reserved)}
10117 @tab @code{p}@var{n...}
10119 See write register.
10121 @tab return @var{r....}
10122 @tab The hex encoded value of the register in target byte order.
10125 @tab @code{P}@var{n...}@code{=}@var{r...}
10127 Write register @var{n...} with value @var{r...}, which contains two hex
10128 digits for each byte in the register (target byte order).
10130 @tab reply @code{OK}
10133 @tab reply @code{E}@var{NN}
10136 @item general query
10137 @tab @code{q}@var{query}
10139 Request info about @var{query}. In general @value{GDBN} queries
10140 have a leading upper case letter. Custom vendor queries should use a
10141 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
10142 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
10143 must ensure that they match the full @var{query} name.
10145 @tab reply @code{XX...}
10146 @tab Hex encoded data from query. The reply can not be empty.
10148 @tab reply @code{E}@var{NN}
10152 @tab Indicating an unrecognized @var{query}.
10155 @tab @code{Q}@var{var}@code{=}@var{val}
10157 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
10158 naming conventions.
10160 @item reset @strong{(deprecated)}
10163 Reset the entire system.
10165 @item remote restart
10166 @tab @code{R}@var{XX}
10168 Restart the program being debugged. @var{XX}, while needed, is ignored.
10169 This packet is only available in extended mode.
10174 The @samp{R} packet has no reply.
10177 @tab @code{s}@var{addr}
10179 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10185 @item step with signal
10186 @tab @code{S}@var{sig}@code{;}@var{addr}
10188 Like @samp{C} but step not continue.
10194 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
10196 Search backwards starting at address @var{addr} for a match with pattern
10197 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
10198 bytes. @var{addr} must be at least 3 digits.
10201 @tab @code{T}@var{XX}
10202 @tab Find out if the thread XX is alive.
10204 @tab reply @code{OK}
10205 @tab thread is still alive
10207 @tab reply @code{E}@var{NN}
10208 @tab thread is dead
10212 @tab Reserved for future use
10216 @tab Reserved for future use
10220 @tab Reserved for future use
10224 @tab Reserved for future use
10228 @tab Reserved for future use
10232 @tab Reserved for future use
10236 @tab Reserved for future use
10238 @item write mem (binary)
10239 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
10241 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
10242 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
10243 escaped using @code{0x7d}.
10245 @tab reply @code{OK}
10248 @tab reply @code{E}@var{NN}
10253 @tab Reserved for future use
10257 @tab Reserved for future use
10259 @item remove break or watchpoint @strong{(draft)}
10260 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10264 @item insert break or watchpoint @strong{(draft)}
10265 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10267 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
10268 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
10269 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
10270 bytes. For a software breakpoint, @var{length} specifies the size of
10271 the instruction to be patched. For hardware breakpoints and watchpoints
10272 @var{length} specifies the memory region to be monitored. To avoid
10273 potential problems with duplicate packets, the operations should be
10274 implemented in an idempotent way.
10276 @tab reply @code{E}@var{NN}
10279 @tab reply @code{OK}
10283 @tab If not supported.
10287 @tab Reserved for future use
10291 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
10292 receive any of the below as a reply. In the case of the @samp{C},
10293 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
10294 when the target halts. In the below the exact meaning of @samp{signal
10295 number} is poorly defined. In general one of the UNIX signal numbering
10296 conventions is used.
10298 @multitable @columnfractions .4 .6
10300 @item @code{S}@var{AA}
10301 @tab @var{AA} is the signal number
10303 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
10305 @var{AA} = two hex digit signal number; @var{n...} = register number
10306 (hex), @var{r...} = target byte ordered register contents, size defined
10307 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
10308 thread process ID, this is a hex integer; @var{n...} = other string not
10309 starting with valid hex digit. @value{GDBN} should ignore this
10310 @var{n...}, @var{r...} pair and go on to the next. This way we can
10311 extend the protocol.
10313 @item @code{W}@var{AA}
10315 The process exited, and @var{AA} is the exit status. This is only
10316 applicable for certains sorts of targets.
10318 @item @code{X}@var{AA}
10320 The process terminated with signal @var{AA}.
10322 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
10324 @var{AA} = signal number; @var{t...} = address of symbol "_start";
10325 @var{d...} = base of data section; @var{b...} = base of bss section.
10326 @emph{Note: only used by Cisco Systems targets. The difference between
10327 this reply and the "qOffsets" query is that the 'N' packet may arrive
10328 spontaneously whereas the 'qOffsets' is a query initiated by the host
10331 @item @code{O}@var{XX...}
10333 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
10334 while the program is running and the debugger should continue to wait
10339 The following set and query packets have already been defined.
10341 @multitable @columnfractions .2 .2 .6
10343 @item current thread
10344 @tab @code{q}@code{C}
10345 @tab Return the current thread id.
10347 @tab reply @code{QC}@var{pid}
10349 Where @var{pid} is a HEX encoded 16 bit process id.
10352 @tab Any other reply implies the old pid.
10354 @item all thread ids
10355 @tab @code{q}@code{fThreadInfo}
10357 @tab @code{q}@code{sThreadInfo}
10359 Obtain a list of active thread ids from the target (OS). Since there
10360 may be too many active threads to fit into one reply packet, this query
10361 works iteratively: it may require more than one query/reply sequence to
10362 obtain the entire list of threads. The first query of the sequence will
10363 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
10364 sequence will be the @code{qs}@code{ThreadInfo} query.
10367 @tab NOTE: replaces the @code{qL} query (see below).
10369 @tab reply @code{m}@var{<id>}
10370 @tab A single thread id
10372 @tab reply @code{m}@var{<id>},@var{<id>...}
10373 @tab a comma-separated list of thread ids
10375 @tab reply @code{l}
10376 @tab (lower case 'el') denotes end of list.
10380 In response to each query, the target will reply with a list of one
10381 or more thread ids, in big-endian hex, separated by commas. GDB will
10382 respond to each reply with a request for more thread ids (using the
10383 @code{qs} form of the query), until the target responds with @code{l}
10384 (lower-case el, for @code{'last'}).
10386 @item extra thread info
10387 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
10392 Where @var{<id>} is a thread-id in big-endian hex.
10393 Obtain a printable string description of a thread's attributes from
10394 the target OS. This string may contain anything that the target OS
10395 thinks is interesting for @value{GDBN} to tell the user about the thread.
10396 The string is displayed in @value{GDBN}'s @samp{info threads} display.
10397 Some examples of possible thread extra info strings are "Runnable", or
10398 "Blocked on Mutex".
10400 @tab reply @var{XX...}
10402 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
10403 printable string containing the extra information about the thread's
10406 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
10407 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
10412 Obtain thread information from RTOS. Where: @var{startflag} (one hex
10413 digit) is one to indicate the first query and zero to indicate a
10414 subsequent query; @var{threadcount} (two hex digits) is the maximum
10415 number of threads the response packet can contain; and @var{nextthread}
10416 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
10417 returned in the response as @var{argthread}.
10420 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
10423 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
10428 Where: @var{count} (two hex digits) is the number of threads being
10429 returned; @var{done} (one hex digit) is zero to indicate more threads
10430 and one indicates no further threads; @var{argthreadid} (eight hex
10431 digits) is @var{nextthread} from the request packet; @var{thread...} is
10432 a sequence of thread IDs from the target. @var{threadid} (eight hex
10433 digits). See @code{remote.c:parse_threadlist_response()}.
10435 @item compute CRC of memory block
10436 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
10439 @tab reply @code{E}@var{NN}
10440 @tab An error (such as memory fault)
10442 @tab reply @code{C}@var{CRC32}
10443 @tab A 32 bit cyclic redundancy check of the specified memory region.
10445 @item query sect offs
10446 @tab @code{q}@code{Offsets}
10448 Get section offsets that the target used when re-locating the downloaded
10449 image. @emph{Note: while a @code{Bss} offset is included in the
10450 response, @value{GDBN} ignores this and instead applies the @code{Data}
10451 offset to the @code{Bss} section.}
10453 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
10455 @item thread info request
10456 @tab @code{q}@code{P}@var{mode}@var{threadid}
10461 Returns information on @var{threadid}. Where: @var{mode} is a hex
10462 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
10466 See @code{remote.c:remote_unpack_thread_info_response()}.
10468 @item remote command
10469 @tab @code{q}@code{Rcmd,}@var{COMMAND}
10474 @var{COMMAND} (hex encoded) is passed to the local interpreter for
10475 execution. Invalid commands should be reported using the output string.
10476 Before the final result packet, the target may also respond with a
10477 number of intermediate @code{O}@var{OUTPUT} console output
10478 packets. @emph{Implementors should note that providing access to a
10479 stubs's interpreter may have security implications}.
10481 @tab reply @code{OK}
10483 A command response with no output.
10485 @tab reply @var{OUTPUT}
10487 A command response with the hex encoded output string @var{OUTPUT}.
10489 @tab reply @code{E}@var{NN}
10491 Indicate a badly formed request.
10496 When @samp{q}@samp{Rcmd} is not recognized.
10498 @item symbol lookup
10499 @tab @code{qSymbol::}
10501 Notify the target that @value{GDBN} is prepared to serve symbol lookup
10502 requests. Accept requests from the target for the values of symbols.
10507 @tab reply @code{OK}
10509 The target does not need to look up any (more) symbols.
10511 @tab reply @code{qSymbol:}@var{sym_name}
10513 The target requests the value of symbol @var{sym_name} (hex encoded).
10514 @value{GDBN} may provide the value by using the
10515 @code{qSymbol:}@var{sym_value}:@var{sym_name}
10516 message, described below.
10519 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
10521 Set the value of SYM_NAME to SYM_VALUE.
10525 @var{sym_name} (hex encoded) is the name of a symbol whose value
10526 the target has previously requested.
10530 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
10531 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
10532 field will be empty.
10534 @tab reply @code{OK}
10536 The target does not need to look up any (more) symbols.
10538 @tab reply @code{qSymbol:}@var{sym_name}
10540 The target requests the value of a new symbol @var{sym_name} (hex encoded).
10541 @value{GDBN} will continue to supply the values of symbols (if available),
10542 until the target ceases to request them.
10546 The following @samp{g}/@samp{G} packets have previously been defined.
10547 In the below, some thirty-two bit registers are transferred as sixty-four
10548 bits. Those registers should be zero/sign extended (which?) to fill the
10549 space allocated. Register bytes are transfered in target byte order.
10550 The two nibbles within a register byte are transfered most-significant -
10553 @multitable @columnfractions .5 .5
10557 All registers are transfered as thirty-two bit quantities in the order:
10558 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
10559 registers; fsr; fir; fp.
10563 All registers are transfered as sixty-four bit quantities (including
10564 thirty-two bit registers such as @code{sr}). The ordering is the same
10569 Example sequence of a target being re-started. Notice how the restart
10570 does not get any direct output:
10575 @emph{target restarts}
10578 -> @code{T001:1234123412341234}
10582 Example sequence of a target being stepped by a single instruction:
10590 -> @code{T001:1234123412341234}
10599 @subsubsection Using the @code{gdbserver} program
10602 @cindex remote connection without stubs
10603 @code{gdbserver} is a control program for Unix-like systems, which
10604 allows you to connect your program with a remote @value{GDBN} via
10605 @code{target remote}---but without linking in the usual debugging stub.
10607 @code{gdbserver} is not a complete replacement for the debugging stubs,
10608 because it requires essentially the same operating-system facilities
10609 that @value{GDBN} itself does. In fact, a system that can run
10610 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10611 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10612 because it is a much smaller program than @value{GDBN} itself. It is
10613 also easier to port than all of @value{GDBN}, so you may be able to get
10614 started more quickly on a new system by using @code{gdbserver}.
10615 Finally, if you develop code for real-time systems, you may find that
10616 the tradeoffs involved in real-time operation make it more convenient to
10617 do as much development work as possible on another system, for example
10618 by cross-compiling. You can use @code{gdbserver} to make a similar
10619 choice for debugging.
10621 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10622 or a TCP connection, using the standard @value{GDBN} remote serial
10626 @item On the target machine,
10627 you need to have a copy of the program you want to debug.
10628 @code{gdbserver} does not need your program's symbol table, so you can
10629 strip the program if necessary to save space. @value{GDBN} on the host
10630 system does all the symbol handling.
10632 To use the server, you must tell it how to communicate with @value{GDBN};
10633 the name of your program; and the arguments for your program. The
10637 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10640 @var{comm} is either a device name (to use a serial line) or a TCP
10641 hostname and portnumber. For example, to debug Emacs with the argument
10642 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10646 target> gdbserver /dev/com1 emacs foo.txt
10649 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10652 To use a TCP connection instead of a serial line:
10655 target> gdbserver host:2345 emacs foo.txt
10658 The only difference from the previous example is the first argument,
10659 specifying that you are communicating with the host @value{GDBN} via
10660 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10661 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10662 (Currently, the @samp{host} part is ignored.) You can choose any number
10663 you want for the port number as long as it does not conflict with any
10664 TCP ports already in use on the target system (for example, @code{23} is
10665 reserved for @code{telnet}).@footnote{If you choose a port number that
10666 conflicts with another service, @code{gdbserver} prints an error message
10667 and exits.} You must use the same port number with the host @value{GDBN}
10668 @code{target remote} command.
10670 @item On the @value{GDBN} host machine,
10671 you need an unstripped copy of your program, since @value{GDBN} needs
10672 symbols and debugging information. Start up @value{GDBN} as usual,
10673 using the name of the local copy of your program as the first argument.
10674 (You may also need the @w{@samp{--baud}} option if the serial line is
10675 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10676 remote} to establish communications with @code{gdbserver}. Its argument
10677 is either a device name (usually a serial device, like
10678 @file{/dev/ttyb}), or a TCP port descriptor in the form
10679 @code{@var{host}:@var{PORT}}. For example:
10682 (@value{GDBP}) target remote /dev/ttyb
10686 communicates with the server via serial line @file{/dev/ttyb}, and
10689 (@value{GDBP}) target remote the-target:2345
10693 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10694 For TCP connections, you must start up @code{gdbserver} prior to using
10695 the @code{target remote} command. Otherwise you may get an error whose
10696 text depends on the host system, but which usually looks something like
10697 @samp{Connection refused}.
10701 @subsubsection Using the @code{gdbserve.nlm} program
10703 @kindex gdbserve.nlm
10704 @code{gdbserve.nlm} is a control program for NetWare systems, which
10705 allows you to connect your program with a remote @value{GDBN} via
10706 @code{target remote}.
10708 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10709 using the standard @value{GDBN} remote serial protocol.
10712 @item On the target machine,
10713 you need to have a copy of the program you want to debug.
10714 @code{gdbserve.nlm} does not need your program's symbol table, so you
10715 can strip the program if necessary to save space. @value{GDBN} on the
10716 host system does all the symbol handling.
10718 To use the server, you must tell it how to communicate with
10719 @value{GDBN}; the name of your program; and the arguments for your
10720 program. The syntax is:
10723 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10724 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10727 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10728 the baud rate used by the connection. @var{port} and @var{node} default
10729 to 0, @var{baud} defaults to 9600@dmn{bps}.
10731 For example, to debug Emacs with the argument @samp{foo.txt}and
10732 communicate with @value{GDBN} over serial port number 2 or board 1
10733 using a 19200@dmn{bps} connection:
10736 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10739 @item On the @value{GDBN} host machine,
10740 you need an unstripped copy of your program, since @value{GDBN} needs
10741 symbols and debugging information. Start up @value{GDBN} as usual,
10742 using the name of the local copy of your program as the first argument.
10743 (You may also need the @w{@samp{--baud}} option if the serial line is
10744 running at anything other than 9600@dmn{bps}. After that, use @code{target
10745 remote} to establish communications with @code{gdbserve.nlm}. Its
10746 argument is a device name (usually a serial device, like
10747 @file{/dev/ttyb}). For example:
10750 (@value{GDBP}) target remote /dev/ttyb
10754 communications with the server via serial line @file{/dev/ttyb}.
10758 @section Kernel Object Display
10760 @cindex kernel object display
10761 @cindex kernel object
10764 Some targets support kernel object display. Using this facility,
10765 @value{GDBN} communicates specially with the underlying operating system
10766 and can display information about operating system-level objects such as
10767 mutexes and other synchronization objects. Exactly which objects can be
10768 displayed is determined on a per-OS basis.
10770 Use the @code{set os} command to set the operating system. This tells
10771 @value{GDBN} which kernel object display module to initialize:
10774 (@value{GDBP}) set os cisco
10777 If @code{set os} succeeds, @value{GDBN} will display some information
10778 about the operating system, and will create a new @code{info} command
10779 which can be used to query the target. The @code{info} command is named
10780 after the operating system:
10783 (@value{GDBP}) info cisco
10784 List of Cisco Kernel Objects
10786 any Any and all objects
10789 Further subcommands can be used to query about particular objects known
10792 There is currently no way to determine whether a given operating system
10793 is supported other than to try it.
10796 @node Configurations
10797 @chapter Configuration-Specific Information
10799 While nearly all @value{GDBN} commands are available for all native and
10800 cross versions of the debugger, there are some exceptions. This chapter
10801 describes things that are only available in certain configurations.
10803 There are three major categories of configurations: native
10804 configurations, where the host and target are the same, embedded
10805 operating system configurations, which are usually the same for several
10806 different processor architectures, and bare embedded processors, which
10807 are quite different from each other.
10812 * Embedded Processors::
10819 This section describes details specific to particular native
10824 * SVR4 Process Information:: SVR4 process information
10825 * DJGPP Native:: Features specific to the DJGPP port
10831 On HP-UX systems, if you refer to a function or variable name that
10832 begins with a dollar sign, @value{GDBN} searches for a user or system
10833 name first, before it searches for a convenience variable.
10835 @node SVR4 Process Information
10836 @subsection SVR4 process information
10839 @cindex process image
10841 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10842 used to examine the image of a running process using file-system
10843 subroutines. If @value{GDBN} is configured for an operating system with
10844 this facility, the command @code{info proc} is available to report on
10845 several kinds of information about the process running your program.
10846 @code{info proc} works only on SVR4 systems that include the
10847 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10848 and Unixware, but not HP-UX or Linux, for example.
10853 Summarize available information about the process.
10855 @kindex info proc mappings
10856 @item info proc mappings
10857 Report on the address ranges accessible in the program, with information
10858 on whether your program may read, write, or execute each range.
10860 @kindex info proc times
10861 @item info proc times
10862 Starting time, user CPU time, and system CPU time for your program and
10865 @kindex info proc id
10867 Report on the process IDs related to your program: its own process ID,
10868 the ID of its parent, the process group ID, and the session ID.
10870 @kindex info proc status
10871 @item info proc status
10872 General information on the state of the process. If the process is
10873 stopped, this report includes the reason for stopping, and any signal
10876 @item info proc all
10877 Show all the above information about the process.
10881 @subsection Features for Debugging @sc{djgpp} Programs
10882 @cindex @sc{djgpp} debugging
10883 @cindex native @sc{djgpp} debugging
10884 @cindex MS-DOS-specific commands
10886 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10887 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10888 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10889 top of real-mode DOS systems and their emulations.
10891 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10892 defines a few commands specific to the @sc{djgpp} port. This
10893 subsection describes those commands.
10898 This is a prefix of @sc{djgpp}-specific commands which print
10899 information about the target system and important OS structures.
10902 @cindex MS-DOS system info
10903 @cindex free memory information (MS-DOS)
10904 @item info dos sysinfo
10905 This command displays assorted information about the underlying
10906 platform: the CPU type and features, the OS version and flavor, the
10907 DPMI version, and the available conventional and DPMI memory.
10912 @cindex segment descriptor tables
10913 @cindex descriptor tables display
10915 @itemx info dos ldt
10916 @itemx info dos idt
10917 These 3 commands display entries from, respectively, Global, Local,
10918 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10919 tables are data structures which store a descriptor for each segment
10920 that is currently in use. The segment's selector is an index into a
10921 descriptor table; the table entry for that index holds the
10922 descriptor's base address and limit, and its attributes and access
10925 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10926 segment (used for both data and the stack), and a DOS segment (which
10927 allows access to DOS/BIOS data structures and absolute addresses in
10928 conventional memory). However, the DPMI host will usually define
10929 additional segments in order to support the DPMI environment.
10931 @cindex garbled pointers
10932 These commands allow to display entries from the descriptor tables.
10933 Without an argument, all entries from the specified table are
10934 displayed. An argument, which should be an integer expression, means
10935 display a single entry whose index is given by the argument. For
10936 example, here's a convenient way to display information about the
10937 debugged program's data segment:
10940 (@value{GDBP}) info dos ldt $ds
10941 0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
10945 This comes in handy when you want to see whether a pointer is outside
10946 the data segment's limit (i.e.@: @dfn{garbled}).
10948 @cindex page tables display (MS-DOS)
10950 @itemx info dos pte
10951 These two commands display entries from, respectively, the Page
10952 Directory and the Page Tables. Page Directories and Page Tables are
10953 data structures which control how virtual memory addresses are mapped
10954 into physical addresses. A Page Table includes an entry for every
10955 page of memory that is mapped into the program's address space; there
10956 may be several Page Tables, each one holding up to 4096 entries. A
10957 Page Directory has up to 4096 entries, one each for every Page Table
10958 that is currently in use.
10960 Without an argument, @kbd{info dos pde} displays the entire Page
10961 Directory, and @kbd{info dos pte} displays all the entries in all of
10962 the Page Tables. An argument, an integer expression, given to the
10963 @kbd{info dos pde} command means display only that entry from the Page
10964 Directory table. An argument given to the @kbd{info dos pte} command
10965 means display entries from a single Page Table, the one pointed to by
10966 the specified entry in the Page Directory.
10968 These commands are useful when your program uses @dfn{DMA} (Direct
10969 Memory Access), which needs physical addresses to program the DMA
10972 These commands are supported only with some DPMI servers.
10974 @cindex physical address from linear address
10975 @item info dos address-pte
10976 This command displays the Page Table entry for a specified linear
10977 address. The argument linear address should already have the
10978 appropriate segment's base address added to it, because this command
10979 accepts addresses which may belong to @emph{any} segment. For
10980 example, here's how to display the Page Table entry for the page where
10981 the variable @code{i} is stored:
10984 (@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i
10985 Page Table entry for address 0x11a00d30:
10986 Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
10990 This says that @code{i} is stored at offset @code{0xd30} from the page
10991 whose physical base address is @code{0x02698000}, and prints all the
10992 attributes of that page.
10994 Note that you must cast the addresses of variables to a @code{char *},
10995 since otherwise the value of @code{__djgpp_base_address}, the base
10996 address of all variables and functions in a @sc{djgpp} program, will
10997 be added using the rules of C pointer arithmetics: if @code{i} is
10998 declared an @code{int}, @value{GDBN} will add 4 times the value of
10999 @code{__djgpp_base_address} to the address of @code{i}.
11001 Here's another example, it displays the Page Table entry for the
11005 (@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)
11006 Page Table entry for address 0x29110:
11007 Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
11011 (The @code{+ 3} offset is because the transfer buffer's address is the
11012 3rd member of the @code{_go32_info_block} structure.) The output of
11013 this command clearly shows that addresses in conventional memory are
11014 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11016 This command is supported only with some DPMI servers.
11020 @section Embedded Operating Systems
11022 This section describes configurations involving the debugging of
11023 embedded operating systems that are available for several different
11027 * VxWorks:: Using @value{GDBN} with VxWorks
11030 @value{GDBN} includes the ability to debug programs running on
11031 various real-time operating systems.
11034 @subsection Using @value{GDBN} with VxWorks
11040 @kindex target vxworks
11041 @item target vxworks @var{machinename}
11042 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11043 is the target system's machine name or IP address.
11047 On VxWorks, @code{load} links @var{filename} dynamically on the
11048 current target system as well as adding its symbols in @value{GDBN}.
11050 @value{GDBN} enables developers to spawn and debug tasks running on networked
11051 VxWorks targets from a Unix host. Already-running tasks spawned from
11052 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11053 both the Unix host and on the VxWorks target. The program
11054 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11055 installed with the name @code{vxgdb}, to distinguish it from a
11056 @value{GDBN} for debugging programs on the host itself.)
11059 @item VxWorks-timeout @var{args}
11060 @kindex vxworks-timeout
11061 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11062 This option is set by the user, and @var{args} represents the number of
11063 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11064 your VxWorks target is a slow software simulator or is on the far side
11065 of a thin network line.
11068 The following information on connecting to VxWorks was current when
11069 this manual was produced; newer releases of VxWorks may use revised
11072 @kindex INCLUDE_RDB
11073 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11074 to include the remote debugging interface routines in the VxWorks
11075 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11076 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11077 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11078 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11079 information on configuring and remaking VxWorks, see the manufacturer's
11081 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11083 Once you have included @file{rdb.a} in your VxWorks system image and set
11084 your Unix execution search path to find @value{GDBN}, you are ready to
11085 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11086 @code{vxgdb}, depending on your installation).
11088 @value{GDBN} comes up showing the prompt:
11095 * VxWorks Connection:: Connecting to VxWorks
11096 * VxWorks Download:: VxWorks download
11097 * VxWorks Attach:: Running tasks
11100 @node VxWorks Connection
11101 @subsubsection Connecting to VxWorks
11103 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11104 network. To connect to a target whose host name is ``@code{tt}'', type:
11107 (vxgdb) target vxworks tt
11111 @value{GDBN} displays messages like these:
11114 Attaching remote machine across net...
11119 @value{GDBN} then attempts to read the symbol tables of any object modules
11120 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11121 these files by searching the directories listed in the command search
11122 path (@pxref{Environment, ,Your program's environment}); if it fails
11123 to find an object file, it displays a message such as:
11126 prog.o: No such file or directory.
11129 When this happens, add the appropriate directory to the search path with
11130 the @value{GDBN} command @code{path}, and execute the @code{target}
11133 @node VxWorks Download
11134 @subsubsection VxWorks download
11136 @cindex download to VxWorks
11137 If you have connected to the VxWorks target and you want to debug an
11138 object that has not yet been loaded, you can use the @value{GDBN}
11139 @code{load} command to download a file from Unix to VxWorks
11140 incrementally. The object file given as an argument to the @code{load}
11141 command is actually opened twice: first by the VxWorks target in order
11142 to download the code, then by @value{GDBN} in order to read the symbol
11143 table. This can lead to problems if the current working directories on
11144 the two systems differ. If both systems have NFS mounted the same
11145 filesystems, you can avoid these problems by using absolute paths.
11146 Otherwise, it is simplest to set the working directory on both systems
11147 to the directory in which the object file resides, and then to reference
11148 the file by its name, without any path. For instance, a program
11149 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11150 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11151 program, type this on VxWorks:
11154 -> cd "@var{vxpath}/vw/demo/rdb"
11158 Then, in @value{GDBN}, type:
11161 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11162 (vxgdb) load prog.o
11165 @value{GDBN} displays a response similar to this:
11168 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11171 You can also use the @code{load} command to reload an object module
11172 after editing and recompiling the corresponding source file. Note that
11173 this makes @value{GDBN} delete all currently-defined breakpoints,
11174 auto-displays, and convenience variables, and to clear the value
11175 history. (This is necessary in order to preserve the integrity of
11176 debugger's data structures that reference the target system's symbol
11179 @node VxWorks Attach
11180 @subsubsection Running tasks
11182 @cindex running VxWorks tasks
11183 You can also attach to an existing task using the @code{attach} command as
11187 (vxgdb) attach @var{task}
11191 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11192 or suspended when you attach to it. Running tasks are suspended at
11193 the time of attachment.
11195 @node Embedded Processors
11196 @section Embedded Processors
11198 This section goes into details specific to particular embedded
11202 * A29K Embedded:: AMD A29K Embedded
11204 * H8/300:: Hitachi H8/300
11205 * H8/500:: Hitachi H8/500
11206 * i960:: Intel i960
11207 * M32R/D:: Mitsubishi M32R/D
11208 * M68K:: Motorola M68K
11209 * M88K:: Motorola M88K
11210 * MIPS Embedded:: MIPS Embedded
11211 * PA:: HP PA Embedded
11214 * Sparclet:: Tsqware Sparclet
11215 * Sparclite:: Fujitsu Sparclite
11216 * ST2000:: Tandem ST2000
11217 * Z8000:: Zilog Z8000
11220 @node A29K Embedded
11221 @subsection AMD A29K Embedded
11226 * Comms (EB29K):: Communications setup
11227 * gdb-EB29K:: EB29K cross-debugging
11228 * Remote Log:: Remote log
11233 @kindex target adapt
11234 @item target adapt @var{dev}
11235 Adapt monitor for A29K.
11237 @kindex target amd-eb
11238 @item target amd-eb @var{dev} @var{speed} @var{PROG}
11240 Remote PC-resident AMD EB29K board, attached over serial lines.
11241 @var{dev} is the serial device, as for @code{target remote};
11242 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
11243 name of the program to be debugged, as it appears to DOS on the PC.
11244 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
11249 @subsubsection A29K UDI
11252 @cindex AMD29K via UDI
11254 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
11255 protocol for debugging the a29k processor family. To use this
11256 configuration with AMD targets running the MiniMON monitor, you need the
11257 program @code{MONTIP}, available from AMD at no charge. You can also
11258 use @value{GDBN} with the UDI-conformant a29k simulator program
11259 @code{ISSTIP}, also available from AMD.
11262 @item target udi @var{keyword}
11264 Select the UDI interface to a remote a29k board or simulator, where
11265 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
11266 This file contains keyword entries which specify parameters used to
11267 connect to a29k targets. If the @file{udi_soc} file is not in your
11268 working directory, you must set the environment variable @samp{UDICONF}
11273 @subsubsection EBMON protocol for AMD29K
11275 @cindex EB29K board
11276 @cindex running 29K programs
11278 AMD distributes a 29K development board meant to fit in a PC, together
11279 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
11280 term, this development system is called the ``EB29K''. To use
11281 @value{GDBN} from a Unix system to run programs on the EB29K board, you
11282 must first connect a serial cable between the PC (which hosts the EB29K
11283 board) and a serial port on the Unix system. In the following, we
11284 assume you've hooked the cable between the PC's @file{COM1} port and
11285 @file{/dev/ttya} on the Unix system.
11287 @node Comms (EB29K)
11288 @subsubsection Communications setup
11290 The next step is to set up the PC's port, by doing something like this
11294 C:\> MODE com1:9600,n,8,1,none
11298 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
11299 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
11300 you must match the communications parameters when establishing the Unix
11301 end of the connection as well.
11302 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
11303 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
11305 @c It's optional, but it's unwise to omit it: who knows what is the
11306 @c default value set when the DOS machines boots? "No retry" means that
11307 @c the DOS serial device driver won't retry the operation if it fails;
11308 @c I understand that this is needed because the GDB serial protocol
11309 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
11311 To give control of the PC to the Unix side of the serial line, type
11312 the following at the DOS console:
11319 (Later, if you wish to return control to the DOS console, you can use
11320 the command @code{CTTY con}---but you must send it over the device that
11321 had control, in our example over the @file{COM1} serial line.)
11323 From the Unix host, use a communications program such as @code{tip} or
11324 @code{cu} to communicate with the PC; for example,
11327 cu -s 9600 -l /dev/ttya
11331 The @code{cu} options shown specify, respectively, the linespeed and the
11332 serial port to use. If you use @code{tip} instead, your command line
11333 may look something like the following:
11336 tip -9600 /dev/ttya
11340 Your system may require a different name where we show
11341 @file{/dev/ttya} as the argument to @code{tip}. The communications
11342 parameters, including which port to use, are associated with the
11343 @code{tip} argument in the ``remote'' descriptions file---normally the
11344 system table @file{/etc/remote}.
11345 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
11346 @c the DOS side's comms setup? cu can support -o (odd
11347 @c parity), -e (even parity)---apparently no settings for no parity or
11348 @c for character size. Taken from stty maybe...? John points out tip
11349 @c can set these as internal variables, eg ~s parity=none; man stty
11350 @c suggests that it *might* work to stty these options with stdin or
11351 @c stdout redirected... ---doc@cygnus.com, 25feb91
11353 @c There's nothing to be done for the "none" part of the DOS MODE
11354 @c command. The rest of the parameters should be matched by the
11355 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
11358 Using the @code{tip} or @code{cu} connection, change the DOS working
11359 directory to the directory containing a copy of your 29K program, then
11360 start the PC program @code{EBMON} (an EB29K control program supplied
11361 with your board by AMD). You should see an initial display from
11362 @code{EBMON} similar to the one that follows, ending with the
11363 @code{EBMON} prompt @samp{#}---
11368 G:\> CD \usr\joe\work29k
11370 G:\USR\JOE\WORK29K> EBMON
11371 Am29000 PC Coprocessor Board Monitor, version 3.0-18
11372 Copyright 1990 Advanced Micro Devices, Inc.
11373 Written by Gibbons and Associates, Inc.
11375 Enter '?' or 'H' for help
11377 PC Coprocessor Type = EB29K
11379 Memory Base = 0xd0000
11381 Data Memory Size = 2048KB
11382 Available I-RAM Range = 0x8000 to 0x1fffff
11383 Available D-RAM Range = 0x80002000 to 0x801fffff
11386 Register Stack Size = 0x800
11387 Memory Stack Size = 0x1800
11390 Am29027 Available = No
11391 Byte Write Available = Yes
11396 Then exit the @code{cu} or @code{tip} program (done in the example by
11397 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
11398 running, ready for @value{GDBN} to take over.
11400 For this example, we've assumed what is probably the most convenient
11401 way to make sure the same 29K program is on both the PC and the Unix
11402 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
11403 PC as a file system on the Unix host. If you do not have PC/NFS or
11404 something similar connecting the two systems, you must arrange some
11405 other way---perhaps floppy-disk transfer---of getting the 29K program
11406 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
11410 @subsubsection EB29K cross-debugging
11412 Finally, @code{cd} to the directory containing an image of your 29K
11413 program on the Unix system, and start @value{GDBN}---specifying as argument the
11414 name of your 29K program:
11417 cd /usr/joe/work29k
11422 Now you can use the @code{target} command:
11425 target amd-eb /dev/ttya 9600 MYFOO
11426 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
11427 @c emphasize that this is the name as seen by DOS (since I think DOS is
11428 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
11432 In this example, we've assumed your program is in a file called
11433 @file{myfoo}. Note that the filename given as the last argument to
11434 @code{target amd-eb} should be the name of the program as it appears to DOS.
11435 In our example this is simply @code{MYFOO}, but in general it can include
11436 a DOS path, and depending on your transfer mechanism may not resemble
11437 the name on the Unix side.
11439 At this point, you can set any breakpoints you wish; when you are ready
11440 to see your program run on the 29K board, use the @value{GDBN} command
11443 To stop debugging the remote program, use the @value{GDBN} @code{detach}
11446 To return control of the PC to its console, use @code{tip} or @code{cu}
11447 once again, after your @value{GDBN} session has concluded, to attach to
11448 @code{EBMON}. You can then type the command @code{q} to shut down
11449 @code{EBMON}, returning control to the DOS command-line interpreter.
11450 Type @kbd{CTTY con} to return command input to the main DOS console,
11451 and type @kbd{~.} to leave @code{tip} or @code{cu}.
11454 @subsubsection Remote log
11455 @cindex @file{eb.log}, a log file for EB29K
11456 @cindex log file for EB29K
11458 The @code{target amd-eb} command creates a file @file{eb.log} in the
11459 current working directory, to help debug problems with the connection.
11460 @file{eb.log} records all the output from @code{EBMON}, including echoes
11461 of the commands sent to it. Running @samp{tail -f} on this file in
11462 another window often helps to understand trouble with @code{EBMON}, or
11463 unexpected events on the PC side of the connection.
11471 @item target rdi @var{dev}
11472 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11473 use this target to communicate with both boards running the Angel
11474 monitor, or with the EmbeddedICE JTAG debug device.
11477 @item target rdp @var{dev}
11483 @subsection Hitachi H8/300
11487 @kindex target hms@r{, with H8/300}
11488 @item target hms @var{dev}
11489 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11490 Use special commands @code{device} and @code{speed} to control the serial
11491 line and the communications speed used.
11493 @kindex target e7000@r{, with H8/300}
11494 @item target e7000 @var{dev}
11495 E7000 emulator for Hitachi H8 and SH.
11497 @kindex target sh3@r{, with H8/300}
11498 @kindex target sh3e@r{, with H8/300}
11499 @item target sh3 @var{dev}
11500 @itemx target sh3e @var{dev}
11501 Hitachi SH-3 and SH-3E target systems.
11505 @cindex download to H8/300 or H8/500
11506 @cindex H8/300 or H8/500 download
11507 @cindex download to Hitachi SH
11508 @cindex Hitachi SH download
11509 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11510 board, the @code{load} command downloads your program to the Hitachi
11511 board and also opens it as the current executable target for
11512 @value{GDBN} on your host (like the @code{file} command).
11514 @value{GDBN} needs to know these things to talk to your
11515 Hitachi SH, H8/300, or H8/500:
11519 that you want to use @samp{target hms}, the remote debugging interface
11520 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11521 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11522 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11523 H8/300, or H8/500.)
11526 what serial device connects your host to your Hitachi board (the first
11527 serial device available on your host is the default).
11530 what speed to use over the serial device.
11534 * Hitachi Boards:: Connecting to Hitachi boards.
11535 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11536 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11539 @node Hitachi Boards
11540 @subsubsection Connecting to Hitachi boards
11542 @c only for Unix hosts
11544 @cindex serial device, Hitachi micros
11545 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11546 need to explicitly set the serial device. The default @var{port} is the
11547 first available port on your host. This is only necessary on Unix
11548 hosts, where it is typically something like @file{/dev/ttya}.
11551 @cindex serial line speed, Hitachi micros
11552 @code{@value{GDBN}} has another special command to set the communications
11553 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11554 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11555 the DOS @code{mode} command (for instance,
11556 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11558 The @samp{device} and @samp{speed} commands are available only when you
11559 use a Unix host to debug your Hitachi microprocessor programs. If you
11561 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11562 called @code{asynctsr} to communicate with the development board
11563 through a PC serial port. You must also use the DOS @code{mode} command
11564 to set up the serial port on the DOS side.
11566 The following sample session illustrates the steps needed to start a
11567 program under @value{GDBN} control on an H8/300. The example uses a
11568 sample H8/300 program called @file{t.x}. The procedure is the same for
11569 the Hitachi SH and the H8/500.
11571 First hook up your development board. In this example, we use a
11572 board attached to serial port @code{COM2}; if you use a different serial
11573 port, substitute its name in the argument of the @code{mode} command.
11574 When you call @code{asynctsr}, the auxiliary comms program used by the
11575 debugger, you give it just the numeric part of the serial port's name;
11576 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11580 C:\H8300\TEST> asynctsr 2
11581 C:\H8300\TEST> mode com2:9600,n,8,1,p
11583 Resident portion of MODE loaded
11585 COM2: 9600, n, 8, 1, p
11590 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11591 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11592 disable it, or even boot without it, to use @code{asynctsr} to control
11593 your development board.
11596 @kindex target hms@r{, and serial protocol}
11597 Now that serial communications are set up, and the development board is
11598 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11599 the name of your program as the argument. @code{@value{GDBN}} prompts
11600 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11601 commands to begin your debugging session: @samp{target hms} to specify
11602 cross-debugging to the Hitachi board, and the @code{load} command to
11603 download your program to the board. @code{load} displays the names of
11604 the program's sections, and a @samp{*} for each 2K of data downloaded.
11605 (If you want to refresh @value{GDBN} data on symbols or on the
11606 executable file without downloading, use the @value{GDBN} commands
11607 @code{file} or @code{symbol-file}. These commands, and @code{load}
11608 itself, are described in @ref{Files,,Commands to specify files}.)
11611 (eg-C:\H8300\TEST) @value{GDBP} t.x
11612 @value{GDBN} is free software and you are welcome to distribute copies
11613 of it under certain conditions; type "show copying" to see
11615 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11617 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11618 (@value{GDBP}) target hms
11619 Connected to remote H8/300 HMS system.
11620 (@value{GDBP}) load t.x
11621 .text : 0x8000 .. 0xabde ***********
11622 .data : 0xabde .. 0xad30 *
11623 .stack : 0xf000 .. 0xf014 *
11626 At this point, you're ready to run or debug your program. From here on,
11627 you can use all the usual @value{GDBN} commands. The @code{break} command
11628 sets breakpoints; the @code{run} command starts your program;
11629 @code{print} or @code{x} display data; the @code{continue} command
11630 resumes execution after stopping at a breakpoint. You can use the
11631 @code{help} command at any time to find out more about @value{GDBN} commands.
11633 Remember, however, that @emph{operating system} facilities aren't
11634 available on your development board; for example, if your program hangs,
11635 you can't send an interrupt---but you can press the @sc{reset} switch!
11637 Use the @sc{reset} button on the development board
11640 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11641 no way to pass an interrupt signal to the development board); and
11644 to return to the @value{GDBN} command prompt after your program finishes
11645 normally. The communications protocol provides no other way for @value{GDBN}
11646 to detect program completion.
11649 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11650 development board as a ``normal exit'' of your program.
11653 @subsubsection Using the E7000 in-circuit emulator
11655 @kindex target e7000@r{, with Hitachi ICE}
11656 You can use the E7000 in-circuit emulator to develop code for either the
11657 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11658 e7000} command to connect @value{GDBN} to your E7000:
11661 @item target e7000 @var{port} @var{speed}
11662 Use this form if your E7000 is connected to a serial port. The
11663 @var{port} argument identifies what serial port to use (for example,
11664 @samp{com2}). The third argument is the line speed in bits per second
11665 (for example, @samp{9600}).
11667 @item target e7000 @var{hostname}
11668 If your E7000 is installed as a host on a TCP/IP network, you can just
11669 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11672 @node Hitachi Special
11673 @subsubsection Special @value{GDBN} commands for Hitachi micros
11675 Some @value{GDBN} commands are available only for the H8/300:
11679 @kindex set machine
11680 @kindex show machine
11681 @item set machine h8300
11682 @itemx set machine h8300h
11683 Condition @value{GDBN} for one of the two variants of the H8/300
11684 architecture with @samp{set machine}. You can use @samp{show machine}
11685 to check which variant is currently in effect.
11694 @kindex set memory @var{mod}
11695 @cindex memory models, H8/500
11696 @item set memory @var{mod}
11698 Specify which H8/500 memory model (@var{mod}) you are using with
11699 @samp{set memory}; check which memory model is in effect with @samp{show
11700 memory}. The accepted values for @var{mod} are @code{small},
11701 @code{big}, @code{medium}, and @code{compact}.
11706 @subsection Intel i960
11710 @kindex target mon960
11711 @item target mon960 @var{dev}
11712 MON960 monitor for Intel i960.
11714 @kindex target nindy
11715 @item target nindy @var{devicename}
11716 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11717 the name of the serial device to use for the connection, e.g.
11724 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11725 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11726 tell @value{GDBN} how to connect to the 960 in several ways:
11730 Through command line options specifying serial port, version of the
11731 Nindy protocol, and communications speed;
11734 By responding to a prompt on startup;
11737 By using the @code{target} command at any point during your @value{GDBN}
11738 session. @xref{Target Commands, ,Commands for managing targets}.
11742 @cindex download to Nindy-960
11743 With the Nindy interface to an Intel 960 board, @code{load}
11744 downloads @var{filename} to the 960 as well as adding its symbols in
11748 * Nindy Startup:: Startup with Nindy
11749 * Nindy Options:: Options for Nindy
11750 * Nindy Reset:: Nindy reset command
11753 @node Nindy Startup
11754 @subsubsection Startup with Nindy
11756 If you simply start @code{@value{GDBP}} without using any command-line
11757 options, you are prompted for what serial port to use, @emph{before} you
11758 reach the ordinary @value{GDBN} prompt:
11761 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11765 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11766 identifies the serial port you want to use. You can, if you choose,
11767 simply start up with no Nindy connection by responding to the prompt
11768 with an empty line. If you do this and later wish to attach to Nindy,
11769 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11771 @node Nindy Options
11772 @subsubsection Options for Nindy
11774 These are the startup options for beginning your @value{GDBN} session with a
11775 Nindy-960 board attached:
11778 @item -r @var{port}
11779 Specify the serial port name of a serial interface to be used to connect
11780 to the target system. This option is only available when @value{GDBN} is
11781 configured for the Intel 960 target architecture. You may specify
11782 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11783 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11784 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11787 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11788 the ``old'' Nindy monitor protocol to connect to the target system.
11789 This option is only available when @value{GDBN} is configured for the Intel 960
11790 target architecture.
11793 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11794 connect to a target system that expects the newer protocol, the connection
11795 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11796 attempts to reconnect at several different line speeds. You can abort
11797 this process with an interrupt.
11801 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11802 system, in an attempt to reset it, before connecting to a Nindy target.
11805 @emph{Warning:} Many target systems do not have the hardware that this
11806 requires; it only works with a few boards.
11810 The standard @samp{-b} option controls the line speed used on the serial
11815 @subsubsection Nindy reset command
11820 For a Nindy target, this command sends a ``break'' to the remote target
11821 system; this is only useful if the target has been equipped with a
11822 circuit to perform a hard reset (or some other interesting action) when
11823 a break is detected.
11828 @subsection Mitsubishi M32R/D
11832 @kindex target m32r
11833 @item target m32r @var{dev}
11834 Mitsubishi M32R/D ROM monitor.
11841 The Motorola m68k configuration includes ColdFire support, and
11842 target command for the following ROM monitors.
11846 @kindex target abug
11847 @item target abug @var{dev}
11848 ABug ROM monitor for M68K.
11850 @kindex target cpu32bug
11851 @item target cpu32bug @var{dev}
11852 CPU32BUG monitor, running on a CPU32 (M68K) board.
11854 @kindex target dbug
11855 @item target dbug @var{dev}
11856 dBUG ROM monitor for Motorola ColdFire.
11859 @item target est @var{dev}
11860 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11862 @kindex target rom68k
11863 @item target rom68k @var{dev}
11864 ROM 68K monitor, running on an M68K IDP board.
11868 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11869 instead have only a single special target command:
11873 @kindex target es1800
11874 @item target es1800 @var{dev}
11875 ES-1800 emulator for M68K.
11883 @kindex target rombug
11884 @item target rombug @var{dev}
11885 ROMBUG ROM monitor for OS/9000.
11895 @item target bug @var{dev}
11896 BUG monitor, running on a MVME187 (m88k) board.
11900 @node MIPS Embedded
11901 @subsection MIPS Embedded
11903 @cindex MIPS boards
11904 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11905 MIPS board attached to a serial line. This is available when
11906 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11909 Use these @value{GDBN} commands to specify the connection to your target board:
11912 @item target mips @var{port}
11913 @kindex target mips @var{port}
11914 To run a program on the board, start up @code{@value{GDBP}} with the
11915 name of your program as the argument. To connect to the board, use the
11916 command @samp{target mips @var{port}}, where @var{port} is the name of
11917 the serial port connected to the board. If the program has not already
11918 been downloaded to the board, you may use the @code{load} command to
11919 download it. You can then use all the usual @value{GDBN} commands.
11921 For example, this sequence connects to the target board through a serial
11922 port, and loads and runs a program called @var{prog} through the
11926 host$ @value{GDBP} @var{prog}
11927 @value{GDBN} is free software and @dots{}
11928 (@value{GDBP}) target mips /dev/ttyb
11929 (@value{GDBP}) load @var{prog}
11933 @item target mips @var{hostname}:@var{portnumber}
11934 On some @value{GDBN} host configurations, you can specify a TCP
11935 connection (for instance, to a serial line managed by a terminal
11936 concentrator) instead of a serial port, using the syntax
11937 @samp{@var{hostname}:@var{portnumber}}.
11939 @item target pmon @var{port}
11940 @kindex target pmon @var{port}
11943 @item target ddb @var{port}
11944 @kindex target ddb @var{port}
11945 NEC's DDB variant of PMON for Vr4300.
11947 @item target lsi @var{port}
11948 @kindex target lsi @var{port}
11949 LSI variant of PMON.
11951 @kindex target r3900
11952 @item target r3900 @var{dev}
11953 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11955 @kindex target array
11956 @item target array @var{dev}
11957 Array Tech LSI33K RAID controller board.
11963 @value{GDBN} also supports these special commands for MIPS targets:
11966 @item set processor @var{args}
11967 @itemx show processor
11968 @kindex set processor @var{args}
11969 @kindex show processor
11970 Use the @code{set processor} command to set the type of MIPS
11971 processor when you want to access processor-type-specific registers.
11972 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11973 to use the CPU registers appropriate for the 3041 chip.
11974 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11975 is using. Use the @code{info reg} command to see what registers
11976 @value{GDBN} is using.
11978 @item set mipsfpu double
11979 @itemx set mipsfpu single
11980 @itemx set mipsfpu none
11981 @itemx show mipsfpu
11982 @kindex set mipsfpu
11983 @kindex show mipsfpu
11984 @cindex MIPS remote floating point
11985 @cindex floating point, MIPS remote
11986 If your target board does not support the MIPS floating point
11987 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11988 need this, you may wish to put the command in your @value{GDBN} init
11989 file). This tells @value{GDBN} how to find the return value of
11990 functions which return floating point values. It also allows
11991 @value{GDBN} to avoid saving the floating point registers when calling
11992 functions on the board. If you are using a floating point coprocessor
11993 with only single precision floating point support, as on the @sc{r4650}
11994 processor, use the command @samp{set mipsfpu single}. The default
11995 double precision floating point coprocessor may be selected using
11996 @samp{set mipsfpu double}.
11998 In previous versions the only choices were double precision or no
11999 floating point, so @samp{set mipsfpu on} will select double precision
12000 and @samp{set mipsfpu off} will select no floating point.
12002 As usual, you can inquire about the @code{mipsfpu} variable with
12003 @samp{show mipsfpu}.
12005 @item set remotedebug @var{n}
12006 @itemx show remotedebug
12007 @kindex set remotedebug@r{, MIPS protocol}
12008 @kindex show remotedebug@r{, MIPS protocol}
12009 @cindex @code{remotedebug}, MIPS protocol
12010 @cindex MIPS @code{remotedebug} protocol
12011 @c FIXME! For this to be useful, you must know something about the MIPS
12012 @c FIXME...protocol. Where is it described?
12013 You can see some debugging information about communications with the board
12014 by setting the @code{remotedebug} variable. If you set it to @code{1} using
12015 @samp{set remotedebug 1}, every packet is displayed. If you set it
12016 to @code{2}, every character is displayed. You can check the current value
12017 at any time with the command @samp{show remotedebug}.
12019 @item set timeout @var{seconds}
12020 @itemx set retransmit-timeout @var{seconds}
12021 @itemx show timeout
12022 @itemx show retransmit-timeout
12023 @cindex @code{timeout}, MIPS protocol
12024 @cindex @code{retransmit-timeout}, MIPS protocol
12025 @kindex set timeout
12026 @kindex show timeout
12027 @kindex set retransmit-timeout
12028 @kindex show retransmit-timeout
12029 You can control the timeout used while waiting for a packet, in the MIPS
12030 remote protocol, with the @code{set timeout @var{seconds}} command. The
12031 default is 5 seconds. Similarly, you can control the timeout used while
12032 waiting for an acknowledgement of a packet with the @code{set
12033 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
12034 You can inspect both values with @code{show timeout} and @code{show
12035 retransmit-timeout}. (These commands are @emph{only} available when
12036 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
12038 The timeout set by @code{set timeout} does not apply when @value{GDBN}
12039 is waiting for your program to stop. In that case, @value{GDBN} waits
12040 forever because it has no way of knowing how long the program is going
12041 to run before stopping.
12045 @subsection PowerPC
12049 @kindex target dink32
12050 @item target dink32 @var{dev}
12051 DINK32 ROM monitor.
12053 @kindex target ppcbug
12054 @item target ppcbug @var{dev}
12055 @kindex target ppcbug1
12056 @item target ppcbug1 @var{dev}
12057 PPCBUG ROM monitor for PowerPC.
12060 @item target sds @var{dev}
12061 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
12066 @subsection HP PA Embedded
12070 @kindex target op50n
12071 @item target op50n @var{dev}
12072 OP50N monitor, running on an OKI HPPA board.
12074 @kindex target w89k
12075 @item target w89k @var{dev}
12076 W89K monitor, running on a Winbond HPPA board.
12081 @subsection Hitachi SH
12085 @kindex target hms@r{, with Hitachi SH}
12086 @item target hms @var{dev}
12087 A Hitachi SH board attached via serial line to your host. Use special
12088 commands @code{device} and @code{speed} to control the serial line and
12089 the communications speed used.
12091 @kindex target e7000@r{, with Hitachi SH}
12092 @item target e7000 @var{dev}
12093 E7000 emulator for Hitachi SH.
12095 @kindex target sh3@r{, with SH}
12096 @kindex target sh3e@r{, with SH}
12097 @item target sh3 @var{dev}
12098 @item target sh3e @var{dev}
12099 Hitachi SH-3 and SH-3E target systems.
12104 @subsection Tsqware Sparclet
12108 @value{GDBN} enables developers to debug tasks running on
12109 Sparclet targets from a Unix host.
12110 @value{GDBN} uses code that runs on
12111 both the Unix host and on the Sparclet target. The program
12112 @code{@value{GDBP}} is installed and executed on the Unix host.
12115 @item remotetimeout @var{args}
12116 @kindex remotetimeout
12117 @value{GDBN} supports the option @code{remotetimeout}.
12118 This option is set by the user, and @var{args} represents the number of
12119 seconds @value{GDBN} waits for responses.
12122 @cindex compiling, on Sparclet
12123 When compiling for debugging, include the options @samp{-g} to get debug
12124 information and @samp{-Ttext} to relocate the program to where you wish to
12125 load it on the target. You may also want to add the options @samp{-n} or
12126 @samp{-N} in order to reduce the size of the sections. Example:
12129 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12132 You can use @code{objdump} to verify that the addresses are what you intended:
12135 sparclet-aout-objdump --headers --syms prog
12138 @cindex running, on Sparclet
12140 your Unix execution search path to find @value{GDBN}, you are ready to
12141 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12142 (or @code{sparclet-aout-gdb}, depending on your installation).
12144 @value{GDBN} comes up showing the prompt:
12151 * Sparclet File:: Setting the file to debug
12152 * Sparclet Connection:: Connecting to Sparclet
12153 * Sparclet Download:: Sparclet download
12154 * Sparclet Execution:: Running and debugging
12157 @node Sparclet File
12158 @subsubsection Setting file to debug
12160 The @value{GDBN} command @code{file} lets you choose with program to debug.
12163 (gdbslet) file prog
12167 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12168 @value{GDBN} locates
12169 the file by searching the directories listed in the command search
12171 If the file was compiled with debug information (option "-g"), source
12172 files will be searched as well.
12173 @value{GDBN} locates
12174 the source files by searching the directories listed in the directory search
12175 path (@pxref{Environment, ,Your program's environment}).
12177 to find a file, it displays a message such as:
12180 prog: No such file or directory.
12183 When this happens, add the appropriate directories to the search paths with
12184 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12185 @code{target} command again.
12187 @node Sparclet Connection
12188 @subsubsection Connecting to Sparclet
12190 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12191 To connect to a target on serial port ``@code{ttya}'', type:
12194 (gdbslet) target sparclet /dev/ttya
12195 Remote target sparclet connected to /dev/ttya
12196 main () at ../prog.c:3
12200 @value{GDBN} displays messages like these:
12206 @node Sparclet Download
12207 @subsubsection Sparclet download
12209 @cindex download to Sparclet
12210 Once connected to the Sparclet target,
12211 you can use the @value{GDBN}
12212 @code{load} command to download the file from the host to the target.
12213 The file name and load offset should be given as arguments to the @code{load}
12215 Since the file format is aout, the program must be loaded to the starting
12216 address. You can use @code{objdump} to find out what this value is. The load
12217 offset is an offset which is added to the VMA (virtual memory address)
12218 of each of the file's sections.
12219 For instance, if the program
12220 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12221 and bss at 0x12010170, in @value{GDBN}, type:
12224 (gdbslet) load prog 0x12010000
12225 Loading section .text, size 0xdb0 vma 0x12010000
12228 If the code is loaded at a different address then what the program was linked
12229 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12230 to tell @value{GDBN} where to map the symbol table.
12232 @node Sparclet Execution
12233 @subsubsection Running and debugging
12235 @cindex running and debugging Sparclet programs
12236 You can now begin debugging the task using @value{GDBN}'s execution control
12237 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12238 manual for the list of commands.
12242 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12244 Starting program: prog
12245 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12246 3 char *symarg = 0;
12248 4 char *execarg = "hello!";
12253 @subsection Fujitsu Sparclite
12257 @kindex target sparclite
12258 @item target sparclite @var{dev}
12259 Fujitsu sparclite boards, used only for the purpose of loading.
12260 You must use an additional command to debug the program.
12261 For example: target remote @var{dev} using @value{GDBN} standard
12267 @subsection Tandem ST2000
12269 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12272 To connect your ST2000 to the host system, see the manufacturer's
12273 manual. Once the ST2000 is physically attached, you can run:
12276 target st2000 @var{dev} @var{speed}
12280 to establish it as your debugging environment. @var{dev} is normally
12281 the name of a serial device, such as @file{/dev/ttya}, connected to the
12282 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12283 connection (for example, to a serial line attached via a terminal
12284 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12286 The @code{load} and @code{attach} commands are @emph{not} defined for
12287 this target; you must load your program into the ST2000 as you normally
12288 would for standalone operation. @value{GDBN} reads debugging information
12289 (such as symbols) from a separate, debugging version of the program
12290 available on your host computer.
12291 @c FIXME!! This is terribly vague; what little content is here is
12292 @c basically hearsay.
12294 @cindex ST2000 auxiliary commands
12295 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12299 @item st2000 @var{command}
12300 @kindex st2000 @var{cmd}
12301 @cindex STDBUG commands (ST2000)
12302 @cindex commands to STDBUG (ST2000)
12303 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12304 manual for available commands.
12307 @cindex connect (to STDBUG)
12308 Connect the controlling terminal to the STDBUG command monitor. When
12309 you are done interacting with STDBUG, typing either of two character
12310 sequences gets you back to the @value{GDBN} command prompt:
12311 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12312 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12316 @subsection Zilog Z8000
12319 @cindex simulator, Z8000
12320 @cindex Zilog Z8000 simulator
12322 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12325 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12326 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12327 segmented variant). The simulator recognizes which architecture is
12328 appropriate by inspecting the object code.
12331 @item target sim @var{args}
12333 @kindex target sim@r{, with Z8000}
12334 Debug programs on a simulated CPU. If the simulator supports setup
12335 options, specify them via @var{args}.
12339 After specifying this target, you can debug programs for the simulated
12340 CPU in the same style as programs for your host computer; use the
12341 @code{file} command to load a new program image, the @code{run} command
12342 to run your program, and so on.
12344 As well as making available all the usual machine registers
12345 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12346 additional items of information as specially named registers:
12351 Counts clock-ticks in the simulator.
12354 Counts instructions run in the simulator.
12357 Execution time in 60ths of a second.
12361 You can refer to these values in @value{GDBN} expressions with the usual
12362 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12363 conditional breakpoint that suspends only after at least 5000
12364 simulated clock ticks.
12366 @node Architectures
12367 @section Architectures
12369 This section describes characteristics of architectures that affect
12370 all uses of @value{GDBN} with the architecture, both native and cross.
12383 @kindex set rstack_high_address
12384 @cindex AMD 29K register stack
12385 @cindex register stack, AMD29K
12386 @item set rstack_high_address @var{address}
12387 On AMD 29000 family processors, registers are saved in a separate
12388 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12389 extent of this stack. Normally, @value{GDBN} just assumes that the
12390 stack is ``large enough''. This may result in @value{GDBN} referencing
12391 memory locations that do not exist. If necessary, you can get around
12392 this problem by specifying the ending address of the register stack with
12393 the @code{set rstack_high_address} command. The argument should be an
12394 address, which you probably want to precede with @samp{0x} to specify in
12397 @kindex show rstack_high_address
12398 @item show rstack_high_address
12399 Display the current limit of the register stack, on AMD 29000 family
12407 See the following section.
12412 @cindex stack on Alpha
12413 @cindex stack on MIPS
12414 @cindex Alpha stack
12416 Alpha- and MIPS-based computers use an unusual stack frame, which
12417 sometimes requires @value{GDBN} to search backward in the object code to
12418 find the beginning of a function.
12420 @cindex response time, MIPS debugging
12421 To improve response time (especially for embedded applications, where
12422 @value{GDBN} may be restricted to a slow serial line for this search)
12423 you may want to limit the size of this search, using one of these
12427 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12428 @item set heuristic-fence-post @var{limit}
12429 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12430 search for the beginning of a function. A value of @var{0} (the
12431 default) means there is no limit. However, except for @var{0}, the
12432 larger the limit the more bytes @code{heuristic-fence-post} must search
12433 and therefore the longer it takes to run.
12435 @item show heuristic-fence-post
12436 Display the current limit.
12440 These commands are available @emph{only} when @value{GDBN} is configured
12441 for debugging programs on Alpha or MIPS processors.
12444 @node Controlling GDB
12445 @chapter Controlling @value{GDBN}
12447 You can alter the way @value{GDBN} interacts with you by using the
12448 @code{set} command. For commands controlling how @value{GDBN} displays
12449 data, see @ref{Print Settings, ,Print settings}. Other settings are
12454 * Editing:: Command editing
12455 * History:: Command history
12456 * Screen Size:: Screen size
12457 * Numbers:: Numbers
12458 * Messages/Warnings:: Optional warnings and messages
12459 * Debugging Output:: Optional messages about internal happenings
12467 @value{GDBN} indicates its readiness to read a command by printing a string
12468 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12469 can change the prompt string with the @code{set prompt} command. For
12470 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12471 the prompt in one of the @value{GDBN} sessions so that you can always tell
12472 which one you are talking to.
12474 @emph{Note:} @code{set prompt} does not add a space for you after the
12475 prompt you set. This allows you to set a prompt which ends in a space
12476 or a prompt that does not.
12480 @item set prompt @var{newprompt}
12481 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12483 @kindex show prompt
12485 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12489 @section Command editing
12491 @cindex command line editing
12493 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12494 @sc{gnu} library provides consistent behavior for programs which provide a
12495 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12496 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12497 substitution, and a storage and recall of command history across
12498 debugging sessions.
12500 You may control the behavior of command line editing in @value{GDBN} with the
12501 command @code{set}.
12504 @kindex set editing
12507 @itemx set editing on
12508 Enable command line editing (enabled by default).
12510 @item set editing off
12511 Disable command line editing.
12513 @kindex show editing
12515 Show whether command line editing is enabled.
12519 @section Command history
12521 @value{GDBN} can keep track of the commands you type during your
12522 debugging sessions, so that you can be certain of precisely what
12523 happened. Use these commands to manage the @value{GDBN} command
12527 @cindex history substitution
12528 @cindex history file
12529 @kindex set history filename
12530 @kindex GDBHISTFILE
12531 @item set history filename @var{fname}
12532 Set the name of the @value{GDBN} command history file to @var{fname}.
12533 This is the file where @value{GDBN} reads an initial command history
12534 list, and where it writes the command history from this session when it
12535 exits. You can access this list through history expansion or through
12536 the history command editing characters listed below. This file defaults
12537 to the value of the environment variable @code{GDBHISTFILE}, or to
12538 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12541 @cindex history save
12542 @kindex set history save
12543 @item set history save
12544 @itemx set history save on
12545 Record command history in a file, whose name may be specified with the
12546 @code{set history filename} command. By default, this option is disabled.
12548 @item set history save off
12549 Stop recording command history in a file.
12551 @cindex history size
12552 @kindex set history size
12553 @item set history size @var{size}
12554 Set the number of commands which @value{GDBN} keeps in its history list.
12555 This defaults to the value of the environment variable
12556 @code{HISTSIZE}, or to 256 if this variable is not set.
12559 @cindex history expansion
12560 History expansion assigns special meaning to the character @kbd{!}.
12561 @ifset have-readline-appendices
12562 @xref{Event Designators}.
12565 Since @kbd{!} is also the logical not operator in C, history expansion
12566 is off by default. If you decide to enable history expansion with the
12567 @code{set history expansion on} command, you may sometimes need to
12568 follow @kbd{!} (when it is used as logical not, in an expression) with
12569 a space or a tab to prevent it from being expanded. The readline
12570 history facilities do not attempt substitution on the strings
12571 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12573 The commands to control history expansion are:
12576 @kindex set history expansion
12577 @item set history expansion on
12578 @itemx set history expansion
12579 Enable history expansion. History expansion is off by default.
12581 @item set history expansion off
12582 Disable history expansion.
12584 The readline code comes with more complete documentation of
12585 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12586 or @code{vi} may wish to read it.
12587 @ifset have-readline-appendices
12588 @xref{Command Line Editing}.
12592 @kindex show history
12594 @itemx show history filename
12595 @itemx show history save
12596 @itemx show history size
12597 @itemx show history expansion
12598 These commands display the state of the @value{GDBN} history parameters.
12599 @code{show history} by itself displays all four states.
12605 @item show commands
12606 Display the last ten commands in the command history.
12608 @item show commands @var{n}
12609 Print ten commands centered on command number @var{n}.
12611 @item show commands +
12612 Print ten commands just after the commands last printed.
12616 @section Screen size
12617 @cindex size of screen
12618 @cindex pauses in output
12620 Certain commands to @value{GDBN} may produce large amounts of
12621 information output to the screen. To help you read all of it,
12622 @value{GDBN} pauses and asks you for input at the end of each page of
12623 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12624 to discard the remaining output. Also, the screen width setting
12625 determines when to wrap lines of output. Depending on what is being
12626 printed, @value{GDBN} tries to break the line at a readable place,
12627 rather than simply letting it overflow onto the following line.
12629 Normally @value{GDBN} knows the size of the screen from the terminal
12630 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12631 together with the value of the @code{TERM} environment variable and the
12632 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12633 you can override it with the @code{set height} and @code{set
12640 @kindex show height
12641 @item set height @var{lpp}
12643 @itemx set width @var{cpl}
12645 These @code{set} commands specify a screen height of @var{lpp} lines and
12646 a screen width of @var{cpl} characters. The associated @code{show}
12647 commands display the current settings.
12649 If you specify a height of zero lines, @value{GDBN} does not pause during
12650 output no matter how long the output is. This is useful if output is to a
12651 file or to an editor buffer.
12653 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12654 from wrapping its output.
12659 @cindex number representation
12660 @cindex entering numbers
12662 You can always enter numbers in octal, decimal, or hexadecimal in
12663 @value{GDBN} by the usual conventions: octal numbers begin with
12664 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12665 begin with @samp{0x}. Numbers that begin with none of these are, by
12666 default, entered in base 10; likewise, the default display for
12667 numbers---when no particular format is specified---is base 10. You can
12668 change the default base for both input and output with the @code{set
12672 @kindex set input-radix
12673 @item set input-radix @var{base}
12674 Set the default base for numeric input. Supported choices
12675 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12676 specified either unambiguously or using the current default radix; for
12686 sets the base to decimal. On the other hand, @samp{set radix 10}
12687 leaves the radix unchanged no matter what it was.
12689 @kindex set output-radix
12690 @item set output-radix @var{base}
12691 Set the default base for numeric display. Supported choices
12692 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12693 specified either unambiguously or using the current default radix.
12695 @kindex show input-radix
12696 @item show input-radix
12697 Display the current default base for numeric input.
12699 @kindex show output-radix
12700 @item show output-radix
12701 Display the current default base for numeric display.
12704 @node Messages/Warnings
12705 @section Optional warnings and messages
12707 By default, @value{GDBN} is silent about its inner workings. If you are
12708 running on a slow machine, you may want to use the @code{set verbose}
12709 command. This makes @value{GDBN} tell you when it does a lengthy
12710 internal operation, so you will not think it has crashed.
12712 Currently, the messages controlled by @code{set verbose} are those
12713 which announce that the symbol table for a source file is being read;
12714 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12717 @kindex set verbose
12718 @item set verbose on
12719 Enables @value{GDBN} output of certain informational messages.
12721 @item set verbose off
12722 Disables @value{GDBN} output of certain informational messages.
12724 @kindex show verbose
12726 Displays whether @code{set verbose} is on or off.
12729 By default, if @value{GDBN} encounters bugs in the symbol table of an
12730 object file, it is silent; but if you are debugging a compiler, you may
12731 find this information useful (@pxref{Symbol Errors, ,Errors reading
12736 @kindex set complaints
12737 @item set complaints @var{limit}
12738 Permits @value{GDBN} to output @var{limit} complaints about each type of
12739 unusual symbols before becoming silent about the problem. Set
12740 @var{limit} to zero to suppress all complaints; set it to a large number
12741 to prevent complaints from being suppressed.
12743 @kindex show complaints
12744 @item show complaints
12745 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12749 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12750 lot of stupid questions to confirm certain commands. For example, if
12751 you try to run a program which is already running:
12755 The program being debugged has been started already.
12756 Start it from the beginning? (y or n)
12759 If you are willing to unflinchingly face the consequences of your own
12760 commands, you can disable this ``feature'':
12764 @kindex set confirm
12766 @cindex confirmation
12767 @cindex stupid questions
12768 @item set confirm off
12769 Disables confirmation requests.
12771 @item set confirm on
12772 Enables confirmation requests (the default).
12774 @kindex show confirm
12776 Displays state of confirmation requests.
12780 @node Debugging Output
12781 @section Optional messages about internal happenings
12783 @kindex set debug arch
12784 @item set debug arch
12785 Turns on or off display of gdbarch debugging info. The default is off
12786 @kindex show debug arch
12787 @item show debug arch
12788 Displays the current state of displaying gdbarch debugging info.
12789 @kindex set debug event
12790 @item set debug event
12791 Turns on or off display of @value{GDBN} event debugging info. The
12793 @kindex show debug event
12794 @item show debug event
12795 Displays the current state of displaying @value{GDBN} event debugging
12797 @kindex set debug expression
12798 @item set debug expression
12799 Turns on or off display of @value{GDBN} expression debugging info. The
12801 @kindex show debug expression
12802 @item show debug expression
12803 Displays the current state of displaying @value{GDBN} expression
12805 @kindex set debug overload
12806 @item set debug overload
12807 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12808 info. This includes info such as ranking of functions, etc. The default
12810 @kindex show debug overload
12811 @item show debug overload
12812 Displays the current state of displaying @value{GDBN} C@t{++} overload
12814 @kindex set debug remote
12815 @cindex packets, reporting on stdout
12816 @cindex serial connections, debugging
12817 @item set debug remote
12818 Turns on or off display of reports on all packets sent back and forth across
12819 the serial line to the remote machine. The info is printed on the
12820 @value{GDBN} standard output stream. The default is off.
12821 @kindex show debug remote
12822 @item show debug remote
12823 Displays the state of display of remote packets.
12824 @kindex set debug serial
12825 @item set debug serial
12826 Turns on or off display of @value{GDBN} serial debugging info. The
12828 @kindex show debug serial
12829 @item show debug serial
12830 Displays the current state of displaying @value{GDBN} serial debugging
12832 @kindex set debug target
12833 @item set debug target
12834 Turns on or off display of @value{GDBN} target debugging info. This info
12835 includes what is going on at the target level of GDB, as it happens. The
12837 @kindex show debug target
12838 @item show debug target
12839 Displays the current state of displaying @value{GDBN} target debugging
12841 @kindex set debug varobj
12842 @item set debug varobj
12843 Turns on or off display of @value{GDBN} variable object debugging
12844 info. The default is off.
12845 @kindex show debug varobj
12846 @item show debug varobj
12847 Displays the current state of displaying @value{GDBN} variable object
12852 @chapter Canned Sequences of Commands
12854 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12855 command lists}), @value{GDBN} provides two ways to store sequences of
12856 commands for execution as a unit: user-defined commands and command
12860 * Define:: User-defined commands
12861 * Hooks:: User-defined command hooks
12862 * Command Files:: Command files
12863 * Output:: Commands for controlled output
12867 @section User-defined commands
12869 @cindex user-defined command
12870 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12871 which you assign a new name as a command. This is done with the
12872 @code{define} command. User commands may accept up to 10 arguments
12873 separated by whitespace. Arguments are accessed within the user command
12874 via @var{$arg0@dots{}$arg9}. A trivial example:
12878 print $arg0 + $arg1 + $arg2
12882 To execute the command use:
12889 This defines the command @code{adder}, which prints the sum of
12890 its three arguments. Note the arguments are text substitutions, so they may
12891 reference variables, use complex expressions, or even perform inferior
12897 @item define @var{commandname}
12898 Define a command named @var{commandname}. If there is already a command
12899 by that name, you are asked to confirm that you want to redefine it.
12901 The definition of the command is made up of other @value{GDBN} command lines,
12902 which are given following the @code{define} command. The end of these
12903 commands is marked by a line containing @code{end}.
12908 Takes a single argument, which is an expression to evaluate.
12909 It is followed by a series of commands that are executed
12910 only if the expression is true (nonzero).
12911 There can then optionally be a line @code{else}, followed
12912 by a series of commands that are only executed if the expression
12913 was false. The end of the list is marked by a line containing @code{end}.
12917 The syntax is similar to @code{if}: the command takes a single argument,
12918 which is an expression to evaluate, and must be followed by the commands to
12919 execute, one per line, terminated by an @code{end}.
12920 The commands are executed repeatedly as long as the expression
12924 @item document @var{commandname}
12925 Document the user-defined command @var{commandname}, so that it can be
12926 accessed by @code{help}. The command @var{commandname} must already be
12927 defined. This command reads lines of documentation just as @code{define}
12928 reads the lines of the command definition, ending with @code{end}.
12929 After the @code{document} command is finished, @code{help} on command
12930 @var{commandname} displays the documentation you have written.
12932 You may use the @code{document} command again to change the
12933 documentation of a command. Redefining the command with @code{define}
12934 does not change the documentation.
12936 @kindex help user-defined
12937 @item help user-defined
12938 List all user-defined commands, with the first line of the documentation
12943 @itemx show user @var{commandname}
12944 Display the @value{GDBN} commands used to define @var{commandname} (but
12945 not its documentation). If no @var{commandname} is given, display the
12946 definitions for all user-defined commands.
12950 When user-defined commands are executed, the
12951 commands of the definition are not printed. An error in any command
12952 stops execution of the user-defined command.
12954 If used interactively, commands that would ask for confirmation proceed
12955 without asking when used inside a user-defined command. Many @value{GDBN}
12956 commands that normally print messages to say what they are doing omit the
12957 messages when used in a user-defined command.
12960 @section User-defined command hooks
12961 @cindex command hooks
12962 @cindex hooks, for commands
12963 @cindex hooks, pre-command
12967 You may define @dfn{hooks}, which are a special kind of user-defined
12968 command. Whenever you run the command @samp{foo}, if the user-defined
12969 command @samp{hook-foo} exists, it is executed (with no arguments)
12970 before that command.
12972 @cindex hooks, post-command
12975 A hook may also be defined which is run after the command you executed.
12976 Whenever you run the command @samp{foo}, if the user-defined command
12977 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12978 that command. Post-execution hooks may exist simultaneously with
12979 pre-execution hooks, for the same command.
12981 It is valid for a hook to call the command which it hooks. If this
12982 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12984 @c It would be nice if hookpost could be passed a parameter indicating
12985 @c if the command it hooks executed properly or not. FIXME!
12987 @kindex stop@r{, a pseudo-command}
12988 In addition, a pseudo-command, @samp{stop} exists. Defining
12989 (@samp{hook-stop}) makes the associated commands execute every time
12990 execution stops in your program: before breakpoint commands are run,
12991 displays are printed, or the stack frame is printed.
12993 For example, to ignore @code{SIGALRM} signals while
12994 single-stepping, but treat them normally during normal execution,
12999 handle SIGALRM nopass
13003 handle SIGALRM pass
13006 define hook-continue
13007 handle SIGLARM pass
13011 As a further example, to hook at the begining and end of the @code{echo}
13012 command, and to add extra text to the beginning and end of the message,
13020 define hookpost-echo
13024 (@value{GDBP}) echo Hello World
13025 <<<---Hello World--->>>
13030 You can define a hook for any single-word command in @value{GDBN}, but
13031 not for command aliases; you should define a hook for the basic command
13032 name, e.g. @code{backtrace} rather than @code{bt}.
13033 @c FIXME! So how does Joe User discover whether a command is an alias
13035 If an error occurs during the execution of your hook, execution of
13036 @value{GDBN} commands stops and @value{GDBN} issues a prompt
13037 (before the command that you actually typed had a chance to run).
13039 If you try to define a hook which does not match any known command, you
13040 get a warning from the @code{define} command.
13042 @node Command Files
13043 @section Command files
13045 @cindex command files
13046 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
13047 commands. Comments (lines starting with @kbd{#}) may also be included.
13048 An empty line in a command file does nothing; it does not mean to repeat
13049 the last command, as it would from the terminal.
13052 @cindex @file{.gdbinit}
13053 @cindex @file{gdb.ini}
13054 When you start @value{GDBN}, it automatically executes commands from its
13055 @dfn{init files}. These are files named @file{.gdbinit} on Unix and
13056 @file{gdb.ini} on DOS/Windows. During startup, @value{GDBN} does the
13061 Reads the init file (if any) in your home directory@footnote{On
13062 DOS/Windows systems, the home directory is the one pointed to by the
13063 @code{HOME} environment variable.}.
13066 Processes command line options and operands.
13069 Reads the init file (if any) in the current working directory.
13072 Reads command files specified by the @samp{-x} option.
13075 The init file in your home directory can set options (such as @samp{set
13076 complaints}) that affect subsequent processing of command line options
13077 and operands. Init files are not executed if you use the @samp{-nx}
13078 option (@pxref{Mode Options, ,Choosing modes}).
13080 @cindex init file name
13081 On some configurations of @value{GDBN}, the init file is known by a
13082 different name (these are typically environments where a specialized
13083 form of @value{GDBN} may need to coexist with other forms, hence a
13084 different name for the specialized version's init file). These are the
13085 environments with special init file names:
13087 @cindex @file{.vxgdbinit}
13090 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13092 @cindex @file{.os68gdbinit}
13094 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13096 @cindex @file{.esgdbinit}
13098 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13101 You can also request the execution of a command file with the
13102 @code{source} command:
13106 @item source @var{filename}
13107 Execute the command file @var{filename}.
13110 The lines in a command file are executed sequentially. They are not
13111 printed as they are executed. An error in any command terminates execution
13112 of the command file.
13114 Commands that would ask for confirmation if used interactively proceed
13115 without asking when used in a command file. Many @value{GDBN} commands that
13116 normally print messages to say what they are doing omit the messages
13117 when called from command files.
13119 @value{GDBN} also accepts command input from standard input. In this
13120 mode, normal output goes to standard output and error output goes to
13121 standard error. Errors in a command file supplied on standard input do
13122 not terminate execution of the command file --- execution continues with
13126 gdb < cmds > log 2>&1
13129 (The syntax above will vary depending on the shell used.) This example
13130 will execute commands from the file @file{cmds}. All output and errors
13131 would be directed to @file{log}.
13134 @section Commands for controlled output
13136 During the execution of a command file or a user-defined command, normal
13137 @value{GDBN} output is suppressed; the only output that appears is what is
13138 explicitly printed by the commands in the definition. This section
13139 describes three commands useful for generating exactly the output you
13144 @item echo @var{text}
13145 @c I do not consider backslash-space a standard C escape sequence
13146 @c because it is not in ANSI.
13147 Print @var{text}. Nonprinting characters can be included in
13148 @var{text} using C escape sequences, such as @samp{\n} to print a
13149 newline. @strong{No newline is printed unless you specify one.}
13150 In addition to the standard C escape sequences, a backslash followed
13151 by a space stands for a space. This is useful for displaying a
13152 string with spaces at the beginning or the end, since leading and
13153 trailing spaces are otherwise trimmed from all arguments.
13154 To print @samp{@w{ }and foo =@w{ }}, use the command
13155 @samp{echo \@w{ }and foo = \@w{ }}.
13157 A backslash at the end of @var{text} can be used, as in C, to continue
13158 the command onto subsequent lines. For example,
13161 echo This is some text\n\
13162 which is continued\n\
13163 onto several lines.\n
13166 produces the same output as
13169 echo This is some text\n
13170 echo which is continued\n
13171 echo onto several lines.\n
13175 @item output @var{expression}
13176 Print the value of @var{expression} and nothing but that value: no
13177 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13178 value history either. @xref{Expressions, ,Expressions}, for more information
13181 @item output/@var{fmt} @var{expression}
13182 Print the value of @var{expression} in format @var{fmt}. You can use
13183 the same formats as for @code{print}. @xref{Output Formats,,Output
13184 formats}, for more information.
13187 @item printf @var{string}, @var{expressions}@dots{}
13188 Print the values of the @var{expressions} under the control of
13189 @var{string}. The @var{expressions} are separated by commas and may be
13190 either numbers or pointers. Their values are printed as specified by
13191 @var{string}, exactly as if your program were to execute the C
13193 @c FIXME: the above implies that at least all ANSI C formats are
13194 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13195 @c Either this is a bug, or the manual should document what formats are
13199 printf (@var{string}, @var{expressions}@dots{});
13202 For example, you can print two values in hex like this:
13205 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13208 The only backslash-escape sequences that you can use in the format
13209 string are the simple ones that consist of backslash followed by a
13214 @chapter @value{GDBN} Text User Interface
13218 * TUI Overview:: TUI overview
13219 * TUI Keys:: TUI key bindings
13220 * TUI Commands:: TUI specific commands
13221 * TUI Configuration:: TUI configuration variables
13224 The @value{GDBN} Text User Interface, TUI in short,
13225 is a terminal interface which uses the @code{curses} library
13226 to show the source file, the assembly output, the program registers
13227 and @value{GDBN} commands in separate text windows.
13228 The TUI is available only when @value{GDBN} is configured
13229 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13232 @section TUI overview
13234 The TUI has two display modes that can be switched while
13239 A curses (or TUI) mode in which it displays several text
13240 windows on the terminal.
13243 A standard mode which corresponds to the @value{GDBN} configured without
13247 In the TUI mode, @value{GDBN} can display several text window
13252 This window is the @value{GDBN} command window with the @value{GDBN}
13253 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13254 managed using readline but through the TUI. The @emph{command}
13255 window is always visible.
13258 The source window shows the source file of the program. The current
13259 line as well as active breakpoints are displayed in this window.
13260 The current program position is shown with the @samp{>} marker and
13261 active breakpoints are shown with @samp{*} markers.
13264 The assembly window shows the disassembly output of the program.
13267 This window shows the processor registers. It detects when
13268 a register is changed and when this is the case, registers that have
13269 changed are highlighted.
13273 The source, assembly and register windows are attached to the thread
13274 and the frame position. They are updated when the current thread
13275 changes, when the frame changes or when the program counter changes.
13276 These three windows are arranged by the TUI according to several
13277 layouts. The layout defines which of these three windows are visible.
13278 The following layouts are available:
13288 source and assembly
13291 source and registers
13294 assembly and registers
13299 @section TUI Key Bindings
13300 @cindex TUI key bindings
13302 The TUI installs several key bindings in the readline keymaps
13303 (@pxref{Command Line Editing}).
13304 They allow to leave or enter in the TUI mode or they operate
13305 directly on the TUI layout and windows. The following key bindings
13306 are installed for both TUI mode and the @value{GDBN} standard mode.
13315 Enter or leave the TUI mode. When the TUI mode is left,
13316 the curses window management is left and @value{GDBN} operates using
13317 its standard mode writing on the terminal directly. When the TUI
13318 mode is entered, the control is given back to the curses windows.
13319 The screen is then refreshed.
13323 Use a TUI layout with only one window. The layout will
13324 either be @samp{source} or @samp{assembly}. When the TUI mode
13325 is not active, it will switch to the TUI mode.
13327 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13331 Use a TUI layout with at least two windows. When the current
13332 layout shows already two windows, a next layout with two windows is used.
13333 When a new layout is chosen, one window will always be common to the
13334 previous layout and the new one.
13336 Think of it as the Emacs @kbd{C-x 2} binding.
13340 The following key bindings are handled only by the TUI mode:
13345 Scroll the active window one page up.
13349 Scroll the active window one page down.
13353 Scroll the active window one line up.
13357 Scroll the active window one line down.
13361 Scroll the active window one column left.
13365 Scroll the active window one column right.
13369 Refresh the screen.
13373 In the TUI mode, the arrow keys are used by the active window
13374 for scrolling. This means they are not available for readline. It is
13375 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13376 @key{C-b} and @key{C-f}.
13379 @section TUI specific commands
13380 @cindex TUI commands
13382 The TUI has specific commands to control the text windows.
13383 These commands are always available, that is they do not depend on
13384 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13385 is in the standard mode, using these commands will automatically switch
13390 @kindex layout next
13391 Display the next layout.
13394 @kindex layout prev
13395 Display the previous layout.
13399 Display the source window only.
13403 Display the assembly window only.
13406 @kindex layout split
13407 Display the source and assembly window.
13410 @kindex layout regs
13411 Display the register window together with the source or assembly window.
13413 @item focus next | prev | src | asm | regs | split
13415 Set the focus to the named window.
13416 This command allows to change the active window so that scrolling keys
13417 can be affected to another window.
13421 Refresh the screen. This is similar to using @key{C-L} key.
13425 Update the source window and the current execution point.
13427 @item winheight @var{name} +@var{count}
13428 @itemx winheight @var{name} -@var{count}
13430 Change the height of the window @var{name} by @var{count}
13431 lines. Positive counts increase the height, while negative counts
13436 @node TUI Configuration
13437 @section TUI configuration variables
13438 @cindex TUI configuration variables
13440 The TUI has several configuration variables that control the
13441 appearance of windows on the terminal.
13444 @item set tui border-kind @var{kind}
13445 @kindex set tui border-kind
13446 Select the border appearance for the source, assembly and register windows.
13447 The possible values are the following:
13450 Use a space character to draw the border.
13453 Use ascii characters + - and | to draw the border.
13456 Use the Alternate Character Set to draw the border. The border is
13457 drawn using character line graphics if the terminal supports them.
13461 @item set tui active-border-mode @var{mode}
13462 @kindex set tui active-border-mode
13463 Select the attributes to display the border of the active window.
13464 The possible values are @code{normal}, @code{standout}, @code{reverse},
13465 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13467 @item set tui border-mode @var{mode}
13468 @kindex set tui border-mode
13469 Select the attributes to display the border of other windows.
13470 The @var{mode} can be one of the following:
13473 Use normal attributes to display the border.
13479 Use reverse video mode.
13482 Use half bright mode.
13484 @item half-standout
13485 Use half bright and standout mode.
13488 Use extra bright or bold mode.
13490 @item bold-standout
13491 Use extra bright or bold and standout mode.
13498 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13501 @cindex @sc{gnu} Emacs
13502 A special interface allows you to use @sc{gnu} Emacs to view (and
13503 edit) the source files for the program you are debugging with
13506 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13507 executable file you want to debug as an argument. This command starts
13508 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13509 created Emacs buffer.
13510 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13512 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13517 All ``terminal'' input and output goes through the Emacs buffer.
13520 This applies both to @value{GDBN} commands and their output, and to the input
13521 and output done by the program you are debugging.
13523 This is useful because it means that you can copy the text of previous
13524 commands and input them again; you can even use parts of the output
13527 All the facilities of Emacs' Shell mode are available for interacting
13528 with your program. In particular, you can send signals the usual
13529 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13534 @value{GDBN} displays source code through Emacs.
13537 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13538 source file for that frame and puts an arrow (@samp{=>}) at the
13539 left margin of the current line. Emacs uses a separate buffer for
13540 source display, and splits the screen to show both your @value{GDBN} session
13543 Explicit @value{GDBN} @code{list} or search commands still produce output as
13544 usual, but you probably have no reason to use them from Emacs.
13547 @emph{Warning:} If the directory where your program resides is not your
13548 current directory, it can be easy to confuse Emacs about the location of
13549 the source files, in which case the auxiliary display buffer does not
13550 appear to show your source. @value{GDBN} can find programs by searching your
13551 environment's @code{PATH} variable, so the @value{GDBN} input and output
13552 session proceeds normally; but Emacs does not get enough information
13553 back from @value{GDBN} to locate the source files in this situation. To
13554 avoid this problem, either start @value{GDBN} mode from the directory where
13555 your program resides, or specify an absolute file name when prompted for the
13556 @kbd{M-x gdb} argument.
13558 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13559 switch to debugging a program in some other location, from an existing
13560 @value{GDBN} buffer in Emacs.
13563 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13564 you need to call @value{GDBN} by a different name (for example, if you keep
13565 several configurations around, with different names) you can set the
13566 Emacs variable @code{gdb-command-name}; for example,
13569 (setq gdb-command-name "mygdb")
13573 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13574 in your @file{.emacs} file) makes Emacs call the program named
13575 ``@code{mygdb}'' instead.
13577 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13578 addition to the standard Shell mode commands:
13582 Describe the features of Emacs' @value{GDBN} Mode.
13585 Execute to another source line, like the @value{GDBN} @code{step} command; also
13586 update the display window to show the current file and location.
13589 Execute to next source line in this function, skipping all function
13590 calls, like the @value{GDBN} @code{next} command. Then update the display window
13591 to show the current file and location.
13594 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13595 display window accordingly.
13597 @item M-x gdb-nexti
13598 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13599 display window accordingly.
13602 Execute until exit from the selected stack frame, like the @value{GDBN}
13603 @code{finish} command.
13606 Continue execution of your program, like the @value{GDBN} @code{continue}
13609 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13612 Go up the number of frames indicated by the numeric argument
13613 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13614 like the @value{GDBN} @code{up} command.
13616 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13619 Go down the number of frames indicated by the numeric argument, like the
13620 @value{GDBN} @code{down} command.
13622 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13625 Read the number where the cursor is positioned, and insert it at the end
13626 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13627 around an address that was displayed earlier, type @kbd{disassemble};
13628 then move the cursor to the address display, and pick up the
13629 argument for @code{disassemble} by typing @kbd{C-x &}.
13631 You can customize this further by defining elements of the list
13632 @code{gdb-print-command}; once it is defined, you can format or
13633 otherwise process numbers picked up by @kbd{C-x &} before they are
13634 inserted. A numeric argument to @kbd{C-x &} indicates that you
13635 wish special formatting, and also acts as an index to pick an element of the
13636 list. If the list element is a string, the number to be inserted is
13637 formatted using the Emacs function @code{format}; otherwise the number
13638 is passed as an argument to the corresponding list element.
13641 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13642 tells @value{GDBN} to set a breakpoint on the source line point is on.
13644 If you accidentally delete the source-display buffer, an easy way to get
13645 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13646 request a frame display; when you run under Emacs, this recreates
13647 the source buffer if necessary to show you the context of the current
13650 The source files displayed in Emacs are in ordinary Emacs buffers
13651 which are visiting the source files in the usual way. You can edit
13652 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13653 communicates with Emacs in terms of line numbers. If you add or
13654 delete lines from the text, the line numbers that @value{GDBN} knows cease
13655 to correspond properly with the code.
13657 @c The following dropped because Epoch is nonstandard. Reactivate
13658 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13660 @kindex Emacs Epoch environment
13664 Version 18 of @sc{gnu} Emacs has a built-in window system
13665 called the @code{epoch}
13666 environment. Users of this environment can use a new command,
13667 @code{inspect} which performs identically to @code{print} except that
13668 each value is printed in its own window.
13671 @include annotate.texi
13672 @include gdbmi.texinfo
13675 @chapter Reporting Bugs in @value{GDBN}
13676 @cindex bugs in @value{GDBN}
13677 @cindex reporting bugs in @value{GDBN}
13679 Your bug reports play an essential role in making @value{GDBN} reliable.
13681 Reporting a bug may help you by bringing a solution to your problem, or it
13682 may not. But in any case the principal function of a bug report is to help
13683 the entire community by making the next version of @value{GDBN} work better. Bug
13684 reports are your contribution to the maintenance of @value{GDBN}.
13686 In order for a bug report to serve its purpose, you must include the
13687 information that enables us to fix the bug.
13690 * Bug Criteria:: Have you found a bug?
13691 * Bug Reporting:: How to report bugs
13695 @section Have you found a bug?
13696 @cindex bug criteria
13698 If you are not sure whether you have found a bug, here are some guidelines:
13701 @cindex fatal signal
13702 @cindex debugger crash
13703 @cindex crash of debugger
13705 If the debugger gets a fatal signal, for any input whatever, that is a
13706 @value{GDBN} bug. Reliable debuggers never crash.
13708 @cindex error on valid input
13710 If @value{GDBN} produces an error message for valid input, that is a
13711 bug. (Note that if you're cross debugging, the problem may also be
13712 somewhere in the connection to the target.)
13714 @cindex invalid input
13716 If @value{GDBN} does not produce an error message for invalid input,
13717 that is a bug. However, you should note that your idea of
13718 ``invalid input'' might be our idea of ``an extension'' or ``support
13719 for traditional practice''.
13722 If you are an experienced user of debugging tools, your suggestions
13723 for improvement of @value{GDBN} are welcome in any case.
13726 @node Bug Reporting
13727 @section How to report bugs
13728 @cindex bug reports
13729 @cindex @value{GDBN} bugs, reporting
13731 A number of companies and individuals offer support for @sc{gnu} products.
13732 If you obtained @value{GDBN} from a support organization, we recommend you
13733 contact that organization first.
13735 You can find contact information for many support companies and
13736 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13738 @c should add a web page ref...
13740 In any event, we also recommend that you send bug reports for
13741 @value{GDBN} to this addresses:
13747 @strong{Do not send bug reports to @samp{info-gdb}, or to
13748 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13749 not want to receive bug reports. Those that do have arranged to receive
13752 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13753 serves as a repeater. The mailing list and the newsgroup carry exactly
13754 the same messages. Often people think of posting bug reports to the
13755 newsgroup instead of mailing them. This appears to work, but it has one
13756 problem which can be crucial: a newsgroup posting often lacks a mail
13757 path back to the sender. Thus, if we need to ask for more information,
13758 we may be unable to reach you. For this reason, it is better to send
13759 bug reports to the mailing list.
13761 As a last resort, send bug reports on paper to:
13764 @sc{gnu} Debugger Bugs
13765 Free Software Foundation Inc.
13766 59 Temple Place - Suite 330
13767 Boston, MA 02111-1307
13771 The fundamental principle of reporting bugs usefully is this:
13772 @strong{report all the facts}. If you are not sure whether to state a
13773 fact or leave it out, state it!
13775 Often people omit facts because they think they know what causes the
13776 problem and assume that some details do not matter. Thus, you might
13777 assume that the name of the variable you use in an example does not matter.
13778 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13779 stray memory reference which happens to fetch from the location where that
13780 name is stored in memory; perhaps, if the name were different, the contents
13781 of that location would fool the debugger into doing the right thing despite
13782 the bug. Play it safe and give a specific, complete example. That is the
13783 easiest thing for you to do, and the most helpful.
13785 Keep in mind that the purpose of a bug report is to enable us to fix the
13786 bug. It may be that the bug has been reported previously, but neither
13787 you nor we can know that unless your bug report is complete and
13790 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13791 bell?'' Those bug reports are useless, and we urge everyone to
13792 @emph{refuse to respond to them} except to chide the sender to report
13795 To enable us to fix the bug, you should include all these things:
13799 The version of @value{GDBN}. @value{GDBN} announces it if you start
13800 with no arguments; you can also print it at any time using @code{show
13803 Without this, we will not know whether there is any point in looking for
13804 the bug in the current version of @value{GDBN}.
13807 The type of machine you are using, and the operating system name and
13811 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13812 ``@value{GCC}--2.8.1''.
13815 What compiler (and its version) was used to compile the program you are
13816 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13817 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13818 information; for other compilers, see the documentation for those
13822 The command arguments you gave the compiler to compile your example and
13823 observe the bug. For example, did you use @samp{-O}? To guarantee
13824 you will not omit something important, list them all. A copy of the
13825 Makefile (or the output from make) is sufficient.
13827 If we were to try to guess the arguments, we would probably guess wrong
13828 and then we might not encounter the bug.
13831 A complete input script, and all necessary source files, that will
13835 A description of what behavior you observe that you believe is
13836 incorrect. For example, ``It gets a fatal signal.''
13838 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13839 will certainly notice it. But if the bug is incorrect output, we might
13840 not notice unless it is glaringly wrong. You might as well not give us
13841 a chance to make a mistake.
13843 Even if the problem you experience is a fatal signal, you should still
13844 say so explicitly. Suppose something strange is going on, such as, your
13845 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13846 the C library on your system. (This has happened!) Your copy might
13847 crash and ours would not. If you told us to expect a crash, then when
13848 ours fails to crash, we would know that the bug was not happening for
13849 us. If you had not told us to expect a crash, then we would not be able
13850 to draw any conclusion from our observations.
13853 If you wish to suggest changes to the @value{GDBN} source, send us context
13854 diffs. If you even discuss something in the @value{GDBN} source, refer to
13855 it by context, not by line number.
13857 The line numbers in our development sources will not match those in your
13858 sources. Your line numbers would convey no useful information to us.
13862 Here are some things that are not necessary:
13866 A description of the envelope of the bug.
13868 Often people who encounter a bug spend a lot of time investigating
13869 which changes to the input file will make the bug go away and which
13870 changes will not affect it.
13872 This is often time consuming and not very useful, because the way we
13873 will find the bug is by running a single example under the debugger
13874 with breakpoints, not by pure deduction from a series of examples.
13875 We recommend that you save your time for something else.
13877 Of course, if you can find a simpler example to report @emph{instead}
13878 of the original one, that is a convenience for us. Errors in the
13879 output will be easier to spot, running under the debugger will take
13880 less time, and so on.
13882 However, simplification is not vital; if you do not want to do this,
13883 report the bug anyway and send us the entire test case you used.
13886 A patch for the bug.
13888 A patch for the bug does help us if it is a good one. But do not omit
13889 the necessary information, such as the test case, on the assumption that
13890 a patch is all we need. We might see problems with your patch and decide
13891 to fix the problem another way, or we might not understand it at all.
13893 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13894 construct an example that will make the program follow a certain path
13895 through the code. If you do not send us the example, we will not be able
13896 to construct one, so we will not be able to verify that the bug is fixed.
13898 And if we cannot understand what bug you are trying to fix, or why your
13899 patch should be an improvement, we will not install it. A test case will
13900 help us to understand.
13903 A guess about what the bug is or what it depends on.
13905 Such guesses are usually wrong. Even we cannot guess right about such
13906 things without first using the debugger to find the facts.
13909 @c The readline documentation is distributed with the readline code
13910 @c and consists of the two following files:
13912 @c inc-hist.texinfo
13913 @c Use -I with makeinfo to point to the appropriate directory,
13914 @c environment var TEXINPUTS with TeX.
13915 @include rluser.texinfo
13916 @include inc-hist.texinfo
13919 @node Formatting Documentation
13920 @appendix Formatting Documentation
13922 @cindex @value{GDBN} reference card
13923 @cindex reference card
13924 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13925 for printing with PostScript or Ghostscript, in the @file{gdb}
13926 subdirectory of the main source directory@footnote{In
13927 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13928 release.}. If you can use PostScript or Ghostscript with your printer,
13929 you can print the reference card immediately with @file{refcard.ps}.
13931 The release also includes the source for the reference card. You
13932 can format it, using @TeX{}, by typing:
13938 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13939 mode on US ``letter'' size paper;
13940 that is, on a sheet 11 inches wide by 8.5 inches
13941 high. You will need to specify this form of printing as an option to
13942 your @sc{dvi} output program.
13944 @cindex documentation
13946 All the documentation for @value{GDBN} comes as part of the machine-readable
13947 distribution. The documentation is written in Texinfo format, which is
13948 a documentation system that uses a single source file to produce both
13949 on-line information and a printed manual. You can use one of the Info
13950 formatting commands to create the on-line version of the documentation
13951 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13953 @value{GDBN} includes an already formatted copy of the on-line Info
13954 version of this manual in the @file{gdb} subdirectory. The main Info
13955 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13956 subordinate files matching @samp{gdb.info*} in the same directory. If
13957 necessary, you can print out these files, or read them with any editor;
13958 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13959 Emacs or the standalone @code{info} program, available as part of the
13960 @sc{gnu} Texinfo distribution.
13962 If you want to format these Info files yourself, you need one of the
13963 Info formatting programs, such as @code{texinfo-format-buffer} or
13966 If you have @code{makeinfo} installed, and are in the top level
13967 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13968 version @value{GDBVN}), you can make the Info file by typing:
13975 If you want to typeset and print copies of this manual, you need @TeX{},
13976 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13977 Texinfo definitions file.
13979 @TeX{} is a typesetting program; it does not print files directly, but
13980 produces output files called @sc{dvi} files. To print a typeset
13981 document, you need a program to print @sc{dvi} files. If your system
13982 has @TeX{} installed, chances are it has such a program. The precise
13983 command to use depends on your system; @kbd{lpr -d} is common; another
13984 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
13985 require a file name without any extension or a @samp{.dvi} extension.
13987 @TeX{} also requires a macro definitions file called
13988 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
13989 written in Texinfo format. On its own, @TeX{} cannot either read or
13990 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
13991 and is located in the @file{gdb-@var{version-number}/texinfo}
13994 If you have @TeX{} and a @sc{dvi} printer program installed, you can
13995 typeset and print this manual. First switch to the the @file{gdb}
13996 subdirectory of the main source directory (for example, to
13997 @file{gdb-@value{GDBVN}/gdb}) and type:
14003 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14005 @node Installing GDB
14006 @appendix Installing @value{GDBN}
14007 @cindex configuring @value{GDBN}
14008 @cindex installation
14010 @value{GDBN} comes with a @code{configure} script that automates the process
14011 of preparing @value{GDBN} for installation; you can then use @code{make} to
14012 build the @code{gdb} program.
14014 @c irrelevant in info file; it's as current as the code it lives with.
14015 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14016 look at the @file{README} file in the sources; we may have improved the
14017 installation procedures since publishing this manual.}
14020 The @value{GDBN} distribution includes all the source code you need for
14021 @value{GDBN} in a single directory, whose name is usually composed by
14022 appending the version number to @samp{gdb}.
14024 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14025 @file{gdb-@value{GDBVN}} directory. That directory contains:
14028 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14029 script for configuring @value{GDBN} and all its supporting libraries
14031 @item gdb-@value{GDBVN}/gdb
14032 the source specific to @value{GDBN} itself
14034 @item gdb-@value{GDBVN}/bfd
14035 source for the Binary File Descriptor library
14037 @item gdb-@value{GDBVN}/include
14038 @sc{gnu} include files
14040 @item gdb-@value{GDBVN}/libiberty
14041 source for the @samp{-liberty} free software library
14043 @item gdb-@value{GDBVN}/opcodes
14044 source for the library of opcode tables and disassemblers
14046 @item gdb-@value{GDBVN}/readline
14047 source for the @sc{gnu} command-line interface
14049 @item gdb-@value{GDBVN}/glob
14050 source for the @sc{gnu} filename pattern-matching subroutine
14052 @item gdb-@value{GDBVN}/mmalloc
14053 source for the @sc{gnu} memory-mapped malloc package
14056 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14057 from the @file{gdb-@var{version-number}} source directory, which in
14058 this example is the @file{gdb-@value{GDBVN}} directory.
14060 First switch to the @file{gdb-@var{version-number}} source directory
14061 if you are not already in it; then run @code{configure}. Pass the
14062 identifier for the platform on which @value{GDBN} will run as an
14068 cd gdb-@value{GDBVN}
14069 ./configure @var{host}
14074 where @var{host} is an identifier such as @samp{sun4} or
14075 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14076 (You can often leave off @var{host}; @code{configure} tries to guess the
14077 correct value by examining your system.)
14079 Running @samp{configure @var{host}} and then running @code{make} builds the
14080 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14081 libraries, then @code{gdb} itself. The configured source files, and the
14082 binaries, are left in the corresponding source directories.
14085 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14086 system does not recognize this automatically when you run a different
14087 shell, you may need to run @code{sh} on it explicitly:
14090 sh configure @var{host}
14093 If you run @code{configure} from a directory that contains source
14094 directories for multiple libraries or programs, such as the
14095 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14096 creates configuration files for every directory level underneath (unless
14097 you tell it not to, with the @samp{--norecursion} option).
14099 You can run the @code{configure} script from any of the
14100 subordinate directories in the @value{GDBN} distribution if you only want to
14101 configure that subdirectory, but be sure to specify a path to it.
14103 For example, with version @value{GDBVN}, type the following to configure only
14104 the @code{bfd} subdirectory:
14108 cd gdb-@value{GDBVN}/bfd
14109 ../configure @var{host}
14113 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14114 However, you should make sure that the shell on your path (named by
14115 the @samp{SHELL} environment variable) is publicly readable. Remember
14116 that @value{GDBN} uses the shell to start your program---some systems refuse to
14117 let @value{GDBN} debug child processes whose programs are not readable.
14120 * Separate Objdir:: Compiling @value{GDBN} in another directory
14121 * Config Names:: Specifying names for hosts and targets
14122 * Configure Options:: Summary of options for configure
14125 @node Separate Objdir
14126 @section Compiling @value{GDBN} in another directory
14128 If you want to run @value{GDBN} versions for several host or target machines,
14129 you need a different @code{gdb} compiled for each combination of
14130 host and target. @code{configure} is designed to make this easy by
14131 allowing you to generate each configuration in a separate subdirectory,
14132 rather than in the source directory. If your @code{make} program
14133 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14134 @code{make} in each of these directories builds the @code{gdb}
14135 program specified there.
14137 To build @code{gdb} in a separate directory, run @code{configure}
14138 with the @samp{--srcdir} option to specify where to find the source.
14139 (You also need to specify a path to find @code{configure}
14140 itself from your working directory. If the path to @code{configure}
14141 would be the same as the argument to @samp{--srcdir}, you can leave out
14142 the @samp{--srcdir} option; it is assumed.)
14144 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14145 separate directory for a Sun 4 like this:
14149 cd gdb-@value{GDBVN}
14152 ../gdb-@value{GDBVN}/configure sun4
14157 When @code{configure} builds a configuration using a remote source
14158 directory, it creates a tree for the binaries with the same structure
14159 (and using the same names) as the tree under the source directory. In
14160 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14161 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14162 @file{gdb-sun4/gdb}.
14164 One popular reason to build several @value{GDBN} configurations in separate
14165 directories is to configure @value{GDBN} for cross-compiling (where
14166 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14167 programs that run on another machine---the @dfn{target}).
14168 You specify a cross-debugging target by
14169 giving the @samp{--target=@var{target}} option to @code{configure}.
14171 When you run @code{make} to build a program or library, you must run
14172 it in a configured directory---whatever directory you were in when you
14173 called @code{configure} (or one of its subdirectories).
14175 The @code{Makefile} that @code{configure} generates in each source
14176 directory also runs recursively. If you type @code{make} in a source
14177 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14178 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14179 will build all the required libraries, and then build GDB.
14181 When you have multiple hosts or targets configured in separate
14182 directories, you can run @code{make} on them in parallel (for example,
14183 if they are NFS-mounted on each of the hosts); they will not interfere
14187 @section Specifying names for hosts and targets
14189 The specifications used for hosts and targets in the @code{configure}
14190 script are based on a three-part naming scheme, but some short predefined
14191 aliases are also supported. The full naming scheme encodes three pieces
14192 of information in the following pattern:
14195 @var{architecture}-@var{vendor}-@var{os}
14198 For example, you can use the alias @code{sun4} as a @var{host} argument,
14199 or as the value for @var{target} in a @code{--target=@var{target}}
14200 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14202 The @code{configure} script accompanying @value{GDBN} does not provide
14203 any query facility to list all supported host and target names or
14204 aliases. @code{configure} calls the Bourne shell script
14205 @code{config.sub} to map abbreviations to full names; you can read the
14206 script, if you wish, or you can use it to test your guesses on
14207 abbreviations---for example:
14210 % sh config.sub i386-linux
14212 % sh config.sub alpha-linux
14213 alpha-unknown-linux-gnu
14214 % sh config.sub hp9k700
14216 % sh config.sub sun4
14217 sparc-sun-sunos4.1.1
14218 % sh config.sub sun3
14219 m68k-sun-sunos4.1.1
14220 % sh config.sub i986v
14221 Invalid configuration `i986v': machine `i986v' not recognized
14225 @code{config.sub} is also distributed in the @value{GDBN} source
14226 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14228 @node Configure Options
14229 @section @code{configure} options
14231 Here is a summary of the @code{configure} options and arguments that
14232 are most often useful for building @value{GDBN}. @code{configure} also has
14233 several other options not listed here. @inforef{What Configure
14234 Does,,configure.info}, for a full explanation of @code{configure}.
14237 configure @r{[}--help@r{]}
14238 @r{[}--prefix=@var{dir}@r{]}
14239 @r{[}--exec-prefix=@var{dir}@r{]}
14240 @r{[}--srcdir=@var{dirname}@r{]}
14241 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14242 @r{[}--target=@var{target}@r{]}
14247 You may introduce options with a single @samp{-} rather than
14248 @samp{--} if you prefer; but you may abbreviate option names if you use
14253 Display a quick summary of how to invoke @code{configure}.
14255 @item --prefix=@var{dir}
14256 Configure the source to install programs and files under directory
14259 @item --exec-prefix=@var{dir}
14260 Configure the source to install programs under directory
14263 @c avoid splitting the warning from the explanation:
14265 @item --srcdir=@var{dirname}
14266 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14267 @code{make} that implements the @code{VPATH} feature.}@*
14268 Use this option to make configurations in directories separate from the
14269 @value{GDBN} source directories. Among other things, you can use this to
14270 build (or maintain) several configurations simultaneously, in separate
14271 directories. @code{configure} writes configuration specific files in
14272 the current directory, but arranges for them to use the source in the
14273 directory @var{dirname}. @code{configure} creates directories under
14274 the working directory in parallel to the source directories below
14277 @item --norecursion
14278 Configure only the directory level where @code{configure} is executed; do not
14279 propagate configuration to subdirectories.
14281 @item --target=@var{target}
14282 Configure @value{GDBN} for cross-debugging programs running on the specified
14283 @var{target}. Without this option, @value{GDBN} is configured to debug
14284 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14286 There is no convenient way to generate a list of all available targets.
14288 @item @var{host} @dots{}
14289 Configure @value{GDBN} to run on the specified @var{host}.
14291 There is no convenient way to generate a list of all available hosts.
14294 There are many other options available as well, but they are generally
14295 needed for special purposes only.
14303 % I think something like @colophon should be in texinfo. In the
14305 \long\def\colophon{\hbox to0pt{}\vfill
14306 \centerline{The body of this manual is set in}
14307 \centerline{\fontname\tenrm,}
14308 \centerline{with headings in {\bf\fontname\tenbf}}
14309 \centerline{and examples in {\tt\fontname\tentt}.}
14310 \centerline{{\it\fontname\tenit\/},}
14311 \centerline{{\bf\fontname\tenbf}, and}
14312 \centerline{{\sl\fontname\tensl\/}}
14313 \centerline{are used for emphasis.}\vfill}
14315 % Blame: doc@cygnus.com, 1991.
14318 @c TeX can handle the contents at the start but makeinfo 3.12 can not