1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
4 @c Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
25 @c readline appendices use @vindex, @findex and @ftable,
26 @c annotate.texi and gdbmi use @findex.
30 @c !!set GDB manual's edition---not the same as GDB version!
33 @c !!set GDB manual's revision date
36 @c THIS MANUAL REQUIRES TEXINFO 3.12 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Programming & development tools.
42 * Gdb: (gdb). The @sc{gnu} debugger.
46 This file documents the @sc{gnu} debugger @value{GDBN}.
49 This is the @value{EDITION} Edition, @value{DATE},
50 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
51 for @value{GDBN} Version @value{GDBVN}.
53 Copyright (C) 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
54 Free Software Foundation, Inc.
56 Permission is granted to copy, distribute and/or modify this document
57 under the terms of the GNU Free Documentation License, Version 1.1 or
58 any later version published by the Free Software Foundation; with the
59 Invariant Sections being ``A Sample GDB Session'' and ``Free
60 Software'', with the Front-Cover texts being ``A GNU Manual,'' and
61 with the Back-Cover Texts as in (a) below.
63 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
64 this GNU Manual, like GNU software. Copies published by the Free
65 Software Foundation raise funds for GNU development.''
69 @title Debugging with @value{GDBN}
70 @subtitle The @sc{gnu} Source-Level Debugger
72 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
73 @subtitle @value{DATE}
74 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
78 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
79 \hfill {\it Debugging with @value{GDBN}}\par
80 \hfill \TeX{}info \texinfoversion\par
84 @vskip 0pt plus 1filll
85 Copyright @copyright{} 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
86 Free Software Foundation, Inc.
88 Published by the Free Software Foundation @*
89 59 Temple Place - Suite 330, @*
90 Boston, MA 02111-1307 USA @*
93 Permission is granted to copy, distribute and/or modify this document
94 under the terms of the GNU Free Documentation License, Version 1.1 or
95 any later version published by the Free Software Foundation; with the
96 Invariant Sections being ``A Sample GDB Session'' and ``Free
97 Software'', with the Front-Cover texts being ``A GNU Manual,'' and
98 with the Back-Cover Texts as in (a) below.
100 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
101 this GNU Manual, like GNU software. Copies published by the Free
102 Software Foundation raise funds for GNU development.''
107 @node Top, Summary, (dir), (dir)
109 @top Debugging with @value{GDBN}
111 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
113 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
116 Copyright (C) 1988-2001 Free Software Foundation, Inc.
119 * Summary:: Summary of @value{GDBN}
120 * Sample Session:: A sample @value{GDBN} session
122 * Invocation:: Getting in and out of @value{GDBN}
123 * Commands:: @value{GDBN} commands
124 * Running:: Running programs under @value{GDBN}
125 * Stopping:: Stopping and continuing
126 * Stack:: Examining the stack
127 * Source:: Examining source files
128 * Data:: Examining data
129 * Tracepoints:: Debugging remote targets non-intrusively
131 * Languages:: Using @value{GDBN} with different languages
133 * Symbols:: Examining the symbol table
134 * Altering:: Altering execution
135 * GDB Files:: @value{GDBN} files
136 * Targets:: Specifying a debugging target
137 * Configurations:: Configuration-specific information
138 * Controlling GDB:: Controlling @value{GDBN}
139 * Sequences:: Canned sequences of commands
140 * TUI:: @value{GDBN} Text User Interface
141 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
142 * Annotations:: @value{GDBN}'s annotation interface.
143 * GDB/MI:: @value{GDBN}'s Machine Interface.
145 * GDB Bugs:: Reporting bugs in @value{GDBN}
146 * Formatting Documentation:: How to format and print @value{GDBN} documentation
148 * Command Line Editing:: Command Line Editing
149 * Using History Interactively:: Using History Interactively
150 * Installing GDB:: Installing GDB
156 @c the replication sucks, but this avoids a texinfo 3.12 lameness
161 @top Debugging with @value{GDBN}
163 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
165 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
168 Copyright (C) 1988-2000 Free Software Foundation, Inc.
171 * Summary:: Summary of @value{GDBN}
172 * Sample Session:: A sample @value{GDBN} session
174 * Invocation:: Getting in and out of @value{GDBN}
175 * Commands:: @value{GDBN} commands
176 * Running:: Running programs under @value{GDBN}
177 * Stopping:: Stopping and continuing
178 * Stack:: Examining the stack
179 * Source:: Examining source files
180 * Data:: Examining data
181 * Tracepoints:: Debugging remote targets non-intrusively
183 * Languages:: Using @value{GDBN} with different languages
185 * Symbols:: Examining the symbol table
186 * Altering:: Altering execution
187 * GDB Files:: @value{GDBN} files
188 * Targets:: Specifying a debugging target
189 * Configurations:: Configuration-specific information
190 * Controlling GDB:: Controlling @value{GDBN}
191 * Sequences:: Canned sequences of commands
192 * TUI:: @value{GDBN} Text User Interface
193 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
194 * Annotations:: @value{GDBN}'s annotation interface.
195 * GDB/MI:: @value{GDBN}'s Machine Interface.
197 * GDB Bugs:: Reporting bugs in @value{GDBN}
198 * Formatting Documentation:: How to format and print @value{GDBN} documentation
200 * Command Line Editing:: Command Line Editing
201 * Using History Interactively:: Using History Interactively
202 * Installing GDB:: Installing GDB
208 @c TeX can handle the contents at the start but makeinfo 3.12 can not
214 @unnumbered Summary of @value{GDBN}
216 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
217 going on ``inside'' another program while it executes---or what another
218 program was doing at the moment it crashed.
220 @value{GDBN} can do four main kinds of things (plus other things in support of
221 these) to help you catch bugs in the act:
225 Start your program, specifying anything that might affect its behavior.
228 Make your program stop on specified conditions.
231 Examine what has happened, when your program has stopped.
234 Change things in your program, so you can experiment with correcting the
235 effects of one bug and go on to learn about another.
238 You can use @value{GDBN} to debug programs written in C and C++.
239 For more information, see @ref{Support,,Supported languages}.
240 For more information, see @ref{C,,C and C++}.
244 Support for Modula-2 and Chill is partial. For information on Modula-2,
245 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
248 Debugging Pascal programs which use sets, subranges, file variables, or
249 nested functions does not currently work. @value{GDBN} does not support
250 entering expressions, printing values, or similar features using Pascal
254 @value{GDBN} can be used to debug programs written in Fortran, although
255 it may be necessary to refer to some variables with a trailing
259 * Free Software:: Freely redistributable software
260 * Contributors:: Contributors to GDB
264 @unnumberedsec Free software
266 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
267 General Public License
268 (GPL). The GPL gives you the freedom to copy or adapt a licensed
269 program---but every person getting a copy also gets with it the
270 freedom to modify that copy (which means that they must get access to
271 the source code), and the freedom to distribute further copies.
272 Typical software companies use copyrights to limit your freedoms; the
273 Free Software Foundation uses the GPL to preserve these freedoms.
275 Fundamentally, the General Public License is a license which says that
276 you have these freedoms and that you cannot take these freedoms away
280 @unnumberedsec Contributors to @value{GDBN}
282 Richard Stallman was the original author of @value{GDBN}, and of many
283 other @sc{gnu} programs. Many others have contributed to its
284 development. This section attempts to credit major contributors. One
285 of the virtues of free software is that everyone is free to contribute
286 to it; with regret, we cannot actually acknowledge everyone here. The
287 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
288 blow-by-blow account.
290 Changes much prior to version 2.0 are lost in the mists of time.
293 @emph{Plea:} Additions to this section are particularly welcome. If you
294 or your friends (or enemies, to be evenhanded) have been unfairly
295 omitted from this list, we would like to add your names!
298 So that they may not regard their many labors as thankless, we
299 particularly thank those who shepherded @value{GDBN} through major
301 Andrew Cagney (releases 5.0 and 5.1);
302 Jim Blandy (release 4.18);
303 Jason Molenda (release 4.17);
304 Stan Shebs (release 4.14);
305 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
306 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
307 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
308 Jim Kingdon (releases 3.5, 3.4, and 3.3);
309 and Randy Smith (releases 3.2, 3.1, and 3.0).
311 Richard Stallman, assisted at various times by Peter TerMaat, Chris
312 Hanson, and Richard Mlynarik, handled releases through 2.8.
314 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
315 in @value{GDBN}, with significant additional contributions from Per
316 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
317 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
318 much general update work leading to release 3.0).
320 @value{GDBN} uses the BFD subroutine library to examine multiple
321 object-file formats; BFD was a joint project of David V.
322 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
324 David Johnson wrote the original COFF support; Pace Willison did
325 the original support for encapsulated COFF.
327 Brent Benson of Harris Computer Systems contributed DWARF2 support.
329 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
330 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
332 Jean-Daniel Fekete contributed Sun 386i support.
333 Chris Hanson improved the HP9000 support.
334 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
335 David Johnson contributed Encore Umax support.
336 Jyrki Kuoppala contributed Altos 3068 support.
337 Jeff Law contributed HP PA and SOM support.
338 Keith Packard contributed NS32K support.
339 Doug Rabson contributed Acorn Risc Machine support.
340 Bob Rusk contributed Harris Nighthawk CX-UX support.
341 Chris Smith contributed Convex support (and Fortran debugging).
342 Jonathan Stone contributed Pyramid support.
343 Michael Tiemann contributed SPARC support.
344 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
345 Pace Willison contributed Intel 386 support.
346 Jay Vosburgh contributed Symmetry support.
348 Andreas Schwab contributed M68K Linux support.
350 Rich Schaefer and Peter Schauer helped with support of SunOS shared
353 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
354 about several machine instruction sets.
356 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
357 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
358 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
359 and RDI targets, respectively.
361 Brian Fox is the author of the readline libraries providing
362 command-line editing and command history.
364 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
365 Modula-2 support, and contributed the Languages chapter of this manual.
367 Fred Fish wrote most of the support for Unix System Vr4.
368 He also enhanced the command-completion support to cover C@t{++} overloaded
371 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
374 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
376 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
378 Toshiba sponsored the support for the TX39 Mips processor.
380 Matsushita sponsored the support for the MN10200 and MN10300 processors.
382 Fujitsu sponsored the support for SPARClite and FR30 processors.
384 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
387 Michael Snyder added support for tracepoints.
389 Stu Grossman wrote gdbserver.
391 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
392 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
394 The following people at the Hewlett-Packard Company contributed
395 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
396 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
397 compiler, and the terminal user interface: Ben Krepp, Richard Title,
398 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
399 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
400 information in this manual.
402 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
403 Robert Hoehne made significant contributions to the DJGPP port.
405 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
406 development since 1991. Cygnus engineers who have worked on @value{GDBN}
407 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
408 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
409 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
410 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
411 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
412 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
413 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
414 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
415 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
416 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
417 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
418 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
419 Zuhn have made contributions both large and small.
423 @chapter A Sample @value{GDBN} Session
425 You can use this manual at your leisure to read all about @value{GDBN}.
426 However, a handful of commands are enough to get started using the
427 debugger. This chapter illustrates those commands.
430 In this sample session, we emphasize user input like this: @b{input},
431 to make it easier to pick out from the surrounding output.
434 @c FIXME: this example may not be appropriate for some configs, where
435 @c FIXME...primary interest is in remote use.
437 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
438 processor) exhibits the following bug: sometimes, when we change its
439 quote strings from the default, the commands used to capture one macro
440 definition within another stop working. In the following short @code{m4}
441 session, we define a macro @code{foo} which expands to @code{0000}; we
442 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
443 same thing. However, when we change the open quote string to
444 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
445 procedure fails to define a new synonym @code{baz}:
454 @b{define(bar,defn(`foo'))}
458 @b{changequote(<QUOTE>,<UNQUOTE>)}
460 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
463 m4: End of input: 0: fatal error: EOF in string
467 Let us use @value{GDBN} to try to see what is going on.
470 $ @b{@value{GDBP} m4}
471 @c FIXME: this falsifies the exact text played out, to permit smallbook
472 @c FIXME... format to come out better.
473 @value{GDBN} is free software and you are welcome to distribute copies
474 of it under certain conditions; type "show copying" to see
476 There is absolutely no warranty for @value{GDBN}; type "show warranty"
479 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
484 @value{GDBN} reads only enough symbol data to know where to find the
485 rest when needed; as a result, the first prompt comes up very quickly.
486 We now tell @value{GDBN} to use a narrower display width than usual, so
487 that examples fit in this manual.
490 (@value{GDBP}) @b{set width 70}
494 We need to see how the @code{m4} built-in @code{changequote} works.
495 Having looked at the source, we know the relevant subroutine is
496 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
497 @code{break} command.
500 (@value{GDBP}) @b{break m4_changequote}
501 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
505 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
506 control; as long as control does not reach the @code{m4_changequote}
507 subroutine, the program runs as usual:
510 (@value{GDBP}) @b{run}
511 Starting program: /work/Editorial/gdb/gnu/m4/m4
519 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
520 suspends execution of @code{m4}, displaying information about the
521 context where it stops.
524 @b{changequote(<QUOTE>,<UNQUOTE>)}
526 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
528 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
532 Now we use the command @code{n} (@code{next}) to advance execution to
533 the next line of the current function.
537 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
542 @code{set_quotes} looks like a promising subroutine. We can go into it
543 by using the command @code{s} (@code{step}) instead of @code{next}.
544 @code{step} goes to the next line to be executed in @emph{any}
545 subroutine, so it steps into @code{set_quotes}.
549 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
551 530 if (lquote != def_lquote)
555 The display that shows the subroutine where @code{m4} is now
556 suspended (and its arguments) is called a stack frame display. It
557 shows a summary of the stack. We can use the @code{backtrace}
558 command (which can also be spelled @code{bt}), to see where we are
559 in the stack as a whole: the @code{backtrace} command displays a
560 stack frame for each active subroutine.
563 (@value{GDBP}) @b{bt}
564 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
566 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
568 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
569 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
571 #4 0x79dc in expand_input () at macro.c:40
572 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
576 We step through a few more lines to see what happens. The first two
577 times, we can use @samp{s}; the next two times we use @code{n} to avoid
578 falling into the @code{xstrdup} subroutine.
582 0x3b5c 532 if (rquote != def_rquote)
584 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
585 def_lquote : xstrdup(lq);
587 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
590 538 len_lquote = strlen(rquote);
594 The last line displayed looks a little odd; we can examine the variables
595 @code{lquote} and @code{rquote} to see if they are in fact the new left
596 and right quotes we specified. We use the command @code{p}
597 (@code{print}) to see their values.
600 (@value{GDBP}) @b{p lquote}
601 $1 = 0x35d40 "<QUOTE>"
602 (@value{GDBP}) @b{p rquote}
603 $2 = 0x35d50 "<UNQUOTE>"
607 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
608 To look at some context, we can display ten lines of source
609 surrounding the current line with the @code{l} (@code{list}) command.
615 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
617 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
620 538 len_lquote = strlen(rquote);
621 539 len_rquote = strlen(lquote);
628 Let us step past the two lines that set @code{len_lquote} and
629 @code{len_rquote}, and then examine the values of those variables.
633 539 len_rquote = strlen(lquote);
636 (@value{GDBP}) @b{p len_lquote}
638 (@value{GDBP}) @b{p len_rquote}
643 That certainly looks wrong, assuming @code{len_lquote} and
644 @code{len_rquote} are meant to be the lengths of @code{lquote} and
645 @code{rquote} respectively. We can set them to better values using
646 the @code{p} command, since it can print the value of
647 any expression---and that expression can include subroutine calls and
651 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
653 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
658 Is that enough to fix the problem of using the new quotes with the
659 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
660 executing with the @code{c} (@code{continue}) command, and then try the
661 example that caused trouble initially:
667 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
674 Success! The new quotes now work just as well as the default ones. The
675 problem seems to have been just the two typos defining the wrong
676 lengths. We allow @code{m4} exit by giving it an EOF as input:
680 Program exited normally.
684 The message @samp{Program exited normally.} is from @value{GDBN}; it
685 indicates @code{m4} has finished executing. We can end our @value{GDBN}
686 session with the @value{GDBN} @code{quit} command.
689 (@value{GDBP}) @b{quit}
693 @chapter Getting In and Out of @value{GDBN}
695 This chapter discusses how to start @value{GDBN}, and how to get out of it.
699 type @samp{@value{GDBP}} to start @value{GDBN}.
701 type @kbd{quit} or @kbd{C-d} to exit.
705 * Invoking GDB:: How to start @value{GDBN}
706 * Quitting GDB:: How to quit @value{GDBN}
707 * Shell Commands:: How to use shell commands inside @value{GDBN}
711 @section Invoking @value{GDBN}
713 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
714 @value{GDBN} reads commands from the terminal until you tell it to exit.
716 You can also run @code{@value{GDBP}} with a variety of arguments and options,
717 to specify more of your debugging environment at the outset.
719 The command-line options described here are designed
720 to cover a variety of situations; in some environments, some of these
721 options may effectively be unavailable.
723 The most usual way to start @value{GDBN} is with one argument,
724 specifying an executable program:
727 @value{GDBP} @var{program}
731 You can also start with both an executable program and a core file
735 @value{GDBP} @var{program} @var{core}
738 You can, instead, specify a process ID as a second argument, if you want
739 to debug a running process:
742 @value{GDBP} @var{program} 1234
746 would attach @value{GDBN} to process @code{1234} (unless you also have a file
747 named @file{1234}; @value{GDBN} does check for a core file first).
749 Taking advantage of the second command-line argument requires a fairly
750 complete operating system; when you use @value{GDBN} as a remote
751 debugger attached to a bare board, there may not be any notion of
752 ``process'', and there is often no way to get a core dump. @value{GDBN}
753 will warn you if it is unable to attach or to read core dumps.
755 You can optionally have @code{@value{GDBP}} pass any arguments after the
756 executable file to the inferior using @code{--args}. This option stops
759 gdb --args gcc -O2 -c foo.c
761 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
762 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
764 You can run @code{@value{GDBP}} without printing the front material, which describes
765 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
772 You can further control how @value{GDBN} starts up by using command-line
773 options. @value{GDBN} itself can remind you of the options available.
783 to display all available options and briefly describe their use
784 (@samp{@value{GDBP} -h} is a shorter equivalent).
786 All options and command line arguments you give are processed
787 in sequential order. The order makes a difference when the
788 @samp{-x} option is used.
792 * File Options:: Choosing files
793 * Mode Options:: Choosing modes
797 @subsection Choosing files
799 When @value{GDBN} starts, it reads any arguments other than options as
800 specifying an executable file and core file (or process ID). This is
801 the same as if the arguments were specified by the @samp{-se} and
802 @samp{-c} options respectively. (@value{GDBN} reads the first argument
803 that does not have an associated option flag as equivalent to the
804 @samp{-se} option followed by that argument; and the second argument
805 that does not have an associated option flag, if any, as equivalent to
806 the @samp{-c} option followed by that argument.)
808 If @value{GDBN} has not been configured to included core file support,
809 such as for most embedded targets, then it will complain about a second
810 argument and ignore it.
812 Many options have both long and short forms; both are shown in the
813 following list. @value{GDBN} also recognizes the long forms if you truncate
814 them, so long as enough of the option is present to be unambiguous.
815 (If you prefer, you can flag option arguments with @samp{--} rather
816 than @samp{-}, though we illustrate the more usual convention.)
818 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
819 @c way, both those who look for -foo and --foo in the index, will find
823 @item -symbols @var{file}
825 @cindex @code{--symbols}
827 Read symbol table from file @var{file}.
829 @item -exec @var{file}
831 @cindex @code{--exec}
833 Use file @var{file} as the executable file to execute when appropriate,
834 and for examining pure data in conjunction with a core dump.
838 Read symbol table from file @var{file} and use it as the executable
841 @item -core @var{file}
843 @cindex @code{--core}
845 Use file @var{file} as a core dump to examine.
847 @item -c @var{number}
848 Connect to process ID @var{number}, as with the @code{attach} command
849 (unless there is a file in core-dump format named @var{number}, in which
850 case @samp{-c} specifies that file as a core dump to read).
852 @item -command @var{file}
854 @cindex @code{--command}
856 Execute @value{GDBN} commands from file @var{file}. @xref{Command
857 Files,, Command files}.
859 @item -directory @var{directory}
860 @itemx -d @var{directory}
861 @cindex @code{--directory}
863 Add @var{directory} to the path to search for source files.
867 @cindex @code{--mapped}
869 @emph{Warning: this option depends on operating system facilities that are not
870 supported on all systems.}@*
871 If memory-mapped files are available on your system through the @code{mmap}
872 system call, you can use this option
873 to have @value{GDBN} write the symbols from your
874 program into a reusable file in the current directory. If the program you are debugging is
875 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
876 Future @value{GDBN} debugging sessions notice the presence of this file,
877 and can quickly map in symbol information from it, rather than reading
878 the symbol table from the executable program.
880 The @file{.syms} file is specific to the host machine where @value{GDBN}
881 is run. It holds an exact image of the internal @value{GDBN} symbol
882 table. It cannot be shared across multiple host platforms.
886 @cindex @code{--readnow}
888 Read each symbol file's entire symbol table immediately, rather than
889 the default, which is to read it incrementally as it is needed.
890 This makes startup slower, but makes future operations faster.
894 You typically combine the @code{-mapped} and @code{-readnow} options in
895 order to build a @file{.syms} file that contains complete symbol
896 information. (@xref{Files,,Commands to specify files}, for information
897 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
898 but build a @file{.syms} file for future use is:
901 gdb -batch -nx -mapped -readnow programname
905 @subsection Choosing modes
907 You can run @value{GDBN} in various alternative modes---for example, in
908 batch mode or quiet mode.
915 Do not execute commands found in any initialization files. Normally,
916 @value{GDBN} executes the commands in these files after all the command
917 options and arguments have been processed. @xref{Command Files,,Command
923 @cindex @code{--quiet}
924 @cindex @code{--silent}
926 ``Quiet''. Do not print the introductory and copyright messages. These
927 messages are also suppressed in batch mode.
930 @cindex @code{--batch}
931 Run in batch mode. Exit with status @code{0} after processing all the
932 command files specified with @samp{-x} (and all commands from
933 initialization files, if not inhibited with @samp{-n}). Exit with
934 nonzero status if an error occurs in executing the @value{GDBN} commands
935 in the command files.
937 Batch mode may be useful for running @value{GDBN} as a filter, for
938 example to download and run a program on another computer; in order to
939 make this more useful, the message
942 Program exited normally.
946 (which is ordinarily issued whenever a program running under
947 @value{GDBN} control terminates) is not issued when running in batch
952 @cindex @code{--nowindows}
954 ``No windows''. If @value{GDBN} comes with a graphical user interface
955 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
956 interface. If no GUI is available, this option has no effect.
960 @cindex @code{--windows}
962 If @value{GDBN} includes a GUI, then this option requires it to be
965 @item -cd @var{directory}
967 Run @value{GDBN} using @var{directory} as its working directory,
968 instead of the current directory.
972 @cindex @code{--fullname}
974 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
975 subprocess. It tells @value{GDBN} to output the full file name and line
976 number in a standard, recognizable fashion each time a stack frame is
977 displayed (which includes each time your program stops). This
978 recognizable format looks like two @samp{\032} characters, followed by
979 the file name, line number and character position separated by colons,
980 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
981 @samp{\032} characters as a signal to display the source code for the
985 @cindex @code{--epoch}
986 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
987 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
988 routines so as to allow Epoch to display values of expressions in a
991 @item -annotate @var{level}
992 @cindex @code{--annotate}
993 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
994 effect is identical to using @samp{set annotate @var{level}}
995 (@pxref{Annotations}).
996 Annotation level controls how much information does @value{GDBN} print
997 together with its prompt, values of expressions, source lines, and other
998 types of output. Level 0 is the normal, level 1 is for use when
999 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1000 maximum annotation suitable for programs that control @value{GDBN}.
1003 @cindex @code{--async}
1004 Use the asynchronous event loop for the command-line interface.
1005 @value{GDBN} processes all events, such as user keyboard input, via a
1006 special event loop. This allows @value{GDBN} to accept and process user
1007 commands in parallel with the debugged process being
1008 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1009 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1010 suspended when the debuggee runs.}, so you don't need to wait for
1011 control to return to @value{GDBN} before you type the next command.
1012 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1013 operation is not yet in place, so @samp{-async} does not work fully
1015 @c FIXME: when the target side of the event loop is done, the above NOTE
1016 @c should be removed.
1018 When the standard input is connected to a terminal device, @value{GDBN}
1019 uses the asynchronous event loop by default, unless disabled by the
1020 @samp{-noasync} option.
1023 @cindex @code{--noasync}
1024 Disable the asynchronous event loop for the command-line interface.
1027 @cindex @code{--args}
1028 Change interpretation of command line so that arguments following the
1029 executable file are passed as command line arguments to the inferior.
1030 This option stops option processing.
1032 @item -baud @var{bps}
1034 @cindex @code{--baud}
1036 Set the line speed (baud rate or bits per second) of any serial
1037 interface used by @value{GDBN} for remote debugging.
1039 @item -tty @var{device}
1040 @itemx -t @var{device}
1041 @cindex @code{--tty}
1043 Run using @var{device} for your program's standard input and output.
1044 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1046 @c resolve the situation of these eventually
1048 @cindex @code{--tui}
1049 Activate the Terminal User Interface when starting.
1050 The Terminal User Interface manages several text windows on the terminal,
1051 showing source, assembly, registers and @value{GDBN} command outputs
1052 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1053 Do not use this option if you run @value{GDBN} from Emacs
1054 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1057 @c @cindex @code{--xdb}
1058 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1059 @c For information, see the file @file{xdb_trans.html}, which is usually
1060 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1063 @item -interpreter @var{interp}
1064 @cindex @code{--interpreter}
1065 Use the interpreter @var{interp} for interface with the controlling
1066 program or device. This option is meant to be set by programs which
1067 communicate with @value{GDBN} using it as a back end.
1069 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1070 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1071 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1072 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1075 @cindex @code{--write}
1076 Open the executable and core files for both reading and writing. This
1077 is equivalent to the @samp{set write on} command inside @value{GDBN}
1081 @cindex @code{--statistics}
1082 This option causes @value{GDBN} to print statistics about time and
1083 memory usage after it completes each command and returns to the prompt.
1086 @cindex @code{--version}
1087 This option causes @value{GDBN} to print its version number and
1088 no-warranty blurb, and exit.
1093 @section Quitting @value{GDBN}
1094 @cindex exiting @value{GDBN}
1095 @cindex leaving @value{GDBN}
1098 @kindex quit @r{[}@var{expression}@r{]}
1099 @kindex q @r{(@code{quit})}
1100 @item quit @r{[}@var{expression}@r{]}
1102 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1103 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1104 do not supply @var{expression}, @value{GDBN} will terminate normally;
1105 otherwise it will terminate using the result of @var{expression} as the
1110 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1111 terminates the action of any @value{GDBN} command that is in progress and
1112 returns to @value{GDBN} command level. It is safe to type the interrupt
1113 character at any time because @value{GDBN} does not allow it to take effect
1114 until a time when it is safe.
1116 If you have been using @value{GDBN} to control an attached process or
1117 device, you can release it with the @code{detach} command
1118 (@pxref{Attach, ,Debugging an already-running process}).
1120 @node Shell Commands
1121 @section Shell commands
1123 If you need to execute occasional shell commands during your
1124 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1125 just use the @code{shell} command.
1129 @cindex shell escape
1130 @item shell @var{command string}
1131 Invoke a standard shell to execute @var{command string}.
1132 If it exists, the environment variable @code{SHELL} determines which
1133 shell to run. Otherwise @value{GDBN} uses the default shell
1134 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1137 The utility @code{make} is often needed in development environments.
1138 You do not have to use the @code{shell} command for this purpose in
1143 @cindex calling make
1144 @item make @var{make-args}
1145 Execute the @code{make} program with the specified
1146 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1150 @chapter @value{GDBN} Commands
1152 You can abbreviate a @value{GDBN} command to the first few letters of the command
1153 name, if that abbreviation is unambiguous; and you can repeat certain
1154 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1155 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1156 show you the alternatives available, if there is more than one possibility).
1159 * Command Syntax:: How to give commands to @value{GDBN}
1160 * Completion:: Command completion
1161 * Help:: How to ask @value{GDBN} for help
1164 @node Command Syntax
1165 @section Command syntax
1167 A @value{GDBN} command is a single line of input. There is no limit on
1168 how long it can be. It starts with a command name, which is followed by
1169 arguments whose meaning depends on the command name. For example, the
1170 command @code{step} accepts an argument which is the number of times to
1171 step, as in @samp{step 5}. You can also use the @code{step} command
1172 with no arguments. Some commands do not allow any arguments.
1174 @cindex abbreviation
1175 @value{GDBN} command names may always be truncated if that abbreviation is
1176 unambiguous. Other possible command abbreviations are listed in the
1177 documentation for individual commands. In some cases, even ambiguous
1178 abbreviations are allowed; for example, @code{s} is specially defined as
1179 equivalent to @code{step} even though there are other commands whose
1180 names start with @code{s}. You can test abbreviations by using them as
1181 arguments to the @code{help} command.
1183 @cindex repeating commands
1184 @kindex RET @r{(repeat last command)}
1185 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1186 repeat the previous command. Certain commands (for example, @code{run})
1187 will not repeat this way; these are commands whose unintentional
1188 repetition might cause trouble and which you are unlikely to want to
1191 The @code{list} and @code{x} commands, when you repeat them with
1192 @key{RET}, construct new arguments rather than repeating
1193 exactly as typed. This permits easy scanning of source or memory.
1195 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1196 output, in a way similar to the common utility @code{more}
1197 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1198 @key{RET} too many in this situation, @value{GDBN} disables command
1199 repetition after any command that generates this sort of display.
1201 @kindex # @r{(a comment)}
1203 Any text from a @kbd{#} to the end of the line is a comment; it does
1204 nothing. This is useful mainly in command files (@pxref{Command
1205 Files,,Command files}).
1208 @section Command completion
1211 @cindex word completion
1212 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1213 only one possibility; it can also show you what the valid possibilities
1214 are for the next word in a command, at any time. This works for @value{GDBN}
1215 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1217 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1218 of a word. If there is only one possibility, @value{GDBN} fills in the
1219 word, and waits for you to finish the command (or press @key{RET} to
1220 enter it). For example, if you type
1222 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1223 @c complete accuracy in these examples; space introduced for clarity.
1224 @c If texinfo enhancements make it unnecessary, it would be nice to
1225 @c replace " @key" by "@key" in the following...
1227 (@value{GDBP}) info bre @key{TAB}
1231 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1232 the only @code{info} subcommand beginning with @samp{bre}:
1235 (@value{GDBP}) info breakpoints
1239 You can either press @key{RET} at this point, to run the @code{info
1240 breakpoints} command, or backspace and enter something else, if
1241 @samp{breakpoints} does not look like the command you expected. (If you
1242 were sure you wanted @code{info breakpoints} in the first place, you
1243 might as well just type @key{RET} immediately after @samp{info bre},
1244 to exploit command abbreviations rather than command completion).
1246 If there is more than one possibility for the next word when you press
1247 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1248 characters and try again, or just press @key{TAB} a second time;
1249 @value{GDBN} displays all the possible completions for that word. For
1250 example, you might want to set a breakpoint on a subroutine whose name
1251 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1252 just sounds the bell. Typing @key{TAB} again displays all the
1253 function names in your program that begin with those characters, for
1257 (@value{GDBP}) b make_ @key{TAB}
1258 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1259 make_a_section_from_file make_environ
1260 make_abs_section make_function_type
1261 make_blockvector make_pointer_type
1262 make_cleanup make_reference_type
1263 make_command make_symbol_completion_list
1264 (@value{GDBP}) b make_
1268 After displaying the available possibilities, @value{GDBN} copies your
1269 partial input (@samp{b make_} in the example) so you can finish the
1272 If you just want to see the list of alternatives in the first place, you
1273 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1274 means @kbd{@key{META} ?}. You can type this either by holding down a
1275 key designated as the @key{META} shift on your keyboard (if there is
1276 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1278 @cindex quotes in commands
1279 @cindex completion of quoted strings
1280 Sometimes the string you need, while logically a ``word'', may contain
1281 parentheses or other characters that @value{GDBN} normally excludes from
1282 its notion of a word. To permit word completion to work in this
1283 situation, you may enclose words in @code{'} (single quote marks) in
1284 @value{GDBN} commands.
1286 The most likely situation where you might need this is in typing the
1287 name of a C@t{++} function. This is because C@t{++} allows function
1288 overloading (multiple definitions of the same function, distinguished
1289 by argument type). For example, when you want to set a breakpoint you
1290 may need to distinguish whether you mean the version of @code{name}
1291 that takes an @code{int} parameter, @code{name(int)}, or the version
1292 that takes a @code{float} parameter, @code{name(float)}. To use the
1293 word-completion facilities in this situation, type a single quote
1294 @code{'} at the beginning of the function name. This alerts
1295 @value{GDBN} that it may need to consider more information than usual
1296 when you press @key{TAB} or @kbd{M-?} to request word completion:
1299 (@value{GDBP}) b 'bubble( @kbd{M-?}
1300 bubble(double,double) bubble(int,int)
1301 (@value{GDBP}) b 'bubble(
1304 In some cases, @value{GDBN} can tell that completing a name requires using
1305 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1306 completing as much as it can) if you do not type the quote in the first
1310 (@value{GDBP}) b bub @key{TAB}
1311 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1312 (@value{GDBP}) b 'bubble(
1316 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1317 you have not yet started typing the argument list when you ask for
1318 completion on an overloaded symbol.
1320 For more information about overloaded functions, see @ref{C plus plus
1321 expressions, ,C@t{++} expressions}. You can use the command @code{set
1322 overload-resolution off} to disable overload resolution;
1323 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1327 @section Getting help
1328 @cindex online documentation
1331 You can always ask @value{GDBN} itself for information on its commands,
1332 using the command @code{help}.
1335 @kindex h @r{(@code{help})}
1338 You can use @code{help} (abbreviated @code{h}) with no arguments to
1339 display a short list of named classes of commands:
1343 List of classes of commands:
1345 aliases -- Aliases of other commands
1346 breakpoints -- Making program stop at certain points
1347 data -- Examining data
1348 files -- Specifying and examining files
1349 internals -- Maintenance commands
1350 obscure -- Obscure features
1351 running -- Running the program
1352 stack -- Examining the stack
1353 status -- Status inquiries
1354 support -- Support facilities
1355 tracepoints -- Tracing of program execution without@*
1356 stopping the program
1357 user-defined -- User-defined commands
1359 Type "help" followed by a class name for a list of
1360 commands in that class.
1361 Type "help" followed by command name for full
1363 Command name abbreviations are allowed if unambiguous.
1366 @c the above line break eliminates huge line overfull...
1368 @item help @var{class}
1369 Using one of the general help classes as an argument, you can get a
1370 list of the individual commands in that class. For example, here is the
1371 help display for the class @code{status}:
1374 (@value{GDBP}) help status
1379 @c Line break in "show" line falsifies real output, but needed
1380 @c to fit in smallbook page size.
1381 info -- Generic command for showing things
1382 about the program being debugged
1383 show -- Generic command for showing things
1386 Type "help" followed by command name for full
1388 Command name abbreviations are allowed if unambiguous.
1392 @item help @var{command}
1393 With a command name as @code{help} argument, @value{GDBN} displays a
1394 short paragraph on how to use that command.
1397 @item apropos @var{args}
1398 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1399 commands, and their documentation, for the regular expression specified in
1400 @var{args}. It prints out all matches found. For example:
1411 set symbol-reloading -- Set dynamic symbol table reloading
1412 multiple times in one run
1413 show symbol-reloading -- Show dynamic symbol table reloading
1414 multiple times in one run
1419 @item complete @var{args}
1420 The @code{complete @var{args}} command lists all the possible completions
1421 for the beginning of a command. Use @var{args} to specify the beginning of the
1422 command you want completed. For example:
1428 @noindent results in:
1439 @noindent This is intended for use by @sc{gnu} Emacs.
1442 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1443 and @code{show} to inquire about the state of your program, or the state
1444 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1445 manual introduces each of them in the appropriate context. The listings
1446 under @code{info} and under @code{show} in the Index point to
1447 all the sub-commands. @xref{Index}.
1452 @kindex i @r{(@code{info})}
1454 This command (abbreviated @code{i}) is for describing the state of your
1455 program. For example, you can list the arguments given to your program
1456 with @code{info args}, list the registers currently in use with @code{info
1457 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1458 You can get a complete list of the @code{info} sub-commands with
1459 @w{@code{help info}}.
1463 You can assign the result of an expression to an environment variable with
1464 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1465 @code{set prompt $}.
1469 In contrast to @code{info}, @code{show} is for describing the state of
1470 @value{GDBN} itself.
1471 You can change most of the things you can @code{show}, by using the
1472 related command @code{set}; for example, you can control what number
1473 system is used for displays with @code{set radix}, or simply inquire
1474 which is currently in use with @code{show radix}.
1477 To display all the settable parameters and their current
1478 values, you can use @code{show} with no arguments; you may also use
1479 @code{info set}. Both commands produce the same display.
1480 @c FIXME: "info set" violates the rule that "info" is for state of
1481 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1482 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1486 Here are three miscellaneous @code{show} subcommands, all of which are
1487 exceptional in lacking corresponding @code{set} commands:
1490 @kindex show version
1491 @cindex version number
1493 Show what version of @value{GDBN} is running. You should include this
1494 information in @value{GDBN} bug-reports. If multiple versions of
1495 @value{GDBN} are in use at your site, you may need to determine which
1496 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1497 commands are introduced, and old ones may wither away. Also, many
1498 system vendors ship variant versions of @value{GDBN}, and there are
1499 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1500 The version number is the same as the one announced when you start
1503 @kindex show copying
1505 Display information about permission for copying @value{GDBN}.
1507 @kindex show warranty
1509 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1510 if your version of @value{GDBN} comes with one.
1515 @chapter Running Programs Under @value{GDBN}
1517 When you run a program under @value{GDBN}, you must first generate
1518 debugging information when you compile it.
1520 You may start @value{GDBN} with its arguments, if any, in an environment
1521 of your choice. If you are doing native debugging, you may redirect
1522 your program's input and output, debug an already running process, or
1523 kill a child process.
1526 * Compilation:: Compiling for debugging
1527 * Starting:: Starting your program
1528 * Arguments:: Your program's arguments
1529 * Environment:: Your program's environment
1531 * Working Directory:: Your program's working directory
1532 * Input/Output:: Your program's input and output
1533 * Attach:: Debugging an already-running process
1534 * Kill Process:: Killing the child process
1536 * Threads:: Debugging programs with multiple threads
1537 * Processes:: Debugging programs with multiple processes
1541 @section Compiling for debugging
1543 In order to debug a program effectively, you need to generate
1544 debugging information when you compile it. This debugging information
1545 is stored in the object file; it describes the data type of each
1546 variable or function and the correspondence between source line numbers
1547 and addresses in the executable code.
1549 To request debugging information, specify the @samp{-g} option when you run
1552 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1553 options together. Using those compilers, you cannot generate optimized
1554 executables containing debugging information.
1556 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1557 without @samp{-O}, making it possible to debug optimized code. We
1558 recommend that you @emph{always} use @samp{-g} whenever you compile a
1559 program. You may think your program is correct, but there is no sense
1560 in pushing your luck.
1562 @cindex optimized code, debugging
1563 @cindex debugging optimized code
1564 When you debug a program compiled with @samp{-g -O}, remember that the
1565 optimizer is rearranging your code; the debugger shows you what is
1566 really there. Do not be too surprised when the execution path does not
1567 exactly match your source file! An extreme example: if you define a
1568 variable, but never use it, @value{GDBN} never sees that
1569 variable---because the compiler optimizes it out of existence.
1571 Some things do not work as well with @samp{-g -O} as with just
1572 @samp{-g}, particularly on machines with instruction scheduling. If in
1573 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1574 please report it to us as a bug (including a test case!).
1576 Older versions of the @sc{gnu} C compiler permitted a variant option
1577 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1578 format; if your @sc{gnu} C compiler has this option, do not use it.
1582 @section Starting your program
1588 @kindex r @r{(@code{run})}
1591 Use the @code{run} command to start your program under @value{GDBN}.
1592 You must first specify the program name (except on VxWorks) with an
1593 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1594 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1595 (@pxref{Files, ,Commands to specify files}).
1599 If you are running your program in an execution environment that
1600 supports processes, @code{run} creates an inferior process and makes
1601 that process run your program. (In environments without processes,
1602 @code{run} jumps to the start of your program.)
1604 The execution of a program is affected by certain information it
1605 receives from its superior. @value{GDBN} provides ways to specify this
1606 information, which you must do @emph{before} starting your program. (You
1607 can change it after starting your program, but such changes only affect
1608 your program the next time you start it.) This information may be
1609 divided into four categories:
1612 @item The @emph{arguments.}
1613 Specify the arguments to give your program as the arguments of the
1614 @code{run} command. If a shell is available on your target, the shell
1615 is used to pass the arguments, so that you may use normal conventions
1616 (such as wildcard expansion or variable substitution) in describing
1618 In Unix systems, you can control which shell is used with the
1619 @code{SHELL} environment variable.
1620 @xref{Arguments, ,Your program's arguments}.
1622 @item The @emph{environment.}
1623 Your program normally inherits its environment from @value{GDBN}, but you can
1624 use the @value{GDBN} commands @code{set environment} and @code{unset
1625 environment} to change parts of the environment that affect
1626 your program. @xref{Environment, ,Your program's environment}.
1628 @item The @emph{working directory.}
1629 Your program inherits its working directory from @value{GDBN}. You can set
1630 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1631 @xref{Working Directory, ,Your program's working directory}.
1633 @item The @emph{standard input and output.}
1634 Your program normally uses the same device for standard input and
1635 standard output as @value{GDBN} is using. You can redirect input and output
1636 in the @code{run} command line, or you can use the @code{tty} command to
1637 set a different device for your program.
1638 @xref{Input/Output, ,Your program's input and output}.
1641 @emph{Warning:} While input and output redirection work, you cannot use
1642 pipes to pass the output of the program you are debugging to another
1643 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1647 When you issue the @code{run} command, your program begins to execute
1648 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1649 of how to arrange for your program to stop. Once your program has
1650 stopped, you may call functions in your program, using the @code{print}
1651 or @code{call} commands. @xref{Data, ,Examining Data}.
1653 If the modification time of your symbol file has changed since the last
1654 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1655 table, and reads it again. When it does this, @value{GDBN} tries to retain
1656 your current breakpoints.
1659 @section Your program's arguments
1661 @cindex arguments (to your program)
1662 The arguments to your program can be specified by the arguments of the
1664 They are passed to a shell, which expands wildcard characters and
1665 performs redirection of I/O, and thence to your program. Your
1666 @code{SHELL} environment variable (if it exists) specifies what shell
1667 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1668 the default shell (@file{/bin/sh} on Unix).
1670 On non-Unix systems, the program is usually invoked directly by
1671 @value{GDBN}, which emulates I/O redirection via the appropriate system
1672 calls, and the wildcard characters are expanded by the startup code of
1673 the program, not by the shell.
1675 @code{run} with no arguments uses the same arguments used by the previous
1676 @code{run}, or those set by the @code{set args} command.
1681 Specify the arguments to be used the next time your program is run. If
1682 @code{set args} has no arguments, @code{run} executes your program
1683 with no arguments. Once you have run your program with arguments,
1684 using @code{set args} before the next @code{run} is the only way to run
1685 it again without arguments.
1689 Show the arguments to give your program when it is started.
1693 @section Your program's environment
1695 @cindex environment (of your program)
1696 The @dfn{environment} consists of a set of environment variables and
1697 their values. Environment variables conventionally record such things as
1698 your user name, your home directory, your terminal type, and your search
1699 path for programs to run. Usually you set up environment variables with
1700 the shell and they are inherited by all the other programs you run. When
1701 debugging, it can be useful to try running your program with a modified
1702 environment without having to start @value{GDBN} over again.
1706 @item path @var{directory}
1707 Add @var{directory} to the front of the @code{PATH} environment variable
1708 (the search path for executables) that will be passed to your program.
1709 The value of @code{PATH} used by @value{GDBN} does not change.
1710 You may specify several directory names, separated by whitespace or by a
1711 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1712 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1713 is moved to the front, so it is searched sooner.
1715 You can use the string @samp{$cwd} to refer to whatever is the current
1716 working directory at the time @value{GDBN} searches the path. If you
1717 use @samp{.} instead, it refers to the directory where you executed the
1718 @code{path} command. @value{GDBN} replaces @samp{.} in the
1719 @var{directory} argument (with the current path) before adding
1720 @var{directory} to the search path.
1721 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1722 @c document that, since repeating it would be a no-op.
1726 Display the list of search paths for executables (the @code{PATH}
1727 environment variable).
1729 @kindex show environment
1730 @item show environment @r{[}@var{varname}@r{]}
1731 Print the value of environment variable @var{varname} to be given to
1732 your program when it starts. If you do not supply @var{varname},
1733 print the names and values of all environment variables to be given to
1734 your program. You can abbreviate @code{environment} as @code{env}.
1736 @kindex set environment
1737 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1738 Set environment variable @var{varname} to @var{value}. The value
1739 changes for your program only, not for @value{GDBN} itself. @var{value} may
1740 be any string; the values of environment variables are just strings, and
1741 any interpretation is supplied by your program itself. The @var{value}
1742 parameter is optional; if it is eliminated, the variable is set to a
1744 @c "any string" here does not include leading, trailing
1745 @c blanks. Gnu asks: does anyone care?
1747 For example, this command:
1754 tells the debugged program, when subsequently run, that its user is named
1755 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1756 are not actually required.)
1758 @kindex unset environment
1759 @item unset environment @var{varname}
1760 Remove variable @var{varname} from the environment to be passed to your
1761 program. This is different from @samp{set env @var{varname} =};
1762 @code{unset environment} removes the variable from the environment,
1763 rather than assigning it an empty value.
1766 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1768 by your @code{SHELL} environment variable if it exists (or
1769 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1770 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1771 @file{.bashrc} for BASH---any variables you set in that file affect
1772 your program. You may wish to move setting of environment variables to
1773 files that are only run when you sign on, such as @file{.login} or
1776 @node Working Directory
1777 @section Your program's working directory
1779 @cindex working directory (of your program)
1780 Each time you start your program with @code{run}, it inherits its
1781 working directory from the current working directory of @value{GDBN}.
1782 The @value{GDBN} working directory is initially whatever it inherited
1783 from its parent process (typically the shell), but you can specify a new
1784 working directory in @value{GDBN} with the @code{cd} command.
1786 The @value{GDBN} working directory also serves as a default for the commands
1787 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1792 @item cd @var{directory}
1793 Set the @value{GDBN} working directory to @var{directory}.
1797 Print the @value{GDBN} working directory.
1801 @section Your program's input and output
1806 By default, the program you run under @value{GDBN} does input and output to
1807 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1808 to its own terminal modes to interact with you, but it records the terminal
1809 modes your program was using and switches back to them when you continue
1810 running your program.
1813 @kindex info terminal
1815 Displays information recorded by @value{GDBN} about the terminal modes your
1819 You can redirect your program's input and/or output using shell
1820 redirection with the @code{run} command. For example,
1827 starts your program, diverting its output to the file @file{outfile}.
1830 @cindex controlling terminal
1831 Another way to specify where your program should do input and output is
1832 with the @code{tty} command. This command accepts a file name as
1833 argument, and causes this file to be the default for future @code{run}
1834 commands. It also resets the controlling terminal for the child
1835 process, for future @code{run} commands. For example,
1842 directs that processes started with subsequent @code{run} commands
1843 default to do input and output on the terminal @file{/dev/ttyb} and have
1844 that as their controlling terminal.
1846 An explicit redirection in @code{run} overrides the @code{tty} command's
1847 effect on the input/output device, but not its effect on the controlling
1850 When you use the @code{tty} command or redirect input in the @code{run}
1851 command, only the input @emph{for your program} is affected. The input
1852 for @value{GDBN} still comes from your terminal.
1855 @section Debugging an already-running process
1860 @item attach @var{process-id}
1861 This command attaches to a running process---one that was started
1862 outside @value{GDBN}. (@code{info files} shows your active
1863 targets.) The command takes as argument a process ID. The usual way to
1864 find out the process-id of a Unix process is with the @code{ps} utility,
1865 or with the @samp{jobs -l} shell command.
1867 @code{attach} does not repeat if you press @key{RET} a second time after
1868 executing the command.
1871 To use @code{attach}, your program must be running in an environment
1872 which supports processes; for example, @code{attach} does not work for
1873 programs on bare-board targets that lack an operating system. You must
1874 also have permission to send the process a signal.
1876 When you use @code{attach}, the debugger finds the program running in
1877 the process first by looking in the current working directory, then (if
1878 the program is not found) by using the source file search path
1879 (@pxref{Source Path, ,Specifying source directories}). You can also use
1880 the @code{file} command to load the program. @xref{Files, ,Commands to
1883 The first thing @value{GDBN} does after arranging to debug the specified
1884 process is to stop it. You can examine and modify an attached process
1885 with all the @value{GDBN} commands that are ordinarily available when
1886 you start processes with @code{run}. You can insert breakpoints; you
1887 can step and continue; you can modify storage. If you would rather the
1888 process continue running, you may use the @code{continue} command after
1889 attaching @value{GDBN} to the process.
1894 When you have finished debugging the attached process, you can use the
1895 @code{detach} command to release it from @value{GDBN} control. Detaching
1896 the process continues its execution. After the @code{detach} command,
1897 that process and @value{GDBN} become completely independent once more, and you
1898 are ready to @code{attach} another process or start one with @code{run}.
1899 @code{detach} does not repeat if you press @key{RET} again after
1900 executing the command.
1903 If you exit @value{GDBN} or use the @code{run} command while you have an
1904 attached process, you kill that process. By default, @value{GDBN} asks
1905 for confirmation if you try to do either of these things; you can
1906 control whether or not you need to confirm by using the @code{set
1907 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1911 @section Killing the child process
1916 Kill the child process in which your program is running under @value{GDBN}.
1919 This command is useful if you wish to debug a core dump instead of a
1920 running process. @value{GDBN} ignores any core dump file while your program
1923 On some operating systems, a program cannot be executed outside @value{GDBN}
1924 while you have breakpoints set on it inside @value{GDBN}. You can use the
1925 @code{kill} command in this situation to permit running your program
1926 outside the debugger.
1928 The @code{kill} command is also useful if you wish to recompile and
1929 relink your program, since on many systems it is impossible to modify an
1930 executable file while it is running in a process. In this case, when you
1931 next type @code{run}, @value{GDBN} notices that the file has changed, and
1932 reads the symbol table again (while trying to preserve your current
1933 breakpoint settings).
1936 @section Debugging programs with multiple threads
1938 @cindex threads of execution
1939 @cindex multiple threads
1940 @cindex switching threads
1941 In some operating systems, such as HP-UX and Solaris, a single program
1942 may have more than one @dfn{thread} of execution. The precise semantics
1943 of threads differ from one operating system to another, but in general
1944 the threads of a single program are akin to multiple processes---except
1945 that they share one address space (that is, they can all examine and
1946 modify the same variables). On the other hand, each thread has its own
1947 registers and execution stack, and perhaps private memory.
1949 @value{GDBN} provides these facilities for debugging multi-thread
1953 @item automatic notification of new threads
1954 @item @samp{thread @var{threadno}}, a command to switch among threads
1955 @item @samp{info threads}, a command to inquire about existing threads
1956 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1957 a command to apply a command to a list of threads
1958 @item thread-specific breakpoints
1962 @emph{Warning:} These facilities are not yet available on every
1963 @value{GDBN} configuration where the operating system supports threads.
1964 If your @value{GDBN} does not support threads, these commands have no
1965 effect. For example, a system without thread support shows no output
1966 from @samp{info threads}, and always rejects the @code{thread} command,
1970 (@value{GDBP}) info threads
1971 (@value{GDBP}) thread 1
1972 Thread ID 1 not known. Use the "info threads" command to
1973 see the IDs of currently known threads.
1975 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1976 @c doesn't support threads"?
1979 @cindex focus of debugging
1980 @cindex current thread
1981 The @value{GDBN} thread debugging facility allows you to observe all
1982 threads while your program runs---but whenever @value{GDBN} takes
1983 control, one thread in particular is always the focus of debugging.
1984 This thread is called the @dfn{current thread}. Debugging commands show
1985 program information from the perspective of the current thread.
1987 @cindex @code{New} @var{systag} message
1988 @cindex thread identifier (system)
1989 @c FIXME-implementors!! It would be more helpful if the [New...] message
1990 @c included GDB's numeric thread handle, so you could just go to that
1991 @c thread without first checking `info threads'.
1992 Whenever @value{GDBN} detects a new thread in your program, it displays
1993 the target system's identification for the thread with a message in the
1994 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1995 whose form varies depending on the particular system. For example, on
1996 LynxOS, you might see
1999 [New process 35 thread 27]
2003 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2004 the @var{systag} is simply something like @samp{process 368}, with no
2007 @c FIXME!! (1) Does the [New...] message appear even for the very first
2008 @c thread of a program, or does it only appear for the
2009 @c second---i.e., when it becomes obvious we have a multithread
2011 @c (2) *Is* there necessarily a first thread always? Or do some
2012 @c multithread systems permit starting a program with multiple
2013 @c threads ab initio?
2015 @cindex thread number
2016 @cindex thread identifier (GDB)
2017 For debugging purposes, @value{GDBN} associates its own thread
2018 number---always a single integer---with each thread in your program.
2021 @kindex info threads
2023 Display a summary of all threads currently in your
2024 program. @value{GDBN} displays for each thread (in this order):
2027 @item the thread number assigned by @value{GDBN}
2029 @item the target system's thread identifier (@var{systag})
2031 @item the current stack frame summary for that thread
2035 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2036 indicates the current thread.
2040 @c end table here to get a little more width for example
2043 (@value{GDBP}) info threads
2044 3 process 35 thread 27 0x34e5 in sigpause ()
2045 2 process 35 thread 23 0x34e5 in sigpause ()
2046 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2052 @cindex thread number
2053 @cindex thread identifier (GDB)
2054 For debugging purposes, @value{GDBN} associates its own thread
2055 number---a small integer assigned in thread-creation order---with each
2056 thread in your program.
2058 @cindex @code{New} @var{systag} message, on HP-UX
2059 @cindex thread identifier (system), on HP-UX
2060 @c FIXME-implementors!! It would be more helpful if the [New...] message
2061 @c included GDB's numeric thread handle, so you could just go to that
2062 @c thread without first checking `info threads'.
2063 Whenever @value{GDBN} detects a new thread in your program, it displays
2064 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2065 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2066 whose form varies depending on the particular system. For example, on
2070 [New thread 2 (system thread 26594)]
2074 when @value{GDBN} notices a new thread.
2077 @kindex info threads
2079 Display a summary of all threads currently in your
2080 program. @value{GDBN} displays for each thread (in this order):
2083 @item the thread number assigned by @value{GDBN}
2085 @item the target system's thread identifier (@var{systag})
2087 @item the current stack frame summary for that thread
2091 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2092 indicates the current thread.
2096 @c end table here to get a little more width for example
2099 (@value{GDBP}) info threads
2100 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2102 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2103 from /usr/lib/libc.2
2104 1 system thread 27905 0x7b003498 in _brk () \@*
2105 from /usr/lib/libc.2
2109 @kindex thread @var{threadno}
2110 @item thread @var{threadno}
2111 Make thread number @var{threadno} the current thread. The command
2112 argument @var{threadno} is the internal @value{GDBN} thread number, as
2113 shown in the first field of the @samp{info threads} display.
2114 @value{GDBN} responds by displaying the system identifier of the thread
2115 you selected, and its current stack frame summary:
2118 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2119 (@value{GDBP}) thread 2
2120 [Switching to process 35 thread 23]
2121 0x34e5 in sigpause ()
2125 As with the @samp{[New @dots{}]} message, the form of the text after
2126 @samp{Switching to} depends on your system's conventions for identifying
2129 @kindex thread apply
2130 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2131 The @code{thread apply} command allows you to apply a command to one or
2132 more threads. Specify the numbers of the threads that you want affected
2133 with the command argument @var{threadno}. @var{threadno} is the internal
2134 @value{GDBN} thread number, as shown in the first field of the @samp{info
2135 threads} display. To apply a command to all threads, use
2136 @code{thread apply all} @var{args}.
2139 @cindex automatic thread selection
2140 @cindex switching threads automatically
2141 @cindex threads, automatic switching
2142 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2143 signal, it automatically selects the thread where that breakpoint or
2144 signal happened. @value{GDBN} alerts you to the context switch with a
2145 message of the form @samp{[Switching to @var{systag}]} to identify the
2148 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2149 more information about how @value{GDBN} behaves when you stop and start
2150 programs with multiple threads.
2152 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2153 watchpoints in programs with multiple threads.
2156 @section Debugging programs with multiple processes
2158 @cindex fork, debugging programs which call
2159 @cindex multiple processes
2160 @cindex processes, multiple
2161 On most systems, @value{GDBN} has no special support for debugging
2162 programs which create additional processes using the @code{fork}
2163 function. When a program forks, @value{GDBN} will continue to debug the
2164 parent process and the child process will run unimpeded. If you have
2165 set a breakpoint in any code which the child then executes, the child
2166 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2167 will cause it to terminate.
2169 However, if you want to debug the child process there is a workaround
2170 which isn't too painful. Put a call to @code{sleep} in the code which
2171 the child process executes after the fork. It may be useful to sleep
2172 only if a certain environment variable is set, or a certain file exists,
2173 so that the delay need not occur when you don't want to run @value{GDBN}
2174 on the child. While the child is sleeping, use the @code{ps} program to
2175 get its process ID. Then tell @value{GDBN} (a new invocation of
2176 @value{GDBN} if you are also debugging the parent process) to attach to
2177 the child process (@pxref{Attach}). From that point on you can debug
2178 the child process just like any other process which you attached to.
2180 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2181 debugging programs that create additional processes using the
2182 @code{fork} or @code{vfork} function.
2184 By default, when a program forks, @value{GDBN} will continue to debug
2185 the parent process and the child process will run unimpeded.
2187 If you want to follow the child process instead of the parent process,
2188 use the command @w{@code{set follow-fork-mode}}.
2191 @kindex set follow-fork-mode
2192 @item set follow-fork-mode @var{mode}
2193 Set the debugger response to a program call of @code{fork} or
2194 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2195 process. The @var{mode} can be:
2199 The original process is debugged after a fork. The child process runs
2200 unimpeded. This is the default.
2203 The new process is debugged after a fork. The parent process runs
2207 The debugger will ask for one of the above choices.
2210 @item show follow-fork-mode
2211 Display the current debugger response to a @code{fork} or @code{vfork} call.
2214 If you ask to debug a child process and a @code{vfork} is followed by an
2215 @code{exec}, @value{GDBN} executes the new target up to the first
2216 breakpoint in the new target. If you have a breakpoint set on
2217 @code{main} in your original program, the breakpoint will also be set on
2218 the child process's @code{main}.
2220 When a child process is spawned by @code{vfork}, you cannot debug the
2221 child or parent until an @code{exec} call completes.
2223 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2224 call executes, the new target restarts. To restart the parent process,
2225 use the @code{file} command with the parent executable name as its
2228 You can use the @code{catch} command to make @value{GDBN} stop whenever
2229 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2230 Catchpoints, ,Setting catchpoints}.
2233 @chapter Stopping and Continuing
2235 The principal purposes of using a debugger are so that you can stop your
2236 program before it terminates; or so that, if your program runs into
2237 trouble, you can investigate and find out why.
2239 Inside @value{GDBN}, your program may stop for any of several reasons,
2240 such as a signal, a breakpoint, or reaching a new line after a
2241 @value{GDBN} command such as @code{step}. You may then examine and
2242 change variables, set new breakpoints or remove old ones, and then
2243 continue execution. Usually, the messages shown by @value{GDBN} provide
2244 ample explanation of the status of your program---but you can also
2245 explicitly request this information at any time.
2248 @kindex info program
2250 Display information about the status of your program: whether it is
2251 running or not, what process it is, and why it stopped.
2255 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2256 * Continuing and Stepping:: Resuming execution
2258 * Thread Stops:: Stopping and starting multi-thread programs
2262 @section Breakpoints, watchpoints, and catchpoints
2265 A @dfn{breakpoint} makes your program stop whenever a certain point in
2266 the program is reached. For each breakpoint, you can add conditions to
2267 control in finer detail whether your program stops. You can set
2268 breakpoints with the @code{break} command and its variants (@pxref{Set
2269 Breaks, ,Setting breakpoints}), to specify the place where your program
2270 should stop by line number, function name or exact address in the
2273 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2274 breakpoints in shared libraries before the executable is run. There is
2275 a minor limitation on HP-UX systems: you must wait until the executable
2276 is run in order to set breakpoints in shared library routines that are
2277 not called directly by the program (for example, routines that are
2278 arguments in a @code{pthread_create} call).
2281 @cindex memory tracing
2282 @cindex breakpoint on memory address
2283 @cindex breakpoint on variable modification
2284 A @dfn{watchpoint} is a special breakpoint that stops your program
2285 when the value of an expression changes. You must use a different
2286 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2287 watchpoints}), but aside from that, you can manage a watchpoint like
2288 any other breakpoint: you enable, disable, and delete both breakpoints
2289 and watchpoints using the same commands.
2291 You can arrange to have values from your program displayed automatically
2292 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2296 @cindex breakpoint on events
2297 A @dfn{catchpoint} is another special breakpoint that stops your program
2298 when a certain kind of event occurs, such as the throwing of a C@t{++}
2299 exception or the loading of a library. As with watchpoints, you use a
2300 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2301 catchpoints}), but aside from that, you can manage a catchpoint like any
2302 other breakpoint. (To stop when your program receives a signal, use the
2303 @code{handle} command; see @ref{Signals, ,Signals}.)
2305 @cindex breakpoint numbers
2306 @cindex numbers for breakpoints
2307 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2308 catchpoint when you create it; these numbers are successive integers
2309 starting with one. In many of the commands for controlling various
2310 features of breakpoints you use the breakpoint number to say which
2311 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2312 @dfn{disabled}; if disabled, it has no effect on your program until you
2315 @cindex breakpoint ranges
2316 @cindex ranges of breakpoints
2317 Some @value{GDBN} commands accept a range of breakpoints on which to
2318 operate. A breakpoint range is either a single breakpoint number, like
2319 @samp{5}, or two such numbers, in increasing order, separated by a
2320 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2321 all breakpoint in that range are operated on.
2324 * Set Breaks:: Setting breakpoints
2325 * Set Watchpoints:: Setting watchpoints
2326 * Set Catchpoints:: Setting catchpoints
2327 * Delete Breaks:: Deleting breakpoints
2328 * Disabling:: Disabling breakpoints
2329 * Conditions:: Break conditions
2330 * Break Commands:: Breakpoint command lists
2331 * Breakpoint Menus:: Breakpoint menus
2332 * Error in Breakpoints:: ``Cannot insert breakpoints''
2336 @subsection Setting breakpoints
2338 @c FIXME LMB what does GDB do if no code on line of breakpt?
2339 @c consider in particular declaration with/without initialization.
2341 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2344 @kindex b @r{(@code{break})}
2345 @vindex $bpnum@r{, convenience variable}
2346 @cindex latest breakpoint
2347 Breakpoints are set with the @code{break} command (abbreviated
2348 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2349 number of the breakpoint you've set most recently; see @ref{Convenience
2350 Vars,, Convenience variables}, for a discussion of what you can do with
2351 convenience variables.
2353 You have several ways to say where the breakpoint should go.
2356 @item break @var{function}
2357 Set a breakpoint at entry to function @var{function}.
2358 When using source languages that permit overloading of symbols, such as
2359 C@t{++}, @var{function} may refer to more than one possible place to break.
2360 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2362 @item break +@var{offset}
2363 @itemx break -@var{offset}
2364 Set a breakpoint some number of lines forward or back from the position
2365 at which execution stopped in the currently selected @dfn{stack frame}.
2366 (@xref{Frames, ,Frames}, for a description of stack frames.)
2368 @item break @var{linenum}
2369 Set a breakpoint at line @var{linenum} in the current source file.
2370 The current source file is the last file whose source text was printed.
2371 The breakpoint will stop your program just before it executes any of the
2374 @item break @var{filename}:@var{linenum}
2375 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2377 @item break @var{filename}:@var{function}
2378 Set a breakpoint at entry to function @var{function} found in file
2379 @var{filename}. Specifying a file name as well as a function name is
2380 superfluous except when multiple files contain similarly named
2383 @item break *@var{address}
2384 Set a breakpoint at address @var{address}. You can use this to set
2385 breakpoints in parts of your program which do not have debugging
2386 information or source files.
2389 When called without any arguments, @code{break} sets a breakpoint at
2390 the next instruction to be executed in the selected stack frame
2391 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2392 innermost, this makes your program stop as soon as control
2393 returns to that frame. This is similar to the effect of a
2394 @code{finish} command in the frame inside the selected frame---except
2395 that @code{finish} does not leave an active breakpoint. If you use
2396 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2397 the next time it reaches the current location; this may be useful
2400 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2401 least one instruction has been executed. If it did not do this, you
2402 would be unable to proceed past a breakpoint without first disabling the
2403 breakpoint. This rule applies whether or not the breakpoint already
2404 existed when your program stopped.
2406 @item break @dots{} if @var{cond}
2407 Set a breakpoint with condition @var{cond}; evaluate the expression
2408 @var{cond} each time the breakpoint is reached, and stop only if the
2409 value is nonzero---that is, if @var{cond} evaluates as true.
2410 @samp{@dots{}} stands for one of the possible arguments described
2411 above (or no argument) specifying where to break. @xref{Conditions,
2412 ,Break conditions}, for more information on breakpoint conditions.
2415 @item tbreak @var{args}
2416 Set a breakpoint enabled only for one stop. @var{args} are the
2417 same as for the @code{break} command, and the breakpoint is set in the same
2418 way, but the breakpoint is automatically deleted after the first time your
2419 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2422 @item hbreak @var{args}
2423 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2424 @code{break} command and the breakpoint is set in the same way, but the
2425 breakpoint requires hardware support and some target hardware may not
2426 have this support. The main purpose of this is EPROM/ROM code
2427 debugging, so you can set a breakpoint at an instruction without
2428 changing the instruction. This can be used with the new trap-generation
2429 provided by SPARClite DSU and some x86-based targets. These targets
2430 will generate traps when a program accesses some data or instruction
2431 address that is assigned to the debug registers. However the hardware
2432 breakpoint registers can take a limited number of breakpoints. For
2433 example, on the DSU, only two data breakpoints can be set at a time, and
2434 @value{GDBN} will reject this command if more than two are used. Delete
2435 or disable unused hardware breakpoints before setting new ones
2436 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2439 @item thbreak @var{args}
2440 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2441 are the same as for the @code{hbreak} command and the breakpoint is set in
2442 the same way. However, like the @code{tbreak} command,
2443 the breakpoint is automatically deleted after the
2444 first time your program stops there. Also, like the @code{hbreak}
2445 command, the breakpoint requires hardware support and some target hardware
2446 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2447 See also @ref{Conditions, ,Break conditions}.
2450 @cindex regular expression
2451 @item rbreak @var{regex}
2452 Set breakpoints on all functions matching the regular expression
2453 @var{regex}. This command sets an unconditional breakpoint on all
2454 matches, printing a list of all breakpoints it set. Once these
2455 breakpoints are set, they are treated just like the breakpoints set with
2456 the @code{break} command. You can delete them, disable them, or make
2457 them conditional the same way as any other breakpoint.
2459 The syntax of the regular expression is the standard one used with tools
2460 like @file{grep}. Note that this is different from the syntax used by
2461 shells, so for instance @code{foo*} matches all functions that include
2462 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2463 @code{.*} leading and trailing the regular expression you supply, so to
2464 match only functions that begin with @code{foo}, use @code{^foo}.
2466 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2467 breakpoints on overloaded functions that are not members of any special
2470 @kindex info breakpoints
2471 @cindex @code{$_} and @code{info breakpoints}
2472 @item info breakpoints @r{[}@var{n}@r{]}
2473 @itemx info break @r{[}@var{n}@r{]}
2474 @itemx info watchpoints @r{[}@var{n}@r{]}
2475 Print a table of all breakpoints, watchpoints, and catchpoints set and
2476 not deleted, with the following columns for each breakpoint:
2479 @item Breakpoint Numbers
2481 Breakpoint, watchpoint, or catchpoint.
2483 Whether the breakpoint is marked to be disabled or deleted when hit.
2484 @item Enabled or Disabled
2485 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2486 that are not enabled.
2488 Where the breakpoint is in your program, as a memory address.
2490 Where the breakpoint is in the source for your program, as a file and
2495 If a breakpoint is conditional, @code{info break} shows the condition on
2496 the line following the affected breakpoint; breakpoint commands, if any,
2497 are listed after that.
2500 @code{info break} with a breakpoint
2501 number @var{n} as argument lists only that breakpoint. The
2502 convenience variable @code{$_} and the default examining-address for
2503 the @code{x} command are set to the address of the last breakpoint
2504 listed (@pxref{Memory, ,Examining memory}).
2507 @code{info break} displays a count of the number of times the breakpoint
2508 has been hit. This is especially useful in conjunction with the
2509 @code{ignore} command. You can ignore a large number of breakpoint
2510 hits, look at the breakpoint info to see how many times the breakpoint
2511 was hit, and then run again, ignoring one less than that number. This
2512 will get you quickly to the last hit of that breakpoint.
2515 @value{GDBN} allows you to set any number of breakpoints at the same place in
2516 your program. There is nothing silly or meaningless about this. When
2517 the breakpoints are conditional, this is even useful
2518 (@pxref{Conditions, ,Break conditions}).
2520 @cindex negative breakpoint numbers
2521 @cindex internal @value{GDBN} breakpoints
2522 @value{GDBN} itself sometimes sets breakpoints in your program for special
2523 purposes, such as proper handling of @code{longjmp} (in C programs).
2524 These internal breakpoints are assigned negative numbers, starting with
2525 @code{-1}; @samp{info breakpoints} does not display them.
2527 You can see these breakpoints with the @value{GDBN} maintenance command
2528 @samp{maint info breakpoints}.
2531 @kindex maint info breakpoints
2532 @item maint info breakpoints
2533 Using the same format as @samp{info breakpoints}, display both the
2534 breakpoints you've set explicitly, and those @value{GDBN} is using for
2535 internal purposes. Internal breakpoints are shown with negative
2536 breakpoint numbers. The type column identifies what kind of breakpoint
2541 Normal, explicitly set breakpoint.
2544 Normal, explicitly set watchpoint.
2547 Internal breakpoint, used to handle correctly stepping through
2548 @code{longjmp} calls.
2550 @item longjmp resume
2551 Internal breakpoint at the target of a @code{longjmp}.
2554 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2557 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2560 Shared library events.
2567 @node Set Watchpoints
2568 @subsection Setting watchpoints
2570 @cindex setting watchpoints
2571 @cindex software watchpoints
2572 @cindex hardware watchpoints
2573 You can use a watchpoint to stop execution whenever the value of an
2574 expression changes, without having to predict a particular place where
2577 Depending on your system, watchpoints may be implemented in software or
2578 hardware. @value{GDBN} does software watchpointing by single-stepping your
2579 program and testing the variable's value each time, which is hundreds of
2580 times slower than normal execution. (But this may still be worth it, to
2581 catch errors where you have no clue what part of your program is the
2584 On some systems, such as HP-UX, Linux and some other x86-based targets,
2585 @value{GDBN} includes support for
2586 hardware watchpoints, which do not slow down the running of your
2591 @item watch @var{expr}
2592 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2593 is written into by the program and its value changes.
2596 @item rwatch @var{expr}
2597 Set a watchpoint that will break when watch @var{expr} is read by the program.
2600 @item awatch @var{expr}
2601 Set a watchpoint that will break when @var{expr} is either read or written into
2604 @kindex info watchpoints
2605 @item info watchpoints
2606 This command prints a list of watchpoints, breakpoints, and catchpoints;
2607 it is the same as @code{info break}.
2610 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2611 watchpoints execute very quickly, and the debugger reports a change in
2612 value at the exact instruction where the change occurs. If @value{GDBN}
2613 cannot set a hardware watchpoint, it sets a software watchpoint, which
2614 executes more slowly and reports the change in value at the next
2615 statement, not the instruction, after the change occurs.
2617 When you issue the @code{watch} command, @value{GDBN} reports
2620 Hardware watchpoint @var{num}: @var{expr}
2624 if it was able to set a hardware watchpoint.
2626 Currently, the @code{awatch} and @code{rwatch} commands can only set
2627 hardware watchpoints, because accesses to data that don't change the
2628 value of the watched expression cannot be detected without examining
2629 every instruction as it is being executed, and @value{GDBN} does not do
2630 that currently. If @value{GDBN} finds that it is unable to set a
2631 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2632 will print a message like this:
2635 Expression cannot be implemented with read/access watchpoint.
2638 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2639 data type of the watched expression is wider than what a hardware
2640 watchpoint on the target machine can handle. For example, some systems
2641 can only watch regions that are up to 4 bytes wide; on such systems you
2642 cannot set hardware watchpoints for an expression that yields a
2643 double-precision floating-point number (which is typically 8 bytes
2644 wide). As a work-around, it might be possible to break the large region
2645 into a series of smaller ones and watch them with separate watchpoints.
2647 If you set too many hardware watchpoints, @value{GDBN} might be unable
2648 to insert all of them when you resume the execution of your program.
2649 Since the precise number of active watchpoints is unknown until such
2650 time as the program is about to be resumed, @value{GDBN} might not be
2651 able to warn you about this when you set the watchpoints, and the
2652 warning will be printed only when the program is resumed:
2655 Hardware watchpoint @var{num}: Could not insert watchpoint
2659 If this happens, delete or disable some of the watchpoints.
2661 The SPARClite DSU will generate traps when a program accesses some data
2662 or instruction address that is assigned to the debug registers. For the
2663 data addresses, DSU facilitates the @code{watch} command. However the
2664 hardware breakpoint registers can only take two data watchpoints, and
2665 both watchpoints must be the same kind. For example, you can set two
2666 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2667 @strong{or} two with @code{awatch} commands, but you cannot set one
2668 watchpoint with one command and the other with a different command.
2669 @value{GDBN} will reject the command if you try to mix watchpoints.
2670 Delete or disable unused watchpoint commands before setting new ones.
2672 If you call a function interactively using @code{print} or @code{call},
2673 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2674 kind of breakpoint or the call completes.
2676 @value{GDBN} automatically deletes watchpoints that watch local
2677 (automatic) variables, or expressions that involve such variables, when
2678 they go out of scope, that is, when the execution leaves the block in
2679 which these variables were defined. In particular, when the program
2680 being debugged terminates, @emph{all} local variables go out of scope,
2681 and so only watchpoints that watch global variables remain set. If you
2682 rerun the program, you will need to set all such watchpoints again. One
2683 way of doing that would be to set a code breakpoint at the entry to the
2684 @code{main} function and when it breaks, set all the watchpoints.
2687 @cindex watchpoints and threads
2688 @cindex threads and watchpoints
2689 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2690 usefulness. With the current watchpoint implementation, @value{GDBN}
2691 can only watch the value of an expression @emph{in a single thread}. If
2692 you are confident that the expression can only change due to the current
2693 thread's activity (and if you are also confident that no other thread
2694 can become current), then you can use watchpoints as usual. However,
2695 @value{GDBN} may not notice when a non-current thread's activity changes
2698 @c FIXME: this is almost identical to the previous paragraph.
2699 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2700 have only limited usefulness. If @value{GDBN} creates a software
2701 watchpoint, it can only watch the value of an expression @emph{in a
2702 single thread}. If you are confident that the expression can only
2703 change due to the current thread's activity (and if you are also
2704 confident that no other thread can become current), then you can use
2705 software watchpoints as usual. However, @value{GDBN} may not notice
2706 when a non-current thread's activity changes the expression. (Hardware
2707 watchpoints, in contrast, watch an expression in all threads.)
2710 @node Set Catchpoints
2711 @subsection Setting catchpoints
2712 @cindex catchpoints, setting
2713 @cindex exception handlers
2714 @cindex event handling
2716 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2717 kinds of program events, such as C@t{++} exceptions or the loading of a
2718 shared library. Use the @code{catch} command to set a catchpoint.
2722 @item catch @var{event}
2723 Stop when @var{event} occurs. @var{event} can be any of the following:
2727 The throwing of a C@t{++} exception.
2731 The catching of a C@t{++} exception.
2735 A call to @code{exec}. This is currently only available for HP-UX.
2739 A call to @code{fork}. This is currently only available for HP-UX.
2743 A call to @code{vfork}. This is currently only available for HP-UX.
2746 @itemx load @var{libname}
2748 The dynamic loading of any shared library, or the loading of the library
2749 @var{libname}. This is currently only available for HP-UX.
2752 @itemx unload @var{libname}
2753 @kindex catch unload
2754 The unloading of any dynamically loaded shared library, or the unloading
2755 of the library @var{libname}. This is currently only available for HP-UX.
2758 @item tcatch @var{event}
2759 Set a catchpoint that is enabled only for one stop. The catchpoint is
2760 automatically deleted after the first time the event is caught.
2764 Use the @code{info break} command to list the current catchpoints.
2766 There are currently some limitations to C@t{++} exception handling
2767 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2771 If you call a function interactively, @value{GDBN} normally returns
2772 control to you when the function has finished executing. If the call
2773 raises an exception, however, the call may bypass the mechanism that
2774 returns control to you and cause your program either to abort or to
2775 simply continue running until it hits a breakpoint, catches a signal
2776 that @value{GDBN} is listening for, or exits. This is the case even if
2777 you set a catchpoint for the exception; catchpoints on exceptions are
2778 disabled within interactive calls.
2781 You cannot raise an exception interactively.
2784 You cannot install an exception handler interactively.
2787 @cindex raise exceptions
2788 Sometimes @code{catch} is not the best way to debug exception handling:
2789 if you need to know exactly where an exception is raised, it is better to
2790 stop @emph{before} the exception handler is called, since that way you
2791 can see the stack before any unwinding takes place. If you set a
2792 breakpoint in an exception handler instead, it may not be easy to find
2793 out where the exception was raised.
2795 To stop just before an exception handler is called, you need some
2796 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2797 raised by calling a library function named @code{__raise_exception}
2798 which has the following ANSI C interface:
2801 /* @var{addr} is where the exception identifier is stored.
2802 @var{id} is the exception identifier. */
2803 void __raise_exception (void **addr, void *id);
2807 To make the debugger catch all exceptions before any stack
2808 unwinding takes place, set a breakpoint on @code{__raise_exception}
2809 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2811 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2812 that depends on the value of @var{id}, you can stop your program when
2813 a specific exception is raised. You can use multiple conditional
2814 breakpoints to stop your program when any of a number of exceptions are
2819 @subsection Deleting breakpoints
2821 @cindex clearing breakpoints, watchpoints, catchpoints
2822 @cindex deleting breakpoints, watchpoints, catchpoints
2823 It is often necessary to eliminate a breakpoint, watchpoint, or
2824 catchpoint once it has done its job and you no longer want your program
2825 to stop there. This is called @dfn{deleting} the breakpoint. A
2826 breakpoint that has been deleted no longer exists; it is forgotten.
2828 With the @code{clear} command you can delete breakpoints according to
2829 where they are in your program. With the @code{delete} command you can
2830 delete individual breakpoints, watchpoints, or catchpoints by specifying
2831 their breakpoint numbers.
2833 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2834 automatically ignores breakpoints on the first instruction to be executed
2835 when you continue execution without changing the execution address.
2840 Delete any breakpoints at the next instruction to be executed in the
2841 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2842 the innermost frame is selected, this is a good way to delete a
2843 breakpoint where your program just stopped.
2845 @item clear @var{function}
2846 @itemx clear @var{filename}:@var{function}
2847 Delete any breakpoints set at entry to the function @var{function}.
2849 @item clear @var{linenum}
2850 @itemx clear @var{filename}:@var{linenum}
2851 Delete any breakpoints set at or within the code of the specified line.
2853 @cindex delete breakpoints
2855 @kindex d @r{(@code{delete})}
2856 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2857 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2858 ranges specified as arguments. If no argument is specified, delete all
2859 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2860 confirm off}). You can abbreviate this command as @code{d}.
2864 @subsection Disabling breakpoints
2866 @kindex disable breakpoints
2867 @kindex enable breakpoints
2868 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2869 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2870 it had been deleted, but remembers the information on the breakpoint so
2871 that you can @dfn{enable} it again later.
2873 You disable and enable breakpoints, watchpoints, and catchpoints with
2874 the @code{enable} and @code{disable} commands, optionally specifying one
2875 or more breakpoint numbers as arguments. Use @code{info break} or
2876 @code{info watch} to print a list of breakpoints, watchpoints, and
2877 catchpoints if you do not know which numbers to use.
2879 A breakpoint, watchpoint, or catchpoint can have any of four different
2880 states of enablement:
2884 Enabled. The breakpoint stops your program. A breakpoint set
2885 with the @code{break} command starts out in this state.
2887 Disabled. The breakpoint has no effect on your program.
2889 Enabled once. The breakpoint stops your program, but then becomes
2892 Enabled for deletion. The breakpoint stops your program, but
2893 immediately after it does so it is deleted permanently. A breakpoint
2894 set with the @code{tbreak} command starts out in this state.
2897 You can use the following commands to enable or disable breakpoints,
2898 watchpoints, and catchpoints:
2901 @kindex disable breakpoints
2903 @kindex dis @r{(@code{disable})}
2904 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2905 Disable the specified breakpoints---or all breakpoints, if none are
2906 listed. A disabled breakpoint has no effect but is not forgotten. All
2907 options such as ignore-counts, conditions and commands are remembered in
2908 case the breakpoint is enabled again later. You may abbreviate
2909 @code{disable} as @code{dis}.
2911 @kindex enable breakpoints
2913 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2914 Enable the specified breakpoints (or all defined breakpoints). They
2915 become effective once again in stopping your program.
2917 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2918 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2919 of these breakpoints immediately after stopping your program.
2921 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2922 Enable the specified breakpoints to work once, then die. @value{GDBN}
2923 deletes any of these breakpoints as soon as your program stops there.
2926 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2927 @c confusing: tbreak is also initially enabled.
2928 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2929 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2930 subsequently, they become disabled or enabled only when you use one of
2931 the commands above. (The command @code{until} can set and delete a
2932 breakpoint of its own, but it does not change the state of your other
2933 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2937 @subsection Break conditions
2938 @cindex conditional breakpoints
2939 @cindex breakpoint conditions
2941 @c FIXME what is scope of break condition expr? Context where wanted?
2942 @c in particular for a watchpoint?
2943 The simplest sort of breakpoint breaks every time your program reaches a
2944 specified place. You can also specify a @dfn{condition} for a
2945 breakpoint. A condition is just a Boolean expression in your
2946 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2947 a condition evaluates the expression each time your program reaches it,
2948 and your program stops only if the condition is @emph{true}.
2950 This is the converse of using assertions for program validation; in that
2951 situation, you want to stop when the assertion is violated---that is,
2952 when the condition is false. In C, if you want to test an assertion expressed
2953 by the condition @var{assert}, you should set the condition
2954 @samp{! @var{assert}} on the appropriate breakpoint.
2956 Conditions are also accepted for watchpoints; you may not need them,
2957 since a watchpoint is inspecting the value of an expression anyhow---but
2958 it might be simpler, say, to just set a watchpoint on a variable name,
2959 and specify a condition that tests whether the new value is an interesting
2962 Break conditions can have side effects, and may even call functions in
2963 your program. This can be useful, for example, to activate functions
2964 that log program progress, or to use your own print functions to
2965 format special data structures. The effects are completely predictable
2966 unless there is another enabled breakpoint at the same address. (In
2967 that case, @value{GDBN} might see the other breakpoint first and stop your
2968 program without checking the condition of this one.) Note that
2969 breakpoint commands are usually more convenient and flexible than break
2971 purpose of performing side effects when a breakpoint is reached
2972 (@pxref{Break Commands, ,Breakpoint command lists}).
2974 Break conditions can be specified when a breakpoint is set, by using
2975 @samp{if} in the arguments to the @code{break} command. @xref{Set
2976 Breaks, ,Setting breakpoints}. They can also be changed at any time
2977 with the @code{condition} command.
2979 You can also use the @code{if} keyword with the @code{watch} command.
2980 The @code{catch} command does not recognize the @code{if} keyword;
2981 @code{condition} is the only way to impose a further condition on a
2986 @item condition @var{bnum} @var{expression}
2987 Specify @var{expression} as the break condition for breakpoint,
2988 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2989 breakpoint @var{bnum} stops your program only if the value of
2990 @var{expression} is true (nonzero, in C). When you use
2991 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2992 syntactic correctness, and to determine whether symbols in it have
2993 referents in the context of your breakpoint. If @var{expression} uses
2994 symbols not referenced in the context of the breakpoint, @value{GDBN}
2995 prints an error message:
2998 No symbol "foo" in current context.
3003 not actually evaluate @var{expression} at the time the @code{condition}
3004 command (or a command that sets a breakpoint with a condition, like
3005 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3007 @item condition @var{bnum}
3008 Remove the condition from breakpoint number @var{bnum}. It becomes
3009 an ordinary unconditional breakpoint.
3012 @cindex ignore count (of breakpoint)
3013 A special case of a breakpoint condition is to stop only when the
3014 breakpoint has been reached a certain number of times. This is so
3015 useful that there is a special way to do it, using the @dfn{ignore
3016 count} of the breakpoint. Every breakpoint has an ignore count, which
3017 is an integer. Most of the time, the ignore count is zero, and
3018 therefore has no effect. But if your program reaches a breakpoint whose
3019 ignore count is positive, then instead of stopping, it just decrements
3020 the ignore count by one and continues. As a result, if the ignore count
3021 value is @var{n}, the breakpoint does not stop the next @var{n} times
3022 your program reaches it.
3026 @item ignore @var{bnum} @var{count}
3027 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3028 The next @var{count} times the breakpoint is reached, your program's
3029 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3032 To make the breakpoint stop the next time it is reached, specify
3035 When you use @code{continue} to resume execution of your program from a
3036 breakpoint, you can specify an ignore count directly as an argument to
3037 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3038 Stepping,,Continuing and stepping}.
3040 If a breakpoint has a positive ignore count and a condition, the
3041 condition is not checked. Once the ignore count reaches zero,
3042 @value{GDBN} resumes checking the condition.
3044 You could achieve the effect of the ignore count with a condition such
3045 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3046 is decremented each time. @xref{Convenience Vars, ,Convenience
3050 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3053 @node Break Commands
3054 @subsection Breakpoint command lists
3056 @cindex breakpoint commands
3057 You can give any breakpoint (or watchpoint or catchpoint) a series of
3058 commands to execute when your program stops due to that breakpoint. For
3059 example, you might want to print the values of certain expressions, or
3060 enable other breakpoints.
3065 @item commands @r{[}@var{bnum}@r{]}
3066 @itemx @dots{} @var{command-list} @dots{}
3068 Specify a list of commands for breakpoint number @var{bnum}. The commands
3069 themselves appear on the following lines. Type a line containing just
3070 @code{end} to terminate the commands.
3072 To remove all commands from a breakpoint, type @code{commands} and
3073 follow it immediately with @code{end}; that is, give no commands.
3075 With no @var{bnum} argument, @code{commands} refers to the last
3076 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3077 recently encountered).
3080 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3081 disabled within a @var{command-list}.
3083 You can use breakpoint commands to start your program up again. Simply
3084 use the @code{continue} command, or @code{step}, or any other command
3085 that resumes execution.
3087 Any other commands in the command list, after a command that resumes
3088 execution, are ignored. This is because any time you resume execution
3089 (even with a simple @code{next} or @code{step}), you may encounter
3090 another breakpoint---which could have its own command list, leading to
3091 ambiguities about which list to execute.
3094 If the first command you specify in a command list is @code{silent}, the
3095 usual message about stopping at a breakpoint is not printed. This may
3096 be desirable for breakpoints that are to print a specific message and
3097 then continue. If none of the remaining commands print anything, you
3098 see no sign that the breakpoint was reached. @code{silent} is
3099 meaningful only at the beginning of a breakpoint command list.
3101 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3102 print precisely controlled output, and are often useful in silent
3103 breakpoints. @xref{Output, ,Commands for controlled output}.
3105 For example, here is how you could use breakpoint commands to print the
3106 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3112 printf "x is %d\n",x
3117 One application for breakpoint commands is to compensate for one bug so
3118 you can test for another. Put a breakpoint just after the erroneous line
3119 of code, give it a condition to detect the case in which something
3120 erroneous has been done, and give it commands to assign correct values
3121 to any variables that need them. End with the @code{continue} command
3122 so that your program does not stop, and start with the @code{silent}
3123 command so that no output is produced. Here is an example:
3134 @node Breakpoint Menus
3135 @subsection Breakpoint menus
3137 @cindex symbol overloading
3139 Some programming languages (notably C@t{++}) permit a single function name
3140 to be defined several times, for application in different contexts.
3141 This is called @dfn{overloading}. When a function name is overloaded,
3142 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3143 a breakpoint. If you realize this is a problem, you can use
3144 something like @samp{break @var{function}(@var{types})} to specify which
3145 particular version of the function you want. Otherwise, @value{GDBN} offers
3146 you a menu of numbered choices for different possible breakpoints, and
3147 waits for your selection with the prompt @samp{>}. The first two
3148 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3149 sets a breakpoint at each definition of @var{function}, and typing
3150 @kbd{0} aborts the @code{break} command without setting any new
3153 For example, the following session excerpt shows an attempt to set a
3154 breakpoint at the overloaded symbol @code{String::after}.
3155 We choose three particular definitions of that function name:
3157 @c FIXME! This is likely to change to show arg type lists, at least
3160 (@value{GDBP}) b String::after
3163 [2] file:String.cc; line number:867
3164 [3] file:String.cc; line number:860
3165 [4] file:String.cc; line number:875
3166 [5] file:String.cc; line number:853
3167 [6] file:String.cc; line number:846
3168 [7] file:String.cc; line number:735
3170 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3171 Breakpoint 2 at 0xb344: file String.cc, line 875.
3172 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3173 Multiple breakpoints were set.
3174 Use the "delete" command to delete unwanted
3180 @c @ifclear BARETARGET
3181 @node Error in Breakpoints
3182 @subsection ``Cannot insert breakpoints''
3184 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3186 Under some operating systems, breakpoints cannot be used in a program if
3187 any other process is running that program. In this situation,
3188 attempting to run or continue a program with a breakpoint causes
3189 @value{GDBN} to print an error message:
3192 Cannot insert breakpoints.
3193 The same program may be running in another process.
3196 When this happens, you have three ways to proceed:
3200 Remove or disable the breakpoints, then continue.
3203 Suspend @value{GDBN}, and copy the file containing your program to a new
3204 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3205 that @value{GDBN} should run your program under that name.
3206 Then start your program again.
3209 Relink your program so that the text segment is nonsharable, using the
3210 linker option @samp{-N}. The operating system limitation may not apply
3211 to nonsharable executables.
3215 A similar message can be printed if you request too many active
3216 hardware-assisted breakpoints and watchpoints:
3218 @c FIXME: the precise wording of this message may change; the relevant
3219 @c source change is not committed yet (Sep 3, 1999).
3221 Stopped; cannot insert breakpoints.
3222 You may have requested too many hardware breakpoints and watchpoints.
3226 This message is printed when you attempt to resume the program, since
3227 only then @value{GDBN} knows exactly how many hardware breakpoints and
3228 watchpoints it needs to insert.
3230 When this message is printed, you need to disable or remove some of the
3231 hardware-assisted breakpoints and watchpoints, and then continue.
3234 @node Continuing and Stepping
3235 @section Continuing and stepping
3239 @cindex resuming execution
3240 @dfn{Continuing} means resuming program execution until your program
3241 completes normally. In contrast, @dfn{stepping} means executing just
3242 one more ``step'' of your program, where ``step'' may mean either one
3243 line of source code, or one machine instruction (depending on what
3244 particular command you use). Either when continuing or when stepping,
3245 your program may stop even sooner, due to a breakpoint or a signal. (If
3246 it stops due to a signal, you may want to use @code{handle}, or use
3247 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3251 @kindex c @r{(@code{continue})}
3252 @kindex fg @r{(resume foreground execution)}
3253 @item continue @r{[}@var{ignore-count}@r{]}
3254 @itemx c @r{[}@var{ignore-count}@r{]}
3255 @itemx fg @r{[}@var{ignore-count}@r{]}
3256 Resume program execution, at the address where your program last stopped;
3257 any breakpoints set at that address are bypassed. The optional argument
3258 @var{ignore-count} allows you to specify a further number of times to
3259 ignore a breakpoint at this location; its effect is like that of
3260 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3262 The argument @var{ignore-count} is meaningful only when your program
3263 stopped due to a breakpoint. At other times, the argument to
3264 @code{continue} is ignored.
3266 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3267 debugged program is deemed to be the foreground program) are provided
3268 purely for convenience, and have exactly the same behavior as
3272 To resume execution at a different place, you can use @code{return}
3273 (@pxref{Returning, ,Returning from a function}) to go back to the
3274 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3275 different address}) to go to an arbitrary location in your program.
3277 A typical technique for using stepping is to set a breakpoint
3278 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3279 beginning of the function or the section of your program where a problem
3280 is believed to lie, run your program until it stops at that breakpoint,
3281 and then step through the suspect area, examining the variables that are
3282 interesting, until you see the problem happen.
3286 @kindex s @r{(@code{step})}
3288 Continue running your program until control reaches a different source
3289 line, then stop it and return control to @value{GDBN}. This command is
3290 abbreviated @code{s}.
3293 @c "without debugging information" is imprecise; actually "without line
3294 @c numbers in the debugging information". (gcc -g1 has debugging info but
3295 @c not line numbers). But it seems complex to try to make that
3296 @c distinction here.
3297 @emph{Warning:} If you use the @code{step} command while control is
3298 within a function that was compiled without debugging information,
3299 execution proceeds until control reaches a function that does have
3300 debugging information. Likewise, it will not step into a function which
3301 is compiled without debugging information. To step through functions
3302 without debugging information, use the @code{stepi} command, described
3306 The @code{step} command only stops at the first instruction of a source
3307 line. This prevents the multiple stops that could otherwise occur in
3308 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3309 to stop if a function that has debugging information is called within
3310 the line. In other words, @code{step} @emph{steps inside} any functions
3311 called within the line.
3313 Also, the @code{step} command only enters a function if there is line
3314 number information for the function. Otherwise it acts like the
3315 @code{next} command. This avoids problems when using @code{cc -gl}
3316 on MIPS machines. Previously, @code{step} entered subroutines if there
3317 was any debugging information about the routine.
3319 @item step @var{count}
3320 Continue running as in @code{step}, but do so @var{count} times. If a
3321 breakpoint is reached, or a signal not related to stepping occurs before
3322 @var{count} steps, stepping stops right away.
3325 @kindex n @r{(@code{next})}
3326 @item next @r{[}@var{count}@r{]}
3327 Continue to the next source line in the current (innermost) stack frame.
3328 This is similar to @code{step}, but function calls that appear within
3329 the line of code are executed without stopping. Execution stops when
3330 control reaches a different line of code at the original stack level
3331 that was executing when you gave the @code{next} command. This command
3332 is abbreviated @code{n}.
3334 An argument @var{count} is a repeat count, as for @code{step}.
3337 @c FIX ME!! Do we delete this, or is there a way it fits in with
3338 @c the following paragraph? --- Vctoria
3340 @c @code{next} within a function that lacks debugging information acts like
3341 @c @code{step}, but any function calls appearing within the code of the
3342 @c function are executed without stopping.
3344 The @code{next} command only stops at the first instruction of a
3345 source line. This prevents multiple stops that could otherwise occur in
3346 @code{switch} statements, @code{for} loops, etc.
3348 @kindex set step-mode
3350 @cindex functions without line info, and stepping
3351 @cindex stepping into functions with no line info
3352 @itemx set step-mode on
3353 The @code{set step-mode on} command causes the @code{step} command to
3354 stop at the first instruction of a function which contains no debug line
3355 information rather than stepping over it.
3357 This is useful in cases where you may be interested in inspecting the
3358 machine instructions of a function which has no symbolic info and do not
3359 want @value{GDBN} to automatically skip over this function.
3361 @item set step-mode off
3362 Causes the @code{step} command to step over any functions which contains no
3363 debug information. This is the default.
3367 Continue running until just after function in the selected stack frame
3368 returns. Print the returned value (if any).
3370 Contrast this with the @code{return} command (@pxref{Returning,
3371 ,Returning from a function}).
3374 @kindex u @r{(@code{until})}
3377 Continue running until a source line past the current line, in the
3378 current stack frame, is reached. This command is used to avoid single
3379 stepping through a loop more than once. It is like the @code{next}
3380 command, except that when @code{until} encounters a jump, it
3381 automatically continues execution until the program counter is greater
3382 than the address of the jump.
3384 This means that when you reach the end of a loop after single stepping
3385 though it, @code{until} makes your program continue execution until it
3386 exits the loop. In contrast, a @code{next} command at the end of a loop
3387 simply steps back to the beginning of the loop, which forces you to step
3388 through the next iteration.
3390 @code{until} always stops your program if it attempts to exit the current
3393 @code{until} may produce somewhat counterintuitive results if the order
3394 of machine code does not match the order of the source lines. For
3395 example, in the following excerpt from a debugging session, the @code{f}
3396 (@code{frame}) command shows that execution is stopped at line
3397 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3401 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3403 (@value{GDBP}) until
3404 195 for ( ; argc > 0; NEXTARG) @{
3407 This happened because, for execution efficiency, the compiler had
3408 generated code for the loop closure test at the end, rather than the
3409 start, of the loop---even though the test in a C @code{for}-loop is
3410 written before the body of the loop. The @code{until} command appeared
3411 to step back to the beginning of the loop when it advanced to this
3412 expression; however, it has not really gone to an earlier
3413 statement---not in terms of the actual machine code.
3415 @code{until} with no argument works by means of single
3416 instruction stepping, and hence is slower than @code{until} with an
3419 @item until @var{location}
3420 @itemx u @var{location}
3421 Continue running your program until either the specified location is
3422 reached, or the current stack frame returns. @var{location} is any of
3423 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3424 ,Setting breakpoints}). This form of the command uses breakpoints,
3425 and hence is quicker than @code{until} without an argument.
3428 @kindex si @r{(@code{stepi})}
3430 @itemx stepi @var{arg}
3432 Execute one machine instruction, then stop and return to the debugger.
3434 It is often useful to do @samp{display/i $pc} when stepping by machine
3435 instructions. This makes @value{GDBN} automatically display the next
3436 instruction to be executed, each time your program stops. @xref{Auto
3437 Display,, Automatic display}.
3439 An argument is a repeat count, as in @code{step}.
3443 @kindex ni @r{(@code{nexti})}
3445 @itemx nexti @var{arg}
3447 Execute one machine instruction, but if it is a function call,
3448 proceed until the function returns.
3450 An argument is a repeat count, as in @code{next}.
3457 A signal is an asynchronous event that can happen in a program. The
3458 operating system defines the possible kinds of signals, and gives each
3459 kind a name and a number. For example, in Unix @code{SIGINT} is the
3460 signal a program gets when you type an interrupt character (often @kbd{C-c});
3461 @code{SIGSEGV} is the signal a program gets from referencing a place in
3462 memory far away from all the areas in use; @code{SIGALRM} occurs when
3463 the alarm clock timer goes off (which happens only if your program has
3464 requested an alarm).
3466 @cindex fatal signals
3467 Some signals, including @code{SIGALRM}, are a normal part of the
3468 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3469 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3470 program has not specified in advance some other way to handle the signal.
3471 @code{SIGINT} does not indicate an error in your program, but it is normally
3472 fatal so it can carry out the purpose of the interrupt: to kill the program.
3474 @value{GDBN} has the ability to detect any occurrence of a signal in your
3475 program. You can tell @value{GDBN} in advance what to do for each kind of
3478 @cindex handling signals
3479 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3480 @code{SIGALRM} be silently passed to your program
3481 (so as not to interfere with their role in the program's functioning)
3482 but to stop your program immediately whenever an error signal happens.
3483 You can change these settings with the @code{handle} command.
3486 @kindex info signals
3489 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3490 handle each one. You can use this to see the signal numbers of all
3491 the defined types of signals.
3493 @code{info handle} is an alias for @code{info signals}.
3496 @item handle @var{signal} @var{keywords}@dots{}
3497 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3498 can be the number of a signal or its name (with or without the
3499 @samp{SIG} at the beginning); a list of signal numbers of the form
3500 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3501 known signals. The @var{keywords} say what change to make.
3505 The keywords allowed by the @code{handle} command can be abbreviated.
3506 Their full names are:
3510 @value{GDBN} should not stop your program when this signal happens. It may
3511 still print a message telling you that the signal has come in.
3514 @value{GDBN} should stop your program when this signal happens. This implies
3515 the @code{print} keyword as well.
3518 @value{GDBN} should print a message when this signal happens.
3521 @value{GDBN} should not mention the occurrence of the signal at all. This
3522 implies the @code{nostop} keyword as well.
3526 @value{GDBN} should allow your program to see this signal; your program
3527 can handle the signal, or else it may terminate if the signal is fatal
3528 and not handled. @code{pass} and @code{noignore} are synonyms.
3532 @value{GDBN} should not allow your program to see this signal.
3533 @code{nopass} and @code{ignore} are synonyms.
3537 When a signal stops your program, the signal is not visible to the
3539 continue. Your program sees the signal then, if @code{pass} is in
3540 effect for the signal in question @emph{at that time}. In other words,
3541 after @value{GDBN} reports a signal, you can use the @code{handle}
3542 command with @code{pass} or @code{nopass} to control whether your
3543 program sees that signal when you continue.
3545 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3546 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3547 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3550 You can also use the @code{signal} command to prevent your program from
3551 seeing a signal, or cause it to see a signal it normally would not see,
3552 or to give it any signal at any time. For example, if your program stopped
3553 due to some sort of memory reference error, you might store correct
3554 values into the erroneous variables and continue, hoping to see more
3555 execution; but your program would probably terminate immediately as
3556 a result of the fatal signal once it saw the signal. To prevent this,
3557 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3561 @section Stopping and starting multi-thread programs
3563 When your program has multiple threads (@pxref{Threads,, Debugging
3564 programs with multiple threads}), you can choose whether to set
3565 breakpoints on all threads, or on a particular thread.
3568 @cindex breakpoints and threads
3569 @cindex thread breakpoints
3570 @kindex break @dots{} thread @var{threadno}
3571 @item break @var{linespec} thread @var{threadno}
3572 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3573 @var{linespec} specifies source lines; there are several ways of
3574 writing them, but the effect is always to specify some source line.
3576 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3577 to specify that you only want @value{GDBN} to stop the program when a
3578 particular thread reaches this breakpoint. @var{threadno} is one of the
3579 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3580 column of the @samp{info threads} display.
3582 If you do not specify @samp{thread @var{threadno}} when you set a
3583 breakpoint, the breakpoint applies to @emph{all} threads of your
3586 You can use the @code{thread} qualifier on conditional breakpoints as
3587 well; in this case, place @samp{thread @var{threadno}} before the
3588 breakpoint condition, like this:
3591 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3596 @cindex stopped threads
3597 @cindex threads, stopped
3598 Whenever your program stops under @value{GDBN} for any reason,
3599 @emph{all} threads of execution stop, not just the current thread. This
3600 allows you to examine the overall state of the program, including
3601 switching between threads, without worrying that things may change
3604 @cindex continuing threads
3605 @cindex threads, continuing
3606 Conversely, whenever you restart the program, @emph{all} threads start
3607 executing. @emph{This is true even when single-stepping} with commands
3608 like @code{step} or @code{next}.
3610 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3611 Since thread scheduling is up to your debugging target's operating
3612 system (not controlled by @value{GDBN}), other threads may
3613 execute more than one statement while the current thread completes a
3614 single step. Moreover, in general other threads stop in the middle of a
3615 statement, rather than at a clean statement boundary, when the program
3618 You might even find your program stopped in another thread after
3619 continuing or even single-stepping. This happens whenever some other
3620 thread runs into a breakpoint, a signal, or an exception before the
3621 first thread completes whatever you requested.
3623 On some OSes, you can lock the OS scheduler and thus allow only a single
3627 @item set scheduler-locking @var{mode}
3628 Set the scheduler locking mode. If it is @code{off}, then there is no
3629 locking and any thread may run at any time. If @code{on}, then only the
3630 current thread may run when the inferior is resumed. The @code{step}
3631 mode optimizes for single-stepping. It stops other threads from
3632 ``seizing the prompt'' by preempting the current thread while you are
3633 stepping. Other threads will only rarely (or never) get a chance to run
3634 when you step. They are more likely to run when you @samp{next} over a
3635 function call, and they are completely free to run when you use commands
3636 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3637 thread hits a breakpoint during its timeslice, they will never steal the
3638 @value{GDBN} prompt away from the thread that you are debugging.
3640 @item show scheduler-locking
3641 Display the current scheduler locking mode.
3646 @chapter Examining the Stack
3648 When your program has stopped, the first thing you need to know is where it
3649 stopped and how it got there.
3652 Each time your program performs a function call, information about the call
3654 That information includes the location of the call in your program,
3655 the arguments of the call,
3656 and the local variables of the function being called.
3657 The information is saved in a block of data called a @dfn{stack frame}.
3658 The stack frames are allocated in a region of memory called the @dfn{call
3661 When your program stops, the @value{GDBN} commands for examining the
3662 stack allow you to see all of this information.
3664 @cindex selected frame
3665 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3666 @value{GDBN} commands refer implicitly to the selected frame. In
3667 particular, whenever you ask @value{GDBN} for the value of a variable in
3668 your program, the value is found in the selected frame. There are
3669 special @value{GDBN} commands to select whichever frame you are
3670 interested in. @xref{Selection, ,Selecting a frame}.
3672 When your program stops, @value{GDBN} automatically selects the
3673 currently executing frame and describes it briefly, similar to the
3674 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3677 * Frames:: Stack frames
3678 * Backtrace:: Backtraces
3679 * Selection:: Selecting a frame
3680 * Frame Info:: Information on a frame
3685 @section Stack frames
3687 @cindex frame, definition
3689 The call stack is divided up into contiguous pieces called @dfn{stack
3690 frames}, or @dfn{frames} for short; each frame is the data associated
3691 with one call to one function. The frame contains the arguments given
3692 to the function, the function's local variables, and the address at
3693 which the function is executing.
3695 @cindex initial frame
3696 @cindex outermost frame
3697 @cindex innermost frame
3698 When your program is started, the stack has only one frame, that of the
3699 function @code{main}. This is called the @dfn{initial} frame or the
3700 @dfn{outermost} frame. Each time a function is called, a new frame is
3701 made. Each time a function returns, the frame for that function invocation
3702 is eliminated. If a function is recursive, there can be many frames for
3703 the same function. The frame for the function in which execution is
3704 actually occurring is called the @dfn{innermost} frame. This is the most
3705 recently created of all the stack frames that still exist.
3707 @cindex frame pointer
3708 Inside your program, stack frames are identified by their addresses. A
3709 stack frame consists of many bytes, each of which has its own address; each
3710 kind of computer has a convention for choosing one byte whose
3711 address serves as the address of the frame. Usually this address is kept
3712 in a register called the @dfn{frame pointer register} while execution is
3713 going on in that frame.
3715 @cindex frame number
3716 @value{GDBN} assigns numbers to all existing stack frames, starting with
3717 zero for the innermost frame, one for the frame that called it,
3718 and so on upward. These numbers do not really exist in your program;
3719 they are assigned by @value{GDBN} to give you a way of designating stack
3720 frames in @value{GDBN} commands.
3722 @c The -fomit-frame-pointer below perennially causes hbox overflow
3723 @c underflow problems.
3724 @cindex frameless execution
3725 Some compilers provide a way to compile functions so that they operate
3726 without stack frames. (For example, the @value{GCC} option
3728 @samp{-fomit-frame-pointer}
3730 generates functions without a frame.)
3731 This is occasionally done with heavily used library functions to save
3732 the frame setup time. @value{GDBN} has limited facilities for dealing
3733 with these function invocations. If the innermost function invocation
3734 has no stack frame, @value{GDBN} nevertheless regards it as though
3735 it had a separate frame, which is numbered zero as usual, allowing
3736 correct tracing of the function call chain. However, @value{GDBN} has
3737 no provision for frameless functions elsewhere in the stack.
3740 @kindex frame@r{, command}
3741 @cindex current stack frame
3742 @item frame @var{args}
3743 The @code{frame} command allows you to move from one stack frame to another,
3744 and to print the stack frame you select. @var{args} may be either the
3745 address of the frame or the stack frame number. Without an argument,
3746 @code{frame} prints the current stack frame.
3748 @kindex select-frame
3749 @cindex selecting frame silently
3751 The @code{select-frame} command allows you to move from one stack frame
3752 to another without printing the frame. This is the silent version of
3761 @cindex stack traces
3762 A backtrace is a summary of how your program got where it is. It shows one
3763 line per frame, for many frames, starting with the currently executing
3764 frame (frame zero), followed by its caller (frame one), and on up the
3769 @kindex bt @r{(@code{backtrace})}
3772 Print a backtrace of the entire stack: one line per frame for all
3773 frames in the stack.
3775 You can stop the backtrace at any time by typing the system interrupt
3776 character, normally @kbd{C-c}.
3778 @item backtrace @var{n}
3780 Similar, but print only the innermost @var{n} frames.
3782 @item backtrace -@var{n}
3784 Similar, but print only the outermost @var{n} frames.
3789 @kindex info s @r{(@code{info stack})}
3790 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3791 are additional aliases for @code{backtrace}.
3793 Each line in the backtrace shows the frame number and the function name.
3794 The program counter value is also shown---unless you use @code{set
3795 print address off}. The backtrace also shows the source file name and
3796 line number, as well as the arguments to the function. The program
3797 counter value is omitted if it is at the beginning of the code for that
3800 Here is an example of a backtrace. It was made with the command
3801 @samp{bt 3}, so it shows the innermost three frames.
3805 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3807 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3808 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3810 (More stack frames follow...)
3815 The display for frame zero does not begin with a program counter
3816 value, indicating that your program has stopped at the beginning of the
3817 code for line @code{993} of @code{builtin.c}.
3820 @section Selecting a frame
3822 Most commands for examining the stack and other data in your program work on
3823 whichever stack frame is selected at the moment. Here are the commands for
3824 selecting a stack frame; all of them finish by printing a brief description
3825 of the stack frame just selected.
3828 @kindex frame@r{, selecting}
3829 @kindex f @r{(@code{frame})}
3832 Select frame number @var{n}. Recall that frame zero is the innermost
3833 (currently executing) frame, frame one is the frame that called the
3834 innermost one, and so on. The highest-numbered frame is the one for
3837 @item frame @var{addr}
3839 Select the frame at address @var{addr}. This is useful mainly if the
3840 chaining of stack frames has been damaged by a bug, making it
3841 impossible for @value{GDBN} to assign numbers properly to all frames. In
3842 addition, this can be useful when your program has multiple stacks and
3843 switches between them.
3845 On the SPARC architecture, @code{frame} needs two addresses to
3846 select an arbitrary frame: a frame pointer and a stack pointer.
3848 On the MIPS and Alpha architecture, it needs two addresses: a stack
3849 pointer and a program counter.
3851 On the 29k architecture, it needs three addresses: a register stack
3852 pointer, a program counter, and a memory stack pointer.
3853 @c note to future updaters: this is conditioned on a flag
3854 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3855 @c as of 27 Jan 1994.
3859 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3860 advances toward the outermost frame, to higher frame numbers, to frames
3861 that have existed longer. @var{n} defaults to one.
3864 @kindex do @r{(@code{down})}
3866 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3867 advances toward the innermost frame, to lower frame numbers, to frames
3868 that were created more recently. @var{n} defaults to one. You may
3869 abbreviate @code{down} as @code{do}.
3872 All of these commands end by printing two lines of output describing the
3873 frame. The first line shows the frame number, the function name, the
3874 arguments, and the source file and line number of execution in that
3875 frame. The second line shows the text of that source line.
3883 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3885 10 read_input_file (argv[i]);
3889 After such a printout, the @code{list} command with no arguments
3890 prints ten lines centered on the point of execution in the frame.
3891 @xref{List, ,Printing source lines}.
3894 @kindex down-silently
3896 @item up-silently @var{n}
3897 @itemx down-silently @var{n}
3898 These two commands are variants of @code{up} and @code{down},
3899 respectively; they differ in that they do their work silently, without
3900 causing display of the new frame. They are intended primarily for use
3901 in @value{GDBN} command scripts, where the output might be unnecessary and
3906 @section Information about a frame
3908 There are several other commands to print information about the selected
3914 When used without any argument, this command does not change which
3915 frame is selected, but prints a brief description of the currently
3916 selected stack frame. It can be abbreviated @code{f}. With an
3917 argument, this command is used to select a stack frame.
3918 @xref{Selection, ,Selecting a frame}.
3921 @kindex info f @r{(@code{info frame})}
3924 This command prints a verbose description of the selected stack frame,
3929 the address of the frame
3931 the address of the next frame down (called by this frame)
3933 the address of the next frame up (caller of this frame)
3935 the language in which the source code corresponding to this frame is written
3937 the address of the frame's arguments
3939 the address of the frame's local variables
3941 the program counter saved in it (the address of execution in the caller frame)
3943 which registers were saved in the frame
3946 @noindent The verbose description is useful when
3947 something has gone wrong that has made the stack format fail to fit
3948 the usual conventions.
3950 @item info frame @var{addr}
3951 @itemx info f @var{addr}
3952 Print a verbose description of the frame at address @var{addr}, without
3953 selecting that frame. The selected frame remains unchanged by this
3954 command. This requires the same kind of address (more than one for some
3955 architectures) that you specify in the @code{frame} command.
3956 @xref{Selection, ,Selecting a frame}.
3960 Print the arguments of the selected frame, each on a separate line.
3964 Print the local variables of the selected frame, each on a separate
3965 line. These are all variables (declared either static or automatic)
3966 accessible at the point of execution of the selected frame.
3969 @cindex catch exceptions, list active handlers
3970 @cindex exception handlers, how to list
3972 Print a list of all the exception handlers that are active in the
3973 current stack frame at the current point of execution. To see other
3974 exception handlers, visit the associated frame (using the @code{up},
3975 @code{down}, or @code{frame} commands); then type @code{info catch}.
3976 @xref{Set Catchpoints, , Setting catchpoints}.
3982 @chapter Examining Source Files
3984 @value{GDBN} can print parts of your program's source, since the debugging
3985 information recorded in the program tells @value{GDBN} what source files were
3986 used to build it. When your program stops, @value{GDBN} spontaneously prints
3987 the line where it stopped. Likewise, when you select a stack frame
3988 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3989 execution in that frame has stopped. You can print other portions of
3990 source files by explicit command.
3992 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3993 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3994 @value{GDBN} under @sc{gnu} Emacs}.
3997 * List:: Printing source lines
3998 * Search:: Searching source files
3999 * Source Path:: Specifying source directories
4000 * Machine Code:: Source and machine code
4004 @section Printing source lines
4007 @kindex l @r{(@code{list})}
4008 To print lines from a source file, use the @code{list} command
4009 (abbreviated @code{l}). By default, ten lines are printed.
4010 There are several ways to specify what part of the file you want to print.
4012 Here are the forms of the @code{list} command most commonly used:
4015 @item list @var{linenum}
4016 Print lines centered around line number @var{linenum} in the
4017 current source file.
4019 @item list @var{function}
4020 Print lines centered around the beginning of function
4024 Print more lines. If the last lines printed were printed with a
4025 @code{list} command, this prints lines following the last lines
4026 printed; however, if the last line printed was a solitary line printed
4027 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4028 Stack}), this prints lines centered around that line.
4031 Print lines just before the lines last printed.
4034 By default, @value{GDBN} prints ten source lines with any of these forms of
4035 the @code{list} command. You can change this using @code{set listsize}:
4038 @kindex set listsize
4039 @item set listsize @var{count}
4040 Make the @code{list} command display @var{count} source lines (unless
4041 the @code{list} argument explicitly specifies some other number).
4043 @kindex show listsize
4045 Display the number of lines that @code{list} prints.
4048 Repeating a @code{list} command with @key{RET} discards the argument,
4049 so it is equivalent to typing just @code{list}. This is more useful
4050 than listing the same lines again. An exception is made for an
4051 argument of @samp{-}; that argument is preserved in repetition so that
4052 each repetition moves up in the source file.
4055 In general, the @code{list} command expects you to supply zero, one or two
4056 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4057 of writing them, but the effect is always to specify some source line.
4058 Here is a complete description of the possible arguments for @code{list}:
4061 @item list @var{linespec}
4062 Print lines centered around the line specified by @var{linespec}.
4064 @item list @var{first},@var{last}
4065 Print lines from @var{first} to @var{last}. Both arguments are
4068 @item list ,@var{last}
4069 Print lines ending with @var{last}.
4071 @item list @var{first},
4072 Print lines starting with @var{first}.
4075 Print lines just after the lines last printed.
4078 Print lines just before the lines last printed.
4081 As described in the preceding table.
4084 Here are the ways of specifying a single source line---all the
4089 Specifies line @var{number} of the current source file.
4090 When a @code{list} command has two linespecs, this refers to
4091 the same source file as the first linespec.
4094 Specifies the line @var{offset} lines after the last line printed.
4095 When used as the second linespec in a @code{list} command that has
4096 two, this specifies the line @var{offset} lines down from the
4100 Specifies the line @var{offset} lines before the last line printed.
4102 @item @var{filename}:@var{number}
4103 Specifies line @var{number} in the source file @var{filename}.
4105 @item @var{function}
4106 Specifies the line that begins the body of the function @var{function}.
4107 For example: in C, this is the line with the open brace.
4109 @item @var{filename}:@var{function}
4110 Specifies the line of the open-brace that begins the body of the
4111 function @var{function} in the file @var{filename}. You only need the
4112 file name with a function name to avoid ambiguity when there are
4113 identically named functions in different source files.
4115 @item *@var{address}
4116 Specifies the line containing the program address @var{address}.
4117 @var{address} may be any expression.
4121 @section Searching source files
4123 @kindex reverse-search
4125 There are two commands for searching through the current source file for a
4130 @kindex forward-search
4131 @item forward-search @var{regexp}
4132 @itemx search @var{regexp}
4133 The command @samp{forward-search @var{regexp}} checks each line,
4134 starting with the one following the last line listed, for a match for
4135 @var{regexp}. It lists the line that is found. You can use the
4136 synonym @samp{search @var{regexp}} or abbreviate the command name as
4139 @item reverse-search @var{regexp}
4140 The command @samp{reverse-search @var{regexp}} checks each line, starting
4141 with the one before the last line listed and going backward, for a match
4142 for @var{regexp}. It lists the line that is found. You can abbreviate
4143 this command as @code{rev}.
4147 @section Specifying source directories
4150 @cindex directories for source files
4151 Executable programs sometimes do not record the directories of the source
4152 files from which they were compiled, just the names. Even when they do,
4153 the directories could be moved between the compilation and your debugging
4154 session. @value{GDBN} has a list of directories to search for source files;
4155 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4156 it tries all the directories in the list, in the order they are present
4157 in the list, until it finds a file with the desired name. Note that
4158 the executable search path is @emph{not} used for this purpose. Neither is
4159 the current working directory, unless it happens to be in the source
4162 If @value{GDBN} cannot find a source file in the source path, and the
4163 object program records a directory, @value{GDBN} tries that directory
4164 too. If the source path is empty, and there is no record of the
4165 compilation directory, @value{GDBN} looks in the current directory as a
4168 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4169 any information it has cached about where source files are found and where
4170 each line is in the file.
4174 When you start @value{GDBN}, its source path includes only @samp{cdir}
4175 and @samp{cwd}, in that order.
4176 To add other directories, use the @code{directory} command.
4179 @item directory @var{dirname} @dots{}
4180 @item dir @var{dirname} @dots{}
4181 Add directory @var{dirname} to the front of the source path. Several
4182 directory names may be given to this command, separated by @samp{:}
4183 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4184 part of absolute file names) or
4185 whitespace. You may specify a directory that is already in the source
4186 path; this moves it forward, so @value{GDBN} searches it sooner.
4190 @vindex $cdir@r{, convenience variable}
4191 @vindex $cwdr@r{, convenience variable}
4192 @cindex compilation directory
4193 @cindex current directory
4194 @cindex working directory
4195 @cindex directory, current
4196 @cindex directory, compilation
4197 You can use the string @samp{$cdir} to refer to the compilation
4198 directory (if one is recorded), and @samp{$cwd} to refer to the current
4199 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4200 tracks the current working directory as it changes during your @value{GDBN}
4201 session, while the latter is immediately expanded to the current
4202 directory at the time you add an entry to the source path.
4205 Reset the source path to empty again. This requires confirmation.
4207 @c RET-repeat for @code{directory} is explicitly disabled, but since
4208 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4210 @item show directories
4211 @kindex show directories
4212 Print the source path: show which directories it contains.
4215 If your source path is cluttered with directories that are no longer of
4216 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4217 versions of source. You can correct the situation as follows:
4221 Use @code{directory} with no argument to reset the source path to empty.
4224 Use @code{directory} with suitable arguments to reinstall the
4225 directories you want in the source path. You can add all the
4226 directories in one command.
4230 @section Source and machine code
4232 You can use the command @code{info line} to map source lines to program
4233 addresses (and vice versa), and the command @code{disassemble} to display
4234 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4235 mode, the @code{info line} command causes the arrow to point to the
4236 line specified. Also, @code{info line} prints addresses in symbolic form as
4241 @item info line @var{linespec}
4242 Print the starting and ending addresses of the compiled code for
4243 source line @var{linespec}. You can specify source lines in any of
4244 the ways understood by the @code{list} command (@pxref{List, ,Printing
4248 For example, we can use @code{info line} to discover the location of
4249 the object code for the first line of function
4250 @code{m4_changequote}:
4252 @c FIXME: I think this example should also show the addresses in
4253 @c symbolic form, as they usually would be displayed.
4255 (@value{GDBP}) info line m4_changequote
4256 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4260 We can also inquire (using @code{*@var{addr}} as the form for
4261 @var{linespec}) what source line covers a particular address:
4263 (@value{GDBP}) info line *0x63ff
4264 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4267 @cindex @code{$_} and @code{info line}
4268 @kindex x@r{(examine), and} info line
4269 After @code{info line}, the default address for the @code{x} command
4270 is changed to the starting address of the line, so that @samp{x/i} is
4271 sufficient to begin examining the machine code (@pxref{Memory,
4272 ,Examining memory}). Also, this address is saved as the value of the
4273 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4278 @cindex assembly instructions
4279 @cindex instructions, assembly
4280 @cindex machine instructions
4281 @cindex listing machine instructions
4283 This specialized command dumps a range of memory as machine
4284 instructions. The default memory range is the function surrounding the
4285 program counter of the selected frame. A single argument to this
4286 command is a program counter value; @value{GDBN} dumps the function
4287 surrounding this value. Two arguments specify a range of addresses
4288 (first inclusive, second exclusive) to dump.
4291 The following example shows the disassembly of a range of addresses of
4292 HP PA-RISC 2.0 code:
4295 (@value{GDBP}) disas 0x32c4 0x32e4
4296 Dump of assembler code from 0x32c4 to 0x32e4:
4297 0x32c4 <main+204>: addil 0,dp
4298 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4299 0x32cc <main+212>: ldil 0x3000,r31
4300 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4301 0x32d4 <main+220>: ldo 0(r31),rp
4302 0x32d8 <main+224>: addil -0x800,dp
4303 0x32dc <main+228>: ldo 0x588(r1),r26
4304 0x32e0 <main+232>: ldil 0x3000,r31
4305 End of assembler dump.
4308 Some architectures have more than one commonly-used set of instruction
4309 mnemonics or other syntax.
4312 @kindex set disassembly-flavor
4313 @cindex assembly instructions
4314 @cindex instructions, assembly
4315 @cindex machine instructions
4316 @cindex listing machine instructions
4317 @cindex Intel disassembly flavor
4318 @cindex AT&T disassembly flavor
4319 @item set disassembly-flavor @var{instruction-set}
4320 Select the instruction set to use when disassembling the
4321 program via the @code{disassemble} or @code{x/i} commands.
4323 Currently this command is only defined for the Intel x86 family. You
4324 can set @var{instruction-set} to either @code{intel} or @code{att}.
4325 The default is @code{att}, the AT&T flavor used by default by Unix
4326 assemblers for x86-based targets.
4331 @chapter Examining Data
4333 @cindex printing data
4334 @cindex examining data
4337 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4338 @c document because it is nonstandard... Under Epoch it displays in a
4339 @c different window or something like that.
4340 The usual way to examine data in your program is with the @code{print}
4341 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4342 evaluates and prints the value of an expression of the language your
4343 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4344 Different Languages}).
4347 @item print @var{expr}
4348 @itemx print /@var{f} @var{expr}
4349 @var{expr} is an expression (in the source language). By default the
4350 value of @var{expr} is printed in a format appropriate to its data type;
4351 you can choose a different format by specifying @samp{/@var{f}}, where
4352 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4356 @itemx print /@var{f}
4357 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4358 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4359 conveniently inspect the same value in an alternative format.
4362 A more low-level way of examining data is with the @code{x} command.
4363 It examines data in memory at a specified address and prints it in a
4364 specified format. @xref{Memory, ,Examining memory}.
4366 If you are interested in information about types, or about how the
4367 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4368 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4372 * Expressions:: Expressions
4373 * Variables:: Program variables
4374 * Arrays:: Artificial arrays
4375 * Output Formats:: Output formats
4376 * Memory:: Examining memory
4377 * Auto Display:: Automatic display
4378 * Print Settings:: Print settings
4379 * Value History:: Value history
4380 * Convenience Vars:: Convenience variables
4381 * Registers:: Registers
4382 * Floating Point Hardware:: Floating point hardware
4383 * Memory Region Attributes:: Memory region attributes
4387 @section Expressions
4390 @code{print} and many other @value{GDBN} commands accept an expression and
4391 compute its value. Any kind of constant, variable or operator defined
4392 by the programming language you are using is valid in an expression in
4393 @value{GDBN}. This includes conditional expressions, function calls, casts
4394 and string constants. It unfortunately does not include symbols defined
4395 by preprocessor @code{#define} commands.
4397 @value{GDBN} supports array constants in expressions input by
4398 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4399 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4400 memory that is @code{malloc}ed in the target program.
4402 Because C is so widespread, most of the expressions shown in examples in
4403 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4404 Languages}, for information on how to use expressions in other
4407 In this section, we discuss operators that you can use in @value{GDBN}
4408 expressions regardless of your programming language.
4410 Casts are supported in all languages, not just in C, because it is so
4411 useful to cast a number into a pointer in order to examine a structure
4412 at that address in memory.
4413 @c FIXME: casts supported---Mod2 true?
4415 @value{GDBN} supports these operators, in addition to those common
4416 to programming languages:
4420 @samp{@@} is a binary operator for treating parts of memory as arrays.
4421 @xref{Arrays, ,Artificial arrays}, for more information.
4424 @samp{::} allows you to specify a variable in terms of the file or
4425 function where it is defined. @xref{Variables, ,Program variables}.
4427 @cindex @{@var{type}@}
4428 @cindex type casting memory
4429 @cindex memory, viewing as typed object
4430 @cindex casts, to view memory
4431 @item @{@var{type}@} @var{addr}
4432 Refers to an object of type @var{type} stored at address @var{addr} in
4433 memory. @var{addr} may be any expression whose value is an integer or
4434 pointer (but parentheses are required around binary operators, just as in
4435 a cast). This construct is allowed regardless of what kind of data is
4436 normally supposed to reside at @var{addr}.
4440 @section Program variables
4442 The most common kind of expression to use is the name of a variable
4445 Variables in expressions are understood in the selected stack frame
4446 (@pxref{Selection, ,Selecting a frame}); they must be either:
4450 global (or file-static)
4457 visible according to the scope rules of the
4458 programming language from the point of execution in that frame
4461 @noindent This means that in the function
4476 you can examine and use the variable @code{a} whenever your program is
4477 executing within the function @code{foo}, but you can only use or
4478 examine the variable @code{b} while your program is executing inside
4479 the block where @code{b} is declared.
4481 @cindex variable name conflict
4482 There is an exception: you can refer to a variable or function whose
4483 scope is a single source file even if the current execution point is not
4484 in this file. But it is possible to have more than one such variable or
4485 function with the same name (in different source files). If that
4486 happens, referring to that name has unpredictable effects. If you wish,
4487 you can specify a static variable in a particular function or file,
4488 using the colon-colon notation:
4490 @cindex colon-colon, context for variables/functions
4492 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4493 @cindex @code{::}, context for variables/functions
4496 @var{file}::@var{variable}
4497 @var{function}::@var{variable}
4501 Here @var{file} or @var{function} is the name of the context for the
4502 static @var{variable}. In the case of file names, you can use quotes to
4503 make sure @value{GDBN} parses the file name as a single word---for example,
4504 to print a global value of @code{x} defined in @file{f2.c}:
4507 (@value{GDBP}) p 'f2.c'::x
4510 @cindex C@t{++} scope resolution
4511 This use of @samp{::} is very rarely in conflict with the very similar
4512 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4513 scope resolution operator in @value{GDBN} expressions.
4514 @c FIXME: Um, so what happens in one of those rare cases where it's in
4517 @cindex wrong values
4518 @cindex variable values, wrong
4520 @emph{Warning:} Occasionally, a local variable may appear to have the
4521 wrong value at certain points in a function---just after entry to a new
4522 scope, and just before exit.
4524 You may see this problem when you are stepping by machine instructions.
4525 This is because, on most machines, it takes more than one instruction to
4526 set up a stack frame (including local variable definitions); if you are
4527 stepping by machine instructions, variables may appear to have the wrong
4528 values until the stack frame is completely built. On exit, it usually
4529 also takes more than one machine instruction to destroy a stack frame;
4530 after you begin stepping through that group of instructions, local
4531 variable definitions may be gone.
4533 This may also happen when the compiler does significant optimizations.
4534 To be sure of always seeing accurate values, turn off all optimization
4537 @cindex ``No symbol "foo" in current context''
4538 Another possible effect of compiler optimizations is to optimize
4539 unused variables out of existence, or assign variables to registers (as
4540 opposed to memory addresses). Depending on the support for such cases
4541 offered by the debug info format used by the compiler, @value{GDBN}
4542 might not be able to display values for such local variables. If that
4543 happens, @value{GDBN} will print a message like this:
4546 No symbol "foo" in current context.
4549 To solve such problems, either recompile without optimizations, or use a
4550 different debug info format, if the compiler supports several such
4551 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4552 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4553 in a format that is superior to formats such as COFF. You may be able
4554 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4555 debug info. See @ref{Debugging Options,,Options for Debugging Your
4556 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4561 @section Artificial arrays
4563 @cindex artificial array
4564 @kindex @@@r{, referencing memory as an array}
4565 It is often useful to print out several successive objects of the
4566 same type in memory; a section of an array, or an array of
4567 dynamically determined size for which only a pointer exists in the
4570 You can do this by referring to a contiguous span of memory as an
4571 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4572 operand of @samp{@@} should be the first element of the desired array
4573 and be an individual object. The right operand should be the desired length
4574 of the array. The result is an array value whose elements are all of
4575 the type of the left argument. The first element is actually the left
4576 argument; the second element comes from bytes of memory immediately
4577 following those that hold the first element, and so on. Here is an
4578 example. If a program says
4581 int *array = (int *) malloc (len * sizeof (int));
4585 you can print the contents of @code{array} with
4591 The left operand of @samp{@@} must reside in memory. Array values made
4592 with @samp{@@} in this way behave just like other arrays in terms of
4593 subscripting, and are coerced to pointers when used in expressions.
4594 Artificial arrays most often appear in expressions via the value history
4595 (@pxref{Value History, ,Value history}), after printing one out.
4597 Another way to create an artificial array is to use a cast.
4598 This re-interprets a value as if it were an array.
4599 The value need not be in memory:
4601 (@value{GDBP}) p/x (short[2])0x12345678
4602 $1 = @{0x1234, 0x5678@}
4605 As a convenience, if you leave the array length out (as in
4606 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4607 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4609 (@value{GDBP}) p/x (short[])0x12345678
4610 $2 = @{0x1234, 0x5678@}
4613 Sometimes the artificial array mechanism is not quite enough; in
4614 moderately complex data structures, the elements of interest may not
4615 actually be adjacent---for example, if you are interested in the values
4616 of pointers in an array. One useful work-around in this situation is
4617 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4618 variables}) as a counter in an expression that prints the first
4619 interesting value, and then repeat that expression via @key{RET}. For
4620 instance, suppose you have an array @code{dtab} of pointers to
4621 structures, and you are interested in the values of a field @code{fv}
4622 in each structure. Here is an example of what you might type:
4632 @node Output Formats
4633 @section Output formats
4635 @cindex formatted output
4636 @cindex output formats
4637 By default, @value{GDBN} prints a value according to its data type. Sometimes
4638 this is not what you want. For example, you might want to print a number
4639 in hex, or a pointer in decimal. Or you might want to view data in memory
4640 at a certain address as a character string or as an instruction. To do
4641 these things, specify an @dfn{output format} when you print a value.
4643 The simplest use of output formats is to say how to print a value
4644 already computed. This is done by starting the arguments of the
4645 @code{print} command with a slash and a format letter. The format
4646 letters supported are:
4650 Regard the bits of the value as an integer, and print the integer in
4654 Print as integer in signed decimal.
4657 Print as integer in unsigned decimal.
4660 Print as integer in octal.
4663 Print as integer in binary. The letter @samp{t} stands for ``two''.
4664 @footnote{@samp{b} cannot be used because these format letters are also
4665 used with the @code{x} command, where @samp{b} stands for ``byte'';
4666 see @ref{Memory,,Examining memory}.}
4669 @cindex unknown address, locating
4670 @cindex locate address
4671 Print as an address, both absolute in hexadecimal and as an offset from
4672 the nearest preceding symbol. You can use this format used to discover
4673 where (in what function) an unknown address is located:
4676 (@value{GDBP}) p/a 0x54320
4677 $3 = 0x54320 <_initialize_vx+396>
4681 The command @code{info symbol 0x54320} yields similar results.
4682 @xref{Symbols, info symbol}.
4685 Regard as an integer and print it as a character constant.
4688 Regard the bits of the value as a floating point number and print
4689 using typical floating point syntax.
4692 For example, to print the program counter in hex (@pxref{Registers}), type
4699 Note that no space is required before the slash; this is because command
4700 names in @value{GDBN} cannot contain a slash.
4702 To reprint the last value in the value history with a different format,
4703 you can use the @code{print} command with just a format and no
4704 expression. For example, @samp{p/x} reprints the last value in hex.
4707 @section Examining memory
4709 You can use the command @code{x} (for ``examine'') to examine memory in
4710 any of several formats, independently of your program's data types.
4712 @cindex examining memory
4714 @kindex x @r{(examine memory)}
4715 @item x/@var{nfu} @var{addr}
4718 Use the @code{x} command to examine memory.
4721 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4722 much memory to display and how to format it; @var{addr} is an
4723 expression giving the address where you want to start displaying memory.
4724 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4725 Several commands set convenient defaults for @var{addr}.
4728 @item @var{n}, the repeat count
4729 The repeat count is a decimal integer; the default is 1. It specifies
4730 how much memory (counting by units @var{u}) to display.
4731 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4734 @item @var{f}, the display format
4735 The display format is one of the formats used by @code{print},
4736 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4737 The default is @samp{x} (hexadecimal) initially.
4738 The default changes each time you use either @code{x} or @code{print}.
4740 @item @var{u}, the unit size
4741 The unit size is any of
4747 Halfwords (two bytes).
4749 Words (four bytes). This is the initial default.
4751 Giant words (eight bytes).
4754 Each time you specify a unit size with @code{x}, that size becomes the
4755 default unit the next time you use @code{x}. (For the @samp{s} and
4756 @samp{i} formats, the unit size is ignored and is normally not written.)
4758 @item @var{addr}, starting display address
4759 @var{addr} is the address where you want @value{GDBN} to begin displaying
4760 memory. The expression need not have a pointer value (though it may);
4761 it is always interpreted as an integer address of a byte of memory.
4762 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4763 @var{addr} is usually just after the last address examined---but several
4764 other commands also set the default address: @code{info breakpoints} (to
4765 the address of the last breakpoint listed), @code{info line} (to the
4766 starting address of a line), and @code{print} (if you use it to display
4767 a value from memory).
4770 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4771 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4772 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4773 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4774 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4776 Since the letters indicating unit sizes are all distinct from the
4777 letters specifying output formats, you do not have to remember whether
4778 unit size or format comes first; either order works. The output
4779 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4780 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4782 Even though the unit size @var{u} is ignored for the formats @samp{s}
4783 and @samp{i}, you might still want to use a count @var{n}; for example,
4784 @samp{3i} specifies that you want to see three machine instructions,
4785 including any operands. The command @code{disassemble} gives an
4786 alternative way of inspecting machine instructions; see @ref{Machine
4787 Code,,Source and machine code}.
4789 All the defaults for the arguments to @code{x} are designed to make it
4790 easy to continue scanning memory with minimal specifications each time
4791 you use @code{x}. For example, after you have inspected three machine
4792 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4793 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4794 the repeat count @var{n} is used again; the other arguments default as
4795 for successive uses of @code{x}.
4797 @cindex @code{$_}, @code{$__}, and value history
4798 The addresses and contents printed by the @code{x} command are not saved
4799 in the value history because there is often too much of them and they
4800 would get in the way. Instead, @value{GDBN} makes these values available for
4801 subsequent use in expressions as values of the convenience variables
4802 @code{$_} and @code{$__}. After an @code{x} command, the last address
4803 examined is available for use in expressions in the convenience variable
4804 @code{$_}. The contents of that address, as examined, are available in
4805 the convenience variable @code{$__}.
4807 If the @code{x} command has a repeat count, the address and contents saved
4808 are from the last memory unit printed; this is not the same as the last
4809 address printed if several units were printed on the last line of output.
4812 @section Automatic display
4813 @cindex automatic display
4814 @cindex display of expressions
4816 If you find that you want to print the value of an expression frequently
4817 (to see how it changes), you might want to add it to the @dfn{automatic
4818 display list} so that @value{GDBN} prints its value each time your program stops.
4819 Each expression added to the list is given a number to identify it;
4820 to remove an expression from the list, you specify that number.
4821 The automatic display looks like this:
4825 3: bar[5] = (struct hack *) 0x3804
4829 This display shows item numbers, expressions and their current values. As with
4830 displays you request manually using @code{x} or @code{print}, you can
4831 specify the output format you prefer; in fact, @code{display} decides
4832 whether to use @code{print} or @code{x} depending on how elaborate your
4833 format specification is---it uses @code{x} if you specify a unit size,
4834 or one of the two formats (@samp{i} and @samp{s}) that are only
4835 supported by @code{x}; otherwise it uses @code{print}.
4839 @item display @var{expr}
4840 Add the expression @var{expr} to the list of expressions to display
4841 each time your program stops. @xref{Expressions, ,Expressions}.
4843 @code{display} does not repeat if you press @key{RET} again after using it.
4845 @item display/@var{fmt} @var{expr}
4846 For @var{fmt} specifying only a display format and not a size or
4847 count, add the expression @var{expr} to the auto-display list but
4848 arrange to display it each time in the specified format @var{fmt}.
4849 @xref{Output Formats,,Output formats}.
4851 @item display/@var{fmt} @var{addr}
4852 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4853 number of units, add the expression @var{addr} as a memory address to
4854 be examined each time your program stops. Examining means in effect
4855 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4858 For example, @samp{display/i $pc} can be helpful, to see the machine
4859 instruction about to be executed each time execution stops (@samp{$pc}
4860 is a common name for the program counter; @pxref{Registers, ,Registers}).
4863 @kindex delete display
4865 @item undisplay @var{dnums}@dots{}
4866 @itemx delete display @var{dnums}@dots{}
4867 Remove item numbers @var{dnums} from the list of expressions to display.
4869 @code{undisplay} does not repeat if you press @key{RET} after using it.
4870 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4872 @kindex disable display
4873 @item disable display @var{dnums}@dots{}
4874 Disable the display of item numbers @var{dnums}. A disabled display
4875 item is not printed automatically, but is not forgotten. It may be
4876 enabled again later.
4878 @kindex enable display
4879 @item enable display @var{dnums}@dots{}
4880 Enable display of item numbers @var{dnums}. It becomes effective once
4881 again in auto display of its expression, until you specify otherwise.
4884 Display the current values of the expressions on the list, just as is
4885 done when your program stops.
4887 @kindex info display
4889 Print the list of expressions previously set up to display
4890 automatically, each one with its item number, but without showing the
4891 values. This includes disabled expressions, which are marked as such.
4892 It also includes expressions which would not be displayed right now
4893 because they refer to automatic variables not currently available.
4896 If a display expression refers to local variables, then it does not make
4897 sense outside the lexical context for which it was set up. Such an
4898 expression is disabled when execution enters a context where one of its
4899 variables is not defined. For example, if you give the command
4900 @code{display last_char} while inside a function with an argument
4901 @code{last_char}, @value{GDBN} displays this argument while your program
4902 continues to stop inside that function. When it stops elsewhere---where
4903 there is no variable @code{last_char}---the display is disabled
4904 automatically. The next time your program stops where @code{last_char}
4905 is meaningful, you can enable the display expression once again.
4907 @node Print Settings
4908 @section Print settings
4910 @cindex format options
4911 @cindex print settings
4912 @value{GDBN} provides the following ways to control how arrays, structures,
4913 and symbols are printed.
4916 These settings are useful for debugging programs in any language:
4919 @kindex set print address
4920 @item set print address
4921 @itemx set print address on
4922 @value{GDBN} prints memory addresses showing the location of stack
4923 traces, structure values, pointer values, breakpoints, and so forth,
4924 even when it also displays the contents of those addresses. The default
4925 is @code{on}. For example, this is what a stack frame display looks like with
4926 @code{set print address on}:
4931 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4933 530 if (lquote != def_lquote)
4937 @item set print address off
4938 Do not print addresses when displaying their contents. For example,
4939 this is the same stack frame displayed with @code{set print address off}:
4943 (@value{GDBP}) set print addr off
4945 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4946 530 if (lquote != def_lquote)
4950 You can use @samp{set print address off} to eliminate all machine
4951 dependent displays from the @value{GDBN} interface. For example, with
4952 @code{print address off}, you should get the same text for backtraces on
4953 all machines---whether or not they involve pointer arguments.
4955 @kindex show print address
4956 @item show print address
4957 Show whether or not addresses are to be printed.
4960 When @value{GDBN} prints a symbolic address, it normally prints the
4961 closest earlier symbol plus an offset. If that symbol does not uniquely
4962 identify the address (for example, it is a name whose scope is a single
4963 source file), you may need to clarify. One way to do this is with
4964 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4965 you can set @value{GDBN} to print the source file and line number when
4966 it prints a symbolic address:
4969 @kindex set print symbol-filename
4970 @item set print symbol-filename on
4971 Tell @value{GDBN} to print the source file name and line number of a
4972 symbol in the symbolic form of an address.
4974 @item set print symbol-filename off
4975 Do not print source file name and line number of a symbol. This is the
4978 @kindex show print symbol-filename
4979 @item show print symbol-filename
4980 Show whether or not @value{GDBN} will print the source file name and
4981 line number of a symbol in the symbolic form of an address.
4984 Another situation where it is helpful to show symbol filenames and line
4985 numbers is when disassembling code; @value{GDBN} shows you the line
4986 number and source file that corresponds to each instruction.
4988 Also, you may wish to see the symbolic form only if the address being
4989 printed is reasonably close to the closest earlier symbol:
4992 @kindex set print max-symbolic-offset
4993 @item set print max-symbolic-offset @var{max-offset}
4994 Tell @value{GDBN} to only display the symbolic form of an address if the
4995 offset between the closest earlier symbol and the address is less than
4996 @var{max-offset}. The default is 0, which tells @value{GDBN}
4997 to always print the symbolic form of an address if any symbol precedes it.
4999 @kindex show print max-symbolic-offset
5000 @item show print max-symbolic-offset
5001 Ask how large the maximum offset is that @value{GDBN} prints in a
5005 @cindex wild pointer, interpreting
5006 @cindex pointer, finding referent
5007 If you have a pointer and you are not sure where it points, try
5008 @samp{set print symbol-filename on}. Then you can determine the name
5009 and source file location of the variable where it points, using
5010 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5011 For example, here @value{GDBN} shows that a variable @code{ptt} points
5012 at another variable @code{t}, defined in @file{hi2.c}:
5015 (@value{GDBP}) set print symbol-filename on
5016 (@value{GDBP}) p/a ptt
5017 $4 = 0xe008 <t in hi2.c>
5021 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5022 does not show the symbol name and filename of the referent, even with
5023 the appropriate @code{set print} options turned on.
5026 Other settings control how different kinds of objects are printed:
5029 @kindex set print array
5030 @item set print array
5031 @itemx set print array on
5032 Pretty print arrays. This format is more convenient to read,
5033 but uses more space. The default is off.
5035 @item set print array off
5036 Return to compressed format for arrays.
5038 @kindex show print array
5039 @item show print array
5040 Show whether compressed or pretty format is selected for displaying
5043 @kindex set print elements
5044 @item set print elements @var{number-of-elements}
5045 Set a limit on how many elements of an array @value{GDBN} will print.
5046 If @value{GDBN} is printing a large array, it stops printing after it has
5047 printed the number of elements set by the @code{set print elements} command.
5048 This limit also applies to the display of strings.
5049 When @value{GDBN} starts, this limit is set to 200.
5050 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5052 @kindex show print elements
5053 @item show print elements
5054 Display the number of elements of a large array that @value{GDBN} will print.
5055 If the number is 0, then the printing is unlimited.
5057 @kindex set print null-stop
5058 @item set print null-stop
5059 Cause @value{GDBN} to stop printing the characters of an array when the first
5060 @sc{null} is encountered. This is useful when large arrays actually
5061 contain only short strings.
5064 @kindex set print pretty
5065 @item set print pretty on
5066 Cause @value{GDBN} to print structures in an indented format with one member
5067 per line, like this:
5082 @item set print pretty off
5083 Cause @value{GDBN} to print structures in a compact format, like this:
5087 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5088 meat = 0x54 "Pork"@}
5093 This is the default format.
5095 @kindex show print pretty
5096 @item show print pretty
5097 Show which format @value{GDBN} is using to print structures.
5099 @kindex set print sevenbit-strings
5100 @item set print sevenbit-strings on
5101 Print using only seven-bit characters; if this option is set,
5102 @value{GDBN} displays any eight-bit characters (in strings or
5103 character values) using the notation @code{\}@var{nnn}. This setting is
5104 best if you are working in English (@sc{ascii}) and you use the
5105 high-order bit of characters as a marker or ``meta'' bit.
5107 @item set print sevenbit-strings off
5108 Print full eight-bit characters. This allows the use of more
5109 international character sets, and is the default.
5111 @kindex show print sevenbit-strings
5112 @item show print sevenbit-strings
5113 Show whether or not @value{GDBN} is printing only seven-bit characters.
5115 @kindex set print union
5116 @item set print union on
5117 Tell @value{GDBN} to print unions which are contained in structures. This
5118 is the default setting.
5120 @item set print union off
5121 Tell @value{GDBN} not to print unions which are contained in structures.
5123 @kindex show print union
5124 @item show print union
5125 Ask @value{GDBN} whether or not it will print unions which are contained in
5128 For example, given the declarations
5131 typedef enum @{Tree, Bug@} Species;
5132 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5133 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5144 struct thing foo = @{Tree, @{Acorn@}@};
5148 with @code{set print union on} in effect @samp{p foo} would print
5151 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5155 and with @code{set print union off} in effect it would print
5158 $1 = @{it = Tree, form = @{...@}@}
5164 These settings are of interest when debugging C@t{++} programs:
5168 @kindex set print demangle
5169 @item set print demangle
5170 @itemx set print demangle on
5171 Print C@t{++} names in their source form rather than in the encoded
5172 (``mangled'') form passed to the assembler and linker for type-safe
5173 linkage. The default is on.
5175 @kindex show print demangle
5176 @item show print demangle
5177 Show whether C@t{++} names are printed in mangled or demangled form.
5179 @kindex set print asm-demangle
5180 @item set print asm-demangle
5181 @itemx set print asm-demangle on
5182 Print C@t{++} names in their source form rather than their mangled form, even
5183 in assembler code printouts such as instruction disassemblies.
5186 @kindex show print asm-demangle
5187 @item show print asm-demangle
5188 Show whether C@t{++} names in assembly listings are printed in mangled
5191 @kindex set demangle-style
5192 @cindex C@t{++} symbol decoding style
5193 @cindex symbol decoding style, C@t{++}
5194 @item set demangle-style @var{style}
5195 Choose among several encoding schemes used by different compilers to
5196 represent C@t{++} names. The choices for @var{style} are currently:
5200 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5203 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5204 This is the default.
5207 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5210 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5213 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5214 @strong{Warning:} this setting alone is not sufficient to allow
5215 debugging @code{cfront}-generated executables. @value{GDBN} would
5216 require further enhancement to permit that.
5219 If you omit @var{style}, you will see a list of possible formats.
5221 @kindex show demangle-style
5222 @item show demangle-style
5223 Display the encoding style currently in use for decoding C@t{++} symbols.
5225 @kindex set print object
5226 @item set print object
5227 @itemx set print object on
5228 When displaying a pointer to an object, identify the @emph{actual}
5229 (derived) type of the object rather than the @emph{declared} type, using
5230 the virtual function table.
5232 @item set print object off
5233 Display only the declared type of objects, without reference to the
5234 virtual function table. This is the default setting.
5236 @kindex show print object
5237 @item show print object
5238 Show whether actual, or declared, object types are displayed.
5240 @kindex set print static-members
5241 @item set print static-members
5242 @itemx set print static-members on
5243 Print static members when displaying a C@t{++} object. The default is on.
5245 @item set print static-members off
5246 Do not print static members when displaying a C@t{++} object.
5248 @kindex show print static-members
5249 @item show print static-members
5250 Show whether C@t{++} static members are printed, or not.
5252 @c These don't work with HP ANSI C++ yet.
5253 @kindex set print vtbl
5254 @item set print vtbl
5255 @itemx set print vtbl on
5256 Pretty print C@t{++} virtual function tables. The default is off.
5257 (The @code{vtbl} commands do not work on programs compiled with the HP
5258 ANSI C@t{++} compiler (@code{aCC}).)
5260 @item set print vtbl off
5261 Do not pretty print C@t{++} virtual function tables.
5263 @kindex show print vtbl
5264 @item show print vtbl
5265 Show whether C@t{++} virtual function tables are pretty printed, or not.
5269 @section Value history
5271 @cindex value history
5272 Values printed by the @code{print} command are saved in the @value{GDBN}
5273 @dfn{value history}. This allows you to refer to them in other expressions.
5274 Values are kept until the symbol table is re-read or discarded
5275 (for example with the @code{file} or @code{symbol-file} commands).
5276 When the symbol table changes, the value history is discarded,
5277 since the values may contain pointers back to the types defined in the
5282 @cindex history number
5283 The values printed are given @dfn{history numbers} by which you can
5284 refer to them. These are successive integers starting with one.
5285 @code{print} shows you the history number assigned to a value by
5286 printing @samp{$@var{num} = } before the value; here @var{num} is the
5289 To refer to any previous value, use @samp{$} followed by the value's
5290 history number. The way @code{print} labels its output is designed to
5291 remind you of this. Just @code{$} refers to the most recent value in
5292 the history, and @code{$$} refers to the value before that.
5293 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5294 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5295 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5297 For example, suppose you have just printed a pointer to a structure and
5298 want to see the contents of the structure. It suffices to type
5304 If you have a chain of structures where the component @code{next} points
5305 to the next one, you can print the contents of the next one with this:
5312 You can print successive links in the chain by repeating this
5313 command---which you can do by just typing @key{RET}.
5315 Note that the history records values, not expressions. If the value of
5316 @code{x} is 4 and you type these commands:
5324 then the value recorded in the value history by the @code{print} command
5325 remains 4 even though the value of @code{x} has changed.
5330 Print the last ten values in the value history, with their item numbers.
5331 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5332 values} does not change the history.
5334 @item show values @var{n}
5335 Print ten history values centered on history item number @var{n}.
5338 Print ten history values just after the values last printed. If no more
5339 values are available, @code{show values +} produces no display.
5342 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5343 same effect as @samp{show values +}.
5345 @node Convenience Vars
5346 @section Convenience variables
5348 @cindex convenience variables
5349 @value{GDBN} provides @dfn{convenience variables} that you can use within
5350 @value{GDBN} to hold on to a value and refer to it later. These variables
5351 exist entirely within @value{GDBN}; they are not part of your program, and
5352 setting a convenience variable has no direct effect on further execution
5353 of your program. That is why you can use them freely.
5355 Convenience variables are prefixed with @samp{$}. Any name preceded by
5356 @samp{$} can be used for a convenience variable, unless it is one of
5357 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5358 (Value history references, in contrast, are @emph{numbers} preceded
5359 by @samp{$}. @xref{Value History, ,Value history}.)
5361 You can save a value in a convenience variable with an assignment
5362 expression, just as you would set a variable in your program.
5366 set $foo = *object_ptr
5370 would save in @code{$foo} the value contained in the object pointed to by
5373 Using a convenience variable for the first time creates it, but its
5374 value is @code{void} until you assign a new value. You can alter the
5375 value with another assignment at any time.
5377 Convenience variables have no fixed types. You can assign a convenience
5378 variable any type of value, including structures and arrays, even if
5379 that variable already has a value of a different type. The convenience
5380 variable, when used as an expression, has the type of its current value.
5383 @kindex show convenience
5384 @item show convenience
5385 Print a list of convenience variables used so far, and their values.
5386 Abbreviated @code{show conv}.
5389 One of the ways to use a convenience variable is as a counter to be
5390 incremented or a pointer to be advanced. For example, to print
5391 a field from successive elements of an array of structures:
5395 print bar[$i++]->contents
5399 Repeat that command by typing @key{RET}.
5401 Some convenience variables are created automatically by @value{GDBN} and given
5402 values likely to be useful.
5405 @vindex $_@r{, convenience variable}
5407 The variable @code{$_} is automatically set by the @code{x} command to
5408 the last address examined (@pxref{Memory, ,Examining memory}). Other
5409 commands which provide a default address for @code{x} to examine also
5410 set @code{$_} to that address; these commands include @code{info line}
5411 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5412 except when set by the @code{x} command, in which case it is a pointer
5413 to the type of @code{$__}.
5415 @vindex $__@r{, convenience variable}
5417 The variable @code{$__} is automatically set by the @code{x} command
5418 to the value found in the last address examined. Its type is chosen
5419 to match the format in which the data was printed.
5422 @vindex $_exitcode@r{, convenience variable}
5423 The variable @code{$_exitcode} is automatically set to the exit code when
5424 the program being debugged terminates.
5427 On HP-UX systems, if you refer to a function or variable name that
5428 begins with a dollar sign, @value{GDBN} searches for a user or system
5429 name first, before it searches for a convenience variable.
5435 You can refer to machine register contents, in expressions, as variables
5436 with names starting with @samp{$}. The names of registers are different
5437 for each machine; use @code{info registers} to see the names used on
5441 @kindex info registers
5442 @item info registers
5443 Print the names and values of all registers except floating-point
5444 registers (in the selected stack frame).
5446 @kindex info all-registers
5447 @cindex floating point registers
5448 @item info all-registers
5449 Print the names and values of all registers, including floating-point
5452 @item info registers @var{regname} @dots{}
5453 Print the @dfn{relativized} value of each specified register @var{regname}.
5454 As discussed in detail below, register values are normally relative to
5455 the selected stack frame. @var{regname} may be any register name valid on
5456 the machine you are using, with or without the initial @samp{$}.
5459 @value{GDBN} has four ``standard'' register names that are available (in
5460 expressions) on most machines---whenever they do not conflict with an
5461 architecture's canonical mnemonics for registers. The register names
5462 @code{$pc} and @code{$sp} are used for the program counter register and
5463 the stack pointer. @code{$fp} is used for a register that contains a
5464 pointer to the current stack frame, and @code{$ps} is used for a
5465 register that contains the processor status. For example,
5466 you could print the program counter in hex with
5473 or print the instruction to be executed next with
5480 or add four to the stack pointer@footnote{This is a way of removing
5481 one word from the stack, on machines where stacks grow downward in
5482 memory (most machines, nowadays). This assumes that the innermost
5483 stack frame is selected; setting @code{$sp} is not allowed when other
5484 stack frames are selected. To pop entire frames off the stack,
5485 regardless of machine architecture, use @code{return};
5486 see @ref{Returning, ,Returning from a function}.} with
5492 Whenever possible, these four standard register names are available on
5493 your machine even though the machine has different canonical mnemonics,
5494 so long as there is no conflict. The @code{info registers} command
5495 shows the canonical names. For example, on the SPARC, @code{info
5496 registers} displays the processor status register as @code{$psr} but you
5497 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5498 is an alias for the @sc{eflags} register.
5500 @value{GDBN} always considers the contents of an ordinary register as an
5501 integer when the register is examined in this way. Some machines have
5502 special registers which can hold nothing but floating point; these
5503 registers are considered to have floating point values. There is no way
5504 to refer to the contents of an ordinary register as floating point value
5505 (although you can @emph{print} it as a floating point value with
5506 @samp{print/f $@var{regname}}).
5508 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5509 means that the data format in which the register contents are saved by
5510 the operating system is not the same one that your program normally
5511 sees. For example, the registers of the 68881 floating point
5512 coprocessor are always saved in ``extended'' (raw) format, but all C
5513 programs expect to work with ``double'' (virtual) format. In such
5514 cases, @value{GDBN} normally works with the virtual format only (the format
5515 that makes sense for your program), but the @code{info registers} command
5516 prints the data in both formats.
5518 Normally, register values are relative to the selected stack frame
5519 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5520 value that the register would contain if all stack frames farther in
5521 were exited and their saved registers restored. In order to see the
5522 true contents of hardware registers, you must select the innermost
5523 frame (with @samp{frame 0}).
5525 However, @value{GDBN} must deduce where registers are saved, from the machine
5526 code generated by your compiler. If some registers are not saved, or if
5527 @value{GDBN} is unable to locate the saved registers, the selected stack
5528 frame makes no difference.
5530 @node Floating Point Hardware
5531 @section Floating point hardware
5532 @cindex floating point
5534 Depending on the configuration, @value{GDBN} may be able to give
5535 you more information about the status of the floating point hardware.
5540 Display hardware-dependent information about the floating
5541 point unit. The exact contents and layout vary depending on the
5542 floating point chip. Currently, @samp{info float} is supported on
5543 the ARM and x86 machines.
5546 @node Memory Region Attributes
5547 @section Memory Region Attributes
5548 @cindex memory region attributes
5550 @dfn{Memory region attributes} allow you to describe special handling
5551 required by regions of your target's memory. @value{GDBN} uses attributes
5552 to determine whether to allow certain types of memory accesses; whether to
5553 use specific width accesses; and whether to cache target memory.
5555 Defined memory regions can be individually enabled and disabled. When a
5556 memory region is disabled, @value{GDBN} uses the default attributes when
5557 accessing memory in that region. Similarly, if no memory regions have
5558 been defined, @value{GDBN} uses the default attributes when accessing
5561 When a memory region is defined, it is given a number to identify it;
5562 to enable, disable, or remove a memory region, you specify that number.
5566 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5567 Define memory region bounded by @var{address1} and @var{address2}
5568 with attributes @var{attributes}@dots{}.
5571 @item delete mem @var{nums}@dots{}
5572 Remove memory region numbers @var{nums}.
5575 @item disable mem @var{nums}@dots{}
5576 Disable memory region numbers @var{nums}.
5577 A disabled memory region is not forgotten.
5578 It may be enabled again later.
5581 @item enable mem @var{nums}@dots{}
5582 Enable memory region numbers @var{nums}.
5586 Print a table of all defined memory regions, with the following columns
5590 @item Memory Region Number
5591 @item Enabled or Disabled.
5592 Enabled memory regions are marked with @samp{y}.
5593 Disabled memory regions are marked with @samp{n}.
5596 The address defining the inclusive lower bound of the memory region.
5599 The address defining the exclusive upper bound of the memory region.
5602 The list of attributes set for this memory region.
5607 @subsection Attributes
5609 @subsubsection Memory Access Mode
5610 The access mode attributes set whether @value{GDBN} may make read or
5611 write accesses to a memory region.
5613 While these attributes prevent @value{GDBN} from performing invalid
5614 memory accesses, they do nothing to prevent the target system, I/O DMA,
5615 etc. from accessing memory.
5619 Memory is read only.
5621 Memory is write only.
5623 Memory is read/write (default).
5626 @subsubsection Memory Access Size
5627 The acccess size attributes tells @value{GDBN} to use specific sized
5628 accesses in the memory region. Often memory mapped device registers
5629 require specific sized accesses. If no access size attribute is
5630 specified, @value{GDBN} may use accesses of any size.
5634 Use 8 bit memory accesses.
5636 Use 16 bit memory accesses.
5638 Use 32 bit memory accesses.
5640 Use 64 bit memory accesses.
5643 @c @subsubsection Hardware/Software Breakpoints
5644 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5645 @c will use hardware or software breakpoints for the internal breakpoints
5646 @c used by the step, next, finish, until, etc. commands.
5650 @c Always use hardware breakpoints
5651 @c @item swbreak (default)
5654 @subsubsection Data Cache
5655 The data cache attributes set whether @value{GDBN} will cache target
5656 memory. While this generally improves performance by reducing debug
5657 protocol overhead, it can lead to incorrect results because @value{GDBN}
5658 does not know about volatile variables or memory mapped device
5663 Enable @value{GDBN} to cache target memory.
5664 @item nocache (default)
5665 Disable @value{GDBN} from caching target memory.
5668 @c @subsubsection Memory Write Verification
5669 @c The memory write verification attributes set whether @value{GDBN}
5670 @c will re-reads data after each write to verify the write was successful.
5674 @c @item noverify (default)
5678 @chapter Tracepoints
5679 @c This chapter is based on the documentation written by Michael
5680 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
5683 In some applications, it is not feasible for the debugger to interrupt
5684 the program's execution long enough for the developer to learn
5685 anything helpful about its behavior. If the program's correctness
5686 depends on its real-time behavior, delays introduced by a debugger
5687 might cause the program to change its behavior drastically, or perhaps
5688 fail, even when the code itself is correct. It is useful to be able
5689 to observe the program's behavior without interrupting it.
5691 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
5692 specify locations in the program, called @dfn{tracepoints}, and
5693 arbitrary expressions to evaluate when those tracepoints are reached.
5694 Later, using the @code{tfind} command, you can examine the values
5695 those expressions had when the program hit the tracepoints. The
5696 expressions may also denote objects in memory---structures or arrays,
5697 for example---whose values @value{GDBN} should record; while visiting
5698 a particular tracepoint, you may inspect those objects as if they were
5699 in memory at that moment. However, because @value{GDBN} records these
5700 values without interacting with you, it can do so quickly and
5701 unobtrusively, hopefully not disturbing the program's behavior.
5703 The tracepoint facility is currently available only for remote
5704 targets. @xref{Targets}.
5706 This chapter describes the tracepoint commands and features.
5710 * Analyze Collected Data::
5711 * Tracepoint Variables::
5714 @node Set Tracepoints
5715 @section Commands to Set Tracepoints
5717 Before running such a @dfn{trace experiment}, an arbitrary number of
5718 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
5719 tracepoint has a number assigned to it by @value{GDBN}. Like with
5720 breakpoints, tracepoint numbers are successive integers starting from
5721 one. Many of the commands associated with tracepoints take the
5722 tracepoint number as their argument, to identify which tracepoint to
5725 For each tracepoint, you can specify, in advance, some arbitrary set
5726 of data that you want the target to collect in the trace buffer when
5727 it hits that tracepoint. The collected data can include registers,
5728 local variables, or global data. Later, you can use @value{GDBN}
5729 commands to examine the values these data had at the time the
5732 This section describes commands to set tracepoints and associated
5733 conditions and actions.
5736 * Create and Delete Tracepoints::
5737 * Enable and Disable Tracepoints::
5738 * Tracepoint Passcounts::
5739 * Tracepoint Actions::
5740 * Listing Tracepoints::
5741 * Starting and Stopping Trace Experiment::
5744 @node Create and Delete Tracepoints
5745 @subsection Create and Delete Tracepoints
5748 @cindex set tracepoint
5751 The @code{trace} command is very similar to the @code{break} command.
5752 Its argument can be a source line, a function name, or an address in
5753 the target program. @xref{Set Breaks}. The @code{trace} command
5754 defines a tracepoint, which is a point in the target program where the
5755 debugger will briefly stop, collect some data, and then allow the
5756 program to continue. Setting a tracepoint or changing its commands
5757 doesn't take effect until the next @code{tstart} command; thus, you
5758 cannot change the tracepoint attributes once a trace experiment is
5761 Here are some examples of using the @code{trace} command:
5764 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
5766 (@value{GDBP}) @b{trace +2} // 2 lines forward
5768 (@value{GDBP}) @b{trace my_function} // first source line of function
5770 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
5772 (@value{GDBP}) @b{trace *0x2117c4} // an address
5776 You can abbreviate @code{trace} as @code{tr}.
5779 @cindex last tracepoint number
5780 @cindex recent tracepoint number
5781 @cindex tracepoint number
5782 The convenience variable @code{$tpnum} records the tracepoint number
5783 of the most recently set tracepoint.
5785 @kindex delete tracepoint
5786 @cindex tracepoint deletion
5787 @item delete tracepoint @r{[}@var{num}@r{]}
5788 Permanently delete one or more tracepoints. With no argument, the
5789 default is to delete all tracepoints.
5794 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
5796 (@value{GDBP}) @b{delete trace} // remove all tracepoints
5800 You can abbreviate this command as @code{del tr}.
5803 @node Enable and Disable Tracepoints
5804 @subsection Enable and Disable Tracepoints
5807 @kindex disable tracepoint
5808 @item disable tracepoint @r{[}@var{num}@r{]}
5809 Disable tracepoint @var{num}, or all tracepoints if no argument
5810 @var{num} is given. A disabled tracepoint will have no effect during
5811 the next trace experiment, but it is not forgotten. You can re-enable
5812 a disabled tracepoint using the @code{enable tracepoint} command.
5814 @kindex enable tracepoint
5815 @item enable tracepoint @r{[}@var{num}@r{]}
5816 Enable tracepoint @var{num}, or all tracepoints. The enabled
5817 tracepoints will become effective the next time a trace experiment is
5821 @node Tracepoint Passcounts
5822 @subsection Tracepoint Passcounts
5826 @cindex tracepoint pass count
5827 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
5828 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
5829 automatically stop a trace experiment. If a tracepoint's passcount is
5830 @var{n}, then the trace experiment will be automatically stopped on
5831 the @var{n}'th time that tracepoint is hit. If the tracepoint number
5832 @var{num} is not specified, the @code{passcount} command sets the
5833 passcount of the most recently defined tracepoint. If no passcount is
5834 given, the trace experiment will run until stopped explicitly by the
5840 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of tracepoint 2
5842 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
5843 // most recently defined tracepoint.
5844 (@value{GDBP}) @b{trace foo}
5845 (@value{GDBP}) @b{pass 3}
5846 (@value{GDBP}) @b{trace bar}
5847 (@value{GDBP}) @b{pass 2}
5848 (@value{GDBP}) @b{trace baz}
5849 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
5850 // executed 3 times OR when bar has
5851 // been executed 2 times
5852 // OR when baz has been executed 1 time.
5856 @node Tracepoint Actions
5857 @subsection Tracepoint Action Lists
5861 @cindex tracepoint actions
5862 @item actions @r{[}@var{num}@r{]}
5863 This command will prompt for a list of actions to be taken when the
5864 tracepoint is hit. If the tracepoint number @var{num} is not
5865 specified, this command sets the actions for the one that was most
5866 recently defined (so that you can define a tracepoint and then say
5867 @code{actions} without bothering about its number). You specify the
5868 actions themselves on the following lines, one action at a time, and
5869 terminate the actions list with a line containing just @code{end}. So
5870 far, the only defined actions are @code{collect} and
5871 @code{while-stepping}.
5873 @cindex remove actions from a tracepoint
5874 To remove all actions from a tracepoint, type @samp{actions @var{num}}
5875 and follow it immediately with @samp{end}.
5878 (@value{GDBP}) @b{collect @var{data}} // collect some data
5880 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times and collect data
5882 (@value{GDBP}) @b{end} // signals the end of actions.
5885 In the following example, the action list begins with @code{collect}
5886 commands indicating the things to be collected when the tracepoint is
5887 hit. Then, in order to single-step and collect additional data
5888 following the tracepoint, a @code{while-stepping} command is used,
5889 followed by the list of things to be collected while stepping. The
5890 @code{while-stepping} command is terminated by its own separate
5891 @code{end} command. Lastly, the action list is terminated by an
5895 (@value{GDBP}) @b{trace foo}
5896 (@value{GDBP}) @b{actions}
5897 Enter actions for tracepoint 1, one per line:
5906 @kindex collect @r{(tracepoints)}
5907 @item collect @var{expr1}, @var{expr2}, @dots{}
5908 Collect values of the given expressions when the tracepoint is hit.
5909 This command accepts a comma-separated list of any valid expressions.
5910 In addition to global, static, or local variables, the following
5911 special arguments are supported:
5915 collect all registers
5918 collect all function arguments
5921 collect all local variables.
5924 You can give several consecutive @code{collect} commands, each one
5925 with a single argument, or one @code{collect} command with several
5926 arguments separated by commas: the effect is the same.
5928 The command @code{info scope} (@pxref{Symbols, info scope}) is
5929 particularly useful for figuring out what data to collect.
5931 @kindex while-stepping @r{(tracepoints)}
5932 @item while-stepping @var{n}
5933 Perform @var{n} single-step traces after the tracepoint, collecting
5934 new data at each step. The @code{while-stepping} command is
5935 followed by the list of what to collect while stepping (followed by
5936 its own @code{end} command):
5940 > collect $regs, myglobal
5946 You may abbreviate @code{while-stepping} as @code{ws} or
5950 @node Listing Tracepoints
5951 @subsection Listing Tracepoints
5954 @kindex info tracepoints
5955 @cindex information about tracepoints
5956 @item info tracepoints @r{[}@var{num}@r{]}
5957 Display information the tracepoint @var{num}. If you don't specify a
5958 tracepoint number displays information about all the tracepoints
5959 defined so far. For each tracepoint, the following information is
5966 whether it is enabled or disabled
5970 its passcount as given by the @code{passcount @var{n}} command
5972 its step count as given by the @code{while-stepping @var{n}} command
5974 where in the source files is the tracepoint set
5976 its action list as given by the @code{actions} command
5980 (@value{GDBP}) @b{info trace}
5981 Num Enb Address PassC StepC What
5982 1 y 0x002117c4 0 0 <gdb_asm>
5983 2 y 0x0020dc64 0 0 in gdb_test at gdb_test.c:375
5984 3 y 0x0020b1f4 0 0 in collect_data at ../foo.c:1741
5989 This command can be abbreviated @code{info tp}.
5992 @node Starting and Stopping Trace Experiment
5993 @subsection Starting and Stopping Trace Experiment
5997 @cindex start a new trace experiment
5998 @cindex collected data discarded
6000 This command takes no arguments. It starts the trace experiment, and
6001 begins collecting data. This has the side effect of discarding all
6002 the data collected in the trace buffer during the previous trace
6006 @cindex stop a running trace experiment
6008 This command takes no arguments. It ends the trace experiment, and
6009 stops collecting data.
6011 @strong{Note:} a trace experiment and data collection may stop
6012 automatically if any tracepoint's passcount is reached
6013 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6016 @cindex status of trace data collection
6017 @cindex trace experiment, status of
6019 This command displays the status of the current trace data
6023 Here is an example of the commands we described so far:
6026 (@value{GDBP}) @b{trace gdb_c_test}
6027 (@value{GDBP}) @b{actions}
6028 Enter actions for tracepoint #1, one per line.
6029 > collect $regs,$locals,$args
6034 (@value{GDBP}) @b{tstart}
6035 [time passes @dots{}]
6036 (@value{GDBP}) @b{tstop}
6040 @node Analyze Collected Data
6041 @section Using the collected data
6043 After the tracepoint experiment ends, you use @value{GDBN} commands
6044 for examining the trace data. The basic idea is that each tracepoint
6045 collects a trace @dfn{snapshot} every time it is hit and another
6046 snapshot every time it single-steps. All these snapshots are
6047 consecutively numbered from zero and go into a buffer, and you can
6048 examine them later. The way you examine them is to @dfn{focus} on a
6049 specific trace snapshot. When the remote stub is focused on a trace
6050 snapshot, it will respond to all @value{GDBN} requests for memory and
6051 registers by reading from the buffer which belongs to that snapshot,
6052 rather than from @emph{real} memory or registers of the program being
6053 debugged. This means that @strong{all} @value{GDBN} commands
6054 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6055 behave as if we were currently debugging the program state as it was
6056 when the tracepoint occurred. Any requests for data that are not in
6057 the buffer will fail.
6060 * tfind:: How to select a trace snapshot
6061 * tdump:: How to display all data for a snapshot
6062 * save-tracepoints:: How to save tracepoints for a future run
6066 @subsection @code{tfind @var{n}}
6069 @cindex select trace snapshot
6070 @cindex find trace snapshot
6071 The basic command for selecting a trace snapshot from the buffer is
6072 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6073 counting from zero. If no argument @var{n} is given, the next
6074 snapshot is selected.
6076 Here are the various forms of using the @code{tfind} command.
6080 Find the first snapshot in the buffer. This is a synonym for
6081 @code{tfind 0} (since 0 is the number of the first snapshot).
6084 Stop debugging trace snapshots, resume @emph{live} debugging.
6087 Same as @samp{tfind none}.
6090 No argument means find the next trace snapshot.
6093 Find the previous trace snapshot before the current one. This permits
6094 retracing earlier steps.
6096 @item tfind tracepoint @var{num}
6097 Find the next snapshot associated with tracepoint @var{num}. Search
6098 proceeds forward from the last examined trace snapshot. If no
6099 argument @var{num} is given, it means find the next snapshot collected
6100 for the same tracepoint as the current snapshot.
6102 @item tfind pc @var{addr}
6103 Find the next snapshot associated with the value @var{addr} of the
6104 program counter. Search proceeds forward from the last examined trace
6105 snapshot. If no argument @var{addr} is given, it means find the next
6106 snapshot with the same value of PC as the current snapshot.
6108 @item tfind outside @var{addr1}, @var{addr2}
6109 Find the next snapshot whose PC is outside the given range of
6112 @item tfind range @var{addr1}, @var{addr2}
6113 Find the next snapshot whose PC is between @var{addr1} and
6114 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6116 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6117 Find the next snapshot associated with the source line @var{n}. If
6118 the optional argument @var{file} is given, refer to line @var{n} in
6119 that source file. Search proceeds forward from the last examined
6120 trace snapshot. If no argument @var{n} is given, it means find the
6121 next line other than the one currently being examined; thus saying
6122 @code{tfind line} repeatedly can appear to have the same effect as
6123 stepping from line to line in a @emph{live} debugging session.
6126 The default arguments for the @code{tfind} commands are specifically
6127 designed to make it easy to scan through the trace buffer. For
6128 instance, @code{tfind} with no argument selects the next trace
6129 snapshot, and @code{tfind -} with no argument selects the previous
6130 trace snapshot. So, by giving one @code{tfind} command, and then
6131 simply hitting @key{RET} repeatedly you can examine all the trace
6132 snapshots in order. Or, by saying @code{tfind -} and then hitting
6133 @key{RET} repeatedly you can examine the snapshots in reverse order.
6134 The @code{tfind line} command with no argument selects the snapshot
6135 for the next source line executed. The @code{tfind pc} command with
6136 no argument selects the next snapshot with the same program counter
6137 (PC) as the current frame. The @code{tfind tracepoint} command with
6138 no argument selects the next trace snapshot collected by the same
6139 tracepoint as the current one.
6141 In addition to letting you scan through the trace buffer manually,
6142 these commands make it easy to construct @value{GDBN} scripts that
6143 scan through the trace buffer and print out whatever collected data
6144 you are interested in. Thus, if we want to examine the PC, FP, and SP
6145 registers from each trace frame in the buffer, we can say this:
6148 (@value{GDBP}) @b{tfind start}
6149 (@value{GDBP}) @b{while ($trace_frame != -1)}
6150 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6151 $trace_frame, $pc, $sp, $fp
6155 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6156 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6157 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6158 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6159 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6160 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6161 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6162 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6163 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6164 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6165 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6168 Or, if we want to examine the variable @code{X} at each source line in
6172 (@value{GDBP}) @b{tfind start}
6173 (@value{GDBP}) @b{while ($trace_frame != -1)}
6174 > printf "Frame %d, X == %d\n", $trace_frame, X
6184 @subsection @code{tdump}
6186 @cindex dump all data collected at tracepoint
6187 @cindex tracepoint data, display
6189 This command takes no arguments. It prints all the data collected at
6190 the current trace snapshot.
6193 (@value{GDBP}) @b{trace 444}
6194 (@value{GDBP}) @b{actions}
6195 Enter actions for tracepoint #2, one per line:
6196 > collect $regs, $locals, $args, gdb_long_test
6199 (@value{GDBP}) @b{tstart}
6201 (@value{GDBP}) @b{tfind line 444}
6202 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6204 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6206 (@value{GDBP}) @b{tdump}
6207 Data collected at tracepoint 2, trace frame 1:
6208 d0 0xc4aa0085 -995491707
6212 d4 0x71aea3d 119204413
6217 a1 0x3000668 50333288
6220 a4 0x3000698 50333336
6222 fp 0x30bf3c 0x30bf3c
6223 sp 0x30bf34 0x30bf34
6225 pc 0x20b2c8 0x20b2c8
6229 p = 0x20e5b4 "gdb-test"
6236 gdb_long_test = 17 '\021'
6241 @node save-tracepoints
6242 @subsection @code{save-tracepoints @var{filename}}
6243 @kindex save-tracepoints
6244 @cindex save tracepoints for future sessions
6246 This command saves all current tracepoint definitions together with
6247 their actions and passcounts, into a file @file{@var{filename}}
6248 suitable for use in a later debugging session. To read the saved
6249 tracepoint definitions, use the @code{source} command (@pxref{Command
6252 @node Tracepoint Variables
6253 @section Convenience Variables for Tracepoints
6254 @cindex tracepoint variables
6255 @cindex convenience variables for tracepoints
6258 @vindex $trace_frame
6259 @item (int) $trace_frame
6260 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6261 snapshot is selected.
6264 @item (int) $tracepoint
6265 The tracepoint for the current trace snapshot.
6268 @item (int) $trace_line
6269 The line number for the current trace snapshot.
6272 @item (char []) $trace_file
6273 The source file for the current trace snapshot.
6276 @item (char []) $trace_func
6277 The name of the function containing @code{$tracepoint}.
6280 Note: @code{$trace_file} is not suitable for use in @code{printf},
6281 use @code{output} instead.
6283 Here's a simple example of using these convenience variables for
6284 stepping through all the trace snapshots and printing some of their
6288 (@value{GDBP}) @b{tfind start}
6290 (@value{GDBP}) @b{while $trace_frame != -1}
6291 > output $trace_file
6292 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6298 @chapter Using @value{GDBN} with Different Languages
6301 Although programming languages generally have common aspects, they are
6302 rarely expressed in the same manner. For instance, in ANSI C,
6303 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6304 Modula-2, it is accomplished by @code{p^}. Values can also be
6305 represented (and displayed) differently. Hex numbers in C appear as
6306 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6308 @cindex working language
6309 Language-specific information is built into @value{GDBN} for some languages,
6310 allowing you to express operations like the above in your program's
6311 native language, and allowing @value{GDBN} to output values in a manner
6312 consistent with the syntax of your program's native language. The
6313 language you use to build expressions is called the @dfn{working
6317 * Setting:: Switching between source languages
6318 * Show:: Displaying the language
6319 * Checks:: Type and range checks
6320 * Support:: Supported languages
6324 @section Switching between source languages
6326 There are two ways to control the working language---either have @value{GDBN}
6327 set it automatically, or select it manually yourself. You can use the
6328 @code{set language} command for either purpose. On startup, @value{GDBN}
6329 defaults to setting the language automatically. The working language is
6330 used to determine how expressions you type are interpreted, how values
6333 In addition to the working language, every source file that
6334 @value{GDBN} knows about has its own working language. For some object
6335 file formats, the compiler might indicate which language a particular
6336 source file is in. However, most of the time @value{GDBN} infers the
6337 language from the name of the file. The language of a source file
6338 controls whether C@t{++} names are demangled---this way @code{backtrace} can
6339 show each frame appropriately for its own language. There is no way to
6340 set the language of a source file from within @value{GDBN}, but you can
6341 set the language associated with a filename extension. @xref{Show, ,
6342 Displaying the language}.
6344 This is most commonly a problem when you use a program, such
6345 as @code{cfront} or @code{f2c}, that generates C but is written in
6346 another language. In that case, make the
6347 program use @code{#line} directives in its C output; that way
6348 @value{GDBN} will know the correct language of the source code of the original
6349 program, and will display that source code, not the generated C code.
6352 * Filenames:: Filename extensions and languages.
6353 * Manually:: Setting the working language manually
6354 * Automatically:: Having @value{GDBN} infer the source language
6358 @subsection List of filename extensions and languages
6360 If a source file name ends in one of the following extensions, then
6361 @value{GDBN} infers that its language is the one indicated.
6386 Modula-2 source file
6390 Assembler source file. This actually behaves almost like C, but
6391 @value{GDBN} does not skip over function prologues when stepping.
6394 In addition, you may set the language associated with a filename
6395 extension. @xref{Show, , Displaying the language}.
6398 @subsection Setting the working language
6400 If you allow @value{GDBN} to set the language automatically,
6401 expressions are interpreted the same way in your debugging session and
6404 @kindex set language
6405 If you wish, you may set the language manually. To do this, issue the
6406 command @samp{set language @var{lang}}, where @var{lang} is the name of
6408 @code{c} or @code{modula-2}.
6409 For a list of the supported languages, type @samp{set language}.
6411 Setting the language manually prevents @value{GDBN} from updating the working
6412 language automatically. This can lead to confusion if you try
6413 to debug a program when the working language is not the same as the
6414 source language, when an expression is acceptable to both
6415 languages---but means different things. For instance, if the current
6416 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6424 might not have the effect you intended. In C, this means to add
6425 @code{b} and @code{c} and place the result in @code{a}. The result
6426 printed would be the value of @code{a}. In Modula-2, this means to compare
6427 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6430 @subsection Having @value{GDBN} infer the source language
6432 To have @value{GDBN} set the working language automatically, use
6433 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6434 then infers the working language. That is, when your program stops in a
6435 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6436 working language to the language recorded for the function in that
6437 frame. If the language for a frame is unknown (that is, if the function
6438 or block corresponding to the frame was defined in a source file that
6439 does not have a recognized extension), the current working language is
6440 not changed, and @value{GDBN} issues a warning.
6442 This may not seem necessary for most programs, which are written
6443 entirely in one source language. However, program modules and libraries
6444 written in one source language can be used by a main program written in
6445 a different source language. Using @samp{set language auto} in this
6446 case frees you from having to set the working language manually.
6449 @section Displaying the language
6451 The following commands help you find out which language is the
6452 working language, and also what language source files were written in.
6454 @kindex show language
6455 @kindex info frame@r{, show the source language}
6456 @kindex info source@r{, show the source language}
6459 Display the current working language. This is the
6460 language you can use with commands such as @code{print} to
6461 build and compute expressions that may involve variables in your program.
6464 Display the source language for this frame. This language becomes the
6465 working language if you use an identifier from this frame.
6466 @xref{Frame Info, ,Information about a frame}, to identify the other
6467 information listed here.
6470 Display the source language of this source file.
6471 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6472 information listed here.
6475 In unusual circumstances, you may have source files with extensions
6476 not in the standard list. You can then set the extension associated
6477 with a language explicitly:
6479 @kindex set extension-language
6480 @kindex info extensions
6482 @item set extension-language @var{.ext} @var{language}
6483 Set source files with extension @var{.ext} to be assumed to be in
6484 the source language @var{language}.
6486 @item info extensions
6487 List all the filename extensions and the associated languages.
6491 @section Type and range checking
6494 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6495 checking are included, but they do not yet have any effect. This
6496 section documents the intended facilities.
6498 @c FIXME remove warning when type/range code added
6500 Some languages are designed to guard you against making seemingly common
6501 errors through a series of compile- and run-time checks. These include
6502 checking the type of arguments to functions and operators, and making
6503 sure mathematical overflows are caught at run time. Checks such as
6504 these help to ensure a program's correctness once it has been compiled
6505 by eliminating type mismatches, and providing active checks for range
6506 errors when your program is running.
6508 @value{GDBN} can check for conditions like the above if you wish.
6509 Although @value{GDBN} does not check the statements in your program, it
6510 can check expressions entered directly into @value{GDBN} for evaluation via
6511 the @code{print} command, for example. As with the working language,
6512 @value{GDBN} can also decide whether or not to check automatically based on
6513 your program's source language. @xref{Support, ,Supported languages},
6514 for the default settings of supported languages.
6517 * Type Checking:: An overview of type checking
6518 * Range Checking:: An overview of range checking
6521 @cindex type checking
6522 @cindex checks, type
6524 @subsection An overview of type checking
6526 Some languages, such as Modula-2, are strongly typed, meaning that the
6527 arguments to operators and functions have to be of the correct type,
6528 otherwise an error occurs. These checks prevent type mismatch
6529 errors from ever causing any run-time problems. For example,
6537 The second example fails because the @code{CARDINAL} 1 is not
6538 type-compatible with the @code{REAL} 2.3.
6540 For the expressions you use in @value{GDBN} commands, you can tell the
6541 @value{GDBN} type checker to skip checking;
6542 to treat any mismatches as errors and abandon the expression;
6543 or to only issue warnings when type mismatches occur,
6544 but evaluate the expression anyway. When you choose the last of
6545 these, @value{GDBN} evaluates expressions like the second example above, but
6546 also issues a warning.
6548 Even if you turn type checking off, there may be other reasons
6549 related to type that prevent @value{GDBN} from evaluating an expression.
6550 For instance, @value{GDBN} does not know how to add an @code{int} and
6551 a @code{struct foo}. These particular type errors have nothing to do
6552 with the language in use, and usually arise from expressions, such as
6553 the one described above, which make little sense to evaluate anyway.
6555 Each language defines to what degree it is strict about type. For
6556 instance, both Modula-2 and C require the arguments to arithmetical
6557 operators to be numbers. In C, enumerated types and pointers can be
6558 represented as numbers, so that they are valid arguments to mathematical
6559 operators. @xref{Support, ,Supported languages}, for further
6560 details on specific languages.
6562 @value{GDBN} provides some additional commands for controlling the type checker:
6564 @kindex set check@r{, type}
6565 @kindex set check type
6566 @kindex show check type
6568 @item set check type auto
6569 Set type checking on or off based on the current working language.
6570 @xref{Support, ,Supported languages}, for the default settings for
6573 @item set check type on
6574 @itemx set check type off
6575 Set type checking on or off, overriding the default setting for the
6576 current working language. Issue a warning if the setting does not
6577 match the language default. If any type mismatches occur in
6578 evaluating an expression while type checking is on, @value{GDBN} prints a
6579 message and aborts evaluation of the expression.
6581 @item set check type warn
6582 Cause the type checker to issue warnings, but to always attempt to
6583 evaluate the expression. Evaluating the expression may still
6584 be impossible for other reasons. For example, @value{GDBN} cannot add
6585 numbers and structures.
6588 Show the current setting of the type checker, and whether or not @value{GDBN}
6589 is setting it automatically.
6592 @cindex range checking
6593 @cindex checks, range
6594 @node Range Checking
6595 @subsection An overview of range checking
6597 In some languages (such as Modula-2), it is an error to exceed the
6598 bounds of a type; this is enforced with run-time checks. Such range
6599 checking is meant to ensure program correctness by making sure
6600 computations do not overflow, or indices on an array element access do
6601 not exceed the bounds of the array.
6603 For expressions you use in @value{GDBN} commands, you can tell
6604 @value{GDBN} to treat range errors in one of three ways: ignore them,
6605 always treat them as errors and abandon the expression, or issue
6606 warnings but evaluate the expression anyway.
6608 A range error can result from numerical overflow, from exceeding an
6609 array index bound, or when you type a constant that is not a member
6610 of any type. Some languages, however, do not treat overflows as an
6611 error. In many implementations of C, mathematical overflow causes the
6612 result to ``wrap around'' to lower values---for example, if @var{m} is
6613 the largest integer value, and @var{s} is the smallest, then
6616 @var{m} + 1 @result{} @var{s}
6619 This, too, is specific to individual languages, and in some cases
6620 specific to individual compilers or machines. @xref{Support, ,
6621 Supported languages}, for further details on specific languages.
6623 @value{GDBN} provides some additional commands for controlling the range checker:
6625 @kindex set check@r{, range}
6626 @kindex set check range
6627 @kindex show check range
6629 @item set check range auto
6630 Set range checking on or off based on the current working language.
6631 @xref{Support, ,Supported languages}, for the default settings for
6634 @item set check range on
6635 @itemx set check range off
6636 Set range checking on or off, overriding the default setting for the
6637 current working language. A warning is issued if the setting does not
6638 match the language default. If a range error occurs and range checking is on,
6639 then a message is printed and evaluation of the expression is aborted.
6641 @item set check range warn
6642 Output messages when the @value{GDBN} range checker detects a range error,
6643 but attempt to evaluate the expression anyway. Evaluating the
6644 expression may still be impossible for other reasons, such as accessing
6645 memory that the process does not own (a typical example from many Unix
6649 Show the current setting of the range checker, and whether or not it is
6650 being set automatically by @value{GDBN}.
6654 @section Supported languages
6656 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
6657 @c This is false ...
6658 Some @value{GDBN} features may be used in expressions regardless of the
6659 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6660 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6661 ,Expressions}) can be used with the constructs of any supported
6664 The following sections detail to what degree each source language is
6665 supported by @value{GDBN}. These sections are not meant to be language
6666 tutorials or references, but serve only as a reference guide to what the
6667 @value{GDBN} expression parser accepts, and what input and output
6668 formats should look like for different languages. There are many good
6669 books written on each of these languages; please look to these for a
6670 language reference or tutorial.
6674 * Modula-2:: Modula-2
6679 @subsection C and C@t{++}
6681 @cindex C and C@t{++}
6682 @cindex expressions in C or C@t{++}
6684 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
6685 to both languages. Whenever this is the case, we discuss those languages
6689 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
6690 @cindex @sc{gnu} C@t{++}
6691 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
6692 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
6693 effectively, you must compile your C@t{++} programs with a supported
6694 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
6695 compiler (@code{aCC}).
6697 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
6698 format. You can select that format explicitly with the @code{g++}
6699 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6700 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
6701 CC, gcc.info, Using @sc{gnu} CC}, for more information.
6704 * C Operators:: C and C@t{++} operators
6705 * C Constants:: C and C@t{++} constants
6706 * C plus plus expressions:: C@t{++} expressions
6707 * C Defaults:: Default settings for C and C@t{++}
6708 * C Checks:: C and C@t{++} type and range checks
6709 * Debugging C:: @value{GDBN} and C
6710 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
6714 @subsubsection C and C@t{++} operators
6716 @cindex C and C@t{++} operators
6718 Operators must be defined on values of specific types. For instance,
6719 @code{+} is defined on numbers, but not on structures. Operators are
6720 often defined on groups of types.
6722 For the purposes of C and C@t{++}, the following definitions hold:
6727 @emph{Integral types} include @code{int} with any of its storage-class
6728 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
6731 @emph{Floating-point types} include @code{float}, @code{double}, and
6732 @code{long double} (if supported by the target platform).
6735 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
6738 @emph{Scalar types} include all of the above.
6743 The following operators are supported. They are listed here
6744 in order of increasing precedence:
6748 The comma or sequencing operator. Expressions in a comma-separated list
6749 are evaluated from left to right, with the result of the entire
6750 expression being the last expression evaluated.
6753 Assignment. The value of an assignment expression is the value
6754 assigned. Defined on scalar types.
6757 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6758 and translated to @w{@code{@var{a} = @var{a op b}}}.
6759 @w{@code{@var{op}=}} and @code{=} have the same precedence.
6760 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6761 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6764 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6765 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6769 Logical @sc{or}. Defined on integral types.
6772 Logical @sc{and}. Defined on integral types.
6775 Bitwise @sc{or}. Defined on integral types.
6778 Bitwise exclusive-@sc{or}. Defined on integral types.
6781 Bitwise @sc{and}. Defined on integral types.
6784 Equality and inequality. Defined on scalar types. The value of these
6785 expressions is 0 for false and non-zero for true.
6787 @item <@r{, }>@r{, }<=@r{, }>=
6788 Less than, greater than, less than or equal, greater than or equal.
6789 Defined on scalar types. The value of these expressions is 0 for false
6790 and non-zero for true.
6793 left shift, and right shift. Defined on integral types.
6796 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6799 Addition and subtraction. Defined on integral types, floating-point types and
6802 @item *@r{, }/@r{, }%
6803 Multiplication, division, and modulus. Multiplication and division are
6804 defined on integral and floating-point types. Modulus is defined on
6808 Increment and decrement. When appearing before a variable, the
6809 operation is performed before the variable is used in an expression;
6810 when appearing after it, the variable's value is used before the
6811 operation takes place.
6814 Pointer dereferencing. Defined on pointer types. Same precedence as
6818 Address operator. Defined on variables. Same precedence as @code{++}.
6820 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
6821 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
6822 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6823 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
6827 Negative. Defined on integral and floating-point types. Same
6828 precedence as @code{++}.
6831 Logical negation. Defined on integral types. Same precedence as
6835 Bitwise complement operator. Defined on integral types. Same precedence as
6840 Structure member, and pointer-to-structure member. For convenience,
6841 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6842 pointer based on the stored type information.
6843 Defined on @code{struct} and @code{union} data.
6846 Dereferences of pointers to members.
6849 Array indexing. @code{@var{a}[@var{i}]} is defined as
6850 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6853 Function parameter list. Same precedence as @code{->}.
6856 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
6857 and @code{class} types.
6860 Doubled colons also represent the @value{GDBN} scope operator
6861 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6865 If an operator is redefined in the user code, @value{GDBN} usually
6866 attempts to invoke the redefined version instead of using the operator's
6874 @subsubsection C and C@t{++} constants
6876 @cindex C and C@t{++} constants
6878 @value{GDBN} allows you to express the constants of C and C@t{++} in the
6883 Integer constants are a sequence of digits. Octal constants are
6884 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6885 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6886 @samp{l}, specifying that the constant should be treated as a
6890 Floating point constants are a sequence of digits, followed by a decimal
6891 point, followed by a sequence of digits, and optionally followed by an
6892 exponent. An exponent is of the form:
6893 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6894 sequence of digits. The @samp{+} is optional for positive exponents.
6895 A floating-point constant may also end with a letter @samp{f} or
6896 @samp{F}, specifying that the constant should be treated as being of
6897 the @code{float} (as opposed to the default @code{double}) type; or with
6898 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6902 Enumerated constants consist of enumerated identifiers, or their
6903 integral equivalents.
6906 Character constants are a single character surrounded by single quotes
6907 (@code{'}), or a number---the ordinal value of the corresponding character
6908 (usually its @sc{ascii} value). Within quotes, the single character may
6909 be represented by a letter or by @dfn{escape sequences}, which are of
6910 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6911 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6912 @samp{@var{x}} is a predefined special character---for example,
6913 @samp{\n} for newline.
6916 String constants are a sequence of character constants surrounded by
6917 double quotes (@code{"}). Any valid character constant (as described
6918 above) may appear. Double quotes within the string must be preceded by
6919 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6923 Pointer constants are an integral value. You can also write pointers
6924 to constants using the C operator @samp{&}.
6927 Array constants are comma-separated lists surrounded by braces @samp{@{}
6928 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6929 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6930 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6934 * C plus plus expressions::
6941 @node C plus plus expressions
6942 @subsubsection C@t{++} expressions
6944 @cindex expressions in C@t{++}
6945 @value{GDBN} expression handling can interpret most C@t{++} expressions.
6947 @cindex C@t{++} support, not in @sc{coff}
6948 @cindex @sc{coff} versus C@t{++}
6949 @cindex C@t{++} and object formats
6950 @cindex object formats and C@t{++}
6951 @cindex a.out and C@t{++}
6952 @cindex @sc{ecoff} and C@t{++}
6953 @cindex @sc{xcoff} and C@t{++}
6954 @cindex @sc{elf}/stabs and C@t{++}
6955 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
6956 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6957 @c periodically whether this has happened...
6959 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
6960 proper compiler. Typically, C@t{++} debugging depends on the use of
6961 additional debugging information in the symbol table, and thus requires
6962 special support. In particular, if your compiler generates a.out, MIPS
6963 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6964 symbol table, these facilities are all available. (With @sc{gnu} CC,
6965 you can use the @samp{-gstabs} option to request stabs debugging
6966 extensions explicitly.) Where the object code format is standard
6967 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
6968 support in @value{GDBN} does @emph{not} work.
6973 @cindex member functions
6975 Member function calls are allowed; you can use expressions like
6978 count = aml->GetOriginal(x, y)
6981 @vindex this@r{, inside C@t{++} member functions}
6982 @cindex namespace in C@t{++}
6984 While a member function is active (in the selected stack frame), your
6985 expressions have the same namespace available as the member function;
6986 that is, @value{GDBN} allows implicit references to the class instance
6987 pointer @code{this} following the same rules as C@t{++}.
6989 @cindex call overloaded functions
6990 @cindex overloaded functions, calling
6991 @cindex type conversions in C@t{++}
6993 You can call overloaded functions; @value{GDBN} resolves the function
6994 call to the right definition, with some restrictions. @value{GDBN} does not
6995 perform overload resolution involving user-defined type conversions,
6996 calls to constructors, or instantiations of templates that do not exist
6997 in the program. It also cannot handle ellipsis argument lists or
7000 It does perform integral conversions and promotions, floating-point
7001 promotions, arithmetic conversions, pointer conversions, conversions of
7002 class objects to base classes, and standard conversions such as those of
7003 functions or arrays to pointers; it requires an exact match on the
7004 number of function arguments.
7006 Overload resolution is always performed, unless you have specified
7007 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7008 ,@value{GDBN} features for C@t{++}}.
7010 You must specify @code{set overload-resolution off} in order to use an
7011 explicit function signature to call an overloaded function, as in
7013 p 'foo(char,int)'('x', 13)
7016 The @value{GDBN} command-completion facility can simplify this;
7017 see @ref{Completion, ,Command completion}.
7019 @cindex reference declarations
7021 @value{GDBN} understands variables declared as C@t{++} references; you can use
7022 them in expressions just as you do in C@t{++} source---they are automatically
7025 In the parameter list shown when @value{GDBN} displays a frame, the values of
7026 reference variables are not displayed (unlike other variables); this
7027 avoids clutter, since references are often used for large structures.
7028 The @emph{address} of a reference variable is always shown, unless
7029 you have specified @samp{set print address off}.
7032 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7033 expressions can use it just as expressions in your program do. Since
7034 one scope may be defined in another, you can use @code{::} repeatedly if
7035 necessary, for example in an expression like
7036 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7037 resolving name scope by reference to source files, in both C and C@t{++}
7038 debugging (@pxref{Variables, ,Program variables}).
7041 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7042 calling virtual functions correctly, printing out virtual bases of
7043 objects, calling functions in a base subobject, casting objects, and
7044 invoking user-defined operators.
7047 @subsubsection C and C@t{++} defaults
7049 @cindex C and C@t{++} defaults
7051 If you allow @value{GDBN} to set type and range checking automatically, they
7052 both default to @code{off} whenever the working language changes to
7053 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7054 selects the working language.
7056 If you allow @value{GDBN} to set the language automatically, it
7057 recognizes source files whose names end with @file{.c}, @file{.C}, or
7058 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7059 these files, it sets the working language to C or C@t{++}.
7060 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7061 for further details.
7063 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7064 @c unimplemented. If (b) changes, it might make sense to let this node
7065 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7068 @subsubsection C and C@t{++} type and range checks
7070 @cindex C and C@t{++} checks
7072 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7073 is not used. However, if you turn type checking on, @value{GDBN}
7074 considers two variables type equivalent if:
7078 The two variables are structured and have the same structure, union, or
7082 The two variables have the same type name, or types that have been
7083 declared equivalent through @code{typedef}.
7086 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7089 The two @code{struct}, @code{union}, or @code{enum} variables are
7090 declared in the same declaration. (Note: this may not be true for all C
7095 Range checking, if turned on, is done on mathematical operations. Array
7096 indices are not checked, since they are often used to index a pointer
7097 that is not itself an array.
7100 @subsubsection @value{GDBN} and C
7102 The @code{set print union} and @code{show print union} commands apply to
7103 the @code{union} type. When set to @samp{on}, any @code{union} that is
7104 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7105 appears as @samp{@{...@}}.
7107 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7108 with pointers and a memory allocation function. @xref{Expressions,
7112 * Debugging C plus plus::
7115 @node Debugging C plus plus
7116 @subsubsection @value{GDBN} features for C@t{++}
7118 @cindex commands for C@t{++}
7120 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7121 designed specifically for use with C@t{++}. Here is a summary:
7124 @cindex break in overloaded functions
7125 @item @r{breakpoint menus}
7126 When you want a breakpoint in a function whose name is overloaded,
7127 @value{GDBN} breakpoint menus help you specify which function definition
7128 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7130 @cindex overloading in C@t{++}
7131 @item rbreak @var{regex}
7132 Setting breakpoints using regular expressions is helpful for setting
7133 breakpoints on overloaded functions that are not members of any special
7135 @xref{Set Breaks, ,Setting breakpoints}.
7137 @cindex C@t{++} exception handling
7140 Debug C@t{++} exception handling using these commands. @xref{Set
7141 Catchpoints, , Setting catchpoints}.
7144 @item ptype @var{typename}
7145 Print inheritance relationships as well as other information for type
7147 @xref{Symbols, ,Examining the Symbol Table}.
7149 @cindex C@t{++} symbol display
7150 @item set print demangle
7151 @itemx show print demangle
7152 @itemx set print asm-demangle
7153 @itemx show print asm-demangle
7154 Control whether C@t{++} symbols display in their source form, both when
7155 displaying code as C@t{++} source and when displaying disassemblies.
7156 @xref{Print Settings, ,Print settings}.
7158 @item set print object
7159 @itemx show print object
7160 Choose whether to print derived (actual) or declared types of objects.
7161 @xref{Print Settings, ,Print settings}.
7163 @item set print vtbl
7164 @itemx show print vtbl
7165 Control the format for printing virtual function tables.
7166 @xref{Print Settings, ,Print settings}.
7167 (The @code{vtbl} commands do not work on programs compiled with the HP
7168 ANSI C@t{++} compiler (@code{aCC}).)
7170 @kindex set overload-resolution
7171 @cindex overloaded functions, overload resolution
7172 @item set overload-resolution on
7173 Enable overload resolution for C@t{++} expression evaluation. The default
7174 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7175 and searches for a function whose signature matches the argument types,
7176 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7177 expressions}, for details). If it cannot find a match, it emits a
7180 @item set overload-resolution off
7181 Disable overload resolution for C@t{++} expression evaluation. For
7182 overloaded functions that are not class member functions, @value{GDBN}
7183 chooses the first function of the specified name that it finds in the
7184 symbol table, whether or not its arguments are of the correct type. For
7185 overloaded functions that are class member functions, @value{GDBN}
7186 searches for a function whose signature @emph{exactly} matches the
7189 @item @r{Overloaded symbol names}
7190 You can specify a particular definition of an overloaded symbol, using
7191 the same notation that is used to declare such symbols in C@t{++}: type
7192 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7193 also use the @value{GDBN} command-line word completion facilities to list the
7194 available choices, or to finish the type list for you.
7195 @xref{Completion,, Command completion}, for details on how to do this.
7199 @subsection Modula-2
7201 @cindex Modula-2, @value{GDBN} support
7203 The extensions made to @value{GDBN} to support Modula-2 only support
7204 output from the @sc{gnu} Modula-2 compiler (which is currently being
7205 developed). Other Modula-2 compilers are not currently supported, and
7206 attempting to debug executables produced by them is most likely
7207 to give an error as @value{GDBN} reads in the executable's symbol
7210 @cindex expressions in Modula-2
7212 * M2 Operators:: Built-in operators
7213 * Built-In Func/Proc:: Built-in functions and procedures
7214 * M2 Constants:: Modula-2 constants
7215 * M2 Defaults:: Default settings for Modula-2
7216 * Deviations:: Deviations from standard Modula-2
7217 * M2 Checks:: Modula-2 type and range checks
7218 * M2 Scope:: The scope operators @code{::} and @code{.}
7219 * GDB/M2:: @value{GDBN} and Modula-2
7223 @subsubsection Operators
7224 @cindex Modula-2 operators
7226 Operators must be defined on values of specific types. For instance,
7227 @code{+} is defined on numbers, but not on structures. Operators are
7228 often defined on groups of types. For the purposes of Modula-2, the
7229 following definitions hold:
7234 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7238 @emph{Character types} consist of @code{CHAR} and its subranges.
7241 @emph{Floating-point types} consist of @code{REAL}.
7244 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7248 @emph{Scalar types} consist of all of the above.
7251 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7254 @emph{Boolean types} consist of @code{BOOLEAN}.
7258 The following operators are supported, and appear in order of
7259 increasing precedence:
7263 Function argument or array index separator.
7266 Assignment. The value of @var{var} @code{:=} @var{value} is
7270 Less than, greater than on integral, floating-point, or enumerated
7274 Less than or equal to, greater than or equal to
7275 on integral, floating-point and enumerated types, or set inclusion on
7276 set types. Same precedence as @code{<}.
7278 @item =@r{, }<>@r{, }#
7279 Equality and two ways of expressing inequality, valid on scalar types.
7280 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7281 available for inequality, since @code{#} conflicts with the script
7285 Set membership. Defined on set types and the types of their members.
7286 Same precedence as @code{<}.
7289 Boolean disjunction. Defined on boolean types.
7292 Boolean conjunction. Defined on boolean types.
7295 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7298 Addition and subtraction on integral and floating-point types, or union
7299 and difference on set types.
7302 Multiplication on integral and floating-point types, or set intersection
7306 Division on floating-point types, or symmetric set difference on set
7307 types. Same precedence as @code{*}.
7310 Integer division and remainder. Defined on integral types. Same
7311 precedence as @code{*}.
7314 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7317 Pointer dereferencing. Defined on pointer types.
7320 Boolean negation. Defined on boolean types. Same precedence as
7324 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7325 precedence as @code{^}.
7328 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7331 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7335 @value{GDBN} and Modula-2 scope operators.
7339 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7340 treats the use of the operator @code{IN}, or the use of operators
7341 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7342 @code{<=}, and @code{>=} on sets as an error.
7346 @node Built-In Func/Proc
7347 @subsubsection Built-in functions and procedures
7348 @cindex Modula-2 built-ins
7350 Modula-2 also makes available several built-in procedures and functions.
7351 In describing these, the following metavariables are used:
7356 represents an @code{ARRAY} variable.
7359 represents a @code{CHAR} constant or variable.
7362 represents a variable or constant of integral type.
7365 represents an identifier that belongs to a set. Generally used in the
7366 same function with the metavariable @var{s}. The type of @var{s} should
7367 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7370 represents a variable or constant of integral or floating-point type.
7373 represents a variable or constant of floating-point type.
7379 represents a variable.
7382 represents a variable or constant of one of many types. See the
7383 explanation of the function for details.
7386 All Modula-2 built-in procedures also return a result, described below.
7390 Returns the absolute value of @var{n}.
7393 If @var{c} is a lower case letter, it returns its upper case
7394 equivalent, otherwise it returns its argument.
7397 Returns the character whose ordinal value is @var{i}.
7400 Decrements the value in the variable @var{v} by one. Returns the new value.
7402 @item DEC(@var{v},@var{i})
7403 Decrements the value in the variable @var{v} by @var{i}. Returns the
7406 @item EXCL(@var{m},@var{s})
7407 Removes the element @var{m} from the set @var{s}. Returns the new
7410 @item FLOAT(@var{i})
7411 Returns the floating point equivalent of the integer @var{i}.
7414 Returns the index of the last member of @var{a}.
7417 Increments the value in the variable @var{v} by one. Returns the new value.
7419 @item INC(@var{v},@var{i})
7420 Increments the value in the variable @var{v} by @var{i}. Returns the
7423 @item INCL(@var{m},@var{s})
7424 Adds the element @var{m} to the set @var{s} if it is not already
7425 there. Returns the new set.
7428 Returns the maximum value of the type @var{t}.
7431 Returns the minimum value of the type @var{t}.
7434 Returns boolean TRUE if @var{i} is an odd number.
7437 Returns the ordinal value of its argument. For example, the ordinal
7438 value of a character is its @sc{ascii} value (on machines supporting the
7439 @sc{ascii} character set). @var{x} must be of an ordered type, which include
7440 integral, character and enumerated types.
7443 Returns the size of its argument. @var{x} can be a variable or a type.
7445 @item TRUNC(@var{r})
7446 Returns the integral part of @var{r}.
7448 @item VAL(@var{t},@var{i})
7449 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7453 @emph{Warning:} Sets and their operations are not yet supported, so
7454 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7458 @cindex Modula-2 constants
7460 @subsubsection Constants
7462 @value{GDBN} allows you to express the constants of Modula-2 in the following
7468 Integer constants are simply a sequence of digits. When used in an
7469 expression, a constant is interpreted to be type-compatible with the
7470 rest of the expression. Hexadecimal integers are specified by a
7471 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7474 Floating point constants appear as a sequence of digits, followed by a
7475 decimal point and another sequence of digits. An optional exponent can
7476 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7477 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7478 digits of the floating point constant must be valid decimal (base 10)
7482 Character constants consist of a single character enclosed by a pair of
7483 like quotes, either single (@code{'}) or double (@code{"}). They may
7484 also be expressed by their ordinal value (their @sc{ascii} value, usually)
7485 followed by a @samp{C}.
7488 String constants consist of a sequence of characters enclosed by a
7489 pair of like quotes, either single (@code{'}) or double (@code{"}).
7490 Escape sequences in the style of C are also allowed. @xref{C
7491 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
7495 Enumerated constants consist of an enumerated identifier.
7498 Boolean constants consist of the identifiers @code{TRUE} and
7502 Pointer constants consist of integral values only.
7505 Set constants are not yet supported.
7509 @subsubsection Modula-2 defaults
7510 @cindex Modula-2 defaults
7512 If type and range checking are set automatically by @value{GDBN}, they
7513 both default to @code{on} whenever the working language changes to
7514 Modula-2. This happens regardless of whether you or @value{GDBN}
7515 selected the working language.
7517 If you allow @value{GDBN} to set the language automatically, then entering
7518 code compiled from a file whose name ends with @file{.mod} sets the
7519 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
7520 the language automatically}, for further details.
7523 @subsubsection Deviations from standard Modula-2
7524 @cindex Modula-2, deviations from
7526 A few changes have been made to make Modula-2 programs easier to debug.
7527 This is done primarily via loosening its type strictness:
7531 Unlike in standard Modula-2, pointer constants can be formed by
7532 integers. This allows you to modify pointer variables during
7533 debugging. (In standard Modula-2, the actual address contained in a
7534 pointer variable is hidden from you; it can only be modified
7535 through direct assignment to another pointer variable or expression that
7536 returned a pointer.)
7539 C escape sequences can be used in strings and characters to represent
7540 non-printable characters. @value{GDBN} prints out strings with these
7541 escape sequences embedded. Single non-printable characters are
7542 printed using the @samp{CHR(@var{nnn})} format.
7545 The assignment operator (@code{:=}) returns the value of its right-hand
7549 All built-in procedures both modify @emph{and} return their argument.
7553 @subsubsection Modula-2 type and range checks
7554 @cindex Modula-2 checks
7557 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
7560 @c FIXME remove warning when type/range checks added
7562 @value{GDBN} considers two Modula-2 variables type equivalent if:
7566 They are of types that have been declared equivalent via a @code{TYPE
7567 @var{t1} = @var{t2}} statement
7570 They have been declared on the same line. (Note: This is true of the
7571 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
7574 As long as type checking is enabled, any attempt to combine variables
7575 whose types are not equivalent is an error.
7577 Range checking is done on all mathematical operations, assignment, array
7578 index bounds, and all built-in functions and procedures.
7581 @subsubsection The scope operators @code{::} and @code{.}
7583 @cindex @code{.}, Modula-2 scope operator
7584 @cindex colon, doubled as scope operator
7586 @vindex colon-colon@r{, in Modula-2}
7587 @c Info cannot handle :: but TeX can.
7590 @vindex ::@r{, in Modula-2}
7593 There are a few subtle differences between the Modula-2 scope operator
7594 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
7599 @var{module} . @var{id}
7600 @var{scope} :: @var{id}
7604 where @var{scope} is the name of a module or a procedure,
7605 @var{module} the name of a module, and @var{id} is any declared
7606 identifier within your program, except another module.
7608 Using the @code{::} operator makes @value{GDBN} search the scope
7609 specified by @var{scope} for the identifier @var{id}. If it is not
7610 found in the specified scope, then @value{GDBN} searches all scopes
7611 enclosing the one specified by @var{scope}.
7613 Using the @code{.} operator makes @value{GDBN} search the current scope for
7614 the identifier specified by @var{id} that was imported from the
7615 definition module specified by @var{module}. With this operator, it is
7616 an error if the identifier @var{id} was not imported from definition
7617 module @var{module}, or if @var{id} is not an identifier in
7621 @subsubsection @value{GDBN} and Modula-2
7623 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
7624 Five subcommands of @code{set print} and @code{show print} apply
7625 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
7626 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
7627 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
7628 analogue in Modula-2.
7630 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
7631 with any language, is not useful with Modula-2. Its
7632 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
7633 created in Modula-2 as they can in C or C@t{++}. However, because an
7634 address can be specified by an integral constant, the construct
7635 @samp{@{@var{type}@}@var{adrexp}} is still useful.
7637 @cindex @code{#} in Modula-2
7638 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
7639 interpreted as the beginning of a comment. Use @code{<>} instead.
7644 The extensions made to @value{GDBN} to support Chill only support output
7645 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
7646 supported, and attempting to debug executables produced by them is most
7647 likely to give an error as @value{GDBN} reads in the executable's symbol
7650 @c This used to say "... following Chill related topics ...", but since
7651 @c menus are not shown in the printed manual, it would look awkward.
7652 This section covers the Chill related topics and the features
7653 of @value{GDBN} which support these topics.
7656 * How modes are displayed:: How modes are displayed
7657 * Locations:: Locations and their accesses
7658 * Values and their Operations:: Values and their Operations
7659 * Chill type and range checks::
7663 @node How modes are displayed
7664 @subsubsection How modes are displayed
7666 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
7667 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
7668 slightly from the standard specification of the Chill language. The
7671 @c FIXME: this @table's contents effectively disable @code by using @r
7672 @c on every @item. So why does it need @code?
7674 @item @r{@emph{Discrete modes:}}
7677 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
7680 @emph{Boolean Mode} which is predefined by @code{BOOL},
7682 @emph{Character Mode} which is predefined by @code{CHAR},
7684 @emph{Set Mode} which is displayed by the keyword @code{SET}.
7686 (@value{GDBP}) ptype x
7687 type = SET (karli = 10, susi = 20, fritzi = 100)
7689 If the type is an unnumbered set the set element values are omitted.
7691 @emph{Range Mode} which is displayed by
7693 @code{type = <basemode>(<lower bound> : <upper bound>)}
7695 where @code{<lower bound>, <upper bound>} can be of any discrete literal
7696 expression (e.g. set element names).
7699 @item @r{@emph{Powerset Mode:}}
7700 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7701 the member mode of the powerset. The member mode can be any discrete mode.
7703 (@value{GDBP}) ptype x
7704 type = POWERSET SET (egon, hugo, otto)
7707 @item @r{@emph{Reference Modes:}}
7710 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
7711 followed by the mode name to which the reference is bound.
7713 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7716 @item @r{@emph{Procedure mode}}
7717 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7718 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7719 list>} is a list of the parameter modes. @code{<return mode>} indicates
7720 the mode of the result of the procedure if any. The exceptionlist lists
7721 all possible exceptions which can be raised by the procedure.
7724 @item @r{@emph{Instance mode}}
7725 The instance mode is represented by a structure, which has a static
7726 type, and is therefore not really of interest.
7729 @item @r{@emph{Synchronization Modes:}}
7732 @emph{Event Mode} which is displayed by
7734 @code{EVENT (<event length>)}
7736 where @code{(<event length>)} is optional.
7738 @emph{Buffer Mode} which is displayed by
7740 @code{BUFFER (<buffer length>)<buffer element mode>}
7742 where @code{(<buffer length>)} is optional.
7745 @item @r{@emph{Timing Modes:}}
7748 @emph{Duration Mode} which is predefined by @code{DURATION}
7750 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7753 @item @r{@emph{Real Modes:}}
7754 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7756 @item @r{@emph{String Modes:}}
7759 @emph{Character String Mode} which is displayed by
7761 @code{CHARS(<string length>)}
7763 followed by the keyword @code{VARYING} if the String Mode is a varying
7766 @emph{Bit String Mode} which is displayed by
7773 @item @r{@emph{Array Mode:}}
7774 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7775 followed by the element mode (which may in turn be an array mode).
7777 (@value{GDBP}) ptype x
7780 SET (karli = 10, susi = 20, fritzi = 100)
7783 @item @r{@emph{Structure Mode}}
7784 The Structure mode is displayed by the keyword @code{STRUCT(<field
7785 list>)}. The @code{<field list>} consists of names and modes of fields
7786 of the structure. Variant structures have the keyword @code{CASE <field>
7787 OF <variant fields> ESAC} in their field list. Since the current version
7788 of the GNU Chill compiler doesn't implement tag processing (no runtime
7789 checks of variant fields, and therefore no debugging info), the output
7790 always displays all variant fields.
7792 (@value{GDBP}) ptype str
7807 @subsubsection Locations and their accesses
7809 A location in Chill is an object which can contain values.
7811 A value of a location is generally accessed by the (declared) name of
7812 the location. The output conforms to the specification of values in
7813 Chill programs. How values are specified
7814 is the topic of the next section, @ref{Values and their Operations}.
7816 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7817 display or change the result of a currently-active procedure:
7824 This does the same as the Chill action @code{RESULT EXPR} (which
7825 is not available in @value{GDBN}).
7827 Values of reference mode locations are printed by @code{PTR(<hex
7828 value>)} in case of a free reference mode, and by @code{(REF <reference
7829 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7830 represents the address where the reference points to. To access the
7831 value of the location referenced by the pointer, use the dereference
7834 Values of procedure mode locations are displayed by
7837 (<argument modes> ) <return mode> @} <address> <name of procedure
7840 @code{<argument modes>} is a list of modes according to the parameter
7841 specification of the procedure and @code{<address>} shows the address of
7845 Locations of instance modes are displayed just like a structure with two
7846 fields specifying the @emph{process type} and the @emph{copy number} of
7847 the investigated instance location@footnote{This comes from the current
7848 implementation of instances. They are implemented as a structure (no
7849 na). The output should be something like @code{[<name of the process>;
7850 <instance number>]}.}. The field names are @code{__proc_type} and
7853 Locations of synchronization modes are displayed like a structure with
7854 the field name @code{__event_data} in case of a event mode location, and
7855 like a structure with the field @code{__buffer_data} in case of a buffer
7856 mode location (refer to previous paragraph).
7858 Structure Mode locations are printed by @code{[.<field name>: <value>,
7859 ...]}. The @code{<field name>} corresponds to the structure mode
7860 definition and the layout of @code{<value>} varies depending of the mode
7861 of the field. If the investigated structure mode location is of variant
7862 structure mode, the variant parts of the structure are enclosed in curled
7863 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
7864 on the same memory location and represent the current values of the
7865 memory location in their specific modes. Since no tag processing is done
7866 all variants are displayed. A variant field is printed by
7867 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7870 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7871 [.cs: []], (susi) = [.ds: susi]}]
7875 Substructures of string mode-, array mode- or structure mode-values
7876 (e.g. array slices, fields of structure locations) are accessed using
7877 certain operations which are described in the next section, @ref{Values
7878 and their Operations}.
7880 A location value may be interpreted as having a different mode using the
7881 location conversion. This mode conversion is written as @code{<mode
7882 name>(<location>)}. The user has to consider that the sizes of the modes
7883 have to be equal otherwise an error occurs. Furthermore, no range
7884 checking of the location against the destination mode is performed, and
7885 therefore the result can be quite confusing.
7888 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7891 @node Values and their Operations
7892 @subsubsection Values and their Operations
7894 Values are used to alter locations, to investigate complex structures in
7895 more detail or to filter relevant information out of a large amount of
7896 data. There are several (mode dependent) operations defined which enable
7897 such investigations. These operations are not only applicable to
7898 constant values but also to locations, which can become quite useful
7899 when debugging complex structures. During parsing the command line
7900 (e.g. evaluating an expression) @value{GDBN} treats location names as
7901 the values behind these locations.
7903 This section describes how values have to be specified and which
7904 operations are legal to be used with such values.
7907 @item Literal Values
7908 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7909 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7911 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7912 @c be converted to a @ref.
7917 @emph{Integer Literals} are specified in the same manner as in Chill
7918 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7920 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7922 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7925 @emph{Set Literals} are defined by a name which was specified in a set
7926 mode. The value delivered by a Set Literal is the set value. This is
7927 comparable to an enumeration in C/C@t{++} language.
7929 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7930 emptiness literal delivers either the empty reference value, the empty
7931 procedure value or the empty instance value.
7934 @emph{Character String Literals} are defined by a sequence of characters
7935 enclosed in single- or double quotes. If a single- or double quote has
7936 to be part of the string literal it has to be stuffed (specified twice).
7938 @emph{Bitstring Literals} are specified in the same manner as in Chill
7939 programs (refer z200/88 chpt 5.2.4.8).
7941 @emph{Floating point literals} are specified in the same manner as in
7942 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7947 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7948 name>} can be omitted if the mode of the tuple is unambiguous. This
7949 unambiguity is derived from the context of a evaluated expression.
7950 @code{<tuple>} can be one of the following:
7953 @item @emph{Powerset Tuple}
7954 @item @emph{Array Tuple}
7955 @item @emph{Structure Tuple}
7956 Powerset tuples, array tuples and structure tuples are specified in the
7957 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7960 @item String Element Value
7961 A string element value is specified by
7963 @code{<string value>(<index>)}
7965 where @code{<index>} is a integer expression. It delivers a character
7966 value which is equivalent to the character indexed by @code{<index>} in
7969 @item String Slice Value
7970 A string slice value is specified by @code{<string value>(<slice
7971 spec>)}, where @code{<slice spec>} can be either a range of integer
7972 expressions or specified by @code{<start expr> up <size>}.
7973 @code{<size>} denotes the number of elements which the slice contains.
7974 The delivered value is a string value, which is part of the specified
7977 @item Array Element Values
7978 An array element value is specified by @code{<array value>(<expr>)} and
7979 delivers a array element value of the mode of the specified array.
7981 @item Array Slice Values
7982 An array slice is specified by @code{<array value>(<slice spec>)}, where
7983 @code{<slice spec>} can be either a range specified by expressions or by
7984 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7985 arrayelements the slice contains. The delivered value is an array value
7986 which is part of the specified array.
7988 @item Structure Field Values
7989 A structure field value is derived by @code{<structure value>.<field
7990 name>}, where @code{<field name>} indicates the name of a field specified
7991 in the mode definition of the structure. The mode of the delivered value
7992 corresponds to this mode definition in the structure definition.
7994 @item Procedure Call Value
7995 The procedure call value is derived from the return value of the
7996 procedure@footnote{If a procedure call is used for instance in an
7997 expression, then this procedure is called with all its side
7998 effects. This can lead to confusing results if used carelessly.}.
8000 Values of duration mode locations are represented by @code{ULONG} literals.
8002 Values of time mode locations appear as
8004 @code{TIME(<secs>:<nsecs>)}
8009 This is not implemented yet:
8010 @item Built-in Value
8012 The following built in functions are provided:
8024 @item @code{UPPER()}
8025 @item @code{LOWER()}
8026 @item @code{LENGTH()}
8030 @item @code{ARCSIN()}
8031 @item @code{ARCCOS()}
8032 @item @code{ARCTAN()}
8039 For a detailed description refer to the GNU Chill implementation manual
8043 @item Zero-adic Operator Value
8044 The zero-adic operator value is derived from the instance value for the
8045 current active process.
8047 @item Expression Values
8048 The value delivered by an expression is the result of the evaluation of
8049 the specified expression. If there are error conditions (mode
8050 incompatibility, etc.) the evaluation of expressions is aborted with a
8051 corresponding error message. Expressions may be parenthesised which
8052 causes the evaluation of this expression before any other expression
8053 which uses the result of the parenthesised expression. The following
8054 operators are supported by @value{GDBN}:
8057 @item @code{OR, ORIF, XOR}
8058 @itemx @code{AND, ANDIF}
8060 Logical operators defined over operands of boolean mode.
8063 Equality and inequality operators defined over all modes.
8067 Relational operators defined over predefined modes.
8070 @itemx @code{*, /, MOD, REM}
8071 Arithmetic operators defined over predefined modes.
8074 Change sign operator.
8077 String concatenation operator.
8080 String repetition operator.
8083 Referenced location operator which can be used either to take the
8084 address of a location (@code{->loc}), or to dereference a reference
8085 location (@code{loc->}).
8087 @item @code{OR, XOR}
8090 Powerset and bitstring operators.
8094 Powerset inclusion operators.
8097 Membership operator.
8101 @node Chill type and range checks
8102 @subsubsection Chill type and range checks
8104 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8105 of the two modes are equal. This rule applies recursively to more
8106 complex datatypes which means that complex modes are treated
8107 equivalent if all element modes (which also can be complex modes like
8108 structures, arrays, etc.) have the same size.
8110 Range checking is done on all mathematical operations, assignment, array
8111 index bounds and all built in procedures.
8113 Strong type checks are forced using the @value{GDBN} command @code{set
8114 check strong}. This enforces strong type and range checks on all
8115 operations where Chill constructs are used (expressions, built in
8116 functions, etc.) in respect to the semantics as defined in the z.200
8117 language specification.
8119 All checks can be disabled by the @value{GDBN} command @code{set check
8123 @c Deviations from the Chill Standard Z200/88
8124 see last paragraph ?
8127 @node Chill defaults
8128 @subsubsection Chill defaults
8130 If type and range checking are set automatically by @value{GDBN}, they
8131 both default to @code{on} whenever the working language changes to
8132 Chill. This happens regardless of whether you or @value{GDBN}
8133 selected the working language.
8135 If you allow @value{GDBN} to set the language automatically, then entering
8136 code compiled from a file whose name ends with @file{.ch} sets the
8137 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8138 the language automatically}, for further details.
8141 @chapter Examining the Symbol Table
8143 The commands described in this chapter allow you to inquire about the
8144 symbols (names of variables, functions and types) defined in your
8145 program. This information is inherent in the text of your program and
8146 does not change as your program executes. @value{GDBN} finds it in your
8147 program's symbol table, in the file indicated when you started @value{GDBN}
8148 (@pxref{File Options, ,Choosing files}), or by one of the
8149 file-management commands (@pxref{Files, ,Commands to specify files}).
8151 @cindex symbol names
8152 @cindex names of symbols
8153 @cindex quoting names
8154 Occasionally, you may need to refer to symbols that contain unusual
8155 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8156 most frequent case is in referring to static variables in other
8157 source files (@pxref{Variables,,Program variables}). File names
8158 are recorded in object files as debugging symbols, but @value{GDBN} would
8159 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8160 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8161 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8168 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8171 @kindex info address
8172 @cindex address of a symbol
8173 @item info address @var{symbol}
8174 Describe where the data for @var{symbol} is stored. For a register
8175 variable, this says which register it is kept in. For a non-register
8176 local variable, this prints the stack-frame offset at which the variable
8179 Note the contrast with @samp{print &@var{symbol}}, which does not work
8180 at all for a register variable, and for a stack local variable prints
8181 the exact address of the current instantiation of the variable.
8184 @cindex symbol from address
8185 @item info symbol @var{addr}
8186 Print the name of a symbol which is stored at the address @var{addr}.
8187 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8188 nearest symbol and an offset from it:
8191 (@value{GDBP}) info symbol 0x54320
8192 _initialize_vx + 396 in section .text
8196 This is the opposite of the @code{info address} command. You can use
8197 it to find out the name of a variable or a function given its address.
8200 @item whatis @var{expr}
8201 Print the data type of expression @var{expr}. @var{expr} is not
8202 actually evaluated, and any side-effecting operations (such as
8203 assignments or function calls) inside it do not take place.
8204 @xref{Expressions, ,Expressions}.
8207 Print the data type of @code{$}, the last value in the value history.
8210 @item ptype @var{typename}
8211 Print a description of data type @var{typename}. @var{typename} may be
8212 the name of a type, or for C code it may have the form @samp{class
8213 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8214 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8216 @item ptype @var{expr}
8218 Print a description of the type of expression @var{expr}. @code{ptype}
8219 differs from @code{whatis} by printing a detailed description, instead
8220 of just the name of the type.
8222 For example, for this variable declaration:
8225 struct complex @{double real; double imag;@} v;
8229 the two commands give this output:
8233 (@value{GDBP}) whatis v
8234 type = struct complex
8235 (@value{GDBP}) ptype v
8236 type = struct complex @{
8244 As with @code{whatis}, using @code{ptype} without an argument refers to
8245 the type of @code{$}, the last value in the value history.
8248 @item info types @var{regexp}
8250 Print a brief description of all types whose names match @var{regexp}
8251 (or all types in your program, if you supply no argument). Each
8252 complete typename is matched as though it were a complete line; thus,
8253 @samp{i type value} gives information on all types in your program whose
8254 names include the string @code{value}, but @samp{i type ^value$} gives
8255 information only on types whose complete name is @code{value}.
8257 This command differs from @code{ptype} in two ways: first, like
8258 @code{whatis}, it does not print a detailed description; second, it
8259 lists all source files where a type is defined.
8262 @cindex local variables
8263 @item info scope @var{addr}
8264 List all the variables local to a particular scope. This command
8265 accepts a location---a function name, a source line, or an address
8266 preceded by a @samp{*}, and prints all the variables local to the
8267 scope defined by that location. For example:
8270 (@value{GDBP}) @b{info scope command_line_handler}
8271 Scope for command_line_handler:
8272 Symbol rl is an argument at stack/frame offset 8, length 4.
8273 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8274 Symbol linelength is in static storage at address 0x150a1c, length 4.
8275 Symbol p is a local variable in register $esi, length 4.
8276 Symbol p1 is a local variable in register $ebx, length 4.
8277 Symbol nline is a local variable in register $edx, length 4.
8278 Symbol repeat is a local variable at frame offset -8, length 4.
8282 This command is especially useful for determining what data to collect
8283 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8288 Show the name of the current source file---that is, the source file for
8289 the function containing the current point of execution---and the language
8292 @kindex info sources
8294 Print the names of all source files in your program for which there is
8295 debugging information, organized into two lists: files whose symbols
8296 have already been read, and files whose symbols will be read when needed.
8298 @kindex info functions
8299 @item info functions
8300 Print the names and data types of all defined functions.
8302 @item info functions @var{regexp}
8303 Print the names and data types of all defined functions
8304 whose names contain a match for regular expression @var{regexp}.
8305 Thus, @samp{info fun step} finds all functions whose names
8306 include @code{step}; @samp{info fun ^step} finds those whose names
8307 start with @code{step}. If a function name contains characters
8308 that conflict with the regular expression language (eg.
8309 @samp{operator*()}), they may be quoted with a backslash.
8311 @kindex info variables
8312 @item info variables
8313 Print the names and data types of all variables that are declared
8314 outside of functions (i.e., excluding local variables).
8316 @item info variables @var{regexp}
8317 Print the names and data types of all variables (except for local
8318 variables) whose names contain a match for regular expression
8322 This was never implemented.
8323 @kindex info methods
8325 @itemx info methods @var{regexp}
8326 The @code{info methods} command permits the user to examine all defined
8327 methods within C@t{++} program, or (with the @var{regexp} argument) a
8328 specific set of methods found in the various C@t{++} classes. Many
8329 C@t{++} classes provide a large number of methods. Thus, the output
8330 from the @code{ptype} command can be overwhelming and hard to use. The
8331 @code{info-methods} command filters the methods, printing only those
8332 which match the regular-expression @var{regexp}.
8335 @cindex reloading symbols
8336 Some systems allow individual object files that make up your program to
8337 be replaced without stopping and restarting your program. For example,
8338 in VxWorks you can simply recompile a defective object file and keep on
8339 running. If you are running on one of these systems, you can allow
8340 @value{GDBN} to reload the symbols for automatically relinked modules:
8343 @kindex set symbol-reloading
8344 @item set symbol-reloading on
8345 Replace symbol definitions for the corresponding source file when an
8346 object file with a particular name is seen again.
8348 @item set symbol-reloading off
8349 Do not replace symbol definitions when encountering object files of the
8350 same name more than once. This is the default state; if you are not
8351 running on a system that permits automatic relinking of modules, you
8352 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8353 may discard symbols when linking large programs, that may contain
8354 several modules (from different directories or libraries) with the same
8357 @kindex show symbol-reloading
8358 @item show symbol-reloading
8359 Show the current @code{on} or @code{off} setting.
8362 @kindex set opaque-type-resolution
8363 @item set opaque-type-resolution on
8364 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8365 declared as a pointer to a @code{struct}, @code{class}, or
8366 @code{union}---for example, @code{struct MyType *}---that is used in one
8367 source file although the full declaration of @code{struct MyType} is in
8368 another source file. The default is on.
8370 A change in the setting of this subcommand will not take effect until
8371 the next time symbols for a file are loaded.
8373 @item set opaque-type-resolution off
8374 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8375 is printed as follows:
8377 @{<no data fields>@}
8380 @kindex show opaque-type-resolution
8381 @item show opaque-type-resolution
8382 Show whether opaque types are resolved or not.
8384 @kindex maint print symbols
8386 @kindex maint print psymbols
8387 @cindex partial symbol dump
8388 @item maint print symbols @var{filename}
8389 @itemx maint print psymbols @var{filename}
8390 @itemx maint print msymbols @var{filename}
8391 Write a dump of debugging symbol data into the file @var{filename}.
8392 These commands are used to debug the @value{GDBN} symbol-reading code. Only
8393 symbols with debugging data are included. If you use @samp{maint print
8394 symbols}, @value{GDBN} includes all the symbols for which it has already
8395 collected full details: that is, @var{filename} reflects symbols for
8396 only those files whose symbols @value{GDBN} has read. You can use the
8397 command @code{info sources} to find out which files these are. If you
8398 use @samp{maint print psymbols} instead, the dump shows information about
8399 symbols that @value{GDBN} only knows partially---that is, symbols defined in
8400 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
8401 @samp{maint print msymbols} dumps just the minimal symbol information
8402 required for each object file from which @value{GDBN} has read some symbols.
8403 @xref{Files, ,Commands to specify files}, for a discussion of how
8404 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
8408 @chapter Altering Execution
8410 Once you think you have found an error in your program, you might want to
8411 find out for certain whether correcting the apparent error would lead to
8412 correct results in the rest of the run. You can find the answer by
8413 experiment, using the @value{GDBN} features for altering execution of the
8416 For example, you can store new values into variables or memory
8417 locations, give your program a signal, restart it at a different
8418 address, or even return prematurely from a function.
8421 * Assignment:: Assignment to variables
8422 * Jumping:: Continuing at a different address
8423 * Signaling:: Giving your program a signal
8424 * Returning:: Returning from a function
8425 * Calling:: Calling your program's functions
8426 * Patching:: Patching your program
8430 @section Assignment to variables
8433 @cindex setting variables
8434 To alter the value of a variable, evaluate an assignment expression.
8435 @xref{Expressions, ,Expressions}. For example,
8442 stores the value 4 into the variable @code{x}, and then prints the
8443 value of the assignment expression (which is 4).
8444 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
8445 information on operators in supported languages.
8447 @kindex set variable
8448 @cindex variables, setting
8449 If you are not interested in seeing the value of the assignment, use the
8450 @code{set} command instead of the @code{print} command. @code{set} is
8451 really the same as @code{print} except that the expression's value is
8452 not printed and is not put in the value history (@pxref{Value History,
8453 ,Value history}). The expression is evaluated only for its effects.
8455 If the beginning of the argument string of the @code{set} command
8456 appears identical to a @code{set} subcommand, use the @code{set
8457 variable} command instead of just @code{set}. This command is identical
8458 to @code{set} except for its lack of subcommands. For example, if your
8459 program has a variable @code{width}, you get an error if you try to set
8460 a new value with just @samp{set width=13}, because @value{GDBN} has the
8461 command @code{set width}:
8464 (@value{GDBP}) whatis width
8466 (@value{GDBP}) p width
8468 (@value{GDBP}) set width=47
8469 Invalid syntax in expression.
8473 The invalid expression, of course, is @samp{=47}. In
8474 order to actually set the program's variable @code{width}, use
8477 (@value{GDBP}) set var width=47
8480 Because the @code{set} command has many subcommands that can conflict
8481 with the names of program variables, it is a good idea to use the
8482 @code{set variable} command instead of just @code{set}. For example, if
8483 your program has a variable @code{g}, you run into problems if you try
8484 to set a new value with just @samp{set g=4}, because @value{GDBN} has
8485 the command @code{set gnutarget}, abbreviated @code{set g}:
8489 (@value{GDBP}) whatis g
8493 (@value{GDBP}) set g=4
8497 The program being debugged has been started already.
8498 Start it from the beginning? (y or n) y
8499 Starting program: /home/smith/cc_progs/a.out
8500 "/home/smith/cc_progs/a.out": can't open to read symbols:
8502 (@value{GDBP}) show g
8503 The current BFD target is "=4".
8508 The program variable @code{g} did not change, and you silently set the
8509 @code{gnutarget} to an invalid value. In order to set the variable
8513 (@value{GDBP}) set var g=4
8516 @value{GDBN} allows more implicit conversions in assignments than C; you can
8517 freely store an integer value into a pointer variable or vice versa,
8518 and you can convert any structure to any other structure that is the
8519 same length or shorter.
8520 @comment FIXME: how do structs align/pad in these conversions?
8521 @comment /doc@cygnus.com 18dec1990
8523 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
8524 construct to generate a value of specified type at a specified address
8525 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
8526 to memory location @code{0x83040} as an integer (which implies a certain size
8527 and representation in memory), and
8530 set @{int@}0x83040 = 4
8534 stores the value 4 into that memory location.
8537 @section Continuing at a different address
8539 Ordinarily, when you continue your program, you do so at the place where
8540 it stopped, with the @code{continue} command. You can instead continue at
8541 an address of your own choosing, with the following commands:
8545 @item jump @var{linespec}
8546 Resume execution at line @var{linespec}. Execution stops again
8547 immediately if there is a breakpoint there. @xref{List, ,Printing
8548 source lines}, for a description of the different forms of
8549 @var{linespec}. It is common practice to use the @code{tbreak} command
8550 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
8553 The @code{jump} command does not change the current stack frame, or
8554 the stack pointer, or the contents of any memory location or any
8555 register other than the program counter. If line @var{linespec} is in
8556 a different function from the one currently executing, the results may
8557 be bizarre if the two functions expect different patterns of arguments or
8558 of local variables. For this reason, the @code{jump} command requests
8559 confirmation if the specified line is not in the function currently
8560 executing. However, even bizarre results are predictable if you are
8561 well acquainted with the machine-language code of your program.
8563 @item jump *@var{address}
8564 Resume execution at the instruction at address @var{address}.
8567 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
8568 On many systems, you can get much the same effect as the @code{jump}
8569 command by storing a new value into the register @code{$pc}. The
8570 difference is that this does not start your program running; it only
8571 changes the address of where it @emph{will} run when you continue. For
8579 makes the next @code{continue} command or stepping command execute at
8580 address @code{0x485}, rather than at the address where your program stopped.
8581 @xref{Continuing and Stepping, ,Continuing and stepping}.
8583 The most common occasion to use the @code{jump} command is to back
8584 up---perhaps with more breakpoints set---over a portion of a program
8585 that has already executed, in order to examine its execution in more
8590 @section Giving your program a signal
8594 @item signal @var{signal}
8595 Resume execution where your program stopped, but immediately give it the
8596 signal @var{signal}. @var{signal} can be the name or the number of a
8597 signal. For example, on many systems @code{signal 2} and @code{signal
8598 SIGINT} are both ways of sending an interrupt signal.
8600 Alternatively, if @var{signal} is zero, continue execution without
8601 giving a signal. This is useful when your program stopped on account of
8602 a signal and would ordinary see the signal when resumed with the
8603 @code{continue} command; @samp{signal 0} causes it to resume without a
8606 @code{signal} does not repeat when you press @key{RET} a second time
8607 after executing the command.
8611 Invoking the @code{signal} command is not the same as invoking the
8612 @code{kill} utility from the shell. Sending a signal with @code{kill}
8613 causes @value{GDBN} to decide what to do with the signal depending on
8614 the signal handling tables (@pxref{Signals}). The @code{signal} command
8615 passes the signal directly to your program.
8619 @section Returning from a function
8622 @cindex returning from a function
8625 @itemx return @var{expression}
8626 You can cancel execution of a function call with the @code{return}
8627 command. If you give an
8628 @var{expression} argument, its value is used as the function's return
8632 When you use @code{return}, @value{GDBN} discards the selected stack frame
8633 (and all frames within it). You can think of this as making the
8634 discarded frame return prematurely. If you wish to specify a value to
8635 be returned, give that value as the argument to @code{return}.
8637 This pops the selected stack frame (@pxref{Selection, ,Selecting a
8638 frame}), and any other frames inside of it, leaving its caller as the
8639 innermost remaining frame. That frame becomes selected. The
8640 specified value is stored in the registers used for returning values
8643 The @code{return} command does not resume execution; it leaves the
8644 program stopped in the state that would exist if the function had just
8645 returned. In contrast, the @code{finish} command (@pxref{Continuing
8646 and Stepping, ,Continuing and stepping}) resumes execution until the
8647 selected stack frame returns naturally.
8650 @section Calling program functions
8652 @cindex calling functions
8655 @item call @var{expr}
8656 Evaluate the expression @var{expr} without displaying @code{void}
8660 You can use this variant of the @code{print} command if you want to
8661 execute a function from your program, but without cluttering the output
8662 with @code{void} returned values. If the result is not void, it
8663 is printed and saved in the value history.
8665 For the A29K, a user-controlled variable @code{call_scratch_address},
8666 specifies the location of a scratch area to be used when @value{GDBN}
8667 calls a function in the target. This is necessary because the usual
8668 method of putting the scratch area on the stack does not work in systems
8669 that have separate instruction and data spaces.
8672 @section Patching programs
8674 @cindex patching binaries
8675 @cindex writing into executables
8676 @cindex writing into corefiles
8678 By default, @value{GDBN} opens the file containing your program's
8679 executable code (or the corefile) read-only. This prevents accidental
8680 alterations to machine code; but it also prevents you from intentionally
8681 patching your program's binary.
8683 If you'd like to be able to patch the binary, you can specify that
8684 explicitly with the @code{set write} command. For example, you might
8685 want to turn on internal debugging flags, or even to make emergency
8691 @itemx set write off
8692 If you specify @samp{set write on}, @value{GDBN} opens executable and
8693 core files for both reading and writing; if you specify @samp{set write
8694 off} (the default), @value{GDBN} opens them read-only.
8696 If you have already loaded a file, you must load it again (using the
8697 @code{exec-file} or @code{core-file} command) after changing @code{set
8698 write}, for your new setting to take effect.
8702 Display whether executable files and core files are opened for writing
8707 @chapter @value{GDBN} Files
8709 @value{GDBN} needs to know the file name of the program to be debugged,
8710 both in order to read its symbol table and in order to start your
8711 program. To debug a core dump of a previous run, you must also tell
8712 @value{GDBN} the name of the core dump file.
8715 * Files:: Commands to specify files
8716 * Symbol Errors:: Errors reading symbol files
8720 @section Commands to specify files
8722 @cindex symbol table
8723 @cindex core dump file
8725 You may want to specify executable and core dump file names. The usual
8726 way to do this is at start-up time, using the arguments to
8727 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
8728 Out of @value{GDBN}}).
8730 Occasionally it is necessary to change to a different file during a
8731 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8732 a file you want to use. In these situations the @value{GDBN} commands
8733 to specify new files are useful.
8736 @cindex executable file
8738 @item file @var{filename}
8739 Use @var{filename} as the program to be debugged. It is read for its
8740 symbols and for the contents of pure memory. It is also the program
8741 executed when you use the @code{run} command. If you do not specify a
8742 directory and the file is not found in the @value{GDBN} working directory,
8743 @value{GDBN} uses the environment variable @code{PATH} as a list of
8744 directories to search, just as the shell does when looking for a program
8745 to run. You can change the value of this variable, for both @value{GDBN}
8746 and your program, using the @code{path} command.
8748 On systems with memory-mapped files, an auxiliary file named
8749 @file{@var{filename}.syms} may hold symbol table information for
8750 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8751 @file{@var{filename}.syms}, starting up more quickly. See the
8752 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8753 (available on the command line, and with the commands @code{file},
8754 @code{symbol-file}, or @code{add-symbol-file}, described below),
8755 for more information.
8758 @code{file} with no argument makes @value{GDBN} discard any information it
8759 has on both executable file and the symbol table.
8762 @item exec-file @r{[} @var{filename} @r{]}
8763 Specify that the program to be run (but not the symbol table) is found
8764 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8765 if necessary to locate your program. Omitting @var{filename} means to
8766 discard information on the executable file.
8769 @item symbol-file @r{[} @var{filename} @r{]}
8770 Read symbol table information from file @var{filename}. @code{PATH} is
8771 searched when necessary. Use the @code{file} command to get both symbol
8772 table and program to run from the same file.
8774 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8775 program's symbol table.
8777 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8778 of its convenience variables, the value history, and all breakpoints and
8779 auto-display expressions. This is because they may contain pointers to
8780 the internal data recording symbols and data types, which are part of
8781 the old symbol table data being discarded inside @value{GDBN}.
8783 @code{symbol-file} does not repeat if you press @key{RET} again after
8786 When @value{GDBN} is configured for a particular environment, it
8787 understands debugging information in whatever format is the standard
8788 generated for that environment; you may use either a @sc{gnu} compiler, or
8789 other compilers that adhere to the local conventions.
8790 Best results are usually obtained from @sc{gnu} compilers; for example,
8791 using @code{@value{GCC}} you can generate debugging information for
8794 For most kinds of object files, with the exception of old SVR3 systems
8795 using COFF, the @code{symbol-file} command does not normally read the
8796 symbol table in full right away. Instead, it scans the symbol table
8797 quickly to find which source files and which symbols are present. The
8798 details are read later, one source file at a time, as they are needed.
8800 The purpose of this two-stage reading strategy is to make @value{GDBN}
8801 start up faster. For the most part, it is invisible except for
8802 occasional pauses while the symbol table details for a particular source
8803 file are being read. (The @code{set verbose} command can turn these
8804 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8805 warnings and messages}.)
8807 We have not implemented the two-stage strategy for COFF yet. When the
8808 symbol table is stored in COFF format, @code{symbol-file} reads the
8809 symbol table data in full right away. Note that ``stabs-in-COFF''
8810 still does the two-stage strategy, since the debug info is actually
8814 @cindex reading symbols immediately
8815 @cindex symbols, reading immediately
8817 @cindex memory-mapped symbol file
8818 @cindex saving symbol table
8819 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8820 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8821 You can override the @value{GDBN} two-stage strategy for reading symbol
8822 tables by using the @samp{-readnow} option with any of the commands that
8823 load symbol table information, if you want to be sure @value{GDBN} has the
8824 entire symbol table available.
8826 If memory-mapped files are available on your system through the
8827 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8828 cause @value{GDBN} to write the symbols for your program into a reusable
8829 file. Future @value{GDBN} debugging sessions map in symbol information
8830 from this auxiliary symbol file (if the program has not changed), rather
8831 than spending time reading the symbol table from the executable
8832 program. Using the @samp{-mapped} option has the same effect as
8833 starting @value{GDBN} with the @samp{-mapped} command-line option.
8835 You can use both options together, to make sure the auxiliary symbol
8836 file has all the symbol information for your program.
8838 The auxiliary symbol file for a program called @var{myprog} is called
8839 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8840 than the corresponding executable), @value{GDBN} always attempts to use
8841 it when you debug @var{myprog}; no special options or commands are
8844 The @file{.syms} file is specific to the host machine where you run
8845 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8846 symbol table. It cannot be shared across multiple host platforms.
8848 @c FIXME: for now no mention of directories, since this seems to be in
8849 @c flux. 13mar1992 status is that in theory GDB would look either in
8850 @c current dir or in same dir as myprog; but issues like competing
8851 @c GDB's, or clutter in system dirs, mean that in practice right now
8852 @c only current dir is used. FFish says maybe a special GDB hierarchy
8853 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8858 @item core-file @r{[} @var{filename} @r{]}
8859 Specify the whereabouts of a core dump file to be used as the ``contents
8860 of memory''. Traditionally, core files contain only some parts of the
8861 address space of the process that generated them; @value{GDBN} can access the
8862 executable file itself for other parts.
8864 @code{core-file} with no argument specifies that no core file is
8867 Note that the core file is ignored when your program is actually running
8868 under @value{GDBN}. So, if you have been running your program and you
8869 wish to debug a core file instead, you must kill the subprocess in which
8870 the program is running. To do this, use the @code{kill} command
8871 (@pxref{Kill Process, ,Killing the child process}).
8873 @kindex add-symbol-file
8874 @cindex dynamic linking
8875 @item add-symbol-file @var{filename} @var{address}
8876 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8877 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
8878 The @code{add-symbol-file} command reads additional symbol table
8879 information from the file @var{filename}. You would use this command
8880 when @var{filename} has been dynamically loaded (by some other means)
8881 into the program that is running. @var{address} should be the memory
8882 address at which the file has been loaded; @value{GDBN} cannot figure
8883 this out for itself. You can additionally specify an arbitrary number
8884 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
8885 section name and base address for that section. You can specify any
8886 @var{address} as an expression.
8888 The symbol table of the file @var{filename} is added to the symbol table
8889 originally read with the @code{symbol-file} command. You can use the
8890 @code{add-symbol-file} command any number of times; the new symbol data
8891 thus read keeps adding to the old. To discard all old symbol data
8892 instead, use the @code{symbol-file} command without any arguments.
8894 @cindex relocatable object files, reading symbols from
8895 @cindex object files, relocatable, reading symbols from
8896 @cindex reading symbols from relocatable object files
8897 @cindex symbols, reading from relocatable object files
8898 @cindex @file{.o} files, reading symbols from
8899 Although @var{filename} is typically a shared library file, an
8900 executable file, or some other object file which has been fully
8901 relocated for loading into a process, you can also load symbolic
8902 information from relocatable @file{.o} files, as long as:
8906 the file's symbolic information refers only to linker symbols defined in
8907 that file, not to symbols defined by other object files,
8909 every section the file's symbolic information refers to has actually
8910 been loaded into the inferior, as it appears in the file, and
8912 you can determine the address at which every section was loaded, and
8913 provide these to the @code{add-symbol-file} command.
8917 Some embedded operating systems, like Sun Chorus and VxWorks, can load
8918 relocatable files into an already running program; such systems
8919 typically make the requirements above easy to meet. However, it's
8920 important to recognize that many native systems use complex link
8921 procedures (@code{.linkonce} section factoring and C++ constructor table
8922 assembly, for example) that make the requirements difficult to meet. In
8923 general, one cannot assume that using @code{add-symbol-file} to read a
8924 relocatable object file's symbolic information will have the same effect
8925 as linking the relocatable object file into the program in the normal
8928 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8930 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8931 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8932 table information for @var{filename}.
8934 @kindex add-shared-symbol-file
8935 @item add-shared-symbol-file
8936 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8937 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8938 shared libraries, however if @value{GDBN} does not find yours, you can run
8939 @code{add-shared-symbol-file}. It takes no arguments.
8943 The @code{section} command changes the base address of section SECTION of
8944 the exec file to ADDR. This can be used if the exec file does not contain
8945 section addresses, (such as in the a.out format), or when the addresses
8946 specified in the file itself are wrong. Each section must be changed
8947 separately. The @code{info files} command, described below, lists all
8948 the sections and their addresses.
8954 @code{info files} and @code{info target} are synonymous; both print the
8955 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8956 including the names of the executable and core dump files currently in
8957 use by @value{GDBN}, and the files from which symbols were loaded. The
8958 command @code{help target} lists all possible targets rather than
8963 All file-specifying commands allow both absolute and relative file names
8964 as arguments. @value{GDBN} always converts the file name to an absolute file
8965 name and remembers it that way.
8967 @cindex shared libraries
8968 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8971 @value{GDBN} automatically loads symbol definitions from shared libraries
8972 when you use the @code{run} command, or when you examine a core file.
8973 (Before you issue the @code{run} command, @value{GDBN} does not understand
8974 references to a function in a shared library, however---unless you are
8975 debugging a core file).
8977 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8978 automatically loads the symbols at the time of the @code{shl_load} call.
8980 @c FIXME: some @value{GDBN} release may permit some refs to undef
8981 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8982 @c FIXME...lib; check this from time to time when updating manual
8984 There are times, however, when you may wish to not automatically load
8985 symbol definitions from shared libraries, such as when they are
8986 particularly large or there are many of them.
8988 To control the automatic loading of shared library symbols, use the
8992 @kindex set auto-solib-add
8993 @item set auto-solib-add @var{mode}
8994 If @var{mode} is @code{on}, symbols from all shared object libraries
8995 will be loaded automatically when the inferior begins execution, you
8996 attach to an independently started inferior, or when the dynamic linker
8997 informs @value{GDBN} that a new library has been loaded. If @var{mode}
8998 is @code{off}, symbols must be loaded manually, using the
8999 @code{sharedlibrary} command. The default value is @code{on}.
9001 @kindex show auto-solib-add
9002 @item show auto-solib-add
9003 Display the current autoloading mode.
9006 To explicitly load shared library symbols, use the @code{sharedlibrary}
9010 @kindex info sharedlibrary
9013 @itemx info sharedlibrary
9014 Print the names of the shared libraries which are currently loaded.
9016 @kindex sharedlibrary
9018 @item sharedlibrary @var{regex}
9019 @itemx share @var{regex}
9020 Load shared object library symbols for files matching a
9021 Unix regular expression.
9022 As with files loaded automatically, it only loads shared libraries
9023 required by your program for a core file or after typing @code{run}. If
9024 @var{regex} is omitted all shared libraries required by your program are
9028 On some systems, such as HP-UX systems, @value{GDBN} supports
9029 autoloading shared library symbols until a limiting threshold size is
9030 reached. This provides the benefit of allowing autoloading to remain on
9031 by default, but avoids autoloading excessively large shared libraries,
9032 up to a threshold that is initially set, but which you can modify if you
9035 Beyond that threshold, symbols from shared libraries must be explicitly
9036 loaded. To load these symbols, use the command @code{sharedlibrary
9037 @var{filename}}. The base address of the shared library is determined
9038 automatically by @value{GDBN} and need not be specified.
9040 To display or set the threshold, use the commands:
9043 @kindex set auto-solib-limit
9044 @item set auto-solib-limit @var{threshold}
9045 Set the autoloading size threshold, in an integral number of megabytes.
9046 If @var{threshold} is nonzero and shared library autoloading is enabled,
9047 symbols from all shared object libraries will be loaded until the total
9048 size of the loaded shared library symbols exceeds this threshold.
9049 Otherwise, symbols must be loaded manually, using the
9050 @code{sharedlibrary} command. The default threshold is 100 (i.e. 100
9053 @kindex show auto-solib-limit
9054 @item show auto-solib-limit
9055 Display the current autoloading size threshold, in megabytes.
9059 @section Errors reading symbol files
9061 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9062 such as symbol types it does not recognize, or known bugs in compiler
9063 output. By default, @value{GDBN} does not notify you of such problems, since
9064 they are relatively common and primarily of interest to people
9065 debugging compilers. If you are interested in seeing information
9066 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9067 only one message about each such type of problem, no matter how many
9068 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9069 to see how many times the problems occur, with the @code{set
9070 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9073 The messages currently printed, and their meanings, include:
9076 @item inner block not inside outer block in @var{symbol}
9078 The symbol information shows where symbol scopes begin and end
9079 (such as at the start of a function or a block of statements). This
9080 error indicates that an inner scope block is not fully contained
9081 in its outer scope blocks.
9083 @value{GDBN} circumvents the problem by treating the inner block as if it had
9084 the same scope as the outer block. In the error message, @var{symbol}
9085 may be shown as ``@code{(don't know)}'' if the outer block is not a
9088 @item block at @var{address} out of order
9090 The symbol information for symbol scope blocks should occur in
9091 order of increasing addresses. This error indicates that it does not
9094 @value{GDBN} does not circumvent this problem, and has trouble
9095 locating symbols in the source file whose symbols it is reading. (You
9096 can often determine what source file is affected by specifying
9097 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9100 @item bad block start address patched
9102 The symbol information for a symbol scope block has a start address
9103 smaller than the address of the preceding source line. This is known
9104 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9106 @value{GDBN} circumvents the problem by treating the symbol scope block as
9107 starting on the previous source line.
9109 @item bad string table offset in symbol @var{n}
9112 Symbol number @var{n} contains a pointer into the string table which is
9113 larger than the size of the string table.
9115 @value{GDBN} circumvents the problem by considering the symbol to have the
9116 name @code{foo}, which may cause other problems if many symbols end up
9119 @item unknown symbol type @code{0x@var{nn}}
9121 The symbol information contains new data types that @value{GDBN} does
9122 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9123 uncomprehended information, in hexadecimal.
9125 @value{GDBN} circumvents the error by ignoring this symbol information.
9126 This usually allows you to debug your program, though certain symbols
9127 are not accessible. If you encounter such a problem and feel like
9128 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9129 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9130 and examine @code{*bufp} to see the symbol.
9132 @item stub type has NULL name
9134 @value{GDBN} could not find the full definition for a struct or class.
9136 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9137 The symbol information for a C@t{++} member function is missing some
9138 information that recent versions of the compiler should have output for
9141 @item info mismatch between compiler and debugger
9143 @value{GDBN} could not parse a type specification output by the compiler.
9148 @chapter Specifying a Debugging Target
9150 @cindex debugging target
9153 A @dfn{target} is the execution environment occupied by your program.
9155 Often, @value{GDBN} runs in the same host environment as your program;
9156 in that case, the debugging target is specified as a side effect when
9157 you use the @code{file} or @code{core} commands. When you need more
9158 flexibility---for example, running @value{GDBN} on a physically separate
9159 host, or controlling a standalone system over a serial port or a
9160 realtime system over a TCP/IP connection---you can use the @code{target}
9161 command to specify one of the target types configured for @value{GDBN}
9162 (@pxref{Target Commands, ,Commands for managing targets}).
9165 * Active Targets:: Active targets
9166 * Target Commands:: Commands for managing targets
9167 * Byte Order:: Choosing target byte order
9168 * Remote:: Remote debugging
9169 * KOD:: Kernel Object Display
9173 @node Active Targets
9174 @section Active targets
9176 @cindex stacking targets
9177 @cindex active targets
9178 @cindex multiple targets
9180 There are three classes of targets: processes, core files, and
9181 executable files. @value{GDBN} can work concurrently on up to three
9182 active targets, one in each class. This allows you to (for example)
9183 start a process and inspect its activity without abandoning your work on
9186 For example, if you execute @samp{gdb a.out}, then the executable file
9187 @code{a.out} is the only active target. If you designate a core file as
9188 well---presumably from a prior run that crashed and coredumped---then
9189 @value{GDBN} has two active targets and uses them in tandem, looking
9190 first in the corefile target, then in the executable file, to satisfy
9191 requests for memory addresses. (Typically, these two classes of target
9192 are complementary, since core files contain only a program's
9193 read-write memory---variables and so on---plus machine status, while
9194 executable files contain only the program text and initialized data.)
9196 When you type @code{run}, your executable file becomes an active process
9197 target as well. When a process target is active, all @value{GDBN}
9198 commands requesting memory addresses refer to that target; addresses in
9199 an active core file or executable file target are obscured while the
9200 process target is active.
9202 Use the @code{core-file} and @code{exec-file} commands to select a new
9203 core file or executable target (@pxref{Files, ,Commands to specify
9204 files}). To specify as a target a process that is already running, use
9205 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9208 @node Target Commands
9209 @section Commands for managing targets
9212 @item target @var{type} @var{parameters}
9213 Connects the @value{GDBN} host environment to a target machine or
9214 process. A target is typically a protocol for talking to debugging
9215 facilities. You use the argument @var{type} to specify the type or
9216 protocol of the target machine.
9218 Further @var{parameters} are interpreted by the target protocol, but
9219 typically include things like device names or host names to connect
9220 with, process numbers, and baud rates.
9222 The @code{target} command does not repeat if you press @key{RET} again
9223 after executing the command.
9227 Displays the names of all targets available. To display targets
9228 currently selected, use either @code{info target} or @code{info files}
9229 (@pxref{Files, ,Commands to specify files}).
9231 @item help target @var{name}
9232 Describe a particular target, including any parameters necessary to
9235 @kindex set gnutarget
9236 @item set gnutarget @var{args}
9237 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9238 knows whether it is reading an @dfn{executable},
9239 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9240 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9241 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9244 @emph{Warning:} To specify a file format with @code{set gnutarget},
9245 you must know the actual BFD name.
9249 @xref{Files, , Commands to specify files}.
9251 @kindex show gnutarget
9252 @item show gnutarget
9253 Use the @code{show gnutarget} command to display what file format
9254 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9255 @value{GDBN} will determine the file format for each file automatically,
9256 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9259 Here are some common targets (available, or not, depending on the GDB
9264 @item target exec @var{program}
9265 An executable file. @samp{target exec @var{program}} is the same as
9266 @samp{exec-file @var{program}}.
9269 @item target core @var{filename}
9270 A core dump file. @samp{target core @var{filename}} is the same as
9271 @samp{core-file @var{filename}}.
9273 @kindex target remote
9274 @item target remote @var{dev}
9275 Remote serial target in GDB-specific protocol. The argument @var{dev}
9276 specifies what serial device to use for the connection (e.g.
9277 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9278 supports the @code{load} command. This is only useful if you have
9279 some other way of getting the stub to the target system, and you can put
9280 it somewhere in memory where it won't get clobbered by the download.
9284 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9292 works; however, you cannot assume that a specific memory map, device
9293 drivers, or even basic I/O is available, although some simulators do
9294 provide these. For info about any processor-specific simulator details,
9295 see the appropriate section in @ref{Embedded Processors, ,Embedded
9300 Some configurations may include these targets as well:
9305 @item target nrom @var{dev}
9306 NetROM ROM emulator. This target only supports downloading.
9310 Different targets are available on different configurations of @value{GDBN};
9311 your configuration may have more or fewer targets.
9313 Many remote targets require you to download the executable's code
9314 once you've successfully established a connection.
9318 @kindex load @var{filename}
9319 @item load @var{filename}
9320 Depending on what remote debugging facilities are configured into
9321 @value{GDBN}, the @code{load} command may be available. Where it exists, it
9322 is meant to make @var{filename} (an executable) available for debugging
9323 on the remote system---by downloading, or dynamic linking, for example.
9324 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
9325 the @code{add-symbol-file} command.
9327 If your @value{GDBN} does not have a @code{load} command, attempting to
9328 execute it gets the error message ``@code{You can't do that when your
9329 target is @dots{}}''
9331 The file is loaded at whatever address is specified in the executable.
9332 For some object file formats, you can specify the load address when you
9333 link the program; for other formats, like a.out, the object file format
9334 specifies a fixed address.
9335 @c FIXME! This would be a good place for an xref to the GNU linker doc.
9337 @code{load} does not repeat if you press @key{RET} again after using it.
9341 @section Choosing target byte order
9343 @cindex choosing target byte order
9344 @cindex target byte order
9346 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
9347 offer the ability to run either big-endian or little-endian byte
9348 orders. Usually the executable or symbol will include a bit to
9349 designate the endian-ness, and you will not need to worry about
9350 which to use. However, you may still find it useful to adjust
9351 @value{GDBN}'s idea of processor endian-ness manually.
9354 @kindex set endian big
9355 @item set endian big
9356 Instruct @value{GDBN} to assume the target is big-endian.
9358 @kindex set endian little
9359 @item set endian little
9360 Instruct @value{GDBN} to assume the target is little-endian.
9362 @kindex set endian auto
9363 @item set endian auto
9364 Instruct @value{GDBN} to use the byte order associated with the
9368 Display @value{GDBN}'s current idea of the target byte order.
9372 Note that these commands merely adjust interpretation of symbolic
9373 data on the host, and that they have absolutely no effect on the
9377 @section Remote debugging
9378 @cindex remote debugging
9380 If you are trying to debug a program running on a machine that cannot run
9381 @value{GDBN} in the usual way, it is often useful to use remote debugging.
9382 For example, you might use remote debugging on an operating system kernel,
9383 or on a small system which does not have a general purpose operating system
9384 powerful enough to run a full-featured debugger.
9386 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
9387 to make this work with particular debugging targets. In addition,
9388 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
9389 but not specific to any particular target system) which you can use if you
9390 write the remote stubs---the code that runs on the remote system to
9391 communicate with @value{GDBN}.
9393 Other remote targets may be available in your
9394 configuration of @value{GDBN}; use @code{help target} to list them.
9397 * Remote Serial:: @value{GDBN} remote serial protocol
9401 @subsection The @value{GDBN} remote serial protocol
9403 @cindex remote serial debugging, overview
9404 To debug a program running on another machine (the debugging
9405 @dfn{target} machine), you must first arrange for all the usual
9406 prerequisites for the program to run by itself. For example, for a C
9411 A startup routine to set up the C runtime environment; these usually
9412 have a name like @file{crt0}. The startup routine may be supplied by
9413 your hardware supplier, or you may have to write your own.
9416 A C subroutine library to support your program's
9417 subroutine calls, notably managing input and output.
9420 A way of getting your program to the other machine---for example, a
9421 download program. These are often supplied by the hardware
9422 manufacturer, but you may have to write your own from hardware
9426 The next step is to arrange for your program to use a serial port to
9427 communicate with the machine where @value{GDBN} is running (the @dfn{host}
9428 machine). In general terms, the scheme looks like this:
9432 @value{GDBN} already understands how to use this protocol; when everything
9433 else is set up, you can simply use the @samp{target remote} command
9434 (@pxref{Targets,,Specifying a Debugging Target}).
9436 @item On the target,
9437 you must link with your program a few special-purpose subroutines that
9438 implement the @value{GDBN} remote serial protocol. The file containing these
9439 subroutines is called a @dfn{debugging stub}.
9441 On certain remote targets, you can use an auxiliary program
9442 @code{gdbserver} instead of linking a stub into your program.
9443 @xref{Server,,Using the @code{gdbserver} program}, for details.
9446 The debugging stub is specific to the architecture of the remote
9447 machine; for example, use @file{sparc-stub.c} to debug programs on
9450 @cindex remote serial stub list
9451 These working remote stubs are distributed with @value{GDBN}:
9456 @cindex @file{i386-stub.c}
9459 For Intel 386 and compatible architectures.
9462 @cindex @file{m68k-stub.c}
9463 @cindex Motorola 680x0
9465 For Motorola 680x0 architectures.
9468 @cindex @file{sh-stub.c}
9471 For Hitachi SH architectures.
9474 @cindex @file{sparc-stub.c}
9476 For @sc{sparc} architectures.
9479 @cindex @file{sparcl-stub.c}
9482 For Fujitsu @sc{sparclite} architectures.
9486 The @file{README} file in the @value{GDBN} distribution may list other
9487 recently added stubs.
9490 * Stub Contents:: What the stub can do for you
9491 * Bootstrapping:: What you must do for the stub
9492 * Debug Session:: Putting it all together
9493 * Protocol:: Definition of the communication protocol
9494 * Server:: Using the `gdbserver' program
9495 * NetWare:: Using the `gdbserve.nlm' program
9499 @subsubsection What the stub can do for you
9501 @cindex remote serial stub
9502 The debugging stub for your architecture supplies these three
9506 @item set_debug_traps
9507 @kindex set_debug_traps
9508 @cindex remote serial stub, initialization
9509 This routine arranges for @code{handle_exception} to run when your
9510 program stops. You must call this subroutine explicitly near the
9511 beginning of your program.
9513 @item handle_exception
9514 @kindex handle_exception
9515 @cindex remote serial stub, main routine
9516 This is the central workhorse, but your program never calls it
9517 explicitly---the setup code arranges for @code{handle_exception} to
9518 run when a trap is triggered.
9520 @code{handle_exception} takes control when your program stops during
9521 execution (for example, on a breakpoint), and mediates communications
9522 with @value{GDBN} on the host machine. This is where the communications
9523 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
9524 representative on the target machine. It begins by sending summary
9525 information on the state of your program, then continues to execute,
9526 retrieving and transmitting any information @value{GDBN} needs, until you
9527 execute a @value{GDBN} command that makes your program resume; at that point,
9528 @code{handle_exception} returns control to your own code on the target
9532 @cindex @code{breakpoint} subroutine, remote
9533 Use this auxiliary subroutine to make your program contain a
9534 breakpoint. Depending on the particular situation, this may be the only
9535 way for @value{GDBN} to get control. For instance, if your target
9536 machine has some sort of interrupt button, you won't need to call this;
9537 pressing the interrupt button transfers control to
9538 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
9539 simply receiving characters on the serial port may also trigger a trap;
9540 again, in that situation, you don't need to call @code{breakpoint} from
9541 your own program---simply running @samp{target remote} from the host
9542 @value{GDBN} session gets control.
9544 Call @code{breakpoint} if none of these is true, or if you simply want
9545 to make certain your program stops at a predetermined point for the
9546 start of your debugging session.
9550 @subsubsection What you must do for the stub
9552 @cindex remote stub, support routines
9553 The debugging stubs that come with @value{GDBN} are set up for a particular
9554 chip architecture, but they have no information about the rest of your
9555 debugging target machine.
9557 First of all you need to tell the stub how to communicate with the
9561 @item int getDebugChar()
9562 @kindex getDebugChar
9563 Write this subroutine to read a single character from the serial port.
9564 It may be identical to @code{getchar} for your target system; a
9565 different name is used to allow you to distinguish the two if you wish.
9567 @item void putDebugChar(int)
9568 @kindex putDebugChar
9569 Write this subroutine to write a single character to the serial port.
9570 It may be identical to @code{putchar} for your target system; a
9571 different name is used to allow you to distinguish the two if you wish.
9574 @cindex control C, and remote debugging
9575 @cindex interrupting remote targets
9576 If you want @value{GDBN} to be able to stop your program while it is
9577 running, you need to use an interrupt-driven serial driver, and arrange
9578 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
9579 character). That is the character which @value{GDBN} uses to tell the
9580 remote system to stop.
9582 Getting the debugging target to return the proper status to @value{GDBN}
9583 probably requires changes to the standard stub; one quick and dirty way
9584 is to just execute a breakpoint instruction (the ``dirty'' part is that
9585 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
9587 Other routines you need to supply are:
9590 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
9591 @kindex exceptionHandler
9592 Write this function to install @var{exception_address} in the exception
9593 handling tables. You need to do this because the stub does not have any
9594 way of knowing what the exception handling tables on your target system
9595 are like (for example, the processor's table might be in @sc{rom},
9596 containing entries which point to a table in @sc{ram}).
9597 @var{exception_number} is the exception number which should be changed;
9598 its meaning is architecture-dependent (for example, different numbers
9599 might represent divide by zero, misaligned access, etc). When this
9600 exception occurs, control should be transferred directly to
9601 @var{exception_address}, and the processor state (stack, registers,
9602 and so on) should be just as it is when a processor exception occurs. So if
9603 you want to use a jump instruction to reach @var{exception_address}, it
9604 should be a simple jump, not a jump to subroutine.
9606 For the 386, @var{exception_address} should be installed as an interrupt
9607 gate so that interrupts are masked while the handler runs. The gate
9608 should be at privilege level 0 (the most privileged level). The
9609 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
9610 help from @code{exceptionHandler}.
9612 @item void flush_i_cache()
9613 @kindex flush_i_cache
9614 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
9615 instruction cache, if any, on your target machine. If there is no
9616 instruction cache, this subroutine may be a no-op.
9618 On target machines that have instruction caches, @value{GDBN} requires this
9619 function to make certain that the state of your program is stable.
9623 You must also make sure this library routine is available:
9626 @item void *memset(void *, int, int)
9628 This is the standard library function @code{memset} that sets an area of
9629 memory to a known value. If you have one of the free versions of
9630 @code{libc.a}, @code{memset} can be found there; otherwise, you must
9631 either obtain it from your hardware manufacturer, or write your own.
9634 If you do not use the GNU C compiler, you may need other standard
9635 library subroutines as well; this varies from one stub to another,
9636 but in general the stubs are likely to use any of the common library
9637 subroutines which @code{@value{GCC}} generates as inline code.
9641 @subsubsection Putting it all together
9643 @cindex remote serial debugging summary
9644 In summary, when your program is ready to debug, you must follow these
9649 Make sure you have defined the supporting low-level routines
9650 (@pxref{Bootstrapping,,What you must do for the stub}):
9652 @code{getDebugChar}, @code{putDebugChar},
9653 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
9657 Insert these lines near the top of your program:
9665 For the 680x0 stub only, you need to provide a variable called
9666 @code{exceptionHook}. Normally you just use:
9669 void (*exceptionHook)() = 0;
9673 but if before calling @code{set_debug_traps}, you set it to point to a
9674 function in your program, that function is called when
9675 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
9676 error). The function indicated by @code{exceptionHook} is called with
9677 one parameter: an @code{int} which is the exception number.
9680 Compile and link together: your program, the @value{GDBN} debugging stub for
9681 your target architecture, and the supporting subroutines.
9684 Make sure you have a serial connection between your target machine and
9685 the @value{GDBN} host, and identify the serial port on the host.
9688 @c The "remote" target now provides a `load' command, so we should
9689 @c document that. FIXME.
9690 Download your program to your target machine (or get it there by
9691 whatever means the manufacturer provides), and start it.
9694 To start remote debugging, run @value{GDBN} on the host machine, and specify
9695 as an executable file the program that is running in the remote machine.
9696 This tells @value{GDBN} how to find your program's symbols and the contents
9700 @cindex serial line, @code{target remote}
9701 Establish communication using the @code{target remote} command.
9702 Its argument specifies how to communicate with the target
9703 machine---either via a devicename attached to a direct serial line, or a
9704 TCP port (usually to a terminal server which in turn has a serial line
9705 to the target). For example, to use a serial line connected to the
9706 device named @file{/dev/ttyb}:
9709 target remote /dev/ttyb
9712 @cindex TCP port, @code{target remote}
9713 To use a TCP connection, use an argument of the form
9714 @code{@var{host}:port}. For example, to connect to port 2828 on a
9715 terminal server named @code{manyfarms}:
9718 target remote manyfarms:2828
9721 If your remote target is actually running on the same machine as
9722 your debugger session (e.g.@: a simulator of your target running on
9723 the same host), you can omit the hostname. For example, to connect
9724 to port 1234 on your local machine:
9731 Note that the colon is still required here.
9734 Now you can use all the usual commands to examine and change data and to
9735 step and continue the remote program.
9737 To resume the remote program and stop debugging it, use the @code{detach}
9740 @cindex interrupting remote programs
9741 @cindex remote programs, interrupting
9742 Whenever @value{GDBN} is waiting for the remote program, if you type the
9743 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
9744 program. This may or may not succeed, depending in part on the hardware
9745 and the serial drivers the remote system uses. If you type the
9746 interrupt character once again, @value{GDBN} displays this prompt:
9749 Interrupted while waiting for the program.
9750 Give up (and stop debugging it)? (y or n)
9753 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
9754 (If you decide you want to try again later, you can use @samp{target
9755 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
9756 goes back to waiting.
9759 @subsubsection Communication protocol
9761 @cindex debugging stub, example
9762 @cindex remote stub, example
9763 @cindex stub example, remote debugging
9764 The stub files provided with @value{GDBN} implement the target side of the
9765 communication protocol, and the @value{GDBN} side is implemented in the
9766 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
9767 these subroutines to communicate, and ignore the details. (If you're
9768 implementing your own stub file, you can still ignore the details: start
9769 with one of the existing stub files. @file{sparc-stub.c} is the best
9770 organized, and therefore the easiest to read.)
9772 However, there may be occasions when you need to know something about
9773 the protocol---for example, if there is only one serial port to your
9774 target machine, you might want your program to do something special if
9775 it recognizes a packet meant for @value{GDBN}.
9777 In the examples below, @samp{<-} and @samp{->} are used to indicate
9778 transmitted and received data respectfully.
9780 @cindex protocol, @value{GDBN} remote serial
9781 @cindex serial protocol, @value{GDBN} remote
9782 @cindex remote serial protocol
9783 All @value{GDBN} commands and responses (other than acknowledgments) are
9784 sent as a @var{packet}. A @var{packet} is introduced with the character
9785 @samp{$}, the actual @var{packet-data}, and the terminating character
9786 @samp{#} followed by a two-digit @var{checksum}:
9789 @code{$}@var{packet-data}@code{#}@var{checksum}
9793 @cindex checksum, for @value{GDBN} remote
9795 The two-digit @var{checksum} is computed as the modulo 256 sum of all
9796 characters between the leading @samp{$} and the trailing @samp{#} (an
9797 eight bit unsigned checksum).
9799 Implementors should note that prior to @value{GDBN} 5.0 the protocol
9800 specification also included an optional two-digit @var{sequence-id}:
9803 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
9806 @cindex sequence-id, for @value{GDBN} remote
9808 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
9809 has never output @var{sequence-id}s. Stubs that handle packets added
9810 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
9812 @cindex acknowledgment, for @value{GDBN} remote
9813 When either the host or the target machine receives a packet, the first
9814 response expected is an acknowledgment: either @samp{+} (to indicate
9815 the package was received correctly) or @samp{-} (to request
9819 <- @code{$}@var{packet-data}@code{#}@var{checksum}
9824 The host (@value{GDBN}) sends @var{command}s, and the target (the
9825 debugging stub incorporated in your program) sends a @var{response}. In
9826 the case of step and continue @var{command}s, the response is only sent
9827 when the operation has completed (the target has again stopped).
9829 @var{packet-data} consists of a sequence of characters with the
9830 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
9833 Fields within the packet should be separated using @samp{,} @samp{;} or
9834 @samp{:}. Except where otherwise noted all numbers are represented in
9835 HEX with leading zeros suppressed.
9837 Implementors should note that prior to @value{GDBN} 5.0, the character
9838 @samp{:} could not appear as the third character in a packet (as it
9839 would potentially conflict with the @var{sequence-id}).
9841 Response @var{data} can be run-length encoded to save space. A @samp{*}
9842 means that the next character is an @sc{ascii} encoding giving a repeat count
9843 which stands for that many repetitions of the character preceding the
9844 @samp{*}. The encoding is @code{n+29}, yielding a printable character
9845 where @code{n >=3} (which is where rle starts to win). The printable
9846 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
9847 value greater than 126 should not be used.
9849 Some remote systems have used a different run-length encoding mechanism
9850 loosely refered to as the cisco encoding. Following the @samp{*}
9851 character are two hex digits that indicate the size of the packet.
9858 means the same as "0000".
9860 The error response returned for some packets includes a two character
9861 error number. That number is not well defined.
9863 For any @var{command} not supported by the stub, an empty response
9864 (@samp{$#00}) should be returned. That way it is possible to extend the
9865 protocol. A newer @value{GDBN} can tell if a packet is supported based
9868 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
9869 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
9872 Below is a complete list of all currently defined @var{command}s and
9873 their corresponding response @var{data}:
9875 @multitable @columnfractions .30 .30 .40
9883 Enable extended mode. In extended mode, the remote server is made
9884 persistent. The @samp{R} packet is used to restart the program being
9887 @tab reply @samp{OK}
9889 The remote target both supports and has enabled extended mode.
9894 Indicate the reason the target halted. The reply is the same as for step
9903 @tab Reserved for future use
9905 @item set program arguments @strong{(reserved)}
9906 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
9911 Initialized @samp{argv[]} array passed into program. @var{arglen}
9912 specifies the number of bytes in the hex encoded byte stream @var{arg}.
9913 See @file{gdbserver} for more details.
9915 @tab reply @code{OK}
9917 @tab reply @code{E}@var{NN}
9919 @item set baud @strong{(deprecated)}
9920 @tab @code{b}@var{baud}
9922 Change the serial line speed to @var{baud}. JTC: @emph{When does the
9923 transport layer state change? When it's received, or after the ACK is
9924 transmitted. In either case, there are problems if the command or the
9925 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
9926 to add something like this, and get it working for the first time, they
9927 ought to modify ser-unix.c to send some kind of out-of-band message to a
9928 specially-setup stub and have the switch happen "in between" packets, so
9929 that from remote protocol's point of view, nothing actually
9932 @item set breakpoint @strong{(deprecated)}
9933 @tab @code{B}@var{addr},@var{mode}
9935 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
9936 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
9940 @tab @code{c}@var{addr}
9942 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9948 @item continue with signal
9949 @tab @code{C}@var{sig}@code{;}@var{addr}
9951 Continue with signal @var{sig} (hex signal number). If
9952 @code{;}@var{addr} is omitted, resume at same address.
9957 @item toggle debug @strong{(deprecated)}
9965 Detach @value{GDBN} from the remote system. Sent to the remote target before
9966 @value{GDBN} disconnects.
9968 @tab reply @emph{no response}
9970 @value{GDBN} does not check for any response after sending this packet.
9974 @tab Reserved for future use
9978 @tab Reserved for future use
9982 @tab Reserved for future use
9986 @tab Reserved for future use
9988 @item read registers
9990 @tab Read general registers.
9992 @tab reply @var{XX...}
9994 Each byte of register data is described by two hex digits. The bytes
9995 with the register are transmitted in target byte order. The size of
9996 each register and their position within the @samp{g} @var{packet} are
9997 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
9998 @var{REGISTER_NAME} macros. The specification of several standard
9999 @code{g} packets is specified below.
10001 @tab @code{E}@var{NN}
10005 @tab @code{G}@var{XX...}
10007 See @samp{g} for a description of the @var{XX...} data.
10009 @tab reply @code{OK}
10012 @tab reply @code{E}@var{NN}
10017 @tab Reserved for future use
10020 @tab @code{H}@var{c}@var{t...}
10022 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
10023 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
10024 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
10025 thread used in other operations. If zero, pick a thread, any thread.
10027 @tab reply @code{OK}
10030 @tab reply @code{E}@var{NN}
10034 @c 'H': How restrictive (or permissive) is the thread model. If a
10035 @c thread is selected and stopped, are other threads allowed
10036 @c to continue to execute? As I mentioned above, I think the
10037 @c semantics of each command when a thread is selected must be
10038 @c described. For example:
10040 @c 'g': If the stub supports threads and a specific thread is
10041 @c selected, returns the register block from that thread;
10042 @c otherwise returns current registers.
10044 @c 'G' If the stub supports threads and a specific thread is
10045 @c selected, sets the registers of the register block of
10046 @c that thread; otherwise sets current registers.
10048 @item cycle step @strong{(draft)}
10049 @tab @code{i}@var{addr}@code{,}@var{nnn}
10051 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
10052 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
10053 step starting at that address.
10055 @item signal then cycle step @strong{(reserved)}
10058 See @samp{i} and @samp{S} for likely syntax and semantics.
10062 @tab Reserved for future use
10066 @tab Reserved for future use
10071 FIXME: @emph{There is no description of how operate when a specific
10072 thread context has been selected (ie. does 'k' kill only that thread?)}.
10076 @tab Reserved for future use
10080 @tab Reserved for future use
10083 @tab @code{m}@var{addr}@code{,}@var{length}
10085 Read @var{length} bytes of memory starting at address @var{addr}.
10086 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
10087 using word alligned accesses. FIXME: @emph{A word aligned memory
10088 transfer mechanism is needed.}
10090 @tab reply @var{XX...}
10092 @var{XX...} is mem contents. Can be fewer bytes than requested if able
10093 to read only part of the data. Neither @value{GDBN} nor the stub assume that
10094 sized memory transfers are assumed using word alligned accesses. FIXME:
10095 @emph{A word aligned memory transfer mechanism is needed.}
10097 @tab reply @code{E}@var{NN}
10098 @tab @var{NN} is errno
10101 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
10103 Write @var{length} bytes of memory starting at address @var{addr}.
10104 @var{XX...} is the data.
10106 @tab reply @code{OK}
10109 @tab reply @code{E}@var{NN}
10111 for an error (this includes the case where only part of the data was
10116 @tab Reserved for future use
10120 @tab Reserved for future use
10124 @tab Reserved for future use
10128 @tab Reserved for future use
10130 @item read reg @strong{(reserved)}
10131 @tab @code{p}@var{n...}
10133 See write register.
10135 @tab return @var{r....}
10136 @tab The hex encoded value of the register in target byte order.
10139 @tab @code{P}@var{n...}@code{=}@var{r...}
10141 Write register @var{n...} with value @var{r...}, which contains two hex
10142 digits for each byte in the register (target byte order).
10144 @tab reply @code{OK}
10147 @tab reply @code{E}@var{NN}
10150 @item general query
10151 @tab @code{q}@var{query}
10153 Request info about @var{query}. In general @value{GDBN} queries
10154 have a leading upper case letter. Custom vendor queries should use a
10155 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
10156 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
10157 must ensure that they match the full @var{query} name.
10159 @tab reply @code{XX...}
10160 @tab Hex encoded data from query. The reply can not be empty.
10162 @tab reply @code{E}@var{NN}
10166 @tab Indicating an unrecognized @var{query}.
10169 @tab @code{Q}@var{var}@code{=}@var{val}
10171 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
10172 naming conventions.
10174 @item reset @strong{(deprecated)}
10177 Reset the entire system.
10179 @item remote restart
10180 @tab @code{R}@var{XX}
10182 Restart the program being debugged. @var{XX}, while needed, is ignored.
10183 This packet is only available in extended mode.
10188 The @samp{R} packet has no reply.
10191 @tab @code{s}@var{addr}
10193 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10199 @item step with signal
10200 @tab @code{S}@var{sig}@code{;}@var{addr}
10202 Like @samp{C} but step not continue.
10208 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
10210 Search backwards starting at address @var{addr} for a match with pattern
10211 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
10212 bytes. @var{addr} must be at least 3 digits.
10215 @tab @code{T}@var{XX}
10216 @tab Find out if the thread XX is alive.
10218 @tab reply @code{OK}
10219 @tab thread is still alive
10221 @tab reply @code{E}@var{NN}
10222 @tab thread is dead
10226 @tab Reserved for future use
10230 @tab Reserved for future use
10234 @tab Reserved for future use
10238 @tab Reserved for future use
10242 @tab Reserved for future use
10246 @tab Reserved for future use
10250 @tab Reserved for future use
10252 @item write mem (binary)
10253 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
10255 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
10256 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
10257 escaped using @code{0x7d}.
10259 @tab reply @code{OK}
10262 @tab reply @code{E}@var{NN}
10267 @tab Reserved for future use
10271 @tab Reserved for future use
10273 @item remove break or watchpoint @strong{(draft)}
10274 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10278 @item insert break or watchpoint @strong{(draft)}
10279 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10281 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
10282 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
10283 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
10284 bytes. For a software breakpoint, @var{length} specifies the size of
10285 the instruction to be patched. For hardware breakpoints and watchpoints
10286 @var{length} specifies the memory region to be monitored. To avoid
10287 potential problems with duplicate packets, the operations should be
10288 implemented in an idempotent way.
10290 @tab reply @code{E}@var{NN}
10293 @tab reply @code{OK}
10297 @tab If not supported.
10301 @tab Reserved for future use
10305 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
10306 receive any of the below as a reply. In the case of the @samp{C},
10307 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
10308 when the target halts. In the below the exact meaning of @samp{signal
10309 number} is poorly defined. In general one of the UNIX signal numbering
10310 conventions is used.
10312 @multitable @columnfractions .4 .6
10314 @item @code{S}@var{AA}
10315 @tab @var{AA} is the signal number
10317 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
10319 @var{AA} = two hex digit signal number; @var{n...} = register number
10320 (hex), @var{r...} = target byte ordered register contents, size defined
10321 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
10322 thread process ID, this is a hex integer; @var{n...} = other string not
10323 starting with valid hex digit. @value{GDBN} should ignore this
10324 @var{n...}, @var{r...} pair and go on to the next. This way we can
10325 extend the protocol.
10327 @item @code{W}@var{AA}
10329 The process exited, and @var{AA} is the exit status. This is only
10330 applicable for certains sorts of targets.
10332 @item @code{X}@var{AA}
10334 The process terminated with signal @var{AA}.
10336 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
10338 @var{AA} = signal number; @var{t...} = address of symbol "_start";
10339 @var{d...} = base of data section; @var{b...} = base of bss section.
10340 @emph{Note: only used by Cisco Systems targets. The difference between
10341 this reply and the "qOffsets" query is that the 'N' packet may arrive
10342 spontaneously whereas the 'qOffsets' is a query initiated by the host
10345 @item @code{O}@var{XX...}
10347 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
10348 while the program is running and the debugger should continue to wait
10353 The following set and query packets have already been defined.
10355 @multitable @columnfractions .2 .2 .6
10357 @item current thread
10358 @tab @code{q}@code{C}
10359 @tab Return the current thread id.
10361 @tab reply @code{QC}@var{pid}
10363 Where @var{pid} is a HEX encoded 16 bit process id.
10366 @tab Any other reply implies the old pid.
10368 @item all thread ids
10369 @tab @code{q}@code{fThreadInfo}
10371 @tab @code{q}@code{sThreadInfo}
10373 Obtain a list of active thread ids from the target (OS). Since there
10374 may be too many active threads to fit into one reply packet, this query
10375 works iteratively: it may require more than one query/reply sequence to
10376 obtain the entire list of threads. The first query of the sequence will
10377 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
10378 sequence will be the @code{qs}@code{ThreadInfo} query.
10381 @tab NOTE: replaces the @code{qL} query (see below).
10383 @tab reply @code{m}@var{<id>}
10384 @tab A single thread id
10386 @tab reply @code{m}@var{<id>},@var{<id>...}
10387 @tab a comma-separated list of thread ids
10389 @tab reply @code{l}
10390 @tab (lower case 'el') denotes end of list.
10394 In response to each query, the target will reply with a list of one
10395 or more thread ids, in big-endian hex, separated by commas. GDB will
10396 respond to each reply with a request for more thread ids (using the
10397 @code{qs} form of the query), until the target responds with @code{l}
10398 (lower-case el, for @code{'last'}).
10400 @item extra thread info
10401 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
10406 Where @var{<id>} is a thread-id in big-endian hex.
10407 Obtain a printable string description of a thread's attributes from
10408 the target OS. This string may contain anything that the target OS
10409 thinks is interesting for @value{GDBN} to tell the user about the thread.
10410 The string is displayed in @value{GDBN}'s @samp{info threads} display.
10411 Some examples of possible thread extra info strings are "Runnable", or
10412 "Blocked on Mutex".
10414 @tab reply @var{XX...}
10416 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
10417 printable string containing the extra information about the thread's
10420 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
10421 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
10426 Obtain thread information from RTOS. Where: @var{startflag} (one hex
10427 digit) is one to indicate the first query and zero to indicate a
10428 subsequent query; @var{threadcount} (two hex digits) is the maximum
10429 number of threads the response packet can contain; and @var{nextthread}
10430 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
10431 returned in the response as @var{argthread}.
10434 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
10437 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
10442 Where: @var{count} (two hex digits) is the number of threads being
10443 returned; @var{done} (one hex digit) is zero to indicate more threads
10444 and one indicates no further threads; @var{argthreadid} (eight hex
10445 digits) is @var{nextthread} from the request packet; @var{thread...} is
10446 a sequence of thread IDs from the target. @var{threadid} (eight hex
10447 digits). See @code{remote.c:parse_threadlist_response()}.
10449 @item compute CRC of memory block
10450 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
10453 @tab reply @code{E}@var{NN}
10454 @tab An error (such as memory fault)
10456 @tab reply @code{C}@var{CRC32}
10457 @tab A 32 bit cyclic redundancy check of the specified memory region.
10459 @item query sect offs
10460 @tab @code{q}@code{Offsets}
10462 Get section offsets that the target used when re-locating the downloaded
10463 image. @emph{Note: while a @code{Bss} offset is included in the
10464 response, @value{GDBN} ignores this and instead applies the @code{Data}
10465 offset to the @code{Bss} section.}
10467 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
10469 @item thread info request
10470 @tab @code{q}@code{P}@var{mode}@var{threadid}
10475 Returns information on @var{threadid}. Where: @var{mode} is a hex
10476 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
10480 See @code{remote.c:remote_unpack_thread_info_response()}.
10482 @item remote command
10483 @tab @code{q}@code{Rcmd,}@var{COMMAND}
10488 @var{COMMAND} (hex encoded) is passed to the local interpreter for
10489 execution. Invalid commands should be reported using the output string.
10490 Before the final result packet, the target may also respond with a
10491 number of intermediate @code{O}@var{OUTPUT} console output
10492 packets. @emph{Implementors should note that providing access to a
10493 stubs's interpreter may have security implications}.
10495 @tab reply @code{OK}
10497 A command response with no output.
10499 @tab reply @var{OUTPUT}
10501 A command response with the hex encoded output string @var{OUTPUT}.
10503 @tab reply @code{E}@var{NN}
10505 Indicate a badly formed request.
10510 When @samp{q}@samp{Rcmd} is not recognized.
10512 @item symbol lookup
10513 @tab @code{qSymbol::}
10515 Notify the target that @value{GDBN} is prepared to serve symbol lookup
10516 requests. Accept requests from the target for the values of symbols.
10521 @tab reply @code{OK}
10523 The target does not need to look up any (more) symbols.
10525 @tab reply @code{qSymbol:}@var{sym_name}
10527 The target requests the value of symbol @var{sym_name} (hex encoded).
10528 @value{GDBN} may provide the value by using the
10529 @code{qSymbol:}@var{sym_value}:@var{sym_name}
10530 message, described below.
10533 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
10535 Set the value of SYM_NAME to SYM_VALUE.
10539 @var{sym_name} (hex encoded) is the name of a symbol whose value
10540 the target has previously requested.
10544 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
10545 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
10546 field will be empty.
10548 @tab reply @code{OK}
10550 The target does not need to look up any (more) symbols.
10552 @tab reply @code{qSymbol:}@var{sym_name}
10554 The target requests the value of a new symbol @var{sym_name} (hex encoded).
10555 @value{GDBN} will continue to supply the values of symbols (if available),
10556 until the target ceases to request them.
10560 The following @samp{g}/@samp{G} packets have previously been defined.
10561 In the below, some thirty-two bit registers are transferred as sixty-four
10562 bits. Those registers should be zero/sign extended (which?) to fill the
10563 space allocated. Register bytes are transfered in target byte order.
10564 The two nibbles within a register byte are transfered most-significant -
10567 @multitable @columnfractions .5 .5
10571 All registers are transfered as thirty-two bit quantities in the order:
10572 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
10573 registers; fsr; fir; fp.
10577 All registers are transfered as sixty-four bit quantities (including
10578 thirty-two bit registers such as @code{sr}). The ordering is the same
10583 Example sequence of a target being re-started. Notice how the restart
10584 does not get any direct output:
10589 @emph{target restarts}
10592 -> @code{T001:1234123412341234}
10596 Example sequence of a target being stepped by a single instruction:
10604 -> @code{T001:1234123412341234}
10613 @subsubsection Using the @code{gdbserver} program
10616 @cindex remote connection without stubs
10617 @code{gdbserver} is a control program for Unix-like systems, which
10618 allows you to connect your program with a remote @value{GDBN} via
10619 @code{target remote}---but without linking in the usual debugging stub.
10621 @code{gdbserver} is not a complete replacement for the debugging stubs,
10622 because it requires essentially the same operating-system facilities
10623 that @value{GDBN} itself does. In fact, a system that can run
10624 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10625 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10626 because it is a much smaller program than @value{GDBN} itself. It is
10627 also easier to port than all of @value{GDBN}, so you may be able to get
10628 started more quickly on a new system by using @code{gdbserver}.
10629 Finally, if you develop code for real-time systems, you may find that
10630 the tradeoffs involved in real-time operation make it more convenient to
10631 do as much development work as possible on another system, for example
10632 by cross-compiling. You can use @code{gdbserver} to make a similar
10633 choice for debugging.
10635 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10636 or a TCP connection, using the standard @value{GDBN} remote serial
10640 @item On the target machine,
10641 you need to have a copy of the program you want to debug.
10642 @code{gdbserver} does not need your program's symbol table, so you can
10643 strip the program if necessary to save space. @value{GDBN} on the host
10644 system does all the symbol handling.
10646 To use the server, you must tell it how to communicate with @value{GDBN};
10647 the name of your program; and the arguments for your program. The
10651 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10654 @var{comm} is either a device name (to use a serial line) or a TCP
10655 hostname and portnumber. For example, to debug Emacs with the argument
10656 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10660 target> gdbserver /dev/com1 emacs foo.txt
10663 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10666 To use a TCP connection instead of a serial line:
10669 target> gdbserver host:2345 emacs foo.txt
10672 The only difference from the previous example is the first argument,
10673 specifying that you are communicating with the host @value{GDBN} via
10674 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10675 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10676 (Currently, the @samp{host} part is ignored.) You can choose any number
10677 you want for the port number as long as it does not conflict with any
10678 TCP ports already in use on the target system (for example, @code{23} is
10679 reserved for @code{telnet}).@footnote{If you choose a port number that
10680 conflicts with another service, @code{gdbserver} prints an error message
10681 and exits.} You must use the same port number with the host @value{GDBN}
10682 @code{target remote} command.
10684 @item On the @value{GDBN} host machine,
10685 you need an unstripped copy of your program, since @value{GDBN} needs
10686 symbols and debugging information. Start up @value{GDBN} as usual,
10687 using the name of the local copy of your program as the first argument.
10688 (You may also need the @w{@samp{--baud}} option if the serial line is
10689 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10690 remote} to establish communications with @code{gdbserver}. Its argument
10691 is either a device name (usually a serial device, like
10692 @file{/dev/ttyb}), or a TCP port descriptor in the form
10693 @code{@var{host}:@var{PORT}}. For example:
10696 (@value{GDBP}) target remote /dev/ttyb
10700 communicates with the server via serial line @file{/dev/ttyb}, and
10703 (@value{GDBP}) target remote the-target:2345
10707 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10708 For TCP connections, you must start up @code{gdbserver} prior to using
10709 the @code{target remote} command. Otherwise you may get an error whose
10710 text depends on the host system, but which usually looks something like
10711 @samp{Connection refused}.
10715 @subsubsection Using the @code{gdbserve.nlm} program
10717 @kindex gdbserve.nlm
10718 @code{gdbserve.nlm} is a control program for NetWare systems, which
10719 allows you to connect your program with a remote @value{GDBN} via
10720 @code{target remote}.
10722 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10723 using the standard @value{GDBN} remote serial protocol.
10726 @item On the target machine,
10727 you need to have a copy of the program you want to debug.
10728 @code{gdbserve.nlm} does not need your program's symbol table, so you
10729 can strip the program if necessary to save space. @value{GDBN} on the
10730 host system does all the symbol handling.
10732 To use the server, you must tell it how to communicate with
10733 @value{GDBN}; the name of your program; and the arguments for your
10734 program. The syntax is:
10737 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10738 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10741 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10742 the baud rate used by the connection. @var{port} and @var{node} default
10743 to 0, @var{baud} defaults to 9600@dmn{bps}.
10745 For example, to debug Emacs with the argument @samp{foo.txt}and
10746 communicate with @value{GDBN} over serial port number 2 or board 1
10747 using a 19200@dmn{bps} connection:
10750 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10753 @item On the @value{GDBN} host machine,
10754 you need an unstripped copy of your program, since @value{GDBN} needs
10755 symbols and debugging information. Start up @value{GDBN} as usual,
10756 using the name of the local copy of your program as the first argument.
10757 (You may also need the @w{@samp{--baud}} option if the serial line is
10758 running at anything other than 9600@dmn{bps}. After that, use @code{target
10759 remote} to establish communications with @code{gdbserve.nlm}. Its
10760 argument is a device name (usually a serial device, like
10761 @file{/dev/ttyb}). For example:
10764 (@value{GDBP}) target remote /dev/ttyb
10768 communications with the server via serial line @file{/dev/ttyb}.
10772 @section Kernel Object Display
10774 @cindex kernel object display
10775 @cindex kernel object
10778 Some targets support kernel object display. Using this facility,
10779 @value{GDBN} communicates specially with the underlying operating system
10780 and can display information about operating system-level objects such as
10781 mutexes and other synchronization objects. Exactly which objects can be
10782 displayed is determined on a per-OS basis.
10784 Use the @code{set os} command to set the operating system. This tells
10785 @value{GDBN} which kernel object display module to initialize:
10788 (@value{GDBP}) set os cisco
10791 If @code{set os} succeeds, @value{GDBN} will display some information
10792 about the operating system, and will create a new @code{info} command
10793 which can be used to query the target. The @code{info} command is named
10794 after the operating system:
10797 (@value{GDBP}) info cisco
10798 List of Cisco Kernel Objects
10800 any Any and all objects
10803 Further subcommands can be used to query about particular objects known
10806 There is currently no way to determine whether a given operating system
10807 is supported other than to try it.
10810 @node Configurations
10811 @chapter Configuration-Specific Information
10813 While nearly all @value{GDBN} commands are available for all native and
10814 cross versions of the debugger, there are some exceptions. This chapter
10815 describes things that are only available in certain configurations.
10817 There are three major categories of configurations: native
10818 configurations, where the host and target are the same, embedded
10819 operating system configurations, which are usually the same for several
10820 different processor architectures, and bare embedded processors, which
10821 are quite different from each other.
10826 * Embedded Processors::
10833 This section describes details specific to particular native
10838 * SVR4 Process Information:: SVR4 process information
10839 * DJGPP Native:: Features specific to the DJGPP port
10845 On HP-UX systems, if you refer to a function or variable name that
10846 begins with a dollar sign, @value{GDBN} searches for a user or system
10847 name first, before it searches for a convenience variable.
10849 @node SVR4 Process Information
10850 @subsection SVR4 process information
10853 @cindex process image
10855 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10856 used to examine the image of a running process using file-system
10857 subroutines. If @value{GDBN} is configured for an operating system with
10858 this facility, the command @code{info proc} is available to report on
10859 several kinds of information about the process running your program.
10860 @code{info proc} works only on SVR4 systems that include the
10861 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10862 and Unixware, but not HP-UX or Linux, for example.
10867 Summarize available information about the process.
10869 @kindex info proc mappings
10870 @item info proc mappings
10871 Report on the address ranges accessible in the program, with information
10872 on whether your program may read, write, or execute each range.
10874 @kindex info proc times
10875 @item info proc times
10876 Starting time, user CPU time, and system CPU time for your program and
10879 @kindex info proc id
10881 Report on the process IDs related to your program: its own process ID,
10882 the ID of its parent, the process group ID, and the session ID.
10884 @kindex info proc status
10885 @item info proc status
10886 General information on the state of the process. If the process is
10887 stopped, this report includes the reason for stopping, and any signal
10890 @item info proc all
10891 Show all the above information about the process.
10895 @subsection Features for Debugging @sc{djgpp} Programs
10896 @cindex @sc{djgpp} debugging
10897 @cindex native @sc{djgpp} debugging
10898 @cindex MS-DOS-specific commands
10900 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10901 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10902 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10903 top of real-mode DOS systems and their emulations.
10905 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10906 defines a few commands specific to the @sc{djgpp} port. This
10907 subsection describes those commands.
10912 This is a prefix of @sc{djgpp}-specific commands which print
10913 information about the target system and important OS structures.
10916 @cindex MS-DOS system info
10917 @cindex free memory information (MS-DOS)
10918 @item info dos sysinfo
10919 This command displays assorted information about the underlying
10920 platform: the CPU type and features, the OS version and flavor, the
10921 DPMI version, and the available conventional and DPMI memory.
10926 @cindex segment descriptor tables
10927 @cindex descriptor tables display
10929 @itemx info dos ldt
10930 @itemx info dos idt
10931 These 3 commands display entries from, respectively, Global, Local,
10932 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10933 tables are data structures which store a descriptor for each segment
10934 that is currently in use. The segment's selector is an index into a
10935 descriptor table; the table entry for that index holds the
10936 descriptor's base address and limit, and its attributes and access
10939 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10940 segment (used for both data and the stack), and a DOS segment (which
10941 allows access to DOS/BIOS data structures and absolute addresses in
10942 conventional memory). However, the DPMI host will usually define
10943 additional segments in order to support the DPMI environment.
10945 @cindex garbled pointers
10946 These commands allow to display entries from the descriptor tables.
10947 Without an argument, all entries from the specified table are
10948 displayed. An argument, which should be an integer expression, means
10949 display a single entry whose index is given by the argument. For
10950 example, here's a convenient way to display information about the
10951 debugged program's data segment:
10954 (@value{GDBP}) info dos ldt $ds
10955 0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
10959 This comes in handy when you want to see whether a pointer is outside
10960 the data segment's limit (i.e.@: @dfn{garbled}).
10962 @cindex page tables display (MS-DOS)
10964 @itemx info dos pte
10965 These two commands display entries from, respectively, the Page
10966 Directory and the Page Tables. Page Directories and Page Tables are
10967 data structures which control how virtual memory addresses are mapped
10968 into physical addresses. A Page Table includes an entry for every
10969 page of memory that is mapped into the program's address space; there
10970 may be several Page Tables, each one holding up to 4096 entries. A
10971 Page Directory has up to 4096 entries, one each for every Page Table
10972 that is currently in use.
10974 Without an argument, @kbd{info dos pde} displays the entire Page
10975 Directory, and @kbd{info dos pte} displays all the entries in all of
10976 the Page Tables. An argument, an integer expression, given to the
10977 @kbd{info dos pde} command means display only that entry from the Page
10978 Directory table. An argument given to the @kbd{info dos pte} command
10979 means display entries from a single Page Table, the one pointed to by
10980 the specified entry in the Page Directory.
10982 These commands are useful when your program uses @dfn{DMA} (Direct
10983 Memory Access), which needs physical addresses to program the DMA
10986 These commands are supported only with some DPMI servers.
10988 @cindex physical address from linear address
10989 @item info dos address-pte
10990 This command displays the Page Table entry for a specified linear
10991 address. The argument linear address should already have the
10992 appropriate segment's base address added to it, because this command
10993 accepts addresses which may belong to @emph{any} segment. For
10994 example, here's how to display the Page Table entry for the page where
10995 the variable @code{i} is stored:
10998 (@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i
10999 Page Table entry for address 0x11a00d30:
11000 Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
11004 This says that @code{i} is stored at offset @code{0xd30} from the page
11005 whose physical base address is @code{0x02698000}, and prints all the
11006 attributes of that page.
11008 Note that you must cast the addresses of variables to a @code{char *},
11009 since otherwise the value of @code{__djgpp_base_address}, the base
11010 address of all variables and functions in a @sc{djgpp} program, will
11011 be added using the rules of C pointer arithmetics: if @code{i} is
11012 declared an @code{int}, @value{GDBN} will add 4 times the value of
11013 @code{__djgpp_base_address} to the address of @code{i}.
11015 Here's another example, it displays the Page Table entry for the
11019 (@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)
11020 Page Table entry for address 0x29110:
11021 Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
11025 (The @code{+ 3} offset is because the transfer buffer's address is the
11026 3rd member of the @code{_go32_info_block} structure.) The output of
11027 this command clearly shows that addresses in conventional memory are
11028 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11030 This command is supported only with some DPMI servers.
11034 @section Embedded Operating Systems
11036 This section describes configurations involving the debugging of
11037 embedded operating systems that are available for several different
11041 * VxWorks:: Using @value{GDBN} with VxWorks
11044 @value{GDBN} includes the ability to debug programs running on
11045 various real-time operating systems.
11048 @subsection Using @value{GDBN} with VxWorks
11054 @kindex target vxworks
11055 @item target vxworks @var{machinename}
11056 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11057 is the target system's machine name or IP address.
11061 On VxWorks, @code{load} links @var{filename} dynamically on the
11062 current target system as well as adding its symbols in @value{GDBN}.
11064 @value{GDBN} enables developers to spawn and debug tasks running on networked
11065 VxWorks targets from a Unix host. Already-running tasks spawned from
11066 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11067 both the Unix host and on the VxWorks target. The program
11068 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11069 installed with the name @code{vxgdb}, to distinguish it from a
11070 @value{GDBN} for debugging programs on the host itself.)
11073 @item VxWorks-timeout @var{args}
11074 @kindex vxworks-timeout
11075 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11076 This option is set by the user, and @var{args} represents the number of
11077 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11078 your VxWorks target is a slow software simulator or is on the far side
11079 of a thin network line.
11082 The following information on connecting to VxWorks was current when
11083 this manual was produced; newer releases of VxWorks may use revised
11086 @kindex INCLUDE_RDB
11087 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11088 to include the remote debugging interface routines in the VxWorks
11089 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11090 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11091 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11092 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11093 information on configuring and remaking VxWorks, see the manufacturer's
11095 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11097 Once you have included @file{rdb.a} in your VxWorks system image and set
11098 your Unix execution search path to find @value{GDBN}, you are ready to
11099 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11100 @code{vxgdb}, depending on your installation).
11102 @value{GDBN} comes up showing the prompt:
11109 * VxWorks Connection:: Connecting to VxWorks
11110 * VxWorks Download:: VxWorks download
11111 * VxWorks Attach:: Running tasks
11114 @node VxWorks Connection
11115 @subsubsection Connecting to VxWorks
11117 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11118 network. To connect to a target whose host name is ``@code{tt}'', type:
11121 (vxgdb) target vxworks tt
11125 @value{GDBN} displays messages like these:
11128 Attaching remote machine across net...
11133 @value{GDBN} then attempts to read the symbol tables of any object modules
11134 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11135 these files by searching the directories listed in the command search
11136 path (@pxref{Environment, ,Your program's environment}); if it fails
11137 to find an object file, it displays a message such as:
11140 prog.o: No such file or directory.
11143 When this happens, add the appropriate directory to the search path with
11144 the @value{GDBN} command @code{path}, and execute the @code{target}
11147 @node VxWorks Download
11148 @subsubsection VxWorks download
11150 @cindex download to VxWorks
11151 If you have connected to the VxWorks target and you want to debug an
11152 object that has not yet been loaded, you can use the @value{GDBN}
11153 @code{load} command to download a file from Unix to VxWorks
11154 incrementally. The object file given as an argument to the @code{load}
11155 command is actually opened twice: first by the VxWorks target in order
11156 to download the code, then by @value{GDBN} in order to read the symbol
11157 table. This can lead to problems if the current working directories on
11158 the two systems differ. If both systems have NFS mounted the same
11159 filesystems, you can avoid these problems by using absolute paths.
11160 Otherwise, it is simplest to set the working directory on both systems
11161 to the directory in which the object file resides, and then to reference
11162 the file by its name, without any path. For instance, a program
11163 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11164 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11165 program, type this on VxWorks:
11168 -> cd "@var{vxpath}/vw/demo/rdb"
11172 Then, in @value{GDBN}, type:
11175 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11176 (vxgdb) load prog.o
11179 @value{GDBN} displays a response similar to this:
11182 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11185 You can also use the @code{load} command to reload an object module
11186 after editing and recompiling the corresponding source file. Note that
11187 this makes @value{GDBN} delete all currently-defined breakpoints,
11188 auto-displays, and convenience variables, and to clear the value
11189 history. (This is necessary in order to preserve the integrity of
11190 debugger's data structures that reference the target system's symbol
11193 @node VxWorks Attach
11194 @subsubsection Running tasks
11196 @cindex running VxWorks tasks
11197 You can also attach to an existing task using the @code{attach} command as
11201 (vxgdb) attach @var{task}
11205 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11206 or suspended when you attach to it. Running tasks are suspended at
11207 the time of attachment.
11209 @node Embedded Processors
11210 @section Embedded Processors
11212 This section goes into details specific to particular embedded
11216 * A29K Embedded:: AMD A29K Embedded
11218 * H8/300:: Hitachi H8/300
11219 * H8/500:: Hitachi H8/500
11220 * i960:: Intel i960
11221 * M32R/D:: Mitsubishi M32R/D
11222 * M68K:: Motorola M68K
11223 * M88K:: Motorola M88K
11224 * MIPS Embedded:: MIPS Embedded
11225 * PA:: HP PA Embedded
11228 * Sparclet:: Tsqware Sparclet
11229 * Sparclite:: Fujitsu Sparclite
11230 * ST2000:: Tandem ST2000
11231 * Z8000:: Zilog Z8000
11234 @node A29K Embedded
11235 @subsection AMD A29K Embedded
11240 * Comms (EB29K):: Communications setup
11241 * gdb-EB29K:: EB29K cross-debugging
11242 * Remote Log:: Remote log
11247 @kindex target adapt
11248 @item target adapt @var{dev}
11249 Adapt monitor for A29K.
11251 @kindex target amd-eb
11252 @item target amd-eb @var{dev} @var{speed} @var{PROG}
11254 Remote PC-resident AMD EB29K board, attached over serial lines.
11255 @var{dev} is the serial device, as for @code{target remote};
11256 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
11257 name of the program to be debugged, as it appears to DOS on the PC.
11258 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
11263 @subsubsection A29K UDI
11266 @cindex AMD29K via UDI
11268 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
11269 protocol for debugging the a29k processor family. To use this
11270 configuration with AMD targets running the MiniMON monitor, you need the
11271 program @code{MONTIP}, available from AMD at no charge. You can also
11272 use @value{GDBN} with the UDI-conformant a29k simulator program
11273 @code{ISSTIP}, also available from AMD.
11276 @item target udi @var{keyword}
11278 Select the UDI interface to a remote a29k board or simulator, where
11279 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
11280 This file contains keyword entries which specify parameters used to
11281 connect to a29k targets. If the @file{udi_soc} file is not in your
11282 working directory, you must set the environment variable @samp{UDICONF}
11287 @subsubsection EBMON protocol for AMD29K
11289 @cindex EB29K board
11290 @cindex running 29K programs
11292 AMD distributes a 29K development board meant to fit in a PC, together
11293 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
11294 term, this development system is called the ``EB29K''. To use
11295 @value{GDBN} from a Unix system to run programs on the EB29K board, you
11296 must first connect a serial cable between the PC (which hosts the EB29K
11297 board) and a serial port on the Unix system. In the following, we
11298 assume you've hooked the cable between the PC's @file{COM1} port and
11299 @file{/dev/ttya} on the Unix system.
11301 @node Comms (EB29K)
11302 @subsubsection Communications setup
11304 The next step is to set up the PC's port, by doing something like this
11308 C:\> MODE com1:9600,n,8,1,none
11312 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
11313 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
11314 you must match the communications parameters when establishing the Unix
11315 end of the connection as well.
11316 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
11317 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
11319 @c It's optional, but it's unwise to omit it: who knows what is the
11320 @c default value set when the DOS machines boots? "No retry" means that
11321 @c the DOS serial device driver won't retry the operation if it fails;
11322 @c I understand that this is needed because the GDB serial protocol
11323 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
11325 To give control of the PC to the Unix side of the serial line, type
11326 the following at the DOS console:
11333 (Later, if you wish to return control to the DOS console, you can use
11334 the command @code{CTTY con}---but you must send it over the device that
11335 had control, in our example over the @file{COM1} serial line.)
11337 From the Unix host, use a communications program such as @code{tip} or
11338 @code{cu} to communicate with the PC; for example,
11341 cu -s 9600 -l /dev/ttya
11345 The @code{cu} options shown specify, respectively, the linespeed and the
11346 serial port to use. If you use @code{tip} instead, your command line
11347 may look something like the following:
11350 tip -9600 /dev/ttya
11354 Your system may require a different name where we show
11355 @file{/dev/ttya} as the argument to @code{tip}. The communications
11356 parameters, including which port to use, are associated with the
11357 @code{tip} argument in the ``remote'' descriptions file---normally the
11358 system table @file{/etc/remote}.
11359 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
11360 @c the DOS side's comms setup? cu can support -o (odd
11361 @c parity), -e (even parity)---apparently no settings for no parity or
11362 @c for character size. Taken from stty maybe...? John points out tip
11363 @c can set these as internal variables, eg ~s parity=none; man stty
11364 @c suggests that it *might* work to stty these options with stdin or
11365 @c stdout redirected... ---doc@cygnus.com, 25feb91
11367 @c There's nothing to be done for the "none" part of the DOS MODE
11368 @c command. The rest of the parameters should be matched by the
11369 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
11372 Using the @code{tip} or @code{cu} connection, change the DOS working
11373 directory to the directory containing a copy of your 29K program, then
11374 start the PC program @code{EBMON} (an EB29K control program supplied
11375 with your board by AMD). You should see an initial display from
11376 @code{EBMON} similar to the one that follows, ending with the
11377 @code{EBMON} prompt @samp{#}---
11382 G:\> CD \usr\joe\work29k
11384 G:\USR\JOE\WORK29K> EBMON
11385 Am29000 PC Coprocessor Board Monitor, version 3.0-18
11386 Copyright 1990 Advanced Micro Devices, Inc.
11387 Written by Gibbons and Associates, Inc.
11389 Enter '?' or 'H' for help
11391 PC Coprocessor Type = EB29K
11393 Memory Base = 0xd0000
11395 Data Memory Size = 2048KB
11396 Available I-RAM Range = 0x8000 to 0x1fffff
11397 Available D-RAM Range = 0x80002000 to 0x801fffff
11400 Register Stack Size = 0x800
11401 Memory Stack Size = 0x1800
11404 Am29027 Available = No
11405 Byte Write Available = Yes
11410 Then exit the @code{cu} or @code{tip} program (done in the example by
11411 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
11412 running, ready for @value{GDBN} to take over.
11414 For this example, we've assumed what is probably the most convenient
11415 way to make sure the same 29K program is on both the PC and the Unix
11416 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
11417 PC as a file system on the Unix host. If you do not have PC/NFS or
11418 something similar connecting the two systems, you must arrange some
11419 other way---perhaps floppy-disk transfer---of getting the 29K program
11420 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
11424 @subsubsection EB29K cross-debugging
11426 Finally, @code{cd} to the directory containing an image of your 29K
11427 program on the Unix system, and start @value{GDBN}---specifying as argument the
11428 name of your 29K program:
11431 cd /usr/joe/work29k
11436 Now you can use the @code{target} command:
11439 target amd-eb /dev/ttya 9600 MYFOO
11440 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
11441 @c emphasize that this is the name as seen by DOS (since I think DOS is
11442 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
11446 In this example, we've assumed your program is in a file called
11447 @file{myfoo}. Note that the filename given as the last argument to
11448 @code{target amd-eb} should be the name of the program as it appears to DOS.
11449 In our example this is simply @code{MYFOO}, but in general it can include
11450 a DOS path, and depending on your transfer mechanism may not resemble
11451 the name on the Unix side.
11453 At this point, you can set any breakpoints you wish; when you are ready
11454 to see your program run on the 29K board, use the @value{GDBN} command
11457 To stop debugging the remote program, use the @value{GDBN} @code{detach}
11460 To return control of the PC to its console, use @code{tip} or @code{cu}
11461 once again, after your @value{GDBN} session has concluded, to attach to
11462 @code{EBMON}. You can then type the command @code{q} to shut down
11463 @code{EBMON}, returning control to the DOS command-line interpreter.
11464 Type @kbd{CTTY con} to return command input to the main DOS console,
11465 and type @kbd{~.} to leave @code{tip} or @code{cu}.
11468 @subsubsection Remote log
11469 @cindex @file{eb.log}, a log file for EB29K
11470 @cindex log file for EB29K
11472 The @code{target amd-eb} command creates a file @file{eb.log} in the
11473 current working directory, to help debug problems with the connection.
11474 @file{eb.log} records all the output from @code{EBMON}, including echoes
11475 of the commands sent to it. Running @samp{tail -f} on this file in
11476 another window often helps to understand trouble with @code{EBMON}, or
11477 unexpected events on the PC side of the connection.
11485 @item target rdi @var{dev}
11486 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11487 use this target to communicate with both boards running the Angel
11488 monitor, or with the EmbeddedICE JTAG debug device.
11491 @item target rdp @var{dev}
11497 @subsection Hitachi H8/300
11501 @kindex target hms@r{, with H8/300}
11502 @item target hms @var{dev}
11503 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11504 Use special commands @code{device} and @code{speed} to control the serial
11505 line and the communications speed used.
11507 @kindex target e7000@r{, with H8/300}
11508 @item target e7000 @var{dev}
11509 E7000 emulator for Hitachi H8 and SH.
11511 @kindex target sh3@r{, with H8/300}
11512 @kindex target sh3e@r{, with H8/300}
11513 @item target sh3 @var{dev}
11514 @itemx target sh3e @var{dev}
11515 Hitachi SH-3 and SH-3E target systems.
11519 @cindex download to H8/300 or H8/500
11520 @cindex H8/300 or H8/500 download
11521 @cindex download to Hitachi SH
11522 @cindex Hitachi SH download
11523 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11524 board, the @code{load} command downloads your program to the Hitachi
11525 board and also opens it as the current executable target for
11526 @value{GDBN} on your host (like the @code{file} command).
11528 @value{GDBN} needs to know these things to talk to your
11529 Hitachi SH, H8/300, or H8/500:
11533 that you want to use @samp{target hms}, the remote debugging interface
11534 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11535 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11536 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11537 H8/300, or H8/500.)
11540 what serial device connects your host to your Hitachi board (the first
11541 serial device available on your host is the default).
11544 what speed to use over the serial device.
11548 * Hitachi Boards:: Connecting to Hitachi boards.
11549 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11550 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11553 @node Hitachi Boards
11554 @subsubsection Connecting to Hitachi boards
11556 @c only for Unix hosts
11558 @cindex serial device, Hitachi micros
11559 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11560 need to explicitly set the serial device. The default @var{port} is the
11561 first available port on your host. This is only necessary on Unix
11562 hosts, where it is typically something like @file{/dev/ttya}.
11565 @cindex serial line speed, Hitachi micros
11566 @code{@value{GDBN}} has another special command to set the communications
11567 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11568 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11569 the DOS @code{mode} command (for instance,
11570 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11572 The @samp{device} and @samp{speed} commands are available only when you
11573 use a Unix host to debug your Hitachi microprocessor programs. If you
11575 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11576 called @code{asynctsr} to communicate with the development board
11577 through a PC serial port. You must also use the DOS @code{mode} command
11578 to set up the serial port on the DOS side.
11580 The following sample session illustrates the steps needed to start a
11581 program under @value{GDBN} control on an H8/300. The example uses a
11582 sample H8/300 program called @file{t.x}. The procedure is the same for
11583 the Hitachi SH and the H8/500.
11585 First hook up your development board. In this example, we use a
11586 board attached to serial port @code{COM2}; if you use a different serial
11587 port, substitute its name in the argument of the @code{mode} command.
11588 When you call @code{asynctsr}, the auxiliary comms program used by the
11589 debugger, you give it just the numeric part of the serial port's name;
11590 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11594 C:\H8300\TEST> asynctsr 2
11595 C:\H8300\TEST> mode com2:9600,n,8,1,p
11597 Resident portion of MODE loaded
11599 COM2: 9600, n, 8, 1, p
11604 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11605 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11606 disable it, or even boot without it, to use @code{asynctsr} to control
11607 your development board.
11610 @kindex target hms@r{, and serial protocol}
11611 Now that serial communications are set up, and the development board is
11612 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11613 the name of your program as the argument. @code{@value{GDBN}} prompts
11614 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11615 commands to begin your debugging session: @samp{target hms} to specify
11616 cross-debugging to the Hitachi board, and the @code{load} command to
11617 download your program to the board. @code{load} displays the names of
11618 the program's sections, and a @samp{*} for each 2K of data downloaded.
11619 (If you want to refresh @value{GDBN} data on symbols or on the
11620 executable file without downloading, use the @value{GDBN} commands
11621 @code{file} or @code{symbol-file}. These commands, and @code{load}
11622 itself, are described in @ref{Files,,Commands to specify files}.)
11625 (eg-C:\H8300\TEST) @value{GDBP} t.x
11626 @value{GDBN} is free software and you are welcome to distribute copies
11627 of it under certain conditions; type "show copying" to see
11629 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11631 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11632 (@value{GDBP}) target hms
11633 Connected to remote H8/300 HMS system.
11634 (@value{GDBP}) load t.x
11635 .text : 0x8000 .. 0xabde ***********
11636 .data : 0xabde .. 0xad30 *
11637 .stack : 0xf000 .. 0xf014 *
11640 At this point, you're ready to run or debug your program. From here on,
11641 you can use all the usual @value{GDBN} commands. The @code{break} command
11642 sets breakpoints; the @code{run} command starts your program;
11643 @code{print} or @code{x} display data; the @code{continue} command
11644 resumes execution after stopping at a breakpoint. You can use the
11645 @code{help} command at any time to find out more about @value{GDBN} commands.
11647 Remember, however, that @emph{operating system} facilities aren't
11648 available on your development board; for example, if your program hangs,
11649 you can't send an interrupt---but you can press the @sc{reset} switch!
11651 Use the @sc{reset} button on the development board
11654 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11655 no way to pass an interrupt signal to the development board); and
11658 to return to the @value{GDBN} command prompt after your program finishes
11659 normally. The communications protocol provides no other way for @value{GDBN}
11660 to detect program completion.
11663 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11664 development board as a ``normal exit'' of your program.
11667 @subsubsection Using the E7000 in-circuit emulator
11669 @kindex target e7000@r{, with Hitachi ICE}
11670 You can use the E7000 in-circuit emulator to develop code for either the
11671 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11672 e7000} command to connect @value{GDBN} to your E7000:
11675 @item target e7000 @var{port} @var{speed}
11676 Use this form if your E7000 is connected to a serial port. The
11677 @var{port} argument identifies what serial port to use (for example,
11678 @samp{com2}). The third argument is the line speed in bits per second
11679 (for example, @samp{9600}).
11681 @item target e7000 @var{hostname}
11682 If your E7000 is installed as a host on a TCP/IP network, you can just
11683 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11686 @node Hitachi Special
11687 @subsubsection Special @value{GDBN} commands for Hitachi micros
11689 Some @value{GDBN} commands are available only for the H8/300:
11693 @kindex set machine
11694 @kindex show machine
11695 @item set machine h8300
11696 @itemx set machine h8300h
11697 Condition @value{GDBN} for one of the two variants of the H8/300
11698 architecture with @samp{set machine}. You can use @samp{show machine}
11699 to check which variant is currently in effect.
11708 @kindex set memory @var{mod}
11709 @cindex memory models, H8/500
11710 @item set memory @var{mod}
11712 Specify which H8/500 memory model (@var{mod}) you are using with
11713 @samp{set memory}; check which memory model is in effect with @samp{show
11714 memory}. The accepted values for @var{mod} are @code{small},
11715 @code{big}, @code{medium}, and @code{compact}.
11720 @subsection Intel i960
11724 @kindex target mon960
11725 @item target mon960 @var{dev}
11726 MON960 monitor for Intel i960.
11728 @kindex target nindy
11729 @item target nindy @var{devicename}
11730 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11731 the name of the serial device to use for the connection, e.g.
11738 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11739 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11740 tell @value{GDBN} how to connect to the 960 in several ways:
11744 Through command line options specifying serial port, version of the
11745 Nindy protocol, and communications speed;
11748 By responding to a prompt on startup;
11751 By using the @code{target} command at any point during your @value{GDBN}
11752 session. @xref{Target Commands, ,Commands for managing targets}.
11756 @cindex download to Nindy-960
11757 With the Nindy interface to an Intel 960 board, @code{load}
11758 downloads @var{filename} to the 960 as well as adding its symbols in
11762 * Nindy Startup:: Startup with Nindy
11763 * Nindy Options:: Options for Nindy
11764 * Nindy Reset:: Nindy reset command
11767 @node Nindy Startup
11768 @subsubsection Startup with Nindy
11770 If you simply start @code{@value{GDBP}} without using any command-line
11771 options, you are prompted for what serial port to use, @emph{before} you
11772 reach the ordinary @value{GDBN} prompt:
11775 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11779 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11780 identifies the serial port you want to use. You can, if you choose,
11781 simply start up with no Nindy connection by responding to the prompt
11782 with an empty line. If you do this and later wish to attach to Nindy,
11783 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11785 @node Nindy Options
11786 @subsubsection Options for Nindy
11788 These are the startup options for beginning your @value{GDBN} session with a
11789 Nindy-960 board attached:
11792 @item -r @var{port}
11793 Specify the serial port name of a serial interface to be used to connect
11794 to the target system. This option is only available when @value{GDBN} is
11795 configured for the Intel 960 target architecture. You may specify
11796 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11797 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11798 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11801 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11802 the ``old'' Nindy monitor protocol to connect to the target system.
11803 This option is only available when @value{GDBN} is configured for the Intel 960
11804 target architecture.
11807 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11808 connect to a target system that expects the newer protocol, the connection
11809 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11810 attempts to reconnect at several different line speeds. You can abort
11811 this process with an interrupt.
11815 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11816 system, in an attempt to reset it, before connecting to a Nindy target.
11819 @emph{Warning:} Many target systems do not have the hardware that this
11820 requires; it only works with a few boards.
11824 The standard @samp{-b} option controls the line speed used on the serial
11829 @subsubsection Nindy reset command
11834 For a Nindy target, this command sends a ``break'' to the remote target
11835 system; this is only useful if the target has been equipped with a
11836 circuit to perform a hard reset (or some other interesting action) when
11837 a break is detected.
11842 @subsection Mitsubishi M32R/D
11846 @kindex target m32r
11847 @item target m32r @var{dev}
11848 Mitsubishi M32R/D ROM monitor.
11855 The Motorola m68k configuration includes ColdFire support, and
11856 target command for the following ROM monitors.
11860 @kindex target abug
11861 @item target abug @var{dev}
11862 ABug ROM monitor for M68K.
11864 @kindex target cpu32bug
11865 @item target cpu32bug @var{dev}
11866 CPU32BUG monitor, running on a CPU32 (M68K) board.
11868 @kindex target dbug
11869 @item target dbug @var{dev}
11870 dBUG ROM monitor for Motorola ColdFire.
11873 @item target est @var{dev}
11874 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11876 @kindex target rom68k
11877 @item target rom68k @var{dev}
11878 ROM 68K monitor, running on an M68K IDP board.
11882 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11883 instead have only a single special target command:
11887 @kindex target es1800
11888 @item target es1800 @var{dev}
11889 ES-1800 emulator for M68K.
11897 @kindex target rombug
11898 @item target rombug @var{dev}
11899 ROMBUG ROM monitor for OS/9000.
11909 @item target bug @var{dev}
11910 BUG monitor, running on a MVME187 (m88k) board.
11914 @node MIPS Embedded
11915 @subsection MIPS Embedded
11917 @cindex MIPS boards
11918 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11919 MIPS board attached to a serial line. This is available when
11920 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11923 Use these @value{GDBN} commands to specify the connection to your target board:
11926 @item target mips @var{port}
11927 @kindex target mips @var{port}
11928 To run a program on the board, start up @code{@value{GDBP}} with the
11929 name of your program as the argument. To connect to the board, use the
11930 command @samp{target mips @var{port}}, where @var{port} is the name of
11931 the serial port connected to the board. If the program has not already
11932 been downloaded to the board, you may use the @code{load} command to
11933 download it. You can then use all the usual @value{GDBN} commands.
11935 For example, this sequence connects to the target board through a serial
11936 port, and loads and runs a program called @var{prog} through the
11940 host$ @value{GDBP} @var{prog}
11941 @value{GDBN} is free software and @dots{}
11942 (@value{GDBP}) target mips /dev/ttyb
11943 (@value{GDBP}) load @var{prog}
11947 @item target mips @var{hostname}:@var{portnumber}
11948 On some @value{GDBN} host configurations, you can specify a TCP
11949 connection (for instance, to a serial line managed by a terminal
11950 concentrator) instead of a serial port, using the syntax
11951 @samp{@var{hostname}:@var{portnumber}}.
11953 @item target pmon @var{port}
11954 @kindex target pmon @var{port}
11957 @item target ddb @var{port}
11958 @kindex target ddb @var{port}
11959 NEC's DDB variant of PMON for Vr4300.
11961 @item target lsi @var{port}
11962 @kindex target lsi @var{port}
11963 LSI variant of PMON.
11965 @kindex target r3900
11966 @item target r3900 @var{dev}
11967 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11969 @kindex target array
11970 @item target array @var{dev}
11971 Array Tech LSI33K RAID controller board.
11977 @value{GDBN} also supports these special commands for MIPS targets:
11980 @item set processor @var{args}
11981 @itemx show processor
11982 @kindex set processor @var{args}
11983 @kindex show processor
11984 Use the @code{set processor} command to set the type of MIPS
11985 processor when you want to access processor-type-specific registers.
11986 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11987 to use the CPU registers appropriate for the 3041 chip.
11988 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11989 is using. Use the @code{info reg} command to see what registers
11990 @value{GDBN} is using.
11992 @item set mipsfpu double
11993 @itemx set mipsfpu single
11994 @itemx set mipsfpu none
11995 @itemx show mipsfpu
11996 @kindex set mipsfpu
11997 @kindex show mipsfpu
11998 @cindex MIPS remote floating point
11999 @cindex floating point, MIPS remote
12000 If your target board does not support the MIPS floating point
12001 coprocessor, you should use the command @samp{set mipsfpu none} (if you
12002 need this, you may wish to put the command in your @value{GDBN} init
12003 file). This tells @value{GDBN} how to find the return value of
12004 functions which return floating point values. It also allows
12005 @value{GDBN} to avoid saving the floating point registers when calling
12006 functions on the board. If you are using a floating point coprocessor
12007 with only single precision floating point support, as on the @sc{r4650}
12008 processor, use the command @samp{set mipsfpu single}. The default
12009 double precision floating point coprocessor may be selected using
12010 @samp{set mipsfpu double}.
12012 In previous versions the only choices were double precision or no
12013 floating point, so @samp{set mipsfpu on} will select double precision
12014 and @samp{set mipsfpu off} will select no floating point.
12016 As usual, you can inquire about the @code{mipsfpu} variable with
12017 @samp{show mipsfpu}.
12019 @item set remotedebug @var{n}
12020 @itemx show remotedebug
12021 @kindex set remotedebug@r{, MIPS protocol}
12022 @kindex show remotedebug@r{, MIPS protocol}
12023 @cindex @code{remotedebug}, MIPS protocol
12024 @cindex MIPS @code{remotedebug} protocol
12025 @c FIXME! For this to be useful, you must know something about the MIPS
12026 @c FIXME...protocol. Where is it described?
12027 You can see some debugging information about communications with the board
12028 by setting the @code{remotedebug} variable. If you set it to @code{1} using
12029 @samp{set remotedebug 1}, every packet is displayed. If you set it
12030 to @code{2}, every character is displayed. You can check the current value
12031 at any time with the command @samp{show remotedebug}.
12033 @item set timeout @var{seconds}
12034 @itemx set retransmit-timeout @var{seconds}
12035 @itemx show timeout
12036 @itemx show retransmit-timeout
12037 @cindex @code{timeout}, MIPS protocol
12038 @cindex @code{retransmit-timeout}, MIPS protocol
12039 @kindex set timeout
12040 @kindex show timeout
12041 @kindex set retransmit-timeout
12042 @kindex show retransmit-timeout
12043 You can control the timeout used while waiting for a packet, in the MIPS
12044 remote protocol, with the @code{set timeout @var{seconds}} command. The
12045 default is 5 seconds. Similarly, you can control the timeout used while
12046 waiting for an acknowledgement of a packet with the @code{set
12047 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
12048 You can inspect both values with @code{show timeout} and @code{show
12049 retransmit-timeout}. (These commands are @emph{only} available when
12050 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
12052 The timeout set by @code{set timeout} does not apply when @value{GDBN}
12053 is waiting for your program to stop. In that case, @value{GDBN} waits
12054 forever because it has no way of knowing how long the program is going
12055 to run before stopping.
12059 @subsection PowerPC
12063 @kindex target dink32
12064 @item target dink32 @var{dev}
12065 DINK32 ROM monitor.
12067 @kindex target ppcbug
12068 @item target ppcbug @var{dev}
12069 @kindex target ppcbug1
12070 @item target ppcbug1 @var{dev}
12071 PPCBUG ROM monitor for PowerPC.
12074 @item target sds @var{dev}
12075 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
12080 @subsection HP PA Embedded
12084 @kindex target op50n
12085 @item target op50n @var{dev}
12086 OP50N monitor, running on an OKI HPPA board.
12088 @kindex target w89k
12089 @item target w89k @var{dev}
12090 W89K monitor, running on a Winbond HPPA board.
12095 @subsection Hitachi SH
12099 @kindex target hms@r{, with Hitachi SH}
12100 @item target hms @var{dev}
12101 A Hitachi SH board attached via serial line to your host. Use special
12102 commands @code{device} and @code{speed} to control the serial line and
12103 the communications speed used.
12105 @kindex target e7000@r{, with Hitachi SH}
12106 @item target e7000 @var{dev}
12107 E7000 emulator for Hitachi SH.
12109 @kindex target sh3@r{, with SH}
12110 @kindex target sh3e@r{, with SH}
12111 @item target sh3 @var{dev}
12112 @item target sh3e @var{dev}
12113 Hitachi SH-3 and SH-3E target systems.
12118 @subsection Tsqware Sparclet
12122 @value{GDBN} enables developers to debug tasks running on
12123 Sparclet targets from a Unix host.
12124 @value{GDBN} uses code that runs on
12125 both the Unix host and on the Sparclet target. The program
12126 @code{@value{GDBP}} is installed and executed on the Unix host.
12129 @item remotetimeout @var{args}
12130 @kindex remotetimeout
12131 @value{GDBN} supports the option @code{remotetimeout}.
12132 This option is set by the user, and @var{args} represents the number of
12133 seconds @value{GDBN} waits for responses.
12136 @cindex compiling, on Sparclet
12137 When compiling for debugging, include the options @samp{-g} to get debug
12138 information and @samp{-Ttext} to relocate the program to where you wish to
12139 load it on the target. You may also want to add the options @samp{-n} or
12140 @samp{-N} in order to reduce the size of the sections. Example:
12143 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12146 You can use @code{objdump} to verify that the addresses are what you intended:
12149 sparclet-aout-objdump --headers --syms prog
12152 @cindex running, on Sparclet
12154 your Unix execution search path to find @value{GDBN}, you are ready to
12155 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12156 (or @code{sparclet-aout-gdb}, depending on your installation).
12158 @value{GDBN} comes up showing the prompt:
12165 * Sparclet File:: Setting the file to debug
12166 * Sparclet Connection:: Connecting to Sparclet
12167 * Sparclet Download:: Sparclet download
12168 * Sparclet Execution:: Running and debugging
12171 @node Sparclet File
12172 @subsubsection Setting file to debug
12174 The @value{GDBN} command @code{file} lets you choose with program to debug.
12177 (gdbslet) file prog
12181 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12182 @value{GDBN} locates
12183 the file by searching the directories listed in the command search
12185 If the file was compiled with debug information (option "-g"), source
12186 files will be searched as well.
12187 @value{GDBN} locates
12188 the source files by searching the directories listed in the directory search
12189 path (@pxref{Environment, ,Your program's environment}).
12191 to find a file, it displays a message such as:
12194 prog: No such file or directory.
12197 When this happens, add the appropriate directories to the search paths with
12198 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12199 @code{target} command again.
12201 @node Sparclet Connection
12202 @subsubsection Connecting to Sparclet
12204 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12205 To connect to a target on serial port ``@code{ttya}'', type:
12208 (gdbslet) target sparclet /dev/ttya
12209 Remote target sparclet connected to /dev/ttya
12210 main () at ../prog.c:3
12214 @value{GDBN} displays messages like these:
12220 @node Sparclet Download
12221 @subsubsection Sparclet download
12223 @cindex download to Sparclet
12224 Once connected to the Sparclet target,
12225 you can use the @value{GDBN}
12226 @code{load} command to download the file from the host to the target.
12227 The file name and load offset should be given as arguments to the @code{load}
12229 Since the file format is aout, the program must be loaded to the starting
12230 address. You can use @code{objdump} to find out what this value is. The load
12231 offset is an offset which is added to the VMA (virtual memory address)
12232 of each of the file's sections.
12233 For instance, if the program
12234 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12235 and bss at 0x12010170, in @value{GDBN}, type:
12238 (gdbslet) load prog 0x12010000
12239 Loading section .text, size 0xdb0 vma 0x12010000
12242 If the code is loaded at a different address then what the program was linked
12243 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12244 to tell @value{GDBN} where to map the symbol table.
12246 @node Sparclet Execution
12247 @subsubsection Running and debugging
12249 @cindex running and debugging Sparclet programs
12250 You can now begin debugging the task using @value{GDBN}'s execution control
12251 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12252 manual for the list of commands.
12256 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12258 Starting program: prog
12259 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12260 3 char *symarg = 0;
12262 4 char *execarg = "hello!";
12267 @subsection Fujitsu Sparclite
12271 @kindex target sparclite
12272 @item target sparclite @var{dev}
12273 Fujitsu sparclite boards, used only for the purpose of loading.
12274 You must use an additional command to debug the program.
12275 For example: target remote @var{dev} using @value{GDBN} standard
12281 @subsection Tandem ST2000
12283 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12286 To connect your ST2000 to the host system, see the manufacturer's
12287 manual. Once the ST2000 is physically attached, you can run:
12290 target st2000 @var{dev} @var{speed}
12294 to establish it as your debugging environment. @var{dev} is normally
12295 the name of a serial device, such as @file{/dev/ttya}, connected to the
12296 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12297 connection (for example, to a serial line attached via a terminal
12298 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12300 The @code{load} and @code{attach} commands are @emph{not} defined for
12301 this target; you must load your program into the ST2000 as you normally
12302 would for standalone operation. @value{GDBN} reads debugging information
12303 (such as symbols) from a separate, debugging version of the program
12304 available on your host computer.
12305 @c FIXME!! This is terribly vague; what little content is here is
12306 @c basically hearsay.
12308 @cindex ST2000 auxiliary commands
12309 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12313 @item st2000 @var{command}
12314 @kindex st2000 @var{cmd}
12315 @cindex STDBUG commands (ST2000)
12316 @cindex commands to STDBUG (ST2000)
12317 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12318 manual for available commands.
12321 @cindex connect (to STDBUG)
12322 Connect the controlling terminal to the STDBUG command monitor. When
12323 you are done interacting with STDBUG, typing either of two character
12324 sequences gets you back to the @value{GDBN} command prompt:
12325 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12326 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12330 @subsection Zilog Z8000
12333 @cindex simulator, Z8000
12334 @cindex Zilog Z8000 simulator
12336 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12339 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12340 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12341 segmented variant). The simulator recognizes which architecture is
12342 appropriate by inspecting the object code.
12345 @item target sim @var{args}
12347 @kindex target sim@r{, with Z8000}
12348 Debug programs on a simulated CPU. If the simulator supports setup
12349 options, specify them via @var{args}.
12353 After specifying this target, you can debug programs for the simulated
12354 CPU in the same style as programs for your host computer; use the
12355 @code{file} command to load a new program image, the @code{run} command
12356 to run your program, and so on.
12358 As well as making available all the usual machine registers
12359 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12360 additional items of information as specially named registers:
12365 Counts clock-ticks in the simulator.
12368 Counts instructions run in the simulator.
12371 Execution time in 60ths of a second.
12375 You can refer to these values in @value{GDBN} expressions with the usual
12376 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12377 conditional breakpoint that suspends only after at least 5000
12378 simulated clock ticks.
12380 @node Architectures
12381 @section Architectures
12383 This section describes characteristics of architectures that affect
12384 all uses of @value{GDBN} with the architecture, both native and cross.
12397 @kindex set rstack_high_address
12398 @cindex AMD 29K register stack
12399 @cindex register stack, AMD29K
12400 @item set rstack_high_address @var{address}
12401 On AMD 29000 family processors, registers are saved in a separate
12402 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12403 extent of this stack. Normally, @value{GDBN} just assumes that the
12404 stack is ``large enough''. This may result in @value{GDBN} referencing
12405 memory locations that do not exist. If necessary, you can get around
12406 this problem by specifying the ending address of the register stack with
12407 the @code{set rstack_high_address} command. The argument should be an
12408 address, which you probably want to precede with @samp{0x} to specify in
12411 @kindex show rstack_high_address
12412 @item show rstack_high_address
12413 Display the current limit of the register stack, on AMD 29000 family
12421 See the following section.
12426 @cindex stack on Alpha
12427 @cindex stack on MIPS
12428 @cindex Alpha stack
12430 Alpha- and MIPS-based computers use an unusual stack frame, which
12431 sometimes requires @value{GDBN} to search backward in the object code to
12432 find the beginning of a function.
12434 @cindex response time, MIPS debugging
12435 To improve response time (especially for embedded applications, where
12436 @value{GDBN} may be restricted to a slow serial line for this search)
12437 you may want to limit the size of this search, using one of these
12441 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12442 @item set heuristic-fence-post @var{limit}
12443 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12444 search for the beginning of a function. A value of @var{0} (the
12445 default) means there is no limit. However, except for @var{0}, the
12446 larger the limit the more bytes @code{heuristic-fence-post} must search
12447 and therefore the longer it takes to run.
12449 @item show heuristic-fence-post
12450 Display the current limit.
12454 These commands are available @emph{only} when @value{GDBN} is configured
12455 for debugging programs on Alpha or MIPS processors.
12458 @node Controlling GDB
12459 @chapter Controlling @value{GDBN}
12461 You can alter the way @value{GDBN} interacts with you by using the
12462 @code{set} command. For commands controlling how @value{GDBN} displays
12463 data, see @ref{Print Settings, ,Print settings}. Other settings are
12468 * Editing:: Command editing
12469 * History:: Command history
12470 * Screen Size:: Screen size
12471 * Numbers:: Numbers
12472 * Messages/Warnings:: Optional warnings and messages
12473 * Debugging Output:: Optional messages about internal happenings
12481 @value{GDBN} indicates its readiness to read a command by printing a string
12482 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12483 can change the prompt string with the @code{set prompt} command. For
12484 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12485 the prompt in one of the @value{GDBN} sessions so that you can always tell
12486 which one you are talking to.
12488 @emph{Note:} @code{set prompt} does not add a space for you after the
12489 prompt you set. This allows you to set a prompt which ends in a space
12490 or a prompt that does not.
12494 @item set prompt @var{newprompt}
12495 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12497 @kindex show prompt
12499 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12503 @section Command editing
12505 @cindex command line editing
12507 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12508 @sc{gnu} library provides consistent behavior for programs which provide a
12509 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12510 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12511 substitution, and a storage and recall of command history across
12512 debugging sessions.
12514 You may control the behavior of command line editing in @value{GDBN} with the
12515 command @code{set}.
12518 @kindex set editing
12521 @itemx set editing on
12522 Enable command line editing (enabled by default).
12524 @item set editing off
12525 Disable command line editing.
12527 @kindex show editing
12529 Show whether command line editing is enabled.
12533 @section Command history
12535 @value{GDBN} can keep track of the commands you type during your
12536 debugging sessions, so that you can be certain of precisely what
12537 happened. Use these commands to manage the @value{GDBN} command
12541 @cindex history substitution
12542 @cindex history file
12543 @kindex set history filename
12544 @kindex GDBHISTFILE
12545 @item set history filename @var{fname}
12546 Set the name of the @value{GDBN} command history file to @var{fname}.
12547 This is the file where @value{GDBN} reads an initial command history
12548 list, and where it writes the command history from this session when it
12549 exits. You can access this list through history expansion or through
12550 the history command editing characters listed below. This file defaults
12551 to the value of the environment variable @code{GDBHISTFILE}, or to
12552 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12555 @cindex history save
12556 @kindex set history save
12557 @item set history save
12558 @itemx set history save on
12559 Record command history in a file, whose name may be specified with the
12560 @code{set history filename} command. By default, this option is disabled.
12562 @item set history save off
12563 Stop recording command history in a file.
12565 @cindex history size
12566 @kindex set history size
12567 @item set history size @var{size}
12568 Set the number of commands which @value{GDBN} keeps in its history list.
12569 This defaults to the value of the environment variable
12570 @code{HISTSIZE}, or to 256 if this variable is not set.
12573 @cindex history expansion
12574 History expansion assigns special meaning to the character @kbd{!}.
12575 @ifset have-readline-appendices
12576 @xref{Event Designators}.
12579 Since @kbd{!} is also the logical not operator in C, history expansion
12580 is off by default. If you decide to enable history expansion with the
12581 @code{set history expansion on} command, you may sometimes need to
12582 follow @kbd{!} (when it is used as logical not, in an expression) with
12583 a space or a tab to prevent it from being expanded. The readline
12584 history facilities do not attempt substitution on the strings
12585 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12587 The commands to control history expansion are:
12590 @kindex set history expansion
12591 @item set history expansion on
12592 @itemx set history expansion
12593 Enable history expansion. History expansion is off by default.
12595 @item set history expansion off
12596 Disable history expansion.
12598 The readline code comes with more complete documentation of
12599 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12600 or @code{vi} may wish to read it.
12601 @ifset have-readline-appendices
12602 @xref{Command Line Editing}.
12606 @kindex show history
12608 @itemx show history filename
12609 @itemx show history save
12610 @itemx show history size
12611 @itemx show history expansion
12612 These commands display the state of the @value{GDBN} history parameters.
12613 @code{show history} by itself displays all four states.
12619 @item show commands
12620 Display the last ten commands in the command history.
12622 @item show commands @var{n}
12623 Print ten commands centered on command number @var{n}.
12625 @item show commands +
12626 Print ten commands just after the commands last printed.
12630 @section Screen size
12631 @cindex size of screen
12632 @cindex pauses in output
12634 Certain commands to @value{GDBN} may produce large amounts of
12635 information output to the screen. To help you read all of it,
12636 @value{GDBN} pauses and asks you for input at the end of each page of
12637 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12638 to discard the remaining output. Also, the screen width setting
12639 determines when to wrap lines of output. Depending on what is being
12640 printed, @value{GDBN} tries to break the line at a readable place,
12641 rather than simply letting it overflow onto the following line.
12643 Normally @value{GDBN} knows the size of the screen from the terminal
12644 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12645 together with the value of the @code{TERM} environment variable and the
12646 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12647 you can override it with the @code{set height} and @code{set
12654 @kindex show height
12655 @item set height @var{lpp}
12657 @itemx set width @var{cpl}
12659 These @code{set} commands specify a screen height of @var{lpp} lines and
12660 a screen width of @var{cpl} characters. The associated @code{show}
12661 commands display the current settings.
12663 If you specify a height of zero lines, @value{GDBN} does not pause during
12664 output no matter how long the output is. This is useful if output is to a
12665 file or to an editor buffer.
12667 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12668 from wrapping its output.
12673 @cindex number representation
12674 @cindex entering numbers
12676 You can always enter numbers in octal, decimal, or hexadecimal in
12677 @value{GDBN} by the usual conventions: octal numbers begin with
12678 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12679 begin with @samp{0x}. Numbers that begin with none of these are, by
12680 default, entered in base 10; likewise, the default display for
12681 numbers---when no particular format is specified---is base 10. You can
12682 change the default base for both input and output with the @code{set
12686 @kindex set input-radix
12687 @item set input-radix @var{base}
12688 Set the default base for numeric input. Supported choices
12689 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12690 specified either unambiguously or using the current default radix; for
12700 sets the base to decimal. On the other hand, @samp{set radix 10}
12701 leaves the radix unchanged no matter what it was.
12703 @kindex set output-radix
12704 @item set output-radix @var{base}
12705 Set the default base for numeric display. Supported choices
12706 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12707 specified either unambiguously or using the current default radix.
12709 @kindex show input-radix
12710 @item show input-radix
12711 Display the current default base for numeric input.
12713 @kindex show output-radix
12714 @item show output-radix
12715 Display the current default base for numeric display.
12718 @node Messages/Warnings
12719 @section Optional warnings and messages
12721 By default, @value{GDBN} is silent about its inner workings. If you are
12722 running on a slow machine, you may want to use the @code{set verbose}
12723 command. This makes @value{GDBN} tell you when it does a lengthy
12724 internal operation, so you will not think it has crashed.
12726 Currently, the messages controlled by @code{set verbose} are those
12727 which announce that the symbol table for a source file is being read;
12728 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12731 @kindex set verbose
12732 @item set verbose on
12733 Enables @value{GDBN} output of certain informational messages.
12735 @item set verbose off
12736 Disables @value{GDBN} output of certain informational messages.
12738 @kindex show verbose
12740 Displays whether @code{set verbose} is on or off.
12743 By default, if @value{GDBN} encounters bugs in the symbol table of an
12744 object file, it is silent; but if you are debugging a compiler, you may
12745 find this information useful (@pxref{Symbol Errors, ,Errors reading
12750 @kindex set complaints
12751 @item set complaints @var{limit}
12752 Permits @value{GDBN} to output @var{limit} complaints about each type of
12753 unusual symbols before becoming silent about the problem. Set
12754 @var{limit} to zero to suppress all complaints; set it to a large number
12755 to prevent complaints from being suppressed.
12757 @kindex show complaints
12758 @item show complaints
12759 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12763 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12764 lot of stupid questions to confirm certain commands. For example, if
12765 you try to run a program which is already running:
12769 The program being debugged has been started already.
12770 Start it from the beginning? (y or n)
12773 If you are willing to unflinchingly face the consequences of your own
12774 commands, you can disable this ``feature'':
12778 @kindex set confirm
12780 @cindex confirmation
12781 @cindex stupid questions
12782 @item set confirm off
12783 Disables confirmation requests.
12785 @item set confirm on
12786 Enables confirmation requests (the default).
12788 @kindex show confirm
12790 Displays state of confirmation requests.
12794 @node Debugging Output
12795 @section Optional messages about internal happenings
12797 @kindex set debug arch
12798 @item set debug arch
12799 Turns on or off display of gdbarch debugging info. The default is off
12800 @kindex show debug arch
12801 @item show debug arch
12802 Displays the current state of displaying gdbarch debugging info.
12803 @kindex set debug event
12804 @item set debug event
12805 Turns on or off display of @value{GDBN} event debugging info. The
12807 @kindex show debug event
12808 @item show debug event
12809 Displays the current state of displaying @value{GDBN} event debugging
12811 @kindex set debug expression
12812 @item set debug expression
12813 Turns on or off display of @value{GDBN} expression debugging info. The
12815 @kindex show debug expression
12816 @item show debug expression
12817 Displays the current state of displaying @value{GDBN} expression
12819 @kindex set debug overload
12820 @item set debug overload
12821 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12822 info. This includes info such as ranking of functions, etc. The default
12824 @kindex show debug overload
12825 @item show debug overload
12826 Displays the current state of displaying @value{GDBN} C@t{++} overload
12828 @kindex set debug remote
12829 @cindex packets, reporting on stdout
12830 @cindex serial connections, debugging
12831 @item set debug remote
12832 Turns on or off display of reports on all packets sent back and forth across
12833 the serial line to the remote machine. The info is printed on the
12834 @value{GDBN} standard output stream. The default is off.
12835 @kindex show debug remote
12836 @item show debug remote
12837 Displays the state of display of remote packets.
12838 @kindex set debug serial
12839 @item set debug serial
12840 Turns on or off display of @value{GDBN} serial debugging info. The
12842 @kindex show debug serial
12843 @item show debug serial
12844 Displays the current state of displaying @value{GDBN} serial debugging
12846 @kindex set debug target
12847 @item set debug target
12848 Turns on or off display of @value{GDBN} target debugging info. This info
12849 includes what is going on at the target level of GDB, as it happens. The
12851 @kindex show debug target
12852 @item show debug target
12853 Displays the current state of displaying @value{GDBN} target debugging
12855 @kindex set debug varobj
12856 @item set debug varobj
12857 Turns on or off display of @value{GDBN} variable object debugging
12858 info. The default is off.
12859 @kindex show debug varobj
12860 @item show debug varobj
12861 Displays the current state of displaying @value{GDBN} variable object
12866 @chapter Canned Sequences of Commands
12868 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12869 command lists}), @value{GDBN} provides two ways to store sequences of
12870 commands for execution as a unit: user-defined commands and command
12874 * Define:: User-defined commands
12875 * Hooks:: User-defined command hooks
12876 * Command Files:: Command files
12877 * Output:: Commands for controlled output
12881 @section User-defined commands
12883 @cindex user-defined command
12884 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12885 which you assign a new name as a command. This is done with the
12886 @code{define} command. User commands may accept up to 10 arguments
12887 separated by whitespace. Arguments are accessed within the user command
12888 via @var{$arg0@dots{}$arg9}. A trivial example:
12892 print $arg0 + $arg1 + $arg2
12896 To execute the command use:
12903 This defines the command @code{adder}, which prints the sum of
12904 its three arguments. Note the arguments are text substitutions, so they may
12905 reference variables, use complex expressions, or even perform inferior
12911 @item define @var{commandname}
12912 Define a command named @var{commandname}. If there is already a command
12913 by that name, you are asked to confirm that you want to redefine it.
12915 The definition of the command is made up of other @value{GDBN} command lines,
12916 which are given following the @code{define} command. The end of these
12917 commands is marked by a line containing @code{end}.
12922 Takes a single argument, which is an expression to evaluate.
12923 It is followed by a series of commands that are executed
12924 only if the expression is true (nonzero).
12925 There can then optionally be a line @code{else}, followed
12926 by a series of commands that are only executed if the expression
12927 was false. The end of the list is marked by a line containing @code{end}.
12931 The syntax is similar to @code{if}: the command takes a single argument,
12932 which is an expression to evaluate, and must be followed by the commands to
12933 execute, one per line, terminated by an @code{end}.
12934 The commands are executed repeatedly as long as the expression
12938 @item document @var{commandname}
12939 Document the user-defined command @var{commandname}, so that it can be
12940 accessed by @code{help}. The command @var{commandname} must already be
12941 defined. This command reads lines of documentation just as @code{define}
12942 reads the lines of the command definition, ending with @code{end}.
12943 After the @code{document} command is finished, @code{help} on command
12944 @var{commandname} displays the documentation you have written.
12946 You may use the @code{document} command again to change the
12947 documentation of a command. Redefining the command with @code{define}
12948 does not change the documentation.
12950 @kindex help user-defined
12951 @item help user-defined
12952 List all user-defined commands, with the first line of the documentation
12957 @itemx show user @var{commandname}
12958 Display the @value{GDBN} commands used to define @var{commandname} (but
12959 not its documentation). If no @var{commandname} is given, display the
12960 definitions for all user-defined commands.
12964 When user-defined commands are executed, the
12965 commands of the definition are not printed. An error in any command
12966 stops execution of the user-defined command.
12968 If used interactively, commands that would ask for confirmation proceed
12969 without asking when used inside a user-defined command. Many @value{GDBN}
12970 commands that normally print messages to say what they are doing omit the
12971 messages when used in a user-defined command.
12974 @section User-defined command hooks
12975 @cindex command hooks
12976 @cindex hooks, for commands
12977 @cindex hooks, pre-command
12981 You may define @dfn{hooks}, which are a special kind of user-defined
12982 command. Whenever you run the command @samp{foo}, if the user-defined
12983 command @samp{hook-foo} exists, it is executed (with no arguments)
12984 before that command.
12986 @cindex hooks, post-command
12989 A hook may also be defined which is run after the command you executed.
12990 Whenever you run the command @samp{foo}, if the user-defined command
12991 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12992 that command. Post-execution hooks may exist simultaneously with
12993 pre-execution hooks, for the same command.
12995 It is valid for a hook to call the command which it hooks. If this
12996 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12998 @c It would be nice if hookpost could be passed a parameter indicating
12999 @c if the command it hooks executed properly or not. FIXME!
13001 @kindex stop@r{, a pseudo-command}
13002 In addition, a pseudo-command, @samp{stop} exists. Defining
13003 (@samp{hook-stop}) makes the associated commands execute every time
13004 execution stops in your program: before breakpoint commands are run,
13005 displays are printed, or the stack frame is printed.
13007 For example, to ignore @code{SIGALRM} signals while
13008 single-stepping, but treat them normally during normal execution,
13013 handle SIGALRM nopass
13017 handle SIGALRM pass
13020 define hook-continue
13021 handle SIGLARM pass
13025 As a further example, to hook at the begining and end of the @code{echo}
13026 command, and to add extra text to the beginning and end of the message,
13034 define hookpost-echo
13038 (@value{GDBP}) echo Hello World
13039 <<<---Hello World--->>>
13044 You can define a hook for any single-word command in @value{GDBN}, but
13045 not for command aliases; you should define a hook for the basic command
13046 name, e.g. @code{backtrace} rather than @code{bt}.
13047 @c FIXME! So how does Joe User discover whether a command is an alias
13049 If an error occurs during the execution of your hook, execution of
13050 @value{GDBN} commands stops and @value{GDBN} issues a prompt
13051 (before the command that you actually typed had a chance to run).
13053 If you try to define a hook which does not match any known command, you
13054 get a warning from the @code{define} command.
13056 @node Command Files
13057 @section Command files
13059 @cindex command files
13060 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
13061 commands. Comments (lines starting with @kbd{#}) may also be included.
13062 An empty line in a command file does nothing; it does not mean to repeat
13063 the last command, as it would from the terminal.
13066 @cindex @file{.gdbinit}
13067 @cindex @file{gdb.ini}
13068 When you start @value{GDBN}, it automatically executes commands from its
13069 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
13070 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
13071 limitations of file names imposed by DOS filesystems.}.
13072 During startup, @value{GDBN} does the following:
13076 Reads the init file (if any) in your home directory@footnote{On
13077 DOS/Windows systems, the home directory is the one pointed to by the
13078 @code{HOME} environment variable.}.
13081 Processes command line options and operands.
13084 Reads the init file (if any) in the current working directory.
13087 Reads command files specified by the @samp{-x} option.
13090 The init file in your home directory can set options (such as @samp{set
13091 complaints}) that affect subsequent processing of command line options
13092 and operands. Init files are not executed if you use the @samp{-nx}
13093 option (@pxref{Mode Options, ,Choosing modes}).
13095 @cindex init file name
13096 On some configurations of @value{GDBN}, the init file is known by a
13097 different name (these are typically environments where a specialized
13098 form of @value{GDBN} may need to coexist with other forms, hence a
13099 different name for the specialized version's init file). These are the
13100 environments with special init file names:
13102 @cindex @file{.vxgdbinit}
13105 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13107 @cindex @file{.os68gdbinit}
13109 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13111 @cindex @file{.esgdbinit}
13113 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13116 You can also request the execution of a command file with the
13117 @code{source} command:
13121 @item source @var{filename}
13122 Execute the command file @var{filename}.
13125 The lines in a command file are executed sequentially. They are not
13126 printed as they are executed. An error in any command terminates execution
13127 of the command file.
13129 Commands that would ask for confirmation if used interactively proceed
13130 without asking when used in a command file. Many @value{GDBN} commands that
13131 normally print messages to say what they are doing omit the messages
13132 when called from command files.
13134 @value{GDBN} also accepts command input from standard input. In this
13135 mode, normal output goes to standard output and error output goes to
13136 standard error. Errors in a command file supplied on standard input do
13137 not terminate execution of the command file --- execution continues with
13141 gdb < cmds > log 2>&1
13144 (The syntax above will vary depending on the shell used.) This example
13145 will execute commands from the file @file{cmds}. All output and errors
13146 would be directed to @file{log}.
13149 @section Commands for controlled output
13151 During the execution of a command file or a user-defined command, normal
13152 @value{GDBN} output is suppressed; the only output that appears is what is
13153 explicitly printed by the commands in the definition. This section
13154 describes three commands useful for generating exactly the output you
13159 @item echo @var{text}
13160 @c I do not consider backslash-space a standard C escape sequence
13161 @c because it is not in ANSI.
13162 Print @var{text}. Nonprinting characters can be included in
13163 @var{text} using C escape sequences, such as @samp{\n} to print a
13164 newline. @strong{No newline is printed unless you specify one.}
13165 In addition to the standard C escape sequences, a backslash followed
13166 by a space stands for a space. This is useful for displaying a
13167 string with spaces at the beginning or the end, since leading and
13168 trailing spaces are otherwise trimmed from all arguments.
13169 To print @samp{@w{ }and foo =@w{ }}, use the command
13170 @samp{echo \@w{ }and foo = \@w{ }}.
13172 A backslash at the end of @var{text} can be used, as in C, to continue
13173 the command onto subsequent lines. For example,
13176 echo This is some text\n\
13177 which is continued\n\
13178 onto several lines.\n
13181 produces the same output as
13184 echo This is some text\n
13185 echo which is continued\n
13186 echo onto several lines.\n
13190 @item output @var{expression}
13191 Print the value of @var{expression} and nothing but that value: no
13192 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13193 value history either. @xref{Expressions, ,Expressions}, for more information
13196 @item output/@var{fmt} @var{expression}
13197 Print the value of @var{expression} in format @var{fmt}. You can use
13198 the same formats as for @code{print}. @xref{Output Formats,,Output
13199 formats}, for more information.
13202 @item printf @var{string}, @var{expressions}@dots{}
13203 Print the values of the @var{expressions} under the control of
13204 @var{string}. The @var{expressions} are separated by commas and may be
13205 either numbers or pointers. Their values are printed as specified by
13206 @var{string}, exactly as if your program were to execute the C
13208 @c FIXME: the above implies that at least all ANSI C formats are
13209 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13210 @c Either this is a bug, or the manual should document what formats are
13214 printf (@var{string}, @var{expressions}@dots{});
13217 For example, you can print two values in hex like this:
13220 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13223 The only backslash-escape sequences that you can use in the format
13224 string are the simple ones that consist of backslash followed by a
13229 @chapter @value{GDBN} Text User Interface
13233 * TUI Overview:: TUI overview
13234 * TUI Keys:: TUI key bindings
13235 * TUI Commands:: TUI specific commands
13236 * TUI Configuration:: TUI configuration variables
13239 The @value{GDBN} Text User Interface, TUI in short,
13240 is a terminal interface which uses the @code{curses} library
13241 to show the source file, the assembly output, the program registers
13242 and @value{GDBN} commands in separate text windows.
13243 The TUI is available only when @value{GDBN} is configured
13244 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13247 @section TUI overview
13249 The TUI has two display modes that can be switched while
13254 A curses (or TUI) mode in which it displays several text
13255 windows on the terminal.
13258 A standard mode which corresponds to the @value{GDBN} configured without
13262 In the TUI mode, @value{GDBN} can display several text window
13267 This window is the @value{GDBN} command window with the @value{GDBN}
13268 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13269 managed using readline but through the TUI. The @emph{command}
13270 window is always visible.
13273 The source window shows the source file of the program. The current
13274 line as well as active breakpoints are displayed in this window.
13275 The current program position is shown with the @samp{>} marker and
13276 active breakpoints are shown with @samp{*} markers.
13279 The assembly window shows the disassembly output of the program.
13282 This window shows the processor registers. It detects when
13283 a register is changed and when this is the case, registers that have
13284 changed are highlighted.
13288 The source, assembly and register windows are attached to the thread
13289 and the frame position. They are updated when the current thread
13290 changes, when the frame changes or when the program counter changes.
13291 These three windows are arranged by the TUI according to several
13292 layouts. The layout defines which of these three windows are visible.
13293 The following layouts are available:
13303 source and assembly
13306 source and registers
13309 assembly and registers
13314 @section TUI Key Bindings
13315 @cindex TUI key bindings
13317 The TUI installs several key bindings in the readline keymaps
13318 (@pxref{Command Line Editing}).
13319 They allow to leave or enter in the TUI mode or they operate
13320 directly on the TUI layout and windows. The following key bindings
13321 are installed for both TUI mode and the @value{GDBN} standard mode.
13330 Enter or leave the TUI mode. When the TUI mode is left,
13331 the curses window management is left and @value{GDBN} operates using
13332 its standard mode writing on the terminal directly. When the TUI
13333 mode is entered, the control is given back to the curses windows.
13334 The screen is then refreshed.
13338 Use a TUI layout with only one window. The layout will
13339 either be @samp{source} or @samp{assembly}. When the TUI mode
13340 is not active, it will switch to the TUI mode.
13342 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13346 Use a TUI layout with at least two windows. When the current
13347 layout shows already two windows, a next layout with two windows is used.
13348 When a new layout is chosen, one window will always be common to the
13349 previous layout and the new one.
13351 Think of it as the Emacs @kbd{C-x 2} binding.
13355 The following key bindings are handled only by the TUI mode:
13360 Scroll the active window one page up.
13364 Scroll the active window one page down.
13368 Scroll the active window one line up.
13372 Scroll the active window one line down.
13376 Scroll the active window one column left.
13380 Scroll the active window one column right.
13384 Refresh the screen.
13388 In the TUI mode, the arrow keys are used by the active window
13389 for scrolling. This means they are not available for readline. It is
13390 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13391 @key{C-b} and @key{C-f}.
13394 @section TUI specific commands
13395 @cindex TUI commands
13397 The TUI has specific commands to control the text windows.
13398 These commands are always available, that is they do not depend on
13399 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13400 is in the standard mode, using these commands will automatically switch
13405 @kindex layout next
13406 Display the next layout.
13409 @kindex layout prev
13410 Display the previous layout.
13414 Display the source window only.
13418 Display the assembly window only.
13421 @kindex layout split
13422 Display the source and assembly window.
13425 @kindex layout regs
13426 Display the register window together with the source or assembly window.
13428 @item focus next | prev | src | asm | regs | split
13430 Set the focus to the named window.
13431 This command allows to change the active window so that scrolling keys
13432 can be affected to another window.
13436 Refresh the screen. This is similar to using @key{C-L} key.
13440 Update the source window and the current execution point.
13442 @item winheight @var{name} +@var{count}
13443 @itemx winheight @var{name} -@var{count}
13445 Change the height of the window @var{name} by @var{count}
13446 lines. Positive counts increase the height, while negative counts
13451 @node TUI Configuration
13452 @section TUI configuration variables
13453 @cindex TUI configuration variables
13455 The TUI has several configuration variables that control the
13456 appearance of windows on the terminal.
13459 @item set tui border-kind @var{kind}
13460 @kindex set tui border-kind
13461 Select the border appearance for the source, assembly and register windows.
13462 The possible values are the following:
13465 Use a space character to draw the border.
13468 Use ascii characters + - and | to draw the border.
13471 Use the Alternate Character Set to draw the border. The border is
13472 drawn using character line graphics if the terminal supports them.
13476 @item set tui active-border-mode @var{mode}
13477 @kindex set tui active-border-mode
13478 Select the attributes to display the border of the active window.
13479 The possible values are @code{normal}, @code{standout}, @code{reverse},
13480 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13482 @item set tui border-mode @var{mode}
13483 @kindex set tui border-mode
13484 Select the attributes to display the border of other windows.
13485 The @var{mode} can be one of the following:
13488 Use normal attributes to display the border.
13494 Use reverse video mode.
13497 Use half bright mode.
13499 @item half-standout
13500 Use half bright and standout mode.
13503 Use extra bright or bold mode.
13505 @item bold-standout
13506 Use extra bright or bold and standout mode.
13513 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13516 @cindex @sc{gnu} Emacs
13517 A special interface allows you to use @sc{gnu} Emacs to view (and
13518 edit) the source files for the program you are debugging with
13521 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13522 executable file you want to debug as an argument. This command starts
13523 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13524 created Emacs buffer.
13525 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13527 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13532 All ``terminal'' input and output goes through the Emacs buffer.
13535 This applies both to @value{GDBN} commands and their output, and to the input
13536 and output done by the program you are debugging.
13538 This is useful because it means that you can copy the text of previous
13539 commands and input them again; you can even use parts of the output
13542 All the facilities of Emacs' Shell mode are available for interacting
13543 with your program. In particular, you can send signals the usual
13544 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13549 @value{GDBN} displays source code through Emacs.
13552 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13553 source file for that frame and puts an arrow (@samp{=>}) at the
13554 left margin of the current line. Emacs uses a separate buffer for
13555 source display, and splits the screen to show both your @value{GDBN} session
13558 Explicit @value{GDBN} @code{list} or search commands still produce output as
13559 usual, but you probably have no reason to use them from Emacs.
13562 @emph{Warning:} If the directory where your program resides is not your
13563 current directory, it can be easy to confuse Emacs about the location of
13564 the source files, in which case the auxiliary display buffer does not
13565 appear to show your source. @value{GDBN} can find programs by searching your
13566 environment's @code{PATH} variable, so the @value{GDBN} input and output
13567 session proceeds normally; but Emacs does not get enough information
13568 back from @value{GDBN} to locate the source files in this situation. To
13569 avoid this problem, either start @value{GDBN} mode from the directory where
13570 your program resides, or specify an absolute file name when prompted for the
13571 @kbd{M-x gdb} argument.
13573 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13574 switch to debugging a program in some other location, from an existing
13575 @value{GDBN} buffer in Emacs.
13578 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13579 you need to call @value{GDBN} by a different name (for example, if you keep
13580 several configurations around, with different names) you can set the
13581 Emacs variable @code{gdb-command-name}; for example,
13584 (setq gdb-command-name "mygdb")
13588 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13589 in your @file{.emacs} file) makes Emacs call the program named
13590 ``@code{mygdb}'' instead.
13592 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13593 addition to the standard Shell mode commands:
13597 Describe the features of Emacs' @value{GDBN} Mode.
13600 Execute to another source line, like the @value{GDBN} @code{step} command; also
13601 update the display window to show the current file and location.
13604 Execute to next source line in this function, skipping all function
13605 calls, like the @value{GDBN} @code{next} command. Then update the display window
13606 to show the current file and location.
13609 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13610 display window accordingly.
13612 @item M-x gdb-nexti
13613 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13614 display window accordingly.
13617 Execute until exit from the selected stack frame, like the @value{GDBN}
13618 @code{finish} command.
13621 Continue execution of your program, like the @value{GDBN} @code{continue}
13624 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13627 Go up the number of frames indicated by the numeric argument
13628 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13629 like the @value{GDBN} @code{up} command.
13631 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13634 Go down the number of frames indicated by the numeric argument, like the
13635 @value{GDBN} @code{down} command.
13637 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13640 Read the number where the cursor is positioned, and insert it at the end
13641 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13642 around an address that was displayed earlier, type @kbd{disassemble};
13643 then move the cursor to the address display, and pick up the
13644 argument for @code{disassemble} by typing @kbd{C-x &}.
13646 You can customize this further by defining elements of the list
13647 @code{gdb-print-command}; once it is defined, you can format or
13648 otherwise process numbers picked up by @kbd{C-x &} before they are
13649 inserted. A numeric argument to @kbd{C-x &} indicates that you
13650 wish special formatting, and also acts as an index to pick an element of the
13651 list. If the list element is a string, the number to be inserted is
13652 formatted using the Emacs function @code{format}; otherwise the number
13653 is passed as an argument to the corresponding list element.
13656 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13657 tells @value{GDBN} to set a breakpoint on the source line point is on.
13659 If you accidentally delete the source-display buffer, an easy way to get
13660 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13661 request a frame display; when you run under Emacs, this recreates
13662 the source buffer if necessary to show you the context of the current
13665 The source files displayed in Emacs are in ordinary Emacs buffers
13666 which are visiting the source files in the usual way. You can edit
13667 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13668 communicates with Emacs in terms of line numbers. If you add or
13669 delete lines from the text, the line numbers that @value{GDBN} knows cease
13670 to correspond properly with the code.
13672 @c The following dropped because Epoch is nonstandard. Reactivate
13673 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13675 @kindex Emacs Epoch environment
13679 Version 18 of @sc{gnu} Emacs has a built-in window system
13680 called the @code{epoch}
13681 environment. Users of this environment can use a new command,
13682 @code{inspect} which performs identically to @code{print} except that
13683 each value is printed in its own window.
13686 @include annotate.texi
13687 @include gdbmi.texinfo
13690 @chapter Reporting Bugs in @value{GDBN}
13691 @cindex bugs in @value{GDBN}
13692 @cindex reporting bugs in @value{GDBN}
13694 Your bug reports play an essential role in making @value{GDBN} reliable.
13696 Reporting a bug may help you by bringing a solution to your problem, or it
13697 may not. But in any case the principal function of a bug report is to help
13698 the entire community by making the next version of @value{GDBN} work better. Bug
13699 reports are your contribution to the maintenance of @value{GDBN}.
13701 In order for a bug report to serve its purpose, you must include the
13702 information that enables us to fix the bug.
13705 * Bug Criteria:: Have you found a bug?
13706 * Bug Reporting:: How to report bugs
13710 @section Have you found a bug?
13711 @cindex bug criteria
13713 If you are not sure whether you have found a bug, here are some guidelines:
13716 @cindex fatal signal
13717 @cindex debugger crash
13718 @cindex crash of debugger
13720 If the debugger gets a fatal signal, for any input whatever, that is a
13721 @value{GDBN} bug. Reliable debuggers never crash.
13723 @cindex error on valid input
13725 If @value{GDBN} produces an error message for valid input, that is a
13726 bug. (Note that if you're cross debugging, the problem may also be
13727 somewhere in the connection to the target.)
13729 @cindex invalid input
13731 If @value{GDBN} does not produce an error message for invalid input,
13732 that is a bug. However, you should note that your idea of
13733 ``invalid input'' might be our idea of ``an extension'' or ``support
13734 for traditional practice''.
13737 If you are an experienced user of debugging tools, your suggestions
13738 for improvement of @value{GDBN} are welcome in any case.
13741 @node Bug Reporting
13742 @section How to report bugs
13743 @cindex bug reports
13744 @cindex @value{GDBN} bugs, reporting
13746 A number of companies and individuals offer support for @sc{gnu} products.
13747 If you obtained @value{GDBN} from a support organization, we recommend you
13748 contact that organization first.
13750 You can find contact information for many support companies and
13751 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13753 @c should add a web page ref...
13755 In any event, we also recommend that you send bug reports for
13756 @value{GDBN} to this addresses:
13762 @strong{Do not send bug reports to @samp{info-gdb}, or to
13763 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13764 not want to receive bug reports. Those that do have arranged to receive
13767 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13768 serves as a repeater. The mailing list and the newsgroup carry exactly
13769 the same messages. Often people think of posting bug reports to the
13770 newsgroup instead of mailing them. This appears to work, but it has one
13771 problem which can be crucial: a newsgroup posting often lacks a mail
13772 path back to the sender. Thus, if we need to ask for more information,
13773 we may be unable to reach you. For this reason, it is better to send
13774 bug reports to the mailing list.
13776 As a last resort, send bug reports on paper to:
13779 @sc{gnu} Debugger Bugs
13780 Free Software Foundation Inc.
13781 59 Temple Place - Suite 330
13782 Boston, MA 02111-1307
13786 The fundamental principle of reporting bugs usefully is this:
13787 @strong{report all the facts}. If you are not sure whether to state a
13788 fact or leave it out, state it!
13790 Often people omit facts because they think they know what causes the
13791 problem and assume that some details do not matter. Thus, you might
13792 assume that the name of the variable you use in an example does not matter.
13793 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13794 stray memory reference which happens to fetch from the location where that
13795 name is stored in memory; perhaps, if the name were different, the contents
13796 of that location would fool the debugger into doing the right thing despite
13797 the bug. Play it safe and give a specific, complete example. That is the
13798 easiest thing for you to do, and the most helpful.
13800 Keep in mind that the purpose of a bug report is to enable us to fix the
13801 bug. It may be that the bug has been reported previously, but neither
13802 you nor we can know that unless your bug report is complete and
13805 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13806 bell?'' Those bug reports are useless, and we urge everyone to
13807 @emph{refuse to respond to them} except to chide the sender to report
13810 To enable us to fix the bug, you should include all these things:
13814 The version of @value{GDBN}. @value{GDBN} announces it if you start
13815 with no arguments; you can also print it at any time using @code{show
13818 Without this, we will not know whether there is any point in looking for
13819 the bug in the current version of @value{GDBN}.
13822 The type of machine you are using, and the operating system name and
13826 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13827 ``@value{GCC}--2.8.1''.
13830 What compiler (and its version) was used to compile the program you are
13831 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13832 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13833 information; for other compilers, see the documentation for those
13837 The command arguments you gave the compiler to compile your example and
13838 observe the bug. For example, did you use @samp{-O}? To guarantee
13839 you will not omit something important, list them all. A copy of the
13840 Makefile (or the output from make) is sufficient.
13842 If we were to try to guess the arguments, we would probably guess wrong
13843 and then we might not encounter the bug.
13846 A complete input script, and all necessary source files, that will
13850 A description of what behavior you observe that you believe is
13851 incorrect. For example, ``It gets a fatal signal.''
13853 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13854 will certainly notice it. But if the bug is incorrect output, we might
13855 not notice unless it is glaringly wrong. You might as well not give us
13856 a chance to make a mistake.
13858 Even if the problem you experience is a fatal signal, you should still
13859 say so explicitly. Suppose something strange is going on, such as, your
13860 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13861 the C library on your system. (This has happened!) Your copy might
13862 crash and ours would not. If you told us to expect a crash, then when
13863 ours fails to crash, we would know that the bug was not happening for
13864 us. If you had not told us to expect a crash, then we would not be able
13865 to draw any conclusion from our observations.
13868 If you wish to suggest changes to the @value{GDBN} source, send us context
13869 diffs. If you even discuss something in the @value{GDBN} source, refer to
13870 it by context, not by line number.
13872 The line numbers in our development sources will not match those in your
13873 sources. Your line numbers would convey no useful information to us.
13877 Here are some things that are not necessary:
13881 A description of the envelope of the bug.
13883 Often people who encounter a bug spend a lot of time investigating
13884 which changes to the input file will make the bug go away and which
13885 changes will not affect it.
13887 This is often time consuming and not very useful, because the way we
13888 will find the bug is by running a single example under the debugger
13889 with breakpoints, not by pure deduction from a series of examples.
13890 We recommend that you save your time for something else.
13892 Of course, if you can find a simpler example to report @emph{instead}
13893 of the original one, that is a convenience for us. Errors in the
13894 output will be easier to spot, running under the debugger will take
13895 less time, and so on.
13897 However, simplification is not vital; if you do not want to do this,
13898 report the bug anyway and send us the entire test case you used.
13901 A patch for the bug.
13903 A patch for the bug does help us if it is a good one. But do not omit
13904 the necessary information, such as the test case, on the assumption that
13905 a patch is all we need. We might see problems with your patch and decide
13906 to fix the problem another way, or we might not understand it at all.
13908 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13909 construct an example that will make the program follow a certain path
13910 through the code. If you do not send us the example, we will not be able
13911 to construct one, so we will not be able to verify that the bug is fixed.
13913 And if we cannot understand what bug you are trying to fix, or why your
13914 patch should be an improvement, we will not install it. A test case will
13915 help us to understand.
13918 A guess about what the bug is or what it depends on.
13920 Such guesses are usually wrong. Even we cannot guess right about such
13921 things without first using the debugger to find the facts.
13924 @c The readline documentation is distributed with the readline code
13925 @c and consists of the two following files:
13927 @c inc-hist.texinfo
13928 @c Use -I with makeinfo to point to the appropriate directory,
13929 @c environment var TEXINPUTS with TeX.
13930 @include rluser.texinfo
13931 @include inc-hist.texinfo
13934 @node Formatting Documentation
13935 @appendix Formatting Documentation
13937 @cindex @value{GDBN} reference card
13938 @cindex reference card
13939 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13940 for printing with PostScript or Ghostscript, in the @file{gdb}
13941 subdirectory of the main source directory@footnote{In
13942 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13943 release.}. If you can use PostScript or Ghostscript with your printer,
13944 you can print the reference card immediately with @file{refcard.ps}.
13946 The release also includes the source for the reference card. You
13947 can format it, using @TeX{}, by typing:
13953 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13954 mode on US ``letter'' size paper;
13955 that is, on a sheet 11 inches wide by 8.5 inches
13956 high. You will need to specify this form of printing as an option to
13957 your @sc{dvi} output program.
13959 @cindex documentation
13961 All the documentation for @value{GDBN} comes as part of the machine-readable
13962 distribution. The documentation is written in Texinfo format, which is
13963 a documentation system that uses a single source file to produce both
13964 on-line information and a printed manual. You can use one of the Info
13965 formatting commands to create the on-line version of the documentation
13966 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13968 @value{GDBN} includes an already formatted copy of the on-line Info
13969 version of this manual in the @file{gdb} subdirectory. The main Info
13970 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13971 subordinate files matching @samp{gdb.info*} in the same directory. If
13972 necessary, you can print out these files, or read them with any editor;
13973 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13974 Emacs or the standalone @code{info} program, available as part of the
13975 @sc{gnu} Texinfo distribution.
13977 If you want to format these Info files yourself, you need one of the
13978 Info formatting programs, such as @code{texinfo-format-buffer} or
13981 If you have @code{makeinfo} installed, and are in the top level
13982 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13983 version @value{GDBVN}), you can make the Info file by typing:
13990 If you want to typeset and print copies of this manual, you need @TeX{},
13991 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13992 Texinfo definitions file.
13994 @TeX{} is a typesetting program; it does not print files directly, but
13995 produces output files called @sc{dvi} files. To print a typeset
13996 document, you need a program to print @sc{dvi} files. If your system
13997 has @TeX{} installed, chances are it has such a program. The precise
13998 command to use depends on your system; @kbd{lpr -d} is common; another
13999 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
14000 require a file name without any extension or a @samp{.dvi} extension.
14002 @TeX{} also requires a macro definitions file called
14003 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
14004 written in Texinfo format. On its own, @TeX{} cannot either read or
14005 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
14006 and is located in the @file{gdb-@var{version-number}/texinfo}
14009 If you have @TeX{} and a @sc{dvi} printer program installed, you can
14010 typeset and print this manual. First switch to the the @file{gdb}
14011 subdirectory of the main source directory (for example, to
14012 @file{gdb-@value{GDBVN}/gdb}) and type:
14018 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14020 @node Installing GDB
14021 @appendix Installing @value{GDBN}
14022 @cindex configuring @value{GDBN}
14023 @cindex installation
14025 @value{GDBN} comes with a @code{configure} script that automates the process
14026 of preparing @value{GDBN} for installation; you can then use @code{make} to
14027 build the @code{gdb} program.
14029 @c irrelevant in info file; it's as current as the code it lives with.
14030 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14031 look at the @file{README} file in the sources; we may have improved the
14032 installation procedures since publishing this manual.}
14035 The @value{GDBN} distribution includes all the source code you need for
14036 @value{GDBN} in a single directory, whose name is usually composed by
14037 appending the version number to @samp{gdb}.
14039 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14040 @file{gdb-@value{GDBVN}} directory. That directory contains:
14043 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14044 script for configuring @value{GDBN} and all its supporting libraries
14046 @item gdb-@value{GDBVN}/gdb
14047 the source specific to @value{GDBN} itself
14049 @item gdb-@value{GDBVN}/bfd
14050 source for the Binary File Descriptor library
14052 @item gdb-@value{GDBVN}/include
14053 @sc{gnu} include files
14055 @item gdb-@value{GDBVN}/libiberty
14056 source for the @samp{-liberty} free software library
14058 @item gdb-@value{GDBVN}/opcodes
14059 source for the library of opcode tables and disassemblers
14061 @item gdb-@value{GDBVN}/readline
14062 source for the @sc{gnu} command-line interface
14064 @item gdb-@value{GDBVN}/glob
14065 source for the @sc{gnu} filename pattern-matching subroutine
14067 @item gdb-@value{GDBVN}/mmalloc
14068 source for the @sc{gnu} memory-mapped malloc package
14071 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14072 from the @file{gdb-@var{version-number}} source directory, which in
14073 this example is the @file{gdb-@value{GDBVN}} directory.
14075 First switch to the @file{gdb-@var{version-number}} source directory
14076 if you are not already in it; then run @code{configure}. Pass the
14077 identifier for the platform on which @value{GDBN} will run as an
14083 cd gdb-@value{GDBVN}
14084 ./configure @var{host}
14089 where @var{host} is an identifier such as @samp{sun4} or
14090 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14091 (You can often leave off @var{host}; @code{configure} tries to guess the
14092 correct value by examining your system.)
14094 Running @samp{configure @var{host}} and then running @code{make} builds the
14095 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14096 libraries, then @code{gdb} itself. The configured source files, and the
14097 binaries, are left in the corresponding source directories.
14100 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14101 system does not recognize this automatically when you run a different
14102 shell, you may need to run @code{sh} on it explicitly:
14105 sh configure @var{host}
14108 If you run @code{configure} from a directory that contains source
14109 directories for multiple libraries or programs, such as the
14110 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14111 creates configuration files for every directory level underneath (unless
14112 you tell it not to, with the @samp{--norecursion} option).
14114 You can run the @code{configure} script from any of the
14115 subordinate directories in the @value{GDBN} distribution if you only want to
14116 configure that subdirectory, but be sure to specify a path to it.
14118 For example, with version @value{GDBVN}, type the following to configure only
14119 the @code{bfd} subdirectory:
14123 cd gdb-@value{GDBVN}/bfd
14124 ../configure @var{host}
14128 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14129 However, you should make sure that the shell on your path (named by
14130 the @samp{SHELL} environment variable) is publicly readable. Remember
14131 that @value{GDBN} uses the shell to start your program---some systems refuse to
14132 let @value{GDBN} debug child processes whose programs are not readable.
14135 * Separate Objdir:: Compiling @value{GDBN} in another directory
14136 * Config Names:: Specifying names for hosts and targets
14137 * Configure Options:: Summary of options for configure
14140 @node Separate Objdir
14141 @section Compiling @value{GDBN} in another directory
14143 If you want to run @value{GDBN} versions for several host or target machines,
14144 you need a different @code{gdb} compiled for each combination of
14145 host and target. @code{configure} is designed to make this easy by
14146 allowing you to generate each configuration in a separate subdirectory,
14147 rather than in the source directory. If your @code{make} program
14148 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14149 @code{make} in each of these directories builds the @code{gdb}
14150 program specified there.
14152 To build @code{gdb} in a separate directory, run @code{configure}
14153 with the @samp{--srcdir} option to specify where to find the source.
14154 (You also need to specify a path to find @code{configure}
14155 itself from your working directory. If the path to @code{configure}
14156 would be the same as the argument to @samp{--srcdir}, you can leave out
14157 the @samp{--srcdir} option; it is assumed.)
14159 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14160 separate directory for a Sun 4 like this:
14164 cd gdb-@value{GDBVN}
14167 ../gdb-@value{GDBVN}/configure sun4
14172 When @code{configure} builds a configuration using a remote source
14173 directory, it creates a tree for the binaries with the same structure
14174 (and using the same names) as the tree under the source directory. In
14175 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14176 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14177 @file{gdb-sun4/gdb}.
14179 One popular reason to build several @value{GDBN} configurations in separate
14180 directories is to configure @value{GDBN} for cross-compiling (where
14181 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14182 programs that run on another machine---the @dfn{target}).
14183 You specify a cross-debugging target by
14184 giving the @samp{--target=@var{target}} option to @code{configure}.
14186 When you run @code{make} to build a program or library, you must run
14187 it in a configured directory---whatever directory you were in when you
14188 called @code{configure} (or one of its subdirectories).
14190 The @code{Makefile} that @code{configure} generates in each source
14191 directory also runs recursively. If you type @code{make} in a source
14192 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14193 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14194 will build all the required libraries, and then build GDB.
14196 When you have multiple hosts or targets configured in separate
14197 directories, you can run @code{make} on them in parallel (for example,
14198 if they are NFS-mounted on each of the hosts); they will not interfere
14202 @section Specifying names for hosts and targets
14204 The specifications used for hosts and targets in the @code{configure}
14205 script are based on a three-part naming scheme, but some short predefined
14206 aliases are also supported. The full naming scheme encodes three pieces
14207 of information in the following pattern:
14210 @var{architecture}-@var{vendor}-@var{os}
14213 For example, you can use the alias @code{sun4} as a @var{host} argument,
14214 or as the value for @var{target} in a @code{--target=@var{target}}
14215 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14217 The @code{configure} script accompanying @value{GDBN} does not provide
14218 any query facility to list all supported host and target names or
14219 aliases. @code{configure} calls the Bourne shell script
14220 @code{config.sub} to map abbreviations to full names; you can read the
14221 script, if you wish, or you can use it to test your guesses on
14222 abbreviations---for example:
14225 % sh config.sub i386-linux
14227 % sh config.sub alpha-linux
14228 alpha-unknown-linux-gnu
14229 % sh config.sub hp9k700
14231 % sh config.sub sun4
14232 sparc-sun-sunos4.1.1
14233 % sh config.sub sun3
14234 m68k-sun-sunos4.1.1
14235 % sh config.sub i986v
14236 Invalid configuration `i986v': machine `i986v' not recognized
14240 @code{config.sub} is also distributed in the @value{GDBN} source
14241 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14243 @node Configure Options
14244 @section @code{configure} options
14246 Here is a summary of the @code{configure} options and arguments that
14247 are most often useful for building @value{GDBN}. @code{configure} also has
14248 several other options not listed here. @inforef{What Configure
14249 Does,,configure.info}, for a full explanation of @code{configure}.
14252 configure @r{[}--help@r{]}
14253 @r{[}--prefix=@var{dir}@r{]}
14254 @r{[}--exec-prefix=@var{dir}@r{]}
14255 @r{[}--srcdir=@var{dirname}@r{]}
14256 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14257 @r{[}--target=@var{target}@r{]}
14262 You may introduce options with a single @samp{-} rather than
14263 @samp{--} if you prefer; but you may abbreviate option names if you use
14268 Display a quick summary of how to invoke @code{configure}.
14270 @item --prefix=@var{dir}
14271 Configure the source to install programs and files under directory
14274 @item --exec-prefix=@var{dir}
14275 Configure the source to install programs under directory
14278 @c avoid splitting the warning from the explanation:
14280 @item --srcdir=@var{dirname}
14281 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14282 @code{make} that implements the @code{VPATH} feature.}@*
14283 Use this option to make configurations in directories separate from the
14284 @value{GDBN} source directories. Among other things, you can use this to
14285 build (or maintain) several configurations simultaneously, in separate
14286 directories. @code{configure} writes configuration specific files in
14287 the current directory, but arranges for them to use the source in the
14288 directory @var{dirname}. @code{configure} creates directories under
14289 the working directory in parallel to the source directories below
14292 @item --norecursion
14293 Configure only the directory level where @code{configure} is executed; do not
14294 propagate configuration to subdirectories.
14296 @item --target=@var{target}
14297 Configure @value{GDBN} for cross-debugging programs running on the specified
14298 @var{target}. Without this option, @value{GDBN} is configured to debug
14299 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14301 There is no convenient way to generate a list of all available targets.
14303 @item @var{host} @dots{}
14304 Configure @value{GDBN} to run on the specified @var{host}.
14306 There is no convenient way to generate a list of all available hosts.
14309 There are many other options available as well, but they are generally
14310 needed for special purposes only.
14318 % I think something like @colophon should be in texinfo. In the
14320 \long\def\colophon{\hbox to0pt{}\vfill
14321 \centerline{The body of this manual is set in}
14322 \centerline{\fontname\tenrm,}
14323 \centerline{with headings in {\bf\fontname\tenbf}}
14324 \centerline{and examples in {\tt\fontname\tentt}.}
14325 \centerline{{\it\fontname\tenit\/},}
14326 \centerline{{\bf\fontname\tenbf}, and}
14327 \centerline{{\sl\fontname\tensl\/}}
14328 \centerline{are used for emphasis.}\vfill}
14330 % Blame: doc@cygnus.com, 1991.
14333 @c TeX can handle the contents at the start but makeinfo 3.12 can not