1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002
4 @c Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
25 @c readline appendices use @vindex, @findex and @ftable,
26 @c annotate.texi and gdbmi use @findex.
30 @c !!set GDB manual's edition---not the same as GDB version!
33 @c !!set GDB manual's revision date
34 @set DATE December 2001
36 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Programming & development tools.
42 * Gdb: (gdb). The @sc{gnu} debugger.
46 This file documents the @sc{gnu} debugger @value{GDBN}.
49 This is the @value{EDITION} Edition, @value{DATE},
50 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
51 for @value{GDBN} Version @value{GDBVN}.
53 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,@*
54 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
56 Permission is granted to copy, distribute and/or modify this document
57 under the terms of the GNU Free Documentation License, Version 1.1 or
58 any later version published by the Free Software Foundation; with the
59 Invariant Sections being ``Free Software'' and ``Free Software Needs
60 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
61 and with the Back-Cover Texts as in (a) below.
63 (a) The Free Software Foundation's Back-Cover Text is: ``You have
64 freedom to copy and modify this GNU Manual, like GNU software. Copies
65 published by the Free Software Foundation raise funds for GNU
70 @title Debugging with @value{GDBN}
71 @subtitle The @sc{gnu} Source-Level Debugger
73 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
74 @subtitle @value{DATE}
75 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
79 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
80 \hfill {\it Debugging with @value{GDBN}}\par
81 \hfill \TeX{}info \texinfoversion\par
85 @vskip 0pt plus 1filll
86 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
87 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
89 Published by the Free Software Foundation @*
90 59 Temple Place - Suite 330, @*
91 Boston, MA 02111-1307 USA @*
94 Permission is granted to copy, distribute and/or modify this document
95 under the terms of the GNU Free Documentation License, Version 1.1 or
96 any later version published by the Free Software Foundation; with the
97 Invariant Sections being ``Free Software'' and ``Free Software Needs
98 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
99 and with the Back-Cover Texts as in (a) below.
101 (a) The Free Software Foundation's Back-Cover Text is: ``You have
102 freedom to copy and modify this GNU Manual, like GNU software. Copies
103 published by the Free Software Foundation raise funds for GNU
109 @node Top, Summary, (dir), (dir)
111 @top Debugging with @value{GDBN}
113 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
115 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
118 Copyright (C) 1988-2002 Free Software Foundation, Inc.
121 * Summary:: Summary of @value{GDBN}
122 * Sample Session:: A sample @value{GDBN} session
124 * Invocation:: Getting in and out of @value{GDBN}
125 * Commands:: @value{GDBN} commands
126 * Running:: Running programs under @value{GDBN}
127 * Stopping:: Stopping and continuing
128 * Stack:: Examining the stack
129 * Source:: Examining source files
130 * Data:: Examining data
131 * Macros:: Preprocessor Macros
132 * Tracepoints:: Debugging remote targets non-intrusively
133 * Overlays:: Debugging programs that use overlays
135 * Languages:: Using @value{GDBN} with different languages
137 * Symbols:: Examining the symbol table
138 * Altering:: Altering execution
139 * GDB Files:: @value{GDBN} files
140 * Targets:: Specifying a debugging target
141 * Remote Debugging:: Debugging remote programs
142 * Configurations:: Configuration-specific information
143 * Controlling GDB:: Controlling @value{GDBN}
144 * Sequences:: Canned sequences of commands
145 * TUI:: @value{GDBN} Text User Interface
146 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
147 * Annotations:: @value{GDBN}'s annotation interface.
148 * GDB/MI:: @value{GDBN}'s Machine Interface.
150 * GDB Bugs:: Reporting bugs in @value{GDBN}
151 * Formatting Documentation:: How to format and print @value{GDBN} documentation
153 * Command Line Editing:: Command Line Editing
154 * Using History Interactively:: Using History Interactively
155 * Installing GDB:: Installing GDB
156 * Maintenance Commands:: Maintenance Commands
157 * Remote Protocol:: GDB Remote Serial Protocol
158 * Copying:: GNU General Public License says
159 how you can copy and share GDB
160 * GNU Free Documentation License:: The license for this documentation
169 @unnumbered Summary of @value{GDBN}
171 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
172 going on ``inside'' another program while it executes---or what another
173 program was doing at the moment it crashed.
175 @value{GDBN} can do four main kinds of things (plus other things in support of
176 these) to help you catch bugs in the act:
180 Start your program, specifying anything that might affect its behavior.
183 Make your program stop on specified conditions.
186 Examine what has happened, when your program has stopped.
189 Change things in your program, so you can experiment with correcting the
190 effects of one bug and go on to learn about another.
193 You can use @value{GDBN} to debug programs written in C and C++.
194 For more information, see @ref{Support,,Supported languages}.
195 For more information, see @ref{C,,C and C++}.
199 Support for Modula-2 and Chill is partial. For information on Modula-2,
200 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
203 Debugging Pascal programs which use sets, subranges, file variables, or
204 nested functions does not currently work. @value{GDBN} does not support
205 entering expressions, printing values, or similar features using Pascal
209 @value{GDBN} can be used to debug programs written in Fortran, although
210 it may be necessary to refer to some variables with a trailing
214 * Free Software:: Freely redistributable software
215 * Contributors:: Contributors to GDB
219 @unnumberedsec Free software
221 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
222 General Public License
223 (GPL). The GPL gives you the freedom to copy or adapt a licensed
224 program---but every person getting a copy also gets with it the
225 freedom to modify that copy (which means that they must get access to
226 the source code), and the freedom to distribute further copies.
227 Typical software companies use copyrights to limit your freedoms; the
228 Free Software Foundation uses the GPL to preserve these freedoms.
230 Fundamentally, the General Public License is a license which says that
231 you have these freedoms and that you cannot take these freedoms away
234 @unnumberedsec Free Software Needs Free Documentation
236 The biggest deficiency in the free software community today is not in
237 the software---it is the lack of good free documentation that we can
238 include with the free software. Many of our most important
239 programs do not come with free reference manuals and free introductory
240 texts. Documentation is an essential part of any software package;
241 when an important free software package does not come with a free
242 manual and a free tutorial, that is a major gap. We have many such
245 Consider Perl, for instance. The tutorial manuals that people
246 normally use are non-free. How did this come about? Because the
247 authors of those manuals published them with restrictive terms---no
248 copying, no modification, source files not available---which exclude
249 them from the free software world.
251 That wasn't the first time this sort of thing happened, and it was far
252 from the last. Many times we have heard a GNU user eagerly describe a
253 manual that he is writing, his intended contribution to the community,
254 only to learn that he had ruined everything by signing a publication
255 contract to make it non-free.
257 Free documentation, like free software, is a matter of freedom, not
258 price. The problem with the non-free manual is not that publishers
259 charge a price for printed copies---that in itself is fine. (The Free
260 Software Foundation sells printed copies of manuals, too.) The
261 problem is the restrictions on the use of the manual. Free manuals
262 are available in source code form, and give you permission to copy and
263 modify. Non-free manuals do not allow this.
265 The criteria of freedom for a free manual are roughly the same as for
266 free software. Redistribution (including the normal kinds of
267 commercial redistribution) must be permitted, so that the manual can
268 accompany every copy of the program, both on-line and on paper.
270 Permission for modification of the technical content is crucial too.
271 When people modify the software, adding or changing features, if they
272 are conscientious they will change the manual too---so they can
273 provide accurate and clear documentation for the modified program. A
274 manual that leaves you no choice but to write a new manual to document
275 a changed version of the program is not really available to our
278 Some kinds of limits on the way modification is handled are
279 acceptable. For example, requirements to preserve the original
280 author's copyright notice, the distribution terms, or the list of
281 authors, are ok. It is also no problem to require modified versions
282 to include notice that they were modified. Even entire sections that
283 may not be deleted or changed are acceptable, as long as they deal
284 with nontechnical topics (like this one). These kinds of restrictions
285 are acceptable because they don't obstruct the community's normal use
288 However, it must be possible to modify all the @emph{technical}
289 content of the manual, and then distribute the result in all the usual
290 media, through all the usual channels. Otherwise, the restrictions
291 obstruct the use of the manual, it is not free, and we need another
292 manual to replace it.
294 Please spread the word about this issue. Our community continues to
295 lose manuals to proprietary publishing. If we spread the word that
296 free software needs free reference manuals and free tutorials, perhaps
297 the next person who wants to contribute by writing documentation will
298 realize, before it is too late, that only free manuals contribute to
299 the free software community.
301 If you are writing documentation, please insist on publishing it under
302 the GNU Free Documentation License or another free documentation
303 license. Remember that this decision requires your approval---you
304 don't have to let the publisher decide. Some commercial publishers
305 will use a free license if you insist, but they will not propose the
306 option; it is up to you to raise the issue and say firmly that this is
307 what you want. If the publisher you are dealing with refuses, please
308 try other publishers. If you're not sure whether a proposed license
309 is free, write to @email{licensing@@gnu.org}.
311 You can encourage commercial publishers to sell more free, copylefted
312 manuals and tutorials by buying them, and particularly by buying
313 copies from the publishers that paid for their writing or for major
314 improvements. Meanwhile, try to avoid buying non-free documentation
315 at all. Check the distribution terms of a manual before you buy it,
316 and insist that whoever seeks your business must respect your freedom.
317 Check the history of the book, and try to reward the publishers that
318 have paid or pay the authors to work on it.
320 The Free Software Foundation maintains a list of free documentation
321 published by other publishers, at
322 @url{http://www.fsf.org/doc/other-free-books.html}.
325 @unnumberedsec Contributors to @value{GDBN}
327 Richard Stallman was the original author of @value{GDBN}, and of many
328 other @sc{gnu} programs. Many others have contributed to its
329 development. This section attempts to credit major contributors. One
330 of the virtues of free software is that everyone is free to contribute
331 to it; with regret, we cannot actually acknowledge everyone here. The
332 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
333 blow-by-blow account.
335 Changes much prior to version 2.0 are lost in the mists of time.
338 @emph{Plea:} Additions to this section are particularly welcome. If you
339 or your friends (or enemies, to be evenhanded) have been unfairly
340 omitted from this list, we would like to add your names!
343 So that they may not regard their many labors as thankless, we
344 particularly thank those who shepherded @value{GDBN} through major
346 Andrew Cagney (releases 5.0 and 5.1);
347 Jim Blandy (release 4.18);
348 Jason Molenda (release 4.17);
349 Stan Shebs (release 4.14);
350 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
351 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
352 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
353 Jim Kingdon (releases 3.5, 3.4, and 3.3);
354 and Randy Smith (releases 3.2, 3.1, and 3.0).
356 Richard Stallman, assisted at various times by Peter TerMaat, Chris
357 Hanson, and Richard Mlynarik, handled releases through 2.8.
359 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
360 in @value{GDBN}, with significant additional contributions from Per
361 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
362 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
363 much general update work leading to release 3.0).
365 @value{GDBN} uses the BFD subroutine library to examine multiple
366 object-file formats; BFD was a joint project of David V.
367 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
369 David Johnson wrote the original COFF support; Pace Willison did
370 the original support for encapsulated COFF.
372 Brent Benson of Harris Computer Systems contributed DWARF2 support.
374 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
375 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
377 Jean-Daniel Fekete contributed Sun 386i support.
378 Chris Hanson improved the HP9000 support.
379 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
380 David Johnson contributed Encore Umax support.
381 Jyrki Kuoppala contributed Altos 3068 support.
382 Jeff Law contributed HP PA and SOM support.
383 Keith Packard contributed NS32K support.
384 Doug Rabson contributed Acorn Risc Machine support.
385 Bob Rusk contributed Harris Nighthawk CX-UX support.
386 Chris Smith contributed Convex support (and Fortran debugging).
387 Jonathan Stone contributed Pyramid support.
388 Michael Tiemann contributed SPARC support.
389 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
390 Pace Willison contributed Intel 386 support.
391 Jay Vosburgh contributed Symmetry support.
393 Andreas Schwab contributed M68K Linux support.
395 Rich Schaefer and Peter Schauer helped with support of SunOS shared
398 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
399 about several machine instruction sets.
401 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
402 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
403 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
404 and RDI targets, respectively.
406 Brian Fox is the author of the readline libraries providing
407 command-line editing and command history.
409 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
410 Modula-2 support, and contributed the Languages chapter of this manual.
412 Fred Fish wrote most of the support for Unix System Vr4.
413 He also enhanced the command-completion support to cover C@t{++} overloaded
416 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
419 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
421 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
423 Toshiba sponsored the support for the TX39 Mips processor.
425 Matsushita sponsored the support for the MN10200 and MN10300 processors.
427 Fujitsu sponsored the support for SPARClite and FR30 processors.
429 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
432 Michael Snyder added support for tracepoints.
434 Stu Grossman wrote gdbserver.
436 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
437 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
439 The following people at the Hewlett-Packard Company contributed
440 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
441 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
442 compiler, and the terminal user interface: Ben Krepp, Richard Title,
443 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
444 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
445 information in this manual.
447 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
448 Robert Hoehne made significant contributions to the DJGPP port.
450 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
451 development since 1991. Cygnus engineers who have worked on @value{GDBN}
452 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
453 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
454 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
455 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
456 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
457 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
458 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
459 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
460 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
461 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
462 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
463 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
464 Zuhn have made contributions both large and small.
466 Jim Blandy added support for preprocessor macros, while working for Red
470 @chapter A Sample @value{GDBN} Session
472 You can use this manual at your leisure to read all about @value{GDBN}.
473 However, a handful of commands are enough to get started using the
474 debugger. This chapter illustrates those commands.
477 In this sample session, we emphasize user input like this: @b{input},
478 to make it easier to pick out from the surrounding output.
481 @c FIXME: this example may not be appropriate for some configs, where
482 @c FIXME...primary interest is in remote use.
484 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
485 processor) exhibits the following bug: sometimes, when we change its
486 quote strings from the default, the commands used to capture one macro
487 definition within another stop working. In the following short @code{m4}
488 session, we define a macro @code{foo} which expands to @code{0000}; we
489 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
490 same thing. However, when we change the open quote string to
491 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
492 procedure fails to define a new synonym @code{baz}:
501 @b{define(bar,defn(`foo'))}
505 @b{changequote(<QUOTE>,<UNQUOTE>)}
507 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
510 m4: End of input: 0: fatal error: EOF in string
514 Let us use @value{GDBN} to try to see what is going on.
517 $ @b{@value{GDBP} m4}
518 @c FIXME: this falsifies the exact text played out, to permit smallbook
519 @c FIXME... format to come out better.
520 @value{GDBN} is free software and you are welcome to distribute copies
521 of it under certain conditions; type "show copying" to see
523 There is absolutely no warranty for @value{GDBN}; type "show warranty"
526 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
531 @value{GDBN} reads only enough symbol data to know where to find the
532 rest when needed; as a result, the first prompt comes up very quickly.
533 We now tell @value{GDBN} to use a narrower display width than usual, so
534 that examples fit in this manual.
537 (@value{GDBP}) @b{set width 70}
541 We need to see how the @code{m4} built-in @code{changequote} works.
542 Having looked at the source, we know the relevant subroutine is
543 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
544 @code{break} command.
547 (@value{GDBP}) @b{break m4_changequote}
548 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
552 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
553 control; as long as control does not reach the @code{m4_changequote}
554 subroutine, the program runs as usual:
557 (@value{GDBP}) @b{run}
558 Starting program: /work/Editorial/gdb/gnu/m4/m4
566 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
567 suspends execution of @code{m4}, displaying information about the
568 context where it stops.
571 @b{changequote(<QUOTE>,<UNQUOTE>)}
573 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
575 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
579 Now we use the command @code{n} (@code{next}) to advance execution to
580 the next line of the current function.
584 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
589 @code{set_quotes} looks like a promising subroutine. We can go into it
590 by using the command @code{s} (@code{step}) instead of @code{next}.
591 @code{step} goes to the next line to be executed in @emph{any}
592 subroutine, so it steps into @code{set_quotes}.
596 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
598 530 if (lquote != def_lquote)
602 The display that shows the subroutine where @code{m4} is now
603 suspended (and its arguments) is called a stack frame display. It
604 shows a summary of the stack. We can use the @code{backtrace}
605 command (which can also be spelled @code{bt}), to see where we are
606 in the stack as a whole: the @code{backtrace} command displays a
607 stack frame for each active subroutine.
610 (@value{GDBP}) @b{bt}
611 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
613 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
615 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
616 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
618 #4 0x79dc in expand_input () at macro.c:40
619 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
623 We step through a few more lines to see what happens. The first two
624 times, we can use @samp{s}; the next two times we use @code{n} to avoid
625 falling into the @code{xstrdup} subroutine.
629 0x3b5c 532 if (rquote != def_rquote)
631 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
632 def_lquote : xstrdup(lq);
634 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
637 538 len_lquote = strlen(rquote);
641 The last line displayed looks a little odd; we can examine the variables
642 @code{lquote} and @code{rquote} to see if they are in fact the new left
643 and right quotes we specified. We use the command @code{p}
644 (@code{print}) to see their values.
647 (@value{GDBP}) @b{p lquote}
648 $1 = 0x35d40 "<QUOTE>"
649 (@value{GDBP}) @b{p rquote}
650 $2 = 0x35d50 "<UNQUOTE>"
654 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
655 To look at some context, we can display ten lines of source
656 surrounding the current line with the @code{l} (@code{list}) command.
662 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
664 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
667 538 len_lquote = strlen(rquote);
668 539 len_rquote = strlen(lquote);
675 Let us step past the two lines that set @code{len_lquote} and
676 @code{len_rquote}, and then examine the values of those variables.
680 539 len_rquote = strlen(lquote);
683 (@value{GDBP}) @b{p len_lquote}
685 (@value{GDBP}) @b{p len_rquote}
690 That certainly looks wrong, assuming @code{len_lquote} and
691 @code{len_rquote} are meant to be the lengths of @code{lquote} and
692 @code{rquote} respectively. We can set them to better values using
693 the @code{p} command, since it can print the value of
694 any expression---and that expression can include subroutine calls and
698 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
700 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
705 Is that enough to fix the problem of using the new quotes with the
706 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
707 executing with the @code{c} (@code{continue}) command, and then try the
708 example that caused trouble initially:
714 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
721 Success! The new quotes now work just as well as the default ones. The
722 problem seems to have been just the two typos defining the wrong
723 lengths. We allow @code{m4} exit by giving it an EOF as input:
727 Program exited normally.
731 The message @samp{Program exited normally.} is from @value{GDBN}; it
732 indicates @code{m4} has finished executing. We can end our @value{GDBN}
733 session with the @value{GDBN} @code{quit} command.
736 (@value{GDBP}) @b{quit}
740 @chapter Getting In and Out of @value{GDBN}
742 This chapter discusses how to start @value{GDBN}, and how to get out of it.
746 type @samp{@value{GDBP}} to start @value{GDBN}.
748 type @kbd{quit} or @kbd{C-d} to exit.
752 * Invoking GDB:: How to start @value{GDBN}
753 * Quitting GDB:: How to quit @value{GDBN}
754 * Shell Commands:: How to use shell commands inside @value{GDBN}
758 @section Invoking @value{GDBN}
760 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
761 @value{GDBN} reads commands from the terminal until you tell it to exit.
763 You can also run @code{@value{GDBP}} with a variety of arguments and options,
764 to specify more of your debugging environment at the outset.
766 The command-line options described here are designed
767 to cover a variety of situations; in some environments, some of these
768 options may effectively be unavailable.
770 The most usual way to start @value{GDBN} is with one argument,
771 specifying an executable program:
774 @value{GDBP} @var{program}
778 You can also start with both an executable program and a core file
782 @value{GDBP} @var{program} @var{core}
785 You can, instead, specify a process ID as a second argument, if you want
786 to debug a running process:
789 @value{GDBP} @var{program} 1234
793 would attach @value{GDBN} to process @code{1234} (unless you also have a file
794 named @file{1234}; @value{GDBN} does check for a core file first).
796 Taking advantage of the second command-line argument requires a fairly
797 complete operating system; when you use @value{GDBN} as a remote
798 debugger attached to a bare board, there may not be any notion of
799 ``process'', and there is often no way to get a core dump. @value{GDBN}
800 will warn you if it is unable to attach or to read core dumps.
802 You can optionally have @code{@value{GDBP}} pass any arguments after the
803 executable file to the inferior using @code{--args}. This option stops
806 gdb --args gcc -O2 -c foo.c
808 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
809 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
811 You can run @code{@value{GDBP}} without printing the front material, which describes
812 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
819 You can further control how @value{GDBN} starts up by using command-line
820 options. @value{GDBN} itself can remind you of the options available.
830 to display all available options and briefly describe their use
831 (@samp{@value{GDBP} -h} is a shorter equivalent).
833 All options and command line arguments you give are processed
834 in sequential order. The order makes a difference when the
835 @samp{-x} option is used.
839 * File Options:: Choosing files
840 * Mode Options:: Choosing modes
844 @subsection Choosing files
846 When @value{GDBN} starts, it reads any arguments other than options as
847 specifying an executable file and core file (or process ID). This is
848 the same as if the arguments were specified by the @samp{-se} and
849 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
850 first argument that does not have an associated option flag as
851 equivalent to the @samp{-se} option followed by that argument; and the
852 second argument that does not have an associated option flag, if any, as
853 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
854 If the second argument begins with a decimal digit, @value{GDBN} will
855 first attempt to attach to it as a process, and if that fails, attempt
856 to open it as a corefile. If you have a corefile whose name begins with
857 a digit, you can prevent @value{GDBN} from treating it as a pid by
858 prefixing it with @file{./}, eg. @file{./12345}.
860 If @value{GDBN} has not been configured to included core file support,
861 such as for most embedded targets, then it will complain about a second
862 argument and ignore it.
864 Many options have both long and short forms; both are shown in the
865 following list. @value{GDBN} also recognizes the long forms if you truncate
866 them, so long as enough of the option is present to be unambiguous.
867 (If you prefer, you can flag option arguments with @samp{--} rather
868 than @samp{-}, though we illustrate the more usual convention.)
870 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
871 @c way, both those who look for -foo and --foo in the index, will find
875 @item -symbols @var{file}
877 @cindex @code{--symbols}
879 Read symbol table from file @var{file}.
881 @item -exec @var{file}
883 @cindex @code{--exec}
885 Use file @var{file} as the executable file to execute when appropriate,
886 and for examining pure data in conjunction with a core dump.
890 Read symbol table from file @var{file} and use it as the executable
893 @item -core @var{file}
895 @cindex @code{--core}
897 Use file @var{file} as a core dump to examine.
899 @item -c @var{number}
900 @item -pid @var{number}
901 @itemx -p @var{number}
904 Connect to process ID @var{number}, as with the @code{attach} command.
905 If there is no such process, @value{GDBN} will attempt to open a core
906 file named @var{number}.
908 @item -command @var{file}
910 @cindex @code{--command}
912 Execute @value{GDBN} commands from file @var{file}. @xref{Command
913 Files,, Command files}.
915 @item -directory @var{directory}
916 @itemx -d @var{directory}
917 @cindex @code{--directory}
919 Add @var{directory} to the path to search for source files.
923 @cindex @code{--mapped}
925 @emph{Warning: this option depends on operating system facilities that are not
926 supported on all systems.}@*
927 If memory-mapped files are available on your system through the @code{mmap}
928 system call, you can use this option
929 to have @value{GDBN} write the symbols from your
930 program into a reusable file in the current directory. If the program you are debugging is
931 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
932 Future @value{GDBN} debugging sessions notice the presence of this file,
933 and can quickly map in symbol information from it, rather than reading
934 the symbol table from the executable program.
936 The @file{.syms} file is specific to the host machine where @value{GDBN}
937 is run. It holds an exact image of the internal @value{GDBN} symbol
938 table. It cannot be shared across multiple host platforms.
942 @cindex @code{--readnow}
944 Read each symbol file's entire symbol table immediately, rather than
945 the default, which is to read it incrementally as it is needed.
946 This makes startup slower, but makes future operations faster.
950 You typically combine the @code{-mapped} and @code{-readnow} options in
951 order to build a @file{.syms} file that contains complete symbol
952 information. (@xref{Files,,Commands to specify files}, for information
953 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
954 but build a @file{.syms} file for future use is:
957 gdb -batch -nx -mapped -readnow programname
961 @subsection Choosing modes
963 You can run @value{GDBN} in various alternative modes---for example, in
964 batch mode or quiet mode.
971 Do not execute commands found in any initialization files. Normally,
972 @value{GDBN} executes the commands in these files after all the command
973 options and arguments have been processed. @xref{Command Files,,Command
979 @cindex @code{--quiet}
980 @cindex @code{--silent}
982 ``Quiet''. Do not print the introductory and copyright messages. These
983 messages are also suppressed in batch mode.
986 @cindex @code{--batch}
987 Run in batch mode. Exit with status @code{0} after processing all the
988 command files specified with @samp{-x} (and all commands from
989 initialization files, if not inhibited with @samp{-n}). Exit with
990 nonzero status if an error occurs in executing the @value{GDBN} commands
991 in the command files.
993 Batch mode may be useful for running @value{GDBN} as a filter, for
994 example to download and run a program on another computer; in order to
995 make this more useful, the message
998 Program exited normally.
1002 (which is ordinarily issued whenever a program running under
1003 @value{GDBN} control terminates) is not issued when running in batch
1008 @cindex @code{--nowindows}
1010 ``No windows''. If @value{GDBN} comes with a graphical user interface
1011 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1012 interface. If no GUI is available, this option has no effect.
1016 @cindex @code{--windows}
1018 If @value{GDBN} includes a GUI, then this option requires it to be
1021 @item -cd @var{directory}
1023 Run @value{GDBN} using @var{directory} as its working directory,
1024 instead of the current directory.
1028 @cindex @code{--fullname}
1030 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1031 subprocess. It tells @value{GDBN} to output the full file name and line
1032 number in a standard, recognizable fashion each time a stack frame is
1033 displayed (which includes each time your program stops). This
1034 recognizable format looks like two @samp{\032} characters, followed by
1035 the file name, line number and character position separated by colons,
1036 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1037 @samp{\032} characters as a signal to display the source code for the
1041 @cindex @code{--epoch}
1042 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1043 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1044 routines so as to allow Epoch to display values of expressions in a
1047 @item -annotate @var{level}
1048 @cindex @code{--annotate}
1049 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1050 effect is identical to using @samp{set annotate @var{level}}
1051 (@pxref{Annotations}).
1052 Annotation level controls how much information does @value{GDBN} print
1053 together with its prompt, values of expressions, source lines, and other
1054 types of output. Level 0 is the normal, level 1 is for use when
1055 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1056 maximum annotation suitable for programs that control @value{GDBN}.
1059 @cindex @code{--async}
1060 Use the asynchronous event loop for the command-line interface.
1061 @value{GDBN} processes all events, such as user keyboard input, via a
1062 special event loop. This allows @value{GDBN} to accept and process user
1063 commands in parallel with the debugged process being
1064 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1065 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1066 suspended when the debuggee runs.}, so you don't need to wait for
1067 control to return to @value{GDBN} before you type the next command.
1068 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1069 operation is not yet in place, so @samp{-async} does not work fully
1071 @c FIXME: when the target side of the event loop is done, the above NOTE
1072 @c should be removed.
1074 When the standard input is connected to a terminal device, @value{GDBN}
1075 uses the asynchronous event loop by default, unless disabled by the
1076 @samp{-noasync} option.
1079 @cindex @code{--noasync}
1080 Disable the asynchronous event loop for the command-line interface.
1083 @cindex @code{--args}
1084 Change interpretation of command line so that arguments following the
1085 executable file are passed as command line arguments to the inferior.
1086 This option stops option processing.
1088 @item -baud @var{bps}
1090 @cindex @code{--baud}
1092 Set the line speed (baud rate or bits per second) of any serial
1093 interface used by @value{GDBN} for remote debugging.
1095 @item -tty @var{device}
1096 @itemx -t @var{device}
1097 @cindex @code{--tty}
1099 Run using @var{device} for your program's standard input and output.
1100 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1102 @c resolve the situation of these eventually
1104 @cindex @code{--tui}
1105 Activate the Terminal User Interface when starting.
1106 The Terminal User Interface manages several text windows on the terminal,
1107 showing source, assembly, registers and @value{GDBN} command outputs
1108 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1109 Do not use this option if you run @value{GDBN} from Emacs
1110 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1113 @c @cindex @code{--xdb}
1114 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1115 @c For information, see the file @file{xdb_trans.html}, which is usually
1116 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1119 @item -interpreter @var{interp}
1120 @cindex @code{--interpreter}
1121 Use the interpreter @var{interp} for interface with the controlling
1122 program or device. This option is meant to be set by programs which
1123 communicate with @value{GDBN} using it as a back end.
1125 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1126 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1127 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1128 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1131 @cindex @code{--write}
1132 Open the executable and core files for both reading and writing. This
1133 is equivalent to the @samp{set write on} command inside @value{GDBN}
1137 @cindex @code{--statistics}
1138 This option causes @value{GDBN} to print statistics about time and
1139 memory usage after it completes each command and returns to the prompt.
1142 @cindex @code{--version}
1143 This option causes @value{GDBN} to print its version number and
1144 no-warranty blurb, and exit.
1149 @section Quitting @value{GDBN}
1150 @cindex exiting @value{GDBN}
1151 @cindex leaving @value{GDBN}
1154 @kindex quit @r{[}@var{expression}@r{]}
1155 @kindex q @r{(@code{quit})}
1156 @item quit @r{[}@var{expression}@r{]}
1158 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1159 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1160 do not supply @var{expression}, @value{GDBN} will terminate normally;
1161 otherwise it will terminate using the result of @var{expression} as the
1166 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1167 terminates the action of any @value{GDBN} command that is in progress and
1168 returns to @value{GDBN} command level. It is safe to type the interrupt
1169 character at any time because @value{GDBN} does not allow it to take effect
1170 until a time when it is safe.
1172 If you have been using @value{GDBN} to control an attached process or
1173 device, you can release it with the @code{detach} command
1174 (@pxref{Attach, ,Debugging an already-running process}).
1176 @node Shell Commands
1177 @section Shell commands
1179 If you need to execute occasional shell commands during your
1180 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1181 just use the @code{shell} command.
1185 @cindex shell escape
1186 @item shell @var{command string}
1187 Invoke a standard shell to execute @var{command string}.
1188 If it exists, the environment variable @code{SHELL} determines which
1189 shell to run. Otherwise @value{GDBN} uses the default shell
1190 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1193 The utility @code{make} is often needed in development environments.
1194 You do not have to use the @code{shell} command for this purpose in
1199 @cindex calling make
1200 @item make @var{make-args}
1201 Execute the @code{make} program with the specified
1202 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1206 @chapter @value{GDBN} Commands
1208 You can abbreviate a @value{GDBN} command to the first few letters of the command
1209 name, if that abbreviation is unambiguous; and you can repeat certain
1210 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1211 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1212 show you the alternatives available, if there is more than one possibility).
1215 * Command Syntax:: How to give commands to @value{GDBN}
1216 * Completion:: Command completion
1217 * Help:: How to ask @value{GDBN} for help
1220 @node Command Syntax
1221 @section Command syntax
1223 A @value{GDBN} command is a single line of input. There is no limit on
1224 how long it can be. It starts with a command name, which is followed by
1225 arguments whose meaning depends on the command name. For example, the
1226 command @code{step} accepts an argument which is the number of times to
1227 step, as in @samp{step 5}. You can also use the @code{step} command
1228 with no arguments. Some commands do not allow any arguments.
1230 @cindex abbreviation
1231 @value{GDBN} command names may always be truncated if that abbreviation is
1232 unambiguous. Other possible command abbreviations are listed in the
1233 documentation for individual commands. In some cases, even ambiguous
1234 abbreviations are allowed; for example, @code{s} is specially defined as
1235 equivalent to @code{step} even though there are other commands whose
1236 names start with @code{s}. You can test abbreviations by using them as
1237 arguments to the @code{help} command.
1239 @cindex repeating commands
1240 @kindex RET @r{(repeat last command)}
1241 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1242 repeat the previous command. Certain commands (for example, @code{run})
1243 will not repeat this way; these are commands whose unintentional
1244 repetition might cause trouble and which you are unlikely to want to
1247 The @code{list} and @code{x} commands, when you repeat them with
1248 @key{RET}, construct new arguments rather than repeating
1249 exactly as typed. This permits easy scanning of source or memory.
1251 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1252 output, in a way similar to the common utility @code{more}
1253 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1254 @key{RET} too many in this situation, @value{GDBN} disables command
1255 repetition after any command that generates this sort of display.
1257 @kindex # @r{(a comment)}
1259 Any text from a @kbd{#} to the end of the line is a comment; it does
1260 nothing. This is useful mainly in command files (@pxref{Command
1261 Files,,Command files}).
1263 @cindex repeating command sequences
1264 @kindex C-o @r{(operate-and-get-next)}
1265 The @kbd{C-o} binding is useful for repeating a complex sequence of
1266 commands. This command accepts the current line, like @kbd{RET}, and
1267 then fetches the next line relative to the current line from the history
1271 @section Command completion
1274 @cindex word completion
1275 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1276 only one possibility; it can also show you what the valid possibilities
1277 are for the next word in a command, at any time. This works for @value{GDBN}
1278 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1280 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1281 of a word. If there is only one possibility, @value{GDBN} fills in the
1282 word, and waits for you to finish the command (or press @key{RET} to
1283 enter it). For example, if you type
1285 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1286 @c complete accuracy in these examples; space introduced for clarity.
1287 @c If texinfo enhancements make it unnecessary, it would be nice to
1288 @c replace " @key" by "@key" in the following...
1290 (@value{GDBP}) info bre @key{TAB}
1294 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1295 the only @code{info} subcommand beginning with @samp{bre}:
1298 (@value{GDBP}) info breakpoints
1302 You can either press @key{RET} at this point, to run the @code{info
1303 breakpoints} command, or backspace and enter something else, if
1304 @samp{breakpoints} does not look like the command you expected. (If you
1305 were sure you wanted @code{info breakpoints} in the first place, you
1306 might as well just type @key{RET} immediately after @samp{info bre},
1307 to exploit command abbreviations rather than command completion).
1309 If there is more than one possibility for the next word when you press
1310 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1311 characters and try again, or just press @key{TAB} a second time;
1312 @value{GDBN} displays all the possible completions for that word. For
1313 example, you might want to set a breakpoint on a subroutine whose name
1314 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1315 just sounds the bell. Typing @key{TAB} again displays all the
1316 function names in your program that begin with those characters, for
1320 (@value{GDBP}) b make_ @key{TAB}
1321 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1322 make_a_section_from_file make_environ
1323 make_abs_section make_function_type
1324 make_blockvector make_pointer_type
1325 make_cleanup make_reference_type
1326 make_command make_symbol_completion_list
1327 (@value{GDBP}) b make_
1331 After displaying the available possibilities, @value{GDBN} copies your
1332 partial input (@samp{b make_} in the example) so you can finish the
1335 If you just want to see the list of alternatives in the first place, you
1336 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1337 means @kbd{@key{META} ?}. You can type this either by holding down a
1338 key designated as the @key{META} shift on your keyboard (if there is
1339 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1341 @cindex quotes in commands
1342 @cindex completion of quoted strings
1343 Sometimes the string you need, while logically a ``word'', may contain
1344 parentheses or other characters that @value{GDBN} normally excludes from
1345 its notion of a word. To permit word completion to work in this
1346 situation, you may enclose words in @code{'} (single quote marks) in
1347 @value{GDBN} commands.
1349 The most likely situation where you might need this is in typing the
1350 name of a C@t{++} function. This is because C@t{++} allows function
1351 overloading (multiple definitions of the same function, distinguished
1352 by argument type). For example, when you want to set a breakpoint you
1353 may need to distinguish whether you mean the version of @code{name}
1354 that takes an @code{int} parameter, @code{name(int)}, or the version
1355 that takes a @code{float} parameter, @code{name(float)}. To use the
1356 word-completion facilities in this situation, type a single quote
1357 @code{'} at the beginning of the function name. This alerts
1358 @value{GDBN} that it may need to consider more information than usual
1359 when you press @key{TAB} or @kbd{M-?} to request word completion:
1362 (@value{GDBP}) b 'bubble( @kbd{M-?}
1363 bubble(double,double) bubble(int,int)
1364 (@value{GDBP}) b 'bubble(
1367 In some cases, @value{GDBN} can tell that completing a name requires using
1368 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1369 completing as much as it can) if you do not type the quote in the first
1373 (@value{GDBP}) b bub @key{TAB}
1374 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1375 (@value{GDBP}) b 'bubble(
1379 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1380 you have not yet started typing the argument list when you ask for
1381 completion on an overloaded symbol.
1383 For more information about overloaded functions, see @ref{C plus plus
1384 expressions, ,C@t{++} expressions}. You can use the command @code{set
1385 overload-resolution off} to disable overload resolution;
1386 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1390 @section Getting help
1391 @cindex online documentation
1394 You can always ask @value{GDBN} itself for information on its commands,
1395 using the command @code{help}.
1398 @kindex h @r{(@code{help})}
1401 You can use @code{help} (abbreviated @code{h}) with no arguments to
1402 display a short list of named classes of commands:
1406 List of classes of commands:
1408 aliases -- Aliases of other commands
1409 breakpoints -- Making program stop at certain points
1410 data -- Examining data
1411 files -- Specifying and examining files
1412 internals -- Maintenance commands
1413 obscure -- Obscure features
1414 running -- Running the program
1415 stack -- Examining the stack
1416 status -- Status inquiries
1417 support -- Support facilities
1418 tracepoints -- Tracing of program execution without@*
1419 stopping the program
1420 user-defined -- User-defined commands
1422 Type "help" followed by a class name for a list of
1423 commands in that class.
1424 Type "help" followed by command name for full
1426 Command name abbreviations are allowed if unambiguous.
1429 @c the above line break eliminates huge line overfull...
1431 @item help @var{class}
1432 Using one of the general help classes as an argument, you can get a
1433 list of the individual commands in that class. For example, here is the
1434 help display for the class @code{status}:
1437 (@value{GDBP}) help status
1442 @c Line break in "show" line falsifies real output, but needed
1443 @c to fit in smallbook page size.
1444 info -- Generic command for showing things
1445 about the program being debugged
1446 show -- Generic command for showing things
1449 Type "help" followed by command name for full
1451 Command name abbreviations are allowed if unambiguous.
1455 @item help @var{command}
1456 With a command name as @code{help} argument, @value{GDBN} displays a
1457 short paragraph on how to use that command.
1460 @item apropos @var{args}
1461 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1462 commands, and their documentation, for the regular expression specified in
1463 @var{args}. It prints out all matches found. For example:
1474 set symbol-reloading -- Set dynamic symbol table reloading
1475 multiple times in one run
1476 show symbol-reloading -- Show dynamic symbol table reloading
1477 multiple times in one run
1482 @item complete @var{args}
1483 The @code{complete @var{args}} command lists all the possible completions
1484 for the beginning of a command. Use @var{args} to specify the beginning of the
1485 command you want completed. For example:
1491 @noindent results in:
1502 @noindent This is intended for use by @sc{gnu} Emacs.
1505 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1506 and @code{show} to inquire about the state of your program, or the state
1507 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1508 manual introduces each of them in the appropriate context. The listings
1509 under @code{info} and under @code{show} in the Index point to
1510 all the sub-commands. @xref{Index}.
1515 @kindex i @r{(@code{info})}
1517 This command (abbreviated @code{i}) is for describing the state of your
1518 program. For example, you can list the arguments given to your program
1519 with @code{info args}, list the registers currently in use with @code{info
1520 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1521 You can get a complete list of the @code{info} sub-commands with
1522 @w{@code{help info}}.
1526 You can assign the result of an expression to an environment variable with
1527 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1528 @code{set prompt $}.
1532 In contrast to @code{info}, @code{show} is for describing the state of
1533 @value{GDBN} itself.
1534 You can change most of the things you can @code{show}, by using the
1535 related command @code{set}; for example, you can control what number
1536 system is used for displays with @code{set radix}, or simply inquire
1537 which is currently in use with @code{show radix}.
1540 To display all the settable parameters and their current
1541 values, you can use @code{show} with no arguments; you may also use
1542 @code{info set}. Both commands produce the same display.
1543 @c FIXME: "info set" violates the rule that "info" is for state of
1544 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1545 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1549 Here are three miscellaneous @code{show} subcommands, all of which are
1550 exceptional in lacking corresponding @code{set} commands:
1553 @kindex show version
1554 @cindex version number
1556 Show what version of @value{GDBN} is running. You should include this
1557 information in @value{GDBN} bug-reports. If multiple versions of
1558 @value{GDBN} are in use at your site, you may need to determine which
1559 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1560 commands are introduced, and old ones may wither away. Also, many
1561 system vendors ship variant versions of @value{GDBN}, and there are
1562 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1563 The version number is the same as the one announced when you start
1566 @kindex show copying
1568 Display information about permission for copying @value{GDBN}.
1570 @kindex show warranty
1572 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1573 if your version of @value{GDBN} comes with one.
1578 @chapter Running Programs Under @value{GDBN}
1580 When you run a program under @value{GDBN}, you must first generate
1581 debugging information when you compile it.
1583 You may start @value{GDBN} with its arguments, if any, in an environment
1584 of your choice. If you are doing native debugging, you may redirect
1585 your program's input and output, debug an already running process, or
1586 kill a child process.
1589 * Compilation:: Compiling for debugging
1590 * Starting:: Starting your program
1591 * Arguments:: Your program's arguments
1592 * Environment:: Your program's environment
1594 * Working Directory:: Your program's working directory
1595 * Input/Output:: Your program's input and output
1596 * Attach:: Debugging an already-running process
1597 * Kill Process:: Killing the child process
1599 * Threads:: Debugging programs with multiple threads
1600 * Processes:: Debugging programs with multiple processes
1604 @section Compiling for debugging
1606 In order to debug a program effectively, you need to generate
1607 debugging information when you compile it. This debugging information
1608 is stored in the object file; it describes the data type of each
1609 variable or function and the correspondence between source line numbers
1610 and addresses in the executable code.
1612 To request debugging information, specify the @samp{-g} option when you run
1615 Most compilers do not include information about preprocessor macros in
1616 the debugging information if you specify the @option{-g} flag alone,
1617 because this information is rather large. Version 3.1 of @value{NGCC},
1618 the @sc{gnu} C compiler, provides macro information if you specify the
1619 options @option{-gdwarf-2} and @option{-g3}; the former option requests
1620 debugging information in the Dwarf 2 format, and the latter requests
1621 ``extra information''. In the future, we hope to find more compact ways
1622 to represent macro information, so that it can be included with
1625 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1626 options together. Using those compilers, you cannot generate optimized
1627 executables containing debugging information.
1629 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1630 without @samp{-O}, making it possible to debug optimized code. We
1631 recommend that you @emph{always} use @samp{-g} whenever you compile a
1632 program. You may think your program is correct, but there is no sense
1633 in pushing your luck.
1635 @cindex optimized code, debugging
1636 @cindex debugging optimized code
1637 When you debug a program compiled with @samp{-g -O}, remember that the
1638 optimizer is rearranging your code; the debugger shows you what is
1639 really there. Do not be too surprised when the execution path does not
1640 exactly match your source file! An extreme example: if you define a
1641 variable, but never use it, @value{GDBN} never sees that
1642 variable---because the compiler optimizes it out of existence.
1644 Some things do not work as well with @samp{-g -O} as with just
1645 @samp{-g}, particularly on machines with instruction scheduling. If in
1646 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1647 please report it to us as a bug (including a test case!).
1649 Older versions of the @sc{gnu} C compiler permitted a variant option
1650 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1651 format; if your @sc{gnu} C compiler has this option, do not use it.
1655 @section Starting your program
1661 @kindex r @r{(@code{run})}
1664 Use the @code{run} command to start your program under @value{GDBN}.
1665 You must first specify the program name (except on VxWorks) with an
1666 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1667 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1668 (@pxref{Files, ,Commands to specify files}).
1672 If you are running your program in an execution environment that
1673 supports processes, @code{run} creates an inferior process and makes
1674 that process run your program. (In environments without processes,
1675 @code{run} jumps to the start of your program.)
1677 The execution of a program is affected by certain information it
1678 receives from its superior. @value{GDBN} provides ways to specify this
1679 information, which you must do @emph{before} starting your program. (You
1680 can change it after starting your program, but such changes only affect
1681 your program the next time you start it.) This information may be
1682 divided into four categories:
1685 @item The @emph{arguments.}
1686 Specify the arguments to give your program as the arguments of the
1687 @code{run} command. If a shell is available on your target, the shell
1688 is used to pass the arguments, so that you may use normal conventions
1689 (such as wildcard expansion or variable substitution) in describing
1691 In Unix systems, you can control which shell is used with the
1692 @code{SHELL} environment variable.
1693 @xref{Arguments, ,Your program's arguments}.
1695 @item The @emph{environment.}
1696 Your program normally inherits its environment from @value{GDBN}, but you can
1697 use the @value{GDBN} commands @code{set environment} and @code{unset
1698 environment} to change parts of the environment that affect
1699 your program. @xref{Environment, ,Your program's environment}.
1701 @item The @emph{working directory.}
1702 Your program inherits its working directory from @value{GDBN}. You can set
1703 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1704 @xref{Working Directory, ,Your program's working directory}.
1706 @item The @emph{standard input and output.}
1707 Your program normally uses the same device for standard input and
1708 standard output as @value{GDBN} is using. You can redirect input and output
1709 in the @code{run} command line, or you can use the @code{tty} command to
1710 set a different device for your program.
1711 @xref{Input/Output, ,Your program's input and output}.
1714 @emph{Warning:} While input and output redirection work, you cannot use
1715 pipes to pass the output of the program you are debugging to another
1716 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1720 When you issue the @code{run} command, your program begins to execute
1721 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1722 of how to arrange for your program to stop. Once your program has
1723 stopped, you may call functions in your program, using the @code{print}
1724 or @code{call} commands. @xref{Data, ,Examining Data}.
1726 If the modification time of your symbol file has changed since the last
1727 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1728 table, and reads it again. When it does this, @value{GDBN} tries to retain
1729 your current breakpoints.
1732 @section Your program's arguments
1734 @cindex arguments (to your program)
1735 The arguments to your program can be specified by the arguments of the
1737 They are passed to a shell, which expands wildcard characters and
1738 performs redirection of I/O, and thence to your program. Your
1739 @code{SHELL} environment variable (if it exists) specifies what shell
1740 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1741 the default shell (@file{/bin/sh} on Unix).
1743 On non-Unix systems, the program is usually invoked directly by
1744 @value{GDBN}, which emulates I/O redirection via the appropriate system
1745 calls, and the wildcard characters are expanded by the startup code of
1746 the program, not by the shell.
1748 @code{run} with no arguments uses the same arguments used by the previous
1749 @code{run}, or those set by the @code{set args} command.
1754 Specify the arguments to be used the next time your program is run. If
1755 @code{set args} has no arguments, @code{run} executes your program
1756 with no arguments. Once you have run your program with arguments,
1757 using @code{set args} before the next @code{run} is the only way to run
1758 it again without arguments.
1762 Show the arguments to give your program when it is started.
1766 @section Your program's environment
1768 @cindex environment (of your program)
1769 The @dfn{environment} consists of a set of environment variables and
1770 their values. Environment variables conventionally record such things as
1771 your user name, your home directory, your terminal type, and your search
1772 path for programs to run. Usually you set up environment variables with
1773 the shell and they are inherited by all the other programs you run. When
1774 debugging, it can be useful to try running your program with a modified
1775 environment without having to start @value{GDBN} over again.
1779 @item path @var{directory}
1780 Add @var{directory} to the front of the @code{PATH} environment variable
1781 (the search path for executables) that will be passed to your program.
1782 The value of @code{PATH} used by @value{GDBN} does not change.
1783 You may specify several directory names, separated by whitespace or by a
1784 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1785 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1786 is moved to the front, so it is searched sooner.
1788 You can use the string @samp{$cwd} to refer to whatever is the current
1789 working directory at the time @value{GDBN} searches the path. If you
1790 use @samp{.} instead, it refers to the directory where you executed the
1791 @code{path} command. @value{GDBN} replaces @samp{.} in the
1792 @var{directory} argument (with the current path) before adding
1793 @var{directory} to the search path.
1794 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1795 @c document that, since repeating it would be a no-op.
1799 Display the list of search paths for executables (the @code{PATH}
1800 environment variable).
1802 @kindex show environment
1803 @item show environment @r{[}@var{varname}@r{]}
1804 Print the value of environment variable @var{varname} to be given to
1805 your program when it starts. If you do not supply @var{varname},
1806 print the names and values of all environment variables to be given to
1807 your program. You can abbreviate @code{environment} as @code{env}.
1809 @kindex set environment
1810 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1811 Set environment variable @var{varname} to @var{value}. The value
1812 changes for your program only, not for @value{GDBN} itself. @var{value} may
1813 be any string; the values of environment variables are just strings, and
1814 any interpretation is supplied by your program itself. The @var{value}
1815 parameter is optional; if it is eliminated, the variable is set to a
1817 @c "any string" here does not include leading, trailing
1818 @c blanks. Gnu asks: does anyone care?
1820 For example, this command:
1827 tells the debugged program, when subsequently run, that its user is named
1828 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1829 are not actually required.)
1831 @kindex unset environment
1832 @item unset environment @var{varname}
1833 Remove variable @var{varname} from the environment to be passed to your
1834 program. This is different from @samp{set env @var{varname} =};
1835 @code{unset environment} removes the variable from the environment,
1836 rather than assigning it an empty value.
1839 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1841 by your @code{SHELL} environment variable if it exists (or
1842 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1843 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1844 @file{.bashrc} for BASH---any variables you set in that file affect
1845 your program. You may wish to move setting of environment variables to
1846 files that are only run when you sign on, such as @file{.login} or
1849 @node Working Directory
1850 @section Your program's working directory
1852 @cindex working directory (of your program)
1853 Each time you start your program with @code{run}, it inherits its
1854 working directory from the current working directory of @value{GDBN}.
1855 The @value{GDBN} working directory is initially whatever it inherited
1856 from its parent process (typically the shell), but you can specify a new
1857 working directory in @value{GDBN} with the @code{cd} command.
1859 The @value{GDBN} working directory also serves as a default for the commands
1860 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1865 @item cd @var{directory}
1866 Set the @value{GDBN} working directory to @var{directory}.
1870 Print the @value{GDBN} working directory.
1874 @section Your program's input and output
1879 By default, the program you run under @value{GDBN} does input and output to
1880 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1881 to its own terminal modes to interact with you, but it records the terminal
1882 modes your program was using and switches back to them when you continue
1883 running your program.
1886 @kindex info terminal
1888 Displays information recorded by @value{GDBN} about the terminal modes your
1892 You can redirect your program's input and/or output using shell
1893 redirection with the @code{run} command. For example,
1900 starts your program, diverting its output to the file @file{outfile}.
1903 @cindex controlling terminal
1904 Another way to specify where your program should do input and output is
1905 with the @code{tty} command. This command accepts a file name as
1906 argument, and causes this file to be the default for future @code{run}
1907 commands. It also resets the controlling terminal for the child
1908 process, for future @code{run} commands. For example,
1915 directs that processes started with subsequent @code{run} commands
1916 default to do input and output on the terminal @file{/dev/ttyb} and have
1917 that as their controlling terminal.
1919 An explicit redirection in @code{run} overrides the @code{tty} command's
1920 effect on the input/output device, but not its effect on the controlling
1923 When you use the @code{tty} command or redirect input in the @code{run}
1924 command, only the input @emph{for your program} is affected. The input
1925 for @value{GDBN} still comes from your terminal.
1928 @section Debugging an already-running process
1933 @item attach @var{process-id}
1934 This command attaches to a running process---one that was started
1935 outside @value{GDBN}. (@code{info files} shows your active
1936 targets.) The command takes as argument a process ID. The usual way to
1937 find out the process-id of a Unix process is with the @code{ps} utility,
1938 or with the @samp{jobs -l} shell command.
1940 @code{attach} does not repeat if you press @key{RET} a second time after
1941 executing the command.
1944 To use @code{attach}, your program must be running in an environment
1945 which supports processes; for example, @code{attach} does not work for
1946 programs on bare-board targets that lack an operating system. You must
1947 also have permission to send the process a signal.
1949 When you use @code{attach}, the debugger finds the program running in
1950 the process first by looking in the current working directory, then (if
1951 the program is not found) by using the source file search path
1952 (@pxref{Source Path, ,Specifying source directories}). You can also use
1953 the @code{file} command to load the program. @xref{Files, ,Commands to
1956 The first thing @value{GDBN} does after arranging to debug the specified
1957 process is to stop it. You can examine and modify an attached process
1958 with all the @value{GDBN} commands that are ordinarily available when
1959 you start processes with @code{run}. You can insert breakpoints; you
1960 can step and continue; you can modify storage. If you would rather the
1961 process continue running, you may use the @code{continue} command after
1962 attaching @value{GDBN} to the process.
1967 When you have finished debugging the attached process, you can use the
1968 @code{detach} command to release it from @value{GDBN} control. Detaching
1969 the process continues its execution. After the @code{detach} command,
1970 that process and @value{GDBN} become completely independent once more, and you
1971 are ready to @code{attach} another process or start one with @code{run}.
1972 @code{detach} does not repeat if you press @key{RET} again after
1973 executing the command.
1976 If you exit @value{GDBN} or use the @code{run} command while you have an
1977 attached process, you kill that process. By default, @value{GDBN} asks
1978 for confirmation if you try to do either of these things; you can
1979 control whether or not you need to confirm by using the @code{set
1980 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1984 @section Killing the child process
1989 Kill the child process in which your program is running under @value{GDBN}.
1992 This command is useful if you wish to debug a core dump instead of a
1993 running process. @value{GDBN} ignores any core dump file while your program
1996 On some operating systems, a program cannot be executed outside @value{GDBN}
1997 while you have breakpoints set on it inside @value{GDBN}. You can use the
1998 @code{kill} command in this situation to permit running your program
1999 outside the debugger.
2001 The @code{kill} command is also useful if you wish to recompile and
2002 relink your program, since on many systems it is impossible to modify an
2003 executable file while it is running in a process. In this case, when you
2004 next type @code{run}, @value{GDBN} notices that the file has changed, and
2005 reads the symbol table again (while trying to preserve your current
2006 breakpoint settings).
2009 @section Debugging programs with multiple threads
2011 @cindex threads of execution
2012 @cindex multiple threads
2013 @cindex switching threads
2014 In some operating systems, such as HP-UX and Solaris, a single program
2015 may have more than one @dfn{thread} of execution. The precise semantics
2016 of threads differ from one operating system to another, but in general
2017 the threads of a single program are akin to multiple processes---except
2018 that they share one address space (that is, they can all examine and
2019 modify the same variables). On the other hand, each thread has its own
2020 registers and execution stack, and perhaps private memory.
2022 @value{GDBN} provides these facilities for debugging multi-thread
2026 @item automatic notification of new threads
2027 @item @samp{thread @var{threadno}}, a command to switch among threads
2028 @item @samp{info threads}, a command to inquire about existing threads
2029 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2030 a command to apply a command to a list of threads
2031 @item thread-specific breakpoints
2035 @emph{Warning:} These facilities are not yet available on every
2036 @value{GDBN} configuration where the operating system supports threads.
2037 If your @value{GDBN} does not support threads, these commands have no
2038 effect. For example, a system without thread support shows no output
2039 from @samp{info threads}, and always rejects the @code{thread} command,
2043 (@value{GDBP}) info threads
2044 (@value{GDBP}) thread 1
2045 Thread ID 1 not known. Use the "info threads" command to
2046 see the IDs of currently known threads.
2048 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2049 @c doesn't support threads"?
2052 @cindex focus of debugging
2053 @cindex current thread
2054 The @value{GDBN} thread debugging facility allows you to observe all
2055 threads while your program runs---but whenever @value{GDBN} takes
2056 control, one thread in particular is always the focus of debugging.
2057 This thread is called the @dfn{current thread}. Debugging commands show
2058 program information from the perspective of the current thread.
2060 @cindex @code{New} @var{systag} message
2061 @cindex thread identifier (system)
2062 @c FIXME-implementors!! It would be more helpful if the [New...] message
2063 @c included GDB's numeric thread handle, so you could just go to that
2064 @c thread without first checking `info threads'.
2065 Whenever @value{GDBN} detects a new thread in your program, it displays
2066 the target system's identification for the thread with a message in the
2067 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2068 whose form varies depending on the particular system. For example, on
2069 LynxOS, you might see
2072 [New process 35 thread 27]
2076 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2077 the @var{systag} is simply something like @samp{process 368}, with no
2080 @c FIXME!! (1) Does the [New...] message appear even for the very first
2081 @c thread of a program, or does it only appear for the
2082 @c second---i.e.@: when it becomes obvious we have a multithread
2084 @c (2) *Is* there necessarily a first thread always? Or do some
2085 @c multithread systems permit starting a program with multiple
2086 @c threads ab initio?
2088 @cindex thread number
2089 @cindex thread identifier (GDB)
2090 For debugging purposes, @value{GDBN} associates its own thread
2091 number---always a single integer---with each thread in your program.
2094 @kindex info threads
2096 Display a summary of all threads currently in your
2097 program. @value{GDBN} displays for each thread (in this order):
2100 @item the thread number assigned by @value{GDBN}
2102 @item the target system's thread identifier (@var{systag})
2104 @item the current stack frame summary for that thread
2108 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2109 indicates the current thread.
2113 @c end table here to get a little more width for example
2116 (@value{GDBP}) info threads
2117 3 process 35 thread 27 0x34e5 in sigpause ()
2118 2 process 35 thread 23 0x34e5 in sigpause ()
2119 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2125 @cindex thread number
2126 @cindex thread identifier (GDB)
2127 For debugging purposes, @value{GDBN} associates its own thread
2128 number---a small integer assigned in thread-creation order---with each
2129 thread in your program.
2131 @cindex @code{New} @var{systag} message, on HP-UX
2132 @cindex thread identifier (system), on HP-UX
2133 @c FIXME-implementors!! It would be more helpful if the [New...] message
2134 @c included GDB's numeric thread handle, so you could just go to that
2135 @c thread without first checking `info threads'.
2136 Whenever @value{GDBN} detects a new thread in your program, it displays
2137 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2138 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2139 whose form varies depending on the particular system. For example, on
2143 [New thread 2 (system thread 26594)]
2147 when @value{GDBN} notices a new thread.
2150 @kindex info threads
2152 Display a summary of all threads currently in your
2153 program. @value{GDBN} displays for each thread (in this order):
2156 @item the thread number assigned by @value{GDBN}
2158 @item the target system's thread identifier (@var{systag})
2160 @item the current stack frame summary for that thread
2164 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2165 indicates the current thread.
2169 @c end table here to get a little more width for example
2172 (@value{GDBP}) info threads
2173 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2175 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2176 from /usr/lib/libc.2
2177 1 system thread 27905 0x7b003498 in _brk () \@*
2178 from /usr/lib/libc.2
2182 @kindex thread @var{threadno}
2183 @item thread @var{threadno}
2184 Make thread number @var{threadno} the current thread. The command
2185 argument @var{threadno} is the internal @value{GDBN} thread number, as
2186 shown in the first field of the @samp{info threads} display.
2187 @value{GDBN} responds by displaying the system identifier of the thread
2188 you selected, and its current stack frame summary:
2191 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2192 (@value{GDBP}) thread 2
2193 [Switching to process 35 thread 23]
2194 0x34e5 in sigpause ()
2198 As with the @samp{[New @dots{}]} message, the form of the text after
2199 @samp{Switching to} depends on your system's conventions for identifying
2202 @kindex thread apply
2203 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2204 The @code{thread apply} command allows you to apply a command to one or
2205 more threads. Specify the numbers of the threads that you want affected
2206 with the command argument @var{threadno}. @var{threadno} is the internal
2207 @value{GDBN} thread number, as shown in the first field of the @samp{info
2208 threads} display. To apply a command to all threads, use
2209 @code{thread apply all} @var{args}.
2212 @cindex automatic thread selection
2213 @cindex switching threads automatically
2214 @cindex threads, automatic switching
2215 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2216 signal, it automatically selects the thread where that breakpoint or
2217 signal happened. @value{GDBN} alerts you to the context switch with a
2218 message of the form @samp{[Switching to @var{systag}]} to identify the
2221 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2222 more information about how @value{GDBN} behaves when you stop and start
2223 programs with multiple threads.
2225 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2226 watchpoints in programs with multiple threads.
2229 @section Debugging programs with multiple processes
2231 @cindex fork, debugging programs which call
2232 @cindex multiple processes
2233 @cindex processes, multiple
2234 On most systems, @value{GDBN} has no special support for debugging
2235 programs which create additional processes using the @code{fork}
2236 function. When a program forks, @value{GDBN} will continue to debug the
2237 parent process and the child process will run unimpeded. If you have
2238 set a breakpoint in any code which the child then executes, the child
2239 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2240 will cause it to terminate.
2242 However, if you want to debug the child process there is a workaround
2243 which isn't too painful. Put a call to @code{sleep} in the code which
2244 the child process executes after the fork. It may be useful to sleep
2245 only if a certain environment variable is set, or a certain file exists,
2246 so that the delay need not occur when you don't want to run @value{GDBN}
2247 on the child. While the child is sleeping, use the @code{ps} program to
2248 get its process ID. Then tell @value{GDBN} (a new invocation of
2249 @value{GDBN} if you are also debugging the parent process) to attach to
2250 the child process (@pxref{Attach}). From that point on you can debug
2251 the child process just like any other process which you attached to.
2253 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2254 debugging programs that create additional processes using the
2255 @code{fork} or @code{vfork} function.
2257 By default, when a program forks, @value{GDBN} will continue to debug
2258 the parent process and the child process will run unimpeded.
2260 If you want to follow the child process instead of the parent process,
2261 use the command @w{@code{set follow-fork-mode}}.
2264 @kindex set follow-fork-mode
2265 @item set follow-fork-mode @var{mode}
2266 Set the debugger response to a program call of @code{fork} or
2267 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2268 process. The @var{mode} can be:
2272 The original process is debugged after a fork. The child process runs
2273 unimpeded. This is the default.
2276 The new process is debugged after a fork. The parent process runs
2280 The debugger will ask for one of the above choices.
2283 @item show follow-fork-mode
2284 Display the current debugger response to a @code{fork} or @code{vfork} call.
2287 If you ask to debug a child process and a @code{vfork} is followed by an
2288 @code{exec}, @value{GDBN} executes the new target up to the first
2289 breakpoint in the new target. If you have a breakpoint set on
2290 @code{main} in your original program, the breakpoint will also be set on
2291 the child process's @code{main}.
2293 When a child process is spawned by @code{vfork}, you cannot debug the
2294 child or parent until an @code{exec} call completes.
2296 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2297 call executes, the new target restarts. To restart the parent process,
2298 use the @code{file} command with the parent executable name as its
2301 You can use the @code{catch} command to make @value{GDBN} stop whenever
2302 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2303 Catchpoints, ,Setting catchpoints}.
2306 @chapter Stopping and Continuing
2308 The principal purposes of using a debugger are so that you can stop your
2309 program before it terminates; or so that, if your program runs into
2310 trouble, you can investigate and find out why.
2312 Inside @value{GDBN}, your program may stop for any of several reasons,
2313 such as a signal, a breakpoint, or reaching a new line after a
2314 @value{GDBN} command such as @code{step}. You may then examine and
2315 change variables, set new breakpoints or remove old ones, and then
2316 continue execution. Usually, the messages shown by @value{GDBN} provide
2317 ample explanation of the status of your program---but you can also
2318 explicitly request this information at any time.
2321 @kindex info program
2323 Display information about the status of your program: whether it is
2324 running or not, what process it is, and why it stopped.
2328 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2329 * Continuing and Stepping:: Resuming execution
2331 * Thread Stops:: Stopping and starting multi-thread programs
2335 @section Breakpoints, watchpoints, and catchpoints
2338 A @dfn{breakpoint} makes your program stop whenever a certain point in
2339 the program is reached. For each breakpoint, you can add conditions to
2340 control in finer detail whether your program stops. You can set
2341 breakpoints with the @code{break} command and its variants (@pxref{Set
2342 Breaks, ,Setting breakpoints}), to specify the place where your program
2343 should stop by line number, function name or exact address in the
2346 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2347 breakpoints in shared libraries before the executable is run. There is
2348 a minor limitation on HP-UX systems: you must wait until the executable
2349 is run in order to set breakpoints in shared library routines that are
2350 not called directly by the program (for example, routines that are
2351 arguments in a @code{pthread_create} call).
2354 @cindex memory tracing
2355 @cindex breakpoint on memory address
2356 @cindex breakpoint on variable modification
2357 A @dfn{watchpoint} is a special breakpoint that stops your program
2358 when the value of an expression changes. You must use a different
2359 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2360 watchpoints}), but aside from that, you can manage a watchpoint like
2361 any other breakpoint: you enable, disable, and delete both breakpoints
2362 and watchpoints using the same commands.
2364 You can arrange to have values from your program displayed automatically
2365 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2369 @cindex breakpoint on events
2370 A @dfn{catchpoint} is another special breakpoint that stops your program
2371 when a certain kind of event occurs, such as the throwing of a C@t{++}
2372 exception or the loading of a library. As with watchpoints, you use a
2373 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2374 catchpoints}), but aside from that, you can manage a catchpoint like any
2375 other breakpoint. (To stop when your program receives a signal, use the
2376 @code{handle} command; see @ref{Signals, ,Signals}.)
2378 @cindex breakpoint numbers
2379 @cindex numbers for breakpoints
2380 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2381 catchpoint when you create it; these numbers are successive integers
2382 starting with one. In many of the commands for controlling various
2383 features of breakpoints you use the breakpoint number to say which
2384 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2385 @dfn{disabled}; if disabled, it has no effect on your program until you
2388 @cindex breakpoint ranges
2389 @cindex ranges of breakpoints
2390 Some @value{GDBN} commands accept a range of breakpoints on which to
2391 operate. A breakpoint range is either a single breakpoint number, like
2392 @samp{5}, or two such numbers, in increasing order, separated by a
2393 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2394 all breakpoint in that range are operated on.
2397 * Set Breaks:: Setting breakpoints
2398 * Set Watchpoints:: Setting watchpoints
2399 * Set Catchpoints:: Setting catchpoints
2400 * Delete Breaks:: Deleting breakpoints
2401 * Disabling:: Disabling breakpoints
2402 * Conditions:: Break conditions
2403 * Break Commands:: Breakpoint command lists
2404 * Breakpoint Menus:: Breakpoint menus
2405 * Error in Breakpoints:: ``Cannot insert breakpoints''
2409 @subsection Setting breakpoints
2411 @c FIXME LMB what does GDB do if no code on line of breakpt?
2412 @c consider in particular declaration with/without initialization.
2414 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2417 @kindex b @r{(@code{break})}
2418 @vindex $bpnum@r{, convenience variable}
2419 @cindex latest breakpoint
2420 Breakpoints are set with the @code{break} command (abbreviated
2421 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2422 number of the breakpoint you've set most recently; see @ref{Convenience
2423 Vars,, Convenience variables}, for a discussion of what you can do with
2424 convenience variables.
2426 You have several ways to say where the breakpoint should go.
2429 @item break @var{function}
2430 Set a breakpoint at entry to function @var{function}.
2431 When using source languages that permit overloading of symbols, such as
2432 C@t{++}, @var{function} may refer to more than one possible place to break.
2433 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2435 @item break +@var{offset}
2436 @itemx break -@var{offset}
2437 Set a breakpoint some number of lines forward or back from the position
2438 at which execution stopped in the currently selected @dfn{stack frame}.
2439 (@xref{Frames, ,Frames}, for a description of stack frames.)
2441 @item break @var{linenum}
2442 Set a breakpoint at line @var{linenum} in the current source file.
2443 The current source file is the last file whose source text was printed.
2444 The breakpoint will stop your program just before it executes any of the
2447 @item break @var{filename}:@var{linenum}
2448 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2450 @item break @var{filename}:@var{function}
2451 Set a breakpoint at entry to function @var{function} found in file
2452 @var{filename}. Specifying a file name as well as a function name is
2453 superfluous except when multiple files contain similarly named
2456 @item break *@var{address}
2457 Set a breakpoint at address @var{address}. You can use this to set
2458 breakpoints in parts of your program which do not have debugging
2459 information or source files.
2462 When called without any arguments, @code{break} sets a breakpoint at
2463 the next instruction to be executed in the selected stack frame
2464 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2465 innermost, this makes your program stop as soon as control
2466 returns to that frame. This is similar to the effect of a
2467 @code{finish} command in the frame inside the selected frame---except
2468 that @code{finish} does not leave an active breakpoint. If you use
2469 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2470 the next time it reaches the current location; this may be useful
2473 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2474 least one instruction has been executed. If it did not do this, you
2475 would be unable to proceed past a breakpoint without first disabling the
2476 breakpoint. This rule applies whether or not the breakpoint already
2477 existed when your program stopped.
2479 @item break @dots{} if @var{cond}
2480 Set a breakpoint with condition @var{cond}; evaluate the expression
2481 @var{cond} each time the breakpoint is reached, and stop only if the
2482 value is nonzero---that is, if @var{cond} evaluates as true.
2483 @samp{@dots{}} stands for one of the possible arguments described
2484 above (or no argument) specifying where to break. @xref{Conditions,
2485 ,Break conditions}, for more information on breakpoint conditions.
2488 @item tbreak @var{args}
2489 Set a breakpoint enabled only for one stop. @var{args} are the
2490 same as for the @code{break} command, and the breakpoint is set in the same
2491 way, but the breakpoint is automatically deleted after the first time your
2492 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2495 @item hbreak @var{args}
2496 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2497 @code{break} command and the breakpoint is set in the same way, but the
2498 breakpoint requires hardware support and some target hardware may not
2499 have this support. The main purpose of this is EPROM/ROM code
2500 debugging, so you can set a breakpoint at an instruction without
2501 changing the instruction. This can be used with the new trap-generation
2502 provided by SPARClite DSU and some x86-based targets. These targets
2503 will generate traps when a program accesses some data or instruction
2504 address that is assigned to the debug registers. However the hardware
2505 breakpoint registers can take a limited number of breakpoints. For
2506 example, on the DSU, only two data breakpoints can be set at a time, and
2507 @value{GDBN} will reject this command if more than two are used. Delete
2508 or disable unused hardware breakpoints before setting new ones
2509 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2512 @item thbreak @var{args}
2513 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2514 are the same as for the @code{hbreak} command and the breakpoint is set in
2515 the same way. However, like the @code{tbreak} command,
2516 the breakpoint is automatically deleted after the
2517 first time your program stops there. Also, like the @code{hbreak}
2518 command, the breakpoint requires hardware support and some target hardware
2519 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2520 See also @ref{Conditions, ,Break conditions}.
2523 @cindex regular expression
2524 @item rbreak @var{regex}
2525 Set breakpoints on all functions matching the regular expression
2526 @var{regex}. This command sets an unconditional breakpoint on all
2527 matches, printing a list of all breakpoints it set. Once these
2528 breakpoints are set, they are treated just like the breakpoints set with
2529 the @code{break} command. You can delete them, disable them, or make
2530 them conditional the same way as any other breakpoint.
2532 The syntax of the regular expression is the standard one used with tools
2533 like @file{grep}. Note that this is different from the syntax used by
2534 shells, so for instance @code{foo*} matches all functions that include
2535 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2536 @code{.*} leading and trailing the regular expression you supply, so to
2537 match only functions that begin with @code{foo}, use @code{^foo}.
2539 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2540 breakpoints on overloaded functions that are not members of any special
2543 @kindex info breakpoints
2544 @cindex @code{$_} and @code{info breakpoints}
2545 @item info breakpoints @r{[}@var{n}@r{]}
2546 @itemx info break @r{[}@var{n}@r{]}
2547 @itemx info watchpoints @r{[}@var{n}@r{]}
2548 Print a table of all breakpoints, watchpoints, and catchpoints set and
2549 not deleted, with the following columns for each breakpoint:
2552 @item Breakpoint Numbers
2554 Breakpoint, watchpoint, or catchpoint.
2556 Whether the breakpoint is marked to be disabled or deleted when hit.
2557 @item Enabled or Disabled
2558 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2559 that are not enabled.
2561 Where the breakpoint is in your program, as a memory address.
2563 Where the breakpoint is in the source for your program, as a file and
2568 If a breakpoint is conditional, @code{info break} shows the condition on
2569 the line following the affected breakpoint; breakpoint commands, if any,
2570 are listed after that.
2573 @code{info break} with a breakpoint
2574 number @var{n} as argument lists only that breakpoint. The
2575 convenience variable @code{$_} and the default examining-address for
2576 the @code{x} command are set to the address of the last breakpoint
2577 listed (@pxref{Memory, ,Examining memory}).
2580 @code{info break} displays a count of the number of times the breakpoint
2581 has been hit. This is especially useful in conjunction with the
2582 @code{ignore} command. You can ignore a large number of breakpoint
2583 hits, look at the breakpoint info to see how many times the breakpoint
2584 was hit, and then run again, ignoring one less than that number. This
2585 will get you quickly to the last hit of that breakpoint.
2588 @value{GDBN} allows you to set any number of breakpoints at the same place in
2589 your program. There is nothing silly or meaningless about this. When
2590 the breakpoints are conditional, this is even useful
2591 (@pxref{Conditions, ,Break conditions}).
2593 @cindex negative breakpoint numbers
2594 @cindex internal @value{GDBN} breakpoints
2595 @value{GDBN} itself sometimes sets breakpoints in your program for
2596 special purposes, such as proper handling of @code{longjmp} (in C
2597 programs). These internal breakpoints are assigned negative numbers,
2598 starting with @code{-1}; @samp{info breakpoints} does not display them.
2599 You can see these breakpoints with the @value{GDBN} maintenance command
2600 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
2603 @node Set Watchpoints
2604 @subsection Setting watchpoints
2606 @cindex setting watchpoints
2607 @cindex software watchpoints
2608 @cindex hardware watchpoints
2609 You can use a watchpoint to stop execution whenever the value of an
2610 expression changes, without having to predict a particular place where
2613 Depending on your system, watchpoints may be implemented in software or
2614 hardware. @value{GDBN} does software watchpointing by single-stepping your
2615 program and testing the variable's value each time, which is hundreds of
2616 times slower than normal execution. (But this may still be worth it, to
2617 catch errors where you have no clue what part of your program is the
2620 On some systems, such as HP-UX, Linux and some other x86-based targets,
2621 @value{GDBN} includes support for
2622 hardware watchpoints, which do not slow down the running of your
2627 @item watch @var{expr}
2628 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2629 is written into by the program and its value changes.
2632 @item rwatch @var{expr}
2633 Set a watchpoint that will break when watch @var{expr} is read by the program.
2636 @item awatch @var{expr}
2637 Set a watchpoint that will break when @var{expr} is either read or written into
2640 @kindex info watchpoints
2641 @item info watchpoints
2642 This command prints a list of watchpoints, breakpoints, and catchpoints;
2643 it is the same as @code{info break}.
2646 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2647 watchpoints execute very quickly, and the debugger reports a change in
2648 value at the exact instruction where the change occurs. If @value{GDBN}
2649 cannot set a hardware watchpoint, it sets a software watchpoint, which
2650 executes more slowly and reports the change in value at the next
2651 statement, not the instruction, after the change occurs.
2653 When you issue the @code{watch} command, @value{GDBN} reports
2656 Hardware watchpoint @var{num}: @var{expr}
2660 if it was able to set a hardware watchpoint.
2662 Currently, the @code{awatch} and @code{rwatch} commands can only set
2663 hardware watchpoints, because accesses to data that don't change the
2664 value of the watched expression cannot be detected without examining
2665 every instruction as it is being executed, and @value{GDBN} does not do
2666 that currently. If @value{GDBN} finds that it is unable to set a
2667 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2668 will print a message like this:
2671 Expression cannot be implemented with read/access watchpoint.
2674 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2675 data type of the watched expression is wider than what a hardware
2676 watchpoint on the target machine can handle. For example, some systems
2677 can only watch regions that are up to 4 bytes wide; on such systems you
2678 cannot set hardware watchpoints for an expression that yields a
2679 double-precision floating-point number (which is typically 8 bytes
2680 wide). As a work-around, it might be possible to break the large region
2681 into a series of smaller ones and watch them with separate watchpoints.
2683 If you set too many hardware watchpoints, @value{GDBN} might be unable
2684 to insert all of them when you resume the execution of your program.
2685 Since the precise number of active watchpoints is unknown until such
2686 time as the program is about to be resumed, @value{GDBN} might not be
2687 able to warn you about this when you set the watchpoints, and the
2688 warning will be printed only when the program is resumed:
2691 Hardware watchpoint @var{num}: Could not insert watchpoint
2695 If this happens, delete or disable some of the watchpoints.
2697 The SPARClite DSU will generate traps when a program accesses some data
2698 or instruction address that is assigned to the debug registers. For the
2699 data addresses, DSU facilitates the @code{watch} command. However the
2700 hardware breakpoint registers can only take two data watchpoints, and
2701 both watchpoints must be the same kind. For example, you can set two
2702 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2703 @strong{or} two with @code{awatch} commands, but you cannot set one
2704 watchpoint with one command and the other with a different command.
2705 @value{GDBN} will reject the command if you try to mix watchpoints.
2706 Delete or disable unused watchpoint commands before setting new ones.
2708 If you call a function interactively using @code{print} or @code{call},
2709 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2710 kind of breakpoint or the call completes.
2712 @value{GDBN} automatically deletes watchpoints that watch local
2713 (automatic) variables, or expressions that involve such variables, when
2714 they go out of scope, that is, when the execution leaves the block in
2715 which these variables were defined. In particular, when the program
2716 being debugged terminates, @emph{all} local variables go out of scope,
2717 and so only watchpoints that watch global variables remain set. If you
2718 rerun the program, you will need to set all such watchpoints again. One
2719 way of doing that would be to set a code breakpoint at the entry to the
2720 @code{main} function and when it breaks, set all the watchpoints.
2723 @cindex watchpoints and threads
2724 @cindex threads and watchpoints
2725 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2726 usefulness. With the current watchpoint implementation, @value{GDBN}
2727 can only watch the value of an expression @emph{in a single thread}. If
2728 you are confident that the expression can only change due to the current
2729 thread's activity (and if you are also confident that no other thread
2730 can become current), then you can use watchpoints as usual. However,
2731 @value{GDBN} may not notice when a non-current thread's activity changes
2734 @c FIXME: this is almost identical to the previous paragraph.
2735 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2736 have only limited usefulness. If @value{GDBN} creates a software
2737 watchpoint, it can only watch the value of an expression @emph{in a
2738 single thread}. If you are confident that the expression can only
2739 change due to the current thread's activity (and if you are also
2740 confident that no other thread can become current), then you can use
2741 software watchpoints as usual. However, @value{GDBN} may not notice
2742 when a non-current thread's activity changes the expression. (Hardware
2743 watchpoints, in contrast, watch an expression in all threads.)
2746 @node Set Catchpoints
2747 @subsection Setting catchpoints
2748 @cindex catchpoints, setting
2749 @cindex exception handlers
2750 @cindex event handling
2752 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2753 kinds of program events, such as C@t{++} exceptions or the loading of a
2754 shared library. Use the @code{catch} command to set a catchpoint.
2758 @item catch @var{event}
2759 Stop when @var{event} occurs. @var{event} can be any of the following:
2763 The throwing of a C@t{++} exception.
2767 The catching of a C@t{++} exception.
2771 A call to @code{exec}. This is currently only available for HP-UX.
2775 A call to @code{fork}. This is currently only available for HP-UX.
2779 A call to @code{vfork}. This is currently only available for HP-UX.
2782 @itemx load @var{libname}
2784 The dynamic loading of any shared library, or the loading of the library
2785 @var{libname}. This is currently only available for HP-UX.
2788 @itemx unload @var{libname}
2789 @kindex catch unload
2790 The unloading of any dynamically loaded shared library, or the unloading
2791 of the library @var{libname}. This is currently only available for HP-UX.
2794 @item tcatch @var{event}
2795 Set a catchpoint that is enabled only for one stop. The catchpoint is
2796 automatically deleted after the first time the event is caught.
2800 Use the @code{info break} command to list the current catchpoints.
2802 There are currently some limitations to C@t{++} exception handling
2803 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2807 If you call a function interactively, @value{GDBN} normally returns
2808 control to you when the function has finished executing. If the call
2809 raises an exception, however, the call may bypass the mechanism that
2810 returns control to you and cause your program either to abort or to
2811 simply continue running until it hits a breakpoint, catches a signal
2812 that @value{GDBN} is listening for, or exits. This is the case even if
2813 you set a catchpoint for the exception; catchpoints on exceptions are
2814 disabled within interactive calls.
2817 You cannot raise an exception interactively.
2820 You cannot install an exception handler interactively.
2823 @cindex raise exceptions
2824 Sometimes @code{catch} is not the best way to debug exception handling:
2825 if you need to know exactly where an exception is raised, it is better to
2826 stop @emph{before} the exception handler is called, since that way you
2827 can see the stack before any unwinding takes place. If you set a
2828 breakpoint in an exception handler instead, it may not be easy to find
2829 out where the exception was raised.
2831 To stop just before an exception handler is called, you need some
2832 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2833 raised by calling a library function named @code{__raise_exception}
2834 which has the following ANSI C interface:
2837 /* @var{addr} is where the exception identifier is stored.
2838 @var{id} is the exception identifier. */
2839 void __raise_exception (void **addr, void *id);
2843 To make the debugger catch all exceptions before any stack
2844 unwinding takes place, set a breakpoint on @code{__raise_exception}
2845 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2847 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2848 that depends on the value of @var{id}, you can stop your program when
2849 a specific exception is raised. You can use multiple conditional
2850 breakpoints to stop your program when any of a number of exceptions are
2855 @subsection Deleting breakpoints
2857 @cindex clearing breakpoints, watchpoints, catchpoints
2858 @cindex deleting breakpoints, watchpoints, catchpoints
2859 It is often necessary to eliminate a breakpoint, watchpoint, or
2860 catchpoint once it has done its job and you no longer want your program
2861 to stop there. This is called @dfn{deleting} the breakpoint. A
2862 breakpoint that has been deleted no longer exists; it is forgotten.
2864 With the @code{clear} command you can delete breakpoints according to
2865 where they are in your program. With the @code{delete} command you can
2866 delete individual breakpoints, watchpoints, or catchpoints by specifying
2867 their breakpoint numbers.
2869 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2870 automatically ignores breakpoints on the first instruction to be executed
2871 when you continue execution without changing the execution address.
2876 Delete any breakpoints at the next instruction to be executed in the
2877 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2878 the innermost frame is selected, this is a good way to delete a
2879 breakpoint where your program just stopped.
2881 @item clear @var{function}
2882 @itemx clear @var{filename}:@var{function}
2883 Delete any breakpoints set at entry to the function @var{function}.
2885 @item clear @var{linenum}
2886 @itemx clear @var{filename}:@var{linenum}
2887 Delete any breakpoints set at or within the code of the specified line.
2889 @cindex delete breakpoints
2891 @kindex d @r{(@code{delete})}
2892 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2893 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2894 ranges specified as arguments. If no argument is specified, delete all
2895 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2896 confirm off}). You can abbreviate this command as @code{d}.
2900 @subsection Disabling breakpoints
2902 @kindex disable breakpoints
2903 @kindex enable breakpoints
2904 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2905 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2906 it had been deleted, but remembers the information on the breakpoint so
2907 that you can @dfn{enable} it again later.
2909 You disable and enable breakpoints, watchpoints, and catchpoints with
2910 the @code{enable} and @code{disable} commands, optionally specifying one
2911 or more breakpoint numbers as arguments. Use @code{info break} or
2912 @code{info watch} to print a list of breakpoints, watchpoints, and
2913 catchpoints if you do not know which numbers to use.
2915 A breakpoint, watchpoint, or catchpoint can have any of four different
2916 states of enablement:
2920 Enabled. The breakpoint stops your program. A breakpoint set
2921 with the @code{break} command starts out in this state.
2923 Disabled. The breakpoint has no effect on your program.
2925 Enabled once. The breakpoint stops your program, but then becomes
2928 Enabled for deletion. The breakpoint stops your program, but
2929 immediately after it does so it is deleted permanently. A breakpoint
2930 set with the @code{tbreak} command starts out in this state.
2933 You can use the following commands to enable or disable breakpoints,
2934 watchpoints, and catchpoints:
2937 @kindex disable breakpoints
2939 @kindex dis @r{(@code{disable})}
2940 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2941 Disable the specified breakpoints---or all breakpoints, if none are
2942 listed. A disabled breakpoint has no effect but is not forgotten. All
2943 options such as ignore-counts, conditions and commands are remembered in
2944 case the breakpoint is enabled again later. You may abbreviate
2945 @code{disable} as @code{dis}.
2947 @kindex enable breakpoints
2949 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2950 Enable the specified breakpoints (or all defined breakpoints). They
2951 become effective once again in stopping your program.
2953 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2954 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2955 of these breakpoints immediately after stopping your program.
2957 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2958 Enable the specified breakpoints to work once, then die. @value{GDBN}
2959 deletes any of these breakpoints as soon as your program stops there.
2962 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2963 @c confusing: tbreak is also initially enabled.
2964 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2965 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2966 subsequently, they become disabled or enabled only when you use one of
2967 the commands above. (The command @code{until} can set and delete a
2968 breakpoint of its own, but it does not change the state of your other
2969 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2973 @subsection Break conditions
2974 @cindex conditional breakpoints
2975 @cindex breakpoint conditions
2977 @c FIXME what is scope of break condition expr? Context where wanted?
2978 @c in particular for a watchpoint?
2979 The simplest sort of breakpoint breaks every time your program reaches a
2980 specified place. You can also specify a @dfn{condition} for a
2981 breakpoint. A condition is just a Boolean expression in your
2982 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2983 a condition evaluates the expression each time your program reaches it,
2984 and your program stops only if the condition is @emph{true}.
2986 This is the converse of using assertions for program validation; in that
2987 situation, you want to stop when the assertion is violated---that is,
2988 when the condition is false. In C, if you want to test an assertion expressed
2989 by the condition @var{assert}, you should set the condition
2990 @samp{! @var{assert}} on the appropriate breakpoint.
2992 Conditions are also accepted for watchpoints; you may not need them,
2993 since a watchpoint is inspecting the value of an expression anyhow---but
2994 it might be simpler, say, to just set a watchpoint on a variable name,
2995 and specify a condition that tests whether the new value is an interesting
2998 Break conditions can have side effects, and may even call functions in
2999 your program. This can be useful, for example, to activate functions
3000 that log program progress, or to use your own print functions to
3001 format special data structures. The effects are completely predictable
3002 unless there is another enabled breakpoint at the same address. (In
3003 that case, @value{GDBN} might see the other breakpoint first and stop your
3004 program without checking the condition of this one.) Note that
3005 breakpoint commands are usually more convenient and flexible than break
3007 purpose of performing side effects when a breakpoint is reached
3008 (@pxref{Break Commands, ,Breakpoint command lists}).
3010 Break conditions can be specified when a breakpoint is set, by using
3011 @samp{if} in the arguments to the @code{break} command. @xref{Set
3012 Breaks, ,Setting breakpoints}. They can also be changed at any time
3013 with the @code{condition} command.
3015 You can also use the @code{if} keyword with the @code{watch} command.
3016 The @code{catch} command does not recognize the @code{if} keyword;
3017 @code{condition} is the only way to impose a further condition on a
3022 @item condition @var{bnum} @var{expression}
3023 Specify @var{expression} as the break condition for breakpoint,
3024 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3025 breakpoint @var{bnum} stops your program only if the value of
3026 @var{expression} is true (nonzero, in C). When you use
3027 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3028 syntactic correctness, and to determine whether symbols in it have
3029 referents in the context of your breakpoint. If @var{expression} uses
3030 symbols not referenced in the context of the breakpoint, @value{GDBN}
3031 prints an error message:
3034 No symbol "foo" in current context.
3039 not actually evaluate @var{expression} at the time the @code{condition}
3040 command (or a command that sets a breakpoint with a condition, like
3041 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3043 @item condition @var{bnum}
3044 Remove the condition from breakpoint number @var{bnum}. It becomes
3045 an ordinary unconditional breakpoint.
3048 @cindex ignore count (of breakpoint)
3049 A special case of a breakpoint condition is to stop only when the
3050 breakpoint has been reached a certain number of times. This is so
3051 useful that there is a special way to do it, using the @dfn{ignore
3052 count} of the breakpoint. Every breakpoint has an ignore count, which
3053 is an integer. Most of the time, the ignore count is zero, and
3054 therefore has no effect. But if your program reaches a breakpoint whose
3055 ignore count is positive, then instead of stopping, it just decrements
3056 the ignore count by one and continues. As a result, if the ignore count
3057 value is @var{n}, the breakpoint does not stop the next @var{n} times
3058 your program reaches it.
3062 @item ignore @var{bnum} @var{count}
3063 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3064 The next @var{count} times the breakpoint is reached, your program's
3065 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3068 To make the breakpoint stop the next time it is reached, specify
3071 When you use @code{continue} to resume execution of your program from a
3072 breakpoint, you can specify an ignore count directly as an argument to
3073 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3074 Stepping,,Continuing and stepping}.
3076 If a breakpoint has a positive ignore count and a condition, the
3077 condition is not checked. Once the ignore count reaches zero,
3078 @value{GDBN} resumes checking the condition.
3080 You could achieve the effect of the ignore count with a condition such
3081 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3082 is decremented each time. @xref{Convenience Vars, ,Convenience
3086 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3089 @node Break Commands
3090 @subsection Breakpoint command lists
3092 @cindex breakpoint commands
3093 You can give any breakpoint (or watchpoint or catchpoint) a series of
3094 commands to execute when your program stops due to that breakpoint. For
3095 example, you might want to print the values of certain expressions, or
3096 enable other breakpoints.
3101 @item commands @r{[}@var{bnum}@r{]}
3102 @itemx @dots{} @var{command-list} @dots{}
3104 Specify a list of commands for breakpoint number @var{bnum}. The commands
3105 themselves appear on the following lines. Type a line containing just
3106 @code{end} to terminate the commands.
3108 To remove all commands from a breakpoint, type @code{commands} and
3109 follow it immediately with @code{end}; that is, give no commands.
3111 With no @var{bnum} argument, @code{commands} refers to the last
3112 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3113 recently encountered).
3116 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3117 disabled within a @var{command-list}.
3119 You can use breakpoint commands to start your program up again. Simply
3120 use the @code{continue} command, or @code{step}, or any other command
3121 that resumes execution.
3123 Any other commands in the command list, after a command that resumes
3124 execution, are ignored. This is because any time you resume execution
3125 (even with a simple @code{next} or @code{step}), you may encounter
3126 another breakpoint---which could have its own command list, leading to
3127 ambiguities about which list to execute.
3130 If the first command you specify in a command list is @code{silent}, the
3131 usual message about stopping at a breakpoint is not printed. This may
3132 be desirable for breakpoints that are to print a specific message and
3133 then continue. If none of the remaining commands print anything, you
3134 see no sign that the breakpoint was reached. @code{silent} is
3135 meaningful only at the beginning of a breakpoint command list.
3137 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3138 print precisely controlled output, and are often useful in silent
3139 breakpoints. @xref{Output, ,Commands for controlled output}.
3141 For example, here is how you could use breakpoint commands to print the
3142 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3148 printf "x is %d\n",x
3153 One application for breakpoint commands is to compensate for one bug so
3154 you can test for another. Put a breakpoint just after the erroneous line
3155 of code, give it a condition to detect the case in which something
3156 erroneous has been done, and give it commands to assign correct values
3157 to any variables that need them. End with the @code{continue} command
3158 so that your program does not stop, and start with the @code{silent}
3159 command so that no output is produced. Here is an example:
3170 @node Breakpoint Menus
3171 @subsection Breakpoint menus
3173 @cindex symbol overloading
3175 Some programming languages (notably C@t{++}) permit a single function name
3176 to be defined several times, for application in different contexts.
3177 This is called @dfn{overloading}. When a function name is overloaded,
3178 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3179 a breakpoint. If you realize this is a problem, you can use
3180 something like @samp{break @var{function}(@var{types})} to specify which
3181 particular version of the function you want. Otherwise, @value{GDBN} offers
3182 you a menu of numbered choices for different possible breakpoints, and
3183 waits for your selection with the prompt @samp{>}. The first two
3184 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3185 sets a breakpoint at each definition of @var{function}, and typing
3186 @kbd{0} aborts the @code{break} command without setting any new
3189 For example, the following session excerpt shows an attempt to set a
3190 breakpoint at the overloaded symbol @code{String::after}.
3191 We choose three particular definitions of that function name:
3193 @c FIXME! This is likely to change to show arg type lists, at least
3196 (@value{GDBP}) b String::after
3199 [2] file:String.cc; line number:867
3200 [3] file:String.cc; line number:860
3201 [4] file:String.cc; line number:875
3202 [5] file:String.cc; line number:853
3203 [6] file:String.cc; line number:846
3204 [7] file:String.cc; line number:735
3206 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3207 Breakpoint 2 at 0xb344: file String.cc, line 875.
3208 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3209 Multiple breakpoints were set.
3210 Use the "delete" command to delete unwanted
3216 @c @ifclear BARETARGET
3217 @node Error in Breakpoints
3218 @subsection ``Cannot insert breakpoints''
3220 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3222 Under some operating systems, breakpoints cannot be used in a program if
3223 any other process is running that program. In this situation,
3224 attempting to run or continue a program with a breakpoint causes
3225 @value{GDBN} to print an error message:
3228 Cannot insert breakpoints.
3229 The same program may be running in another process.
3232 When this happens, you have three ways to proceed:
3236 Remove or disable the breakpoints, then continue.
3239 Suspend @value{GDBN}, and copy the file containing your program to a new
3240 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3241 that @value{GDBN} should run your program under that name.
3242 Then start your program again.
3245 Relink your program so that the text segment is nonsharable, using the
3246 linker option @samp{-N}. The operating system limitation may not apply
3247 to nonsharable executables.
3251 A similar message can be printed if you request too many active
3252 hardware-assisted breakpoints and watchpoints:
3254 @c FIXME: the precise wording of this message may change; the relevant
3255 @c source change is not committed yet (Sep 3, 1999).
3257 Stopped; cannot insert breakpoints.
3258 You may have requested too many hardware breakpoints and watchpoints.
3262 This message is printed when you attempt to resume the program, since
3263 only then @value{GDBN} knows exactly how many hardware breakpoints and
3264 watchpoints it needs to insert.
3266 When this message is printed, you need to disable or remove some of the
3267 hardware-assisted breakpoints and watchpoints, and then continue.
3270 @node Continuing and Stepping
3271 @section Continuing and stepping
3275 @cindex resuming execution
3276 @dfn{Continuing} means resuming program execution until your program
3277 completes normally. In contrast, @dfn{stepping} means executing just
3278 one more ``step'' of your program, where ``step'' may mean either one
3279 line of source code, or one machine instruction (depending on what
3280 particular command you use). Either when continuing or when stepping,
3281 your program may stop even sooner, due to a breakpoint or a signal. (If
3282 it stops due to a signal, you may want to use @code{handle}, or use
3283 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3287 @kindex c @r{(@code{continue})}
3288 @kindex fg @r{(resume foreground execution)}
3289 @item continue @r{[}@var{ignore-count}@r{]}
3290 @itemx c @r{[}@var{ignore-count}@r{]}
3291 @itemx fg @r{[}@var{ignore-count}@r{]}
3292 Resume program execution, at the address where your program last stopped;
3293 any breakpoints set at that address are bypassed. The optional argument
3294 @var{ignore-count} allows you to specify a further number of times to
3295 ignore a breakpoint at this location; its effect is like that of
3296 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3298 The argument @var{ignore-count} is meaningful only when your program
3299 stopped due to a breakpoint. At other times, the argument to
3300 @code{continue} is ignored.
3302 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3303 debugged program is deemed to be the foreground program) are provided
3304 purely for convenience, and have exactly the same behavior as
3308 To resume execution at a different place, you can use @code{return}
3309 (@pxref{Returning, ,Returning from a function}) to go back to the
3310 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3311 different address}) to go to an arbitrary location in your program.
3313 A typical technique for using stepping is to set a breakpoint
3314 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3315 beginning of the function or the section of your program where a problem
3316 is believed to lie, run your program until it stops at that breakpoint,
3317 and then step through the suspect area, examining the variables that are
3318 interesting, until you see the problem happen.
3322 @kindex s @r{(@code{step})}
3324 Continue running your program until control reaches a different source
3325 line, then stop it and return control to @value{GDBN}. This command is
3326 abbreviated @code{s}.
3329 @c "without debugging information" is imprecise; actually "without line
3330 @c numbers in the debugging information". (gcc -g1 has debugging info but
3331 @c not line numbers). But it seems complex to try to make that
3332 @c distinction here.
3333 @emph{Warning:} If you use the @code{step} command while control is
3334 within a function that was compiled without debugging information,
3335 execution proceeds until control reaches a function that does have
3336 debugging information. Likewise, it will not step into a function which
3337 is compiled without debugging information. To step through functions
3338 without debugging information, use the @code{stepi} command, described
3342 The @code{step} command only stops at the first instruction of a source
3343 line. This prevents the multiple stops that could otherwise occur in
3344 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3345 to stop if a function that has debugging information is called within
3346 the line. In other words, @code{step} @emph{steps inside} any functions
3347 called within the line.
3349 Also, the @code{step} command only enters a function if there is line
3350 number information for the function. Otherwise it acts like the
3351 @code{next} command. This avoids problems when using @code{cc -gl}
3352 on MIPS machines. Previously, @code{step} entered subroutines if there
3353 was any debugging information about the routine.
3355 @item step @var{count}
3356 Continue running as in @code{step}, but do so @var{count} times. If a
3357 breakpoint is reached, or a signal not related to stepping occurs before
3358 @var{count} steps, stepping stops right away.
3361 @kindex n @r{(@code{next})}
3362 @item next @r{[}@var{count}@r{]}
3363 Continue to the next source line in the current (innermost) stack frame.
3364 This is similar to @code{step}, but function calls that appear within
3365 the line of code are executed without stopping. Execution stops when
3366 control reaches a different line of code at the original stack level
3367 that was executing when you gave the @code{next} command. This command
3368 is abbreviated @code{n}.
3370 An argument @var{count} is a repeat count, as for @code{step}.
3373 @c FIX ME!! Do we delete this, or is there a way it fits in with
3374 @c the following paragraph? --- Vctoria
3376 @c @code{next} within a function that lacks debugging information acts like
3377 @c @code{step}, but any function calls appearing within the code of the
3378 @c function are executed without stopping.
3380 The @code{next} command only stops at the first instruction of a
3381 source line. This prevents multiple stops that could otherwise occur in
3382 @code{switch} statements, @code{for} loops, etc.
3384 @kindex set step-mode
3386 @cindex functions without line info, and stepping
3387 @cindex stepping into functions with no line info
3388 @itemx set step-mode on
3389 The @code{set step-mode on} command causes the @code{step} command to
3390 stop at the first instruction of a function which contains no debug line
3391 information rather than stepping over it.
3393 This is useful in cases where you may be interested in inspecting the
3394 machine instructions of a function which has no symbolic info and do not
3395 want @value{GDBN} to automatically skip over this function.
3397 @item set step-mode off
3398 Causes the @code{step} command to step over any functions which contains no
3399 debug information. This is the default.
3403 Continue running until just after function in the selected stack frame
3404 returns. Print the returned value (if any).
3406 Contrast this with the @code{return} command (@pxref{Returning,
3407 ,Returning from a function}).
3410 @kindex u @r{(@code{until})}
3413 Continue running until a source line past the current line, in the
3414 current stack frame, is reached. This command is used to avoid single
3415 stepping through a loop more than once. It is like the @code{next}
3416 command, except that when @code{until} encounters a jump, it
3417 automatically continues execution until the program counter is greater
3418 than the address of the jump.
3420 This means that when you reach the end of a loop after single stepping
3421 though it, @code{until} makes your program continue execution until it
3422 exits the loop. In contrast, a @code{next} command at the end of a loop
3423 simply steps back to the beginning of the loop, which forces you to step
3424 through the next iteration.
3426 @code{until} always stops your program if it attempts to exit the current
3429 @code{until} may produce somewhat counterintuitive results if the order
3430 of machine code does not match the order of the source lines. For
3431 example, in the following excerpt from a debugging session, the @code{f}
3432 (@code{frame}) command shows that execution is stopped at line
3433 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3437 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3439 (@value{GDBP}) until
3440 195 for ( ; argc > 0; NEXTARG) @{
3443 This happened because, for execution efficiency, the compiler had
3444 generated code for the loop closure test at the end, rather than the
3445 start, of the loop---even though the test in a C @code{for}-loop is
3446 written before the body of the loop. The @code{until} command appeared
3447 to step back to the beginning of the loop when it advanced to this
3448 expression; however, it has not really gone to an earlier
3449 statement---not in terms of the actual machine code.
3451 @code{until} with no argument works by means of single
3452 instruction stepping, and hence is slower than @code{until} with an
3455 @item until @var{location}
3456 @itemx u @var{location}
3457 Continue running your program until either the specified location is
3458 reached, or the current stack frame returns. @var{location} is any of
3459 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3460 ,Setting breakpoints}). This form of the command uses breakpoints,
3461 and hence is quicker than @code{until} without an argument.
3464 @kindex si @r{(@code{stepi})}
3466 @itemx stepi @var{arg}
3468 Execute one machine instruction, then stop and return to the debugger.
3470 It is often useful to do @samp{display/i $pc} when stepping by machine
3471 instructions. This makes @value{GDBN} automatically display the next
3472 instruction to be executed, each time your program stops. @xref{Auto
3473 Display,, Automatic display}.
3475 An argument is a repeat count, as in @code{step}.
3479 @kindex ni @r{(@code{nexti})}
3481 @itemx nexti @var{arg}
3483 Execute one machine instruction, but if it is a function call,
3484 proceed until the function returns.
3486 An argument is a repeat count, as in @code{next}.
3493 A signal is an asynchronous event that can happen in a program. The
3494 operating system defines the possible kinds of signals, and gives each
3495 kind a name and a number. For example, in Unix @code{SIGINT} is the
3496 signal a program gets when you type an interrupt character (often @kbd{C-c});
3497 @code{SIGSEGV} is the signal a program gets from referencing a place in
3498 memory far away from all the areas in use; @code{SIGALRM} occurs when
3499 the alarm clock timer goes off (which happens only if your program has
3500 requested an alarm).
3502 @cindex fatal signals
3503 Some signals, including @code{SIGALRM}, are a normal part of the
3504 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3505 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3506 program has not specified in advance some other way to handle the signal.
3507 @code{SIGINT} does not indicate an error in your program, but it is normally
3508 fatal so it can carry out the purpose of the interrupt: to kill the program.
3510 @value{GDBN} has the ability to detect any occurrence of a signal in your
3511 program. You can tell @value{GDBN} in advance what to do for each kind of
3514 @cindex handling signals
3515 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3516 @code{SIGALRM} be silently passed to your program
3517 (so as not to interfere with their role in the program's functioning)
3518 but to stop your program immediately whenever an error signal happens.
3519 You can change these settings with the @code{handle} command.
3522 @kindex info signals
3525 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3526 handle each one. You can use this to see the signal numbers of all
3527 the defined types of signals.
3529 @code{info handle} is an alias for @code{info signals}.
3532 @item handle @var{signal} @var{keywords}@dots{}
3533 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3534 can be the number of a signal or its name (with or without the
3535 @samp{SIG} at the beginning); a list of signal numbers of the form
3536 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3537 known signals. The @var{keywords} say what change to make.
3541 The keywords allowed by the @code{handle} command can be abbreviated.
3542 Their full names are:
3546 @value{GDBN} should not stop your program when this signal happens. It may
3547 still print a message telling you that the signal has come in.
3550 @value{GDBN} should stop your program when this signal happens. This implies
3551 the @code{print} keyword as well.
3554 @value{GDBN} should print a message when this signal happens.
3557 @value{GDBN} should not mention the occurrence of the signal at all. This
3558 implies the @code{nostop} keyword as well.
3562 @value{GDBN} should allow your program to see this signal; your program
3563 can handle the signal, or else it may terminate if the signal is fatal
3564 and not handled. @code{pass} and @code{noignore} are synonyms.
3568 @value{GDBN} should not allow your program to see this signal.
3569 @code{nopass} and @code{ignore} are synonyms.
3573 When a signal stops your program, the signal is not visible to the
3575 continue. Your program sees the signal then, if @code{pass} is in
3576 effect for the signal in question @emph{at that time}. In other words,
3577 after @value{GDBN} reports a signal, you can use the @code{handle}
3578 command with @code{pass} or @code{nopass} to control whether your
3579 program sees that signal when you continue.
3581 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3582 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3583 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3586 You can also use the @code{signal} command to prevent your program from
3587 seeing a signal, or cause it to see a signal it normally would not see,
3588 or to give it any signal at any time. For example, if your program stopped
3589 due to some sort of memory reference error, you might store correct
3590 values into the erroneous variables and continue, hoping to see more
3591 execution; but your program would probably terminate immediately as
3592 a result of the fatal signal once it saw the signal. To prevent this,
3593 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3597 @section Stopping and starting multi-thread programs
3599 When your program has multiple threads (@pxref{Threads,, Debugging
3600 programs with multiple threads}), you can choose whether to set
3601 breakpoints on all threads, or on a particular thread.
3604 @cindex breakpoints and threads
3605 @cindex thread breakpoints
3606 @kindex break @dots{} thread @var{threadno}
3607 @item break @var{linespec} thread @var{threadno}
3608 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3609 @var{linespec} specifies source lines; there are several ways of
3610 writing them, but the effect is always to specify some source line.
3612 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3613 to specify that you only want @value{GDBN} to stop the program when a
3614 particular thread reaches this breakpoint. @var{threadno} is one of the
3615 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3616 column of the @samp{info threads} display.
3618 If you do not specify @samp{thread @var{threadno}} when you set a
3619 breakpoint, the breakpoint applies to @emph{all} threads of your
3622 You can use the @code{thread} qualifier on conditional breakpoints as
3623 well; in this case, place @samp{thread @var{threadno}} before the
3624 breakpoint condition, like this:
3627 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3632 @cindex stopped threads
3633 @cindex threads, stopped
3634 Whenever your program stops under @value{GDBN} for any reason,
3635 @emph{all} threads of execution stop, not just the current thread. This
3636 allows you to examine the overall state of the program, including
3637 switching between threads, without worrying that things may change
3640 @cindex continuing threads
3641 @cindex threads, continuing
3642 Conversely, whenever you restart the program, @emph{all} threads start
3643 executing. @emph{This is true even when single-stepping} with commands
3644 like @code{step} or @code{next}.
3646 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3647 Since thread scheduling is up to your debugging target's operating
3648 system (not controlled by @value{GDBN}), other threads may
3649 execute more than one statement while the current thread completes a
3650 single step. Moreover, in general other threads stop in the middle of a
3651 statement, rather than at a clean statement boundary, when the program
3654 You might even find your program stopped in another thread after
3655 continuing or even single-stepping. This happens whenever some other
3656 thread runs into a breakpoint, a signal, or an exception before the
3657 first thread completes whatever you requested.
3659 On some OSes, you can lock the OS scheduler and thus allow only a single
3663 @item set scheduler-locking @var{mode}
3664 Set the scheduler locking mode. If it is @code{off}, then there is no
3665 locking and any thread may run at any time. If @code{on}, then only the
3666 current thread may run when the inferior is resumed. The @code{step}
3667 mode optimizes for single-stepping. It stops other threads from
3668 ``seizing the prompt'' by preempting the current thread while you are
3669 stepping. Other threads will only rarely (or never) get a chance to run
3670 when you step. They are more likely to run when you @samp{next} over a
3671 function call, and they are completely free to run when you use commands
3672 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3673 thread hits a breakpoint during its timeslice, they will never steal the
3674 @value{GDBN} prompt away from the thread that you are debugging.
3676 @item show scheduler-locking
3677 Display the current scheduler locking mode.
3682 @chapter Examining the Stack
3684 When your program has stopped, the first thing you need to know is where it
3685 stopped and how it got there.
3688 Each time your program performs a function call, information about the call
3690 That information includes the location of the call in your program,
3691 the arguments of the call,
3692 and the local variables of the function being called.
3693 The information is saved in a block of data called a @dfn{stack frame}.
3694 The stack frames are allocated in a region of memory called the @dfn{call
3697 When your program stops, the @value{GDBN} commands for examining the
3698 stack allow you to see all of this information.
3700 @cindex selected frame
3701 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3702 @value{GDBN} commands refer implicitly to the selected frame. In
3703 particular, whenever you ask @value{GDBN} for the value of a variable in
3704 your program, the value is found in the selected frame. There are
3705 special @value{GDBN} commands to select whichever frame you are
3706 interested in. @xref{Selection, ,Selecting a frame}.
3708 When your program stops, @value{GDBN} automatically selects the
3709 currently executing frame and describes it briefly, similar to the
3710 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3713 * Frames:: Stack frames
3714 * Backtrace:: Backtraces
3715 * Selection:: Selecting a frame
3716 * Frame Info:: Information on a frame
3721 @section Stack frames
3723 @cindex frame, definition
3725 The call stack is divided up into contiguous pieces called @dfn{stack
3726 frames}, or @dfn{frames} for short; each frame is the data associated
3727 with one call to one function. The frame contains the arguments given
3728 to the function, the function's local variables, and the address at
3729 which the function is executing.
3731 @cindex initial frame
3732 @cindex outermost frame
3733 @cindex innermost frame
3734 When your program is started, the stack has only one frame, that of the
3735 function @code{main}. This is called the @dfn{initial} frame or the
3736 @dfn{outermost} frame. Each time a function is called, a new frame is
3737 made. Each time a function returns, the frame for that function invocation
3738 is eliminated. If a function is recursive, there can be many frames for
3739 the same function. The frame for the function in which execution is
3740 actually occurring is called the @dfn{innermost} frame. This is the most
3741 recently created of all the stack frames that still exist.
3743 @cindex frame pointer
3744 Inside your program, stack frames are identified by their addresses. A
3745 stack frame consists of many bytes, each of which has its own address; each
3746 kind of computer has a convention for choosing one byte whose
3747 address serves as the address of the frame. Usually this address is kept
3748 in a register called the @dfn{frame pointer register} while execution is
3749 going on in that frame.
3751 @cindex frame number
3752 @value{GDBN} assigns numbers to all existing stack frames, starting with
3753 zero for the innermost frame, one for the frame that called it,
3754 and so on upward. These numbers do not really exist in your program;
3755 they are assigned by @value{GDBN} to give you a way of designating stack
3756 frames in @value{GDBN} commands.
3758 @c The -fomit-frame-pointer below perennially causes hbox overflow
3759 @c underflow problems.
3760 @cindex frameless execution
3761 Some compilers provide a way to compile functions so that they operate
3762 without stack frames. (For example, the @value{GCC} option
3764 @samp{-fomit-frame-pointer}
3766 generates functions without a frame.)
3767 This is occasionally done with heavily used library functions to save
3768 the frame setup time. @value{GDBN} has limited facilities for dealing
3769 with these function invocations. If the innermost function invocation
3770 has no stack frame, @value{GDBN} nevertheless regards it as though
3771 it had a separate frame, which is numbered zero as usual, allowing
3772 correct tracing of the function call chain. However, @value{GDBN} has
3773 no provision for frameless functions elsewhere in the stack.
3776 @kindex frame@r{, command}
3777 @cindex current stack frame
3778 @item frame @var{args}
3779 The @code{frame} command allows you to move from one stack frame to another,
3780 and to print the stack frame you select. @var{args} may be either the
3781 address of the frame or the stack frame number. Without an argument,
3782 @code{frame} prints the current stack frame.
3784 @kindex select-frame
3785 @cindex selecting frame silently
3787 The @code{select-frame} command allows you to move from one stack frame
3788 to another without printing the frame. This is the silent version of
3797 @cindex stack traces
3798 A backtrace is a summary of how your program got where it is. It shows one
3799 line per frame, for many frames, starting with the currently executing
3800 frame (frame zero), followed by its caller (frame one), and on up the
3805 @kindex bt @r{(@code{backtrace})}
3808 Print a backtrace of the entire stack: one line per frame for all
3809 frames in the stack.
3811 You can stop the backtrace at any time by typing the system interrupt
3812 character, normally @kbd{C-c}.
3814 @item backtrace @var{n}
3816 Similar, but print only the innermost @var{n} frames.
3818 @item backtrace -@var{n}
3820 Similar, but print only the outermost @var{n} frames.
3825 @kindex info s @r{(@code{info stack})}
3826 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3827 are additional aliases for @code{backtrace}.
3829 Each line in the backtrace shows the frame number and the function name.
3830 The program counter value is also shown---unless you use @code{set
3831 print address off}. The backtrace also shows the source file name and
3832 line number, as well as the arguments to the function. The program
3833 counter value is omitted if it is at the beginning of the code for that
3836 Here is an example of a backtrace. It was made with the command
3837 @samp{bt 3}, so it shows the innermost three frames.
3841 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3843 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3844 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3846 (More stack frames follow...)
3851 The display for frame zero does not begin with a program counter
3852 value, indicating that your program has stopped at the beginning of the
3853 code for line @code{993} of @code{builtin.c}.
3856 @section Selecting a frame
3858 Most commands for examining the stack and other data in your program work on
3859 whichever stack frame is selected at the moment. Here are the commands for
3860 selecting a stack frame; all of them finish by printing a brief description
3861 of the stack frame just selected.
3864 @kindex frame@r{, selecting}
3865 @kindex f @r{(@code{frame})}
3868 Select frame number @var{n}. Recall that frame zero is the innermost
3869 (currently executing) frame, frame one is the frame that called the
3870 innermost one, and so on. The highest-numbered frame is the one for
3873 @item frame @var{addr}
3875 Select the frame at address @var{addr}. This is useful mainly if the
3876 chaining of stack frames has been damaged by a bug, making it
3877 impossible for @value{GDBN} to assign numbers properly to all frames. In
3878 addition, this can be useful when your program has multiple stacks and
3879 switches between them.
3881 On the SPARC architecture, @code{frame} needs two addresses to
3882 select an arbitrary frame: a frame pointer and a stack pointer.
3884 On the MIPS and Alpha architecture, it needs two addresses: a stack
3885 pointer and a program counter.
3887 On the 29k architecture, it needs three addresses: a register stack
3888 pointer, a program counter, and a memory stack pointer.
3889 @c note to future updaters: this is conditioned on a flag
3890 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3891 @c as of 27 Jan 1994.
3895 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3896 advances toward the outermost frame, to higher frame numbers, to frames
3897 that have existed longer. @var{n} defaults to one.
3900 @kindex do @r{(@code{down})}
3902 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3903 advances toward the innermost frame, to lower frame numbers, to frames
3904 that were created more recently. @var{n} defaults to one. You may
3905 abbreviate @code{down} as @code{do}.
3908 All of these commands end by printing two lines of output describing the
3909 frame. The first line shows the frame number, the function name, the
3910 arguments, and the source file and line number of execution in that
3911 frame. The second line shows the text of that source line.
3919 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3921 10 read_input_file (argv[i]);
3925 After such a printout, the @code{list} command with no arguments
3926 prints ten lines centered on the point of execution in the frame.
3927 @xref{List, ,Printing source lines}.
3930 @kindex down-silently
3932 @item up-silently @var{n}
3933 @itemx down-silently @var{n}
3934 These two commands are variants of @code{up} and @code{down},
3935 respectively; they differ in that they do their work silently, without
3936 causing display of the new frame. They are intended primarily for use
3937 in @value{GDBN} command scripts, where the output might be unnecessary and
3942 @section Information about a frame
3944 There are several other commands to print information about the selected
3950 When used without any argument, this command does not change which
3951 frame is selected, but prints a brief description of the currently
3952 selected stack frame. It can be abbreviated @code{f}. With an
3953 argument, this command is used to select a stack frame.
3954 @xref{Selection, ,Selecting a frame}.
3957 @kindex info f @r{(@code{info frame})}
3960 This command prints a verbose description of the selected stack frame,
3965 the address of the frame
3967 the address of the next frame down (called by this frame)
3969 the address of the next frame up (caller of this frame)
3971 the language in which the source code corresponding to this frame is written
3973 the address of the frame's arguments
3975 the address of the frame's local variables
3977 the program counter saved in it (the address of execution in the caller frame)
3979 which registers were saved in the frame
3982 @noindent The verbose description is useful when
3983 something has gone wrong that has made the stack format fail to fit
3984 the usual conventions.
3986 @item info frame @var{addr}
3987 @itemx info f @var{addr}
3988 Print a verbose description of the frame at address @var{addr}, without
3989 selecting that frame. The selected frame remains unchanged by this
3990 command. This requires the same kind of address (more than one for some
3991 architectures) that you specify in the @code{frame} command.
3992 @xref{Selection, ,Selecting a frame}.
3996 Print the arguments of the selected frame, each on a separate line.
4000 Print the local variables of the selected frame, each on a separate
4001 line. These are all variables (declared either static or automatic)
4002 accessible at the point of execution of the selected frame.
4005 @cindex catch exceptions, list active handlers
4006 @cindex exception handlers, how to list
4008 Print a list of all the exception handlers that are active in the
4009 current stack frame at the current point of execution. To see other
4010 exception handlers, visit the associated frame (using the @code{up},
4011 @code{down}, or @code{frame} commands); then type @code{info catch}.
4012 @xref{Set Catchpoints, , Setting catchpoints}.
4018 @chapter Examining Source Files
4020 @value{GDBN} can print parts of your program's source, since the debugging
4021 information recorded in the program tells @value{GDBN} what source files were
4022 used to build it. When your program stops, @value{GDBN} spontaneously prints
4023 the line where it stopped. Likewise, when you select a stack frame
4024 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4025 execution in that frame has stopped. You can print other portions of
4026 source files by explicit command.
4028 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4029 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4030 @value{GDBN} under @sc{gnu} Emacs}.
4033 * List:: Printing source lines
4034 * Search:: Searching source files
4035 * Source Path:: Specifying source directories
4036 * Machine Code:: Source and machine code
4040 @section Printing source lines
4043 @kindex l @r{(@code{list})}
4044 To print lines from a source file, use the @code{list} command
4045 (abbreviated @code{l}). By default, ten lines are printed.
4046 There are several ways to specify what part of the file you want to print.
4048 Here are the forms of the @code{list} command most commonly used:
4051 @item list @var{linenum}
4052 Print lines centered around line number @var{linenum} in the
4053 current source file.
4055 @item list @var{function}
4056 Print lines centered around the beginning of function
4060 Print more lines. If the last lines printed were printed with a
4061 @code{list} command, this prints lines following the last lines
4062 printed; however, if the last line printed was a solitary line printed
4063 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4064 Stack}), this prints lines centered around that line.
4067 Print lines just before the lines last printed.
4070 By default, @value{GDBN} prints ten source lines with any of these forms of
4071 the @code{list} command. You can change this using @code{set listsize}:
4074 @kindex set listsize
4075 @item set listsize @var{count}
4076 Make the @code{list} command display @var{count} source lines (unless
4077 the @code{list} argument explicitly specifies some other number).
4079 @kindex show listsize
4081 Display the number of lines that @code{list} prints.
4084 Repeating a @code{list} command with @key{RET} discards the argument,
4085 so it is equivalent to typing just @code{list}. This is more useful
4086 than listing the same lines again. An exception is made for an
4087 argument of @samp{-}; that argument is preserved in repetition so that
4088 each repetition moves up in the source file.
4091 In general, the @code{list} command expects you to supply zero, one or two
4092 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4093 of writing them, but the effect is always to specify some source line.
4094 Here is a complete description of the possible arguments for @code{list}:
4097 @item list @var{linespec}
4098 Print lines centered around the line specified by @var{linespec}.
4100 @item list @var{first},@var{last}
4101 Print lines from @var{first} to @var{last}. Both arguments are
4104 @item list ,@var{last}
4105 Print lines ending with @var{last}.
4107 @item list @var{first},
4108 Print lines starting with @var{first}.
4111 Print lines just after the lines last printed.
4114 Print lines just before the lines last printed.
4117 As described in the preceding table.
4120 Here are the ways of specifying a single source line---all the
4125 Specifies line @var{number} of the current source file.
4126 When a @code{list} command has two linespecs, this refers to
4127 the same source file as the first linespec.
4130 Specifies the line @var{offset} lines after the last line printed.
4131 When used as the second linespec in a @code{list} command that has
4132 two, this specifies the line @var{offset} lines down from the
4136 Specifies the line @var{offset} lines before the last line printed.
4138 @item @var{filename}:@var{number}
4139 Specifies line @var{number} in the source file @var{filename}.
4141 @item @var{function}
4142 Specifies the line that begins the body of the function @var{function}.
4143 For example: in C, this is the line with the open brace.
4145 @item @var{filename}:@var{function}
4146 Specifies the line of the open-brace that begins the body of the
4147 function @var{function} in the file @var{filename}. You only need the
4148 file name with a function name to avoid ambiguity when there are
4149 identically named functions in different source files.
4151 @item *@var{address}
4152 Specifies the line containing the program address @var{address}.
4153 @var{address} may be any expression.
4157 @section Searching source files
4159 @kindex reverse-search
4161 There are two commands for searching through the current source file for a
4166 @kindex forward-search
4167 @item forward-search @var{regexp}
4168 @itemx search @var{regexp}
4169 The command @samp{forward-search @var{regexp}} checks each line,
4170 starting with the one following the last line listed, for a match for
4171 @var{regexp}. It lists the line that is found. You can use the
4172 synonym @samp{search @var{regexp}} or abbreviate the command name as
4175 @item reverse-search @var{regexp}
4176 The command @samp{reverse-search @var{regexp}} checks each line, starting
4177 with the one before the last line listed and going backward, for a match
4178 for @var{regexp}. It lists the line that is found. You can abbreviate
4179 this command as @code{rev}.
4183 @section Specifying source directories
4186 @cindex directories for source files
4187 Executable programs sometimes do not record the directories of the source
4188 files from which they were compiled, just the names. Even when they do,
4189 the directories could be moved between the compilation and your debugging
4190 session. @value{GDBN} has a list of directories to search for source files;
4191 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4192 it tries all the directories in the list, in the order they are present
4193 in the list, until it finds a file with the desired name. Note that
4194 the executable search path is @emph{not} used for this purpose. Neither is
4195 the current working directory, unless it happens to be in the source
4198 If @value{GDBN} cannot find a source file in the source path, and the
4199 object program records a directory, @value{GDBN} tries that directory
4200 too. If the source path is empty, and there is no record of the
4201 compilation directory, @value{GDBN} looks in the current directory as a
4204 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4205 any information it has cached about where source files are found and where
4206 each line is in the file.
4210 When you start @value{GDBN}, its source path includes only @samp{cdir}
4211 and @samp{cwd}, in that order.
4212 To add other directories, use the @code{directory} command.
4215 @item directory @var{dirname} @dots{}
4216 @item dir @var{dirname} @dots{}
4217 Add directory @var{dirname} to the front of the source path. Several
4218 directory names may be given to this command, separated by @samp{:}
4219 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4220 part of absolute file names) or
4221 whitespace. You may specify a directory that is already in the source
4222 path; this moves it forward, so @value{GDBN} searches it sooner.
4226 @vindex $cdir@r{, convenience variable}
4227 @vindex $cwdr@r{, convenience variable}
4228 @cindex compilation directory
4229 @cindex current directory
4230 @cindex working directory
4231 @cindex directory, current
4232 @cindex directory, compilation
4233 You can use the string @samp{$cdir} to refer to the compilation
4234 directory (if one is recorded), and @samp{$cwd} to refer to the current
4235 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4236 tracks the current working directory as it changes during your @value{GDBN}
4237 session, while the latter is immediately expanded to the current
4238 directory at the time you add an entry to the source path.
4241 Reset the source path to empty again. This requires confirmation.
4243 @c RET-repeat for @code{directory} is explicitly disabled, but since
4244 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4246 @item show directories
4247 @kindex show directories
4248 Print the source path: show which directories it contains.
4251 If your source path is cluttered with directories that are no longer of
4252 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4253 versions of source. You can correct the situation as follows:
4257 Use @code{directory} with no argument to reset the source path to empty.
4260 Use @code{directory} with suitable arguments to reinstall the
4261 directories you want in the source path. You can add all the
4262 directories in one command.
4266 @section Source and machine code
4268 You can use the command @code{info line} to map source lines to program
4269 addresses (and vice versa), and the command @code{disassemble} to display
4270 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4271 mode, the @code{info line} command causes the arrow to point to the
4272 line specified. Also, @code{info line} prints addresses in symbolic form as
4277 @item info line @var{linespec}
4278 Print the starting and ending addresses of the compiled code for
4279 source line @var{linespec}. You can specify source lines in any of
4280 the ways understood by the @code{list} command (@pxref{List, ,Printing
4284 For example, we can use @code{info line} to discover the location of
4285 the object code for the first line of function
4286 @code{m4_changequote}:
4288 @c FIXME: I think this example should also show the addresses in
4289 @c symbolic form, as they usually would be displayed.
4291 (@value{GDBP}) info line m4_changequote
4292 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4296 We can also inquire (using @code{*@var{addr}} as the form for
4297 @var{linespec}) what source line covers a particular address:
4299 (@value{GDBP}) info line *0x63ff
4300 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4303 @cindex @code{$_} and @code{info line}
4304 @kindex x@r{(examine), and} info line
4305 After @code{info line}, the default address for the @code{x} command
4306 is changed to the starting address of the line, so that @samp{x/i} is
4307 sufficient to begin examining the machine code (@pxref{Memory,
4308 ,Examining memory}). Also, this address is saved as the value of the
4309 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4314 @cindex assembly instructions
4315 @cindex instructions, assembly
4316 @cindex machine instructions
4317 @cindex listing machine instructions
4319 This specialized command dumps a range of memory as machine
4320 instructions. The default memory range is the function surrounding the
4321 program counter of the selected frame. A single argument to this
4322 command is a program counter value; @value{GDBN} dumps the function
4323 surrounding this value. Two arguments specify a range of addresses
4324 (first inclusive, second exclusive) to dump.
4327 The following example shows the disassembly of a range of addresses of
4328 HP PA-RISC 2.0 code:
4331 (@value{GDBP}) disas 0x32c4 0x32e4
4332 Dump of assembler code from 0x32c4 to 0x32e4:
4333 0x32c4 <main+204>: addil 0,dp
4334 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4335 0x32cc <main+212>: ldil 0x3000,r31
4336 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4337 0x32d4 <main+220>: ldo 0(r31),rp
4338 0x32d8 <main+224>: addil -0x800,dp
4339 0x32dc <main+228>: ldo 0x588(r1),r26
4340 0x32e0 <main+232>: ldil 0x3000,r31
4341 End of assembler dump.
4344 Some architectures have more than one commonly-used set of instruction
4345 mnemonics or other syntax.
4348 @kindex set disassembly-flavor
4349 @cindex assembly instructions
4350 @cindex instructions, assembly
4351 @cindex machine instructions
4352 @cindex listing machine instructions
4353 @cindex Intel disassembly flavor
4354 @cindex AT&T disassembly flavor
4355 @item set disassembly-flavor @var{instruction-set}
4356 Select the instruction set to use when disassembling the
4357 program via the @code{disassemble} or @code{x/i} commands.
4359 Currently this command is only defined for the Intel x86 family. You
4360 can set @var{instruction-set} to either @code{intel} or @code{att}.
4361 The default is @code{att}, the AT&T flavor used by default by Unix
4362 assemblers for x86-based targets.
4367 @chapter Examining Data
4369 @cindex printing data
4370 @cindex examining data
4373 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4374 @c document because it is nonstandard... Under Epoch it displays in a
4375 @c different window or something like that.
4376 The usual way to examine data in your program is with the @code{print}
4377 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4378 evaluates and prints the value of an expression of the language your
4379 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4380 Different Languages}).
4383 @item print @var{expr}
4384 @itemx print /@var{f} @var{expr}
4385 @var{expr} is an expression (in the source language). By default the
4386 value of @var{expr} is printed in a format appropriate to its data type;
4387 you can choose a different format by specifying @samp{/@var{f}}, where
4388 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4392 @itemx print /@var{f}
4393 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4394 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4395 conveniently inspect the same value in an alternative format.
4398 A more low-level way of examining data is with the @code{x} command.
4399 It examines data in memory at a specified address and prints it in a
4400 specified format. @xref{Memory, ,Examining memory}.
4402 If you are interested in information about types, or about how the
4403 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4404 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4408 * Expressions:: Expressions
4409 * Variables:: Program variables
4410 * Arrays:: Artificial arrays
4411 * Output Formats:: Output formats
4412 * Memory:: Examining memory
4413 * Auto Display:: Automatic display
4414 * Print Settings:: Print settings
4415 * Value History:: Value history
4416 * Convenience Vars:: Convenience variables
4417 * Registers:: Registers
4418 * Floating Point Hardware:: Floating point hardware
4419 * Memory Region Attributes:: Memory region attributes
4420 * Dump/Restore Files:: Copy between memory and a file
4424 @section Expressions
4427 @code{print} and many other @value{GDBN} commands accept an expression and
4428 compute its value. Any kind of constant, variable or operator defined
4429 by the programming language you are using is valid in an expression in
4430 @value{GDBN}. This includes conditional expressions, function calls,
4431 casts, and string constants. It also includes preprocessor macros, if
4432 you compiled your program to include this information; see
4435 @value{GDBN} supports array constants in expressions input by
4436 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4437 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4438 memory that is @code{malloc}ed in the target program.
4440 Because C is so widespread, most of the expressions shown in examples in
4441 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4442 Languages}, for information on how to use expressions in other
4445 In this section, we discuss operators that you can use in @value{GDBN}
4446 expressions regardless of your programming language.
4448 Casts are supported in all languages, not just in C, because it is so
4449 useful to cast a number into a pointer in order to examine a structure
4450 at that address in memory.
4451 @c FIXME: casts supported---Mod2 true?
4453 @value{GDBN} supports these operators, in addition to those common
4454 to programming languages:
4458 @samp{@@} is a binary operator for treating parts of memory as arrays.
4459 @xref{Arrays, ,Artificial arrays}, for more information.
4462 @samp{::} allows you to specify a variable in terms of the file or
4463 function where it is defined. @xref{Variables, ,Program variables}.
4465 @cindex @{@var{type}@}
4466 @cindex type casting memory
4467 @cindex memory, viewing as typed object
4468 @cindex casts, to view memory
4469 @item @{@var{type}@} @var{addr}
4470 Refers to an object of type @var{type} stored at address @var{addr} in
4471 memory. @var{addr} may be any expression whose value is an integer or
4472 pointer (but parentheses are required around binary operators, just as in
4473 a cast). This construct is allowed regardless of what kind of data is
4474 normally supposed to reside at @var{addr}.
4478 @section Program variables
4480 The most common kind of expression to use is the name of a variable
4483 Variables in expressions are understood in the selected stack frame
4484 (@pxref{Selection, ,Selecting a frame}); they must be either:
4488 global (or file-static)
4495 visible according to the scope rules of the
4496 programming language from the point of execution in that frame
4499 @noindent This means that in the function
4514 you can examine and use the variable @code{a} whenever your program is
4515 executing within the function @code{foo}, but you can only use or
4516 examine the variable @code{b} while your program is executing inside
4517 the block where @code{b} is declared.
4519 @cindex variable name conflict
4520 There is an exception: you can refer to a variable or function whose
4521 scope is a single source file even if the current execution point is not
4522 in this file. But it is possible to have more than one such variable or
4523 function with the same name (in different source files). If that
4524 happens, referring to that name has unpredictable effects. If you wish,
4525 you can specify a static variable in a particular function or file,
4526 using the colon-colon notation:
4528 @cindex colon-colon, context for variables/functions
4530 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4531 @cindex @code{::}, context for variables/functions
4534 @var{file}::@var{variable}
4535 @var{function}::@var{variable}
4539 Here @var{file} or @var{function} is the name of the context for the
4540 static @var{variable}. In the case of file names, you can use quotes to
4541 make sure @value{GDBN} parses the file name as a single word---for example,
4542 to print a global value of @code{x} defined in @file{f2.c}:
4545 (@value{GDBP}) p 'f2.c'::x
4548 @cindex C@t{++} scope resolution
4549 This use of @samp{::} is very rarely in conflict with the very similar
4550 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4551 scope resolution operator in @value{GDBN} expressions.
4552 @c FIXME: Um, so what happens in one of those rare cases where it's in
4555 @cindex wrong values
4556 @cindex variable values, wrong
4558 @emph{Warning:} Occasionally, a local variable may appear to have the
4559 wrong value at certain points in a function---just after entry to a new
4560 scope, and just before exit.
4562 You may see this problem when you are stepping by machine instructions.
4563 This is because, on most machines, it takes more than one instruction to
4564 set up a stack frame (including local variable definitions); if you are
4565 stepping by machine instructions, variables may appear to have the wrong
4566 values until the stack frame is completely built. On exit, it usually
4567 also takes more than one machine instruction to destroy a stack frame;
4568 after you begin stepping through that group of instructions, local
4569 variable definitions may be gone.
4571 This may also happen when the compiler does significant optimizations.
4572 To be sure of always seeing accurate values, turn off all optimization
4575 @cindex ``No symbol "foo" in current context''
4576 Another possible effect of compiler optimizations is to optimize
4577 unused variables out of existence, or assign variables to registers (as
4578 opposed to memory addresses). Depending on the support for such cases
4579 offered by the debug info format used by the compiler, @value{GDBN}
4580 might not be able to display values for such local variables. If that
4581 happens, @value{GDBN} will print a message like this:
4584 No symbol "foo" in current context.
4587 To solve such problems, either recompile without optimizations, or use a
4588 different debug info format, if the compiler supports several such
4589 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4590 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4591 in a format that is superior to formats such as COFF. You may be able
4592 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4593 debug info. See @ref{Debugging Options,,Options for Debugging Your
4594 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4599 @section Artificial arrays
4601 @cindex artificial array
4602 @kindex @@@r{, referencing memory as an array}
4603 It is often useful to print out several successive objects of the
4604 same type in memory; a section of an array, or an array of
4605 dynamically determined size for which only a pointer exists in the
4608 You can do this by referring to a contiguous span of memory as an
4609 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4610 operand of @samp{@@} should be the first element of the desired array
4611 and be an individual object. The right operand should be the desired length
4612 of the array. The result is an array value whose elements are all of
4613 the type of the left argument. The first element is actually the left
4614 argument; the second element comes from bytes of memory immediately
4615 following those that hold the first element, and so on. Here is an
4616 example. If a program says
4619 int *array = (int *) malloc (len * sizeof (int));
4623 you can print the contents of @code{array} with
4629 The left operand of @samp{@@} must reside in memory. Array values made
4630 with @samp{@@} in this way behave just like other arrays in terms of
4631 subscripting, and are coerced to pointers when used in expressions.
4632 Artificial arrays most often appear in expressions via the value history
4633 (@pxref{Value History, ,Value history}), after printing one out.
4635 Another way to create an artificial array is to use a cast.
4636 This re-interprets a value as if it were an array.
4637 The value need not be in memory:
4639 (@value{GDBP}) p/x (short[2])0x12345678
4640 $1 = @{0x1234, 0x5678@}
4643 As a convenience, if you leave the array length out (as in
4644 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4645 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4647 (@value{GDBP}) p/x (short[])0x12345678
4648 $2 = @{0x1234, 0x5678@}
4651 Sometimes the artificial array mechanism is not quite enough; in
4652 moderately complex data structures, the elements of interest may not
4653 actually be adjacent---for example, if you are interested in the values
4654 of pointers in an array. One useful work-around in this situation is
4655 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4656 variables}) as a counter in an expression that prints the first
4657 interesting value, and then repeat that expression via @key{RET}. For
4658 instance, suppose you have an array @code{dtab} of pointers to
4659 structures, and you are interested in the values of a field @code{fv}
4660 in each structure. Here is an example of what you might type:
4670 @node Output Formats
4671 @section Output formats
4673 @cindex formatted output
4674 @cindex output formats
4675 By default, @value{GDBN} prints a value according to its data type. Sometimes
4676 this is not what you want. For example, you might want to print a number
4677 in hex, or a pointer in decimal. Or you might want to view data in memory
4678 at a certain address as a character string or as an instruction. To do
4679 these things, specify an @dfn{output format} when you print a value.
4681 The simplest use of output formats is to say how to print a value
4682 already computed. This is done by starting the arguments of the
4683 @code{print} command with a slash and a format letter. The format
4684 letters supported are:
4688 Regard the bits of the value as an integer, and print the integer in
4692 Print as integer in signed decimal.
4695 Print as integer in unsigned decimal.
4698 Print as integer in octal.
4701 Print as integer in binary. The letter @samp{t} stands for ``two''.
4702 @footnote{@samp{b} cannot be used because these format letters are also
4703 used with the @code{x} command, where @samp{b} stands for ``byte'';
4704 see @ref{Memory,,Examining memory}.}
4707 @cindex unknown address, locating
4708 @cindex locate address
4709 Print as an address, both absolute in hexadecimal and as an offset from
4710 the nearest preceding symbol. You can use this format used to discover
4711 where (in what function) an unknown address is located:
4714 (@value{GDBP}) p/a 0x54320
4715 $3 = 0x54320 <_initialize_vx+396>
4719 The command @code{info symbol 0x54320} yields similar results.
4720 @xref{Symbols, info symbol}.
4723 Regard as an integer and print it as a character constant.
4726 Regard the bits of the value as a floating point number and print
4727 using typical floating point syntax.
4730 For example, to print the program counter in hex (@pxref{Registers}), type
4737 Note that no space is required before the slash; this is because command
4738 names in @value{GDBN} cannot contain a slash.
4740 To reprint the last value in the value history with a different format,
4741 you can use the @code{print} command with just a format and no
4742 expression. For example, @samp{p/x} reprints the last value in hex.
4745 @section Examining memory
4747 You can use the command @code{x} (for ``examine'') to examine memory in
4748 any of several formats, independently of your program's data types.
4750 @cindex examining memory
4752 @kindex x @r{(examine memory)}
4753 @item x/@var{nfu} @var{addr}
4756 Use the @code{x} command to examine memory.
4759 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4760 much memory to display and how to format it; @var{addr} is an
4761 expression giving the address where you want to start displaying memory.
4762 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4763 Several commands set convenient defaults for @var{addr}.
4766 @item @var{n}, the repeat count
4767 The repeat count is a decimal integer; the default is 1. It specifies
4768 how much memory (counting by units @var{u}) to display.
4769 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4772 @item @var{f}, the display format
4773 The display format is one of the formats used by @code{print},
4774 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4775 The default is @samp{x} (hexadecimal) initially.
4776 The default changes each time you use either @code{x} or @code{print}.
4778 @item @var{u}, the unit size
4779 The unit size is any of
4785 Halfwords (two bytes).
4787 Words (four bytes). This is the initial default.
4789 Giant words (eight bytes).
4792 Each time you specify a unit size with @code{x}, that size becomes the
4793 default unit the next time you use @code{x}. (For the @samp{s} and
4794 @samp{i} formats, the unit size is ignored and is normally not written.)
4796 @item @var{addr}, starting display address
4797 @var{addr} is the address where you want @value{GDBN} to begin displaying
4798 memory. The expression need not have a pointer value (though it may);
4799 it is always interpreted as an integer address of a byte of memory.
4800 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4801 @var{addr} is usually just after the last address examined---but several
4802 other commands also set the default address: @code{info breakpoints} (to
4803 the address of the last breakpoint listed), @code{info line} (to the
4804 starting address of a line), and @code{print} (if you use it to display
4805 a value from memory).
4808 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4809 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4810 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4811 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4812 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4814 Since the letters indicating unit sizes are all distinct from the
4815 letters specifying output formats, you do not have to remember whether
4816 unit size or format comes first; either order works. The output
4817 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4818 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4820 Even though the unit size @var{u} is ignored for the formats @samp{s}
4821 and @samp{i}, you might still want to use a count @var{n}; for example,
4822 @samp{3i} specifies that you want to see three machine instructions,
4823 including any operands. The command @code{disassemble} gives an
4824 alternative way of inspecting machine instructions; see @ref{Machine
4825 Code,,Source and machine code}.
4827 All the defaults for the arguments to @code{x} are designed to make it
4828 easy to continue scanning memory with minimal specifications each time
4829 you use @code{x}. For example, after you have inspected three machine
4830 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4831 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4832 the repeat count @var{n} is used again; the other arguments default as
4833 for successive uses of @code{x}.
4835 @cindex @code{$_}, @code{$__}, and value history
4836 The addresses and contents printed by the @code{x} command are not saved
4837 in the value history because there is often too much of them and they
4838 would get in the way. Instead, @value{GDBN} makes these values available for
4839 subsequent use in expressions as values of the convenience variables
4840 @code{$_} and @code{$__}. After an @code{x} command, the last address
4841 examined is available for use in expressions in the convenience variable
4842 @code{$_}. The contents of that address, as examined, are available in
4843 the convenience variable @code{$__}.
4845 If the @code{x} command has a repeat count, the address and contents saved
4846 are from the last memory unit printed; this is not the same as the last
4847 address printed if several units were printed on the last line of output.
4850 @section Automatic display
4851 @cindex automatic display
4852 @cindex display of expressions
4854 If you find that you want to print the value of an expression frequently
4855 (to see how it changes), you might want to add it to the @dfn{automatic
4856 display list} so that @value{GDBN} prints its value each time your program stops.
4857 Each expression added to the list is given a number to identify it;
4858 to remove an expression from the list, you specify that number.
4859 The automatic display looks like this:
4863 3: bar[5] = (struct hack *) 0x3804
4867 This display shows item numbers, expressions and their current values. As with
4868 displays you request manually using @code{x} or @code{print}, you can
4869 specify the output format you prefer; in fact, @code{display} decides
4870 whether to use @code{print} or @code{x} depending on how elaborate your
4871 format specification is---it uses @code{x} if you specify a unit size,
4872 or one of the two formats (@samp{i} and @samp{s}) that are only
4873 supported by @code{x}; otherwise it uses @code{print}.
4877 @item display @var{expr}
4878 Add the expression @var{expr} to the list of expressions to display
4879 each time your program stops. @xref{Expressions, ,Expressions}.
4881 @code{display} does not repeat if you press @key{RET} again after using it.
4883 @item display/@var{fmt} @var{expr}
4884 For @var{fmt} specifying only a display format and not a size or
4885 count, add the expression @var{expr} to the auto-display list but
4886 arrange to display it each time in the specified format @var{fmt}.
4887 @xref{Output Formats,,Output formats}.
4889 @item display/@var{fmt} @var{addr}
4890 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4891 number of units, add the expression @var{addr} as a memory address to
4892 be examined each time your program stops. Examining means in effect
4893 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4896 For example, @samp{display/i $pc} can be helpful, to see the machine
4897 instruction about to be executed each time execution stops (@samp{$pc}
4898 is a common name for the program counter; @pxref{Registers, ,Registers}).
4901 @kindex delete display
4903 @item undisplay @var{dnums}@dots{}
4904 @itemx delete display @var{dnums}@dots{}
4905 Remove item numbers @var{dnums} from the list of expressions to display.
4907 @code{undisplay} does not repeat if you press @key{RET} after using it.
4908 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4910 @kindex disable display
4911 @item disable display @var{dnums}@dots{}
4912 Disable the display of item numbers @var{dnums}. A disabled display
4913 item is not printed automatically, but is not forgotten. It may be
4914 enabled again later.
4916 @kindex enable display
4917 @item enable display @var{dnums}@dots{}
4918 Enable display of item numbers @var{dnums}. It becomes effective once
4919 again in auto display of its expression, until you specify otherwise.
4922 Display the current values of the expressions on the list, just as is
4923 done when your program stops.
4925 @kindex info display
4927 Print the list of expressions previously set up to display
4928 automatically, each one with its item number, but without showing the
4929 values. This includes disabled expressions, which are marked as such.
4930 It also includes expressions which would not be displayed right now
4931 because they refer to automatic variables not currently available.
4934 If a display expression refers to local variables, then it does not make
4935 sense outside the lexical context for which it was set up. Such an
4936 expression is disabled when execution enters a context where one of its
4937 variables is not defined. For example, if you give the command
4938 @code{display last_char} while inside a function with an argument
4939 @code{last_char}, @value{GDBN} displays this argument while your program
4940 continues to stop inside that function. When it stops elsewhere---where
4941 there is no variable @code{last_char}---the display is disabled
4942 automatically. The next time your program stops where @code{last_char}
4943 is meaningful, you can enable the display expression once again.
4945 @node Print Settings
4946 @section Print settings
4948 @cindex format options
4949 @cindex print settings
4950 @value{GDBN} provides the following ways to control how arrays, structures,
4951 and symbols are printed.
4954 These settings are useful for debugging programs in any language:
4957 @kindex set print address
4958 @item set print address
4959 @itemx set print address on
4960 @value{GDBN} prints memory addresses showing the location of stack
4961 traces, structure values, pointer values, breakpoints, and so forth,
4962 even when it also displays the contents of those addresses. The default
4963 is @code{on}. For example, this is what a stack frame display looks like with
4964 @code{set print address on}:
4969 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4971 530 if (lquote != def_lquote)
4975 @item set print address off
4976 Do not print addresses when displaying their contents. For example,
4977 this is the same stack frame displayed with @code{set print address off}:
4981 (@value{GDBP}) set print addr off
4983 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4984 530 if (lquote != def_lquote)
4988 You can use @samp{set print address off} to eliminate all machine
4989 dependent displays from the @value{GDBN} interface. For example, with
4990 @code{print address off}, you should get the same text for backtraces on
4991 all machines---whether or not they involve pointer arguments.
4993 @kindex show print address
4994 @item show print address
4995 Show whether or not addresses are to be printed.
4998 When @value{GDBN} prints a symbolic address, it normally prints the
4999 closest earlier symbol plus an offset. If that symbol does not uniquely
5000 identify the address (for example, it is a name whose scope is a single
5001 source file), you may need to clarify. One way to do this is with
5002 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5003 you can set @value{GDBN} to print the source file and line number when
5004 it prints a symbolic address:
5007 @kindex set print symbol-filename
5008 @item set print symbol-filename on
5009 Tell @value{GDBN} to print the source file name and line number of a
5010 symbol in the symbolic form of an address.
5012 @item set print symbol-filename off
5013 Do not print source file name and line number of a symbol. This is the
5016 @kindex show print symbol-filename
5017 @item show print symbol-filename
5018 Show whether or not @value{GDBN} will print the source file name and
5019 line number of a symbol in the symbolic form of an address.
5022 Another situation where it is helpful to show symbol filenames and line
5023 numbers is when disassembling code; @value{GDBN} shows you the line
5024 number and source file that corresponds to each instruction.
5026 Also, you may wish to see the symbolic form only if the address being
5027 printed is reasonably close to the closest earlier symbol:
5030 @kindex set print max-symbolic-offset
5031 @item set print max-symbolic-offset @var{max-offset}
5032 Tell @value{GDBN} to only display the symbolic form of an address if the
5033 offset between the closest earlier symbol and the address is less than
5034 @var{max-offset}. The default is 0, which tells @value{GDBN}
5035 to always print the symbolic form of an address if any symbol precedes it.
5037 @kindex show print max-symbolic-offset
5038 @item show print max-symbolic-offset
5039 Ask how large the maximum offset is that @value{GDBN} prints in a
5043 @cindex wild pointer, interpreting
5044 @cindex pointer, finding referent
5045 If you have a pointer and you are not sure where it points, try
5046 @samp{set print symbol-filename on}. Then you can determine the name
5047 and source file location of the variable where it points, using
5048 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5049 For example, here @value{GDBN} shows that a variable @code{ptt} points
5050 at another variable @code{t}, defined in @file{hi2.c}:
5053 (@value{GDBP}) set print symbol-filename on
5054 (@value{GDBP}) p/a ptt
5055 $4 = 0xe008 <t in hi2.c>
5059 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5060 does not show the symbol name and filename of the referent, even with
5061 the appropriate @code{set print} options turned on.
5064 Other settings control how different kinds of objects are printed:
5067 @kindex set print array
5068 @item set print array
5069 @itemx set print array on
5070 Pretty print arrays. This format is more convenient to read,
5071 but uses more space. The default is off.
5073 @item set print array off
5074 Return to compressed format for arrays.
5076 @kindex show print array
5077 @item show print array
5078 Show whether compressed or pretty format is selected for displaying
5081 @kindex set print elements
5082 @item set print elements @var{number-of-elements}
5083 Set a limit on how many elements of an array @value{GDBN} will print.
5084 If @value{GDBN} is printing a large array, it stops printing after it has
5085 printed the number of elements set by the @code{set print elements} command.
5086 This limit also applies to the display of strings.
5087 When @value{GDBN} starts, this limit is set to 200.
5088 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5090 @kindex show print elements
5091 @item show print elements
5092 Display the number of elements of a large array that @value{GDBN} will print.
5093 If the number is 0, then the printing is unlimited.
5095 @kindex set print null-stop
5096 @item set print null-stop
5097 Cause @value{GDBN} to stop printing the characters of an array when the first
5098 @sc{null} is encountered. This is useful when large arrays actually
5099 contain only short strings.
5102 @kindex set print pretty
5103 @item set print pretty on
5104 Cause @value{GDBN} to print structures in an indented format with one member
5105 per line, like this:
5120 @item set print pretty off
5121 Cause @value{GDBN} to print structures in a compact format, like this:
5125 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5126 meat = 0x54 "Pork"@}
5131 This is the default format.
5133 @kindex show print pretty
5134 @item show print pretty
5135 Show which format @value{GDBN} is using to print structures.
5137 @kindex set print sevenbit-strings
5138 @item set print sevenbit-strings on
5139 Print using only seven-bit characters; if this option is set,
5140 @value{GDBN} displays any eight-bit characters (in strings or
5141 character values) using the notation @code{\}@var{nnn}. This setting is
5142 best if you are working in English (@sc{ascii}) and you use the
5143 high-order bit of characters as a marker or ``meta'' bit.
5145 @item set print sevenbit-strings off
5146 Print full eight-bit characters. This allows the use of more
5147 international character sets, and is the default.
5149 @kindex show print sevenbit-strings
5150 @item show print sevenbit-strings
5151 Show whether or not @value{GDBN} is printing only seven-bit characters.
5153 @kindex set print union
5154 @item set print union on
5155 Tell @value{GDBN} to print unions which are contained in structures. This
5156 is the default setting.
5158 @item set print union off
5159 Tell @value{GDBN} not to print unions which are contained in structures.
5161 @kindex show print union
5162 @item show print union
5163 Ask @value{GDBN} whether or not it will print unions which are contained in
5166 For example, given the declarations
5169 typedef enum @{Tree, Bug@} Species;
5170 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5171 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5182 struct thing foo = @{Tree, @{Acorn@}@};
5186 with @code{set print union on} in effect @samp{p foo} would print
5189 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5193 and with @code{set print union off} in effect it would print
5196 $1 = @{it = Tree, form = @{...@}@}
5202 These settings are of interest when debugging C@t{++} programs:
5206 @kindex set print demangle
5207 @item set print demangle
5208 @itemx set print demangle on
5209 Print C@t{++} names in their source form rather than in the encoded
5210 (``mangled'') form passed to the assembler and linker for type-safe
5211 linkage. The default is on.
5213 @kindex show print demangle
5214 @item show print demangle
5215 Show whether C@t{++} names are printed in mangled or demangled form.
5217 @kindex set print asm-demangle
5218 @item set print asm-demangle
5219 @itemx set print asm-demangle on
5220 Print C@t{++} names in their source form rather than their mangled form, even
5221 in assembler code printouts such as instruction disassemblies.
5224 @kindex show print asm-demangle
5225 @item show print asm-demangle
5226 Show whether C@t{++} names in assembly listings are printed in mangled
5229 @kindex set demangle-style
5230 @cindex C@t{++} symbol decoding style
5231 @cindex symbol decoding style, C@t{++}
5232 @item set demangle-style @var{style}
5233 Choose among several encoding schemes used by different compilers to
5234 represent C@t{++} names. The choices for @var{style} are currently:
5238 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5241 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5242 This is the default.
5245 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5248 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5251 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5252 @strong{Warning:} this setting alone is not sufficient to allow
5253 debugging @code{cfront}-generated executables. @value{GDBN} would
5254 require further enhancement to permit that.
5257 If you omit @var{style}, you will see a list of possible formats.
5259 @kindex show demangle-style
5260 @item show demangle-style
5261 Display the encoding style currently in use for decoding C@t{++} symbols.
5263 @kindex set print object
5264 @item set print object
5265 @itemx set print object on
5266 When displaying a pointer to an object, identify the @emph{actual}
5267 (derived) type of the object rather than the @emph{declared} type, using
5268 the virtual function table.
5270 @item set print object off
5271 Display only the declared type of objects, without reference to the
5272 virtual function table. This is the default setting.
5274 @kindex show print object
5275 @item show print object
5276 Show whether actual, or declared, object types are displayed.
5278 @kindex set print static-members
5279 @item set print static-members
5280 @itemx set print static-members on
5281 Print static members when displaying a C@t{++} object. The default is on.
5283 @item set print static-members off
5284 Do not print static members when displaying a C@t{++} object.
5286 @kindex show print static-members
5287 @item show print static-members
5288 Show whether C@t{++} static members are printed, or not.
5290 @c These don't work with HP ANSI C++ yet.
5291 @kindex set print vtbl
5292 @item set print vtbl
5293 @itemx set print vtbl on
5294 Pretty print C@t{++} virtual function tables. The default is off.
5295 (The @code{vtbl} commands do not work on programs compiled with the HP
5296 ANSI C@t{++} compiler (@code{aCC}).)
5298 @item set print vtbl off
5299 Do not pretty print C@t{++} virtual function tables.
5301 @kindex show print vtbl
5302 @item show print vtbl
5303 Show whether C@t{++} virtual function tables are pretty printed, or not.
5307 @section Value history
5309 @cindex value history
5310 Values printed by the @code{print} command are saved in the @value{GDBN}
5311 @dfn{value history}. This allows you to refer to them in other expressions.
5312 Values are kept until the symbol table is re-read or discarded
5313 (for example with the @code{file} or @code{symbol-file} commands).
5314 When the symbol table changes, the value history is discarded,
5315 since the values may contain pointers back to the types defined in the
5320 @cindex history number
5321 The values printed are given @dfn{history numbers} by which you can
5322 refer to them. These are successive integers starting with one.
5323 @code{print} shows you the history number assigned to a value by
5324 printing @samp{$@var{num} = } before the value; here @var{num} is the
5327 To refer to any previous value, use @samp{$} followed by the value's
5328 history number. The way @code{print} labels its output is designed to
5329 remind you of this. Just @code{$} refers to the most recent value in
5330 the history, and @code{$$} refers to the value before that.
5331 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5332 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5333 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5335 For example, suppose you have just printed a pointer to a structure and
5336 want to see the contents of the structure. It suffices to type
5342 If you have a chain of structures where the component @code{next} points
5343 to the next one, you can print the contents of the next one with this:
5350 You can print successive links in the chain by repeating this
5351 command---which you can do by just typing @key{RET}.
5353 Note that the history records values, not expressions. If the value of
5354 @code{x} is 4 and you type these commands:
5362 then the value recorded in the value history by the @code{print} command
5363 remains 4 even though the value of @code{x} has changed.
5368 Print the last ten values in the value history, with their item numbers.
5369 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5370 values} does not change the history.
5372 @item show values @var{n}
5373 Print ten history values centered on history item number @var{n}.
5376 Print ten history values just after the values last printed. If no more
5377 values are available, @code{show values +} produces no display.
5380 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5381 same effect as @samp{show values +}.
5383 @node Convenience Vars
5384 @section Convenience variables
5386 @cindex convenience variables
5387 @value{GDBN} provides @dfn{convenience variables} that you can use within
5388 @value{GDBN} to hold on to a value and refer to it later. These variables
5389 exist entirely within @value{GDBN}; they are not part of your program, and
5390 setting a convenience variable has no direct effect on further execution
5391 of your program. That is why you can use them freely.
5393 Convenience variables are prefixed with @samp{$}. Any name preceded by
5394 @samp{$} can be used for a convenience variable, unless it is one of
5395 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5396 (Value history references, in contrast, are @emph{numbers} preceded
5397 by @samp{$}. @xref{Value History, ,Value history}.)
5399 You can save a value in a convenience variable with an assignment
5400 expression, just as you would set a variable in your program.
5404 set $foo = *object_ptr
5408 would save in @code{$foo} the value contained in the object pointed to by
5411 Using a convenience variable for the first time creates it, but its
5412 value is @code{void} until you assign a new value. You can alter the
5413 value with another assignment at any time.
5415 Convenience variables have no fixed types. You can assign a convenience
5416 variable any type of value, including structures and arrays, even if
5417 that variable already has a value of a different type. The convenience
5418 variable, when used as an expression, has the type of its current value.
5421 @kindex show convenience
5422 @item show convenience
5423 Print a list of convenience variables used so far, and their values.
5424 Abbreviated @code{show conv}.
5427 One of the ways to use a convenience variable is as a counter to be
5428 incremented or a pointer to be advanced. For example, to print
5429 a field from successive elements of an array of structures:
5433 print bar[$i++]->contents
5437 Repeat that command by typing @key{RET}.
5439 Some convenience variables are created automatically by @value{GDBN} and given
5440 values likely to be useful.
5443 @vindex $_@r{, convenience variable}
5445 The variable @code{$_} is automatically set by the @code{x} command to
5446 the last address examined (@pxref{Memory, ,Examining memory}). Other
5447 commands which provide a default address for @code{x} to examine also
5448 set @code{$_} to that address; these commands include @code{info line}
5449 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5450 except when set by the @code{x} command, in which case it is a pointer
5451 to the type of @code{$__}.
5453 @vindex $__@r{, convenience variable}
5455 The variable @code{$__} is automatically set by the @code{x} command
5456 to the value found in the last address examined. Its type is chosen
5457 to match the format in which the data was printed.
5460 @vindex $_exitcode@r{, convenience variable}
5461 The variable @code{$_exitcode} is automatically set to the exit code when
5462 the program being debugged terminates.
5465 On HP-UX systems, if you refer to a function or variable name that
5466 begins with a dollar sign, @value{GDBN} searches for a user or system
5467 name first, before it searches for a convenience variable.
5473 You can refer to machine register contents, in expressions, as variables
5474 with names starting with @samp{$}. The names of registers are different
5475 for each machine; use @code{info registers} to see the names used on
5479 @kindex info registers
5480 @item info registers
5481 Print the names and values of all registers except floating-point
5482 registers (in the selected stack frame).
5484 @kindex info all-registers
5485 @cindex floating point registers
5486 @item info all-registers
5487 Print the names and values of all registers, including floating-point
5490 @item info registers @var{regname} @dots{}
5491 Print the @dfn{relativized} value of each specified register @var{regname}.
5492 As discussed in detail below, register values are normally relative to
5493 the selected stack frame. @var{regname} may be any register name valid on
5494 the machine you are using, with or without the initial @samp{$}.
5497 @value{GDBN} has four ``standard'' register names that are available (in
5498 expressions) on most machines---whenever they do not conflict with an
5499 architecture's canonical mnemonics for registers. The register names
5500 @code{$pc} and @code{$sp} are used for the program counter register and
5501 the stack pointer. @code{$fp} is used for a register that contains a
5502 pointer to the current stack frame, and @code{$ps} is used for a
5503 register that contains the processor status. For example,
5504 you could print the program counter in hex with
5511 or print the instruction to be executed next with
5518 or add four to the stack pointer@footnote{This is a way of removing
5519 one word from the stack, on machines where stacks grow downward in
5520 memory (most machines, nowadays). This assumes that the innermost
5521 stack frame is selected; setting @code{$sp} is not allowed when other
5522 stack frames are selected. To pop entire frames off the stack,
5523 regardless of machine architecture, use @code{return};
5524 see @ref{Returning, ,Returning from a function}.} with
5530 Whenever possible, these four standard register names are available on
5531 your machine even though the machine has different canonical mnemonics,
5532 so long as there is no conflict. The @code{info registers} command
5533 shows the canonical names. For example, on the SPARC, @code{info
5534 registers} displays the processor status register as @code{$psr} but you
5535 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5536 is an alias for the @sc{eflags} register.
5538 @value{GDBN} always considers the contents of an ordinary register as an
5539 integer when the register is examined in this way. Some machines have
5540 special registers which can hold nothing but floating point; these
5541 registers are considered to have floating point values. There is no way
5542 to refer to the contents of an ordinary register as floating point value
5543 (although you can @emph{print} it as a floating point value with
5544 @samp{print/f $@var{regname}}).
5546 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5547 means that the data format in which the register contents are saved by
5548 the operating system is not the same one that your program normally
5549 sees. For example, the registers of the 68881 floating point
5550 coprocessor are always saved in ``extended'' (raw) format, but all C
5551 programs expect to work with ``double'' (virtual) format. In such
5552 cases, @value{GDBN} normally works with the virtual format only (the format
5553 that makes sense for your program), but the @code{info registers} command
5554 prints the data in both formats.
5556 Normally, register values are relative to the selected stack frame
5557 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5558 value that the register would contain if all stack frames farther in
5559 were exited and their saved registers restored. In order to see the
5560 true contents of hardware registers, you must select the innermost
5561 frame (with @samp{frame 0}).
5563 However, @value{GDBN} must deduce where registers are saved, from the machine
5564 code generated by your compiler. If some registers are not saved, or if
5565 @value{GDBN} is unable to locate the saved registers, the selected stack
5566 frame makes no difference.
5568 @node Floating Point Hardware
5569 @section Floating point hardware
5570 @cindex floating point
5572 Depending on the configuration, @value{GDBN} may be able to give
5573 you more information about the status of the floating point hardware.
5578 Display hardware-dependent information about the floating
5579 point unit. The exact contents and layout vary depending on the
5580 floating point chip. Currently, @samp{info float} is supported on
5581 the ARM and x86 machines.
5584 @node Memory Region Attributes
5585 @section Memory region attributes
5586 @cindex memory region attributes
5588 @dfn{Memory region attributes} allow you to describe special handling
5589 required by regions of your target's memory. @value{GDBN} uses attributes
5590 to determine whether to allow certain types of memory accesses; whether to
5591 use specific width accesses; and whether to cache target memory.
5593 Defined memory regions can be individually enabled and disabled. When a
5594 memory region is disabled, @value{GDBN} uses the default attributes when
5595 accessing memory in that region. Similarly, if no memory regions have
5596 been defined, @value{GDBN} uses the default attributes when accessing
5599 When a memory region is defined, it is given a number to identify it;
5600 to enable, disable, or remove a memory region, you specify that number.
5604 @item mem @var{address1} @var{address2} @var{attributes}@dots{}
5605 Define memory region bounded by @var{address1} and @var{address2}
5606 with attributes @var{attributes}@dots{}.
5609 @item delete mem @var{nums}@dots{}
5610 Remove memory regions @var{nums}@dots{}.
5613 @item disable mem @var{nums}@dots{}
5614 Disable memory regions @var{nums}@dots{}.
5615 A disabled memory region is not forgotten.
5616 It may be enabled again later.
5619 @item enable mem @var{nums}@dots{}
5620 Enable memory regions @var{nums}@dots{}.
5624 Print a table of all defined memory regions, with the following columns
5628 @item Memory Region Number
5629 @item Enabled or Disabled.
5630 Enabled memory regions are marked with @samp{y}.
5631 Disabled memory regions are marked with @samp{n}.
5634 The address defining the inclusive lower bound of the memory region.
5637 The address defining the exclusive upper bound of the memory region.
5640 The list of attributes set for this memory region.
5645 @subsection Attributes
5647 @subsubsection Memory Access Mode
5648 The access mode attributes set whether @value{GDBN} may make read or
5649 write accesses to a memory region.
5651 While these attributes prevent @value{GDBN} from performing invalid
5652 memory accesses, they do nothing to prevent the target system, I/O DMA,
5653 etc. from accessing memory.
5657 Memory is read only.
5659 Memory is write only.
5661 Memory is read/write. This is the default.
5664 @subsubsection Memory Access Size
5665 The acccess size attributes tells @value{GDBN} to use specific sized
5666 accesses in the memory region. Often memory mapped device registers
5667 require specific sized accesses. If no access size attribute is
5668 specified, @value{GDBN} may use accesses of any size.
5672 Use 8 bit memory accesses.
5674 Use 16 bit memory accesses.
5676 Use 32 bit memory accesses.
5678 Use 64 bit memory accesses.
5681 @c @subsubsection Hardware/Software Breakpoints
5682 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5683 @c will use hardware or software breakpoints for the internal breakpoints
5684 @c used by the step, next, finish, until, etc. commands.
5688 @c Always use hardware breakpoints
5689 @c @item swbreak (default)
5692 @subsubsection Data Cache
5693 The data cache attributes set whether @value{GDBN} will cache target
5694 memory. While this generally improves performance by reducing debug
5695 protocol overhead, it can lead to incorrect results because @value{GDBN}
5696 does not know about volatile variables or memory mapped device
5701 Enable @value{GDBN} to cache target memory.
5703 Disable @value{GDBN} from caching target memory. This is the default.
5706 @c @subsubsection Memory Write Verification
5707 @c The memory write verification attributes set whether @value{GDBN}
5708 @c will re-reads data after each write to verify the write was successful.
5712 @c @item noverify (default)
5715 @node Dump/Restore Files
5716 @section Copy between memory and a file
5717 @cindex dump/restore files
5718 @cindex append data to a file
5719 @cindex dump data to a file
5720 @cindex restore data from a file
5725 The commands @code{dump}, @code{append}, and @code{restore} are used
5726 for copying data between target memory and a file. Data is written
5727 into a file using @code{dump} or @code{append}, and restored from a
5728 file into memory by using @code{restore}. Files may be binary, srec,
5729 intel hex, or tekhex (but only binary files can be appended).
5733 @kindex append binary
5734 @item dump binary memory @var{filename} @var{start_addr} @var{end_addr}
5735 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5736 raw binary format file @var{filename}.
5738 @item append binary memory @var{filename} @var{start_addr} @var{end_addr}
5739 Append contents of memory from @var{start_addr} to @var{end_addr} to
5740 raw binary format file @var{filename}.
5742 @item dump binary value @var{filename} @var{expression}
5743 Dump value of @var{expression} into raw binary format file @var{filename}.
5745 @item append binary memory @var{filename} @var{expression}
5746 Append value of @var{expression} to raw binary format file @var{filename}.
5749 @item dump ihex memory @var{filename} @var{start_addr} @var{end_addr}
5750 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5751 intel hex format file @var{filename}.
5753 @item dump ihex value @var{filename} @var{expression}
5754 Dump value of @var{expression} into intel hex format file @var{filename}.
5757 @item dump srec memory @var{filename} @var{start_addr} @var{end_addr}
5758 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5759 srec format file @var{filename}.
5761 @item dump srec value @var{filename} @var{expression}
5762 Dump value of @var{expression} into srec format file @var{filename}.
5765 @item dump tekhex memory @var{filename} @var{start_addr} @var{end_addr}
5766 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5767 tekhex format file @var{filename}.
5769 @item dump tekhex value @var{filename} @var{expression}
5770 Dump value of @var{expression} into tekhex format file @var{filename}.
5772 @item restore @var{filename} @var{[binary]} @var{bias} @var{start} @var{end}
5773 Restore the contents of file @var{filename} into memory. The @code{restore}
5774 command can automatically recognize any known bfd file format, except for
5775 raw binary. To restore a raw binary file you must use the optional argument
5776 @var{binary} after the filename.
5778 If @var{bias} is non-zero, its value will be added to the addresses
5779 contained in the file. Binary files always start at address zero, so
5780 they will be restored at address @var{bias}. Other bfd files have
5781 a built-in location; they will be restored at offset @var{bias}
5784 If @var{start} and/or @var{end} are non-zero, then only data between
5785 file offset @var{start} and file offset @var{end} will be restored.
5786 These offsets are relative to the addresses in the file, before
5787 the @var{bias} argument is applied.
5792 @chapter C Preprocessor Macros
5794 Some languages, such as C and C++, provide a way to define and invoke
5795 ``preprocessor macros'' which expand into strings of tokens.
5796 @value{GDBN} can evaluate expressions containing macro invocations, show
5797 the result of macro expansion, and show a macro's definition, including
5798 where it was defined.
5800 You may need to compile your program specially to provide @value{GDBN}
5801 with information about preprocessor macros. Most compilers do not
5802 include macros in their debugging information, even when you compile
5803 with the @option{-g} flag. @xref{Compilation}.
5805 A program may define a macro at one point, remove that definition later,
5806 and then provide a different definition after that. Thus, at different
5807 points in the program, a macro may have different definitions, or have
5808 no definition at all. If there is a current stack frame, @value{GDBN}
5809 uses the macros in scope at that frame's source code line. Otherwise,
5810 @value{GDBN} uses the macros in scope at the current listing location;
5813 At the moment, @value{GDBN} does not support the @code{##}
5814 token-splicing operator, the @code{#} stringification operator, or
5815 variable-arity macros.
5817 Whenever @value{GDBN} evaluates an expression, it always expands any
5818 macro invocations present in the expression. @value{GDBN} also provides
5819 the following commands for working with macros explicitly.
5823 @kindex macro expand
5824 @cindex macro expansion, showing the results of preprocessor
5825 @cindex preprocessor macro expansion, showing the results of
5826 @cindex expanding preprocessor macros
5827 @item macro expand @var{expression}
5828 @itemx macro exp @var{expression}
5829 Show the results of expanding all preprocessor macro invocations in
5830 @var{expression}. Since @value{GDBN} simply expands macros, but does
5831 not parse the result, @var{expression} need not be a valid expression;
5832 it can be any string of tokens.
5834 @kindex macro expand-once
5835 @item macro expand-once @var{expression}
5836 @itemx macro exp1 @var{expression}
5837 @i{(This command is not yet implemented.)} Show the results of
5838 expanding those preprocessor macro invocations that appear explicitly in
5839 @var{expression}. Macro invocations appearing in that expansion are
5840 left unchanged. This command allows you to see the effect of a
5841 particular macro more clearly, without being confused by further
5842 expansions. Since @value{GDBN} simply expands macros, but does not
5843 parse the result, @var{expression} need not be a valid expression; it
5844 can be any string of tokens.
5847 @cindex macro definition, showing
5848 @cindex definition, showing a macro's
5849 @item info macro @var{macro}
5850 Show the definition of the macro named @var{macro}, and describe the
5851 source location where that definition was established.
5853 @kindex macro define
5854 @cindex user-defined macros
5855 @cindex defining macros interactively
5856 @cindex macros, user-defined
5857 @item macro define @var{macro} @var{replacement-list}
5858 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
5859 @i{(This command is not yet implemented.)} Introduce a definition for a
5860 preprocessor macro named @var{macro}, invocations of which are replaced
5861 by the tokens given in @var{replacement-list}. The first form of this
5862 command defines an ``object-like'' macro, which takes no arguments; the
5863 second form defines a ``function-like'' macro, which takes the arguments
5864 given in @var{arglist}.
5866 A definition introduced by this command is in scope in every expression
5867 evaluated in @value{GDBN}, until it is removed with the @command{macro
5868 undef} command, described below. The definition overrides all
5869 definitions for @var{macro} present in the program being debugged, as
5870 well as any previous user-supplied definition.
5873 @item macro undef @var{macro}
5874 @i{(This command is not yet implemented.)} Remove any user-supplied
5875 definition for the macro named @var{macro}. This command only affects
5876 definitions provided with the @command{macro define} command, described
5877 above; it cannot remove definitions present in the program being
5882 @cindex macros, example of debugging with
5883 Here is a transcript showing the above commands in action. First, we
5884 show our source files:
5892 #define ADD(x) (M + x)
5897 printf ("Hello, world!\n");
5899 printf ("We're so creative.\n");
5901 printf ("Goodbye, world!\n");
5908 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
5909 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
5910 compiler includes information about preprocessor macros in the debugging
5914 $ gcc -gdwarf-2 -g3 sample.c -o sample
5918 Now, we start @value{GDBN} on our sample program:
5922 GNU gdb 2002-05-06-cvs
5923 Copyright 2002 Free Software Foundation, Inc.
5924 GDB is free software, @dots{}
5928 We can expand macros and examine their definitions, even when the
5929 program is not running. @value{GDBN} uses the current listing position
5930 to decide which macro definitions are in scope:
5936 5 #define ADD(x) (M + x)
5941 10 printf ("Hello, world!\n");
5943 12 printf ("We're so creative.\n");
5944 (gdb) info macro ADD
5945 Defined at /home/jimb/gdb/macros/play/sample.c:5
5946 #define ADD(x) (M + x)
5948 Defined at /home/jimb/gdb/macros/play/sample.h:1
5949 included at /home/jimb/gdb/macros/play/sample.c:2
5951 (gdb) macro expand ADD(1)
5952 expands to: (42 + 1)
5953 (gdb) macro expand-once ADD(1)
5954 expands to: once (M + 1)
5958 In the example above, note that @command{macro expand-once} expands only
5959 the macro invocation explicit in the original text --- the invocation of
5960 @code{ADD} --- but does not expand the invocation of the macro @code{M},
5961 which was introduced by @code{ADD}.
5963 Once the program is running, GDB uses the macro definitions in force at
5964 the source line of the current stack frame:
5968 Breakpoint 1 at 0x8048370: file sample.c, line 10.
5970 Starting program: /home/jimb/gdb/macros/play/sample
5972 Breakpoint 1, main () at sample.c:10
5973 10 printf ("Hello, world!\n");
5977 At line 10, the definition of the macro @code{N} at line 9 is in force:
5981 Defined at /home/jimb/gdb/macros/play/sample.c:9
5983 (gdb) macro expand N Q M
5990 As we step over directives that remove @code{N}'s definition, and then
5991 give it a new definition, @value{GDBN} finds the definition (or lack
5992 thereof) in force at each point:
5997 12 printf ("We're so creative.\n");
5999 The symbol `N' has no definition as a C/C++ preprocessor macro
6000 at /home/jimb/gdb/macros/play/sample.c:12
6003 14 printf ("Goodbye, world!\n");
6005 Defined at /home/jimb/gdb/macros/play/sample.c:13
6007 (gdb) macro expand N Q M
6008 expands to: 1729 < 42
6016 @chapter Tracepoints
6017 @c This chapter is based on the documentation written by Michael
6018 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
6021 In some applications, it is not feasible for the debugger to interrupt
6022 the program's execution long enough for the developer to learn
6023 anything helpful about its behavior. If the program's correctness
6024 depends on its real-time behavior, delays introduced by a debugger
6025 might cause the program to change its behavior drastically, or perhaps
6026 fail, even when the code itself is correct. It is useful to be able
6027 to observe the program's behavior without interrupting it.
6029 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
6030 specify locations in the program, called @dfn{tracepoints}, and
6031 arbitrary expressions to evaluate when those tracepoints are reached.
6032 Later, using the @code{tfind} command, you can examine the values
6033 those expressions had when the program hit the tracepoints. The
6034 expressions may also denote objects in memory---structures or arrays,
6035 for example---whose values @value{GDBN} should record; while visiting
6036 a particular tracepoint, you may inspect those objects as if they were
6037 in memory at that moment. However, because @value{GDBN} records these
6038 values without interacting with you, it can do so quickly and
6039 unobtrusively, hopefully not disturbing the program's behavior.
6041 The tracepoint facility is currently available only for remote
6042 targets. @xref{Targets}. In addition, your remote target must know how
6043 to collect trace data. This functionality is implemented in the remote
6044 stub; however, none of the stubs distributed with @value{GDBN} support
6045 tracepoints as of this writing.
6047 This chapter describes the tracepoint commands and features.
6051 * Analyze Collected Data::
6052 * Tracepoint Variables::
6055 @node Set Tracepoints
6056 @section Commands to Set Tracepoints
6058 Before running such a @dfn{trace experiment}, an arbitrary number of
6059 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
6060 tracepoint has a number assigned to it by @value{GDBN}. Like with
6061 breakpoints, tracepoint numbers are successive integers starting from
6062 one. Many of the commands associated with tracepoints take the
6063 tracepoint number as their argument, to identify which tracepoint to
6066 For each tracepoint, you can specify, in advance, some arbitrary set
6067 of data that you want the target to collect in the trace buffer when
6068 it hits that tracepoint. The collected data can include registers,
6069 local variables, or global data. Later, you can use @value{GDBN}
6070 commands to examine the values these data had at the time the
6073 This section describes commands to set tracepoints and associated
6074 conditions and actions.
6077 * Create and Delete Tracepoints::
6078 * Enable and Disable Tracepoints::
6079 * Tracepoint Passcounts::
6080 * Tracepoint Actions::
6081 * Listing Tracepoints::
6082 * Starting and Stopping Trace Experiment::
6085 @node Create and Delete Tracepoints
6086 @subsection Create and Delete Tracepoints
6089 @cindex set tracepoint
6092 The @code{trace} command is very similar to the @code{break} command.
6093 Its argument can be a source line, a function name, or an address in
6094 the target program. @xref{Set Breaks}. The @code{trace} command
6095 defines a tracepoint, which is a point in the target program where the
6096 debugger will briefly stop, collect some data, and then allow the
6097 program to continue. Setting a tracepoint or changing its commands
6098 doesn't take effect until the next @code{tstart} command; thus, you
6099 cannot change the tracepoint attributes once a trace experiment is
6102 Here are some examples of using the @code{trace} command:
6105 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
6107 (@value{GDBP}) @b{trace +2} // 2 lines forward
6109 (@value{GDBP}) @b{trace my_function} // first source line of function
6111 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
6113 (@value{GDBP}) @b{trace *0x2117c4} // an address
6117 You can abbreviate @code{trace} as @code{tr}.
6120 @cindex last tracepoint number
6121 @cindex recent tracepoint number
6122 @cindex tracepoint number
6123 The convenience variable @code{$tpnum} records the tracepoint number
6124 of the most recently set tracepoint.
6126 @kindex delete tracepoint
6127 @cindex tracepoint deletion
6128 @item delete tracepoint @r{[}@var{num}@r{]}
6129 Permanently delete one or more tracepoints. With no argument, the
6130 default is to delete all tracepoints.
6135 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
6137 (@value{GDBP}) @b{delete trace} // remove all tracepoints
6141 You can abbreviate this command as @code{del tr}.
6144 @node Enable and Disable Tracepoints
6145 @subsection Enable and Disable Tracepoints
6148 @kindex disable tracepoint
6149 @item disable tracepoint @r{[}@var{num}@r{]}
6150 Disable tracepoint @var{num}, or all tracepoints if no argument
6151 @var{num} is given. A disabled tracepoint will have no effect during
6152 the next trace experiment, but it is not forgotten. You can re-enable
6153 a disabled tracepoint using the @code{enable tracepoint} command.
6155 @kindex enable tracepoint
6156 @item enable tracepoint @r{[}@var{num}@r{]}
6157 Enable tracepoint @var{num}, or all tracepoints. The enabled
6158 tracepoints will become effective the next time a trace experiment is
6162 @node Tracepoint Passcounts
6163 @subsection Tracepoint Passcounts
6167 @cindex tracepoint pass count
6168 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
6169 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
6170 automatically stop a trace experiment. If a tracepoint's passcount is
6171 @var{n}, then the trace experiment will be automatically stopped on
6172 the @var{n}'th time that tracepoint is hit. If the tracepoint number
6173 @var{num} is not specified, the @code{passcount} command sets the
6174 passcount of the most recently defined tracepoint. If no passcount is
6175 given, the trace experiment will run until stopped explicitly by the
6181 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
6182 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
6184 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
6185 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
6186 (@value{GDBP}) @b{trace foo}
6187 (@value{GDBP}) @b{pass 3}
6188 (@value{GDBP}) @b{trace bar}
6189 (@value{GDBP}) @b{pass 2}
6190 (@value{GDBP}) @b{trace baz}
6191 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
6192 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
6193 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
6194 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
6198 @node Tracepoint Actions
6199 @subsection Tracepoint Action Lists
6203 @cindex tracepoint actions
6204 @item actions @r{[}@var{num}@r{]}
6205 This command will prompt for a list of actions to be taken when the
6206 tracepoint is hit. If the tracepoint number @var{num} is not
6207 specified, this command sets the actions for the one that was most
6208 recently defined (so that you can define a tracepoint and then say
6209 @code{actions} without bothering about its number). You specify the
6210 actions themselves on the following lines, one action at a time, and
6211 terminate the actions list with a line containing just @code{end}. So
6212 far, the only defined actions are @code{collect} and
6213 @code{while-stepping}.
6215 @cindex remove actions from a tracepoint
6216 To remove all actions from a tracepoint, type @samp{actions @var{num}}
6217 and follow it immediately with @samp{end}.
6220 (@value{GDBP}) @b{collect @var{data}} // collect some data
6222 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
6224 (@value{GDBP}) @b{end} // signals the end of actions.
6227 In the following example, the action list begins with @code{collect}
6228 commands indicating the things to be collected when the tracepoint is
6229 hit. Then, in order to single-step and collect additional data
6230 following the tracepoint, a @code{while-stepping} command is used,
6231 followed by the list of things to be collected while stepping. The
6232 @code{while-stepping} command is terminated by its own separate
6233 @code{end} command. Lastly, the action list is terminated by an
6237 (@value{GDBP}) @b{trace foo}
6238 (@value{GDBP}) @b{actions}
6239 Enter actions for tracepoint 1, one per line:
6248 @kindex collect @r{(tracepoints)}
6249 @item collect @var{expr1}, @var{expr2}, @dots{}
6250 Collect values of the given expressions when the tracepoint is hit.
6251 This command accepts a comma-separated list of any valid expressions.
6252 In addition to global, static, or local variables, the following
6253 special arguments are supported:
6257 collect all registers
6260 collect all function arguments
6263 collect all local variables.
6266 You can give several consecutive @code{collect} commands, each one
6267 with a single argument, or one @code{collect} command with several
6268 arguments separated by commas: the effect is the same.
6270 The command @code{info scope} (@pxref{Symbols, info scope}) is
6271 particularly useful for figuring out what data to collect.
6273 @kindex while-stepping @r{(tracepoints)}
6274 @item while-stepping @var{n}
6275 Perform @var{n} single-step traces after the tracepoint, collecting
6276 new data at each step. The @code{while-stepping} command is
6277 followed by the list of what to collect while stepping (followed by
6278 its own @code{end} command):
6282 > collect $regs, myglobal
6288 You may abbreviate @code{while-stepping} as @code{ws} or
6292 @node Listing Tracepoints
6293 @subsection Listing Tracepoints
6296 @kindex info tracepoints
6297 @cindex information about tracepoints
6298 @item info tracepoints @r{[}@var{num}@r{]}
6299 Display information about the tracepoint @var{num}. If you don't specify
6300 a tracepoint number, displays information about all the tracepoints
6301 defined so far. For each tracepoint, the following information is
6308 whether it is enabled or disabled
6312 its passcount as given by the @code{passcount @var{n}} command
6314 its step count as given by the @code{while-stepping @var{n}} command
6316 where in the source files is the tracepoint set
6318 its action list as given by the @code{actions} command
6322 (@value{GDBP}) @b{info trace}
6323 Num Enb Address PassC StepC What
6324 1 y 0x002117c4 0 0 <gdb_asm>
6325 2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
6326 3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
6331 This command can be abbreviated @code{info tp}.
6334 @node Starting and Stopping Trace Experiment
6335 @subsection Starting and Stopping Trace Experiment
6339 @cindex start a new trace experiment
6340 @cindex collected data discarded
6342 This command takes no arguments. It starts the trace experiment, and
6343 begins collecting data. This has the side effect of discarding all
6344 the data collected in the trace buffer during the previous trace
6348 @cindex stop a running trace experiment
6350 This command takes no arguments. It ends the trace experiment, and
6351 stops collecting data.
6353 @strong{Note:} a trace experiment and data collection may stop
6354 automatically if any tracepoint's passcount is reached
6355 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6358 @cindex status of trace data collection
6359 @cindex trace experiment, status of
6361 This command displays the status of the current trace data
6365 Here is an example of the commands we described so far:
6368 (@value{GDBP}) @b{trace gdb_c_test}
6369 (@value{GDBP}) @b{actions}
6370 Enter actions for tracepoint #1, one per line.
6371 > collect $regs,$locals,$args
6376 (@value{GDBP}) @b{tstart}
6377 [time passes @dots{}]
6378 (@value{GDBP}) @b{tstop}
6382 @node Analyze Collected Data
6383 @section Using the collected data
6385 After the tracepoint experiment ends, you use @value{GDBN} commands
6386 for examining the trace data. The basic idea is that each tracepoint
6387 collects a trace @dfn{snapshot} every time it is hit and another
6388 snapshot every time it single-steps. All these snapshots are
6389 consecutively numbered from zero and go into a buffer, and you can
6390 examine them later. The way you examine them is to @dfn{focus} on a
6391 specific trace snapshot. When the remote stub is focused on a trace
6392 snapshot, it will respond to all @value{GDBN} requests for memory and
6393 registers by reading from the buffer which belongs to that snapshot,
6394 rather than from @emph{real} memory or registers of the program being
6395 debugged. This means that @strong{all} @value{GDBN} commands
6396 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6397 behave as if we were currently debugging the program state as it was
6398 when the tracepoint occurred. Any requests for data that are not in
6399 the buffer will fail.
6402 * tfind:: How to select a trace snapshot
6403 * tdump:: How to display all data for a snapshot
6404 * save-tracepoints:: How to save tracepoints for a future run
6408 @subsection @code{tfind @var{n}}
6411 @cindex select trace snapshot
6412 @cindex find trace snapshot
6413 The basic command for selecting a trace snapshot from the buffer is
6414 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6415 counting from zero. If no argument @var{n} is given, the next
6416 snapshot is selected.
6418 Here are the various forms of using the @code{tfind} command.
6422 Find the first snapshot in the buffer. This is a synonym for
6423 @code{tfind 0} (since 0 is the number of the first snapshot).
6426 Stop debugging trace snapshots, resume @emph{live} debugging.
6429 Same as @samp{tfind none}.
6432 No argument means find the next trace snapshot.
6435 Find the previous trace snapshot before the current one. This permits
6436 retracing earlier steps.
6438 @item tfind tracepoint @var{num}
6439 Find the next snapshot associated with tracepoint @var{num}. Search
6440 proceeds forward from the last examined trace snapshot. If no
6441 argument @var{num} is given, it means find the next snapshot collected
6442 for the same tracepoint as the current snapshot.
6444 @item tfind pc @var{addr}
6445 Find the next snapshot associated with the value @var{addr} of the
6446 program counter. Search proceeds forward from the last examined trace
6447 snapshot. If no argument @var{addr} is given, it means find the next
6448 snapshot with the same value of PC as the current snapshot.
6450 @item tfind outside @var{addr1}, @var{addr2}
6451 Find the next snapshot whose PC is outside the given range of
6454 @item tfind range @var{addr1}, @var{addr2}
6455 Find the next snapshot whose PC is between @var{addr1} and
6456 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6458 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6459 Find the next snapshot associated with the source line @var{n}. If
6460 the optional argument @var{file} is given, refer to line @var{n} in
6461 that source file. Search proceeds forward from the last examined
6462 trace snapshot. If no argument @var{n} is given, it means find the
6463 next line other than the one currently being examined; thus saying
6464 @code{tfind line} repeatedly can appear to have the same effect as
6465 stepping from line to line in a @emph{live} debugging session.
6468 The default arguments for the @code{tfind} commands are specifically
6469 designed to make it easy to scan through the trace buffer. For
6470 instance, @code{tfind} with no argument selects the next trace
6471 snapshot, and @code{tfind -} with no argument selects the previous
6472 trace snapshot. So, by giving one @code{tfind} command, and then
6473 simply hitting @key{RET} repeatedly you can examine all the trace
6474 snapshots in order. Or, by saying @code{tfind -} and then hitting
6475 @key{RET} repeatedly you can examine the snapshots in reverse order.
6476 The @code{tfind line} command with no argument selects the snapshot
6477 for the next source line executed. The @code{tfind pc} command with
6478 no argument selects the next snapshot with the same program counter
6479 (PC) as the current frame. The @code{tfind tracepoint} command with
6480 no argument selects the next trace snapshot collected by the same
6481 tracepoint as the current one.
6483 In addition to letting you scan through the trace buffer manually,
6484 these commands make it easy to construct @value{GDBN} scripts that
6485 scan through the trace buffer and print out whatever collected data
6486 you are interested in. Thus, if we want to examine the PC, FP, and SP
6487 registers from each trace frame in the buffer, we can say this:
6490 (@value{GDBP}) @b{tfind start}
6491 (@value{GDBP}) @b{while ($trace_frame != -1)}
6492 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6493 $trace_frame, $pc, $sp, $fp
6497 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6498 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6499 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6500 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6501 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6502 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6503 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6504 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6505 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6506 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6507 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6510 Or, if we want to examine the variable @code{X} at each source line in
6514 (@value{GDBP}) @b{tfind start}
6515 (@value{GDBP}) @b{while ($trace_frame != -1)}
6516 > printf "Frame %d, X == %d\n", $trace_frame, X
6526 @subsection @code{tdump}
6528 @cindex dump all data collected at tracepoint
6529 @cindex tracepoint data, display
6531 This command takes no arguments. It prints all the data collected at
6532 the current trace snapshot.
6535 (@value{GDBP}) @b{trace 444}
6536 (@value{GDBP}) @b{actions}
6537 Enter actions for tracepoint #2, one per line:
6538 > collect $regs, $locals, $args, gdb_long_test
6541 (@value{GDBP}) @b{tstart}
6543 (@value{GDBP}) @b{tfind line 444}
6544 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6546 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6548 (@value{GDBP}) @b{tdump}
6549 Data collected at tracepoint 2, trace frame 1:
6550 d0 0xc4aa0085 -995491707
6554 d4 0x71aea3d 119204413
6559 a1 0x3000668 50333288
6562 a4 0x3000698 50333336
6564 fp 0x30bf3c 0x30bf3c
6565 sp 0x30bf34 0x30bf34
6567 pc 0x20b2c8 0x20b2c8
6571 p = 0x20e5b4 "gdb-test"
6578 gdb_long_test = 17 '\021'
6583 @node save-tracepoints
6584 @subsection @code{save-tracepoints @var{filename}}
6585 @kindex save-tracepoints
6586 @cindex save tracepoints for future sessions
6588 This command saves all current tracepoint definitions together with
6589 their actions and passcounts, into a file @file{@var{filename}}
6590 suitable for use in a later debugging session. To read the saved
6591 tracepoint definitions, use the @code{source} command (@pxref{Command
6594 @node Tracepoint Variables
6595 @section Convenience Variables for Tracepoints
6596 @cindex tracepoint variables
6597 @cindex convenience variables for tracepoints
6600 @vindex $trace_frame
6601 @item (int) $trace_frame
6602 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6603 snapshot is selected.
6606 @item (int) $tracepoint
6607 The tracepoint for the current trace snapshot.
6610 @item (int) $trace_line
6611 The line number for the current trace snapshot.
6614 @item (char []) $trace_file
6615 The source file for the current trace snapshot.
6618 @item (char []) $trace_func
6619 The name of the function containing @code{$tracepoint}.
6622 Note: @code{$trace_file} is not suitable for use in @code{printf},
6623 use @code{output} instead.
6625 Here's a simple example of using these convenience variables for
6626 stepping through all the trace snapshots and printing some of their
6630 (@value{GDBP}) @b{tfind start}
6632 (@value{GDBP}) @b{while $trace_frame != -1}
6633 > output $trace_file
6634 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6640 @chapter Debugging Programs That Use Overlays
6643 If your program is too large to fit completely in your target system's
6644 memory, you can sometimes use @dfn{overlays} to work around this
6645 problem. @value{GDBN} provides some support for debugging programs that
6649 * How Overlays Work:: A general explanation of overlays.
6650 * Overlay Commands:: Managing overlays in @value{GDBN}.
6651 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
6652 mapped by asking the inferior.
6653 * Overlay Sample Program:: A sample program using overlays.
6656 @node How Overlays Work
6657 @section How Overlays Work
6658 @cindex mapped overlays
6659 @cindex unmapped overlays
6660 @cindex load address, overlay's
6661 @cindex mapped address
6662 @cindex overlay area
6664 Suppose you have a computer whose instruction address space is only 64
6665 kilobytes long, but which has much more memory which can be accessed by
6666 other means: special instructions, segment registers, or memory
6667 management hardware, for example. Suppose further that you want to
6668 adapt a program which is larger than 64 kilobytes to run on this system.
6670 One solution is to identify modules of your program which are relatively
6671 independent, and need not call each other directly; call these modules
6672 @dfn{overlays}. Separate the overlays from the main program, and place
6673 their machine code in the larger memory. Place your main program in
6674 instruction memory, but leave at least enough space there to hold the
6675 largest overlay as well.
6677 Now, to call a function located in an overlay, you must first copy that
6678 overlay's machine code from the large memory into the space set aside
6679 for it in the instruction memory, and then jump to its entry point
6682 @c NB: In the below the mapped area's size is greater or equal to the
6683 @c size of all overlays. This is intentional to remind the developer
6684 @c that overlays don't necessarily need to be the same size.
6688 Data Instruction Larger
6689 Address Space Address Space Address Space
6690 +-----------+ +-----------+ +-----------+
6692 +-----------+ +-----------+ +-----------+<-- overlay 1
6693 | program | | main | .----| overlay 1 | load address
6694 | variables | | program | | +-----------+
6695 | and heap | | | | | |
6696 +-----------+ | | | +-----------+<-- overlay 2
6697 | | +-----------+ | | | load address
6698 +-----------+ | | | .-| overlay 2 |
6700 mapped --->+-----------+ | | +-----------+
6702 | overlay | <-' | | |
6703 | area | <---' +-----------+<-- overlay 3
6704 | | <---. | | load address
6705 +-----------+ `--| overlay 3 |
6712 @anchor{A code overlay}A code overlay
6716 The diagram (@pxref{A code overlay}) shows a system with separate data
6717 and instruction address spaces. To map an overlay, the program copies
6718 its code from the larger address space to the instruction address space.
6719 Since the overlays shown here all use the same mapped address, only one
6720 may be mapped at a time. For a system with a single address space for
6721 data and instructions, the diagram would be similar, except that the
6722 program variables and heap would share an address space with the main
6723 program and the overlay area.
6725 An overlay loaded into instruction memory and ready for use is called a
6726 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
6727 instruction memory. An overlay not present (or only partially present)
6728 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
6729 is its address in the larger memory. The mapped address is also called
6730 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
6731 called the @dfn{load memory address}, or @dfn{LMA}.
6733 Unfortunately, overlays are not a completely transparent way to adapt a
6734 program to limited instruction memory. They introduce a new set of
6735 global constraints you must keep in mind as you design your program:
6740 Before calling or returning to a function in an overlay, your program
6741 must make sure that overlay is actually mapped. Otherwise, the call or
6742 return will transfer control to the right address, but in the wrong
6743 overlay, and your program will probably crash.
6746 If the process of mapping an overlay is expensive on your system, you
6747 will need to choose your overlays carefully to minimize their effect on
6748 your program's performance.
6751 The executable file you load onto your system must contain each
6752 overlay's instructions, appearing at the overlay's load address, not its
6753 mapped address. However, each overlay's instructions must be relocated
6754 and its symbols defined as if the overlay were at its mapped address.
6755 You can use GNU linker scripts to specify different load and relocation
6756 addresses for pieces of your program; see @ref{Overlay Description,,,
6757 ld.info, Using ld: the GNU linker}.
6760 The procedure for loading executable files onto your system must be able
6761 to load their contents into the larger address space as well as the
6762 instruction and data spaces.
6766 The overlay system described above is rather simple, and could be
6767 improved in many ways:
6772 If your system has suitable bank switch registers or memory management
6773 hardware, you could use those facilities to make an overlay's load area
6774 contents simply appear at their mapped address in instruction space.
6775 This would probably be faster than copying the overlay to its mapped
6776 area in the usual way.
6779 If your overlays are small enough, you could set aside more than one
6780 overlay area, and have more than one overlay mapped at a time.
6783 You can use overlays to manage data, as well as instructions. In
6784 general, data overlays are even less transparent to your design than
6785 code overlays: whereas code overlays only require care when you call or
6786 return to functions, data overlays require care every time you access
6787 the data. Also, if you change the contents of a data overlay, you
6788 must copy its contents back out to its load address before you can copy a
6789 different data overlay into the same mapped area.
6794 @node Overlay Commands
6795 @section Overlay Commands
6797 To use @value{GDBN}'s overlay support, each overlay in your program must
6798 correspond to a separate section of the executable file. The section's
6799 virtual memory address and load memory address must be the overlay's
6800 mapped and load addresses. Identifying overlays with sections allows
6801 @value{GDBN} to determine the appropriate address of a function or
6802 variable, depending on whether the overlay is mapped or not.
6804 @value{GDBN}'s overlay commands all start with the word @code{overlay};
6805 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
6810 Disable @value{GDBN}'s overlay support. When overlay support is
6811 disabled, @value{GDBN} assumes that all functions and variables are
6812 always present at their mapped addresses. By default, @value{GDBN}'s
6813 overlay support is disabled.
6815 @item overlay manual
6816 @kindex overlay manual
6817 @cindex manual overlay debugging
6818 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
6819 relies on you to tell it which overlays are mapped, and which are not,
6820 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
6821 commands described below.
6823 @item overlay map-overlay @var{overlay}
6824 @itemx overlay map @var{overlay}
6825 @kindex overlay map-overlay
6826 @cindex map an overlay
6827 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
6828 be the name of the object file section containing the overlay. When an
6829 overlay is mapped, @value{GDBN} assumes it can find the overlay's
6830 functions and variables at their mapped addresses. @value{GDBN} assumes
6831 that any other overlays whose mapped ranges overlap that of
6832 @var{overlay} are now unmapped.
6834 @item overlay unmap-overlay @var{overlay}
6835 @itemx overlay unmap @var{overlay}
6836 @kindex overlay unmap-overlay
6837 @cindex unmap an overlay
6838 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
6839 must be the name of the object file section containing the overlay.
6840 When an overlay is unmapped, @value{GDBN} assumes it can find the
6841 overlay's functions and variables at their load addresses.
6844 @kindex overlay auto
6845 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
6846 consults a data structure the overlay manager maintains in the inferior
6847 to see which overlays are mapped. For details, see @ref{Automatic
6850 @item overlay load-target
6852 @kindex overlay load-target
6853 @cindex reloading the overlay table
6854 Re-read the overlay table from the inferior. Normally, @value{GDBN}
6855 re-reads the table @value{GDBN} automatically each time the inferior
6856 stops, so this command should only be necessary if you have changed the
6857 overlay mapping yourself using @value{GDBN}. This command is only
6858 useful when using automatic overlay debugging.
6860 @item overlay list-overlays
6862 @cindex listing mapped overlays
6863 Display a list of the overlays currently mapped, along with their mapped
6864 addresses, load addresses, and sizes.
6868 Normally, when @value{GDBN} prints a code address, it includes the name
6869 of the function the address falls in:
6873 $3 = @{int ()@} 0x11a0 <main>
6876 When overlay debugging is enabled, @value{GDBN} recognizes code in
6877 unmapped overlays, and prints the names of unmapped functions with
6878 asterisks around them. For example, if @code{foo} is a function in an
6879 unmapped overlay, @value{GDBN} prints it this way:
6883 No sections are mapped.
6885 $5 = @{int (int)@} 0x100000 <*foo*>
6888 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
6893 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
6894 mapped at 0x1016 - 0x104a
6896 $6 = @{int (int)@} 0x1016 <foo>
6899 When overlay debugging is enabled, @value{GDBN} can find the correct
6900 address for functions and variables in an overlay, whether or not the
6901 overlay is mapped. This allows most @value{GDBN} commands, like
6902 @code{break} and @code{disassemble}, to work normally, even on unmapped
6903 code. However, @value{GDBN}'s breakpoint support has some limitations:
6907 @cindex breakpoints in overlays
6908 @cindex overlays, setting breakpoints in
6909 You can set breakpoints in functions in unmapped overlays, as long as
6910 @value{GDBN} can write to the overlay at its load address.
6912 @value{GDBN} can not set hardware or simulator-based breakpoints in
6913 unmapped overlays. However, if you set a breakpoint at the end of your
6914 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
6915 you are using manual overlay management), @value{GDBN} will re-set its
6916 breakpoints properly.
6920 @node Automatic Overlay Debugging
6921 @section Automatic Overlay Debugging
6922 @cindex automatic overlay debugging
6924 @value{GDBN} can automatically track which overlays are mapped and which
6925 are not, given some simple co-operation from the overlay manager in the
6926 inferior. If you enable automatic overlay debugging with the
6927 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
6928 looks in the inferior's memory for certain variables describing the
6929 current state of the overlays.
6931 Here are the variables your overlay manager must define to support
6932 @value{GDBN}'s automatic overlay debugging:
6936 @item @code{_ovly_table}:
6937 This variable must be an array of the following structures:
6942 /* The overlay's mapped address. */
6945 /* The size of the overlay, in bytes. */
6948 /* The overlay's load address. */
6951 /* Non-zero if the overlay is currently mapped;
6953 unsigned long mapped;
6957 @item @code{_novlys}:
6958 This variable must be a four-byte signed integer, holding the total
6959 number of elements in @code{_ovly_table}.
6963 To decide whether a particular overlay is mapped or not, @value{GDBN}
6964 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
6965 @code{lma} members equal the VMA and LMA of the overlay's section in the
6966 executable file. When @value{GDBN} finds a matching entry, it consults
6967 the entry's @code{mapped} member to determine whether the overlay is
6970 In addition, your overlay manager may define a function called
6971 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
6972 will silently set a breakpoint there. If the overlay manager then
6973 calls this function whenever it has changed the overlay table, this
6974 will enable @value{GDBN} to accurately keep track of which overlays
6975 are in program memory, and update any breakpoints that may be set
6976 in overlays. This will allow breakpoints to work even if the
6977 overlays are kept in ROM or other non-writable memory while they
6978 are not being executed.
6980 @node Overlay Sample Program
6981 @section Overlay Sample Program
6982 @cindex overlay example program
6984 When linking a program which uses overlays, you must place the overlays
6985 at their load addresses, while relocating them to run at their mapped
6986 addresses. To do this, you must write a linker script (@pxref{Overlay
6987 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
6988 since linker scripts are specific to a particular host system, target
6989 architecture, and target memory layout, this manual cannot provide
6990 portable sample code demonstrating @value{GDBN}'s overlay support.
6992 However, the @value{GDBN} source distribution does contain an overlaid
6993 program, with linker scripts for a few systems, as part of its test
6994 suite. The program consists of the following files from
6995 @file{gdb/testsuite/gdb.base}:
6999 The main program file.
7001 A simple overlay manager, used by @file{overlays.c}.
7006 Overlay modules, loaded and used by @file{overlays.c}.
7009 Linker scripts for linking the test program on the @code{d10v-elf}
7010 and @code{m32r-elf} targets.
7013 You can build the test program using the @code{d10v-elf} GCC
7014 cross-compiler like this:
7017 $ d10v-elf-gcc -g -c overlays.c
7018 $ d10v-elf-gcc -g -c ovlymgr.c
7019 $ d10v-elf-gcc -g -c foo.c
7020 $ d10v-elf-gcc -g -c bar.c
7021 $ d10v-elf-gcc -g -c baz.c
7022 $ d10v-elf-gcc -g -c grbx.c
7023 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
7024 baz.o grbx.o -Wl,-Td10v.ld -o overlays
7027 The build process is identical for any other architecture, except that
7028 you must substitute the appropriate compiler and linker script for the
7029 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
7033 @chapter Using @value{GDBN} with Different Languages
7036 Although programming languages generally have common aspects, they are
7037 rarely expressed in the same manner. For instance, in ANSI C,
7038 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
7039 Modula-2, it is accomplished by @code{p^}. Values can also be
7040 represented (and displayed) differently. Hex numbers in C appear as
7041 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
7043 @cindex working language
7044 Language-specific information is built into @value{GDBN} for some languages,
7045 allowing you to express operations like the above in your program's
7046 native language, and allowing @value{GDBN} to output values in a manner
7047 consistent with the syntax of your program's native language. The
7048 language you use to build expressions is called the @dfn{working
7052 * Setting:: Switching between source languages
7053 * Show:: Displaying the language
7054 * Checks:: Type and range checks
7055 * Support:: Supported languages
7059 @section Switching between source languages
7061 There are two ways to control the working language---either have @value{GDBN}
7062 set it automatically, or select it manually yourself. You can use the
7063 @code{set language} command for either purpose. On startup, @value{GDBN}
7064 defaults to setting the language automatically. The working language is
7065 used to determine how expressions you type are interpreted, how values
7068 In addition to the working language, every source file that
7069 @value{GDBN} knows about has its own working language. For some object
7070 file formats, the compiler might indicate which language a particular
7071 source file is in. However, most of the time @value{GDBN} infers the
7072 language from the name of the file. The language of a source file
7073 controls whether C@t{++} names are demangled---this way @code{backtrace} can
7074 show each frame appropriately for its own language. There is no way to
7075 set the language of a source file from within @value{GDBN}, but you can
7076 set the language associated with a filename extension. @xref{Show, ,
7077 Displaying the language}.
7079 This is most commonly a problem when you use a program, such
7080 as @code{cfront} or @code{f2c}, that generates C but is written in
7081 another language. In that case, make the
7082 program use @code{#line} directives in its C output; that way
7083 @value{GDBN} will know the correct language of the source code of the original
7084 program, and will display that source code, not the generated C code.
7087 * Filenames:: Filename extensions and languages.
7088 * Manually:: Setting the working language manually
7089 * Automatically:: Having @value{GDBN} infer the source language
7093 @subsection List of filename extensions and languages
7095 If a source file name ends in one of the following extensions, then
7096 @value{GDBN} infers that its language is the one indicated.
7121 Modula-2 source file
7125 Assembler source file. This actually behaves almost like C, but
7126 @value{GDBN} does not skip over function prologues when stepping.
7129 In addition, you may set the language associated with a filename
7130 extension. @xref{Show, , Displaying the language}.
7133 @subsection Setting the working language
7135 If you allow @value{GDBN} to set the language automatically,
7136 expressions are interpreted the same way in your debugging session and
7139 @kindex set language
7140 If you wish, you may set the language manually. To do this, issue the
7141 command @samp{set language @var{lang}}, where @var{lang} is the name of
7143 @code{c} or @code{modula-2}.
7144 For a list of the supported languages, type @samp{set language}.
7146 Setting the language manually prevents @value{GDBN} from updating the working
7147 language automatically. This can lead to confusion if you try
7148 to debug a program when the working language is not the same as the
7149 source language, when an expression is acceptable to both
7150 languages---but means different things. For instance, if the current
7151 source file were written in C, and @value{GDBN} was parsing Modula-2, a
7159 might not have the effect you intended. In C, this means to add
7160 @code{b} and @code{c} and place the result in @code{a}. The result
7161 printed would be the value of @code{a}. In Modula-2, this means to compare
7162 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
7165 @subsection Having @value{GDBN} infer the source language
7167 To have @value{GDBN} set the working language automatically, use
7168 @samp{set language local} or @samp{set language auto}. @value{GDBN}
7169 then infers the working language. That is, when your program stops in a
7170 frame (usually by encountering a breakpoint), @value{GDBN} sets the
7171 working language to the language recorded for the function in that
7172 frame. If the language for a frame is unknown (that is, if the function
7173 or block corresponding to the frame was defined in a source file that
7174 does not have a recognized extension), the current working language is
7175 not changed, and @value{GDBN} issues a warning.
7177 This may not seem necessary for most programs, which are written
7178 entirely in one source language. However, program modules and libraries
7179 written in one source language can be used by a main program written in
7180 a different source language. Using @samp{set language auto} in this
7181 case frees you from having to set the working language manually.
7184 @section Displaying the language
7186 The following commands help you find out which language is the
7187 working language, and also what language source files were written in.
7189 @kindex show language
7190 @kindex info frame@r{, show the source language}
7191 @kindex info source@r{, show the source language}
7194 Display the current working language. This is the
7195 language you can use with commands such as @code{print} to
7196 build and compute expressions that may involve variables in your program.
7199 Display the source language for this frame. This language becomes the
7200 working language if you use an identifier from this frame.
7201 @xref{Frame Info, ,Information about a frame}, to identify the other
7202 information listed here.
7205 Display the source language of this source file.
7206 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
7207 information listed here.
7210 In unusual circumstances, you may have source files with extensions
7211 not in the standard list. You can then set the extension associated
7212 with a language explicitly:
7214 @kindex set extension-language
7215 @kindex info extensions
7217 @item set extension-language @var{.ext} @var{language}
7218 Set source files with extension @var{.ext} to be assumed to be in
7219 the source language @var{language}.
7221 @item info extensions
7222 List all the filename extensions and the associated languages.
7226 @section Type and range checking
7229 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
7230 checking are included, but they do not yet have any effect. This
7231 section documents the intended facilities.
7233 @c FIXME remove warning when type/range code added
7235 Some languages are designed to guard you against making seemingly common
7236 errors through a series of compile- and run-time checks. These include
7237 checking the type of arguments to functions and operators, and making
7238 sure mathematical overflows are caught at run time. Checks such as
7239 these help to ensure a program's correctness once it has been compiled
7240 by eliminating type mismatches, and providing active checks for range
7241 errors when your program is running.
7243 @value{GDBN} can check for conditions like the above if you wish.
7244 Although @value{GDBN} does not check the statements in your program, it
7245 can check expressions entered directly into @value{GDBN} for evaluation via
7246 the @code{print} command, for example. As with the working language,
7247 @value{GDBN} can also decide whether or not to check automatically based on
7248 your program's source language. @xref{Support, ,Supported languages},
7249 for the default settings of supported languages.
7252 * Type Checking:: An overview of type checking
7253 * Range Checking:: An overview of range checking
7256 @cindex type checking
7257 @cindex checks, type
7259 @subsection An overview of type checking
7261 Some languages, such as Modula-2, are strongly typed, meaning that the
7262 arguments to operators and functions have to be of the correct type,
7263 otherwise an error occurs. These checks prevent type mismatch
7264 errors from ever causing any run-time problems. For example,
7272 The second example fails because the @code{CARDINAL} 1 is not
7273 type-compatible with the @code{REAL} 2.3.
7275 For the expressions you use in @value{GDBN} commands, you can tell the
7276 @value{GDBN} type checker to skip checking;
7277 to treat any mismatches as errors and abandon the expression;
7278 or to only issue warnings when type mismatches occur,
7279 but evaluate the expression anyway. When you choose the last of
7280 these, @value{GDBN} evaluates expressions like the second example above, but
7281 also issues a warning.
7283 Even if you turn type checking off, there may be other reasons
7284 related to type that prevent @value{GDBN} from evaluating an expression.
7285 For instance, @value{GDBN} does not know how to add an @code{int} and
7286 a @code{struct foo}. These particular type errors have nothing to do
7287 with the language in use, and usually arise from expressions, such as
7288 the one described above, which make little sense to evaluate anyway.
7290 Each language defines to what degree it is strict about type. For
7291 instance, both Modula-2 and C require the arguments to arithmetical
7292 operators to be numbers. In C, enumerated types and pointers can be
7293 represented as numbers, so that they are valid arguments to mathematical
7294 operators. @xref{Support, ,Supported languages}, for further
7295 details on specific languages.
7297 @value{GDBN} provides some additional commands for controlling the type checker:
7299 @kindex set check@r{, type}
7300 @kindex set check type
7301 @kindex show check type
7303 @item set check type auto
7304 Set type checking on or off based on the current working language.
7305 @xref{Support, ,Supported languages}, for the default settings for
7308 @item set check type on
7309 @itemx set check type off
7310 Set type checking on or off, overriding the default setting for the
7311 current working language. Issue a warning if the setting does not
7312 match the language default. If any type mismatches occur in
7313 evaluating an expression while type checking is on, @value{GDBN} prints a
7314 message and aborts evaluation of the expression.
7316 @item set check type warn
7317 Cause the type checker to issue warnings, but to always attempt to
7318 evaluate the expression. Evaluating the expression may still
7319 be impossible for other reasons. For example, @value{GDBN} cannot add
7320 numbers and structures.
7323 Show the current setting of the type checker, and whether or not @value{GDBN}
7324 is setting it automatically.
7327 @cindex range checking
7328 @cindex checks, range
7329 @node Range Checking
7330 @subsection An overview of range checking
7332 In some languages (such as Modula-2), it is an error to exceed the
7333 bounds of a type; this is enforced with run-time checks. Such range
7334 checking is meant to ensure program correctness by making sure
7335 computations do not overflow, or indices on an array element access do
7336 not exceed the bounds of the array.
7338 For expressions you use in @value{GDBN} commands, you can tell
7339 @value{GDBN} to treat range errors in one of three ways: ignore them,
7340 always treat them as errors and abandon the expression, or issue
7341 warnings but evaluate the expression anyway.
7343 A range error can result from numerical overflow, from exceeding an
7344 array index bound, or when you type a constant that is not a member
7345 of any type. Some languages, however, do not treat overflows as an
7346 error. In many implementations of C, mathematical overflow causes the
7347 result to ``wrap around'' to lower values---for example, if @var{m} is
7348 the largest integer value, and @var{s} is the smallest, then
7351 @var{m} + 1 @result{} @var{s}
7354 This, too, is specific to individual languages, and in some cases
7355 specific to individual compilers or machines. @xref{Support, ,
7356 Supported languages}, for further details on specific languages.
7358 @value{GDBN} provides some additional commands for controlling the range checker:
7360 @kindex set check@r{, range}
7361 @kindex set check range
7362 @kindex show check range
7364 @item set check range auto
7365 Set range checking on or off based on the current working language.
7366 @xref{Support, ,Supported languages}, for the default settings for
7369 @item set check range on
7370 @itemx set check range off
7371 Set range checking on or off, overriding the default setting for the
7372 current working language. A warning is issued if the setting does not
7373 match the language default. If a range error occurs and range checking is on,
7374 then a message is printed and evaluation of the expression is aborted.
7376 @item set check range warn
7377 Output messages when the @value{GDBN} range checker detects a range error,
7378 but attempt to evaluate the expression anyway. Evaluating the
7379 expression may still be impossible for other reasons, such as accessing
7380 memory that the process does not own (a typical example from many Unix
7384 Show the current setting of the range checker, and whether or not it is
7385 being set automatically by @value{GDBN}.
7389 @section Supported languages
7391 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
7392 @c This is false ...
7393 Some @value{GDBN} features may be used in expressions regardless of the
7394 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7395 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7396 ,Expressions}) can be used with the constructs of any supported
7399 The following sections detail to what degree each source language is
7400 supported by @value{GDBN}. These sections are not meant to be language
7401 tutorials or references, but serve only as a reference guide to what the
7402 @value{GDBN} expression parser accepts, and what input and output
7403 formats should look like for different languages. There are many good
7404 books written on each of these languages; please look to these for a
7405 language reference or tutorial.
7409 * Modula-2:: Modula-2
7414 @subsection C and C@t{++}
7416 @cindex C and C@t{++}
7417 @cindex expressions in C or C@t{++}
7419 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7420 to both languages. Whenever this is the case, we discuss those languages
7424 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7425 @cindex @sc{gnu} C@t{++}
7426 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7427 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7428 effectively, you must compile your C@t{++} programs with a supported
7429 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7430 compiler (@code{aCC}).
7432 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7433 format. You can select that format explicitly with the @code{g++}
7434 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7435 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7436 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7439 * C Operators:: C and C@t{++} operators
7440 * C Constants:: C and C@t{++} constants
7441 * C plus plus expressions:: C@t{++} expressions
7442 * C Defaults:: Default settings for C and C@t{++}
7443 * C Checks:: C and C@t{++} type and range checks
7444 * Debugging C:: @value{GDBN} and C
7445 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7449 @subsubsection C and C@t{++} operators
7451 @cindex C and C@t{++} operators
7453 Operators must be defined on values of specific types. For instance,
7454 @code{+} is defined on numbers, but not on structures. Operators are
7455 often defined on groups of types.
7457 For the purposes of C and C@t{++}, the following definitions hold:
7462 @emph{Integral types} include @code{int} with any of its storage-class
7463 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7466 @emph{Floating-point types} include @code{float}, @code{double}, and
7467 @code{long double} (if supported by the target platform).
7470 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7473 @emph{Scalar types} include all of the above.
7478 The following operators are supported. They are listed here
7479 in order of increasing precedence:
7483 The comma or sequencing operator. Expressions in a comma-separated list
7484 are evaluated from left to right, with the result of the entire
7485 expression being the last expression evaluated.
7488 Assignment. The value of an assignment expression is the value
7489 assigned. Defined on scalar types.
7492 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7493 and translated to @w{@code{@var{a} = @var{a op b}}}.
7494 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7495 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7496 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7499 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7500 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7504 Logical @sc{or}. Defined on integral types.
7507 Logical @sc{and}. Defined on integral types.
7510 Bitwise @sc{or}. Defined on integral types.
7513 Bitwise exclusive-@sc{or}. Defined on integral types.
7516 Bitwise @sc{and}. Defined on integral types.
7519 Equality and inequality. Defined on scalar types. The value of these
7520 expressions is 0 for false and non-zero for true.
7522 @item <@r{, }>@r{, }<=@r{, }>=
7523 Less than, greater than, less than or equal, greater than or equal.
7524 Defined on scalar types. The value of these expressions is 0 for false
7525 and non-zero for true.
7528 left shift, and right shift. Defined on integral types.
7531 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7534 Addition and subtraction. Defined on integral types, floating-point types and
7537 @item *@r{, }/@r{, }%
7538 Multiplication, division, and modulus. Multiplication and division are
7539 defined on integral and floating-point types. Modulus is defined on
7543 Increment and decrement. When appearing before a variable, the
7544 operation is performed before the variable is used in an expression;
7545 when appearing after it, the variable's value is used before the
7546 operation takes place.
7549 Pointer dereferencing. Defined on pointer types. Same precedence as
7553 Address operator. Defined on variables. Same precedence as @code{++}.
7555 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7556 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7557 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7558 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7562 Negative. Defined on integral and floating-point types. Same
7563 precedence as @code{++}.
7566 Logical negation. Defined on integral types. Same precedence as
7570 Bitwise complement operator. Defined on integral types. Same precedence as
7575 Structure member, and pointer-to-structure member. For convenience,
7576 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7577 pointer based on the stored type information.
7578 Defined on @code{struct} and @code{union} data.
7581 Dereferences of pointers to members.
7584 Array indexing. @code{@var{a}[@var{i}]} is defined as
7585 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7588 Function parameter list. Same precedence as @code{->}.
7591 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7592 and @code{class} types.
7595 Doubled colons also represent the @value{GDBN} scope operator
7596 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7600 If an operator is redefined in the user code, @value{GDBN} usually
7601 attempts to invoke the redefined version instead of using the operator's
7609 @subsubsection C and C@t{++} constants
7611 @cindex C and C@t{++} constants
7613 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7618 Integer constants are a sequence of digits. Octal constants are
7619 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
7620 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7621 @samp{l}, specifying that the constant should be treated as a
7625 Floating point constants are a sequence of digits, followed by a decimal
7626 point, followed by a sequence of digits, and optionally followed by an
7627 exponent. An exponent is of the form:
7628 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7629 sequence of digits. The @samp{+} is optional for positive exponents.
7630 A floating-point constant may also end with a letter @samp{f} or
7631 @samp{F}, specifying that the constant should be treated as being of
7632 the @code{float} (as opposed to the default @code{double}) type; or with
7633 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7637 Enumerated constants consist of enumerated identifiers, or their
7638 integral equivalents.
7641 Character constants are a single character surrounded by single quotes
7642 (@code{'}), or a number---the ordinal value of the corresponding character
7643 (usually its @sc{ascii} value). Within quotes, the single character may
7644 be represented by a letter or by @dfn{escape sequences}, which are of
7645 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
7646 of the character's ordinal value; or of the form @samp{\@var{x}}, where
7647 @samp{@var{x}} is a predefined special character---for example,
7648 @samp{\n} for newline.
7651 String constants are a sequence of character constants surrounded by
7652 double quotes (@code{"}). Any valid character constant (as described
7653 above) may appear. Double quotes within the string must be preceded by
7654 a backslash, so for instance @samp{"a\"b'c"} is a string of five
7658 Pointer constants are an integral value. You can also write pointers
7659 to constants using the C operator @samp{&}.
7662 Array constants are comma-separated lists surrounded by braces @samp{@{}
7663 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
7664 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
7665 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
7669 * C plus plus expressions::
7676 @node C plus plus expressions
7677 @subsubsection C@t{++} expressions
7679 @cindex expressions in C@t{++}
7680 @value{GDBN} expression handling can interpret most C@t{++} expressions.
7682 @cindex C@t{++} support, not in @sc{coff}
7683 @cindex @sc{coff} versus C@t{++}
7684 @cindex C@t{++} and object formats
7685 @cindex object formats and C@t{++}
7686 @cindex a.out and C@t{++}
7687 @cindex @sc{ecoff} and C@t{++}
7688 @cindex @sc{xcoff} and C@t{++}
7689 @cindex @sc{elf}/stabs and C@t{++}
7690 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
7691 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
7692 @c periodically whether this has happened...
7694 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
7695 proper compiler. Typically, C@t{++} debugging depends on the use of
7696 additional debugging information in the symbol table, and thus requires
7697 special support. In particular, if your compiler generates a.out, MIPS
7698 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
7699 symbol table, these facilities are all available. (With @sc{gnu} CC,
7700 you can use the @samp{-gstabs} option to request stabs debugging
7701 extensions explicitly.) Where the object code format is standard
7702 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
7703 support in @value{GDBN} does @emph{not} work.
7708 @cindex member functions
7710 Member function calls are allowed; you can use expressions like
7713 count = aml->GetOriginal(x, y)
7716 @vindex this@r{, inside C@t{++} member functions}
7717 @cindex namespace in C@t{++}
7719 While a member function is active (in the selected stack frame), your
7720 expressions have the same namespace available as the member function;
7721 that is, @value{GDBN} allows implicit references to the class instance
7722 pointer @code{this} following the same rules as C@t{++}.
7724 @cindex call overloaded functions
7725 @cindex overloaded functions, calling
7726 @cindex type conversions in C@t{++}
7728 You can call overloaded functions; @value{GDBN} resolves the function
7729 call to the right definition, with some restrictions. @value{GDBN} does not
7730 perform overload resolution involving user-defined type conversions,
7731 calls to constructors, or instantiations of templates that do not exist
7732 in the program. It also cannot handle ellipsis argument lists or
7735 It does perform integral conversions and promotions, floating-point
7736 promotions, arithmetic conversions, pointer conversions, conversions of
7737 class objects to base classes, and standard conversions such as those of
7738 functions or arrays to pointers; it requires an exact match on the
7739 number of function arguments.
7741 Overload resolution is always performed, unless you have specified
7742 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7743 ,@value{GDBN} features for C@t{++}}.
7745 You must specify @code{set overload-resolution off} in order to use an
7746 explicit function signature to call an overloaded function, as in
7748 p 'foo(char,int)'('x', 13)
7751 The @value{GDBN} command-completion facility can simplify this;
7752 see @ref{Completion, ,Command completion}.
7754 @cindex reference declarations
7756 @value{GDBN} understands variables declared as C@t{++} references; you can use
7757 them in expressions just as you do in C@t{++} source---they are automatically
7760 In the parameter list shown when @value{GDBN} displays a frame, the values of
7761 reference variables are not displayed (unlike other variables); this
7762 avoids clutter, since references are often used for large structures.
7763 The @emph{address} of a reference variable is always shown, unless
7764 you have specified @samp{set print address off}.
7767 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7768 expressions can use it just as expressions in your program do. Since
7769 one scope may be defined in another, you can use @code{::} repeatedly if
7770 necessary, for example in an expression like
7771 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7772 resolving name scope by reference to source files, in both C and C@t{++}
7773 debugging (@pxref{Variables, ,Program variables}).
7776 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7777 calling virtual functions correctly, printing out virtual bases of
7778 objects, calling functions in a base subobject, casting objects, and
7779 invoking user-defined operators.
7782 @subsubsection C and C@t{++} defaults
7784 @cindex C and C@t{++} defaults
7786 If you allow @value{GDBN} to set type and range checking automatically, they
7787 both default to @code{off} whenever the working language changes to
7788 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7789 selects the working language.
7791 If you allow @value{GDBN} to set the language automatically, it
7792 recognizes source files whose names end with @file{.c}, @file{.C}, or
7793 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7794 these files, it sets the working language to C or C@t{++}.
7795 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7796 for further details.
7798 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7799 @c unimplemented. If (b) changes, it might make sense to let this node
7800 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7803 @subsubsection C and C@t{++} type and range checks
7805 @cindex C and C@t{++} checks
7807 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7808 is not used. However, if you turn type checking on, @value{GDBN}
7809 considers two variables type equivalent if:
7813 The two variables are structured and have the same structure, union, or
7817 The two variables have the same type name, or types that have been
7818 declared equivalent through @code{typedef}.
7821 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7824 The two @code{struct}, @code{union}, or @code{enum} variables are
7825 declared in the same declaration. (Note: this may not be true for all C
7830 Range checking, if turned on, is done on mathematical operations. Array
7831 indices are not checked, since they are often used to index a pointer
7832 that is not itself an array.
7835 @subsubsection @value{GDBN} and C
7837 The @code{set print union} and @code{show print union} commands apply to
7838 the @code{union} type. When set to @samp{on}, any @code{union} that is
7839 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7840 appears as @samp{@{...@}}.
7842 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7843 with pointers and a memory allocation function. @xref{Expressions,
7847 * Debugging C plus plus::
7850 @node Debugging C plus plus
7851 @subsubsection @value{GDBN} features for C@t{++}
7853 @cindex commands for C@t{++}
7855 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7856 designed specifically for use with C@t{++}. Here is a summary:
7859 @cindex break in overloaded functions
7860 @item @r{breakpoint menus}
7861 When you want a breakpoint in a function whose name is overloaded,
7862 @value{GDBN} breakpoint menus help you specify which function definition
7863 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7865 @cindex overloading in C@t{++}
7866 @item rbreak @var{regex}
7867 Setting breakpoints using regular expressions is helpful for setting
7868 breakpoints on overloaded functions that are not members of any special
7870 @xref{Set Breaks, ,Setting breakpoints}.
7872 @cindex C@t{++} exception handling
7875 Debug C@t{++} exception handling using these commands. @xref{Set
7876 Catchpoints, , Setting catchpoints}.
7879 @item ptype @var{typename}
7880 Print inheritance relationships as well as other information for type
7882 @xref{Symbols, ,Examining the Symbol Table}.
7884 @cindex C@t{++} symbol display
7885 @item set print demangle
7886 @itemx show print demangle
7887 @itemx set print asm-demangle
7888 @itemx show print asm-demangle
7889 Control whether C@t{++} symbols display in their source form, both when
7890 displaying code as C@t{++} source and when displaying disassemblies.
7891 @xref{Print Settings, ,Print settings}.
7893 @item set print object
7894 @itemx show print object
7895 Choose whether to print derived (actual) or declared types of objects.
7896 @xref{Print Settings, ,Print settings}.
7898 @item set print vtbl
7899 @itemx show print vtbl
7900 Control the format for printing virtual function tables.
7901 @xref{Print Settings, ,Print settings}.
7902 (The @code{vtbl} commands do not work on programs compiled with the HP
7903 ANSI C@t{++} compiler (@code{aCC}).)
7905 @kindex set overload-resolution
7906 @cindex overloaded functions, overload resolution
7907 @item set overload-resolution on
7908 Enable overload resolution for C@t{++} expression evaluation. The default
7909 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7910 and searches for a function whose signature matches the argument types,
7911 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7912 expressions}, for details). If it cannot find a match, it emits a
7915 @item set overload-resolution off
7916 Disable overload resolution for C@t{++} expression evaluation. For
7917 overloaded functions that are not class member functions, @value{GDBN}
7918 chooses the first function of the specified name that it finds in the
7919 symbol table, whether or not its arguments are of the correct type. For
7920 overloaded functions that are class member functions, @value{GDBN}
7921 searches for a function whose signature @emph{exactly} matches the
7924 @item @r{Overloaded symbol names}
7925 You can specify a particular definition of an overloaded symbol, using
7926 the same notation that is used to declare such symbols in C@t{++}: type
7927 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7928 also use the @value{GDBN} command-line word completion facilities to list the
7929 available choices, or to finish the type list for you.
7930 @xref{Completion,, Command completion}, for details on how to do this.
7934 @subsection Modula-2
7936 @cindex Modula-2, @value{GDBN} support
7938 The extensions made to @value{GDBN} to support Modula-2 only support
7939 output from the @sc{gnu} Modula-2 compiler (which is currently being
7940 developed). Other Modula-2 compilers are not currently supported, and
7941 attempting to debug executables produced by them is most likely
7942 to give an error as @value{GDBN} reads in the executable's symbol
7945 @cindex expressions in Modula-2
7947 * M2 Operators:: Built-in operators
7948 * Built-In Func/Proc:: Built-in functions and procedures
7949 * M2 Constants:: Modula-2 constants
7950 * M2 Defaults:: Default settings for Modula-2
7951 * Deviations:: Deviations from standard Modula-2
7952 * M2 Checks:: Modula-2 type and range checks
7953 * M2 Scope:: The scope operators @code{::} and @code{.}
7954 * GDB/M2:: @value{GDBN} and Modula-2
7958 @subsubsection Operators
7959 @cindex Modula-2 operators
7961 Operators must be defined on values of specific types. For instance,
7962 @code{+} is defined on numbers, but not on structures. Operators are
7963 often defined on groups of types. For the purposes of Modula-2, the
7964 following definitions hold:
7969 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7973 @emph{Character types} consist of @code{CHAR} and its subranges.
7976 @emph{Floating-point types} consist of @code{REAL}.
7979 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7983 @emph{Scalar types} consist of all of the above.
7986 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7989 @emph{Boolean types} consist of @code{BOOLEAN}.
7993 The following operators are supported, and appear in order of
7994 increasing precedence:
7998 Function argument or array index separator.
8001 Assignment. The value of @var{var} @code{:=} @var{value} is
8005 Less than, greater than on integral, floating-point, or enumerated
8009 Less than or equal to, greater than or equal to
8010 on integral, floating-point and enumerated types, or set inclusion on
8011 set types. Same precedence as @code{<}.
8013 @item =@r{, }<>@r{, }#
8014 Equality and two ways of expressing inequality, valid on scalar types.
8015 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
8016 available for inequality, since @code{#} conflicts with the script
8020 Set membership. Defined on set types and the types of their members.
8021 Same precedence as @code{<}.
8024 Boolean disjunction. Defined on boolean types.
8027 Boolean conjunction. Defined on boolean types.
8030 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
8033 Addition and subtraction on integral and floating-point types, or union
8034 and difference on set types.
8037 Multiplication on integral and floating-point types, or set intersection
8041 Division on floating-point types, or symmetric set difference on set
8042 types. Same precedence as @code{*}.
8045 Integer division and remainder. Defined on integral types. Same
8046 precedence as @code{*}.
8049 Negative. Defined on @code{INTEGER} and @code{REAL} data.
8052 Pointer dereferencing. Defined on pointer types.
8055 Boolean negation. Defined on boolean types. Same precedence as
8059 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
8060 precedence as @code{^}.
8063 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
8066 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
8070 @value{GDBN} and Modula-2 scope operators.
8074 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
8075 treats the use of the operator @code{IN}, or the use of operators
8076 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
8077 @code{<=}, and @code{>=} on sets as an error.
8081 @node Built-In Func/Proc
8082 @subsubsection Built-in functions and procedures
8083 @cindex Modula-2 built-ins
8085 Modula-2 also makes available several built-in procedures and functions.
8086 In describing these, the following metavariables are used:
8091 represents an @code{ARRAY} variable.
8094 represents a @code{CHAR} constant or variable.
8097 represents a variable or constant of integral type.
8100 represents an identifier that belongs to a set. Generally used in the
8101 same function with the metavariable @var{s}. The type of @var{s} should
8102 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
8105 represents a variable or constant of integral or floating-point type.
8108 represents a variable or constant of floating-point type.
8114 represents a variable.
8117 represents a variable or constant of one of many types. See the
8118 explanation of the function for details.
8121 All Modula-2 built-in procedures also return a result, described below.
8125 Returns the absolute value of @var{n}.
8128 If @var{c} is a lower case letter, it returns its upper case
8129 equivalent, otherwise it returns its argument.
8132 Returns the character whose ordinal value is @var{i}.
8135 Decrements the value in the variable @var{v} by one. Returns the new value.
8137 @item DEC(@var{v},@var{i})
8138 Decrements the value in the variable @var{v} by @var{i}. Returns the
8141 @item EXCL(@var{m},@var{s})
8142 Removes the element @var{m} from the set @var{s}. Returns the new
8145 @item FLOAT(@var{i})
8146 Returns the floating point equivalent of the integer @var{i}.
8149 Returns the index of the last member of @var{a}.
8152 Increments the value in the variable @var{v} by one. Returns the new value.
8154 @item INC(@var{v},@var{i})
8155 Increments the value in the variable @var{v} by @var{i}. Returns the
8158 @item INCL(@var{m},@var{s})
8159 Adds the element @var{m} to the set @var{s} if it is not already
8160 there. Returns the new set.
8163 Returns the maximum value of the type @var{t}.
8166 Returns the minimum value of the type @var{t}.
8169 Returns boolean TRUE if @var{i} is an odd number.
8172 Returns the ordinal value of its argument. For example, the ordinal
8173 value of a character is its @sc{ascii} value (on machines supporting the
8174 @sc{ascii} character set). @var{x} must be of an ordered type, which include
8175 integral, character and enumerated types.
8178 Returns the size of its argument. @var{x} can be a variable or a type.
8180 @item TRUNC(@var{r})
8181 Returns the integral part of @var{r}.
8183 @item VAL(@var{t},@var{i})
8184 Returns the member of the type @var{t} whose ordinal value is @var{i}.
8188 @emph{Warning:} Sets and their operations are not yet supported, so
8189 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
8193 @cindex Modula-2 constants
8195 @subsubsection Constants
8197 @value{GDBN} allows you to express the constants of Modula-2 in the following
8203 Integer constants are simply a sequence of digits. When used in an
8204 expression, a constant is interpreted to be type-compatible with the
8205 rest of the expression. Hexadecimal integers are specified by a
8206 trailing @samp{H}, and octal integers by a trailing @samp{B}.
8209 Floating point constants appear as a sequence of digits, followed by a
8210 decimal point and another sequence of digits. An optional exponent can
8211 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
8212 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
8213 digits of the floating point constant must be valid decimal (base 10)
8217 Character constants consist of a single character enclosed by a pair of
8218 like quotes, either single (@code{'}) or double (@code{"}). They may
8219 also be expressed by their ordinal value (their @sc{ascii} value, usually)
8220 followed by a @samp{C}.
8223 String constants consist of a sequence of characters enclosed by a
8224 pair of like quotes, either single (@code{'}) or double (@code{"}).
8225 Escape sequences in the style of C are also allowed. @xref{C
8226 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
8230 Enumerated constants consist of an enumerated identifier.
8233 Boolean constants consist of the identifiers @code{TRUE} and
8237 Pointer constants consist of integral values only.
8240 Set constants are not yet supported.
8244 @subsubsection Modula-2 defaults
8245 @cindex Modula-2 defaults
8247 If type and range checking are set automatically by @value{GDBN}, they
8248 both default to @code{on} whenever the working language changes to
8249 Modula-2. This happens regardless of whether you or @value{GDBN}
8250 selected the working language.
8252 If you allow @value{GDBN} to set the language automatically, then entering
8253 code compiled from a file whose name ends with @file{.mod} sets the
8254 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8255 the language automatically}, for further details.
8258 @subsubsection Deviations from standard Modula-2
8259 @cindex Modula-2, deviations from
8261 A few changes have been made to make Modula-2 programs easier to debug.
8262 This is done primarily via loosening its type strictness:
8266 Unlike in standard Modula-2, pointer constants can be formed by
8267 integers. This allows you to modify pointer variables during
8268 debugging. (In standard Modula-2, the actual address contained in a
8269 pointer variable is hidden from you; it can only be modified
8270 through direct assignment to another pointer variable or expression that
8271 returned a pointer.)
8274 C escape sequences can be used in strings and characters to represent
8275 non-printable characters. @value{GDBN} prints out strings with these
8276 escape sequences embedded. Single non-printable characters are
8277 printed using the @samp{CHR(@var{nnn})} format.
8280 The assignment operator (@code{:=}) returns the value of its right-hand
8284 All built-in procedures both modify @emph{and} return their argument.
8288 @subsubsection Modula-2 type and range checks
8289 @cindex Modula-2 checks
8292 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8295 @c FIXME remove warning when type/range checks added
8297 @value{GDBN} considers two Modula-2 variables type equivalent if:
8301 They are of types that have been declared equivalent via a @code{TYPE
8302 @var{t1} = @var{t2}} statement
8305 They have been declared on the same line. (Note: This is true of the
8306 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8309 As long as type checking is enabled, any attempt to combine variables
8310 whose types are not equivalent is an error.
8312 Range checking is done on all mathematical operations, assignment, array
8313 index bounds, and all built-in functions and procedures.
8316 @subsubsection The scope operators @code{::} and @code{.}
8318 @cindex @code{.}, Modula-2 scope operator
8319 @cindex colon, doubled as scope operator
8321 @vindex colon-colon@r{, in Modula-2}
8322 @c Info cannot handle :: but TeX can.
8325 @vindex ::@r{, in Modula-2}
8328 There are a few subtle differences between the Modula-2 scope operator
8329 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8334 @var{module} . @var{id}
8335 @var{scope} :: @var{id}
8339 where @var{scope} is the name of a module or a procedure,
8340 @var{module} the name of a module, and @var{id} is any declared
8341 identifier within your program, except another module.
8343 Using the @code{::} operator makes @value{GDBN} search the scope
8344 specified by @var{scope} for the identifier @var{id}. If it is not
8345 found in the specified scope, then @value{GDBN} searches all scopes
8346 enclosing the one specified by @var{scope}.
8348 Using the @code{.} operator makes @value{GDBN} search the current scope for
8349 the identifier specified by @var{id} that was imported from the
8350 definition module specified by @var{module}. With this operator, it is
8351 an error if the identifier @var{id} was not imported from definition
8352 module @var{module}, or if @var{id} is not an identifier in
8356 @subsubsection @value{GDBN} and Modula-2
8358 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8359 Five subcommands of @code{set print} and @code{show print} apply
8360 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8361 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8362 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8363 analogue in Modula-2.
8365 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8366 with any language, is not useful with Modula-2. Its
8367 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8368 created in Modula-2 as they can in C or C@t{++}. However, because an
8369 address can be specified by an integral constant, the construct
8370 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8372 @cindex @code{#} in Modula-2
8373 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8374 interpreted as the beginning of a comment. Use @code{<>} instead.
8379 The extensions made to @value{GDBN} to support Chill only support output
8380 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
8381 supported, and attempting to debug executables produced by them is most
8382 likely to give an error as @value{GDBN} reads in the executable's symbol
8385 @c This used to say "... following Chill related topics ...", but since
8386 @c menus are not shown in the printed manual, it would look awkward.
8387 This section covers the Chill related topics and the features
8388 of @value{GDBN} which support these topics.
8391 * How modes are displayed:: How modes are displayed
8392 * Locations:: Locations and their accesses
8393 * Values and their Operations:: Values and their Operations
8394 * Chill type and range checks::
8398 @node How modes are displayed
8399 @subsubsection How modes are displayed
8401 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
8402 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
8403 slightly from the standard specification of the Chill language. The
8406 @c FIXME: this @table's contents effectively disable @code by using @r
8407 @c on every @item. So why does it need @code?
8409 @item @r{@emph{Discrete modes:}}
8412 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
8415 @emph{Boolean Mode} which is predefined by @code{BOOL},
8417 @emph{Character Mode} which is predefined by @code{CHAR},
8419 @emph{Set Mode} which is displayed by the keyword @code{SET}.
8421 (@value{GDBP}) ptype x
8422 type = SET (karli = 10, susi = 20, fritzi = 100)
8424 If the type is an unnumbered set the set element values are omitted.
8426 @emph{Range Mode} which is displayed by
8428 @code{type = <basemode>(<lower bound> : <upper bound>)}
8430 where @code{<lower bound>, <upper bound>} can be of any discrete literal
8431 expression (e.g. set element names).
8434 @item @r{@emph{Powerset Mode:}}
8435 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
8436 the member mode of the powerset. The member mode can be any discrete mode.
8438 (@value{GDBP}) ptype x
8439 type = POWERSET SET (egon, hugo, otto)
8442 @item @r{@emph{Reference Modes:}}
8445 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
8446 followed by the mode name to which the reference is bound.
8448 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
8451 @item @r{@emph{Procedure mode}}
8452 The procedure mode is displayed by @code{type = PROC(<parameter list>)
8453 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
8454 list>} is a list of the parameter modes. @code{<return mode>} indicates
8455 the mode of the result of the procedure if any. The exceptionlist lists
8456 all possible exceptions which can be raised by the procedure.
8459 @item @r{@emph{Instance mode}}
8460 The instance mode is represented by a structure, which has a static
8461 type, and is therefore not really of interest.
8464 @item @r{@emph{Synchronization Modes:}}
8467 @emph{Event Mode} which is displayed by
8469 @code{EVENT (<event length>)}
8471 where @code{(<event length>)} is optional.
8473 @emph{Buffer Mode} which is displayed by
8475 @code{BUFFER (<buffer length>)<buffer element mode>}
8477 where @code{(<buffer length>)} is optional.
8480 @item @r{@emph{Timing Modes:}}
8483 @emph{Duration Mode} which is predefined by @code{DURATION}
8485 @emph{Absolute Time Mode} which is predefined by @code{TIME}
8488 @item @r{@emph{Real Modes:}}
8489 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
8491 @item @r{@emph{String Modes:}}
8494 @emph{Character String Mode} which is displayed by
8496 @code{CHARS(<string length>)}
8498 followed by the keyword @code{VARYING} if the String Mode is a varying
8501 @emph{Bit String Mode} which is displayed by
8508 @item @r{@emph{Array Mode:}}
8509 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
8510 followed by the element mode (which may in turn be an array mode).
8512 (@value{GDBP}) ptype x
8515 SET (karli = 10, susi = 20, fritzi = 100)
8518 @item @r{@emph{Structure Mode}}
8519 The Structure mode is displayed by the keyword @code{STRUCT(<field
8520 list>)}. The @code{<field list>} consists of names and modes of fields
8521 of the structure. Variant structures have the keyword @code{CASE <field>
8522 OF <variant fields> ESAC} in their field list. Since the current version
8523 of the GNU Chill compiler doesn't implement tag processing (no runtime
8524 checks of variant fields, and therefore no debugging info), the output
8525 always displays all variant fields.
8527 (@value{GDBP}) ptype str
8542 @subsubsection Locations and their accesses
8544 A location in Chill is an object which can contain values.
8546 A value of a location is generally accessed by the (declared) name of
8547 the location. The output conforms to the specification of values in
8548 Chill programs. How values are specified
8549 is the topic of the next section, @ref{Values and their Operations}.
8551 The pseudo-location @code{RESULT} (or @code{result}) can be used to
8552 display or change the result of a currently-active procedure:
8559 This does the same as the Chill action @code{RESULT EXPR} (which
8560 is not available in @value{GDBN}).
8562 Values of reference mode locations are printed by @code{PTR(<hex
8563 value>)} in case of a free reference mode, and by @code{(REF <reference
8564 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
8565 represents the address where the reference points to. To access the
8566 value of the location referenced by the pointer, use the dereference
8569 Values of procedure mode locations are displayed by
8572 (<argument modes> ) <return mode> @} <address> <name of procedure
8575 @code{<argument modes>} is a list of modes according to the parameter
8576 specification of the procedure and @code{<address>} shows the address of
8580 Locations of instance modes are displayed just like a structure with two
8581 fields specifying the @emph{process type} and the @emph{copy number} of
8582 the investigated instance location@footnote{This comes from the current
8583 implementation of instances. They are implemented as a structure (no
8584 na). The output should be something like @code{[<name of the process>;
8585 <instance number>]}.}. The field names are @code{__proc_type} and
8588 Locations of synchronization modes are displayed like a structure with
8589 the field name @code{__event_data} in case of a event mode location, and
8590 like a structure with the field @code{__buffer_data} in case of a buffer
8591 mode location (refer to previous paragraph).
8593 Structure Mode locations are printed by @code{[.<field name>: <value>,
8594 ...]}. The @code{<field name>} corresponds to the structure mode
8595 definition and the layout of @code{<value>} varies depending of the mode
8596 of the field. If the investigated structure mode location is of variant
8597 structure mode, the variant parts of the structure are enclosed in curled
8598 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
8599 on the same memory location and represent the current values of the
8600 memory location in their specific modes. Since no tag processing is done
8601 all variants are displayed. A variant field is printed by
8602 @code{(<variant name>) = .<field name>: <value>}. (who implements the
8605 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
8606 [.cs: []], (susi) = [.ds: susi]}]
8610 Substructures of string mode-, array mode- or structure mode-values
8611 (e.g. array slices, fields of structure locations) are accessed using
8612 certain operations which are described in the next section, @ref{Values
8613 and their Operations}.
8615 A location value may be interpreted as having a different mode using the
8616 location conversion. This mode conversion is written as @code{<mode
8617 name>(<location>)}. The user has to consider that the sizes of the modes
8618 have to be equal otherwise an error occurs. Furthermore, no range
8619 checking of the location against the destination mode is performed, and
8620 therefore the result can be quite confusing.
8623 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
8626 @node Values and their Operations
8627 @subsubsection Values and their Operations
8629 Values are used to alter locations, to investigate complex structures in
8630 more detail or to filter relevant information out of a large amount of
8631 data. There are several (mode dependent) operations defined which enable
8632 such investigations. These operations are not only applicable to
8633 constant values but also to locations, which can become quite useful
8634 when debugging complex structures. During parsing the command line
8635 (e.g. evaluating an expression) @value{GDBN} treats location names as
8636 the values behind these locations.
8638 This section describes how values have to be specified and which
8639 operations are legal to be used with such values.
8642 @item Literal Values
8643 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
8644 For detailed specification refer to the @sc{gnu} Chill implementation Manual
8646 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
8647 @c be converted to a @ref.
8652 @emph{Integer Literals} are specified in the same manner as in Chill
8653 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
8655 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
8657 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
8660 @emph{Set Literals} are defined by a name which was specified in a set
8661 mode. The value delivered by a Set Literal is the set value. This is
8662 comparable to an enumeration in C/C@t{++} language.
8664 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
8665 emptiness literal delivers either the empty reference value, the empty
8666 procedure value or the empty instance value.
8669 @emph{Character String Literals} are defined by a sequence of characters
8670 enclosed in single- or double quotes. If a single- or double quote has
8671 to be part of the string literal it has to be stuffed (specified twice).
8673 @emph{Bitstring Literals} are specified in the same manner as in Chill
8674 programs (refer z200/88 chpt 5.2.4.8).
8676 @emph{Floating point literals} are specified in the same manner as in
8677 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
8682 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
8683 name>} can be omitted if the mode of the tuple is unambiguous. This
8684 unambiguity is derived from the context of a evaluated expression.
8685 @code{<tuple>} can be one of the following:
8688 @item @emph{Powerset Tuple}
8689 @item @emph{Array Tuple}
8690 @item @emph{Structure Tuple}
8691 Powerset tuples, array tuples and structure tuples are specified in the
8692 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
8695 @item String Element Value
8696 A string element value is specified by
8698 @code{<string value>(<index>)}
8700 where @code{<index>} is a integer expression. It delivers a character
8701 value which is equivalent to the character indexed by @code{<index>} in
8704 @item String Slice Value
8705 A string slice value is specified by @code{<string value>(<slice
8706 spec>)}, where @code{<slice spec>} can be either a range of integer
8707 expressions or specified by @code{<start expr> up <size>}.
8708 @code{<size>} denotes the number of elements which the slice contains.
8709 The delivered value is a string value, which is part of the specified
8712 @item Array Element Values
8713 An array element value is specified by @code{<array value>(<expr>)} and
8714 delivers a array element value of the mode of the specified array.
8716 @item Array Slice Values
8717 An array slice is specified by @code{<array value>(<slice spec>)}, where
8718 @code{<slice spec>} can be either a range specified by expressions or by
8719 @code{<start expr> up <size>}. @code{<size>} denotes the number of
8720 arrayelements the slice contains. The delivered value is an array value
8721 which is part of the specified array.
8723 @item Structure Field Values
8724 A structure field value is derived by @code{<structure value>.<field
8725 name>}, where @code{<field name>} indicates the name of a field specified
8726 in the mode definition of the structure. The mode of the delivered value
8727 corresponds to this mode definition in the structure definition.
8729 @item Procedure Call Value
8730 The procedure call value is derived from the return value of the
8731 procedure@footnote{If a procedure call is used for instance in an
8732 expression, then this procedure is called with all its side
8733 effects. This can lead to confusing results if used carelessly.}.
8735 Values of duration mode locations are represented by @code{ULONG} literals.
8737 Values of time mode locations appear as
8739 @code{TIME(<secs>:<nsecs>)}
8744 This is not implemented yet:
8745 @item Built-in Value
8747 The following built in functions are provided:
8759 @item @code{UPPER()}
8760 @item @code{LOWER()}
8761 @item @code{LENGTH()}
8765 @item @code{ARCSIN()}
8766 @item @code{ARCCOS()}
8767 @item @code{ARCTAN()}
8774 For a detailed description refer to the GNU Chill implementation manual
8778 @item Zero-adic Operator Value
8779 The zero-adic operator value is derived from the instance value for the
8780 current active process.
8782 @item Expression Values
8783 The value delivered by an expression is the result of the evaluation of
8784 the specified expression. If there are error conditions (mode
8785 incompatibility, etc.) the evaluation of expressions is aborted with a
8786 corresponding error message. Expressions may be parenthesised which
8787 causes the evaluation of this expression before any other expression
8788 which uses the result of the parenthesised expression. The following
8789 operators are supported by @value{GDBN}:
8792 @item @code{OR, ORIF, XOR}
8793 @itemx @code{AND, ANDIF}
8795 Logical operators defined over operands of boolean mode.
8798 Equality and inequality operators defined over all modes.
8802 Relational operators defined over predefined modes.
8805 @itemx @code{*, /, MOD, REM}
8806 Arithmetic operators defined over predefined modes.
8809 Change sign operator.
8812 String concatenation operator.
8815 String repetition operator.
8818 Referenced location operator which can be used either to take the
8819 address of a location (@code{->loc}), or to dereference a reference
8820 location (@code{loc->}).
8822 @item @code{OR, XOR}
8825 Powerset and bitstring operators.
8829 Powerset inclusion operators.
8832 Membership operator.
8836 @node Chill type and range checks
8837 @subsubsection Chill type and range checks
8839 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8840 of the two modes are equal. This rule applies recursively to more
8841 complex datatypes which means that complex modes are treated
8842 equivalent if all element modes (which also can be complex modes like
8843 structures, arrays, etc.) have the same size.
8845 Range checking is done on all mathematical operations, assignment, array
8846 index bounds and all built in procedures.
8848 Strong type checks are forced using the @value{GDBN} command @code{set
8849 check strong}. This enforces strong type and range checks on all
8850 operations where Chill constructs are used (expressions, built in
8851 functions, etc.) in respect to the semantics as defined in the z.200
8852 language specification.
8854 All checks can be disabled by the @value{GDBN} command @code{set check
8858 @c Deviations from the Chill Standard Z200/88
8859 see last paragraph ?
8862 @node Chill defaults
8863 @subsubsection Chill defaults
8865 If type and range checking are set automatically by @value{GDBN}, they
8866 both default to @code{on} whenever the working language changes to
8867 Chill. This happens regardless of whether you or @value{GDBN}
8868 selected the working language.
8870 If you allow @value{GDBN} to set the language automatically, then entering
8871 code compiled from a file whose name ends with @file{.ch} sets the
8872 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8873 the language automatically}, for further details.
8876 @chapter Examining the Symbol Table
8878 The commands described in this chapter allow you to inquire about the
8879 symbols (names of variables, functions and types) defined in your
8880 program. This information is inherent in the text of your program and
8881 does not change as your program executes. @value{GDBN} finds it in your
8882 program's symbol table, in the file indicated when you started @value{GDBN}
8883 (@pxref{File Options, ,Choosing files}), or by one of the
8884 file-management commands (@pxref{Files, ,Commands to specify files}).
8886 @cindex symbol names
8887 @cindex names of symbols
8888 @cindex quoting names
8889 Occasionally, you may need to refer to symbols that contain unusual
8890 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8891 most frequent case is in referring to static variables in other
8892 source files (@pxref{Variables,,Program variables}). File names
8893 are recorded in object files as debugging symbols, but @value{GDBN} would
8894 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8895 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8896 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8903 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8906 @kindex info address
8907 @cindex address of a symbol
8908 @item info address @var{symbol}
8909 Describe where the data for @var{symbol} is stored. For a register
8910 variable, this says which register it is kept in. For a non-register
8911 local variable, this prints the stack-frame offset at which the variable
8914 Note the contrast with @samp{print &@var{symbol}}, which does not work
8915 at all for a register variable, and for a stack local variable prints
8916 the exact address of the current instantiation of the variable.
8919 @cindex symbol from address
8920 @item info symbol @var{addr}
8921 Print the name of a symbol which is stored at the address @var{addr}.
8922 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8923 nearest symbol and an offset from it:
8926 (@value{GDBP}) info symbol 0x54320
8927 _initialize_vx + 396 in section .text
8931 This is the opposite of the @code{info address} command. You can use
8932 it to find out the name of a variable or a function given its address.
8935 @item whatis @var{expr}
8936 Print the data type of expression @var{expr}. @var{expr} is not
8937 actually evaluated, and any side-effecting operations (such as
8938 assignments or function calls) inside it do not take place.
8939 @xref{Expressions, ,Expressions}.
8942 Print the data type of @code{$}, the last value in the value history.
8945 @item ptype @var{typename}
8946 Print a description of data type @var{typename}. @var{typename} may be
8947 the name of a type, or for C code it may have the form @samp{class
8948 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8949 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8951 @item ptype @var{expr}
8953 Print a description of the type of expression @var{expr}. @code{ptype}
8954 differs from @code{whatis} by printing a detailed description, instead
8955 of just the name of the type.
8957 For example, for this variable declaration:
8960 struct complex @{double real; double imag;@} v;
8964 the two commands give this output:
8968 (@value{GDBP}) whatis v
8969 type = struct complex
8970 (@value{GDBP}) ptype v
8971 type = struct complex @{
8979 As with @code{whatis}, using @code{ptype} without an argument refers to
8980 the type of @code{$}, the last value in the value history.
8983 @item info types @var{regexp}
8985 Print a brief description of all types whose names match @var{regexp}
8986 (or all types in your program, if you supply no argument). Each
8987 complete typename is matched as though it were a complete line; thus,
8988 @samp{i type value} gives information on all types in your program whose
8989 names include the string @code{value}, but @samp{i type ^value$} gives
8990 information only on types whose complete name is @code{value}.
8992 This command differs from @code{ptype} in two ways: first, like
8993 @code{whatis}, it does not print a detailed description; second, it
8994 lists all source files where a type is defined.
8997 @cindex local variables
8998 @item info scope @var{addr}
8999 List all the variables local to a particular scope. This command
9000 accepts a location---a function name, a source line, or an address
9001 preceded by a @samp{*}, and prints all the variables local to the
9002 scope defined by that location. For example:
9005 (@value{GDBP}) @b{info scope command_line_handler}
9006 Scope for command_line_handler:
9007 Symbol rl is an argument at stack/frame offset 8, length 4.
9008 Symbol linebuffer is in static storage at address 0x150a18, length 4.
9009 Symbol linelength is in static storage at address 0x150a1c, length 4.
9010 Symbol p is a local variable in register $esi, length 4.
9011 Symbol p1 is a local variable in register $ebx, length 4.
9012 Symbol nline is a local variable in register $edx, length 4.
9013 Symbol repeat is a local variable at frame offset -8, length 4.
9017 This command is especially useful for determining what data to collect
9018 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
9023 Show information about the current source file---that is, the source file for
9024 the function containing the current point of execution:
9027 the name of the source file, and the directory containing it,
9029 the directory it was compiled in,
9031 its length, in lines,
9033 which programming language it is written in,
9035 whether the executable includes debugging information for that file, and
9036 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
9038 whether the debugging information includes information about
9039 preprocessor macros.
9043 @kindex info sources
9045 Print the names of all source files in your program for which there is
9046 debugging information, organized into two lists: files whose symbols
9047 have already been read, and files whose symbols will be read when needed.
9049 @kindex info functions
9050 @item info functions
9051 Print the names and data types of all defined functions.
9053 @item info functions @var{regexp}
9054 Print the names and data types of all defined functions
9055 whose names contain a match for regular expression @var{regexp}.
9056 Thus, @samp{info fun step} finds all functions whose names
9057 include @code{step}; @samp{info fun ^step} finds those whose names
9058 start with @code{step}. If a function name contains characters
9059 that conflict with the regular expression language (eg.
9060 @samp{operator*()}), they may be quoted with a backslash.
9062 @kindex info variables
9063 @item info variables
9064 Print the names and data types of all variables that are declared
9065 outside of functions (i.e.@: excluding local variables).
9067 @item info variables @var{regexp}
9068 Print the names and data types of all variables (except for local
9069 variables) whose names contain a match for regular expression
9073 This was never implemented.
9074 @kindex info methods
9076 @itemx info methods @var{regexp}
9077 The @code{info methods} command permits the user to examine all defined
9078 methods within C@t{++} program, or (with the @var{regexp} argument) a
9079 specific set of methods found in the various C@t{++} classes. Many
9080 C@t{++} classes provide a large number of methods. Thus, the output
9081 from the @code{ptype} command can be overwhelming and hard to use. The
9082 @code{info-methods} command filters the methods, printing only those
9083 which match the regular-expression @var{regexp}.
9086 @cindex reloading symbols
9087 Some systems allow individual object files that make up your program to
9088 be replaced without stopping and restarting your program. For example,
9089 in VxWorks you can simply recompile a defective object file and keep on
9090 running. If you are running on one of these systems, you can allow
9091 @value{GDBN} to reload the symbols for automatically relinked modules:
9094 @kindex set symbol-reloading
9095 @item set symbol-reloading on
9096 Replace symbol definitions for the corresponding source file when an
9097 object file with a particular name is seen again.
9099 @item set symbol-reloading off
9100 Do not replace symbol definitions when encountering object files of the
9101 same name more than once. This is the default state; if you are not
9102 running on a system that permits automatic relinking of modules, you
9103 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
9104 may discard symbols when linking large programs, that may contain
9105 several modules (from different directories or libraries) with the same
9108 @kindex show symbol-reloading
9109 @item show symbol-reloading
9110 Show the current @code{on} or @code{off} setting.
9113 @kindex set opaque-type-resolution
9114 @item set opaque-type-resolution on
9115 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
9116 declared as a pointer to a @code{struct}, @code{class}, or
9117 @code{union}---for example, @code{struct MyType *}---that is used in one
9118 source file although the full declaration of @code{struct MyType} is in
9119 another source file. The default is on.
9121 A change in the setting of this subcommand will not take effect until
9122 the next time symbols for a file are loaded.
9124 @item set opaque-type-resolution off
9125 Tell @value{GDBN} not to resolve opaque types. In this case, the type
9126 is printed as follows:
9128 @{<no data fields>@}
9131 @kindex show opaque-type-resolution
9132 @item show opaque-type-resolution
9133 Show whether opaque types are resolved or not.
9135 @kindex maint print symbols
9137 @kindex maint print psymbols
9138 @cindex partial symbol dump
9139 @item maint print symbols @var{filename}
9140 @itemx maint print psymbols @var{filename}
9141 @itemx maint print msymbols @var{filename}
9142 Write a dump of debugging symbol data into the file @var{filename}.
9143 These commands are used to debug the @value{GDBN} symbol-reading code. Only
9144 symbols with debugging data are included. If you use @samp{maint print
9145 symbols}, @value{GDBN} includes all the symbols for which it has already
9146 collected full details: that is, @var{filename} reflects symbols for
9147 only those files whose symbols @value{GDBN} has read. You can use the
9148 command @code{info sources} to find out which files these are. If you
9149 use @samp{maint print psymbols} instead, the dump shows information about
9150 symbols that @value{GDBN} only knows partially---that is, symbols defined in
9151 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
9152 @samp{maint print msymbols} dumps just the minimal symbol information
9153 required for each object file from which @value{GDBN} has read some symbols.
9154 @xref{Files, ,Commands to specify files}, for a discussion of how
9155 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
9159 @chapter Altering Execution
9161 Once you think you have found an error in your program, you might want to
9162 find out for certain whether correcting the apparent error would lead to
9163 correct results in the rest of the run. You can find the answer by
9164 experiment, using the @value{GDBN} features for altering execution of the
9167 For example, you can store new values into variables or memory
9168 locations, give your program a signal, restart it at a different
9169 address, or even return prematurely from a function.
9172 * Assignment:: Assignment to variables
9173 * Jumping:: Continuing at a different address
9174 * Signaling:: Giving your program a signal
9175 * Returning:: Returning from a function
9176 * Calling:: Calling your program's functions
9177 * Patching:: Patching your program
9181 @section Assignment to variables
9184 @cindex setting variables
9185 To alter the value of a variable, evaluate an assignment expression.
9186 @xref{Expressions, ,Expressions}. For example,
9193 stores the value 4 into the variable @code{x}, and then prints the
9194 value of the assignment expression (which is 4).
9195 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
9196 information on operators in supported languages.
9198 @kindex set variable
9199 @cindex variables, setting
9200 If you are not interested in seeing the value of the assignment, use the
9201 @code{set} command instead of the @code{print} command. @code{set} is
9202 really the same as @code{print} except that the expression's value is
9203 not printed and is not put in the value history (@pxref{Value History,
9204 ,Value history}). The expression is evaluated only for its effects.
9206 If the beginning of the argument string of the @code{set} command
9207 appears identical to a @code{set} subcommand, use the @code{set
9208 variable} command instead of just @code{set}. This command is identical
9209 to @code{set} except for its lack of subcommands. For example, if your
9210 program has a variable @code{width}, you get an error if you try to set
9211 a new value with just @samp{set width=13}, because @value{GDBN} has the
9212 command @code{set width}:
9215 (@value{GDBP}) whatis width
9217 (@value{GDBP}) p width
9219 (@value{GDBP}) set width=47
9220 Invalid syntax in expression.
9224 The invalid expression, of course, is @samp{=47}. In
9225 order to actually set the program's variable @code{width}, use
9228 (@value{GDBP}) set var width=47
9231 Because the @code{set} command has many subcommands that can conflict
9232 with the names of program variables, it is a good idea to use the
9233 @code{set variable} command instead of just @code{set}. For example, if
9234 your program has a variable @code{g}, you run into problems if you try
9235 to set a new value with just @samp{set g=4}, because @value{GDBN} has
9236 the command @code{set gnutarget}, abbreviated @code{set g}:
9240 (@value{GDBP}) whatis g
9244 (@value{GDBP}) set g=4
9248 The program being debugged has been started already.
9249 Start it from the beginning? (y or n) y
9250 Starting program: /home/smith/cc_progs/a.out
9251 "/home/smith/cc_progs/a.out": can't open to read symbols:
9253 (@value{GDBP}) show g
9254 The current BFD target is "=4".
9259 The program variable @code{g} did not change, and you silently set the
9260 @code{gnutarget} to an invalid value. In order to set the variable
9264 (@value{GDBP}) set var g=4
9267 @value{GDBN} allows more implicit conversions in assignments than C; you can
9268 freely store an integer value into a pointer variable or vice versa,
9269 and you can convert any structure to any other structure that is the
9270 same length or shorter.
9271 @comment FIXME: how do structs align/pad in these conversions?
9272 @comment /doc@cygnus.com 18dec1990
9274 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9275 construct to generate a value of specified type at a specified address
9276 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9277 to memory location @code{0x83040} as an integer (which implies a certain size
9278 and representation in memory), and
9281 set @{int@}0x83040 = 4
9285 stores the value 4 into that memory location.
9288 @section Continuing at a different address
9290 Ordinarily, when you continue your program, you do so at the place where
9291 it stopped, with the @code{continue} command. You can instead continue at
9292 an address of your own choosing, with the following commands:
9296 @item jump @var{linespec}
9297 Resume execution at line @var{linespec}. Execution stops again
9298 immediately if there is a breakpoint there. @xref{List, ,Printing
9299 source lines}, for a description of the different forms of
9300 @var{linespec}. It is common practice to use the @code{tbreak} command
9301 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9304 The @code{jump} command does not change the current stack frame, or
9305 the stack pointer, or the contents of any memory location or any
9306 register other than the program counter. If line @var{linespec} is in
9307 a different function from the one currently executing, the results may
9308 be bizarre if the two functions expect different patterns of arguments or
9309 of local variables. For this reason, the @code{jump} command requests
9310 confirmation if the specified line is not in the function currently
9311 executing. However, even bizarre results are predictable if you are
9312 well acquainted with the machine-language code of your program.
9314 @item jump *@var{address}
9315 Resume execution at the instruction at address @var{address}.
9318 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9319 On many systems, you can get much the same effect as the @code{jump}
9320 command by storing a new value into the register @code{$pc}. The
9321 difference is that this does not start your program running; it only
9322 changes the address of where it @emph{will} run when you continue. For
9330 makes the next @code{continue} command or stepping command execute at
9331 address @code{0x485}, rather than at the address where your program stopped.
9332 @xref{Continuing and Stepping, ,Continuing and stepping}.
9334 The most common occasion to use the @code{jump} command is to back
9335 up---perhaps with more breakpoints set---over a portion of a program
9336 that has already executed, in order to examine its execution in more
9341 @section Giving your program a signal
9345 @item signal @var{signal}
9346 Resume execution where your program stopped, but immediately give it the
9347 signal @var{signal}. @var{signal} can be the name or the number of a
9348 signal. For example, on many systems @code{signal 2} and @code{signal
9349 SIGINT} are both ways of sending an interrupt signal.
9351 Alternatively, if @var{signal} is zero, continue execution without
9352 giving a signal. This is useful when your program stopped on account of
9353 a signal and would ordinary see the signal when resumed with the
9354 @code{continue} command; @samp{signal 0} causes it to resume without a
9357 @code{signal} does not repeat when you press @key{RET} a second time
9358 after executing the command.
9362 Invoking the @code{signal} command is not the same as invoking the
9363 @code{kill} utility from the shell. Sending a signal with @code{kill}
9364 causes @value{GDBN} to decide what to do with the signal depending on
9365 the signal handling tables (@pxref{Signals}). The @code{signal} command
9366 passes the signal directly to your program.
9370 @section Returning from a function
9373 @cindex returning from a function
9376 @itemx return @var{expression}
9377 You can cancel execution of a function call with the @code{return}
9378 command. If you give an
9379 @var{expression} argument, its value is used as the function's return
9383 When you use @code{return}, @value{GDBN} discards the selected stack frame
9384 (and all frames within it). You can think of this as making the
9385 discarded frame return prematurely. If you wish to specify a value to
9386 be returned, give that value as the argument to @code{return}.
9388 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9389 frame}), and any other frames inside of it, leaving its caller as the
9390 innermost remaining frame. That frame becomes selected. The
9391 specified value is stored in the registers used for returning values
9394 The @code{return} command does not resume execution; it leaves the
9395 program stopped in the state that would exist if the function had just
9396 returned. In contrast, the @code{finish} command (@pxref{Continuing
9397 and Stepping, ,Continuing and stepping}) resumes execution until the
9398 selected stack frame returns naturally.
9401 @section Calling program functions
9403 @cindex calling functions
9406 @item call @var{expr}
9407 Evaluate the expression @var{expr} without displaying @code{void}
9411 You can use this variant of the @code{print} command if you want to
9412 execute a function from your program, but without cluttering the output
9413 with @code{void} returned values. If the result is not void, it
9414 is printed and saved in the value history.
9417 @section Patching programs
9419 @cindex patching binaries
9420 @cindex writing into executables
9421 @cindex writing into corefiles
9423 By default, @value{GDBN} opens the file containing your program's
9424 executable code (or the corefile) read-only. This prevents accidental
9425 alterations to machine code; but it also prevents you from intentionally
9426 patching your program's binary.
9428 If you'd like to be able to patch the binary, you can specify that
9429 explicitly with the @code{set write} command. For example, you might
9430 want to turn on internal debugging flags, or even to make emergency
9436 @itemx set write off
9437 If you specify @samp{set write on}, @value{GDBN} opens executable and
9438 core files for both reading and writing; if you specify @samp{set write
9439 off} (the default), @value{GDBN} opens them read-only.
9441 If you have already loaded a file, you must load it again (using the
9442 @code{exec-file} or @code{core-file} command) after changing @code{set
9443 write}, for your new setting to take effect.
9447 Display whether executable files and core files are opened for writing
9452 @chapter @value{GDBN} Files
9454 @value{GDBN} needs to know the file name of the program to be debugged,
9455 both in order to read its symbol table and in order to start your
9456 program. To debug a core dump of a previous run, you must also tell
9457 @value{GDBN} the name of the core dump file.
9460 * Files:: Commands to specify files
9461 * Symbol Errors:: Errors reading symbol files
9465 @section Commands to specify files
9467 @cindex symbol table
9468 @cindex core dump file
9470 You may want to specify executable and core dump file names. The usual
9471 way to do this is at start-up time, using the arguments to
9472 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9473 Out of @value{GDBN}}).
9475 Occasionally it is necessary to change to a different file during a
9476 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9477 a file you want to use. In these situations the @value{GDBN} commands
9478 to specify new files are useful.
9481 @cindex executable file
9483 @item file @var{filename}
9484 Use @var{filename} as the program to be debugged. It is read for its
9485 symbols and for the contents of pure memory. It is also the program
9486 executed when you use the @code{run} command. If you do not specify a
9487 directory and the file is not found in the @value{GDBN} working directory,
9488 @value{GDBN} uses the environment variable @code{PATH} as a list of
9489 directories to search, just as the shell does when looking for a program
9490 to run. You can change the value of this variable, for both @value{GDBN}
9491 and your program, using the @code{path} command.
9493 On systems with memory-mapped files, an auxiliary file named
9494 @file{@var{filename}.syms} may hold symbol table information for
9495 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9496 @file{@var{filename}.syms}, starting up more quickly. See the
9497 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9498 (available on the command line, and with the commands @code{file},
9499 @code{symbol-file}, or @code{add-symbol-file}, described below),
9500 for more information.
9503 @code{file} with no argument makes @value{GDBN} discard any information it
9504 has on both executable file and the symbol table.
9507 @item exec-file @r{[} @var{filename} @r{]}
9508 Specify that the program to be run (but not the symbol table) is found
9509 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9510 if necessary to locate your program. Omitting @var{filename} means to
9511 discard information on the executable file.
9514 @item symbol-file @r{[} @var{filename} @r{]}
9515 Read symbol table information from file @var{filename}. @code{PATH} is
9516 searched when necessary. Use the @code{file} command to get both symbol
9517 table and program to run from the same file.
9519 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9520 program's symbol table.
9522 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9523 of its convenience variables, the value history, and all breakpoints and
9524 auto-display expressions. This is because they may contain pointers to
9525 the internal data recording symbols and data types, which are part of
9526 the old symbol table data being discarded inside @value{GDBN}.
9528 @code{symbol-file} does not repeat if you press @key{RET} again after
9531 When @value{GDBN} is configured for a particular environment, it
9532 understands debugging information in whatever format is the standard
9533 generated for that environment; you may use either a @sc{gnu} compiler, or
9534 other compilers that adhere to the local conventions.
9535 Best results are usually obtained from @sc{gnu} compilers; for example,
9536 using @code{@value{GCC}} you can generate debugging information for
9539 For most kinds of object files, with the exception of old SVR3 systems
9540 using COFF, the @code{symbol-file} command does not normally read the
9541 symbol table in full right away. Instead, it scans the symbol table
9542 quickly to find which source files and which symbols are present. The
9543 details are read later, one source file at a time, as they are needed.
9545 The purpose of this two-stage reading strategy is to make @value{GDBN}
9546 start up faster. For the most part, it is invisible except for
9547 occasional pauses while the symbol table details for a particular source
9548 file are being read. (The @code{set verbose} command can turn these
9549 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9550 warnings and messages}.)
9552 We have not implemented the two-stage strategy for COFF yet. When the
9553 symbol table is stored in COFF format, @code{symbol-file} reads the
9554 symbol table data in full right away. Note that ``stabs-in-COFF''
9555 still does the two-stage strategy, since the debug info is actually
9559 @cindex reading symbols immediately
9560 @cindex symbols, reading immediately
9562 @cindex memory-mapped symbol file
9563 @cindex saving symbol table
9564 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9565 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9566 You can override the @value{GDBN} two-stage strategy for reading symbol
9567 tables by using the @samp{-readnow} option with any of the commands that
9568 load symbol table information, if you want to be sure @value{GDBN} has the
9569 entire symbol table available.
9571 If memory-mapped files are available on your system through the
9572 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9573 cause @value{GDBN} to write the symbols for your program into a reusable
9574 file. Future @value{GDBN} debugging sessions map in symbol information
9575 from this auxiliary symbol file (if the program has not changed), rather
9576 than spending time reading the symbol table from the executable
9577 program. Using the @samp{-mapped} option has the same effect as
9578 starting @value{GDBN} with the @samp{-mapped} command-line option.
9580 You can use both options together, to make sure the auxiliary symbol
9581 file has all the symbol information for your program.
9583 The auxiliary symbol file for a program called @var{myprog} is called
9584 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9585 than the corresponding executable), @value{GDBN} always attempts to use
9586 it when you debug @var{myprog}; no special options or commands are
9589 The @file{.syms} file is specific to the host machine where you run
9590 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9591 symbol table. It cannot be shared across multiple host platforms.
9593 @c FIXME: for now no mention of directories, since this seems to be in
9594 @c flux. 13mar1992 status is that in theory GDB would look either in
9595 @c current dir or in same dir as myprog; but issues like competing
9596 @c GDB's, or clutter in system dirs, mean that in practice right now
9597 @c only current dir is used. FFish says maybe a special GDB hierarchy
9598 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9603 @item core-file @r{[} @var{filename} @r{]}
9604 Specify the whereabouts of a core dump file to be used as the ``contents
9605 of memory''. Traditionally, core files contain only some parts of the
9606 address space of the process that generated them; @value{GDBN} can access the
9607 executable file itself for other parts.
9609 @code{core-file} with no argument specifies that no core file is
9612 Note that the core file is ignored when your program is actually running
9613 under @value{GDBN}. So, if you have been running your program and you
9614 wish to debug a core file instead, you must kill the subprocess in which
9615 the program is running. To do this, use the @code{kill} command
9616 (@pxref{Kill Process, ,Killing the child process}).
9618 @kindex add-symbol-file
9619 @cindex dynamic linking
9620 @item add-symbol-file @var{filename} @var{address}
9621 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9622 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9623 The @code{add-symbol-file} command reads additional symbol table
9624 information from the file @var{filename}. You would use this command
9625 when @var{filename} has been dynamically loaded (by some other means)
9626 into the program that is running. @var{address} should be the memory
9627 address at which the file has been loaded; @value{GDBN} cannot figure
9628 this out for itself. You can additionally specify an arbitrary number
9629 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9630 section name and base address for that section. You can specify any
9631 @var{address} as an expression.
9633 The symbol table of the file @var{filename} is added to the symbol table
9634 originally read with the @code{symbol-file} command. You can use the
9635 @code{add-symbol-file} command any number of times; the new symbol data
9636 thus read keeps adding to the old. To discard all old symbol data
9637 instead, use the @code{symbol-file} command without any arguments.
9639 @cindex relocatable object files, reading symbols from
9640 @cindex object files, relocatable, reading symbols from
9641 @cindex reading symbols from relocatable object files
9642 @cindex symbols, reading from relocatable object files
9643 @cindex @file{.o} files, reading symbols from
9644 Although @var{filename} is typically a shared library file, an
9645 executable file, or some other object file which has been fully
9646 relocated for loading into a process, you can also load symbolic
9647 information from relocatable @file{.o} files, as long as:
9651 the file's symbolic information refers only to linker symbols defined in
9652 that file, not to symbols defined by other object files,
9654 every section the file's symbolic information refers to has actually
9655 been loaded into the inferior, as it appears in the file, and
9657 you can determine the address at which every section was loaded, and
9658 provide these to the @code{add-symbol-file} command.
9662 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9663 relocatable files into an already running program; such systems
9664 typically make the requirements above easy to meet. However, it's
9665 important to recognize that many native systems use complex link
9666 procedures (@code{.linkonce} section factoring and C++ constructor table
9667 assembly, for example) that make the requirements difficult to meet. In
9668 general, one cannot assume that using @code{add-symbol-file} to read a
9669 relocatable object file's symbolic information will have the same effect
9670 as linking the relocatable object file into the program in the normal
9673 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9675 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9676 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9677 table information for @var{filename}.
9679 @kindex add-shared-symbol-file
9680 @item add-shared-symbol-file
9681 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9682 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9683 shared libraries, however if @value{GDBN} does not find yours, you can run
9684 @code{add-shared-symbol-file}. It takes no arguments.
9688 The @code{section} command changes the base address of section SECTION of
9689 the exec file to ADDR. This can be used if the exec file does not contain
9690 section addresses, (such as in the a.out format), or when the addresses
9691 specified in the file itself are wrong. Each section must be changed
9692 separately. The @code{info files} command, described below, lists all
9693 the sections and their addresses.
9699 @code{info files} and @code{info target} are synonymous; both print the
9700 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9701 including the names of the executable and core dump files currently in
9702 use by @value{GDBN}, and the files from which symbols were loaded. The
9703 command @code{help target} lists all possible targets rather than
9706 @kindex maint info sections
9707 @item maint info sections
9708 Another command that can give you extra information about program sections
9709 is @code{maint info sections}. In addition to the section information
9710 displayed by @code{info files}, this command displays the flags and file
9711 offset of each section in the executable and core dump files. In addition,
9712 @code{maint info sections} provides the following command options (which
9713 may be arbitrarily combined):
9717 Display sections for all loaded object files, including shared libraries.
9718 @item @var{sections}
9719 Display info only for named @var{sections}.
9720 @item @var{section-flags}
9721 Display info only for sections for which @var{section-flags} are true.
9722 The section flags that @value{GDBN} currently knows about are:
9725 Section will have space allocated in the process when loaded.
9726 Set for all sections except those containing debug information.
9728 Section will be loaded from the file into the child process memory.
9729 Set for pre-initialized code and data, clear for @code{.bss} sections.
9731 Section needs to be relocated before loading.
9733 Section cannot be modified by the child process.
9735 Section contains executable code only.
9737 Section contains data only (no executable code).
9739 Section will reside in ROM.
9741 Section contains data for constructor/destructor lists.
9743 Section is not empty.
9745 An instruction to the linker to not output the section.
9746 @item COFF_SHARED_LIBRARY
9747 A notification to the linker that the section contains
9748 COFF shared library information.
9750 Section contains common symbols.
9753 @kindex set trust-readonly-sections
9754 @item set trust-readonly-sections on
9755 Tell @value{GDBN} that readonly sections in your object file
9756 really are read-only (i.e.@: that their contents will not change).
9757 In that case, @value{GDBN} can fetch values from these sections
9758 out of the object file, rather than from the target program.
9759 For some targets (notably embedded ones), this can be a significant
9760 enhancement to debugging performance.
9764 @item set trust-readonly-sections off
9765 Tell @value{GDBN} not to trust readonly sections. This means that
9766 the contents of the section might change while the program is running,
9767 and must therefore be fetched from the target when needed.
9770 All file-specifying commands allow both absolute and relative file names
9771 as arguments. @value{GDBN} always converts the file name to an absolute file
9772 name and remembers it that way.
9774 @cindex shared libraries
9775 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9778 @value{GDBN} automatically loads symbol definitions from shared libraries
9779 when you use the @code{run} command, or when you examine a core file.
9780 (Before you issue the @code{run} command, @value{GDBN} does not understand
9781 references to a function in a shared library, however---unless you are
9782 debugging a core file).
9784 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9785 automatically loads the symbols at the time of the @code{shl_load} call.
9787 @c FIXME: some @value{GDBN} release may permit some refs to undef
9788 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9789 @c FIXME...lib; check this from time to time when updating manual
9791 There are times, however, when you may wish to not automatically load
9792 symbol definitions from shared libraries, such as when they are
9793 particularly large or there are many of them.
9795 To control the automatic loading of shared library symbols, use the
9799 @kindex set auto-solib-add
9800 @item set auto-solib-add @var{mode}
9801 If @var{mode} is @code{on}, symbols from all shared object libraries
9802 will be loaded automatically when the inferior begins execution, you
9803 attach to an independently started inferior, or when the dynamic linker
9804 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9805 is @code{off}, symbols must be loaded manually, using the
9806 @code{sharedlibrary} command. The default value is @code{on}.
9808 @kindex show auto-solib-add
9809 @item show auto-solib-add
9810 Display the current autoloading mode.
9813 To explicitly load shared library symbols, use the @code{sharedlibrary}
9817 @kindex info sharedlibrary
9820 @itemx info sharedlibrary
9821 Print the names of the shared libraries which are currently loaded.
9823 @kindex sharedlibrary
9825 @item sharedlibrary @var{regex}
9826 @itemx share @var{regex}
9827 Load shared object library symbols for files matching a
9828 Unix regular expression.
9829 As with files loaded automatically, it only loads shared libraries
9830 required by your program for a core file or after typing @code{run}. If
9831 @var{regex} is omitted all shared libraries required by your program are
9835 On some systems, such as HP-UX systems, @value{GDBN} supports
9836 autoloading shared library symbols until a limiting threshold size is
9837 reached. This provides the benefit of allowing autoloading to remain on
9838 by default, but avoids autoloading excessively large shared libraries,
9839 up to a threshold that is initially set, but which you can modify if you
9842 Beyond that threshold, symbols from shared libraries must be explicitly
9843 loaded. To load these symbols, use the command @code{sharedlibrary
9844 @var{filename}}. The base address of the shared library is determined
9845 automatically by @value{GDBN} and need not be specified.
9847 To display or set the threshold, use the commands:
9850 @kindex set auto-solib-limit
9851 @item set auto-solib-limit @var{threshold}
9852 Set the autoloading size threshold, in an integral number of megabytes.
9853 If @var{threshold} is nonzero and shared library autoloading is enabled,
9854 symbols from all shared object libraries will be loaded until the total
9855 size of the loaded shared library symbols exceeds this threshold.
9856 Otherwise, symbols must be loaded manually, using the
9857 @code{sharedlibrary} command. The default threshold is 100 (i.e.@: 100
9860 @kindex show auto-solib-limit
9861 @item show auto-solib-limit
9862 Display the current autoloading size threshold, in megabytes.
9866 @section Errors reading symbol files
9868 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9869 such as symbol types it does not recognize, or known bugs in compiler
9870 output. By default, @value{GDBN} does not notify you of such problems, since
9871 they are relatively common and primarily of interest to people
9872 debugging compilers. If you are interested in seeing information
9873 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9874 only one message about each such type of problem, no matter how many
9875 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9876 to see how many times the problems occur, with the @code{set
9877 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9880 The messages currently printed, and their meanings, include:
9883 @item inner block not inside outer block in @var{symbol}
9885 The symbol information shows where symbol scopes begin and end
9886 (such as at the start of a function or a block of statements). This
9887 error indicates that an inner scope block is not fully contained
9888 in its outer scope blocks.
9890 @value{GDBN} circumvents the problem by treating the inner block as if it had
9891 the same scope as the outer block. In the error message, @var{symbol}
9892 may be shown as ``@code{(don't know)}'' if the outer block is not a
9895 @item block at @var{address} out of order
9897 The symbol information for symbol scope blocks should occur in
9898 order of increasing addresses. This error indicates that it does not
9901 @value{GDBN} does not circumvent this problem, and has trouble
9902 locating symbols in the source file whose symbols it is reading. (You
9903 can often determine what source file is affected by specifying
9904 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9907 @item bad block start address patched
9909 The symbol information for a symbol scope block has a start address
9910 smaller than the address of the preceding source line. This is known
9911 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9913 @value{GDBN} circumvents the problem by treating the symbol scope block as
9914 starting on the previous source line.
9916 @item bad string table offset in symbol @var{n}
9919 Symbol number @var{n} contains a pointer into the string table which is
9920 larger than the size of the string table.
9922 @value{GDBN} circumvents the problem by considering the symbol to have the
9923 name @code{foo}, which may cause other problems if many symbols end up
9926 @item unknown symbol type @code{0x@var{nn}}
9928 The symbol information contains new data types that @value{GDBN} does
9929 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9930 uncomprehended information, in hexadecimal.
9932 @value{GDBN} circumvents the error by ignoring this symbol information.
9933 This usually allows you to debug your program, though certain symbols
9934 are not accessible. If you encounter such a problem and feel like
9935 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9936 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9937 and examine @code{*bufp} to see the symbol.
9939 @item stub type has NULL name
9941 @value{GDBN} could not find the full definition for a struct or class.
9943 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9944 The symbol information for a C@t{++} member function is missing some
9945 information that recent versions of the compiler should have output for
9948 @item info mismatch between compiler and debugger
9950 @value{GDBN} could not parse a type specification output by the compiler.
9955 @chapter Specifying a Debugging Target
9957 @cindex debugging target
9960 A @dfn{target} is the execution environment occupied by your program.
9962 Often, @value{GDBN} runs in the same host environment as your program;
9963 in that case, the debugging target is specified as a side effect when
9964 you use the @code{file} or @code{core} commands. When you need more
9965 flexibility---for example, running @value{GDBN} on a physically separate
9966 host, or controlling a standalone system over a serial port or a
9967 realtime system over a TCP/IP connection---you can use the @code{target}
9968 command to specify one of the target types configured for @value{GDBN}
9969 (@pxref{Target Commands, ,Commands for managing targets}).
9972 * Active Targets:: Active targets
9973 * Target Commands:: Commands for managing targets
9974 * Byte Order:: Choosing target byte order
9975 * Remote:: Remote debugging
9976 * KOD:: Kernel Object Display
9980 @node Active Targets
9981 @section Active targets
9983 @cindex stacking targets
9984 @cindex active targets
9985 @cindex multiple targets
9987 There are three classes of targets: processes, core files, and
9988 executable files. @value{GDBN} can work concurrently on up to three
9989 active targets, one in each class. This allows you to (for example)
9990 start a process and inspect its activity without abandoning your work on
9993 For example, if you execute @samp{gdb a.out}, then the executable file
9994 @code{a.out} is the only active target. If you designate a core file as
9995 well---presumably from a prior run that crashed and coredumped---then
9996 @value{GDBN} has two active targets and uses them in tandem, looking
9997 first in the corefile target, then in the executable file, to satisfy
9998 requests for memory addresses. (Typically, these two classes of target
9999 are complementary, since core files contain only a program's
10000 read-write memory---variables and so on---plus machine status, while
10001 executable files contain only the program text and initialized data.)
10003 When you type @code{run}, your executable file becomes an active process
10004 target as well. When a process target is active, all @value{GDBN}
10005 commands requesting memory addresses refer to that target; addresses in
10006 an active core file or executable file target are obscured while the
10007 process target is active.
10009 Use the @code{core-file} and @code{exec-file} commands to select a new
10010 core file or executable target (@pxref{Files, ,Commands to specify
10011 files}). To specify as a target a process that is already running, use
10012 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
10015 @node Target Commands
10016 @section Commands for managing targets
10019 @item target @var{type} @var{parameters}
10020 Connects the @value{GDBN} host environment to a target machine or
10021 process. A target is typically a protocol for talking to debugging
10022 facilities. You use the argument @var{type} to specify the type or
10023 protocol of the target machine.
10025 Further @var{parameters} are interpreted by the target protocol, but
10026 typically include things like device names or host names to connect
10027 with, process numbers, and baud rates.
10029 The @code{target} command does not repeat if you press @key{RET} again
10030 after executing the command.
10032 @kindex help target
10034 Displays the names of all targets available. To display targets
10035 currently selected, use either @code{info target} or @code{info files}
10036 (@pxref{Files, ,Commands to specify files}).
10038 @item help target @var{name}
10039 Describe a particular target, including any parameters necessary to
10042 @kindex set gnutarget
10043 @item set gnutarget @var{args}
10044 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
10045 knows whether it is reading an @dfn{executable},
10046 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
10047 with the @code{set gnutarget} command. Unlike most @code{target} commands,
10048 with @code{gnutarget} the @code{target} refers to a program, not a machine.
10051 @emph{Warning:} To specify a file format with @code{set gnutarget},
10052 you must know the actual BFD name.
10056 @xref{Files, , Commands to specify files}.
10058 @kindex show gnutarget
10059 @item show gnutarget
10060 Use the @code{show gnutarget} command to display what file format
10061 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
10062 @value{GDBN} will determine the file format for each file automatically,
10063 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
10066 Here are some common targets (available, or not, depending on the GDB
10070 @kindex target exec
10071 @item target exec @var{program}
10072 An executable file. @samp{target exec @var{program}} is the same as
10073 @samp{exec-file @var{program}}.
10075 @kindex target core
10076 @item target core @var{filename}
10077 A core dump file. @samp{target core @var{filename}} is the same as
10078 @samp{core-file @var{filename}}.
10080 @kindex target remote
10081 @item target remote @var{dev}
10082 Remote serial target in GDB-specific protocol. The argument @var{dev}
10083 specifies what serial device to use for the connection (e.g.
10084 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
10085 supports the @code{load} command. This is only useful if you have
10086 some other way of getting the stub to the target system, and you can put
10087 it somewhere in memory where it won't get clobbered by the download.
10091 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
10099 works; however, you cannot assume that a specific memory map, device
10100 drivers, or even basic I/O is available, although some simulators do
10101 provide these. For info about any processor-specific simulator details,
10102 see the appropriate section in @ref{Embedded Processors, ,Embedded
10107 Some configurations may include these targets as well:
10111 @kindex target nrom
10112 @item target nrom @var{dev}
10113 NetROM ROM emulator. This target only supports downloading.
10117 Different targets are available on different configurations of @value{GDBN};
10118 your configuration may have more or fewer targets.
10120 Many remote targets require you to download the executable's code
10121 once you've successfully established a connection.
10125 @kindex load @var{filename}
10126 @item load @var{filename}
10127 Depending on what remote debugging facilities are configured into
10128 @value{GDBN}, the @code{load} command may be available. Where it exists, it
10129 is meant to make @var{filename} (an executable) available for debugging
10130 on the remote system---by downloading, or dynamic linking, for example.
10131 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
10132 the @code{add-symbol-file} command.
10134 If your @value{GDBN} does not have a @code{load} command, attempting to
10135 execute it gets the error message ``@code{You can't do that when your
10136 target is @dots{}}''
10138 The file is loaded at whatever address is specified in the executable.
10139 For some object file formats, you can specify the load address when you
10140 link the program; for other formats, like a.out, the object file format
10141 specifies a fixed address.
10142 @c FIXME! This would be a good place for an xref to the GNU linker doc.
10144 @code{load} does not repeat if you press @key{RET} again after using it.
10148 @section Choosing target byte order
10150 @cindex choosing target byte order
10151 @cindex target byte order
10153 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
10154 offer the ability to run either big-endian or little-endian byte
10155 orders. Usually the executable or symbol will include a bit to
10156 designate the endian-ness, and you will not need to worry about
10157 which to use. However, you may still find it useful to adjust
10158 @value{GDBN}'s idea of processor endian-ness manually.
10161 @kindex set endian big
10162 @item set endian big
10163 Instruct @value{GDBN} to assume the target is big-endian.
10165 @kindex set endian little
10166 @item set endian little
10167 Instruct @value{GDBN} to assume the target is little-endian.
10169 @kindex set endian auto
10170 @item set endian auto
10171 Instruct @value{GDBN} to use the byte order associated with the
10175 Display @value{GDBN}'s current idea of the target byte order.
10179 Note that these commands merely adjust interpretation of symbolic
10180 data on the host, and that they have absolutely no effect on the
10184 @section Remote debugging
10185 @cindex remote debugging
10187 If you are trying to debug a program running on a machine that cannot run
10188 @value{GDBN} in the usual way, it is often useful to use remote debugging.
10189 For example, you might use remote debugging on an operating system kernel,
10190 or on a small system which does not have a general purpose operating system
10191 powerful enough to run a full-featured debugger.
10193 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
10194 to make this work with particular debugging targets. In addition,
10195 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
10196 but not specific to any particular target system) which you can use if you
10197 write the remote stubs---the code that runs on the remote system to
10198 communicate with @value{GDBN}.
10200 Other remote targets may be available in your
10201 configuration of @value{GDBN}; use @code{help target} to list them.
10204 @section Kernel Object Display
10206 @cindex kernel object display
10207 @cindex kernel object
10210 Some targets support kernel object display. Using this facility,
10211 @value{GDBN} communicates specially with the underlying operating system
10212 and can display information about operating system-level objects such as
10213 mutexes and other synchronization objects. Exactly which objects can be
10214 displayed is determined on a per-OS basis.
10216 Use the @code{set os} command to set the operating system. This tells
10217 @value{GDBN} which kernel object display module to initialize:
10220 (@value{GDBP}) set os cisco
10223 If @code{set os} succeeds, @value{GDBN} will display some information
10224 about the operating system, and will create a new @code{info} command
10225 which can be used to query the target. The @code{info} command is named
10226 after the operating system:
10229 (@value{GDBP}) info cisco
10230 List of Cisco Kernel Objects
10232 any Any and all objects
10235 Further subcommands can be used to query about particular objects known
10238 There is currently no way to determine whether a given operating system
10239 is supported other than to try it.
10242 @node Remote Debugging
10243 @chapter Debugging remote programs
10246 * Server:: Using the gdbserver program
10247 * NetWare:: Using the gdbserve.nlm program
10248 * remote stub:: Implementing a remote stub
10252 @section Using the @code{gdbserver} program
10255 @cindex remote connection without stubs
10256 @code{gdbserver} is a control program for Unix-like systems, which
10257 allows you to connect your program with a remote @value{GDBN} via
10258 @code{target remote}---but without linking in the usual debugging stub.
10260 @code{gdbserver} is not a complete replacement for the debugging stubs,
10261 because it requires essentially the same operating-system facilities
10262 that @value{GDBN} itself does. In fact, a system that can run
10263 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10264 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10265 because it is a much smaller program than @value{GDBN} itself. It is
10266 also easier to port than all of @value{GDBN}, so you may be able to get
10267 started more quickly on a new system by using @code{gdbserver}.
10268 Finally, if you develop code for real-time systems, you may find that
10269 the tradeoffs involved in real-time operation make it more convenient to
10270 do as much development work as possible on another system, for example
10271 by cross-compiling. You can use @code{gdbserver} to make a similar
10272 choice for debugging.
10274 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10275 or a TCP connection, using the standard @value{GDBN} remote serial
10279 @item On the target machine,
10280 you need to have a copy of the program you want to debug.
10281 @code{gdbserver} does not need your program's symbol table, so you can
10282 strip the program if necessary to save space. @value{GDBN} on the host
10283 system does all the symbol handling.
10285 To use the server, you must tell it how to communicate with @value{GDBN};
10286 the name of your program; and the arguments for your program. The usual
10290 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10293 @var{comm} is either a device name (to use a serial line) or a TCP
10294 hostname and portnumber. For example, to debug Emacs with the argument
10295 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10299 target> gdbserver /dev/com1 emacs foo.txt
10302 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10305 To use a TCP connection instead of a serial line:
10308 target> gdbserver host:2345 emacs foo.txt
10311 The only difference from the previous example is the first argument,
10312 specifying that you are communicating with the host @value{GDBN} via
10313 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10314 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10315 (Currently, the @samp{host} part is ignored.) You can choose any number
10316 you want for the port number as long as it does not conflict with any
10317 TCP ports already in use on the target system (for example, @code{23} is
10318 reserved for @code{telnet}).@footnote{If you choose a port number that
10319 conflicts with another service, @code{gdbserver} prints an error message
10320 and exits.} You must use the same port number with the host @value{GDBN}
10321 @code{target remote} command.
10323 On some targets, @code{gdbserver} can also attach to running programs.
10324 This is accomplished via the @code{--attach} argument. The syntax is:
10327 target> gdbserver @var{comm} --attach @var{pid}
10330 @var{pid} is the process ID of a currently running process. It isn't necessary
10331 to point @code{gdbserver} at a binary for the running process.
10333 @item On the @value{GDBN} host machine,
10334 you need an unstripped copy of your program, since @value{GDBN} needs
10335 symbols and debugging information. Start up @value{GDBN} as usual,
10336 using the name of the local copy of your program as the first argument.
10337 (You may also need the @w{@samp{--baud}} option if the serial line is
10338 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10339 remote} to establish communications with @code{gdbserver}. Its argument
10340 is either a device name (usually a serial device, like
10341 @file{/dev/ttyb}), or a TCP port descriptor in the form
10342 @code{@var{host}:@var{PORT}}. For example:
10345 (@value{GDBP}) target remote /dev/ttyb
10349 communicates with the server via serial line @file{/dev/ttyb}, and
10352 (@value{GDBP}) target remote the-target:2345
10356 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10357 For TCP connections, you must start up @code{gdbserver} prior to using
10358 the @code{target remote} command. Otherwise you may get an error whose
10359 text depends on the host system, but which usually looks something like
10360 @samp{Connection refused}.
10364 @section Using the @code{gdbserve.nlm} program
10366 @kindex gdbserve.nlm
10367 @code{gdbserve.nlm} is a control program for NetWare systems, which
10368 allows you to connect your program with a remote @value{GDBN} via
10369 @code{target remote}.
10371 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10372 using the standard @value{GDBN} remote serial protocol.
10375 @item On the target machine,
10376 you need to have a copy of the program you want to debug.
10377 @code{gdbserve.nlm} does not need your program's symbol table, so you
10378 can strip the program if necessary to save space. @value{GDBN} on the
10379 host system does all the symbol handling.
10381 To use the server, you must tell it how to communicate with
10382 @value{GDBN}; the name of your program; and the arguments for your
10383 program. The syntax is:
10386 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10387 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10390 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10391 the baud rate used by the connection. @var{port} and @var{node} default
10392 to 0, @var{baud} defaults to 9600@dmn{bps}.
10394 For example, to debug Emacs with the argument @samp{foo.txt}and
10395 communicate with @value{GDBN} over serial port number 2 or board 1
10396 using a 19200@dmn{bps} connection:
10399 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10402 @item On the @value{GDBN} host machine,
10403 you need an unstripped copy of your program, since @value{GDBN} needs
10404 symbols and debugging information. Start up @value{GDBN} as usual,
10405 using the name of the local copy of your program as the first argument.
10406 (You may also need the @w{@samp{--baud}} option if the serial line is
10407 running at anything other than 9600@dmn{bps}. After that, use @code{target
10408 remote} to establish communications with @code{gdbserve.nlm}. Its
10409 argument is a device name (usually a serial device, like
10410 @file{/dev/ttyb}). For example:
10413 (@value{GDBP}) target remote /dev/ttyb
10417 communications with the server via serial line @file{/dev/ttyb}.
10421 @section Implementing a remote stub
10423 @cindex debugging stub, example
10424 @cindex remote stub, example
10425 @cindex stub example, remote debugging
10426 The stub files provided with @value{GDBN} implement the target side of the
10427 communication protocol, and the @value{GDBN} side is implemented in the
10428 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10429 these subroutines to communicate, and ignore the details. (If you're
10430 implementing your own stub file, you can still ignore the details: start
10431 with one of the existing stub files. @file{sparc-stub.c} is the best
10432 organized, and therefore the easiest to read.)
10434 @cindex remote serial debugging, overview
10435 To debug a program running on another machine (the debugging
10436 @dfn{target} machine), you must first arrange for all the usual
10437 prerequisites for the program to run by itself. For example, for a C
10442 A startup routine to set up the C runtime environment; these usually
10443 have a name like @file{crt0}. The startup routine may be supplied by
10444 your hardware supplier, or you may have to write your own.
10447 A C subroutine library to support your program's
10448 subroutine calls, notably managing input and output.
10451 A way of getting your program to the other machine---for example, a
10452 download program. These are often supplied by the hardware
10453 manufacturer, but you may have to write your own from hardware
10457 The next step is to arrange for your program to use a serial port to
10458 communicate with the machine where @value{GDBN} is running (the @dfn{host}
10459 machine). In general terms, the scheme looks like this:
10463 @value{GDBN} already understands how to use this protocol; when everything
10464 else is set up, you can simply use the @samp{target remote} command
10465 (@pxref{Targets,,Specifying a Debugging Target}).
10467 @item On the target,
10468 you must link with your program a few special-purpose subroutines that
10469 implement the @value{GDBN} remote serial protocol. The file containing these
10470 subroutines is called a @dfn{debugging stub}.
10472 On certain remote targets, you can use an auxiliary program
10473 @code{gdbserver} instead of linking a stub into your program.
10474 @xref{Server,,Using the @code{gdbserver} program}, for details.
10477 The debugging stub is specific to the architecture of the remote
10478 machine; for example, use @file{sparc-stub.c} to debug programs on
10481 @cindex remote serial stub list
10482 These working remote stubs are distributed with @value{GDBN}:
10487 @cindex @file{i386-stub.c}
10490 For Intel 386 and compatible architectures.
10493 @cindex @file{m68k-stub.c}
10494 @cindex Motorola 680x0
10496 For Motorola 680x0 architectures.
10499 @cindex @file{sh-stub.c}
10502 For Hitachi SH architectures.
10505 @cindex @file{sparc-stub.c}
10507 For @sc{sparc} architectures.
10509 @item sparcl-stub.c
10510 @cindex @file{sparcl-stub.c}
10513 For Fujitsu @sc{sparclite} architectures.
10517 The @file{README} file in the @value{GDBN} distribution may list other
10518 recently added stubs.
10521 * Stub Contents:: What the stub can do for you
10522 * Bootstrapping:: What you must do for the stub
10523 * Debug Session:: Putting it all together
10526 @node Stub Contents
10527 @subsection What the stub can do for you
10529 @cindex remote serial stub
10530 The debugging stub for your architecture supplies these three
10534 @item set_debug_traps
10535 @kindex set_debug_traps
10536 @cindex remote serial stub, initialization
10537 This routine arranges for @code{handle_exception} to run when your
10538 program stops. You must call this subroutine explicitly near the
10539 beginning of your program.
10541 @item handle_exception
10542 @kindex handle_exception
10543 @cindex remote serial stub, main routine
10544 This is the central workhorse, but your program never calls it
10545 explicitly---the setup code arranges for @code{handle_exception} to
10546 run when a trap is triggered.
10548 @code{handle_exception} takes control when your program stops during
10549 execution (for example, on a breakpoint), and mediates communications
10550 with @value{GDBN} on the host machine. This is where the communications
10551 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10552 representative on the target machine. It begins by sending summary
10553 information on the state of your program, then continues to execute,
10554 retrieving and transmitting any information @value{GDBN} needs, until you
10555 execute a @value{GDBN} command that makes your program resume; at that point,
10556 @code{handle_exception} returns control to your own code on the target
10560 @cindex @code{breakpoint} subroutine, remote
10561 Use this auxiliary subroutine to make your program contain a
10562 breakpoint. Depending on the particular situation, this may be the only
10563 way for @value{GDBN} to get control. For instance, if your target
10564 machine has some sort of interrupt button, you won't need to call this;
10565 pressing the interrupt button transfers control to
10566 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10567 simply receiving characters on the serial port may also trigger a trap;
10568 again, in that situation, you don't need to call @code{breakpoint} from
10569 your own program---simply running @samp{target remote} from the host
10570 @value{GDBN} session gets control.
10572 Call @code{breakpoint} if none of these is true, or if you simply want
10573 to make certain your program stops at a predetermined point for the
10574 start of your debugging session.
10577 @node Bootstrapping
10578 @subsection What you must do for the stub
10580 @cindex remote stub, support routines
10581 The debugging stubs that come with @value{GDBN} are set up for a particular
10582 chip architecture, but they have no information about the rest of your
10583 debugging target machine.
10585 First of all you need to tell the stub how to communicate with the
10589 @item int getDebugChar()
10590 @kindex getDebugChar
10591 Write this subroutine to read a single character from the serial port.
10592 It may be identical to @code{getchar} for your target system; a
10593 different name is used to allow you to distinguish the two if you wish.
10595 @item void putDebugChar(int)
10596 @kindex putDebugChar
10597 Write this subroutine to write a single character to the serial port.
10598 It may be identical to @code{putchar} for your target system; a
10599 different name is used to allow you to distinguish the two if you wish.
10602 @cindex control C, and remote debugging
10603 @cindex interrupting remote targets
10604 If you want @value{GDBN} to be able to stop your program while it is
10605 running, you need to use an interrupt-driven serial driver, and arrange
10606 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10607 character). That is the character which @value{GDBN} uses to tell the
10608 remote system to stop.
10610 Getting the debugging target to return the proper status to @value{GDBN}
10611 probably requires changes to the standard stub; one quick and dirty way
10612 is to just execute a breakpoint instruction (the ``dirty'' part is that
10613 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10615 Other routines you need to supply are:
10618 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10619 @kindex exceptionHandler
10620 Write this function to install @var{exception_address} in the exception
10621 handling tables. You need to do this because the stub does not have any
10622 way of knowing what the exception handling tables on your target system
10623 are like (for example, the processor's table might be in @sc{rom},
10624 containing entries which point to a table in @sc{ram}).
10625 @var{exception_number} is the exception number which should be changed;
10626 its meaning is architecture-dependent (for example, different numbers
10627 might represent divide by zero, misaligned access, etc). When this
10628 exception occurs, control should be transferred directly to
10629 @var{exception_address}, and the processor state (stack, registers,
10630 and so on) should be just as it is when a processor exception occurs. So if
10631 you want to use a jump instruction to reach @var{exception_address}, it
10632 should be a simple jump, not a jump to subroutine.
10634 For the 386, @var{exception_address} should be installed as an interrupt
10635 gate so that interrupts are masked while the handler runs. The gate
10636 should be at privilege level 0 (the most privileged level). The
10637 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10638 help from @code{exceptionHandler}.
10640 @item void flush_i_cache()
10641 @kindex flush_i_cache
10642 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10643 instruction cache, if any, on your target machine. If there is no
10644 instruction cache, this subroutine may be a no-op.
10646 On target machines that have instruction caches, @value{GDBN} requires this
10647 function to make certain that the state of your program is stable.
10651 You must also make sure this library routine is available:
10654 @item void *memset(void *, int, int)
10656 This is the standard library function @code{memset} that sets an area of
10657 memory to a known value. If you have one of the free versions of
10658 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10659 either obtain it from your hardware manufacturer, or write your own.
10662 If you do not use the GNU C compiler, you may need other standard
10663 library subroutines as well; this varies from one stub to another,
10664 but in general the stubs are likely to use any of the common library
10665 subroutines which @code{@value{GCC}} generates as inline code.
10668 @node Debug Session
10669 @subsection Putting it all together
10671 @cindex remote serial debugging summary
10672 In summary, when your program is ready to debug, you must follow these
10677 Make sure you have defined the supporting low-level routines
10678 (@pxref{Bootstrapping,,What you must do for the stub}):
10680 @code{getDebugChar}, @code{putDebugChar},
10681 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10685 Insert these lines near the top of your program:
10693 For the 680x0 stub only, you need to provide a variable called
10694 @code{exceptionHook}. Normally you just use:
10697 void (*exceptionHook)() = 0;
10701 but if before calling @code{set_debug_traps}, you set it to point to a
10702 function in your program, that function is called when
10703 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10704 error). The function indicated by @code{exceptionHook} is called with
10705 one parameter: an @code{int} which is the exception number.
10708 Compile and link together: your program, the @value{GDBN} debugging stub for
10709 your target architecture, and the supporting subroutines.
10712 Make sure you have a serial connection between your target machine and
10713 the @value{GDBN} host, and identify the serial port on the host.
10716 @c The "remote" target now provides a `load' command, so we should
10717 @c document that. FIXME.
10718 Download your program to your target machine (or get it there by
10719 whatever means the manufacturer provides), and start it.
10722 To start remote debugging, run @value{GDBN} on the host machine, and specify
10723 as an executable file the program that is running in the remote machine.
10724 This tells @value{GDBN} how to find your program's symbols and the contents
10728 @cindex serial line, @code{target remote}
10729 Establish communication using the @code{target remote} command.
10730 Its argument specifies how to communicate with the target
10731 machine---either via a devicename attached to a direct serial line, or a
10732 TCP or UDP port (usually to a terminal server which in turn has a serial line
10733 to the target). For example, to use a serial line connected to the
10734 device named @file{/dev/ttyb}:
10737 target remote /dev/ttyb
10740 @cindex TCP port, @code{target remote}
10741 To use a TCP connection, use an argument of the form
10742 @code{@var{host}:@var{port}} or @code{tcp:@var{host}:@var{port}}.
10743 For example, to connect to port 2828 on a
10744 terminal server named @code{manyfarms}:
10747 target remote manyfarms:2828
10750 If your remote target is actually running on the same machine as
10751 your debugger session (e.g.@: a simulator of your target running on
10752 the same host), you can omit the hostname. For example, to connect
10753 to port 1234 on your local machine:
10756 target remote :1234
10760 Note that the colon is still required here.
10762 @cindex UDP port, @code{target remote}
10763 To use a UDP connection, use an argument of the form
10764 @code{udp:@var{host}:@var{port}}. For example, to connect to UDP port 2828
10765 on a terminal server named @code{manyfarms}:
10768 target remote udp:manyfarms:2828
10771 When using a UDP connection for remote debugging, you should keep in mind
10772 that the `U' stands for ``Unreliable''. UDP can silently drop packets on
10773 busy or unreliable networks, which will cause havoc with your debugging
10778 Now you can use all the usual commands to examine and change data and to
10779 step and continue the remote program.
10781 To resume the remote program and stop debugging it, use the @code{detach}
10784 @cindex interrupting remote programs
10785 @cindex remote programs, interrupting
10786 Whenever @value{GDBN} is waiting for the remote program, if you type the
10787 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10788 program. This may or may not succeed, depending in part on the hardware
10789 and the serial drivers the remote system uses. If you type the
10790 interrupt character once again, @value{GDBN} displays this prompt:
10793 Interrupted while waiting for the program.
10794 Give up (and stop debugging it)? (y or n)
10797 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10798 (If you decide you want to try again later, you can use @samp{target
10799 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10800 goes back to waiting.
10803 @node Configurations
10804 @chapter Configuration-Specific Information
10806 While nearly all @value{GDBN} commands are available for all native and
10807 cross versions of the debugger, there are some exceptions. This chapter
10808 describes things that are only available in certain configurations.
10810 There are three major categories of configurations: native
10811 configurations, where the host and target are the same, embedded
10812 operating system configurations, which are usually the same for several
10813 different processor architectures, and bare embedded processors, which
10814 are quite different from each other.
10819 * Embedded Processors::
10826 This section describes details specific to particular native
10831 * SVR4 Process Information:: SVR4 process information
10832 * DJGPP Native:: Features specific to the DJGPP port
10833 * Cygwin Native:: Features specific to the Cygwin port
10839 On HP-UX systems, if you refer to a function or variable name that
10840 begins with a dollar sign, @value{GDBN} searches for a user or system
10841 name first, before it searches for a convenience variable.
10843 @node SVR4 Process Information
10844 @subsection SVR4 process information
10847 @cindex process image
10849 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10850 used to examine the image of a running process using file-system
10851 subroutines. If @value{GDBN} is configured for an operating system with
10852 this facility, the command @code{info proc} is available to report on
10853 several kinds of information about the process running your program.
10854 @code{info proc} works only on SVR4 systems that include the
10855 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10856 and Unixware, but not HP-UX or Linux, for example.
10861 Summarize available information about the process.
10863 @kindex info proc mappings
10864 @item info proc mappings
10865 Report on the address ranges accessible in the program, with information
10866 on whether your program may read, write, or execute each range.
10868 @comment These sub-options of 'info proc' were not included when
10869 @comment procfs.c was re-written. Keep their descriptions around
10870 @comment against the day when someone finds the time to put them back in.
10871 @kindex info proc times
10872 @item info proc times
10873 Starting time, user CPU time, and system CPU time for your program and
10876 @kindex info proc id
10878 Report on the process IDs related to your program: its own process ID,
10879 the ID of its parent, the process group ID, and the session ID.
10881 @kindex info proc status
10882 @item info proc status
10883 General information on the state of the process. If the process is
10884 stopped, this report includes the reason for stopping, and any signal
10887 @item info proc all
10888 Show all the above information about the process.
10893 @subsection Features for Debugging @sc{djgpp} Programs
10894 @cindex @sc{djgpp} debugging
10895 @cindex native @sc{djgpp} debugging
10896 @cindex MS-DOS-specific commands
10898 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10899 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10900 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10901 top of real-mode DOS systems and their emulations.
10903 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10904 defines a few commands specific to the @sc{djgpp} port. This
10905 subsection describes those commands.
10910 This is a prefix of @sc{djgpp}-specific commands which print
10911 information about the target system and important OS structures.
10914 @cindex MS-DOS system info
10915 @cindex free memory information (MS-DOS)
10916 @item info dos sysinfo
10917 This command displays assorted information about the underlying
10918 platform: the CPU type and features, the OS version and flavor, the
10919 DPMI version, and the available conventional and DPMI memory.
10924 @cindex segment descriptor tables
10925 @cindex descriptor tables display
10927 @itemx info dos ldt
10928 @itemx info dos idt
10929 These 3 commands display entries from, respectively, Global, Local,
10930 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10931 tables are data structures which store a descriptor for each segment
10932 that is currently in use. The segment's selector is an index into a
10933 descriptor table; the table entry for that index holds the
10934 descriptor's base address and limit, and its attributes and access
10937 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10938 segment (used for both data and the stack), and a DOS segment (which
10939 allows access to DOS/BIOS data structures and absolute addresses in
10940 conventional memory). However, the DPMI host will usually define
10941 additional segments in order to support the DPMI environment.
10943 @cindex garbled pointers
10944 These commands allow to display entries from the descriptor tables.
10945 Without an argument, all entries from the specified table are
10946 displayed. An argument, which should be an integer expression, means
10947 display a single entry whose index is given by the argument. For
10948 example, here's a convenient way to display information about the
10949 debugged program's data segment:
10952 @exdent @code{(@value{GDBP}) info dos ldt $ds}
10953 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
10957 This comes in handy when you want to see whether a pointer is outside
10958 the data segment's limit (i.e.@: @dfn{garbled}).
10960 @cindex page tables display (MS-DOS)
10962 @itemx info dos pte
10963 These two commands display entries from, respectively, the Page
10964 Directory and the Page Tables. Page Directories and Page Tables are
10965 data structures which control how virtual memory addresses are mapped
10966 into physical addresses. A Page Table includes an entry for every
10967 page of memory that is mapped into the program's address space; there
10968 may be several Page Tables, each one holding up to 4096 entries. A
10969 Page Directory has up to 4096 entries, one each for every Page Table
10970 that is currently in use.
10972 Without an argument, @kbd{info dos pde} displays the entire Page
10973 Directory, and @kbd{info dos pte} displays all the entries in all of
10974 the Page Tables. An argument, an integer expression, given to the
10975 @kbd{info dos pde} command means display only that entry from the Page
10976 Directory table. An argument given to the @kbd{info dos pte} command
10977 means display entries from a single Page Table, the one pointed to by
10978 the specified entry in the Page Directory.
10980 @cindex direct memory access (DMA) on MS-DOS
10981 These commands are useful when your program uses @dfn{DMA} (Direct
10982 Memory Access), which needs physical addresses to program the DMA
10985 These commands are supported only with some DPMI servers.
10987 @cindex physical address from linear address
10988 @item info dos address-pte @var{addr}
10989 This command displays the Page Table entry for a specified linear
10990 address. The argument linear address @var{addr} should already have the
10991 appropriate segment's base address added to it, because this command
10992 accepts addresses which may belong to @emph{any} segment. For
10993 example, here's how to display the Page Table entry for the page where
10994 the variable @code{i} is stored:
10997 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
10998 @exdent @code{Page Table entry for address 0x11a00d30:}
10999 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
11003 This says that @code{i} is stored at offset @code{0xd30} from the page
11004 whose physical base address is @code{0x02698000}, and prints all the
11005 attributes of that page.
11007 Note that you must cast the addresses of variables to a @code{char *},
11008 since otherwise the value of @code{__djgpp_base_address}, the base
11009 address of all variables and functions in a @sc{djgpp} program, will
11010 be added using the rules of C pointer arithmetics: if @code{i} is
11011 declared an @code{int}, @value{GDBN} will add 4 times the value of
11012 @code{__djgpp_base_address} to the address of @code{i}.
11014 Here's another example, it displays the Page Table entry for the
11018 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
11019 @exdent @code{Page Table entry for address 0x29110:}
11020 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
11024 (The @code{+ 3} offset is because the transfer buffer's address is the
11025 3rd member of the @code{_go32_info_block} structure.) The output of
11026 this command clearly shows that addresses in conventional memory are
11027 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11029 This command is supported only with some DPMI servers.
11032 @node Cygwin Native
11033 @subsection Features for Debugging MS Windows PE executables
11034 @cindex MS Windows debugging
11035 @cindex native Cygwin debugging
11036 @cindex Cygwin-specific commands
11038 @value{GDBN} supports native debugging of MS Windows programs, and
11039 defines a few commands specific to the Cygwin port. This
11040 subsection describes those commands.
11045 This is a prefix of MS Windows specific commands which print
11046 information about the target system and important OS structures.
11048 @item info w32 selector
11049 This command displays information returned by
11050 the Win32 API @code{GetThreadSelectorEntry} function.
11051 It takes an optional argument that is evaluated to
11052 a long value to give the information about this given selector.
11053 Without argument, this command displays information
11054 about the the six segment registers.
11058 This is a Cygwin specific alias of info shared.
11060 @kindex dll-symbols
11062 This command loads symbols from a dll similarly to
11063 add-sym command but without the need to specify a base address.
11065 @kindex set new-console
11066 @item set new-console @var{mode}
11067 If @var{mode} is @code{on} the debuggee will
11068 be started in a new console on next start.
11069 If @var{mode} is @code{off}i, the debuggee will
11070 be started in the same console as the debugger.
11072 @kindex show new-console
11073 @item show new-console
11074 Displays whether a new console is used
11075 when the debuggee is started.
11077 @kindex set new-group
11078 @item set new-group @var{mode}
11079 This boolean value controls whether the debuggee should
11080 start a new group or stay in the same group as the debugger.
11081 This affects the way the Windows OS handles
11084 @kindex show new-group
11085 @item show new-group
11086 Displays current value of new-group boolean.
11088 @kindex set debugevents
11089 @item set debugevents
11090 This boolean value adds debug output concerning events seen by the debugger.
11092 @kindex set debugexec
11093 @item set debugexec
11094 This boolean value adds debug output concerning execute events
11095 seen by the debugger.
11097 @kindex set debugexceptions
11098 @item set debugexceptions
11099 This boolean value adds debug ouptut concerning exception events
11100 seen by the debugger.
11102 @kindex set debugmemory
11103 @item set debugmemory
11104 This boolean value adds debug ouptut concerning memory events
11105 seen by the debugger.
11109 This boolean values specifies whether the debuggee is called
11110 via a shell or directly (default value is on).
11114 Displays if the debuggee will be started with a shell.
11119 @section Embedded Operating Systems
11121 This section describes configurations involving the debugging of
11122 embedded operating systems that are available for several different
11126 * VxWorks:: Using @value{GDBN} with VxWorks
11129 @value{GDBN} includes the ability to debug programs running on
11130 various real-time operating systems.
11133 @subsection Using @value{GDBN} with VxWorks
11139 @kindex target vxworks
11140 @item target vxworks @var{machinename}
11141 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11142 is the target system's machine name or IP address.
11146 On VxWorks, @code{load} links @var{filename} dynamically on the
11147 current target system as well as adding its symbols in @value{GDBN}.
11149 @value{GDBN} enables developers to spawn and debug tasks running on networked
11150 VxWorks targets from a Unix host. Already-running tasks spawned from
11151 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11152 both the Unix host and on the VxWorks target. The program
11153 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11154 installed with the name @code{vxgdb}, to distinguish it from a
11155 @value{GDBN} for debugging programs on the host itself.)
11158 @item VxWorks-timeout @var{args}
11159 @kindex vxworks-timeout
11160 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11161 This option is set by the user, and @var{args} represents the number of
11162 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11163 your VxWorks target is a slow software simulator or is on the far side
11164 of a thin network line.
11167 The following information on connecting to VxWorks was current when
11168 this manual was produced; newer releases of VxWorks may use revised
11171 @kindex INCLUDE_RDB
11172 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11173 to include the remote debugging interface routines in the VxWorks
11174 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11175 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11176 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11177 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11178 information on configuring and remaking VxWorks, see the manufacturer's
11180 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11182 Once you have included @file{rdb.a} in your VxWorks system image and set
11183 your Unix execution search path to find @value{GDBN}, you are ready to
11184 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11185 @code{vxgdb}, depending on your installation).
11187 @value{GDBN} comes up showing the prompt:
11194 * VxWorks Connection:: Connecting to VxWorks
11195 * VxWorks Download:: VxWorks download
11196 * VxWorks Attach:: Running tasks
11199 @node VxWorks Connection
11200 @subsubsection Connecting to VxWorks
11202 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11203 network. To connect to a target whose host name is ``@code{tt}'', type:
11206 (vxgdb) target vxworks tt
11210 @value{GDBN} displays messages like these:
11213 Attaching remote machine across net...
11218 @value{GDBN} then attempts to read the symbol tables of any object modules
11219 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11220 these files by searching the directories listed in the command search
11221 path (@pxref{Environment, ,Your program's environment}); if it fails
11222 to find an object file, it displays a message such as:
11225 prog.o: No such file or directory.
11228 When this happens, add the appropriate directory to the search path with
11229 the @value{GDBN} command @code{path}, and execute the @code{target}
11232 @node VxWorks Download
11233 @subsubsection VxWorks download
11235 @cindex download to VxWorks
11236 If you have connected to the VxWorks target and you want to debug an
11237 object that has not yet been loaded, you can use the @value{GDBN}
11238 @code{load} command to download a file from Unix to VxWorks
11239 incrementally. The object file given as an argument to the @code{load}
11240 command is actually opened twice: first by the VxWorks target in order
11241 to download the code, then by @value{GDBN} in order to read the symbol
11242 table. This can lead to problems if the current working directories on
11243 the two systems differ. If both systems have NFS mounted the same
11244 filesystems, you can avoid these problems by using absolute paths.
11245 Otherwise, it is simplest to set the working directory on both systems
11246 to the directory in which the object file resides, and then to reference
11247 the file by its name, without any path. For instance, a program
11248 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11249 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11250 program, type this on VxWorks:
11253 -> cd "@var{vxpath}/vw/demo/rdb"
11257 Then, in @value{GDBN}, type:
11260 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11261 (vxgdb) load prog.o
11264 @value{GDBN} displays a response similar to this:
11267 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11270 You can also use the @code{load} command to reload an object module
11271 after editing and recompiling the corresponding source file. Note that
11272 this makes @value{GDBN} delete all currently-defined breakpoints,
11273 auto-displays, and convenience variables, and to clear the value
11274 history. (This is necessary in order to preserve the integrity of
11275 debugger's data structures that reference the target system's symbol
11278 @node VxWorks Attach
11279 @subsubsection Running tasks
11281 @cindex running VxWorks tasks
11282 You can also attach to an existing task using the @code{attach} command as
11286 (vxgdb) attach @var{task}
11290 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11291 or suspended when you attach to it. Running tasks are suspended at
11292 the time of attachment.
11294 @node Embedded Processors
11295 @section Embedded Processors
11297 This section goes into details specific to particular embedded
11303 * H8/300:: Hitachi H8/300
11304 * H8/500:: Hitachi H8/500
11305 * i960:: Intel i960
11306 * M32R/D:: Mitsubishi M32R/D
11307 * M68K:: Motorola M68K
11308 * M88K:: Motorola M88K
11309 * MIPS Embedded:: MIPS Embedded
11310 * PA:: HP PA Embedded
11313 * Sparclet:: Tsqware Sparclet
11314 * Sparclite:: Fujitsu Sparclite
11315 * ST2000:: Tandem ST2000
11316 * Z8000:: Zilog Z8000
11325 @item target rdi @var{dev}
11326 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11327 use this target to communicate with both boards running the Angel
11328 monitor, or with the EmbeddedICE JTAG debug device.
11331 @item target rdp @var{dev}
11337 @subsection Hitachi H8/300
11341 @kindex target hms@r{, with H8/300}
11342 @item target hms @var{dev}
11343 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11344 Use special commands @code{device} and @code{speed} to control the serial
11345 line and the communications speed used.
11347 @kindex target e7000@r{, with H8/300}
11348 @item target e7000 @var{dev}
11349 E7000 emulator for Hitachi H8 and SH.
11351 @kindex target sh3@r{, with H8/300}
11352 @kindex target sh3e@r{, with H8/300}
11353 @item target sh3 @var{dev}
11354 @itemx target sh3e @var{dev}
11355 Hitachi SH-3 and SH-3E target systems.
11359 @cindex download to H8/300 or H8/500
11360 @cindex H8/300 or H8/500 download
11361 @cindex download to Hitachi SH
11362 @cindex Hitachi SH download
11363 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11364 board, the @code{load} command downloads your program to the Hitachi
11365 board and also opens it as the current executable target for
11366 @value{GDBN} on your host (like the @code{file} command).
11368 @value{GDBN} needs to know these things to talk to your
11369 Hitachi SH, H8/300, or H8/500:
11373 that you want to use @samp{target hms}, the remote debugging interface
11374 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11375 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11376 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11377 H8/300, or H8/500.)
11380 what serial device connects your host to your Hitachi board (the first
11381 serial device available on your host is the default).
11384 what speed to use over the serial device.
11388 * Hitachi Boards:: Connecting to Hitachi boards.
11389 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11390 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11393 @node Hitachi Boards
11394 @subsubsection Connecting to Hitachi boards
11396 @c only for Unix hosts
11398 @cindex serial device, Hitachi micros
11399 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11400 need to explicitly set the serial device. The default @var{port} is the
11401 first available port on your host. This is only necessary on Unix
11402 hosts, where it is typically something like @file{/dev/ttya}.
11405 @cindex serial line speed, Hitachi micros
11406 @code{@value{GDBN}} has another special command to set the communications
11407 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11408 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11409 the DOS @code{mode} command (for instance,
11410 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11412 The @samp{device} and @samp{speed} commands are available only when you
11413 use a Unix host to debug your Hitachi microprocessor programs. If you
11415 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11416 called @code{asynctsr} to communicate with the development board
11417 through a PC serial port. You must also use the DOS @code{mode} command
11418 to set up the serial port on the DOS side.
11420 The following sample session illustrates the steps needed to start a
11421 program under @value{GDBN} control on an H8/300. The example uses a
11422 sample H8/300 program called @file{t.x}. The procedure is the same for
11423 the Hitachi SH and the H8/500.
11425 First hook up your development board. In this example, we use a
11426 board attached to serial port @code{COM2}; if you use a different serial
11427 port, substitute its name in the argument of the @code{mode} command.
11428 When you call @code{asynctsr}, the auxiliary comms program used by the
11429 debugger, you give it just the numeric part of the serial port's name;
11430 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11434 C:\H8300\TEST> asynctsr 2
11435 C:\H8300\TEST> mode com2:9600,n,8,1,p
11437 Resident portion of MODE loaded
11439 COM2: 9600, n, 8, 1, p
11444 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11445 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11446 disable it, or even boot without it, to use @code{asynctsr} to control
11447 your development board.
11450 @kindex target hms@r{, and serial protocol}
11451 Now that serial communications are set up, and the development board is
11452 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11453 the name of your program as the argument. @code{@value{GDBN}} prompts
11454 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11455 commands to begin your debugging session: @samp{target hms} to specify
11456 cross-debugging to the Hitachi board, and the @code{load} command to
11457 download your program to the board. @code{load} displays the names of
11458 the program's sections, and a @samp{*} for each 2K of data downloaded.
11459 (If you want to refresh @value{GDBN} data on symbols or on the
11460 executable file without downloading, use the @value{GDBN} commands
11461 @code{file} or @code{symbol-file}. These commands, and @code{load}
11462 itself, are described in @ref{Files,,Commands to specify files}.)
11465 (eg-C:\H8300\TEST) @value{GDBP} t.x
11466 @value{GDBN} is free software and you are welcome to distribute copies
11467 of it under certain conditions; type "show copying" to see
11469 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11471 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11472 (@value{GDBP}) target hms
11473 Connected to remote H8/300 HMS system.
11474 (@value{GDBP}) load t.x
11475 .text : 0x8000 .. 0xabde ***********
11476 .data : 0xabde .. 0xad30 *
11477 .stack : 0xf000 .. 0xf014 *
11480 At this point, you're ready to run or debug your program. From here on,
11481 you can use all the usual @value{GDBN} commands. The @code{break} command
11482 sets breakpoints; the @code{run} command starts your program;
11483 @code{print} or @code{x} display data; the @code{continue} command
11484 resumes execution after stopping at a breakpoint. You can use the
11485 @code{help} command at any time to find out more about @value{GDBN} commands.
11487 Remember, however, that @emph{operating system} facilities aren't
11488 available on your development board; for example, if your program hangs,
11489 you can't send an interrupt---but you can press the @sc{reset} switch!
11491 Use the @sc{reset} button on the development board
11494 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11495 no way to pass an interrupt signal to the development board); and
11498 to return to the @value{GDBN} command prompt after your program finishes
11499 normally. The communications protocol provides no other way for @value{GDBN}
11500 to detect program completion.
11503 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11504 development board as a ``normal exit'' of your program.
11507 @subsubsection Using the E7000 in-circuit emulator
11509 @kindex target e7000@r{, with Hitachi ICE}
11510 You can use the E7000 in-circuit emulator to develop code for either the
11511 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11512 e7000} command to connect @value{GDBN} to your E7000:
11515 @item target e7000 @var{port} @var{speed}
11516 Use this form if your E7000 is connected to a serial port. The
11517 @var{port} argument identifies what serial port to use (for example,
11518 @samp{com2}). The third argument is the line speed in bits per second
11519 (for example, @samp{9600}).
11521 @item target e7000 @var{hostname}
11522 If your E7000 is installed as a host on a TCP/IP network, you can just
11523 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11526 @node Hitachi Special
11527 @subsubsection Special @value{GDBN} commands for Hitachi micros
11529 Some @value{GDBN} commands are available only for the H8/300:
11533 @kindex set machine
11534 @kindex show machine
11535 @item set machine h8300
11536 @itemx set machine h8300h
11537 Condition @value{GDBN} for one of the two variants of the H8/300
11538 architecture with @samp{set machine}. You can use @samp{show machine}
11539 to check which variant is currently in effect.
11548 @kindex set memory @var{mod}
11549 @cindex memory models, H8/500
11550 @item set memory @var{mod}
11552 Specify which H8/500 memory model (@var{mod}) you are using with
11553 @samp{set memory}; check which memory model is in effect with @samp{show
11554 memory}. The accepted values for @var{mod} are @code{small},
11555 @code{big}, @code{medium}, and @code{compact}.
11560 @subsection Intel i960
11564 @kindex target mon960
11565 @item target mon960 @var{dev}
11566 MON960 monitor for Intel i960.
11568 @kindex target nindy
11569 @item target nindy @var{devicename}
11570 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11571 the name of the serial device to use for the connection, e.g.
11578 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11579 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11580 tell @value{GDBN} how to connect to the 960 in several ways:
11584 Through command line options specifying serial port, version of the
11585 Nindy protocol, and communications speed;
11588 By responding to a prompt on startup;
11591 By using the @code{target} command at any point during your @value{GDBN}
11592 session. @xref{Target Commands, ,Commands for managing targets}.
11596 @cindex download to Nindy-960
11597 With the Nindy interface to an Intel 960 board, @code{load}
11598 downloads @var{filename} to the 960 as well as adding its symbols in
11602 * Nindy Startup:: Startup with Nindy
11603 * Nindy Options:: Options for Nindy
11604 * Nindy Reset:: Nindy reset command
11607 @node Nindy Startup
11608 @subsubsection Startup with Nindy
11610 If you simply start @code{@value{GDBP}} without using any command-line
11611 options, you are prompted for what serial port to use, @emph{before} you
11612 reach the ordinary @value{GDBN} prompt:
11615 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11619 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11620 identifies the serial port you want to use. You can, if you choose,
11621 simply start up with no Nindy connection by responding to the prompt
11622 with an empty line. If you do this and later wish to attach to Nindy,
11623 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11625 @node Nindy Options
11626 @subsubsection Options for Nindy
11628 These are the startup options for beginning your @value{GDBN} session with a
11629 Nindy-960 board attached:
11632 @item -r @var{port}
11633 Specify the serial port name of a serial interface to be used to connect
11634 to the target system. This option is only available when @value{GDBN} is
11635 configured for the Intel 960 target architecture. You may specify
11636 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11637 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11638 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11641 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11642 the ``old'' Nindy monitor protocol to connect to the target system.
11643 This option is only available when @value{GDBN} is configured for the Intel 960
11644 target architecture.
11647 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11648 connect to a target system that expects the newer protocol, the connection
11649 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11650 attempts to reconnect at several different line speeds. You can abort
11651 this process with an interrupt.
11655 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11656 system, in an attempt to reset it, before connecting to a Nindy target.
11659 @emph{Warning:} Many target systems do not have the hardware that this
11660 requires; it only works with a few boards.
11664 The standard @samp{-b} option controls the line speed used on the serial
11669 @subsubsection Nindy reset command
11674 For a Nindy target, this command sends a ``break'' to the remote target
11675 system; this is only useful if the target has been equipped with a
11676 circuit to perform a hard reset (or some other interesting action) when
11677 a break is detected.
11682 @subsection Mitsubishi M32R/D
11686 @kindex target m32r
11687 @item target m32r @var{dev}
11688 Mitsubishi M32R/D ROM monitor.
11695 The Motorola m68k configuration includes ColdFire support, and
11696 target command for the following ROM monitors.
11700 @kindex target abug
11701 @item target abug @var{dev}
11702 ABug ROM monitor for M68K.
11704 @kindex target cpu32bug
11705 @item target cpu32bug @var{dev}
11706 CPU32BUG monitor, running on a CPU32 (M68K) board.
11708 @kindex target dbug
11709 @item target dbug @var{dev}
11710 dBUG ROM monitor for Motorola ColdFire.
11713 @item target est @var{dev}
11714 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11716 @kindex target rom68k
11717 @item target rom68k @var{dev}
11718 ROM 68K monitor, running on an M68K IDP board.
11722 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11723 instead have only a single special target command:
11727 @kindex target es1800
11728 @item target es1800 @var{dev}
11729 ES-1800 emulator for M68K.
11737 @kindex target rombug
11738 @item target rombug @var{dev}
11739 ROMBUG ROM monitor for OS/9000.
11749 @item target bug @var{dev}
11750 BUG monitor, running on a MVME187 (m88k) board.
11754 @node MIPS Embedded
11755 @subsection MIPS Embedded
11757 @cindex MIPS boards
11758 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11759 MIPS board attached to a serial line. This is available when
11760 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11763 Use these @value{GDBN} commands to specify the connection to your target board:
11766 @item target mips @var{port}
11767 @kindex target mips @var{port}
11768 To run a program on the board, start up @code{@value{GDBP}} with the
11769 name of your program as the argument. To connect to the board, use the
11770 command @samp{target mips @var{port}}, where @var{port} is the name of
11771 the serial port connected to the board. If the program has not already
11772 been downloaded to the board, you may use the @code{load} command to
11773 download it. You can then use all the usual @value{GDBN} commands.
11775 For example, this sequence connects to the target board through a serial
11776 port, and loads and runs a program called @var{prog} through the
11780 host$ @value{GDBP} @var{prog}
11781 @value{GDBN} is free software and @dots{}
11782 (@value{GDBP}) target mips /dev/ttyb
11783 (@value{GDBP}) load @var{prog}
11787 @item target mips @var{hostname}:@var{portnumber}
11788 On some @value{GDBN} host configurations, you can specify a TCP
11789 connection (for instance, to a serial line managed by a terminal
11790 concentrator) instead of a serial port, using the syntax
11791 @samp{@var{hostname}:@var{portnumber}}.
11793 @item target pmon @var{port}
11794 @kindex target pmon @var{port}
11797 @item target ddb @var{port}
11798 @kindex target ddb @var{port}
11799 NEC's DDB variant of PMON for Vr4300.
11801 @item target lsi @var{port}
11802 @kindex target lsi @var{port}
11803 LSI variant of PMON.
11805 @kindex target r3900
11806 @item target r3900 @var{dev}
11807 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11809 @kindex target array
11810 @item target array @var{dev}
11811 Array Tech LSI33K RAID controller board.
11817 @value{GDBN} also supports these special commands for MIPS targets:
11820 @item set processor @var{args}
11821 @itemx show processor
11822 @kindex set processor @var{args}
11823 @kindex show processor
11824 Use the @code{set processor} command to set the type of MIPS
11825 processor when you want to access processor-type-specific registers.
11826 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11827 to use the CPU registers appropriate for the 3041 chip.
11828 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11829 is using. Use the @code{info reg} command to see what registers
11830 @value{GDBN} is using.
11832 @item set mipsfpu double
11833 @itemx set mipsfpu single
11834 @itemx set mipsfpu none
11835 @itemx show mipsfpu
11836 @kindex set mipsfpu
11837 @kindex show mipsfpu
11838 @cindex MIPS remote floating point
11839 @cindex floating point, MIPS remote
11840 If your target board does not support the MIPS floating point
11841 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11842 need this, you may wish to put the command in your @value{GDBN} init
11843 file). This tells @value{GDBN} how to find the return value of
11844 functions which return floating point values. It also allows
11845 @value{GDBN} to avoid saving the floating point registers when calling
11846 functions on the board. If you are using a floating point coprocessor
11847 with only single precision floating point support, as on the @sc{r4650}
11848 processor, use the command @samp{set mipsfpu single}. The default
11849 double precision floating point coprocessor may be selected using
11850 @samp{set mipsfpu double}.
11852 In previous versions the only choices were double precision or no
11853 floating point, so @samp{set mipsfpu on} will select double precision
11854 and @samp{set mipsfpu off} will select no floating point.
11856 As usual, you can inquire about the @code{mipsfpu} variable with
11857 @samp{show mipsfpu}.
11859 @item set remotedebug @var{n}
11860 @itemx show remotedebug
11861 @kindex set remotedebug@r{, MIPS protocol}
11862 @kindex show remotedebug@r{, MIPS protocol}
11863 @cindex @code{remotedebug}, MIPS protocol
11864 @cindex MIPS @code{remotedebug} protocol
11865 @c FIXME! For this to be useful, you must know something about the MIPS
11866 @c FIXME...protocol. Where is it described?
11867 You can see some debugging information about communications with the board
11868 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11869 @samp{set remotedebug 1}, every packet is displayed. If you set it
11870 to @code{2}, every character is displayed. You can check the current value
11871 at any time with the command @samp{show remotedebug}.
11873 @item set timeout @var{seconds}
11874 @itemx set retransmit-timeout @var{seconds}
11875 @itemx show timeout
11876 @itemx show retransmit-timeout
11877 @cindex @code{timeout}, MIPS protocol
11878 @cindex @code{retransmit-timeout}, MIPS protocol
11879 @kindex set timeout
11880 @kindex show timeout
11881 @kindex set retransmit-timeout
11882 @kindex show retransmit-timeout
11883 You can control the timeout used while waiting for a packet, in the MIPS
11884 remote protocol, with the @code{set timeout @var{seconds}} command. The
11885 default is 5 seconds. Similarly, you can control the timeout used while
11886 waiting for an acknowledgement of a packet with the @code{set
11887 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11888 You can inspect both values with @code{show timeout} and @code{show
11889 retransmit-timeout}. (These commands are @emph{only} available when
11890 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11892 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11893 is waiting for your program to stop. In that case, @value{GDBN} waits
11894 forever because it has no way of knowing how long the program is going
11895 to run before stopping.
11899 @subsection PowerPC
11903 @kindex target dink32
11904 @item target dink32 @var{dev}
11905 DINK32 ROM monitor.
11907 @kindex target ppcbug
11908 @item target ppcbug @var{dev}
11909 @kindex target ppcbug1
11910 @item target ppcbug1 @var{dev}
11911 PPCBUG ROM monitor for PowerPC.
11914 @item target sds @var{dev}
11915 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11920 @subsection HP PA Embedded
11924 @kindex target op50n
11925 @item target op50n @var{dev}
11926 OP50N monitor, running on an OKI HPPA board.
11928 @kindex target w89k
11929 @item target w89k @var{dev}
11930 W89K monitor, running on a Winbond HPPA board.
11935 @subsection Hitachi SH
11939 @kindex target hms@r{, with Hitachi SH}
11940 @item target hms @var{dev}
11941 A Hitachi SH board attached via serial line to your host. Use special
11942 commands @code{device} and @code{speed} to control the serial line and
11943 the communications speed used.
11945 @kindex target e7000@r{, with Hitachi SH}
11946 @item target e7000 @var{dev}
11947 E7000 emulator for Hitachi SH.
11949 @kindex target sh3@r{, with SH}
11950 @kindex target sh3e@r{, with SH}
11951 @item target sh3 @var{dev}
11952 @item target sh3e @var{dev}
11953 Hitachi SH-3 and SH-3E target systems.
11958 @subsection Tsqware Sparclet
11962 @value{GDBN} enables developers to debug tasks running on
11963 Sparclet targets from a Unix host.
11964 @value{GDBN} uses code that runs on
11965 both the Unix host and on the Sparclet target. The program
11966 @code{@value{GDBP}} is installed and executed on the Unix host.
11969 @item remotetimeout @var{args}
11970 @kindex remotetimeout
11971 @value{GDBN} supports the option @code{remotetimeout}.
11972 This option is set by the user, and @var{args} represents the number of
11973 seconds @value{GDBN} waits for responses.
11976 @cindex compiling, on Sparclet
11977 When compiling for debugging, include the options @samp{-g} to get debug
11978 information and @samp{-Ttext} to relocate the program to where you wish to
11979 load it on the target. You may also want to add the options @samp{-n} or
11980 @samp{-N} in order to reduce the size of the sections. Example:
11983 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11986 You can use @code{objdump} to verify that the addresses are what you intended:
11989 sparclet-aout-objdump --headers --syms prog
11992 @cindex running, on Sparclet
11994 your Unix execution search path to find @value{GDBN}, you are ready to
11995 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
11996 (or @code{sparclet-aout-gdb}, depending on your installation).
11998 @value{GDBN} comes up showing the prompt:
12005 * Sparclet File:: Setting the file to debug
12006 * Sparclet Connection:: Connecting to Sparclet
12007 * Sparclet Download:: Sparclet download
12008 * Sparclet Execution:: Running and debugging
12011 @node Sparclet File
12012 @subsubsection Setting file to debug
12014 The @value{GDBN} command @code{file} lets you choose with program to debug.
12017 (gdbslet) file prog
12021 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12022 @value{GDBN} locates
12023 the file by searching the directories listed in the command search
12025 If the file was compiled with debug information (option "-g"), source
12026 files will be searched as well.
12027 @value{GDBN} locates
12028 the source files by searching the directories listed in the directory search
12029 path (@pxref{Environment, ,Your program's environment}).
12031 to find a file, it displays a message such as:
12034 prog: No such file or directory.
12037 When this happens, add the appropriate directories to the search paths with
12038 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12039 @code{target} command again.
12041 @node Sparclet Connection
12042 @subsubsection Connecting to Sparclet
12044 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12045 To connect to a target on serial port ``@code{ttya}'', type:
12048 (gdbslet) target sparclet /dev/ttya
12049 Remote target sparclet connected to /dev/ttya
12050 main () at ../prog.c:3
12054 @value{GDBN} displays messages like these:
12060 @node Sparclet Download
12061 @subsubsection Sparclet download
12063 @cindex download to Sparclet
12064 Once connected to the Sparclet target,
12065 you can use the @value{GDBN}
12066 @code{load} command to download the file from the host to the target.
12067 The file name and load offset should be given as arguments to the @code{load}
12069 Since the file format is aout, the program must be loaded to the starting
12070 address. You can use @code{objdump} to find out what this value is. The load
12071 offset is an offset which is added to the VMA (virtual memory address)
12072 of each of the file's sections.
12073 For instance, if the program
12074 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12075 and bss at 0x12010170, in @value{GDBN}, type:
12078 (gdbslet) load prog 0x12010000
12079 Loading section .text, size 0xdb0 vma 0x12010000
12082 If the code is loaded at a different address then what the program was linked
12083 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12084 to tell @value{GDBN} where to map the symbol table.
12086 @node Sparclet Execution
12087 @subsubsection Running and debugging
12089 @cindex running and debugging Sparclet programs
12090 You can now begin debugging the task using @value{GDBN}'s execution control
12091 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12092 manual for the list of commands.
12096 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12098 Starting program: prog
12099 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12100 3 char *symarg = 0;
12102 4 char *execarg = "hello!";
12107 @subsection Fujitsu Sparclite
12111 @kindex target sparclite
12112 @item target sparclite @var{dev}
12113 Fujitsu sparclite boards, used only for the purpose of loading.
12114 You must use an additional command to debug the program.
12115 For example: target remote @var{dev} using @value{GDBN} standard
12121 @subsection Tandem ST2000
12123 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12126 To connect your ST2000 to the host system, see the manufacturer's
12127 manual. Once the ST2000 is physically attached, you can run:
12130 target st2000 @var{dev} @var{speed}
12134 to establish it as your debugging environment. @var{dev} is normally
12135 the name of a serial device, such as @file{/dev/ttya}, connected to the
12136 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12137 connection (for example, to a serial line attached via a terminal
12138 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12140 The @code{load} and @code{attach} commands are @emph{not} defined for
12141 this target; you must load your program into the ST2000 as you normally
12142 would for standalone operation. @value{GDBN} reads debugging information
12143 (such as symbols) from a separate, debugging version of the program
12144 available on your host computer.
12145 @c FIXME!! This is terribly vague; what little content is here is
12146 @c basically hearsay.
12148 @cindex ST2000 auxiliary commands
12149 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12153 @item st2000 @var{command}
12154 @kindex st2000 @var{cmd}
12155 @cindex STDBUG commands (ST2000)
12156 @cindex commands to STDBUG (ST2000)
12157 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12158 manual for available commands.
12161 @cindex connect (to STDBUG)
12162 Connect the controlling terminal to the STDBUG command monitor. When
12163 you are done interacting with STDBUG, typing either of two character
12164 sequences gets you back to the @value{GDBN} command prompt:
12165 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12166 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12170 @subsection Zilog Z8000
12173 @cindex simulator, Z8000
12174 @cindex Zilog Z8000 simulator
12176 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12179 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12180 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12181 segmented variant). The simulator recognizes which architecture is
12182 appropriate by inspecting the object code.
12185 @item target sim @var{args}
12187 @kindex target sim@r{, with Z8000}
12188 Debug programs on a simulated CPU. If the simulator supports setup
12189 options, specify them via @var{args}.
12193 After specifying this target, you can debug programs for the simulated
12194 CPU in the same style as programs for your host computer; use the
12195 @code{file} command to load a new program image, the @code{run} command
12196 to run your program, and so on.
12198 As well as making available all the usual machine registers
12199 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12200 additional items of information as specially named registers:
12205 Counts clock-ticks in the simulator.
12208 Counts instructions run in the simulator.
12211 Execution time in 60ths of a second.
12215 You can refer to these values in @value{GDBN} expressions with the usual
12216 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12217 conditional breakpoint that suspends only after at least 5000
12218 simulated clock ticks.
12220 @node Architectures
12221 @section Architectures
12223 This section describes characteristics of architectures that affect
12224 all uses of @value{GDBN} with the architecture, both native and cross.
12237 @kindex set rstack_high_address
12238 @cindex AMD 29K register stack
12239 @cindex register stack, AMD29K
12240 @item set rstack_high_address @var{address}
12241 On AMD 29000 family processors, registers are saved in a separate
12242 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12243 extent of this stack. Normally, @value{GDBN} just assumes that the
12244 stack is ``large enough''. This may result in @value{GDBN} referencing
12245 memory locations that do not exist. If necessary, you can get around
12246 this problem by specifying the ending address of the register stack with
12247 the @code{set rstack_high_address} command. The argument should be an
12248 address, which you probably want to precede with @samp{0x} to specify in
12251 @kindex show rstack_high_address
12252 @item show rstack_high_address
12253 Display the current limit of the register stack, on AMD 29000 family
12261 See the following section.
12266 @cindex stack on Alpha
12267 @cindex stack on MIPS
12268 @cindex Alpha stack
12270 Alpha- and MIPS-based computers use an unusual stack frame, which
12271 sometimes requires @value{GDBN} to search backward in the object code to
12272 find the beginning of a function.
12274 @cindex response time, MIPS debugging
12275 To improve response time (especially for embedded applications, where
12276 @value{GDBN} may be restricted to a slow serial line for this search)
12277 you may want to limit the size of this search, using one of these
12281 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12282 @item set heuristic-fence-post @var{limit}
12283 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12284 search for the beginning of a function. A value of @var{0} (the
12285 default) means there is no limit. However, except for @var{0}, the
12286 larger the limit the more bytes @code{heuristic-fence-post} must search
12287 and therefore the longer it takes to run.
12289 @item show heuristic-fence-post
12290 Display the current limit.
12294 These commands are available @emph{only} when @value{GDBN} is configured
12295 for debugging programs on Alpha or MIPS processors.
12298 @node Controlling GDB
12299 @chapter Controlling @value{GDBN}
12301 You can alter the way @value{GDBN} interacts with you by using the
12302 @code{set} command. For commands controlling how @value{GDBN} displays
12303 data, see @ref{Print Settings, ,Print settings}. Other settings are
12308 * Editing:: Command editing
12309 * History:: Command history
12310 * Screen Size:: Screen size
12311 * Numbers:: Numbers
12312 * Messages/Warnings:: Optional warnings and messages
12313 * Debugging Output:: Optional messages about internal happenings
12321 @value{GDBN} indicates its readiness to read a command by printing a string
12322 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12323 can change the prompt string with the @code{set prompt} command. For
12324 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12325 the prompt in one of the @value{GDBN} sessions so that you can always tell
12326 which one you are talking to.
12328 @emph{Note:} @code{set prompt} does not add a space for you after the
12329 prompt you set. This allows you to set a prompt which ends in a space
12330 or a prompt that does not.
12334 @item set prompt @var{newprompt}
12335 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12337 @kindex show prompt
12339 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12343 @section Command editing
12345 @cindex command line editing
12347 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12348 @sc{gnu} library provides consistent behavior for programs which provide a
12349 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12350 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12351 substitution, and a storage and recall of command history across
12352 debugging sessions.
12354 You may control the behavior of command line editing in @value{GDBN} with the
12355 command @code{set}.
12358 @kindex set editing
12361 @itemx set editing on
12362 Enable command line editing (enabled by default).
12364 @item set editing off
12365 Disable command line editing.
12367 @kindex show editing
12369 Show whether command line editing is enabled.
12373 @section Command history
12375 @value{GDBN} can keep track of the commands you type during your
12376 debugging sessions, so that you can be certain of precisely what
12377 happened. Use these commands to manage the @value{GDBN} command
12381 @cindex history substitution
12382 @cindex history file
12383 @kindex set history filename
12384 @kindex GDBHISTFILE
12385 @item set history filename @var{fname}
12386 Set the name of the @value{GDBN} command history file to @var{fname}.
12387 This is the file where @value{GDBN} reads an initial command history
12388 list, and where it writes the command history from this session when it
12389 exits. You can access this list through history expansion or through
12390 the history command editing characters listed below. This file defaults
12391 to the value of the environment variable @code{GDBHISTFILE}, or to
12392 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12395 @cindex history save
12396 @kindex set history save
12397 @item set history save
12398 @itemx set history save on
12399 Record command history in a file, whose name may be specified with the
12400 @code{set history filename} command. By default, this option is disabled.
12402 @item set history save off
12403 Stop recording command history in a file.
12405 @cindex history size
12406 @kindex set history size
12407 @item set history size @var{size}
12408 Set the number of commands which @value{GDBN} keeps in its history list.
12409 This defaults to the value of the environment variable
12410 @code{HISTSIZE}, or to 256 if this variable is not set.
12413 @cindex history expansion
12414 History expansion assigns special meaning to the character @kbd{!}.
12415 @ifset have-readline-appendices
12416 @xref{Event Designators}.
12419 Since @kbd{!} is also the logical not operator in C, history expansion
12420 is off by default. If you decide to enable history expansion with the
12421 @code{set history expansion on} command, you may sometimes need to
12422 follow @kbd{!} (when it is used as logical not, in an expression) with
12423 a space or a tab to prevent it from being expanded. The readline
12424 history facilities do not attempt substitution on the strings
12425 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12427 The commands to control history expansion are:
12430 @kindex set history expansion
12431 @item set history expansion on
12432 @itemx set history expansion
12433 Enable history expansion. History expansion is off by default.
12435 @item set history expansion off
12436 Disable history expansion.
12438 The readline code comes with more complete documentation of
12439 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12440 or @code{vi} may wish to read it.
12441 @ifset have-readline-appendices
12442 @xref{Command Line Editing}.
12446 @kindex show history
12448 @itemx show history filename
12449 @itemx show history save
12450 @itemx show history size
12451 @itemx show history expansion
12452 These commands display the state of the @value{GDBN} history parameters.
12453 @code{show history} by itself displays all four states.
12459 @item show commands
12460 Display the last ten commands in the command history.
12462 @item show commands @var{n}
12463 Print ten commands centered on command number @var{n}.
12465 @item show commands +
12466 Print ten commands just after the commands last printed.
12470 @section Screen size
12471 @cindex size of screen
12472 @cindex pauses in output
12474 Certain commands to @value{GDBN} may produce large amounts of
12475 information output to the screen. To help you read all of it,
12476 @value{GDBN} pauses and asks you for input at the end of each page of
12477 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12478 to discard the remaining output. Also, the screen width setting
12479 determines when to wrap lines of output. Depending on what is being
12480 printed, @value{GDBN} tries to break the line at a readable place,
12481 rather than simply letting it overflow onto the following line.
12483 Normally @value{GDBN} knows the size of the screen from the terminal
12484 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12485 together with the value of the @code{TERM} environment variable and the
12486 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12487 you can override it with the @code{set height} and @code{set
12494 @kindex show height
12495 @item set height @var{lpp}
12497 @itemx set width @var{cpl}
12499 These @code{set} commands specify a screen height of @var{lpp} lines and
12500 a screen width of @var{cpl} characters. The associated @code{show}
12501 commands display the current settings.
12503 If you specify a height of zero lines, @value{GDBN} does not pause during
12504 output no matter how long the output is. This is useful if output is to a
12505 file or to an editor buffer.
12507 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12508 from wrapping its output.
12513 @cindex number representation
12514 @cindex entering numbers
12516 You can always enter numbers in octal, decimal, or hexadecimal in
12517 @value{GDBN} by the usual conventions: octal numbers begin with
12518 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12519 begin with @samp{0x}. Numbers that begin with none of these are, by
12520 default, entered in base 10; likewise, the default display for
12521 numbers---when no particular format is specified---is base 10. You can
12522 change the default base for both input and output with the @code{set
12526 @kindex set input-radix
12527 @item set input-radix @var{base}
12528 Set the default base for numeric input. Supported choices
12529 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12530 specified either unambiguously or using the current default radix; for
12540 sets the base to decimal. On the other hand, @samp{set radix 10}
12541 leaves the radix unchanged no matter what it was.
12543 @kindex set output-radix
12544 @item set output-radix @var{base}
12545 Set the default base for numeric display. Supported choices
12546 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12547 specified either unambiguously or using the current default radix.
12549 @kindex show input-radix
12550 @item show input-radix
12551 Display the current default base for numeric input.
12553 @kindex show output-radix
12554 @item show output-radix
12555 Display the current default base for numeric display.
12558 @node Messages/Warnings
12559 @section Optional warnings and messages
12561 By default, @value{GDBN} is silent about its inner workings. If you are
12562 running on a slow machine, you may want to use the @code{set verbose}
12563 command. This makes @value{GDBN} tell you when it does a lengthy
12564 internal operation, so you will not think it has crashed.
12566 Currently, the messages controlled by @code{set verbose} are those
12567 which announce that the symbol table for a source file is being read;
12568 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12571 @kindex set verbose
12572 @item set verbose on
12573 Enables @value{GDBN} output of certain informational messages.
12575 @item set verbose off
12576 Disables @value{GDBN} output of certain informational messages.
12578 @kindex show verbose
12580 Displays whether @code{set verbose} is on or off.
12583 By default, if @value{GDBN} encounters bugs in the symbol table of an
12584 object file, it is silent; but if you are debugging a compiler, you may
12585 find this information useful (@pxref{Symbol Errors, ,Errors reading
12590 @kindex set complaints
12591 @item set complaints @var{limit}
12592 Permits @value{GDBN} to output @var{limit} complaints about each type of
12593 unusual symbols before becoming silent about the problem. Set
12594 @var{limit} to zero to suppress all complaints; set it to a large number
12595 to prevent complaints from being suppressed.
12597 @kindex show complaints
12598 @item show complaints
12599 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12603 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12604 lot of stupid questions to confirm certain commands. For example, if
12605 you try to run a program which is already running:
12609 The program being debugged has been started already.
12610 Start it from the beginning? (y or n)
12613 If you are willing to unflinchingly face the consequences of your own
12614 commands, you can disable this ``feature'':
12618 @kindex set confirm
12620 @cindex confirmation
12621 @cindex stupid questions
12622 @item set confirm off
12623 Disables confirmation requests.
12625 @item set confirm on
12626 Enables confirmation requests (the default).
12628 @kindex show confirm
12630 Displays state of confirmation requests.
12634 @node Debugging Output
12635 @section Optional messages about internal happenings
12637 @kindex set debug arch
12638 @item set debug arch
12639 Turns on or off display of gdbarch debugging info. The default is off
12640 @kindex show debug arch
12641 @item show debug arch
12642 Displays the current state of displaying gdbarch debugging info.
12643 @kindex set debug event
12644 @item set debug event
12645 Turns on or off display of @value{GDBN} event debugging info. The
12647 @kindex show debug event
12648 @item show debug event
12649 Displays the current state of displaying @value{GDBN} event debugging
12651 @kindex set debug expression
12652 @item set debug expression
12653 Turns on or off display of @value{GDBN} expression debugging info. The
12655 @kindex show debug expression
12656 @item show debug expression
12657 Displays the current state of displaying @value{GDBN} expression
12659 @kindex set debug overload
12660 @item set debug overload
12661 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12662 info. This includes info such as ranking of functions, etc. The default
12664 @kindex show debug overload
12665 @item show debug overload
12666 Displays the current state of displaying @value{GDBN} C@t{++} overload
12668 @kindex set debug remote
12669 @cindex packets, reporting on stdout
12670 @cindex serial connections, debugging
12671 @item set debug remote
12672 Turns on or off display of reports on all packets sent back and forth across
12673 the serial line to the remote machine. The info is printed on the
12674 @value{GDBN} standard output stream. The default is off.
12675 @kindex show debug remote
12676 @item show debug remote
12677 Displays the state of display of remote packets.
12678 @kindex set debug serial
12679 @item set debug serial
12680 Turns on or off display of @value{GDBN} serial debugging info. The
12682 @kindex show debug serial
12683 @item show debug serial
12684 Displays the current state of displaying @value{GDBN} serial debugging
12686 @kindex set debug target
12687 @item set debug target
12688 Turns on or off display of @value{GDBN} target debugging info. This info
12689 includes what is going on at the target level of GDB, as it happens. The
12691 @kindex show debug target
12692 @item show debug target
12693 Displays the current state of displaying @value{GDBN} target debugging
12695 @kindex set debug varobj
12696 @item set debug varobj
12697 Turns on or off display of @value{GDBN} variable object debugging
12698 info. The default is off.
12699 @kindex show debug varobj
12700 @item show debug varobj
12701 Displays the current state of displaying @value{GDBN} variable object
12706 @chapter Canned Sequences of Commands
12708 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12709 command lists}), @value{GDBN} provides two ways to store sequences of
12710 commands for execution as a unit: user-defined commands and command
12714 * Define:: User-defined commands
12715 * Hooks:: User-defined command hooks
12716 * Command Files:: Command files
12717 * Output:: Commands for controlled output
12721 @section User-defined commands
12723 @cindex user-defined command
12724 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12725 which you assign a new name as a command. This is done with the
12726 @code{define} command. User commands may accept up to 10 arguments
12727 separated by whitespace. Arguments are accessed within the user command
12728 via @var{$arg0@dots{}$arg9}. A trivial example:
12732 print $arg0 + $arg1 + $arg2
12736 To execute the command use:
12743 This defines the command @code{adder}, which prints the sum of
12744 its three arguments. Note the arguments are text substitutions, so they may
12745 reference variables, use complex expressions, or even perform inferior
12751 @item define @var{commandname}
12752 Define a command named @var{commandname}. If there is already a command
12753 by that name, you are asked to confirm that you want to redefine it.
12755 The definition of the command is made up of other @value{GDBN} command lines,
12756 which are given following the @code{define} command. The end of these
12757 commands is marked by a line containing @code{end}.
12762 Takes a single argument, which is an expression to evaluate.
12763 It is followed by a series of commands that are executed
12764 only if the expression is true (nonzero).
12765 There can then optionally be a line @code{else}, followed
12766 by a series of commands that are only executed if the expression
12767 was false. The end of the list is marked by a line containing @code{end}.
12771 The syntax is similar to @code{if}: the command takes a single argument,
12772 which is an expression to evaluate, and must be followed by the commands to
12773 execute, one per line, terminated by an @code{end}.
12774 The commands are executed repeatedly as long as the expression
12778 @item document @var{commandname}
12779 Document the user-defined command @var{commandname}, so that it can be
12780 accessed by @code{help}. The command @var{commandname} must already be
12781 defined. This command reads lines of documentation just as @code{define}
12782 reads the lines of the command definition, ending with @code{end}.
12783 After the @code{document} command is finished, @code{help} on command
12784 @var{commandname} displays the documentation you have written.
12786 You may use the @code{document} command again to change the
12787 documentation of a command. Redefining the command with @code{define}
12788 does not change the documentation.
12790 @kindex help user-defined
12791 @item help user-defined
12792 List all user-defined commands, with the first line of the documentation
12797 @itemx show user @var{commandname}
12798 Display the @value{GDBN} commands used to define @var{commandname} (but
12799 not its documentation). If no @var{commandname} is given, display the
12800 definitions for all user-defined commands.
12802 @kindex show max-user-call-depth
12803 @kindex set max-user-call-depth
12804 @item show max-user-call-depth
12805 @itemx set max-user-call-depth
12806 The value of @code{max-user-call-depth} controls how many recursion
12807 levels are allowed in user-defined commands before GDB suspects an
12808 infinite recursion and aborts the command.
12812 When user-defined commands are executed, the
12813 commands of the definition are not printed. An error in any command
12814 stops execution of the user-defined command.
12816 If used interactively, commands that would ask for confirmation proceed
12817 without asking when used inside a user-defined command. Many @value{GDBN}
12818 commands that normally print messages to say what they are doing omit the
12819 messages when used in a user-defined command.
12822 @section User-defined command hooks
12823 @cindex command hooks
12824 @cindex hooks, for commands
12825 @cindex hooks, pre-command
12829 You may define @dfn{hooks}, which are a special kind of user-defined
12830 command. Whenever you run the command @samp{foo}, if the user-defined
12831 command @samp{hook-foo} exists, it is executed (with no arguments)
12832 before that command.
12834 @cindex hooks, post-command
12837 A hook may also be defined which is run after the command you executed.
12838 Whenever you run the command @samp{foo}, if the user-defined command
12839 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12840 that command. Post-execution hooks may exist simultaneously with
12841 pre-execution hooks, for the same command.
12843 It is valid for a hook to call the command which it hooks. If this
12844 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12846 @c It would be nice if hookpost could be passed a parameter indicating
12847 @c if the command it hooks executed properly or not. FIXME!
12849 @kindex stop@r{, a pseudo-command}
12850 In addition, a pseudo-command, @samp{stop} exists. Defining
12851 (@samp{hook-stop}) makes the associated commands execute every time
12852 execution stops in your program: before breakpoint commands are run,
12853 displays are printed, or the stack frame is printed.
12855 For example, to ignore @code{SIGALRM} signals while
12856 single-stepping, but treat them normally during normal execution,
12861 handle SIGALRM nopass
12865 handle SIGALRM pass
12868 define hook-continue
12869 handle SIGLARM pass
12873 As a further example, to hook at the begining and end of the @code{echo}
12874 command, and to add extra text to the beginning and end of the message,
12882 define hookpost-echo
12886 (@value{GDBP}) echo Hello World
12887 <<<---Hello World--->>>
12892 You can define a hook for any single-word command in @value{GDBN}, but
12893 not for command aliases; you should define a hook for the basic command
12894 name, e.g. @code{backtrace} rather than @code{bt}.
12895 @c FIXME! So how does Joe User discover whether a command is an alias
12897 If an error occurs during the execution of your hook, execution of
12898 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12899 (before the command that you actually typed had a chance to run).
12901 If you try to define a hook which does not match any known command, you
12902 get a warning from the @code{define} command.
12904 @node Command Files
12905 @section Command files
12907 @cindex command files
12908 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12909 commands. Comments (lines starting with @kbd{#}) may also be included.
12910 An empty line in a command file does nothing; it does not mean to repeat
12911 the last command, as it would from the terminal.
12914 @cindex @file{.gdbinit}
12915 @cindex @file{gdb.ini}
12916 When you start @value{GDBN}, it automatically executes commands from its
12917 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
12918 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
12919 limitations of file names imposed by DOS filesystems.}.
12920 During startup, @value{GDBN} does the following:
12924 Reads the init file (if any) in your home directory@footnote{On
12925 DOS/Windows systems, the home directory is the one pointed to by the
12926 @code{HOME} environment variable.}.
12929 Processes command line options and operands.
12932 Reads the init file (if any) in the current working directory.
12935 Reads command files specified by the @samp{-x} option.
12938 The init file in your home directory can set options (such as @samp{set
12939 complaints}) that affect subsequent processing of command line options
12940 and operands. Init files are not executed if you use the @samp{-nx}
12941 option (@pxref{Mode Options, ,Choosing modes}).
12943 @cindex init file name
12944 On some configurations of @value{GDBN}, the init file is known by a
12945 different name (these are typically environments where a specialized
12946 form of @value{GDBN} may need to coexist with other forms, hence a
12947 different name for the specialized version's init file). These are the
12948 environments with special init file names:
12950 @cindex @file{.vxgdbinit}
12953 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12955 @cindex @file{.os68gdbinit}
12957 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12959 @cindex @file{.esgdbinit}
12961 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12964 You can also request the execution of a command file with the
12965 @code{source} command:
12969 @item source @var{filename}
12970 Execute the command file @var{filename}.
12973 The lines in a command file are executed sequentially. They are not
12974 printed as they are executed. An error in any command terminates execution
12975 of the command file.
12977 Commands that would ask for confirmation if used interactively proceed
12978 without asking when used in a command file. Many @value{GDBN} commands that
12979 normally print messages to say what they are doing omit the messages
12980 when called from command files.
12982 @value{GDBN} also accepts command input from standard input. In this
12983 mode, normal output goes to standard output and error output goes to
12984 standard error. Errors in a command file supplied on standard input do
12985 not terminate execution of the command file --- execution continues with
12989 gdb < cmds > log 2>&1
12992 (The syntax above will vary depending on the shell used.) This example
12993 will execute commands from the file @file{cmds}. All output and errors
12994 would be directed to @file{log}.
12997 @section Commands for controlled output
12999 During the execution of a command file or a user-defined command, normal
13000 @value{GDBN} output is suppressed; the only output that appears is what is
13001 explicitly printed by the commands in the definition. This section
13002 describes three commands useful for generating exactly the output you
13007 @item echo @var{text}
13008 @c I do not consider backslash-space a standard C escape sequence
13009 @c because it is not in ANSI.
13010 Print @var{text}. Nonprinting characters can be included in
13011 @var{text} using C escape sequences, such as @samp{\n} to print a
13012 newline. @strong{No newline is printed unless you specify one.}
13013 In addition to the standard C escape sequences, a backslash followed
13014 by a space stands for a space. This is useful for displaying a
13015 string with spaces at the beginning or the end, since leading and
13016 trailing spaces are otherwise trimmed from all arguments.
13017 To print @samp{@w{ }and foo =@w{ }}, use the command
13018 @samp{echo \@w{ }and foo = \@w{ }}.
13020 A backslash at the end of @var{text} can be used, as in C, to continue
13021 the command onto subsequent lines. For example,
13024 echo This is some text\n\
13025 which is continued\n\
13026 onto several lines.\n
13029 produces the same output as
13032 echo This is some text\n
13033 echo which is continued\n
13034 echo onto several lines.\n
13038 @item output @var{expression}
13039 Print the value of @var{expression} and nothing but that value: no
13040 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13041 value history either. @xref{Expressions, ,Expressions}, for more information
13044 @item output/@var{fmt} @var{expression}
13045 Print the value of @var{expression} in format @var{fmt}. You can use
13046 the same formats as for @code{print}. @xref{Output Formats,,Output
13047 formats}, for more information.
13050 @item printf @var{string}, @var{expressions}@dots{}
13051 Print the values of the @var{expressions} under the control of
13052 @var{string}. The @var{expressions} are separated by commas and may be
13053 either numbers or pointers. Their values are printed as specified by
13054 @var{string}, exactly as if your program were to execute the C
13056 @c FIXME: the above implies that at least all ANSI C formats are
13057 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13058 @c Either this is a bug, or the manual should document what formats are
13062 printf (@var{string}, @var{expressions}@dots{});
13065 For example, you can print two values in hex like this:
13068 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13071 The only backslash-escape sequences that you can use in the format
13072 string are the simple ones that consist of backslash followed by a
13077 @chapter @value{GDBN} Text User Interface
13081 * TUI Overview:: TUI overview
13082 * TUI Keys:: TUI key bindings
13083 * TUI Commands:: TUI specific commands
13084 * TUI Configuration:: TUI configuration variables
13087 The @value{GDBN} Text User Interface, TUI in short,
13088 is a terminal interface which uses the @code{curses} library
13089 to show the source file, the assembly output, the program registers
13090 and @value{GDBN} commands in separate text windows.
13091 The TUI is available only when @value{GDBN} is configured
13092 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13095 @section TUI overview
13097 The TUI has two display modes that can be switched while
13102 A curses (or TUI) mode in which it displays several text
13103 windows on the terminal.
13106 A standard mode which corresponds to the @value{GDBN} configured without
13110 In the TUI mode, @value{GDBN} can display several text window
13115 This window is the @value{GDBN} command window with the @value{GDBN}
13116 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13117 managed using readline but through the TUI. The @emph{command}
13118 window is always visible.
13121 The source window shows the source file of the program. The current
13122 line as well as active breakpoints are displayed in this window.
13123 The current program position is shown with the @samp{>} marker and
13124 active breakpoints are shown with @samp{*} markers.
13127 The assembly window shows the disassembly output of the program.
13130 This window shows the processor registers. It detects when
13131 a register is changed and when this is the case, registers that have
13132 changed are highlighted.
13136 The source, assembly and register windows are attached to the thread
13137 and the frame position. They are updated when the current thread
13138 changes, when the frame changes or when the program counter changes.
13139 These three windows are arranged by the TUI according to several
13140 layouts. The layout defines which of these three windows are visible.
13141 The following layouts are available:
13151 source and assembly
13154 source and registers
13157 assembly and registers
13162 @section TUI Key Bindings
13163 @cindex TUI key bindings
13165 The TUI installs several key bindings in the readline keymaps
13166 (@pxref{Command Line Editing}).
13167 They allow to leave or enter in the TUI mode or they operate
13168 directly on the TUI layout and windows. The following key bindings
13169 are installed for both TUI mode and the @value{GDBN} standard mode.
13178 Enter or leave the TUI mode. When the TUI mode is left,
13179 the curses window management is left and @value{GDBN} operates using
13180 its standard mode writing on the terminal directly. When the TUI
13181 mode is entered, the control is given back to the curses windows.
13182 The screen is then refreshed.
13186 Use a TUI layout with only one window. The layout will
13187 either be @samp{source} or @samp{assembly}. When the TUI mode
13188 is not active, it will switch to the TUI mode.
13190 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13194 Use a TUI layout with at least two windows. When the current
13195 layout shows already two windows, a next layout with two windows is used.
13196 When a new layout is chosen, one window will always be common to the
13197 previous layout and the new one.
13199 Think of it as the Emacs @kbd{C-x 2} binding.
13203 The following key bindings are handled only by the TUI mode:
13208 Scroll the active window one page up.
13212 Scroll the active window one page down.
13216 Scroll the active window one line up.
13220 Scroll the active window one line down.
13224 Scroll the active window one column left.
13228 Scroll the active window one column right.
13232 Refresh the screen.
13236 In the TUI mode, the arrow keys are used by the active window
13237 for scrolling. This means they are not available for readline. It is
13238 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13239 @key{C-b} and @key{C-f}.
13242 @section TUI specific commands
13243 @cindex TUI commands
13245 The TUI has specific commands to control the text windows.
13246 These commands are always available, that is they do not depend on
13247 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13248 is in the standard mode, using these commands will automatically switch
13253 @kindex layout next
13254 Display the next layout.
13257 @kindex layout prev
13258 Display the previous layout.
13262 Display the source window only.
13266 Display the assembly window only.
13269 @kindex layout split
13270 Display the source and assembly window.
13273 @kindex layout regs
13274 Display the register window together with the source or assembly window.
13276 @item focus next | prev | src | asm | regs | split
13278 Set the focus to the named window.
13279 This command allows to change the active window so that scrolling keys
13280 can be affected to another window.
13284 Refresh the screen. This is similar to using @key{C-L} key.
13288 Update the source window and the current execution point.
13290 @item winheight @var{name} +@var{count}
13291 @itemx winheight @var{name} -@var{count}
13293 Change the height of the window @var{name} by @var{count}
13294 lines. Positive counts increase the height, while negative counts
13299 @node TUI Configuration
13300 @section TUI configuration variables
13301 @cindex TUI configuration variables
13303 The TUI has several configuration variables that control the
13304 appearance of windows on the terminal.
13307 @item set tui border-kind @var{kind}
13308 @kindex set tui border-kind
13309 Select the border appearance for the source, assembly and register windows.
13310 The possible values are the following:
13313 Use a space character to draw the border.
13316 Use ascii characters + - and | to draw the border.
13319 Use the Alternate Character Set to draw the border. The border is
13320 drawn using character line graphics if the terminal supports them.
13324 @item set tui active-border-mode @var{mode}
13325 @kindex set tui active-border-mode
13326 Select the attributes to display the border of the active window.
13327 The possible values are @code{normal}, @code{standout}, @code{reverse},
13328 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13330 @item set tui border-mode @var{mode}
13331 @kindex set tui border-mode
13332 Select the attributes to display the border of other windows.
13333 The @var{mode} can be one of the following:
13336 Use normal attributes to display the border.
13342 Use reverse video mode.
13345 Use half bright mode.
13347 @item half-standout
13348 Use half bright and standout mode.
13351 Use extra bright or bold mode.
13353 @item bold-standout
13354 Use extra bright or bold and standout mode.
13361 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13364 @cindex @sc{gnu} Emacs
13365 A special interface allows you to use @sc{gnu} Emacs to view (and
13366 edit) the source files for the program you are debugging with
13369 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13370 executable file you want to debug as an argument. This command starts
13371 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13372 created Emacs buffer.
13373 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13375 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13380 All ``terminal'' input and output goes through the Emacs buffer.
13383 This applies both to @value{GDBN} commands and their output, and to the input
13384 and output done by the program you are debugging.
13386 This is useful because it means that you can copy the text of previous
13387 commands and input them again; you can even use parts of the output
13390 All the facilities of Emacs' Shell mode are available for interacting
13391 with your program. In particular, you can send signals the usual
13392 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13397 @value{GDBN} displays source code through Emacs.
13400 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13401 source file for that frame and puts an arrow (@samp{=>}) at the
13402 left margin of the current line. Emacs uses a separate buffer for
13403 source display, and splits the screen to show both your @value{GDBN} session
13406 Explicit @value{GDBN} @code{list} or search commands still produce output as
13407 usual, but you probably have no reason to use them from Emacs.
13410 @emph{Warning:} If the directory where your program resides is not your
13411 current directory, it can be easy to confuse Emacs about the location of
13412 the source files, in which case the auxiliary display buffer does not
13413 appear to show your source. @value{GDBN} can find programs by searching your
13414 environment's @code{PATH} variable, so the @value{GDBN} input and output
13415 session proceeds normally; but Emacs does not get enough information
13416 back from @value{GDBN} to locate the source files in this situation. To
13417 avoid this problem, either start @value{GDBN} mode from the directory where
13418 your program resides, or specify an absolute file name when prompted for the
13419 @kbd{M-x gdb} argument.
13421 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13422 switch to debugging a program in some other location, from an existing
13423 @value{GDBN} buffer in Emacs.
13426 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13427 you need to call @value{GDBN} by a different name (for example, if you keep
13428 several configurations around, with different names) you can set the
13429 Emacs variable @code{gdb-command-name}; for example,
13432 (setq gdb-command-name "mygdb")
13436 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13437 in your @file{.emacs} file) makes Emacs call the program named
13438 ``@code{mygdb}'' instead.
13440 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13441 addition to the standard Shell mode commands:
13445 Describe the features of Emacs' @value{GDBN} Mode.
13448 Execute to another source line, like the @value{GDBN} @code{step} command; also
13449 update the display window to show the current file and location.
13452 Execute to next source line in this function, skipping all function
13453 calls, like the @value{GDBN} @code{next} command. Then update the display window
13454 to show the current file and location.
13457 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13458 display window accordingly.
13460 @item M-x gdb-nexti
13461 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13462 display window accordingly.
13465 Execute until exit from the selected stack frame, like the @value{GDBN}
13466 @code{finish} command.
13469 Continue execution of your program, like the @value{GDBN} @code{continue}
13472 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13475 Go up the number of frames indicated by the numeric argument
13476 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13477 like the @value{GDBN} @code{up} command.
13479 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13482 Go down the number of frames indicated by the numeric argument, like the
13483 @value{GDBN} @code{down} command.
13485 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13488 Read the number where the cursor is positioned, and insert it at the end
13489 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13490 around an address that was displayed earlier, type @kbd{disassemble};
13491 then move the cursor to the address display, and pick up the
13492 argument for @code{disassemble} by typing @kbd{C-x &}.
13494 You can customize this further by defining elements of the list
13495 @code{gdb-print-command}; once it is defined, you can format or
13496 otherwise process numbers picked up by @kbd{C-x &} before they are
13497 inserted. A numeric argument to @kbd{C-x &} indicates that you
13498 wish special formatting, and also acts as an index to pick an element of the
13499 list. If the list element is a string, the number to be inserted is
13500 formatted using the Emacs function @code{format}; otherwise the number
13501 is passed as an argument to the corresponding list element.
13504 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13505 tells @value{GDBN} to set a breakpoint on the source line point is on.
13507 If you accidentally delete the source-display buffer, an easy way to get
13508 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13509 request a frame display; when you run under Emacs, this recreates
13510 the source buffer if necessary to show you the context of the current
13513 The source files displayed in Emacs are in ordinary Emacs buffers
13514 which are visiting the source files in the usual way. You can edit
13515 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13516 communicates with Emacs in terms of line numbers. If you add or
13517 delete lines from the text, the line numbers that @value{GDBN} knows cease
13518 to correspond properly with the code.
13520 @c The following dropped because Epoch is nonstandard. Reactivate
13521 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13523 @kindex Emacs Epoch environment
13527 Version 18 of @sc{gnu} Emacs has a built-in window system
13528 called the @code{epoch}
13529 environment. Users of this environment can use a new command,
13530 @code{inspect} which performs identically to @code{print} except that
13531 each value is printed in its own window.
13534 @include annotate.texi
13535 @include gdbmi.texinfo
13538 @chapter Reporting Bugs in @value{GDBN}
13539 @cindex bugs in @value{GDBN}
13540 @cindex reporting bugs in @value{GDBN}
13542 Your bug reports play an essential role in making @value{GDBN} reliable.
13544 Reporting a bug may help you by bringing a solution to your problem, or it
13545 may not. But in any case the principal function of a bug report is to help
13546 the entire community by making the next version of @value{GDBN} work better. Bug
13547 reports are your contribution to the maintenance of @value{GDBN}.
13549 In order for a bug report to serve its purpose, you must include the
13550 information that enables us to fix the bug.
13553 * Bug Criteria:: Have you found a bug?
13554 * Bug Reporting:: How to report bugs
13558 @section Have you found a bug?
13559 @cindex bug criteria
13561 If you are not sure whether you have found a bug, here are some guidelines:
13564 @cindex fatal signal
13565 @cindex debugger crash
13566 @cindex crash of debugger
13568 If the debugger gets a fatal signal, for any input whatever, that is a
13569 @value{GDBN} bug. Reliable debuggers never crash.
13571 @cindex error on valid input
13573 If @value{GDBN} produces an error message for valid input, that is a
13574 bug. (Note that if you're cross debugging, the problem may also be
13575 somewhere in the connection to the target.)
13577 @cindex invalid input
13579 If @value{GDBN} does not produce an error message for invalid input,
13580 that is a bug. However, you should note that your idea of
13581 ``invalid input'' might be our idea of ``an extension'' or ``support
13582 for traditional practice''.
13585 If you are an experienced user of debugging tools, your suggestions
13586 for improvement of @value{GDBN} are welcome in any case.
13589 @node Bug Reporting
13590 @section How to report bugs
13591 @cindex bug reports
13592 @cindex @value{GDBN} bugs, reporting
13594 A number of companies and individuals offer support for @sc{gnu} products.
13595 If you obtained @value{GDBN} from a support organization, we recommend you
13596 contact that organization first.
13598 You can find contact information for many support companies and
13599 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13601 @c should add a web page ref...
13603 In any event, we also recommend that you submit bug reports for
13604 @value{GDBN}. The prefered method is to submit them directly using
13605 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
13606 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
13609 @strong{Do not send bug reports to @samp{info-gdb}, or to
13610 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13611 not want to receive bug reports. Those that do have arranged to receive
13614 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13615 serves as a repeater. The mailing list and the newsgroup carry exactly
13616 the same messages. Often people think of posting bug reports to the
13617 newsgroup instead of mailing them. This appears to work, but it has one
13618 problem which can be crucial: a newsgroup posting often lacks a mail
13619 path back to the sender. Thus, if we need to ask for more information,
13620 we may be unable to reach you. For this reason, it is better to send
13621 bug reports to the mailing list.
13623 The fundamental principle of reporting bugs usefully is this:
13624 @strong{report all the facts}. If you are not sure whether to state a
13625 fact or leave it out, state it!
13627 Often people omit facts because they think they know what causes the
13628 problem and assume that some details do not matter. Thus, you might
13629 assume that the name of the variable you use in an example does not matter.
13630 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13631 stray memory reference which happens to fetch from the location where that
13632 name is stored in memory; perhaps, if the name were different, the contents
13633 of that location would fool the debugger into doing the right thing despite
13634 the bug. Play it safe and give a specific, complete example. That is the
13635 easiest thing for you to do, and the most helpful.
13637 Keep in mind that the purpose of a bug report is to enable us to fix the
13638 bug. It may be that the bug has been reported previously, but neither
13639 you nor we can know that unless your bug report is complete and
13642 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13643 bell?'' Those bug reports are useless, and we urge everyone to
13644 @emph{refuse to respond to them} except to chide the sender to report
13647 To enable us to fix the bug, you should include all these things:
13651 The version of @value{GDBN}. @value{GDBN} announces it if you start
13652 with no arguments; you can also print it at any time using @code{show
13655 Without this, we will not know whether there is any point in looking for
13656 the bug in the current version of @value{GDBN}.
13659 The type of machine you are using, and the operating system name and
13663 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13664 ``@value{GCC}--2.8.1''.
13667 What compiler (and its version) was used to compile the program you are
13668 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13669 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13670 information; for other compilers, see the documentation for those
13674 The command arguments you gave the compiler to compile your example and
13675 observe the bug. For example, did you use @samp{-O}? To guarantee
13676 you will not omit something important, list them all. A copy of the
13677 Makefile (or the output from make) is sufficient.
13679 If we were to try to guess the arguments, we would probably guess wrong
13680 and then we might not encounter the bug.
13683 A complete input script, and all necessary source files, that will
13687 A description of what behavior you observe that you believe is
13688 incorrect. For example, ``It gets a fatal signal.''
13690 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13691 will certainly notice it. But if the bug is incorrect output, we might
13692 not notice unless it is glaringly wrong. You might as well not give us
13693 a chance to make a mistake.
13695 Even if the problem you experience is a fatal signal, you should still
13696 say so explicitly. Suppose something strange is going on, such as, your
13697 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13698 the C library on your system. (This has happened!) Your copy might
13699 crash and ours would not. If you told us to expect a crash, then when
13700 ours fails to crash, we would know that the bug was not happening for
13701 us. If you had not told us to expect a crash, then we would not be able
13702 to draw any conclusion from our observations.
13705 If you wish to suggest changes to the @value{GDBN} source, send us context
13706 diffs. If you even discuss something in the @value{GDBN} source, refer to
13707 it by context, not by line number.
13709 The line numbers in our development sources will not match those in your
13710 sources. Your line numbers would convey no useful information to us.
13714 Here are some things that are not necessary:
13718 A description of the envelope of the bug.
13720 Often people who encounter a bug spend a lot of time investigating
13721 which changes to the input file will make the bug go away and which
13722 changes will not affect it.
13724 This is often time consuming and not very useful, because the way we
13725 will find the bug is by running a single example under the debugger
13726 with breakpoints, not by pure deduction from a series of examples.
13727 We recommend that you save your time for something else.
13729 Of course, if you can find a simpler example to report @emph{instead}
13730 of the original one, that is a convenience for us. Errors in the
13731 output will be easier to spot, running under the debugger will take
13732 less time, and so on.
13734 However, simplification is not vital; if you do not want to do this,
13735 report the bug anyway and send us the entire test case you used.
13738 A patch for the bug.
13740 A patch for the bug does help us if it is a good one. But do not omit
13741 the necessary information, such as the test case, on the assumption that
13742 a patch is all we need. We might see problems with your patch and decide
13743 to fix the problem another way, or we might not understand it at all.
13745 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13746 construct an example that will make the program follow a certain path
13747 through the code. If you do not send us the example, we will not be able
13748 to construct one, so we will not be able to verify that the bug is fixed.
13750 And if we cannot understand what bug you are trying to fix, or why your
13751 patch should be an improvement, we will not install it. A test case will
13752 help us to understand.
13755 A guess about what the bug is or what it depends on.
13757 Such guesses are usually wrong. Even we cannot guess right about such
13758 things without first using the debugger to find the facts.
13761 @c The readline documentation is distributed with the readline code
13762 @c and consists of the two following files:
13764 @c inc-hist.texinfo
13765 @c Use -I with makeinfo to point to the appropriate directory,
13766 @c environment var TEXINPUTS with TeX.
13767 @include rluser.texinfo
13768 @include inc-hist.texinfo
13771 @node Formatting Documentation
13772 @appendix Formatting Documentation
13774 @cindex @value{GDBN} reference card
13775 @cindex reference card
13776 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13777 for printing with PostScript or Ghostscript, in the @file{gdb}
13778 subdirectory of the main source directory@footnote{In
13779 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13780 release.}. If you can use PostScript or Ghostscript with your printer,
13781 you can print the reference card immediately with @file{refcard.ps}.
13783 The release also includes the source for the reference card. You
13784 can format it, using @TeX{}, by typing:
13790 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13791 mode on US ``letter'' size paper;
13792 that is, on a sheet 11 inches wide by 8.5 inches
13793 high. You will need to specify this form of printing as an option to
13794 your @sc{dvi} output program.
13796 @cindex documentation
13798 All the documentation for @value{GDBN} comes as part of the machine-readable
13799 distribution. The documentation is written in Texinfo format, which is
13800 a documentation system that uses a single source file to produce both
13801 on-line information and a printed manual. You can use one of the Info
13802 formatting commands to create the on-line version of the documentation
13803 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13805 @value{GDBN} includes an already formatted copy of the on-line Info
13806 version of this manual in the @file{gdb} subdirectory. The main Info
13807 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13808 subordinate files matching @samp{gdb.info*} in the same directory. If
13809 necessary, you can print out these files, or read them with any editor;
13810 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13811 Emacs or the standalone @code{info} program, available as part of the
13812 @sc{gnu} Texinfo distribution.
13814 If you want to format these Info files yourself, you need one of the
13815 Info formatting programs, such as @code{texinfo-format-buffer} or
13818 If you have @code{makeinfo} installed, and are in the top level
13819 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13820 version @value{GDBVN}), you can make the Info file by typing:
13827 If you want to typeset and print copies of this manual, you need @TeX{},
13828 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13829 Texinfo definitions file.
13831 @TeX{} is a typesetting program; it does not print files directly, but
13832 produces output files called @sc{dvi} files. To print a typeset
13833 document, you need a program to print @sc{dvi} files. If your system
13834 has @TeX{} installed, chances are it has such a program. The precise
13835 command to use depends on your system; @kbd{lpr -d} is common; another
13836 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
13837 require a file name without any extension or a @samp{.dvi} extension.
13839 @TeX{} also requires a macro definitions file called
13840 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
13841 written in Texinfo format. On its own, @TeX{} cannot either read or
13842 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
13843 and is located in the @file{gdb-@var{version-number}/texinfo}
13846 If you have @TeX{} and a @sc{dvi} printer program installed, you can
13847 typeset and print this manual. First switch to the the @file{gdb}
13848 subdirectory of the main source directory (for example, to
13849 @file{gdb-@value{GDBVN}/gdb}) and type:
13855 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
13857 @node Installing GDB
13858 @appendix Installing @value{GDBN}
13859 @cindex configuring @value{GDBN}
13860 @cindex installation
13862 @value{GDBN} comes with a @code{configure} script that automates the process
13863 of preparing @value{GDBN} for installation; you can then use @code{make} to
13864 build the @code{gdb} program.
13866 @c irrelevant in info file; it's as current as the code it lives with.
13867 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
13868 look at the @file{README} file in the sources; we may have improved the
13869 installation procedures since publishing this manual.}
13872 The @value{GDBN} distribution includes all the source code you need for
13873 @value{GDBN} in a single directory, whose name is usually composed by
13874 appending the version number to @samp{gdb}.
13876 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
13877 @file{gdb-@value{GDBVN}} directory. That directory contains:
13880 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
13881 script for configuring @value{GDBN} and all its supporting libraries
13883 @item gdb-@value{GDBVN}/gdb
13884 the source specific to @value{GDBN} itself
13886 @item gdb-@value{GDBVN}/bfd
13887 source for the Binary File Descriptor library
13889 @item gdb-@value{GDBVN}/include
13890 @sc{gnu} include files
13892 @item gdb-@value{GDBVN}/libiberty
13893 source for the @samp{-liberty} free software library
13895 @item gdb-@value{GDBVN}/opcodes
13896 source for the library of opcode tables and disassemblers
13898 @item gdb-@value{GDBVN}/readline
13899 source for the @sc{gnu} command-line interface
13901 @item gdb-@value{GDBVN}/glob
13902 source for the @sc{gnu} filename pattern-matching subroutine
13904 @item gdb-@value{GDBVN}/mmalloc
13905 source for the @sc{gnu} memory-mapped malloc package
13908 The simplest way to configure and build @value{GDBN} is to run @code{configure}
13909 from the @file{gdb-@var{version-number}} source directory, which in
13910 this example is the @file{gdb-@value{GDBVN}} directory.
13912 First switch to the @file{gdb-@var{version-number}} source directory
13913 if you are not already in it; then run @code{configure}. Pass the
13914 identifier for the platform on which @value{GDBN} will run as an
13920 cd gdb-@value{GDBVN}
13921 ./configure @var{host}
13926 where @var{host} is an identifier such as @samp{sun4} or
13927 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
13928 (You can often leave off @var{host}; @code{configure} tries to guess the
13929 correct value by examining your system.)
13931 Running @samp{configure @var{host}} and then running @code{make} builds the
13932 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
13933 libraries, then @code{gdb} itself. The configured source files, and the
13934 binaries, are left in the corresponding source directories.
13937 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
13938 system does not recognize this automatically when you run a different
13939 shell, you may need to run @code{sh} on it explicitly:
13942 sh configure @var{host}
13945 If you run @code{configure} from a directory that contains source
13946 directories for multiple libraries or programs, such as the
13947 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
13948 creates configuration files for every directory level underneath (unless
13949 you tell it not to, with the @samp{--norecursion} option).
13951 You can run the @code{configure} script from any of the
13952 subordinate directories in the @value{GDBN} distribution if you only want to
13953 configure that subdirectory, but be sure to specify a path to it.
13955 For example, with version @value{GDBVN}, type the following to configure only
13956 the @code{bfd} subdirectory:
13960 cd gdb-@value{GDBVN}/bfd
13961 ../configure @var{host}
13965 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
13966 However, you should make sure that the shell on your path (named by
13967 the @samp{SHELL} environment variable) is publicly readable. Remember
13968 that @value{GDBN} uses the shell to start your program---some systems refuse to
13969 let @value{GDBN} debug child processes whose programs are not readable.
13972 * Separate Objdir:: Compiling @value{GDBN} in another directory
13973 * Config Names:: Specifying names for hosts and targets
13974 * Configure Options:: Summary of options for configure
13977 @node Separate Objdir
13978 @section Compiling @value{GDBN} in another directory
13980 If you want to run @value{GDBN} versions for several host or target machines,
13981 you need a different @code{gdb} compiled for each combination of
13982 host and target. @code{configure} is designed to make this easy by
13983 allowing you to generate each configuration in a separate subdirectory,
13984 rather than in the source directory. If your @code{make} program
13985 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
13986 @code{make} in each of these directories builds the @code{gdb}
13987 program specified there.
13989 To build @code{gdb} in a separate directory, run @code{configure}
13990 with the @samp{--srcdir} option to specify where to find the source.
13991 (You also need to specify a path to find @code{configure}
13992 itself from your working directory. If the path to @code{configure}
13993 would be the same as the argument to @samp{--srcdir}, you can leave out
13994 the @samp{--srcdir} option; it is assumed.)
13996 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
13997 separate directory for a Sun 4 like this:
14001 cd gdb-@value{GDBVN}
14004 ../gdb-@value{GDBVN}/configure sun4
14009 When @code{configure} builds a configuration using a remote source
14010 directory, it creates a tree for the binaries with the same structure
14011 (and using the same names) as the tree under the source directory. In
14012 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14013 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14014 @file{gdb-sun4/gdb}.
14016 One popular reason to build several @value{GDBN} configurations in separate
14017 directories is to configure @value{GDBN} for cross-compiling (where
14018 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14019 programs that run on another machine---the @dfn{target}).
14020 You specify a cross-debugging target by
14021 giving the @samp{--target=@var{target}} option to @code{configure}.
14023 When you run @code{make} to build a program or library, you must run
14024 it in a configured directory---whatever directory you were in when you
14025 called @code{configure} (or one of its subdirectories).
14027 The @code{Makefile} that @code{configure} generates in each source
14028 directory also runs recursively. If you type @code{make} in a source
14029 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14030 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14031 will build all the required libraries, and then build GDB.
14033 When you have multiple hosts or targets configured in separate
14034 directories, you can run @code{make} on them in parallel (for example,
14035 if they are NFS-mounted on each of the hosts); they will not interfere
14039 @section Specifying names for hosts and targets
14041 The specifications used for hosts and targets in the @code{configure}
14042 script are based on a three-part naming scheme, but some short predefined
14043 aliases are also supported. The full naming scheme encodes three pieces
14044 of information in the following pattern:
14047 @var{architecture}-@var{vendor}-@var{os}
14050 For example, you can use the alias @code{sun4} as a @var{host} argument,
14051 or as the value for @var{target} in a @code{--target=@var{target}}
14052 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14054 The @code{configure} script accompanying @value{GDBN} does not provide
14055 any query facility to list all supported host and target names or
14056 aliases. @code{configure} calls the Bourne shell script
14057 @code{config.sub} to map abbreviations to full names; you can read the
14058 script, if you wish, or you can use it to test your guesses on
14059 abbreviations---for example:
14062 % sh config.sub i386-linux
14064 % sh config.sub alpha-linux
14065 alpha-unknown-linux-gnu
14066 % sh config.sub hp9k700
14068 % sh config.sub sun4
14069 sparc-sun-sunos4.1.1
14070 % sh config.sub sun3
14071 m68k-sun-sunos4.1.1
14072 % sh config.sub i986v
14073 Invalid configuration `i986v': machine `i986v' not recognized
14077 @code{config.sub} is also distributed in the @value{GDBN} source
14078 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14080 @node Configure Options
14081 @section @code{configure} options
14083 Here is a summary of the @code{configure} options and arguments that
14084 are most often useful for building @value{GDBN}. @code{configure} also has
14085 several other options not listed here. @inforef{What Configure
14086 Does,,configure.info}, for a full explanation of @code{configure}.
14089 configure @r{[}--help@r{]}
14090 @r{[}--prefix=@var{dir}@r{]}
14091 @r{[}--exec-prefix=@var{dir}@r{]}
14092 @r{[}--srcdir=@var{dirname}@r{]}
14093 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14094 @r{[}--target=@var{target}@r{]}
14099 You may introduce options with a single @samp{-} rather than
14100 @samp{--} if you prefer; but you may abbreviate option names if you use
14105 Display a quick summary of how to invoke @code{configure}.
14107 @item --prefix=@var{dir}
14108 Configure the source to install programs and files under directory
14111 @item --exec-prefix=@var{dir}
14112 Configure the source to install programs under directory
14115 @c avoid splitting the warning from the explanation:
14117 @item --srcdir=@var{dirname}
14118 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14119 @code{make} that implements the @code{VPATH} feature.}@*
14120 Use this option to make configurations in directories separate from the
14121 @value{GDBN} source directories. Among other things, you can use this to
14122 build (or maintain) several configurations simultaneously, in separate
14123 directories. @code{configure} writes configuration specific files in
14124 the current directory, but arranges for them to use the source in the
14125 directory @var{dirname}. @code{configure} creates directories under
14126 the working directory in parallel to the source directories below
14129 @item --norecursion
14130 Configure only the directory level where @code{configure} is executed; do not
14131 propagate configuration to subdirectories.
14133 @item --target=@var{target}
14134 Configure @value{GDBN} for cross-debugging programs running on the specified
14135 @var{target}. Without this option, @value{GDBN} is configured to debug
14136 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14138 There is no convenient way to generate a list of all available targets.
14140 @item @var{host} @dots{}
14141 Configure @value{GDBN} to run on the specified @var{host}.
14143 There is no convenient way to generate a list of all available hosts.
14146 There are many other options available as well, but they are generally
14147 needed for special purposes only.
14149 @node Maintenance Commands
14150 @appendix Maintenance Commands
14151 @cindex maintenance commands
14152 @cindex internal commands
14154 In addition to commands intended for @value{GDBN} users, @value{GDBN}
14155 includes a number of commands intended for @value{GDBN} developers.
14156 These commands are provided here for reference.
14159 @kindex maint info breakpoints
14160 @item @anchor{maint info breakpoints}maint info breakpoints
14161 Using the same format as @samp{info breakpoints}, display both the
14162 breakpoints you've set explicitly, and those @value{GDBN} is using for
14163 internal purposes. Internal breakpoints are shown with negative
14164 breakpoint numbers. The type column identifies what kind of breakpoint
14169 Normal, explicitly set breakpoint.
14172 Normal, explicitly set watchpoint.
14175 Internal breakpoint, used to handle correctly stepping through
14176 @code{longjmp} calls.
14178 @item longjmp resume
14179 Internal breakpoint at the target of a @code{longjmp}.
14182 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
14185 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
14188 Shared library events.
14195 @node Remote Protocol
14196 @appendix @value{GDBN} Remote Serial Protocol
14198 There may be occasions when you need to know something about the
14199 protocol---for example, if there is only one serial port to your target
14200 machine, you might want your program to do something special if it
14201 recognizes a packet meant for @value{GDBN}.
14203 In the examples below, @samp{<-} and @samp{->} are used to indicate
14204 transmitted and received data respectfully.
14206 @cindex protocol, @value{GDBN} remote serial
14207 @cindex serial protocol, @value{GDBN} remote
14208 @cindex remote serial protocol
14209 All @value{GDBN} commands and responses (other than acknowledgments) are
14210 sent as a @var{packet}. A @var{packet} is introduced with the character
14211 @samp{$}, the actual @var{packet-data}, and the terminating character
14212 @samp{#} followed by a two-digit @var{checksum}:
14215 @code{$}@var{packet-data}@code{#}@var{checksum}
14219 @cindex checksum, for @value{GDBN} remote
14221 The two-digit @var{checksum} is computed as the modulo 256 sum of all
14222 characters between the leading @samp{$} and the trailing @samp{#} (an
14223 eight bit unsigned checksum).
14225 Implementors should note that prior to @value{GDBN} 5.0 the protocol
14226 specification also included an optional two-digit @var{sequence-id}:
14229 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
14232 @cindex sequence-id, for @value{GDBN} remote
14234 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
14235 has never output @var{sequence-id}s. Stubs that handle packets added
14236 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
14238 @cindex acknowledgment, for @value{GDBN} remote
14239 When either the host or the target machine receives a packet, the first
14240 response expected is an acknowledgment: either @samp{+} (to indicate
14241 the package was received correctly) or @samp{-} (to request
14245 <- @code{$}@var{packet-data}@code{#}@var{checksum}
14250 The host (@value{GDBN}) sends @var{command}s, and the target (the
14251 debugging stub incorporated in your program) sends a @var{response}. In
14252 the case of step and continue @var{command}s, the response is only sent
14253 when the operation has completed (the target has again stopped).
14255 @var{packet-data} consists of a sequence of characters with the
14256 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
14259 Fields within the packet should be separated using @samp{,} @samp{;} or
14260 @samp{:}. Except where otherwise noted all numbers are represented in
14261 HEX with leading zeros suppressed.
14263 Implementors should note that prior to @value{GDBN} 5.0, the character
14264 @samp{:} could not appear as the third character in a packet (as it
14265 would potentially conflict with the @var{sequence-id}).
14267 Response @var{data} can be run-length encoded to save space. A @samp{*}
14268 means that the next character is an @sc{ascii} encoding giving a repeat count
14269 which stands for that many repetitions of the character preceding the
14270 @samp{*}. The encoding is @code{n+29}, yielding a printable character
14271 where @code{n >=3} (which is where rle starts to win). The printable
14272 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
14273 value greater than 126 should not be used.
14275 Some remote systems have used a different run-length encoding mechanism
14276 loosely refered to as the cisco encoding. Following the @samp{*}
14277 character are two hex digits that indicate the size of the packet.
14284 means the same as "0000".
14286 The error response returned for some packets includes a two character
14287 error number. That number is not well defined.
14289 For any @var{command} not supported by the stub, an empty response
14290 (@samp{$#00}) should be returned. That way it is possible to extend the
14291 protocol. A newer @value{GDBN} can tell if a packet is supported based
14294 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
14295 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
14298 Below is a complete list of all currently defined @var{command}s and
14299 their corresponding response @var{data}:
14301 @multitable @columnfractions .30 .30 .40
14306 @item extended mode
14309 Enable extended mode. In extended mode, the remote server is made
14310 persistent. The @samp{R} packet is used to restart the program being
14313 @tab reply @samp{OK}
14315 The remote target both supports and has enabled extended mode.
14320 Indicate the reason the target halted. The reply is the same as for step
14329 @tab Reserved for future use
14331 @item set program arguments @strong{(reserved)}
14332 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
14337 Initialized @samp{argv[]} array passed into program. @var{arglen}
14338 specifies the number of bytes in the hex encoded byte stream @var{arg}.
14339 See @file{gdbserver} for more details.
14341 @tab reply @code{OK}
14343 @tab reply @code{E}@var{NN}
14345 @item set baud @strong{(deprecated)}
14346 @tab @code{b}@var{baud}
14348 Change the serial line speed to @var{baud}. JTC: @emph{When does the
14349 transport layer state change? When it's received, or after the ACK is
14350 transmitted. In either case, there are problems if the command or the
14351 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
14352 to add something like this, and get it working for the first time, they
14353 ought to modify ser-unix.c to send some kind of out-of-band message to a
14354 specially-setup stub and have the switch happen "in between" packets, so
14355 that from remote protocol's point of view, nothing actually
14358 @item set breakpoint @strong{(deprecated)}
14359 @tab @code{B}@var{addr},@var{mode}
14361 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
14362 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
14366 @tab @code{c}@var{addr}
14368 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14374 @item continue with signal
14375 @tab @code{C}@var{sig}@code{;}@var{addr}
14377 Continue with signal @var{sig} (hex signal number). If
14378 @code{;}@var{addr} is omitted, resume at same address.
14383 @item toggle debug @strong{(deprecated)}
14391 Detach @value{GDBN} from the remote system. Sent to the remote target before
14392 @value{GDBN} disconnects.
14394 @tab reply @emph{no response}
14396 @value{GDBN} does not check for any response after sending this packet.
14400 @tab Reserved for future use
14404 @tab Reserved for future use
14408 @tab Reserved for future use
14412 @tab Reserved for future use
14414 @item read registers
14416 @tab Read general registers.
14418 @tab reply @var{XX...}
14420 Each byte of register data is described by two hex digits. The bytes
14421 with the register are transmitted in target byte order. The size of
14422 each register and their position within the @samp{g} @var{packet} are
14423 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
14424 @var{REGISTER_NAME} macros. The specification of several standard
14425 @code{g} packets is specified below.
14427 @tab @code{E}@var{NN}
14431 @tab @code{G}@var{XX...}
14433 See @samp{g} for a description of the @var{XX...} data.
14435 @tab reply @code{OK}
14438 @tab reply @code{E}@var{NN}
14443 @tab Reserved for future use
14446 @tab @code{H}@var{c}@var{t...}
14448 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
14449 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
14450 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
14451 thread used in other operations. If zero, pick a thread, any thread.
14453 @tab reply @code{OK}
14456 @tab reply @code{E}@var{NN}
14460 @c 'H': How restrictive (or permissive) is the thread model. If a
14461 @c thread is selected and stopped, are other threads allowed
14462 @c to continue to execute? As I mentioned above, I think the
14463 @c semantics of each command when a thread is selected must be
14464 @c described. For example:
14466 @c 'g': If the stub supports threads and a specific thread is
14467 @c selected, returns the register block from that thread;
14468 @c otherwise returns current registers.
14470 @c 'G' If the stub supports threads and a specific thread is
14471 @c selected, sets the registers of the register block of
14472 @c that thread; otherwise sets current registers.
14474 @item cycle step @strong{(draft)}
14475 @tab @code{i}@var{addr}@code{,}@var{nnn}
14477 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
14478 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
14479 step starting at that address.
14481 @item signal then cycle step @strong{(reserved)}
14484 See @samp{i} and @samp{S} for likely syntax and semantics.
14488 @tab Reserved for future use
14492 @tab Reserved for future use
14497 FIXME: @emph{There is no description of how to operate when a specific
14498 thread context has been selected (i.e.@: does 'k' kill only that thread?)}.
14502 @tab Reserved for future use
14506 @tab Reserved for future use
14509 @tab @code{m}@var{addr}@code{,}@var{length}
14511 Read @var{length} bytes of memory starting at address @var{addr}.
14512 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
14513 using word alligned accesses. FIXME: @emph{A word aligned memory
14514 transfer mechanism is needed.}
14516 @tab reply @var{XX...}
14518 @var{XX...} is mem contents. Can be fewer bytes than requested if able
14519 to read only part of the data. Neither @value{GDBN} nor the stub assume that
14520 sized memory transfers are assumed using word alligned accesses. FIXME:
14521 @emph{A word aligned memory transfer mechanism is needed.}
14523 @tab reply @code{E}@var{NN}
14524 @tab @var{NN} is errno
14527 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
14529 Write @var{length} bytes of memory starting at address @var{addr}.
14530 @var{XX...} is the data.
14532 @tab reply @code{OK}
14535 @tab reply @code{E}@var{NN}
14537 for an error (this includes the case where only part of the data was
14542 @tab Reserved for future use
14546 @tab Reserved for future use
14550 @tab Reserved for future use
14554 @tab Reserved for future use
14556 @item read reg @strong{(reserved)}
14557 @tab @code{p}@var{n...}
14559 See write register.
14561 @tab return @var{r....}
14562 @tab The hex encoded value of the register in target byte order.
14565 @tab @code{P}@var{n...}@code{=}@var{r...}
14567 Write register @var{n...} with value @var{r...}, which contains two hex
14568 digits for each byte in the register (target byte order).
14570 @tab reply @code{OK}
14573 @tab reply @code{E}@var{NN}
14576 @item general query
14577 @tab @code{q}@var{query}
14579 Request info about @var{query}. In general @value{GDBN} queries
14580 have a leading upper case letter. Custom vendor queries should use a
14581 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
14582 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
14583 must ensure that they match the full @var{query} name.
14585 @tab reply @code{XX...}
14586 @tab Hex encoded data from query. The reply can not be empty.
14588 @tab reply @code{E}@var{NN}
14592 @tab Indicating an unrecognized @var{query}.
14595 @tab @code{Q}@var{var}@code{=}@var{val}
14597 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
14598 naming conventions.
14600 @item reset @strong{(deprecated)}
14603 Reset the entire system.
14605 @item remote restart
14606 @tab @code{R}@var{XX}
14608 Restart the program being debugged. @var{XX}, while needed, is ignored.
14609 This packet is only available in extended mode.
14614 The @samp{R} packet has no reply.
14617 @tab @code{s}@var{addr}
14619 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14625 @item step with signal
14626 @tab @code{S}@var{sig}@code{;}@var{addr}
14628 Like @samp{C} but step not continue.
14634 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
14636 Search backwards starting at address @var{addr} for a match with pattern
14637 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
14638 bytes. @var{addr} must be at least 3 digits.
14641 @tab @code{T}@var{XX}
14642 @tab Find out if the thread XX is alive.
14644 @tab reply @code{OK}
14645 @tab thread is still alive
14647 @tab reply @code{E}@var{NN}
14648 @tab thread is dead
14652 @tab Reserved for future use
14656 @tab Reserved for future use
14660 @tab Reserved for future use
14664 @tab Reserved for future use
14668 @tab Reserved for future use
14672 @tab Reserved for future use
14676 @tab Reserved for future use
14678 @item write mem (binary)
14679 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
14681 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
14682 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
14683 escaped using @code{0x7d}.
14685 @tab reply @code{OK}
14688 @tab reply @code{E}@var{NN}
14693 @tab Reserved for future use
14697 @tab Reserved for future use
14699 @item remove break or watchpoint @strong{(draft)}
14700 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
14704 @item insert break or watchpoint @strong{(draft)}
14705 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
14707 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
14708 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
14709 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
14710 bytes. For a software breakpoint, @var{length} specifies the size of
14711 the instruction to be patched. For hardware breakpoints and watchpoints
14712 @var{length} specifies the memory region to be monitored. To avoid
14713 potential problems with duplicate packets, the operations should be
14714 implemented in an idempotent way.
14716 @tab reply @code{E}@var{NN}
14719 @tab reply @code{OK}
14723 @tab If not supported.
14727 @tab Reserved for future use
14731 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
14732 receive any of the below as a reply. In the case of the @samp{C},
14733 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
14734 when the target halts. In the below the exact meaning of @samp{signal
14735 number} is poorly defined. In general one of the UNIX signal numbering
14736 conventions is used.
14738 @multitable @columnfractions .4 .6
14740 @item @code{S}@var{AA}
14741 @tab @var{AA} is the signal number
14743 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
14745 @var{AA} = two hex digit signal number; @var{n...} = register number
14746 (hex), @var{r...} = target byte ordered register contents, size defined
14747 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
14748 thread process ID, this is a hex integer; @var{n...} = other string not
14749 starting with valid hex digit. @value{GDBN} should ignore this
14750 @var{n...}, @var{r...} pair and go on to the next. This way we can
14751 extend the protocol.
14753 @item @code{W}@var{AA}
14755 The process exited, and @var{AA} is the exit status. This is only
14756 applicable for certains sorts of targets.
14758 @item @code{X}@var{AA}
14760 The process terminated with signal @var{AA}.
14762 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
14764 @var{AA} = signal number; @var{t...} = address of symbol "_start";
14765 @var{d...} = base of data section; @var{b...} = base of bss section.
14766 @emph{Note: only used by Cisco Systems targets. The difference between
14767 this reply and the "qOffsets" query is that the 'N' packet may arrive
14768 spontaneously whereas the 'qOffsets' is a query initiated by the host
14771 @item @code{O}@var{XX...}
14773 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
14774 while the program is running and the debugger should continue to wait
14779 The following set and query packets have already been defined.
14781 @multitable @columnfractions .2 .2 .6
14783 @item current thread
14784 @tab @code{q}@code{C}
14785 @tab Return the current thread id.
14787 @tab reply @code{QC}@var{pid}
14789 Where @var{pid} is a HEX encoded 16 bit process id.
14792 @tab Any other reply implies the old pid.
14794 @item all thread ids
14795 @tab @code{q}@code{fThreadInfo}
14797 @tab @code{q}@code{sThreadInfo}
14799 Obtain a list of active thread ids from the target (OS). Since there
14800 may be too many active threads to fit into one reply packet, this query
14801 works iteratively: it may require more than one query/reply sequence to
14802 obtain the entire list of threads. The first query of the sequence will
14803 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
14804 sequence will be the @code{qs}@code{ThreadInfo} query.
14807 @tab NOTE: replaces the @code{qL} query (see below).
14809 @tab reply @code{m}@var{<id>}
14810 @tab A single thread id
14812 @tab reply @code{m}@var{<id>},@var{<id>...}
14813 @tab a comma-separated list of thread ids
14815 @tab reply @code{l}
14816 @tab (lower case 'el') denotes end of list.
14820 In response to each query, the target will reply with a list of one
14821 or more thread ids, in big-endian hex, separated by commas. GDB will
14822 respond to each reply with a request for more thread ids (using the
14823 @code{qs} form of the query), until the target responds with @code{l}
14824 (lower-case el, for @code{'last'}).
14826 @item extra thread info
14827 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
14832 Where @var{<id>} is a thread-id in big-endian hex.
14833 Obtain a printable string description of a thread's attributes from
14834 the target OS. This string may contain anything that the target OS
14835 thinks is interesting for @value{GDBN} to tell the user about the thread.
14836 The string is displayed in @value{GDBN}'s @samp{info threads} display.
14837 Some examples of possible thread extra info strings are "Runnable", or
14838 "Blocked on Mutex".
14840 @tab reply @var{XX...}
14842 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
14843 printable string containing the extra information about the thread's
14846 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
14847 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
14852 Obtain thread information from RTOS. Where: @var{startflag} (one hex
14853 digit) is one to indicate the first query and zero to indicate a
14854 subsequent query; @var{threadcount} (two hex digits) is the maximum
14855 number of threads the response packet can contain; and @var{nextthread}
14856 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
14857 returned in the response as @var{argthread}.
14860 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
14863 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
14868 Where: @var{count} (two hex digits) is the number of threads being
14869 returned; @var{done} (one hex digit) is zero to indicate more threads
14870 and one indicates no further threads; @var{argthreadid} (eight hex
14871 digits) is @var{nextthread} from the request packet; @var{thread...} is
14872 a sequence of thread IDs from the target. @var{threadid} (eight hex
14873 digits). See @code{remote.c:parse_threadlist_response()}.
14875 @item compute CRC of memory block
14876 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
14879 @tab reply @code{E}@var{NN}
14880 @tab An error (such as memory fault)
14882 @tab reply @code{C}@var{CRC32}
14883 @tab A 32 bit cyclic redundancy check of the specified memory region.
14885 @item query sect offs
14886 @tab @code{q}@code{Offsets}
14888 Get section offsets that the target used when re-locating the downloaded
14889 image. @emph{Note: while a @code{Bss} offset is included in the
14890 response, @value{GDBN} ignores this and instead applies the @code{Data}
14891 offset to the @code{Bss} section.}
14893 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
14895 @item thread info request
14896 @tab @code{q}@code{P}@var{mode}@var{threadid}
14901 Returns information on @var{threadid}. Where: @var{mode} is a hex
14902 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
14906 See @code{remote.c:remote_unpack_thread_info_response()}.
14908 @item remote command
14909 @tab @code{q}@code{Rcmd,}@var{COMMAND}
14914 @var{COMMAND} (hex encoded) is passed to the local interpreter for
14915 execution. Invalid commands should be reported using the output string.
14916 Before the final result packet, the target may also respond with a
14917 number of intermediate @code{O}@var{OUTPUT} console output
14918 packets. @emph{Implementors should note that providing access to a
14919 stubs's interpreter may have security implications}.
14921 @tab reply @code{OK}
14923 A command response with no output.
14925 @tab reply @var{OUTPUT}
14927 A command response with the hex encoded output string @var{OUTPUT}.
14929 @tab reply @code{E}@var{NN}
14931 Indicate a badly formed request.
14936 When @samp{q}@samp{Rcmd} is not recognized.
14938 @item symbol lookup
14939 @tab @code{qSymbol::}
14941 Notify the target that @value{GDBN} is prepared to serve symbol lookup
14942 requests. Accept requests from the target for the values of symbols.
14947 @tab reply @code{OK}
14949 The target does not need to look up any (more) symbols.
14951 @tab reply @code{qSymbol:}@var{sym_name}
14955 The target requests the value of symbol @var{sym_name} (hex encoded).
14956 @value{GDBN} may provide the value by using the
14957 @code{qSymbol:}@var{sym_value}:@var{sym_name}
14958 message, described below.
14961 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
14965 Set the value of SYM_NAME to SYM_VALUE.
14969 @var{sym_name} (hex encoded) is the name of a symbol whose value
14970 the target has previously requested.
14974 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
14975 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
14976 field will be empty.
14978 @tab reply @code{OK}
14980 The target does not need to look up any (more) symbols.
14982 @tab reply @code{qSymbol:}@var{sym_name}
14986 The target requests the value of a new symbol @var{sym_name} (hex encoded).
14987 @value{GDBN} will continue to supply the values of symbols (if available),
14988 until the target ceases to request them.
14992 The following @samp{g}/@samp{G} packets have previously been defined.
14993 In the below, some thirty-two bit registers are transferred as sixty-four
14994 bits. Those registers should be zero/sign extended (which?) to fill the
14995 space allocated. Register bytes are transfered in target byte order.
14996 The two nibbles within a register byte are transfered most-significant -
14999 @multitable @columnfractions .5 .5
15003 All registers are transfered as thirty-two bit quantities in the order:
15004 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
15005 registers; fsr; fir; fp.
15009 All registers are transfered as sixty-four bit quantities (including
15010 thirty-two bit registers such as @code{sr}). The ordering is the same
15015 Example sequence of a target being re-started. Notice how the restart
15016 does not get any direct output:
15021 @emph{target restarts}
15024 -> @code{T001:1234123412341234}
15028 Example sequence of a target being stepped by a single instruction:
15036 -> @code{T001:1234123412341234}
15054 % I think something like @colophon should be in texinfo. In the
15056 \long\def\colophon{\hbox to0pt{}\vfill
15057 \centerline{The body of this manual is set in}
15058 \centerline{\fontname\tenrm,}
15059 \centerline{with headings in {\bf\fontname\tenbf}}
15060 \centerline{and examples in {\tt\fontname\tentt}.}
15061 \centerline{{\it\fontname\tenit\/},}
15062 \centerline{{\bf\fontname\tenbf}, and}
15063 \centerline{{\sl\fontname\tensl\/}}
15064 \centerline{are used for emphasis.}\vfill}
15066 % Blame: doc@cygnus.com, 1991.