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 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
141 * Annotations:: @value{GDBN}'s annotation interface.
142 * GDB/MI:: @value{GDBN}'s Machine Interface.
144 * GDB Bugs:: Reporting bugs in @value{GDBN}
145 * Formatting Documentation:: How to format and print @value{GDBN} documentation
147 * Command Line Editing:: Command Line Editing
148 * Using History Interactively:: Using History Interactively
149 * Installing GDB:: Installing GDB
155 @c the replication sucks, but this avoids a texinfo 3.12 lameness
160 @top Debugging with @value{GDBN}
162 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
164 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
167 Copyright (C) 1988-2000 Free Software Foundation, Inc.
170 * Summary:: Summary of @value{GDBN}
171 * Sample Session:: A sample @value{GDBN} session
173 * Invocation:: Getting in and out of @value{GDBN}
174 * Commands:: @value{GDBN} commands
175 * Running:: Running programs under @value{GDBN}
176 * Stopping:: Stopping and continuing
177 * Stack:: Examining the stack
178 * Source:: Examining source files
179 * Data:: Examining data
181 * Languages:: Using @value{GDBN} with different languages
183 * Symbols:: Examining the symbol table
184 * Altering:: Altering execution
185 * GDB Files:: @value{GDBN} files
186 * Targets:: Specifying a debugging target
187 * Configurations:: Configuration-specific information
188 * Controlling GDB:: Controlling @value{GDBN}
189 * Sequences:: Canned sequences of commands
190 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
191 * Annotations:: @value{GDBN}'s annotation interface.
193 * GDB Bugs:: Reporting bugs in @value{GDBN}
194 * Formatting Documentation:: How to format and print @value{GDBN} documentation
196 * Command Line Editing:: Command Line Editing
197 * Using History Interactively:: Using History Interactively
198 * Installing GDB:: Installing GDB
204 @c TeX can handle the contents at the start but makeinfo 3.12 can not
210 @unnumbered Summary of @value{GDBN}
212 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
213 going on ``inside'' another program while it executes---or what another
214 program was doing at the moment it crashed.
216 @value{GDBN} can do four main kinds of things (plus other things in support of
217 these) to help you catch bugs in the act:
221 Start your program, specifying anything that might affect its behavior.
224 Make your program stop on specified conditions.
227 Examine what has happened, when your program has stopped.
230 Change things in your program, so you can experiment with correcting the
231 effects of one bug and go on to learn about another.
234 You can use @value{GDBN} to debug programs written in C and C++.
235 For more information, see @ref{Support,,Supported languages}.
236 For more information, see @ref{C,,C and C++}.
240 Support for Modula-2 and Chill is partial. For information on Modula-2,
241 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
244 Debugging Pascal programs which use sets, subranges, file variables, or
245 nested functions does not currently work. @value{GDBN} does not support
246 entering expressions, printing values, or similar features using Pascal
250 @value{GDBN} can be used to debug programs written in Fortran, although
251 it may be necessary to refer to some variables with a trailing
255 * Free Software:: Freely redistributable software
256 * Contributors:: Contributors to GDB
260 @unnumberedsec Free software
262 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
263 General Public License
264 (GPL). The GPL gives you the freedom to copy or adapt a licensed
265 program---but every person getting a copy also gets with it the
266 freedom to modify that copy (which means that they must get access to
267 the source code), and the freedom to distribute further copies.
268 Typical software companies use copyrights to limit your freedoms; the
269 Free Software Foundation uses the GPL to preserve these freedoms.
271 Fundamentally, the General Public License is a license which says that
272 you have these freedoms and that you cannot take these freedoms away
276 @unnumberedsec Contributors to @value{GDBN}
278 Richard Stallman was the original author of @value{GDBN}, and of many
279 other @sc{gnu} programs. Many others have contributed to its
280 development. This section attempts to credit major contributors. One
281 of the virtues of free software is that everyone is free to contribute
282 to it; with regret, we cannot actually acknowledge everyone here. The
283 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
284 blow-by-blow account.
286 Changes much prior to version 2.0 are lost in the mists of time.
289 @emph{Plea:} Additions to this section are particularly welcome. If you
290 or your friends (or enemies, to be evenhanded) have been unfairly
291 omitted from this list, we would like to add your names!
294 So that they may not regard their many labors as thankless, we
295 particularly thank those who shepherded @value{GDBN} through major
297 Andrew Cagney (releases 5.0 and 5.1);
298 Jim Blandy (release 4.18);
299 Jason Molenda (release 4.17);
300 Stan Shebs (release 4.14);
301 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
302 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
303 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
304 Jim Kingdon (releases 3.5, 3.4, and 3.3);
305 and Randy Smith (releases 3.2, 3.1, and 3.0).
307 Richard Stallman, assisted at various times by Peter TerMaat, Chris
308 Hanson, and Richard Mlynarik, handled releases through 2.8.
310 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
311 in @value{GDBN}, with significant additional contributions from Per
312 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
313 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
314 much general update work leading to release 3.0).
316 @value{GDBN} uses the BFD subroutine library to examine multiple
317 object-file formats; BFD was a joint project of David V.
318 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
320 David Johnson wrote the original COFF support; Pace Willison did
321 the original support for encapsulated COFF.
323 Brent Benson of Harris Computer Systems contributed DWARF2 support.
325 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
326 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
328 Jean-Daniel Fekete contributed Sun 386i support.
329 Chris Hanson improved the HP9000 support.
330 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
331 David Johnson contributed Encore Umax support.
332 Jyrki Kuoppala contributed Altos 3068 support.
333 Jeff Law contributed HP PA and SOM support.
334 Keith Packard contributed NS32K support.
335 Doug Rabson contributed Acorn Risc Machine support.
336 Bob Rusk contributed Harris Nighthawk CX-UX support.
337 Chris Smith contributed Convex support (and Fortran debugging).
338 Jonathan Stone contributed Pyramid support.
339 Michael Tiemann contributed SPARC support.
340 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
341 Pace Willison contributed Intel 386 support.
342 Jay Vosburgh contributed Symmetry support.
344 Andreas Schwab contributed M68K Linux support.
346 Rich Schaefer and Peter Schauer helped with support of SunOS shared
349 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
350 about several machine instruction sets.
352 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
353 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
354 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
355 and RDI targets, respectively.
357 Brian Fox is the author of the readline libraries providing
358 command-line editing and command history.
360 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
361 Modula-2 support, and contributed the Languages chapter of this manual.
363 Fred Fish wrote most of the support for Unix System Vr4.
364 He also enhanced the command-completion support to cover C@t{++} overloaded
367 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
370 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
372 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
374 Toshiba sponsored the support for the TX39 Mips processor.
376 Matsushita sponsored the support for the MN10200 and MN10300 processors.
378 Fujitsu sponsored the support for SPARClite and FR30 processors.
380 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
383 Michael Snyder added support for tracepoints.
385 Stu Grossman wrote gdbserver.
387 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
388 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
390 The following people at the Hewlett-Packard Company contributed
391 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
392 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
393 compiler, and the terminal user interface: Ben Krepp, Richard Title,
394 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
395 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
396 information in this manual.
398 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
399 Robert Hoehne made significant contributions to the DJGPP port.
401 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
402 development since 1991. Cygnus engineers who have worked on @value{GDBN}
403 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
404 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
405 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
406 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
407 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
408 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
409 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
410 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
411 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
412 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
413 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
414 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
415 Zuhn have made contributions both large and small.
419 @chapter A Sample @value{GDBN} Session
421 You can use this manual at your leisure to read all about @value{GDBN}.
422 However, a handful of commands are enough to get started using the
423 debugger. This chapter illustrates those commands.
426 In this sample session, we emphasize user input like this: @b{input},
427 to make it easier to pick out from the surrounding output.
430 @c FIXME: this example may not be appropriate for some configs, where
431 @c FIXME...primary interest is in remote use.
433 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
434 processor) exhibits the following bug: sometimes, when we change its
435 quote strings from the default, the commands used to capture one macro
436 definition within another stop working. In the following short @code{m4}
437 session, we define a macro @code{foo} which expands to @code{0000}; we
438 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
439 same thing. However, when we change the open quote string to
440 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
441 procedure fails to define a new synonym @code{baz}:
450 @b{define(bar,defn(`foo'))}
454 @b{changequote(<QUOTE>,<UNQUOTE>)}
456 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
459 m4: End of input: 0: fatal error: EOF in string
463 Let us use @value{GDBN} to try to see what is going on.
466 $ @b{@value{GDBP} m4}
467 @c FIXME: this falsifies the exact text played out, to permit smallbook
468 @c FIXME... format to come out better.
469 @value{GDBN} is free software and you are welcome to distribute copies
470 of it under certain conditions; type "show copying" to see
472 There is absolutely no warranty for @value{GDBN}; type "show warranty"
475 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
480 @value{GDBN} reads only enough symbol data to know where to find the
481 rest when needed; as a result, the first prompt comes up very quickly.
482 We now tell @value{GDBN} to use a narrower display width than usual, so
483 that examples fit in this manual.
486 (@value{GDBP}) @b{set width 70}
490 We need to see how the @code{m4} built-in @code{changequote} works.
491 Having looked at the source, we know the relevant subroutine is
492 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
493 @code{break} command.
496 (@value{GDBP}) @b{break m4_changequote}
497 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
501 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
502 control; as long as control does not reach the @code{m4_changequote}
503 subroutine, the program runs as usual:
506 (@value{GDBP}) @b{run}
507 Starting program: /work/Editorial/gdb/gnu/m4/m4
515 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
516 suspends execution of @code{m4}, displaying information about the
517 context where it stops.
520 @b{changequote(<QUOTE>,<UNQUOTE>)}
522 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
524 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
528 Now we use the command @code{n} (@code{next}) to advance execution to
529 the next line of the current function.
533 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
538 @code{set_quotes} looks like a promising subroutine. We can go into it
539 by using the command @code{s} (@code{step}) instead of @code{next}.
540 @code{step} goes to the next line to be executed in @emph{any}
541 subroutine, so it steps into @code{set_quotes}.
545 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
547 530 if (lquote != def_lquote)
551 The display that shows the subroutine where @code{m4} is now
552 suspended (and its arguments) is called a stack frame display. It
553 shows a summary of the stack. We can use the @code{backtrace}
554 command (which can also be spelled @code{bt}), to see where we are
555 in the stack as a whole: the @code{backtrace} command displays a
556 stack frame for each active subroutine.
559 (@value{GDBP}) @b{bt}
560 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
562 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
564 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
565 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
567 #4 0x79dc in expand_input () at macro.c:40
568 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
572 We step through a few more lines to see what happens. The first two
573 times, we can use @samp{s}; the next two times we use @code{n} to avoid
574 falling into the @code{xstrdup} subroutine.
578 0x3b5c 532 if (rquote != def_rquote)
580 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
581 def_lquote : xstrdup(lq);
583 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
586 538 len_lquote = strlen(rquote);
590 The last line displayed looks a little odd; we can examine the variables
591 @code{lquote} and @code{rquote} to see if they are in fact the new left
592 and right quotes we specified. We use the command @code{p}
593 (@code{print}) to see their values.
596 (@value{GDBP}) @b{p lquote}
597 $1 = 0x35d40 "<QUOTE>"
598 (@value{GDBP}) @b{p rquote}
599 $2 = 0x35d50 "<UNQUOTE>"
603 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
604 To look at some context, we can display ten lines of source
605 surrounding the current line with the @code{l} (@code{list}) command.
611 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
613 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
616 538 len_lquote = strlen(rquote);
617 539 len_rquote = strlen(lquote);
624 Let us step past the two lines that set @code{len_lquote} and
625 @code{len_rquote}, and then examine the values of those variables.
629 539 len_rquote = strlen(lquote);
632 (@value{GDBP}) @b{p len_lquote}
634 (@value{GDBP}) @b{p len_rquote}
639 That certainly looks wrong, assuming @code{len_lquote} and
640 @code{len_rquote} are meant to be the lengths of @code{lquote} and
641 @code{rquote} respectively. We can set them to better values using
642 the @code{p} command, since it can print the value of
643 any expression---and that expression can include subroutine calls and
647 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
649 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
654 Is that enough to fix the problem of using the new quotes with the
655 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
656 executing with the @code{c} (@code{continue}) command, and then try the
657 example that caused trouble initially:
663 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
670 Success! The new quotes now work just as well as the default ones. The
671 problem seems to have been just the two typos defining the wrong
672 lengths. We allow @code{m4} exit by giving it an EOF as input:
676 Program exited normally.
680 The message @samp{Program exited normally.} is from @value{GDBN}; it
681 indicates @code{m4} has finished executing. We can end our @value{GDBN}
682 session with the @value{GDBN} @code{quit} command.
685 (@value{GDBP}) @b{quit}
689 @chapter Getting In and Out of @value{GDBN}
691 This chapter discusses how to start @value{GDBN}, and how to get out of it.
695 type @samp{@value{GDBP}} to start @value{GDBN}.
697 type @kbd{quit} or @kbd{C-d} to exit.
701 * Invoking GDB:: How to start @value{GDBN}
702 * Quitting GDB:: How to quit @value{GDBN}
703 * Shell Commands:: How to use shell commands inside @value{GDBN}
707 @section Invoking @value{GDBN}
709 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
710 @value{GDBN} reads commands from the terminal until you tell it to exit.
712 You can also run @code{@value{GDBP}} with a variety of arguments and options,
713 to specify more of your debugging environment at the outset.
715 The command-line options described here are designed
716 to cover a variety of situations; in some environments, some of these
717 options may effectively be unavailable.
719 The most usual way to start @value{GDBN} is with one argument,
720 specifying an executable program:
723 @value{GDBP} @var{program}
727 You can also start with both an executable program and a core file
731 @value{GDBP} @var{program} @var{core}
734 You can, instead, specify a process ID as a second argument, if you want
735 to debug a running process:
738 @value{GDBP} @var{program} 1234
742 would attach @value{GDBN} to process @code{1234} (unless you also have a file
743 named @file{1234}; @value{GDBN} does check for a core file first).
745 Taking advantage of the second command-line argument requires a fairly
746 complete operating system; when you use @value{GDBN} as a remote
747 debugger attached to a bare board, there may not be any notion of
748 ``process'', and there is often no way to get a core dump. @value{GDBN}
749 will warn you if it is unable to attach or to read core dumps.
751 You can run @code{@value{GDBP}} without printing the front material, which describes
752 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
759 You can further control how @value{GDBN} starts up by using command-line
760 options. @value{GDBN} itself can remind you of the options available.
770 to display all available options and briefly describe their use
771 (@samp{@value{GDBP} -h} is a shorter equivalent).
773 All options and command line arguments you give are processed
774 in sequential order. The order makes a difference when the
775 @samp{-x} option is used.
779 * File Options:: Choosing files
780 * Mode Options:: Choosing modes
784 @subsection Choosing files
786 When @value{GDBN} starts, it reads any arguments other than options as
787 specifying an executable file and core file (or process ID). This is
788 the same as if the arguments were specified by the @samp{-se} and
789 @samp{-c} options respectively. (@value{GDBN} reads the first argument
790 that does not have an associated option flag as equivalent to the
791 @samp{-se} option followed by that argument; and the second argument
792 that does not have an associated option flag, if any, as equivalent to
793 the @samp{-c} option followed by that argument.)
795 If @value{GDBN} has not been configured to included core file support,
796 such as for most embedded targets, then it will complain about a second
797 argument and ignore it.
799 Many options have both long and short forms; both are shown in the
800 following list. @value{GDBN} also recognizes the long forms if you truncate
801 them, so long as enough of the option is present to be unambiguous.
802 (If you prefer, you can flag option arguments with @samp{--} rather
803 than @samp{-}, though we illustrate the more usual convention.)
805 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
806 @c way, both those who look for -foo and --foo in the index, will find
810 @item -symbols @var{file}
812 @cindex @code{--symbols}
814 Read symbol table from file @var{file}.
816 @item -exec @var{file}
818 @cindex @code{--exec}
820 Use file @var{file} as the executable file to execute when appropriate,
821 and for examining pure data in conjunction with a core dump.
825 Read symbol table from file @var{file} and use it as the executable
828 @item -core @var{file}
830 @cindex @code{--core}
832 Use file @var{file} as a core dump to examine.
834 @item -c @var{number}
835 Connect to process ID @var{number}, as with the @code{attach} command
836 (unless there is a file in core-dump format named @var{number}, in which
837 case @samp{-c} specifies that file as a core dump to read).
839 @item -command @var{file}
841 @cindex @code{--command}
843 Execute @value{GDBN} commands from file @var{file}. @xref{Command
844 Files,, Command files}.
846 @item -directory @var{directory}
847 @itemx -d @var{directory}
848 @cindex @code{--directory}
850 Add @var{directory} to the path to search for source files.
854 @cindex @code{--mapped}
856 @emph{Warning: this option depends on operating system facilities that are not
857 supported on all systems.}@*
858 If memory-mapped files are available on your system through the @code{mmap}
859 system call, you can use this option
860 to have @value{GDBN} write the symbols from your
861 program into a reusable file in the current directory. If the program you are debugging is
862 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
863 Future @value{GDBN} debugging sessions notice the presence of this file,
864 and can quickly map in symbol information from it, rather than reading
865 the symbol table from the executable program.
867 The @file{.syms} file is specific to the host machine where @value{GDBN}
868 is run. It holds an exact image of the internal @value{GDBN} symbol
869 table. It cannot be shared across multiple host platforms.
873 @cindex @code{--readnow}
875 Read each symbol file's entire symbol table immediately, rather than
876 the default, which is to read it incrementally as it is needed.
877 This makes startup slower, but makes future operations faster.
881 You typically combine the @code{-mapped} and @code{-readnow} options in
882 order to build a @file{.syms} file that contains complete symbol
883 information. (@xref{Files,,Commands to specify files}, for information
884 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
885 but build a @file{.syms} file for future use is:
888 gdb -batch -nx -mapped -readnow programname
892 @subsection Choosing modes
894 You can run @value{GDBN} in various alternative modes---for example, in
895 batch mode or quiet mode.
902 Do not execute commands found in any initialization files (normally
903 called @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally,
904 @value{GDBN} executes the commands in these files after all the command
905 options and arguments have been processed. @xref{Command Files,,Command
911 @cindex @code{--quiet}
912 @cindex @code{--silent}
914 ``Quiet''. Do not print the introductory and copyright messages. These
915 messages are also suppressed in batch mode.
918 @cindex @code{--batch}
919 Run in batch mode. Exit with status @code{0} after processing all the
920 command files specified with @samp{-x} (and all commands from
921 initialization files, if not inhibited with @samp{-n}). Exit with
922 nonzero status if an error occurs in executing the @value{GDBN} commands
923 in the command files.
925 Batch mode may be useful for running @value{GDBN} as a filter, for
926 example to download and run a program on another computer; in order to
927 make this more useful, the message
930 Program exited normally.
934 (which is ordinarily issued whenever a program running under
935 @value{GDBN} control terminates) is not issued when running in batch
940 @cindex @code{--nowindows}
942 ``No windows''. If @value{GDBN} comes with a graphical user interface
943 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
944 interface. If no GUI is available, this option has no effect.
948 @cindex @code{--windows}
950 If @value{GDBN} includes a GUI, then this option requires it to be
953 @item -cd @var{directory}
955 Run @value{GDBN} using @var{directory} as its working directory,
956 instead of the current directory.
960 @cindex @code{--fullname}
962 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
963 subprocess. It tells @value{GDBN} to output the full file name and line
964 number in a standard, recognizable fashion each time a stack frame is
965 displayed (which includes each time your program stops). This
966 recognizable format looks like two @samp{\032} characters, followed by
967 the file name, line number and character position separated by colons,
968 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
969 @samp{\032} characters as a signal to display the source code for the
973 @cindex @code{--epoch}
974 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
975 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
976 routines so as to allow Epoch to display values of expressions in a
979 @item -annotate @var{level}
980 @cindex @code{--annotate}
981 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
982 effect is identical to using @samp{set annotate @var{level}}
983 (@pxref{Annotations}).
984 Annotation level controls how much information does @value{GDBN} print
985 together with its prompt, values of expressions, source lines, and other
986 types of output. Level 0 is the normal, level 1 is for use when
987 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
988 maximum annotation suitable for programs that control @value{GDBN}.
991 @cindex @code{--async}
992 Use the asynchronous event loop for the command-line interface.
993 @value{GDBN} processes all events, such as user keyboard input, via a
994 special event loop. This allows @value{GDBN} to accept and process user
995 commands in parallel with the debugged process being
996 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
997 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
998 suspended when the debuggee runs.}, so you don't need to wait for
999 control to return to @value{GDBN} before you type the next command.
1000 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1001 operation is not yet in place, so @samp{-async} does not work fully
1003 @c FIXME: when the target side of the event loop is done, the above NOTE
1004 @c should be removed.
1006 When the standard input is connected to a terminal device, @value{GDBN}
1007 uses the asynchronous event loop by default, unless disabled by the
1008 @samp{-noasync} option.
1011 @cindex @code{--noasync}
1012 Disable the asynchronous event loop for the command-line interface.
1014 @item -baud @var{bps}
1016 @cindex @code{--baud}
1018 Set the line speed (baud rate or bits per second) of any serial
1019 interface used by @value{GDBN} for remote debugging.
1021 @item -tty @var{device}
1022 @itemx -t @var{device}
1023 @cindex @code{--tty}
1025 Run using @var{device} for your program's standard input and output.
1026 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1028 @c resolve the situation of these eventually
1030 @c @cindex @code{--tui}
1031 @c Use a Terminal User Interface. For information, use your Web browser to
1032 @c read the file @file{TUI.html}, which is usually installed in the
1033 @c directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
1034 @c this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
1035 @c @value{GDBN} under @sc{gnu} Emacs}).
1038 @c @cindex @code{--xdb}
1039 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1040 @c For information, see the file @file{xdb_trans.html}, which is usually
1041 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1044 @item -interpreter @var{interp}
1045 @cindex @code{--interpreter}
1046 Use the interpreter @var{interp} for interface with the controlling
1047 program or device. This option is meant to be set by programs which
1048 communicate with @value{GDBN} using it as a back end.
1050 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1051 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1052 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1053 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1056 @cindex @code{--write}
1057 Open the executable and core files for both reading and writing. This
1058 is equivalent to the @samp{set write on} command inside @value{GDBN}
1062 @cindex @code{--statistics}
1063 This option causes @value{GDBN} to print statistics about time and
1064 memory usage after it completes each command and returns to the prompt.
1067 @cindex @code{--version}
1068 This option causes @value{GDBN} to print its version number and
1069 no-warranty blurb, and exit.
1074 @section Quitting @value{GDBN}
1075 @cindex exiting @value{GDBN}
1076 @cindex leaving @value{GDBN}
1079 @kindex quit @r{[}@var{expression}@r{]}
1080 @kindex q @r{(@code{quit})}
1081 @item quit @r{[}@var{expression}@r{]}
1083 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1084 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1085 do not supply @var{expression}, @value{GDBN} will terminate normally;
1086 otherwise it will terminate using the result of @var{expression} as the
1091 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1092 terminates the action of any @value{GDBN} command that is in progress and
1093 returns to @value{GDBN} command level. It is safe to type the interrupt
1094 character at any time because @value{GDBN} does not allow it to take effect
1095 until a time when it is safe.
1097 If you have been using @value{GDBN} to control an attached process or
1098 device, you can release it with the @code{detach} command
1099 (@pxref{Attach, ,Debugging an already-running process}).
1101 @node Shell Commands
1102 @section Shell commands
1104 If you need to execute occasional shell commands during your
1105 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1106 just use the @code{shell} command.
1110 @cindex shell escape
1111 @item shell @var{command string}
1112 Invoke a standard shell to execute @var{command string}.
1113 If it exists, the environment variable @code{SHELL} determines which
1114 shell to run. Otherwise @value{GDBN} uses the default shell
1115 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1118 The utility @code{make} is often needed in development environments.
1119 You do not have to use the @code{shell} command for this purpose in
1124 @cindex calling make
1125 @item make @var{make-args}
1126 Execute the @code{make} program with the specified
1127 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1131 @chapter @value{GDBN} Commands
1133 You can abbreviate a @value{GDBN} command to the first few letters of the command
1134 name, if that abbreviation is unambiguous; and you can repeat certain
1135 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1136 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1137 show you the alternatives available, if there is more than one possibility).
1140 * Command Syntax:: How to give commands to @value{GDBN}
1141 * Completion:: Command completion
1142 * Help:: How to ask @value{GDBN} for help
1145 @node Command Syntax
1146 @section Command syntax
1148 A @value{GDBN} command is a single line of input. There is no limit on
1149 how long it can be. It starts with a command name, which is followed by
1150 arguments whose meaning depends on the command name. For example, the
1151 command @code{step} accepts an argument which is the number of times to
1152 step, as in @samp{step 5}. You can also use the @code{step} command
1153 with no arguments. Some commands do not allow any arguments.
1155 @cindex abbreviation
1156 @value{GDBN} command names may always be truncated if that abbreviation is
1157 unambiguous. Other possible command abbreviations are listed in the
1158 documentation for individual commands. In some cases, even ambiguous
1159 abbreviations are allowed; for example, @code{s} is specially defined as
1160 equivalent to @code{step} even though there are other commands whose
1161 names start with @code{s}. You can test abbreviations by using them as
1162 arguments to the @code{help} command.
1164 @cindex repeating commands
1165 @kindex RET @r{(repeat last command)}
1166 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1167 repeat the previous command. Certain commands (for example, @code{run})
1168 will not repeat this way; these are commands whose unintentional
1169 repetition might cause trouble and which you are unlikely to want to
1172 The @code{list} and @code{x} commands, when you repeat them with
1173 @key{RET}, construct new arguments rather than repeating
1174 exactly as typed. This permits easy scanning of source or memory.
1176 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1177 output, in a way similar to the common utility @code{more}
1178 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1179 @key{RET} too many in this situation, @value{GDBN} disables command
1180 repetition after any command that generates this sort of display.
1182 @kindex # @r{(a comment)}
1184 Any text from a @kbd{#} to the end of the line is a comment; it does
1185 nothing. This is useful mainly in command files (@pxref{Command
1186 Files,,Command files}).
1189 @section Command completion
1192 @cindex word completion
1193 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1194 only one possibility; it can also show you what the valid possibilities
1195 are for the next word in a command, at any time. This works for @value{GDBN}
1196 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1198 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1199 of a word. If there is only one possibility, @value{GDBN} fills in the
1200 word, and waits for you to finish the command (or press @key{RET} to
1201 enter it). For example, if you type
1203 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1204 @c complete accuracy in these examples; space introduced for clarity.
1205 @c If texinfo enhancements make it unnecessary, it would be nice to
1206 @c replace " @key" by "@key" in the following...
1208 (@value{GDBP}) info bre @key{TAB}
1212 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1213 the only @code{info} subcommand beginning with @samp{bre}:
1216 (@value{GDBP}) info breakpoints
1220 You can either press @key{RET} at this point, to run the @code{info
1221 breakpoints} command, or backspace and enter something else, if
1222 @samp{breakpoints} does not look like the command you expected. (If you
1223 were sure you wanted @code{info breakpoints} in the first place, you
1224 might as well just type @key{RET} immediately after @samp{info bre},
1225 to exploit command abbreviations rather than command completion).
1227 If there is more than one possibility for the next word when you press
1228 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1229 characters and try again, or just press @key{TAB} a second time;
1230 @value{GDBN} displays all the possible completions for that word. For
1231 example, you might want to set a breakpoint on a subroutine whose name
1232 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1233 just sounds the bell. Typing @key{TAB} again displays all the
1234 function names in your program that begin with those characters, for
1238 (@value{GDBP}) b make_ @key{TAB}
1239 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1240 make_a_section_from_file make_environ
1241 make_abs_section make_function_type
1242 make_blockvector make_pointer_type
1243 make_cleanup make_reference_type
1244 make_command make_symbol_completion_list
1245 (@value{GDBP}) b make_
1249 After displaying the available possibilities, @value{GDBN} copies your
1250 partial input (@samp{b make_} in the example) so you can finish the
1253 If you just want to see the list of alternatives in the first place, you
1254 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1255 means @kbd{@key{META} ?}. You can type this either by holding down a
1256 key designated as the @key{META} shift on your keyboard (if there is
1257 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1259 @cindex quotes in commands
1260 @cindex completion of quoted strings
1261 Sometimes the string you need, while logically a ``word'', may contain
1262 parentheses or other characters that @value{GDBN} normally excludes from
1263 its notion of a word. To permit word completion to work in this
1264 situation, you may enclose words in @code{'} (single quote marks) in
1265 @value{GDBN} commands.
1267 The most likely situation where you might need this is in typing the
1268 name of a C@t{++} function. This is because C@t{++} allows function
1269 overloading (multiple definitions of the same function, distinguished
1270 by argument type). For example, when you want to set a breakpoint you
1271 may need to distinguish whether you mean the version of @code{name}
1272 that takes an @code{int} parameter, @code{name(int)}, or the version
1273 that takes a @code{float} parameter, @code{name(float)}. To use the
1274 word-completion facilities in this situation, type a single quote
1275 @code{'} at the beginning of the function name. This alerts
1276 @value{GDBN} that it may need to consider more information than usual
1277 when you press @key{TAB} or @kbd{M-?} to request word completion:
1280 (@value{GDBP}) b 'bubble( @kbd{M-?}
1281 bubble(double,double) bubble(int,int)
1282 (@value{GDBP}) b 'bubble(
1285 In some cases, @value{GDBN} can tell that completing a name requires using
1286 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1287 completing as much as it can) if you do not type the quote in the first
1291 (@value{GDBP}) b bub @key{TAB}
1292 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1293 (@value{GDBP}) b 'bubble(
1297 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1298 you have not yet started typing the argument list when you ask for
1299 completion on an overloaded symbol.
1301 For more information about overloaded functions, see @ref{C plus plus
1302 expressions, ,C@t{++} expressions}. You can use the command @code{set
1303 overload-resolution off} to disable overload resolution;
1304 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1308 @section Getting help
1309 @cindex online documentation
1312 You can always ask @value{GDBN} itself for information on its commands,
1313 using the command @code{help}.
1316 @kindex h @r{(@code{help})}
1319 You can use @code{help} (abbreviated @code{h}) with no arguments to
1320 display a short list of named classes of commands:
1324 List of classes of commands:
1326 aliases -- Aliases of other commands
1327 breakpoints -- Making program stop at certain points
1328 data -- Examining data
1329 files -- Specifying and examining files
1330 internals -- Maintenance commands
1331 obscure -- Obscure features
1332 running -- Running the program
1333 stack -- Examining the stack
1334 status -- Status inquiries
1335 support -- Support facilities
1336 tracepoints -- Tracing of program execution without@*
1337 stopping the program
1338 user-defined -- User-defined commands
1340 Type "help" followed by a class name for a list of
1341 commands in that class.
1342 Type "help" followed by command name for full
1344 Command name abbreviations are allowed if unambiguous.
1347 @c the above line break eliminates huge line overfull...
1349 @item help @var{class}
1350 Using one of the general help classes as an argument, you can get a
1351 list of the individual commands in that class. For example, here is the
1352 help display for the class @code{status}:
1355 (@value{GDBP}) help status
1360 @c Line break in "show" line falsifies real output, but needed
1361 @c to fit in smallbook page size.
1362 info -- Generic command for showing things
1363 about the program being debugged
1364 show -- Generic command for showing things
1367 Type "help" followed by command name for full
1369 Command name abbreviations are allowed if unambiguous.
1373 @item help @var{command}
1374 With a command name as @code{help} argument, @value{GDBN} displays a
1375 short paragraph on how to use that command.
1378 @item apropos @var{args}
1379 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1380 commands, and their documentation, for the regular expression specified in
1381 @var{args}. It prints out all matches found. For example:
1392 set symbol-reloading -- Set dynamic symbol table reloading
1393 multiple times in one run
1394 show symbol-reloading -- Show dynamic symbol table reloading
1395 multiple times in one run
1400 @item complete @var{args}
1401 The @code{complete @var{args}} command lists all the possible completions
1402 for the beginning of a command. Use @var{args} to specify the beginning of the
1403 command you want completed. For example:
1409 @noindent results in:
1420 @noindent This is intended for use by @sc{gnu} Emacs.
1423 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1424 and @code{show} to inquire about the state of your program, or the state
1425 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1426 manual introduces each of them in the appropriate context. The listings
1427 under @code{info} and under @code{show} in the Index point to
1428 all the sub-commands. @xref{Index}.
1433 @kindex i @r{(@code{info})}
1435 This command (abbreviated @code{i}) is for describing the state of your
1436 program. For example, you can list the arguments given to your program
1437 with @code{info args}, list the registers currently in use with @code{info
1438 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1439 You can get a complete list of the @code{info} sub-commands with
1440 @w{@code{help info}}.
1444 You can assign the result of an expression to an environment variable with
1445 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1446 @code{set prompt $}.
1450 In contrast to @code{info}, @code{show} is for describing the state of
1451 @value{GDBN} itself.
1452 You can change most of the things you can @code{show}, by using the
1453 related command @code{set}; for example, you can control what number
1454 system is used for displays with @code{set radix}, or simply inquire
1455 which is currently in use with @code{show radix}.
1458 To display all the settable parameters and their current
1459 values, you can use @code{show} with no arguments; you may also use
1460 @code{info set}. Both commands produce the same display.
1461 @c FIXME: "info set" violates the rule that "info" is for state of
1462 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1463 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1467 Here are three miscellaneous @code{show} subcommands, all of which are
1468 exceptional in lacking corresponding @code{set} commands:
1471 @kindex show version
1472 @cindex version number
1474 Show what version of @value{GDBN} is running. You should include this
1475 information in @value{GDBN} bug-reports. If multiple versions of
1476 @value{GDBN} are in use at your site, you may need to determine which
1477 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1478 commands are introduced, and old ones may wither away. Also, many
1479 system vendors ship variant versions of @value{GDBN}, and there are
1480 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1481 The version number is the same as the one announced when you start
1484 @kindex show copying
1486 Display information about permission for copying @value{GDBN}.
1488 @kindex show warranty
1490 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1491 if your version of @value{GDBN} comes with one.
1496 @chapter Running Programs Under @value{GDBN}
1498 When you run a program under @value{GDBN}, you must first generate
1499 debugging information when you compile it.
1501 You may start @value{GDBN} with its arguments, if any, in an environment
1502 of your choice. If you are doing native debugging, you may redirect
1503 your program's input and output, debug an already running process, or
1504 kill a child process.
1507 * Compilation:: Compiling for debugging
1508 * Starting:: Starting your program
1509 * Arguments:: Your program's arguments
1510 * Environment:: Your program's environment
1512 * Working Directory:: Your program's working directory
1513 * Input/Output:: Your program's input and output
1514 * Attach:: Debugging an already-running process
1515 * Kill Process:: Killing the child process
1517 * Threads:: Debugging programs with multiple threads
1518 * Processes:: Debugging programs with multiple processes
1522 @section Compiling for debugging
1524 In order to debug a program effectively, you need to generate
1525 debugging information when you compile it. This debugging information
1526 is stored in the object file; it describes the data type of each
1527 variable or function and the correspondence between source line numbers
1528 and addresses in the executable code.
1530 To request debugging information, specify the @samp{-g} option when you run
1533 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1534 options together. Using those compilers, you cannot generate optimized
1535 executables containing debugging information.
1537 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1538 without @samp{-O}, making it possible to debug optimized code. We
1539 recommend that you @emph{always} use @samp{-g} whenever you compile a
1540 program. You may think your program is correct, but there is no sense
1541 in pushing your luck.
1543 @cindex optimized code, debugging
1544 @cindex debugging optimized code
1545 When you debug a program compiled with @samp{-g -O}, remember that the
1546 optimizer is rearranging your code; the debugger shows you what is
1547 really there. Do not be too surprised when the execution path does not
1548 exactly match your source file! An extreme example: if you define a
1549 variable, but never use it, @value{GDBN} never sees that
1550 variable---because the compiler optimizes it out of existence.
1552 Some things do not work as well with @samp{-g -O} as with just
1553 @samp{-g}, particularly on machines with instruction scheduling. If in
1554 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1555 please report it to us as a bug (including a test case!).
1557 Older versions of the @sc{gnu} C compiler permitted a variant option
1558 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1559 format; if your @sc{gnu} C compiler has this option, do not use it.
1563 @section Starting your program
1569 @kindex r @r{(@code{run})}
1572 Use the @code{run} command to start your program under @value{GDBN}.
1573 You must first specify the program name (except on VxWorks) with an
1574 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1575 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1576 (@pxref{Files, ,Commands to specify files}).
1580 If you are running your program in an execution environment that
1581 supports processes, @code{run} creates an inferior process and makes
1582 that process run your program. (In environments without processes,
1583 @code{run} jumps to the start of your program.)
1585 The execution of a program is affected by certain information it
1586 receives from its superior. @value{GDBN} provides ways to specify this
1587 information, which you must do @emph{before} starting your program. (You
1588 can change it after starting your program, but such changes only affect
1589 your program the next time you start it.) This information may be
1590 divided into four categories:
1593 @item The @emph{arguments.}
1594 Specify the arguments to give your program as the arguments of the
1595 @code{run} command. If a shell is available on your target, the shell
1596 is used to pass the arguments, so that you may use normal conventions
1597 (such as wildcard expansion or variable substitution) in describing
1599 In Unix systems, you can control which shell is used with the
1600 @code{SHELL} environment variable.
1601 @xref{Arguments, ,Your program's arguments}.
1603 @item The @emph{environment.}
1604 Your program normally inherits its environment from @value{GDBN}, but you can
1605 use the @value{GDBN} commands @code{set environment} and @code{unset
1606 environment} to change parts of the environment that affect
1607 your program. @xref{Environment, ,Your program's environment}.
1609 @item The @emph{working directory.}
1610 Your program inherits its working directory from @value{GDBN}. You can set
1611 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1612 @xref{Working Directory, ,Your program's working directory}.
1614 @item The @emph{standard input and output.}
1615 Your program normally uses the same device for standard input and
1616 standard output as @value{GDBN} is using. You can redirect input and output
1617 in the @code{run} command line, or you can use the @code{tty} command to
1618 set a different device for your program.
1619 @xref{Input/Output, ,Your program's input and output}.
1622 @emph{Warning:} While input and output redirection work, you cannot use
1623 pipes to pass the output of the program you are debugging to another
1624 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1628 When you issue the @code{run} command, your program begins to execute
1629 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1630 of how to arrange for your program to stop. Once your program has
1631 stopped, you may call functions in your program, using the @code{print}
1632 or @code{call} commands. @xref{Data, ,Examining Data}.
1634 If the modification time of your symbol file has changed since the last
1635 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1636 table, and reads it again. When it does this, @value{GDBN} tries to retain
1637 your current breakpoints.
1640 @section Your program's arguments
1642 @cindex arguments (to your program)
1643 The arguments to your program can be specified by the arguments of the
1645 They are passed to a shell, which expands wildcard characters and
1646 performs redirection of I/O, and thence to your program. Your
1647 @code{SHELL} environment variable (if it exists) specifies what shell
1648 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1649 the default shell (@file{/bin/sh} on Unix).
1651 On non-Unix systems, the program is usually invoked directly by
1652 @value{GDBN}, which emulates I/O redirection via the appropriate system
1653 calls, and the wildcard characters are expanded by the startup code of
1654 the program, not by the shell.
1656 @code{run} with no arguments uses the same arguments used by the previous
1657 @code{run}, or those set by the @code{set args} command.
1662 Specify the arguments to be used the next time your program is run. If
1663 @code{set args} has no arguments, @code{run} executes your program
1664 with no arguments. Once you have run your program with arguments,
1665 using @code{set args} before the next @code{run} is the only way to run
1666 it again without arguments.
1670 Show the arguments to give your program when it is started.
1674 @section Your program's environment
1676 @cindex environment (of your program)
1677 The @dfn{environment} consists of a set of environment variables and
1678 their values. Environment variables conventionally record such things as
1679 your user name, your home directory, your terminal type, and your search
1680 path for programs to run. Usually you set up environment variables with
1681 the shell and they are inherited by all the other programs you run. When
1682 debugging, it can be useful to try running your program with a modified
1683 environment without having to start @value{GDBN} over again.
1687 @item path @var{directory}
1688 Add @var{directory} to the front of the @code{PATH} environment variable
1689 (the search path for executables) that will be passed to your program.
1690 The value of @code{PATH} used by @value{GDBN} does not change.
1691 You may specify several directory names, separated by whitespace or by a
1692 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1693 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1694 is moved to the front, so it is searched sooner.
1696 You can use the string @samp{$cwd} to refer to whatever is the current
1697 working directory at the time @value{GDBN} searches the path. If you
1698 use @samp{.} instead, it refers to the directory where you executed the
1699 @code{path} command. @value{GDBN} replaces @samp{.} in the
1700 @var{directory} argument (with the current path) before adding
1701 @var{directory} to the search path.
1702 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1703 @c document that, since repeating it would be a no-op.
1707 Display the list of search paths for executables (the @code{PATH}
1708 environment variable).
1710 @kindex show environment
1711 @item show environment @r{[}@var{varname}@r{]}
1712 Print the value of environment variable @var{varname} to be given to
1713 your program when it starts. If you do not supply @var{varname},
1714 print the names and values of all environment variables to be given to
1715 your program. You can abbreviate @code{environment} as @code{env}.
1717 @kindex set environment
1718 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1719 Set environment variable @var{varname} to @var{value}. The value
1720 changes for your program only, not for @value{GDBN} itself. @var{value} may
1721 be any string; the values of environment variables are just strings, and
1722 any interpretation is supplied by your program itself. The @var{value}
1723 parameter is optional; if it is eliminated, the variable is set to a
1725 @c "any string" here does not include leading, trailing
1726 @c blanks. Gnu asks: does anyone care?
1728 For example, this command:
1735 tells the debugged program, when subsequently run, that its user is named
1736 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1737 are not actually required.)
1739 @kindex unset environment
1740 @item unset environment @var{varname}
1741 Remove variable @var{varname} from the environment to be passed to your
1742 program. This is different from @samp{set env @var{varname} =};
1743 @code{unset environment} removes the variable from the environment,
1744 rather than assigning it an empty value.
1747 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1749 by your @code{SHELL} environment variable if it exists (or
1750 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1751 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1752 @file{.bashrc} for BASH---any variables you set in that file affect
1753 your program. You may wish to move setting of environment variables to
1754 files that are only run when you sign on, such as @file{.login} or
1757 @node Working Directory
1758 @section Your program's working directory
1760 @cindex working directory (of your program)
1761 Each time you start your program with @code{run}, it inherits its
1762 working directory from the current working directory of @value{GDBN}.
1763 The @value{GDBN} working directory is initially whatever it inherited
1764 from its parent process (typically the shell), but you can specify a new
1765 working directory in @value{GDBN} with the @code{cd} command.
1767 The @value{GDBN} working directory also serves as a default for the commands
1768 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1773 @item cd @var{directory}
1774 Set the @value{GDBN} working directory to @var{directory}.
1778 Print the @value{GDBN} working directory.
1782 @section Your program's input and output
1787 By default, the program you run under @value{GDBN} does input and output to
1788 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1789 to its own terminal modes to interact with you, but it records the terminal
1790 modes your program was using and switches back to them when you continue
1791 running your program.
1794 @kindex info terminal
1796 Displays information recorded by @value{GDBN} about the terminal modes your
1800 You can redirect your program's input and/or output using shell
1801 redirection with the @code{run} command. For example,
1808 starts your program, diverting its output to the file @file{outfile}.
1811 @cindex controlling terminal
1812 Another way to specify where your program should do input and output is
1813 with the @code{tty} command. This command accepts a file name as
1814 argument, and causes this file to be the default for future @code{run}
1815 commands. It also resets the controlling terminal for the child
1816 process, for future @code{run} commands. For example,
1823 directs that processes started with subsequent @code{run} commands
1824 default to do input and output on the terminal @file{/dev/ttyb} and have
1825 that as their controlling terminal.
1827 An explicit redirection in @code{run} overrides the @code{tty} command's
1828 effect on the input/output device, but not its effect on the controlling
1831 When you use the @code{tty} command or redirect input in the @code{run}
1832 command, only the input @emph{for your program} is affected. The input
1833 for @value{GDBN} still comes from your terminal.
1836 @section Debugging an already-running process
1841 @item attach @var{process-id}
1842 This command attaches to a running process---one that was started
1843 outside @value{GDBN}. (@code{info files} shows your active
1844 targets.) The command takes as argument a process ID. The usual way to
1845 find out the process-id of a Unix process is with the @code{ps} utility,
1846 or with the @samp{jobs -l} shell command.
1848 @code{attach} does not repeat if you press @key{RET} a second time after
1849 executing the command.
1852 To use @code{attach}, your program must be running in an environment
1853 which supports processes; for example, @code{attach} does not work for
1854 programs on bare-board targets that lack an operating system. You must
1855 also have permission to send the process a signal.
1857 When you use @code{attach}, the debugger finds the program running in
1858 the process first by looking in the current working directory, then (if
1859 the program is not found) by using the source file search path
1860 (@pxref{Source Path, ,Specifying source directories}). You can also use
1861 the @code{file} command to load the program. @xref{Files, ,Commands to
1864 The first thing @value{GDBN} does after arranging to debug the specified
1865 process is to stop it. You can examine and modify an attached process
1866 with all the @value{GDBN} commands that are ordinarily available when
1867 you start processes with @code{run}. You can insert breakpoints; you
1868 can step and continue; you can modify storage. If you would rather the
1869 process continue running, you may use the @code{continue} command after
1870 attaching @value{GDBN} to the process.
1875 When you have finished debugging the attached process, you can use the
1876 @code{detach} command to release it from @value{GDBN} control. Detaching
1877 the process continues its execution. After the @code{detach} command,
1878 that process and @value{GDBN} become completely independent once more, and you
1879 are ready to @code{attach} another process or start one with @code{run}.
1880 @code{detach} does not repeat if you press @key{RET} again after
1881 executing the command.
1884 If you exit @value{GDBN} or use the @code{run} command while you have an
1885 attached process, you kill that process. By default, @value{GDBN} asks
1886 for confirmation if you try to do either of these things; you can
1887 control whether or not you need to confirm by using the @code{set
1888 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1892 @section Killing the child process
1897 Kill the child process in which your program is running under @value{GDBN}.
1900 This command is useful if you wish to debug a core dump instead of a
1901 running process. @value{GDBN} ignores any core dump file while your program
1904 On some operating systems, a program cannot be executed outside @value{GDBN}
1905 while you have breakpoints set on it inside @value{GDBN}. You can use the
1906 @code{kill} command in this situation to permit running your program
1907 outside the debugger.
1909 The @code{kill} command is also useful if you wish to recompile and
1910 relink your program, since on many systems it is impossible to modify an
1911 executable file while it is running in a process. In this case, when you
1912 next type @code{run}, @value{GDBN} notices that the file has changed, and
1913 reads the symbol table again (while trying to preserve your current
1914 breakpoint settings).
1917 @section Debugging programs with multiple threads
1919 @cindex threads of execution
1920 @cindex multiple threads
1921 @cindex switching threads
1922 In some operating systems, such as HP-UX and Solaris, a single program
1923 may have more than one @dfn{thread} of execution. The precise semantics
1924 of threads differ from one operating system to another, but in general
1925 the threads of a single program are akin to multiple processes---except
1926 that they share one address space (that is, they can all examine and
1927 modify the same variables). On the other hand, each thread has its own
1928 registers and execution stack, and perhaps private memory.
1930 @value{GDBN} provides these facilities for debugging multi-thread
1934 @item automatic notification of new threads
1935 @item @samp{thread @var{threadno}}, a command to switch among threads
1936 @item @samp{info threads}, a command to inquire about existing threads
1937 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1938 a command to apply a command to a list of threads
1939 @item thread-specific breakpoints
1943 @emph{Warning:} These facilities are not yet available on every
1944 @value{GDBN} configuration where the operating system supports threads.
1945 If your @value{GDBN} does not support threads, these commands have no
1946 effect. For example, a system without thread support shows no output
1947 from @samp{info threads}, and always rejects the @code{thread} command,
1951 (@value{GDBP}) info threads
1952 (@value{GDBP}) thread 1
1953 Thread ID 1 not known. Use the "info threads" command to
1954 see the IDs of currently known threads.
1956 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1957 @c doesn't support threads"?
1960 @cindex focus of debugging
1961 @cindex current thread
1962 The @value{GDBN} thread debugging facility allows you to observe all
1963 threads while your program runs---but whenever @value{GDBN} takes
1964 control, one thread in particular is always the focus of debugging.
1965 This thread is called the @dfn{current thread}. Debugging commands show
1966 program information from the perspective of the current thread.
1968 @cindex @code{New} @var{systag} message
1969 @cindex thread identifier (system)
1970 @c FIXME-implementors!! It would be more helpful if the [New...] message
1971 @c included GDB's numeric thread handle, so you could just go to that
1972 @c thread without first checking `info threads'.
1973 Whenever @value{GDBN} detects a new thread in your program, it displays
1974 the target system's identification for the thread with a message in the
1975 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1976 whose form varies depending on the particular system. For example, on
1977 LynxOS, you might see
1980 [New process 35 thread 27]
1984 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1985 the @var{systag} is simply something like @samp{process 368}, with no
1988 @c FIXME!! (1) Does the [New...] message appear even for the very first
1989 @c thread of a program, or does it only appear for the
1990 @c second---i.e., when it becomes obvious we have a multithread
1992 @c (2) *Is* there necessarily a first thread always? Or do some
1993 @c multithread systems permit starting a program with multiple
1994 @c threads ab initio?
1996 @cindex thread number
1997 @cindex thread identifier (GDB)
1998 For debugging purposes, @value{GDBN} associates its own thread
1999 number---always a single integer---with each thread in your program.
2002 @kindex info threads
2004 Display a summary of all threads currently in your
2005 program. @value{GDBN} displays for each thread (in this order):
2008 @item the thread number assigned by @value{GDBN}
2010 @item the target system's thread identifier (@var{systag})
2012 @item the current stack frame summary for that thread
2016 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2017 indicates the current thread.
2021 @c end table here to get a little more width for example
2024 (@value{GDBP}) info threads
2025 3 process 35 thread 27 0x34e5 in sigpause ()
2026 2 process 35 thread 23 0x34e5 in sigpause ()
2027 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2033 @cindex thread number
2034 @cindex thread identifier (GDB)
2035 For debugging purposes, @value{GDBN} associates its own thread
2036 number---a small integer assigned in thread-creation order---with each
2037 thread in your program.
2039 @cindex @code{New} @var{systag} message, on HP-UX
2040 @cindex thread identifier (system), on HP-UX
2041 @c FIXME-implementors!! It would be more helpful if the [New...] message
2042 @c included GDB's numeric thread handle, so you could just go to that
2043 @c thread without first checking `info threads'.
2044 Whenever @value{GDBN} detects a new thread in your program, it displays
2045 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2046 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2047 whose form varies depending on the particular system. For example, on
2051 [New thread 2 (system thread 26594)]
2055 when @value{GDBN} notices a new thread.
2058 @kindex info threads
2060 Display a summary of all threads currently in your
2061 program. @value{GDBN} displays for each thread (in this order):
2064 @item the thread number assigned by @value{GDBN}
2066 @item the target system's thread identifier (@var{systag})
2068 @item the current stack frame summary for that thread
2072 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2073 indicates the current thread.
2077 @c end table here to get a little more width for example
2080 (@value{GDBP}) info threads
2081 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2083 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2084 from /usr/lib/libc.2
2085 1 system thread 27905 0x7b003498 in _brk () \@*
2086 from /usr/lib/libc.2
2090 @kindex thread @var{threadno}
2091 @item thread @var{threadno}
2092 Make thread number @var{threadno} the current thread. The command
2093 argument @var{threadno} is the internal @value{GDBN} thread number, as
2094 shown in the first field of the @samp{info threads} display.
2095 @value{GDBN} responds by displaying the system identifier of the thread
2096 you selected, and its current stack frame summary:
2099 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2100 (@value{GDBP}) thread 2
2101 [Switching to process 35 thread 23]
2102 0x34e5 in sigpause ()
2106 As with the @samp{[New @dots{}]} message, the form of the text after
2107 @samp{Switching to} depends on your system's conventions for identifying
2110 @kindex thread apply
2111 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2112 The @code{thread apply} command allows you to apply a command to one or
2113 more threads. Specify the numbers of the threads that you want affected
2114 with the command argument @var{threadno}. @var{threadno} is the internal
2115 @value{GDBN} thread number, as shown in the first field of the @samp{info
2116 threads} display. To apply a command to all threads, use
2117 @code{thread apply all} @var{args}.
2120 @cindex automatic thread selection
2121 @cindex switching threads automatically
2122 @cindex threads, automatic switching
2123 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2124 signal, it automatically selects the thread where that breakpoint or
2125 signal happened. @value{GDBN} alerts you to the context switch with a
2126 message of the form @samp{[Switching to @var{systag}]} to identify the
2129 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2130 more information about how @value{GDBN} behaves when you stop and start
2131 programs with multiple threads.
2133 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2134 watchpoints in programs with multiple threads.
2137 @section Debugging programs with multiple processes
2139 @cindex fork, debugging programs which call
2140 @cindex multiple processes
2141 @cindex processes, multiple
2142 On most systems, @value{GDBN} has no special support for debugging
2143 programs which create additional processes using the @code{fork}
2144 function. When a program forks, @value{GDBN} will continue to debug the
2145 parent process and the child process will run unimpeded. If you have
2146 set a breakpoint in any code which the child then executes, the child
2147 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2148 will cause it to terminate.
2150 However, if you want to debug the child process there is a workaround
2151 which isn't too painful. Put a call to @code{sleep} in the code which
2152 the child process executes after the fork. It may be useful to sleep
2153 only if a certain environment variable is set, or a certain file exists,
2154 so that the delay need not occur when you don't want to run @value{GDBN}
2155 on the child. While the child is sleeping, use the @code{ps} program to
2156 get its process ID. Then tell @value{GDBN} (a new invocation of
2157 @value{GDBN} if you are also debugging the parent process) to attach to
2158 the child process (@pxref{Attach}). From that point on you can debug
2159 the child process just like any other process which you attached to.
2161 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2162 debugging programs that create additional processes using the
2163 @code{fork} or @code{vfork} function.
2165 By default, when a program forks, @value{GDBN} will continue to debug
2166 the parent process and the child process will run unimpeded.
2168 If you want to follow the child process instead of the parent process,
2169 use the command @w{@code{set follow-fork-mode}}.
2172 @kindex set follow-fork-mode
2173 @item set follow-fork-mode @var{mode}
2174 Set the debugger response to a program call of @code{fork} or
2175 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2176 process. The @var{mode} can be:
2180 The original process is debugged after a fork. The child process runs
2181 unimpeded. This is the default.
2184 The new process is debugged after a fork. The parent process runs
2188 The debugger will ask for one of the above choices.
2191 @item show follow-fork-mode
2192 Display the current debugger response to a @code{fork} or @code{vfork} call.
2195 If you ask to debug a child process and a @code{vfork} is followed by an
2196 @code{exec}, @value{GDBN} executes the new target up to the first
2197 breakpoint in the new target. If you have a breakpoint set on
2198 @code{main} in your original program, the breakpoint will also be set on
2199 the child process's @code{main}.
2201 When a child process is spawned by @code{vfork}, you cannot debug the
2202 child or parent until an @code{exec} call completes.
2204 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2205 call executes, the new target restarts. To restart the parent process,
2206 use the @code{file} command with the parent executable name as its
2209 You can use the @code{catch} command to make @value{GDBN} stop whenever
2210 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2211 Catchpoints, ,Setting catchpoints}.
2214 @chapter Stopping and Continuing
2216 The principal purposes of using a debugger are so that you can stop your
2217 program before it terminates; or so that, if your program runs into
2218 trouble, you can investigate and find out why.
2220 Inside @value{GDBN}, your program may stop for any of several reasons,
2221 such as a signal, a breakpoint, or reaching a new line after a
2222 @value{GDBN} command such as @code{step}. You may then examine and
2223 change variables, set new breakpoints or remove old ones, and then
2224 continue execution. Usually, the messages shown by @value{GDBN} provide
2225 ample explanation of the status of your program---but you can also
2226 explicitly request this information at any time.
2229 @kindex info program
2231 Display information about the status of your program: whether it is
2232 running or not, what process it is, and why it stopped.
2236 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2237 * Continuing and Stepping:: Resuming execution
2239 * Thread Stops:: Stopping and starting multi-thread programs
2243 @section Breakpoints, watchpoints, and catchpoints
2246 A @dfn{breakpoint} makes your program stop whenever a certain point in
2247 the program is reached. For each breakpoint, you can add conditions to
2248 control in finer detail whether your program stops. You can set
2249 breakpoints with the @code{break} command and its variants (@pxref{Set
2250 Breaks, ,Setting breakpoints}), to specify the place where your program
2251 should stop by line number, function name or exact address in the
2254 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2255 breakpoints in shared libraries before the executable is run. There is
2256 a minor limitation on HP-UX systems: you must wait until the executable
2257 is run in order to set breakpoints in shared library routines that are
2258 not called directly by the program (for example, routines that are
2259 arguments in a @code{pthread_create} call).
2262 @cindex memory tracing
2263 @cindex breakpoint on memory address
2264 @cindex breakpoint on variable modification
2265 A @dfn{watchpoint} is a special breakpoint that stops your program
2266 when the value of an expression changes. You must use a different
2267 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2268 watchpoints}), but aside from that, you can manage a watchpoint like
2269 any other breakpoint: you enable, disable, and delete both breakpoints
2270 and watchpoints using the same commands.
2272 You can arrange to have values from your program displayed automatically
2273 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2277 @cindex breakpoint on events
2278 A @dfn{catchpoint} is another special breakpoint that stops your program
2279 when a certain kind of event occurs, such as the throwing of a C@t{++}
2280 exception or the loading of a library. As with watchpoints, you use a
2281 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2282 catchpoints}), but aside from that, you can manage a catchpoint like any
2283 other breakpoint. (To stop when your program receives a signal, use the
2284 @code{handle} command; see @ref{Signals, ,Signals}.)
2286 @cindex breakpoint numbers
2287 @cindex numbers for breakpoints
2288 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2289 catchpoint when you create it; these numbers are successive integers
2290 starting with one. In many of the commands for controlling various
2291 features of breakpoints you use the breakpoint number to say which
2292 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2293 @dfn{disabled}; if disabled, it has no effect on your program until you
2296 @cindex breakpoint ranges
2297 @cindex ranges of breakpoints
2298 Some @value{GDBN} commands accept a range of breakpoints on which to
2299 operate. A breakpoint range is either a single breakpoint number, like
2300 @samp{5}, or two such numbers, in increasing order, separated by a
2301 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2302 all breakpoint in that range are operated on.
2305 * Set Breaks:: Setting breakpoints
2306 * Set Watchpoints:: Setting watchpoints
2307 * Set Catchpoints:: Setting catchpoints
2308 * Delete Breaks:: Deleting breakpoints
2309 * Disabling:: Disabling breakpoints
2310 * Conditions:: Break conditions
2311 * Break Commands:: Breakpoint command lists
2312 * Breakpoint Menus:: Breakpoint menus
2313 * Error in Breakpoints:: ``Cannot insert breakpoints''
2317 @subsection Setting breakpoints
2319 @c FIXME LMB what does GDB do if no code on line of breakpt?
2320 @c consider in particular declaration with/without initialization.
2322 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2325 @kindex b @r{(@code{break})}
2326 @vindex $bpnum@r{, convenience variable}
2327 @cindex latest breakpoint
2328 Breakpoints are set with the @code{break} command (abbreviated
2329 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2330 number of the breakpoint you've set most recently; see @ref{Convenience
2331 Vars,, Convenience variables}, for a discussion of what you can do with
2332 convenience variables.
2334 You have several ways to say where the breakpoint should go.
2337 @item break @var{function}
2338 Set a breakpoint at entry to function @var{function}.
2339 When using source languages that permit overloading of symbols, such as
2340 C@t{++}, @var{function} may refer to more than one possible place to break.
2341 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2343 @item break +@var{offset}
2344 @itemx break -@var{offset}
2345 Set a breakpoint some number of lines forward or back from the position
2346 at which execution stopped in the currently selected @dfn{stack frame}.
2347 (@xref{Frames, ,Frames}, for a description of stack frames.)
2349 @item break @var{linenum}
2350 Set a breakpoint at line @var{linenum} in the current source file.
2351 The current source file is the last file whose source text was printed.
2352 The breakpoint will stop your program just before it executes any of the
2355 @item break @var{filename}:@var{linenum}
2356 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2358 @item break @var{filename}:@var{function}
2359 Set a breakpoint at entry to function @var{function} found in file
2360 @var{filename}. Specifying a file name as well as a function name is
2361 superfluous except when multiple files contain similarly named
2364 @item break *@var{address}
2365 Set a breakpoint at address @var{address}. You can use this to set
2366 breakpoints in parts of your program which do not have debugging
2367 information or source files.
2370 When called without any arguments, @code{break} sets a breakpoint at
2371 the next instruction to be executed in the selected stack frame
2372 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2373 innermost, this makes your program stop as soon as control
2374 returns to that frame. This is similar to the effect of a
2375 @code{finish} command in the frame inside the selected frame---except
2376 that @code{finish} does not leave an active breakpoint. If you use
2377 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2378 the next time it reaches the current location; this may be useful
2381 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2382 least one instruction has been executed. If it did not do this, you
2383 would be unable to proceed past a breakpoint without first disabling the
2384 breakpoint. This rule applies whether or not the breakpoint already
2385 existed when your program stopped.
2387 @item break @dots{} if @var{cond}
2388 Set a breakpoint with condition @var{cond}; evaluate the expression
2389 @var{cond} each time the breakpoint is reached, and stop only if the
2390 value is nonzero---that is, if @var{cond} evaluates as true.
2391 @samp{@dots{}} stands for one of the possible arguments described
2392 above (or no argument) specifying where to break. @xref{Conditions,
2393 ,Break conditions}, for more information on breakpoint conditions.
2396 @item tbreak @var{args}
2397 Set a breakpoint enabled only for one stop. @var{args} are the
2398 same as for the @code{break} command, and the breakpoint is set in the same
2399 way, but the breakpoint is automatically deleted after the first time your
2400 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2403 @item hbreak @var{args}
2404 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2405 @code{break} command and the breakpoint is set in the same way, but the
2406 breakpoint requires hardware support and some target hardware may not
2407 have this support. The main purpose of this is EPROM/ROM code
2408 debugging, so you can set a breakpoint at an instruction without
2409 changing the instruction. This can be used with the new trap-generation
2410 provided by SPARClite DSU and some x86-based targets. These targets
2411 will generate traps when a program accesses some data or instruction
2412 address that is assigned to the debug registers. However the hardware
2413 breakpoint registers can take a limited number of breakpoints. For
2414 example, on the DSU, only two data breakpoints can be set at a time, and
2415 @value{GDBN} will reject this command if more than two are used. Delete
2416 or disable unused hardware breakpoints before setting new ones
2417 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2420 @item thbreak @var{args}
2421 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2422 are the same as for the @code{hbreak} command and the breakpoint is set in
2423 the same way. However, like the @code{tbreak} command,
2424 the breakpoint is automatically deleted after the
2425 first time your program stops there. Also, like the @code{hbreak}
2426 command, the breakpoint requires hardware support and some target hardware
2427 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2428 See also @ref{Conditions, ,Break conditions}.
2431 @cindex regular expression
2432 @item rbreak @var{regex}
2433 Set breakpoints on all functions matching the regular expression
2434 @var{regex}. This command sets an unconditional breakpoint on all
2435 matches, printing a list of all breakpoints it set. Once these
2436 breakpoints are set, they are treated just like the breakpoints set with
2437 the @code{break} command. You can delete them, disable them, or make
2438 them conditional the same way as any other breakpoint.
2440 The syntax of the regular expression is the standard one used with tools
2441 like @file{grep}. Note that this is different from the syntax used by
2442 shells, so for instance @code{foo*} matches all functions that include
2443 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2444 @code{.*} leading and trailing the regular expression you supply, so to
2445 match only functions that begin with @code{foo}, use @code{^foo}.
2447 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2448 breakpoints on overloaded functions that are not members of any special
2451 @kindex info breakpoints
2452 @cindex @code{$_} and @code{info breakpoints}
2453 @item info breakpoints @r{[}@var{n}@r{]}
2454 @itemx info break @r{[}@var{n}@r{]}
2455 @itemx info watchpoints @r{[}@var{n}@r{]}
2456 Print a table of all breakpoints, watchpoints, and catchpoints set and
2457 not deleted, with the following columns for each breakpoint:
2460 @item Breakpoint Numbers
2462 Breakpoint, watchpoint, or catchpoint.
2464 Whether the breakpoint is marked to be disabled or deleted when hit.
2465 @item Enabled or Disabled
2466 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2467 that are not enabled.
2469 Where the breakpoint is in your program, as a memory address.
2471 Where the breakpoint is in the source for your program, as a file and
2476 If a breakpoint is conditional, @code{info break} shows the condition on
2477 the line following the affected breakpoint; breakpoint commands, if any,
2478 are listed after that.
2481 @code{info break} with a breakpoint
2482 number @var{n} as argument lists only that breakpoint. The
2483 convenience variable @code{$_} and the default examining-address for
2484 the @code{x} command are set to the address of the last breakpoint
2485 listed (@pxref{Memory, ,Examining memory}).
2488 @code{info break} displays a count of the number of times the breakpoint
2489 has been hit. This is especially useful in conjunction with the
2490 @code{ignore} command. You can ignore a large number of breakpoint
2491 hits, look at the breakpoint info to see how many times the breakpoint
2492 was hit, and then run again, ignoring one less than that number. This
2493 will get you quickly to the last hit of that breakpoint.
2496 @value{GDBN} allows you to set any number of breakpoints at the same place in
2497 your program. There is nothing silly or meaningless about this. When
2498 the breakpoints are conditional, this is even useful
2499 (@pxref{Conditions, ,Break conditions}).
2501 @cindex negative breakpoint numbers
2502 @cindex internal @value{GDBN} breakpoints
2503 @value{GDBN} itself sometimes sets breakpoints in your program for special
2504 purposes, such as proper handling of @code{longjmp} (in C programs).
2505 These internal breakpoints are assigned negative numbers, starting with
2506 @code{-1}; @samp{info breakpoints} does not display them.
2508 You can see these breakpoints with the @value{GDBN} maintenance command
2509 @samp{maint info breakpoints}.
2512 @kindex maint info breakpoints
2513 @item maint info breakpoints
2514 Using the same format as @samp{info breakpoints}, display both the
2515 breakpoints you've set explicitly, and those @value{GDBN} is using for
2516 internal purposes. Internal breakpoints are shown with negative
2517 breakpoint numbers. The type column identifies what kind of breakpoint
2522 Normal, explicitly set breakpoint.
2525 Normal, explicitly set watchpoint.
2528 Internal breakpoint, used to handle correctly stepping through
2529 @code{longjmp} calls.
2531 @item longjmp resume
2532 Internal breakpoint at the target of a @code{longjmp}.
2535 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2538 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2541 Shared library events.
2548 @node Set Watchpoints
2549 @subsection Setting watchpoints
2551 @cindex setting watchpoints
2552 @cindex software watchpoints
2553 @cindex hardware watchpoints
2554 You can use a watchpoint to stop execution whenever the value of an
2555 expression changes, without having to predict a particular place where
2558 Depending on your system, watchpoints may be implemented in software or
2559 hardware. @value{GDBN} does software watchpointing by single-stepping your
2560 program and testing the variable's value each time, which is hundreds of
2561 times slower than normal execution. (But this may still be worth it, to
2562 catch errors where you have no clue what part of your program is the
2565 On some systems, such as HP-UX, Linux and some other x86-based targets,
2566 @value{GDBN} includes support for
2567 hardware watchpoints, which do not slow down the running of your
2572 @item watch @var{expr}
2573 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2574 is written into by the program and its value changes.
2577 @item rwatch @var{expr}
2578 Set a watchpoint that will break when watch @var{expr} is read by the program.
2581 @item awatch @var{expr}
2582 Set a watchpoint that will break when @var{expr} is either read or written into
2585 @kindex info watchpoints
2586 @item info watchpoints
2587 This command prints a list of watchpoints, breakpoints, and catchpoints;
2588 it is the same as @code{info break}.
2591 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2592 watchpoints execute very quickly, and the debugger reports a change in
2593 value at the exact instruction where the change occurs. If @value{GDBN}
2594 cannot set a hardware watchpoint, it sets a software watchpoint, which
2595 executes more slowly and reports the change in value at the next
2596 statement, not the instruction, after the change occurs.
2598 When you issue the @code{watch} command, @value{GDBN} reports
2601 Hardware watchpoint @var{num}: @var{expr}
2605 if it was able to set a hardware watchpoint.
2607 Currently, the @code{awatch} and @code{rwatch} commands can only set
2608 hardware watchpoints, because accesses to data that don't change the
2609 value of the watched expression cannot be detected without examining
2610 every instruction as it is being executed, and @value{GDBN} does not do
2611 that currently. If @value{GDBN} finds that it is unable to set a
2612 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2613 will print a message like this:
2616 Expression cannot be implemented with read/access watchpoint.
2619 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2620 data type of the watched expression is wider than what a hardware
2621 watchpoint on the target machine can handle. For example, some systems
2622 can only watch regions that are up to 4 bytes wide; on such systems you
2623 cannot set hardware watchpoints for an expression that yields a
2624 double-precision floating-point number (which is typically 8 bytes
2625 wide). As a work-around, it might be possible to break the large region
2626 into a series of smaller ones and watch them with separate watchpoints.
2628 If you set too many hardware watchpoints, @value{GDBN} might be unable
2629 to insert all of them when you resume the execution of your program.
2630 Since the precise number of active watchpoints is unknown until such
2631 time as the program is about to be resumed, @value{GDBN} might not be
2632 able to warn you about this when you set the watchpoints, and the
2633 warning will be printed only when the program is resumed:
2636 Hardware watchpoint @var{num}: Could not insert watchpoint
2640 If this happens, delete or disable some of the watchpoints.
2642 The SPARClite DSU will generate traps when a program accesses some data
2643 or instruction address that is assigned to the debug registers. For the
2644 data addresses, DSU facilitates the @code{watch} command. However the
2645 hardware breakpoint registers can only take two data watchpoints, and
2646 both watchpoints must be the same kind. For example, you can set two
2647 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2648 @strong{or} two with @code{awatch} commands, but you cannot set one
2649 watchpoint with one command and the other with a different command.
2650 @value{GDBN} will reject the command if you try to mix watchpoints.
2651 Delete or disable unused watchpoint commands before setting new ones.
2653 If you call a function interactively using @code{print} or @code{call},
2654 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2655 kind of breakpoint or the call completes.
2657 @value{GDBN} automatically deletes watchpoints that watch local
2658 (automatic) variables, or expressions that involve such variables, when
2659 they go out of scope, that is, when the execution leaves the block in
2660 which these variables were defined. In particular, when the program
2661 being debugged terminates, @emph{all} local variables go out of scope,
2662 and so only watchpoints that watch global variables remain set. If you
2663 rerun the program, you will need to set all such watchpoints again. One
2664 way of doing that would be to set a code breakpoint at the entry to the
2665 @code{main} function and when it breaks, set all the watchpoints.
2668 @cindex watchpoints and threads
2669 @cindex threads and watchpoints
2670 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2671 usefulness. With the current watchpoint implementation, @value{GDBN}
2672 can only watch the value of an expression @emph{in a single thread}. If
2673 you are confident that the expression can only change due to the current
2674 thread's activity (and if you are also confident that no other thread
2675 can become current), then you can use watchpoints as usual. However,
2676 @value{GDBN} may not notice when a non-current thread's activity changes
2679 @c FIXME: this is almost identical to the previous paragraph.
2680 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2681 have only limited usefulness. If @value{GDBN} creates a software
2682 watchpoint, it can only watch the value of an expression @emph{in a
2683 single thread}. If you are confident that the expression can only
2684 change due to the current thread's activity (and if you are also
2685 confident that no other thread can become current), then you can use
2686 software watchpoints as usual. However, @value{GDBN} may not notice
2687 when a non-current thread's activity changes the expression. (Hardware
2688 watchpoints, in contrast, watch an expression in all threads.)
2691 @node Set Catchpoints
2692 @subsection Setting catchpoints
2693 @cindex catchpoints, setting
2694 @cindex exception handlers
2695 @cindex event handling
2697 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2698 kinds of program events, such as C@t{++} exceptions or the loading of a
2699 shared library. Use the @code{catch} command to set a catchpoint.
2703 @item catch @var{event}
2704 Stop when @var{event} occurs. @var{event} can be any of the following:
2708 The throwing of a C@t{++} exception.
2712 The catching of a C@t{++} exception.
2716 A call to @code{exec}. This is currently only available for HP-UX.
2720 A call to @code{fork}. This is currently only available for HP-UX.
2724 A call to @code{vfork}. This is currently only available for HP-UX.
2727 @itemx load @var{libname}
2729 The dynamic loading of any shared library, or the loading of the library
2730 @var{libname}. This is currently only available for HP-UX.
2733 @itemx unload @var{libname}
2734 @kindex catch unload
2735 The unloading of any dynamically loaded shared library, or the unloading
2736 of the library @var{libname}. This is currently only available for HP-UX.
2739 @item tcatch @var{event}
2740 Set a catchpoint that is enabled only for one stop. The catchpoint is
2741 automatically deleted after the first time the event is caught.
2745 Use the @code{info break} command to list the current catchpoints.
2747 There are currently some limitations to C@t{++} exception handling
2748 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2752 If you call a function interactively, @value{GDBN} normally returns
2753 control to you when the function has finished executing. If the call
2754 raises an exception, however, the call may bypass the mechanism that
2755 returns control to you and cause your program either to abort or to
2756 simply continue running until it hits a breakpoint, catches a signal
2757 that @value{GDBN} is listening for, or exits. This is the case even if
2758 you set a catchpoint for the exception; catchpoints on exceptions are
2759 disabled within interactive calls.
2762 You cannot raise an exception interactively.
2765 You cannot install an exception handler interactively.
2768 @cindex raise exceptions
2769 Sometimes @code{catch} is not the best way to debug exception handling:
2770 if you need to know exactly where an exception is raised, it is better to
2771 stop @emph{before} the exception handler is called, since that way you
2772 can see the stack before any unwinding takes place. If you set a
2773 breakpoint in an exception handler instead, it may not be easy to find
2774 out where the exception was raised.
2776 To stop just before an exception handler is called, you need some
2777 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2778 raised by calling a library function named @code{__raise_exception}
2779 which has the following ANSI C interface:
2782 /* @var{addr} is where the exception identifier is stored.
2783 @var{id} is the exception identifier. */
2784 void __raise_exception (void **addr, void *id);
2788 To make the debugger catch all exceptions before any stack
2789 unwinding takes place, set a breakpoint on @code{__raise_exception}
2790 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2792 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2793 that depends on the value of @var{id}, you can stop your program when
2794 a specific exception is raised. You can use multiple conditional
2795 breakpoints to stop your program when any of a number of exceptions are
2800 @subsection Deleting breakpoints
2802 @cindex clearing breakpoints, watchpoints, catchpoints
2803 @cindex deleting breakpoints, watchpoints, catchpoints
2804 It is often necessary to eliminate a breakpoint, watchpoint, or
2805 catchpoint once it has done its job and you no longer want your program
2806 to stop there. This is called @dfn{deleting} the breakpoint. A
2807 breakpoint that has been deleted no longer exists; it is forgotten.
2809 With the @code{clear} command you can delete breakpoints according to
2810 where they are in your program. With the @code{delete} command you can
2811 delete individual breakpoints, watchpoints, or catchpoints by specifying
2812 their breakpoint numbers.
2814 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2815 automatically ignores breakpoints on the first instruction to be executed
2816 when you continue execution without changing the execution address.
2821 Delete any breakpoints at the next instruction to be executed in the
2822 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2823 the innermost frame is selected, this is a good way to delete a
2824 breakpoint where your program just stopped.
2826 @item clear @var{function}
2827 @itemx clear @var{filename}:@var{function}
2828 Delete any breakpoints set at entry to the function @var{function}.
2830 @item clear @var{linenum}
2831 @itemx clear @var{filename}:@var{linenum}
2832 Delete any breakpoints set at or within the code of the specified line.
2834 @cindex delete breakpoints
2836 @kindex d @r{(@code{delete})}
2837 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2838 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2839 ranges specified as arguments. If no argument is specified, delete all
2840 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2841 confirm off}). You can abbreviate this command as @code{d}.
2845 @subsection Disabling breakpoints
2847 @kindex disable breakpoints
2848 @kindex enable breakpoints
2849 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2850 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2851 it had been deleted, but remembers the information on the breakpoint so
2852 that you can @dfn{enable} it again later.
2854 You disable and enable breakpoints, watchpoints, and catchpoints with
2855 the @code{enable} and @code{disable} commands, optionally specifying one
2856 or more breakpoint numbers as arguments. Use @code{info break} or
2857 @code{info watch} to print a list of breakpoints, watchpoints, and
2858 catchpoints if you do not know which numbers to use.
2860 A breakpoint, watchpoint, or catchpoint can have any of four different
2861 states of enablement:
2865 Enabled. The breakpoint stops your program. A breakpoint set
2866 with the @code{break} command starts out in this state.
2868 Disabled. The breakpoint has no effect on your program.
2870 Enabled once. The breakpoint stops your program, but then becomes
2873 Enabled for deletion. The breakpoint stops your program, but
2874 immediately after it does so it is deleted permanently. A breakpoint
2875 set with the @code{tbreak} command starts out in this state.
2878 You can use the following commands to enable or disable breakpoints,
2879 watchpoints, and catchpoints:
2882 @kindex disable breakpoints
2884 @kindex dis @r{(@code{disable})}
2885 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2886 Disable the specified breakpoints---or all breakpoints, if none are
2887 listed. A disabled breakpoint has no effect but is not forgotten. All
2888 options such as ignore-counts, conditions and commands are remembered in
2889 case the breakpoint is enabled again later. You may abbreviate
2890 @code{disable} as @code{dis}.
2892 @kindex enable breakpoints
2894 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2895 Enable the specified breakpoints (or all defined breakpoints). They
2896 become effective once again in stopping your program.
2898 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2899 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2900 of these breakpoints immediately after stopping your program.
2902 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2903 Enable the specified breakpoints to work once, then die. @value{GDBN}
2904 deletes any of these breakpoints as soon as your program stops there.
2907 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2908 @c confusing: tbreak is also initially enabled.
2909 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2910 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2911 subsequently, they become disabled or enabled only when you use one of
2912 the commands above. (The command @code{until} can set and delete a
2913 breakpoint of its own, but it does not change the state of your other
2914 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2918 @subsection Break conditions
2919 @cindex conditional breakpoints
2920 @cindex breakpoint conditions
2922 @c FIXME what is scope of break condition expr? Context where wanted?
2923 @c in particular for a watchpoint?
2924 The simplest sort of breakpoint breaks every time your program reaches a
2925 specified place. You can also specify a @dfn{condition} for a
2926 breakpoint. A condition is just a Boolean expression in your
2927 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2928 a condition evaluates the expression each time your program reaches it,
2929 and your program stops only if the condition is @emph{true}.
2931 This is the converse of using assertions for program validation; in that
2932 situation, you want to stop when the assertion is violated---that is,
2933 when the condition is false. In C, if you want to test an assertion expressed
2934 by the condition @var{assert}, you should set the condition
2935 @samp{! @var{assert}} on the appropriate breakpoint.
2937 Conditions are also accepted for watchpoints; you may not need them,
2938 since a watchpoint is inspecting the value of an expression anyhow---but
2939 it might be simpler, say, to just set a watchpoint on a variable name,
2940 and specify a condition that tests whether the new value is an interesting
2943 Break conditions can have side effects, and may even call functions in
2944 your program. This can be useful, for example, to activate functions
2945 that log program progress, or to use your own print functions to
2946 format special data structures. The effects are completely predictable
2947 unless there is another enabled breakpoint at the same address. (In
2948 that case, @value{GDBN} might see the other breakpoint first and stop your
2949 program without checking the condition of this one.) Note that
2950 breakpoint commands are usually more convenient and flexible than break
2952 purpose of performing side effects when a breakpoint is reached
2953 (@pxref{Break Commands, ,Breakpoint command lists}).
2955 Break conditions can be specified when a breakpoint is set, by using
2956 @samp{if} in the arguments to the @code{break} command. @xref{Set
2957 Breaks, ,Setting breakpoints}. They can also be changed at any time
2958 with the @code{condition} command.
2960 You can also use the @code{if} keyword with the @code{watch} command.
2961 The @code{catch} command does not recognize the @code{if} keyword;
2962 @code{condition} is the only way to impose a further condition on a
2967 @item condition @var{bnum} @var{expression}
2968 Specify @var{expression} as the break condition for breakpoint,
2969 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2970 breakpoint @var{bnum} stops your program only if the value of
2971 @var{expression} is true (nonzero, in C). When you use
2972 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2973 syntactic correctness, and to determine whether symbols in it have
2974 referents in the context of your breakpoint. If @var{expression} uses
2975 symbols not referenced in the context of the breakpoint, @value{GDBN}
2976 prints an error message:
2979 No symbol "foo" in current context.
2984 not actually evaluate @var{expression} at the time the @code{condition}
2985 command (or a command that sets a breakpoint with a condition, like
2986 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2988 @item condition @var{bnum}
2989 Remove the condition from breakpoint number @var{bnum}. It becomes
2990 an ordinary unconditional breakpoint.
2993 @cindex ignore count (of breakpoint)
2994 A special case of a breakpoint condition is to stop only when the
2995 breakpoint has been reached a certain number of times. This is so
2996 useful that there is a special way to do it, using the @dfn{ignore
2997 count} of the breakpoint. Every breakpoint has an ignore count, which
2998 is an integer. Most of the time, the ignore count is zero, and
2999 therefore has no effect. But if your program reaches a breakpoint whose
3000 ignore count is positive, then instead of stopping, it just decrements
3001 the ignore count by one and continues. As a result, if the ignore count
3002 value is @var{n}, the breakpoint does not stop the next @var{n} times
3003 your program reaches it.
3007 @item ignore @var{bnum} @var{count}
3008 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3009 The next @var{count} times the breakpoint is reached, your program's
3010 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3013 To make the breakpoint stop the next time it is reached, specify
3016 When you use @code{continue} to resume execution of your program from a
3017 breakpoint, you can specify an ignore count directly as an argument to
3018 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3019 Stepping,,Continuing and stepping}.
3021 If a breakpoint has a positive ignore count and a condition, the
3022 condition is not checked. Once the ignore count reaches zero,
3023 @value{GDBN} resumes checking the condition.
3025 You could achieve the effect of the ignore count with a condition such
3026 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3027 is decremented each time. @xref{Convenience Vars, ,Convenience
3031 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3034 @node Break Commands
3035 @subsection Breakpoint command lists
3037 @cindex breakpoint commands
3038 You can give any breakpoint (or watchpoint or catchpoint) a series of
3039 commands to execute when your program stops due to that breakpoint. For
3040 example, you might want to print the values of certain expressions, or
3041 enable other breakpoints.
3046 @item commands @r{[}@var{bnum}@r{]}
3047 @itemx @dots{} @var{command-list} @dots{}
3049 Specify a list of commands for breakpoint number @var{bnum}. The commands
3050 themselves appear on the following lines. Type a line containing just
3051 @code{end} to terminate the commands.
3053 To remove all commands from a breakpoint, type @code{commands} and
3054 follow it immediately with @code{end}; that is, give no commands.
3056 With no @var{bnum} argument, @code{commands} refers to the last
3057 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3058 recently encountered).
3061 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3062 disabled within a @var{command-list}.
3064 You can use breakpoint commands to start your program up again. Simply
3065 use the @code{continue} command, or @code{step}, or any other command
3066 that resumes execution.
3068 Any other commands in the command list, after a command that resumes
3069 execution, are ignored. This is because any time you resume execution
3070 (even with a simple @code{next} or @code{step}), you may encounter
3071 another breakpoint---which could have its own command list, leading to
3072 ambiguities about which list to execute.
3075 If the first command you specify in a command list is @code{silent}, the
3076 usual message about stopping at a breakpoint is not printed. This may
3077 be desirable for breakpoints that are to print a specific message and
3078 then continue. If none of the remaining commands print anything, you
3079 see no sign that the breakpoint was reached. @code{silent} is
3080 meaningful only at the beginning of a breakpoint command list.
3082 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3083 print precisely controlled output, and are often useful in silent
3084 breakpoints. @xref{Output, ,Commands for controlled output}.
3086 For example, here is how you could use breakpoint commands to print the
3087 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3093 printf "x is %d\n",x
3098 One application for breakpoint commands is to compensate for one bug so
3099 you can test for another. Put a breakpoint just after the erroneous line
3100 of code, give it a condition to detect the case in which something
3101 erroneous has been done, and give it commands to assign correct values
3102 to any variables that need them. End with the @code{continue} command
3103 so that your program does not stop, and start with the @code{silent}
3104 command so that no output is produced. Here is an example:
3115 @node Breakpoint Menus
3116 @subsection Breakpoint menus
3118 @cindex symbol overloading
3120 Some programming languages (notably C@t{++}) permit a single function name
3121 to be defined several times, for application in different contexts.
3122 This is called @dfn{overloading}. When a function name is overloaded,
3123 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3124 a breakpoint. If you realize this is a problem, you can use
3125 something like @samp{break @var{function}(@var{types})} to specify which
3126 particular version of the function you want. Otherwise, @value{GDBN} offers
3127 you a menu of numbered choices for different possible breakpoints, and
3128 waits for your selection with the prompt @samp{>}. The first two
3129 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3130 sets a breakpoint at each definition of @var{function}, and typing
3131 @kbd{0} aborts the @code{break} command without setting any new
3134 For example, the following session excerpt shows an attempt to set a
3135 breakpoint at the overloaded symbol @code{String::after}.
3136 We choose three particular definitions of that function name:
3138 @c FIXME! This is likely to change to show arg type lists, at least
3141 (@value{GDBP}) b String::after
3144 [2] file:String.cc; line number:867
3145 [3] file:String.cc; line number:860
3146 [4] file:String.cc; line number:875
3147 [5] file:String.cc; line number:853
3148 [6] file:String.cc; line number:846
3149 [7] file:String.cc; line number:735
3151 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3152 Breakpoint 2 at 0xb344: file String.cc, line 875.
3153 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3154 Multiple breakpoints were set.
3155 Use the "delete" command to delete unwanted
3161 @c @ifclear BARETARGET
3162 @node Error in Breakpoints
3163 @subsection ``Cannot insert breakpoints''
3165 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3167 Under some operating systems, breakpoints cannot be used in a program if
3168 any other process is running that program. In this situation,
3169 attempting to run or continue a program with a breakpoint causes
3170 @value{GDBN} to print an error message:
3173 Cannot insert breakpoints.
3174 The same program may be running in another process.
3177 When this happens, you have three ways to proceed:
3181 Remove or disable the breakpoints, then continue.
3184 Suspend @value{GDBN}, and copy the file containing your program to a new
3185 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3186 that @value{GDBN} should run your program under that name.
3187 Then start your program again.
3190 Relink your program so that the text segment is nonsharable, using the
3191 linker option @samp{-N}. The operating system limitation may not apply
3192 to nonsharable executables.
3196 A similar message can be printed if you request too many active
3197 hardware-assisted breakpoints and watchpoints:
3199 @c FIXME: the precise wording of this message may change; the relevant
3200 @c source change is not committed yet (Sep 3, 1999).
3202 Stopped; cannot insert breakpoints.
3203 You may have requested too many hardware breakpoints and watchpoints.
3207 This message is printed when you attempt to resume the program, since
3208 only then @value{GDBN} knows exactly how many hardware breakpoints and
3209 watchpoints it needs to insert.
3211 When this message is printed, you need to disable or remove some of the
3212 hardware-assisted breakpoints and watchpoints, and then continue.
3215 @node Continuing and Stepping
3216 @section Continuing and stepping
3220 @cindex resuming execution
3221 @dfn{Continuing} means resuming program execution until your program
3222 completes normally. In contrast, @dfn{stepping} means executing just
3223 one more ``step'' of your program, where ``step'' may mean either one
3224 line of source code, or one machine instruction (depending on what
3225 particular command you use). Either when continuing or when stepping,
3226 your program may stop even sooner, due to a breakpoint or a signal. (If
3227 it stops due to a signal, you may want to use @code{handle}, or use
3228 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3232 @kindex c @r{(@code{continue})}
3233 @kindex fg @r{(resume foreground execution)}
3234 @item continue @r{[}@var{ignore-count}@r{]}
3235 @itemx c @r{[}@var{ignore-count}@r{]}
3236 @itemx fg @r{[}@var{ignore-count}@r{]}
3237 Resume program execution, at the address where your program last stopped;
3238 any breakpoints set at that address are bypassed. The optional argument
3239 @var{ignore-count} allows you to specify a further number of times to
3240 ignore a breakpoint at this location; its effect is like that of
3241 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3243 The argument @var{ignore-count} is meaningful only when your program
3244 stopped due to a breakpoint. At other times, the argument to
3245 @code{continue} is ignored.
3247 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3248 debugged program is deemed to be the foreground program) are provided
3249 purely for convenience, and have exactly the same behavior as
3253 To resume execution at a different place, you can use @code{return}
3254 (@pxref{Returning, ,Returning from a function}) to go back to the
3255 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3256 different address}) to go to an arbitrary location in your program.
3258 A typical technique for using stepping is to set a breakpoint
3259 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3260 beginning of the function or the section of your program where a problem
3261 is believed to lie, run your program until it stops at that breakpoint,
3262 and then step through the suspect area, examining the variables that are
3263 interesting, until you see the problem happen.
3267 @kindex s @r{(@code{step})}
3269 Continue running your program until control reaches a different source
3270 line, then stop it and return control to @value{GDBN}. This command is
3271 abbreviated @code{s}.
3274 @c "without debugging information" is imprecise; actually "without line
3275 @c numbers in the debugging information". (gcc -g1 has debugging info but
3276 @c not line numbers). But it seems complex to try to make that
3277 @c distinction here.
3278 @emph{Warning:} If you use the @code{step} command while control is
3279 within a function that was compiled without debugging information,
3280 execution proceeds until control reaches a function that does have
3281 debugging information. Likewise, it will not step into a function which
3282 is compiled without debugging information. To step through functions
3283 without debugging information, use the @code{stepi} command, described
3287 The @code{step} command only stops at the first instruction of a source
3288 line. This prevents the multiple stops that could otherwise occur in
3289 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3290 to stop if a function that has debugging information is called within
3291 the line. In other words, @code{step} @emph{steps inside} any functions
3292 called within the line.
3294 Also, the @code{step} command only enters a function if there is line
3295 number information for the function. Otherwise it acts like the
3296 @code{next} command. This avoids problems when using @code{cc -gl}
3297 on MIPS machines. Previously, @code{step} entered subroutines if there
3298 was any debugging information about the routine.
3300 @item step @var{count}
3301 Continue running as in @code{step}, but do so @var{count} times. If a
3302 breakpoint is reached, or a signal not related to stepping occurs before
3303 @var{count} steps, stepping stops right away.
3306 @kindex n @r{(@code{next})}
3307 @item next @r{[}@var{count}@r{]}
3308 Continue to the next source line in the current (innermost) stack frame.
3309 This is similar to @code{step}, but function calls that appear within
3310 the line of code are executed without stopping. Execution stops when
3311 control reaches a different line of code at the original stack level
3312 that was executing when you gave the @code{next} command. This command
3313 is abbreviated @code{n}.
3315 An argument @var{count} is a repeat count, as for @code{step}.
3318 @c FIX ME!! Do we delete this, or is there a way it fits in with
3319 @c the following paragraph? --- Vctoria
3321 @c @code{next} within a function that lacks debugging information acts like
3322 @c @code{step}, but any function calls appearing within the code of the
3323 @c function are executed without stopping.
3325 The @code{next} command only stops at the first instruction of a
3326 source line. This prevents multiple stops that could otherwise occur in
3327 @code{switch} statements, @code{for} loops, etc.
3329 @kindex set step-mode
3331 @cindex functions without line info, and stepping
3332 @cindex stepping into functions with no line info
3333 @itemx set step-mode on
3334 The @code{set step-mode on} command causes the @code{step} command to
3335 stop at the first instruction of a function which contains no debug line
3336 information rather than stepping over it.
3338 This is useful in cases where you may be interested in inspecting the
3339 machine instructions of a function which has no symbolic info and do not
3340 want @value{GDBN} to automatically skip over this function.
3342 @item set step-mode off
3343 Causes the @code{step} command to step over any functions which contains no
3344 debug information. This is the default.
3348 Continue running until just after function in the selected stack frame
3349 returns. Print the returned value (if any).
3351 Contrast this with the @code{return} command (@pxref{Returning,
3352 ,Returning from a function}).
3355 @kindex u @r{(@code{until})}
3358 Continue running until a source line past the current line, in the
3359 current stack frame, is reached. This command is used to avoid single
3360 stepping through a loop more than once. It is like the @code{next}
3361 command, except that when @code{until} encounters a jump, it
3362 automatically continues execution until the program counter is greater
3363 than the address of the jump.
3365 This means that when you reach the end of a loop after single stepping
3366 though it, @code{until} makes your program continue execution until it
3367 exits the loop. In contrast, a @code{next} command at the end of a loop
3368 simply steps back to the beginning of the loop, which forces you to step
3369 through the next iteration.
3371 @code{until} always stops your program if it attempts to exit the current
3374 @code{until} may produce somewhat counterintuitive results if the order
3375 of machine code does not match the order of the source lines. For
3376 example, in the following excerpt from a debugging session, the @code{f}
3377 (@code{frame}) command shows that execution is stopped at line
3378 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3382 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3384 (@value{GDBP}) until
3385 195 for ( ; argc > 0; NEXTARG) @{
3388 This happened because, for execution efficiency, the compiler had
3389 generated code for the loop closure test at the end, rather than the
3390 start, of the loop---even though the test in a C @code{for}-loop is
3391 written before the body of the loop. The @code{until} command appeared
3392 to step back to the beginning of the loop when it advanced to this
3393 expression; however, it has not really gone to an earlier
3394 statement---not in terms of the actual machine code.
3396 @code{until} with no argument works by means of single
3397 instruction stepping, and hence is slower than @code{until} with an
3400 @item until @var{location}
3401 @itemx u @var{location}
3402 Continue running your program until either the specified location is
3403 reached, or the current stack frame returns. @var{location} is any of
3404 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3405 ,Setting breakpoints}). This form of the command uses breakpoints,
3406 and hence is quicker than @code{until} without an argument.
3409 @kindex si @r{(@code{stepi})}
3411 @itemx stepi @var{arg}
3413 Execute one machine instruction, then stop and return to the debugger.
3415 It is often useful to do @samp{display/i $pc} when stepping by machine
3416 instructions. This makes @value{GDBN} automatically display the next
3417 instruction to be executed, each time your program stops. @xref{Auto
3418 Display,, Automatic display}.
3420 An argument is a repeat count, as in @code{step}.
3424 @kindex ni @r{(@code{nexti})}
3426 @itemx nexti @var{arg}
3428 Execute one machine instruction, but if it is a function call,
3429 proceed until the function returns.
3431 An argument is a repeat count, as in @code{next}.
3438 A signal is an asynchronous event that can happen in a program. The
3439 operating system defines the possible kinds of signals, and gives each
3440 kind a name and a number. For example, in Unix @code{SIGINT} is the
3441 signal a program gets when you type an interrupt character (often @kbd{C-c});
3442 @code{SIGSEGV} is the signal a program gets from referencing a place in
3443 memory far away from all the areas in use; @code{SIGALRM} occurs when
3444 the alarm clock timer goes off (which happens only if your program has
3445 requested an alarm).
3447 @cindex fatal signals
3448 Some signals, including @code{SIGALRM}, are a normal part of the
3449 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3450 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3451 program has not specified in advance some other way to handle the signal.
3452 @code{SIGINT} does not indicate an error in your program, but it is normally
3453 fatal so it can carry out the purpose of the interrupt: to kill the program.
3455 @value{GDBN} has the ability to detect any occurrence of a signal in your
3456 program. You can tell @value{GDBN} in advance what to do for each kind of
3459 @cindex handling signals
3460 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3461 @code{SIGALRM} be silently passed to your program
3462 (so as not to interfere with their role in the program's functioning)
3463 but to stop your program immediately whenever an error signal happens.
3464 You can change these settings with the @code{handle} command.
3467 @kindex info signals
3470 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3471 handle each one. You can use this to see the signal numbers of all
3472 the defined types of signals.
3474 @code{info handle} is an alias for @code{info signals}.
3477 @item handle @var{signal} @var{keywords}@dots{}
3478 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3479 can be the number of a signal or its name (with or without the
3480 @samp{SIG} at the beginning); a list of signal numbers of the form
3481 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3482 known signals. The @var{keywords} say what change to make.
3486 The keywords allowed by the @code{handle} command can be abbreviated.
3487 Their full names are:
3491 @value{GDBN} should not stop your program when this signal happens. It may
3492 still print a message telling you that the signal has come in.
3495 @value{GDBN} should stop your program when this signal happens. This implies
3496 the @code{print} keyword as well.
3499 @value{GDBN} should print a message when this signal happens.
3502 @value{GDBN} should not mention the occurrence of the signal at all. This
3503 implies the @code{nostop} keyword as well.
3507 @value{GDBN} should allow your program to see this signal; your program
3508 can handle the signal, or else it may terminate if the signal is fatal
3509 and not handled. @code{pass} and @code{noignore} are synonyms.
3513 @value{GDBN} should not allow your program to see this signal.
3514 @code{nopass} and @code{ignore} are synonyms.
3518 When a signal stops your program, the signal is not visible to the
3520 continue. Your program sees the signal then, if @code{pass} is in
3521 effect for the signal in question @emph{at that time}. In other words,
3522 after @value{GDBN} reports a signal, you can use the @code{handle}
3523 command with @code{pass} or @code{nopass} to control whether your
3524 program sees that signal when you continue.
3526 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3527 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3528 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3531 You can also use the @code{signal} command to prevent your program from
3532 seeing a signal, or cause it to see a signal it normally would not see,
3533 or to give it any signal at any time. For example, if your program stopped
3534 due to some sort of memory reference error, you might store correct
3535 values into the erroneous variables and continue, hoping to see more
3536 execution; but your program would probably terminate immediately as
3537 a result of the fatal signal once it saw the signal. To prevent this,
3538 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3542 @section Stopping and starting multi-thread programs
3544 When your program has multiple threads (@pxref{Threads,, Debugging
3545 programs with multiple threads}), you can choose whether to set
3546 breakpoints on all threads, or on a particular thread.
3549 @cindex breakpoints and threads
3550 @cindex thread breakpoints
3551 @kindex break @dots{} thread @var{threadno}
3552 @item break @var{linespec} thread @var{threadno}
3553 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3554 @var{linespec} specifies source lines; there are several ways of
3555 writing them, but the effect is always to specify some source line.
3557 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3558 to specify that you only want @value{GDBN} to stop the program when a
3559 particular thread reaches this breakpoint. @var{threadno} is one of the
3560 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3561 column of the @samp{info threads} display.
3563 If you do not specify @samp{thread @var{threadno}} when you set a
3564 breakpoint, the breakpoint applies to @emph{all} threads of your
3567 You can use the @code{thread} qualifier on conditional breakpoints as
3568 well; in this case, place @samp{thread @var{threadno}} before the
3569 breakpoint condition, like this:
3572 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3577 @cindex stopped threads
3578 @cindex threads, stopped
3579 Whenever your program stops under @value{GDBN} for any reason,
3580 @emph{all} threads of execution stop, not just the current thread. This
3581 allows you to examine the overall state of the program, including
3582 switching between threads, without worrying that things may change
3585 @cindex continuing threads
3586 @cindex threads, continuing
3587 Conversely, whenever you restart the program, @emph{all} threads start
3588 executing. @emph{This is true even when single-stepping} with commands
3589 like @code{step} or @code{next}.
3591 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3592 Since thread scheduling is up to your debugging target's operating
3593 system (not controlled by @value{GDBN}), other threads may
3594 execute more than one statement while the current thread completes a
3595 single step. Moreover, in general other threads stop in the middle of a
3596 statement, rather than at a clean statement boundary, when the program
3599 You might even find your program stopped in another thread after
3600 continuing or even single-stepping. This happens whenever some other
3601 thread runs into a breakpoint, a signal, or an exception before the
3602 first thread completes whatever you requested.
3604 On some OSes, you can lock the OS scheduler and thus allow only a single
3608 @item set scheduler-locking @var{mode}
3609 Set the scheduler locking mode. If it is @code{off}, then there is no
3610 locking and any thread may run at any time. If @code{on}, then only the
3611 current thread may run when the inferior is resumed. The @code{step}
3612 mode optimizes for single-stepping. It stops other threads from
3613 ``seizing the prompt'' by preempting the current thread while you are
3614 stepping. Other threads will only rarely (or never) get a chance to run
3615 when you step. They are more likely to run when you @samp{next} over a
3616 function call, and they are completely free to run when you use commands
3617 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3618 thread hits a breakpoint during its timeslice, they will never steal the
3619 @value{GDBN} prompt away from the thread that you are debugging.
3621 @item show scheduler-locking
3622 Display the current scheduler locking mode.
3627 @chapter Examining the Stack
3629 When your program has stopped, the first thing you need to know is where it
3630 stopped and how it got there.
3633 Each time your program performs a function call, information about the call
3635 That information includes the location of the call in your program,
3636 the arguments of the call,
3637 and the local variables of the function being called.
3638 The information is saved in a block of data called a @dfn{stack frame}.
3639 The stack frames are allocated in a region of memory called the @dfn{call
3642 When your program stops, the @value{GDBN} commands for examining the
3643 stack allow you to see all of this information.
3645 @cindex selected frame
3646 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3647 @value{GDBN} commands refer implicitly to the selected frame. In
3648 particular, whenever you ask @value{GDBN} for the value of a variable in
3649 your program, the value is found in the selected frame. There are
3650 special @value{GDBN} commands to select whichever frame you are
3651 interested in. @xref{Selection, ,Selecting a frame}.
3653 When your program stops, @value{GDBN} automatically selects the
3654 currently executing frame and describes it briefly, similar to the
3655 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3658 * Frames:: Stack frames
3659 * Backtrace:: Backtraces
3660 * Selection:: Selecting a frame
3661 * Frame Info:: Information on a frame
3666 @section Stack frames
3668 @cindex frame, definition
3670 The call stack is divided up into contiguous pieces called @dfn{stack
3671 frames}, or @dfn{frames} for short; each frame is the data associated
3672 with one call to one function. The frame contains the arguments given
3673 to the function, the function's local variables, and the address at
3674 which the function is executing.
3676 @cindex initial frame
3677 @cindex outermost frame
3678 @cindex innermost frame
3679 When your program is started, the stack has only one frame, that of the
3680 function @code{main}. This is called the @dfn{initial} frame or the
3681 @dfn{outermost} frame. Each time a function is called, a new frame is
3682 made. Each time a function returns, the frame for that function invocation
3683 is eliminated. If a function is recursive, there can be many frames for
3684 the same function. The frame for the function in which execution is
3685 actually occurring is called the @dfn{innermost} frame. This is the most
3686 recently created of all the stack frames that still exist.
3688 @cindex frame pointer
3689 Inside your program, stack frames are identified by their addresses. A
3690 stack frame consists of many bytes, each of which has its own address; each
3691 kind of computer has a convention for choosing one byte whose
3692 address serves as the address of the frame. Usually this address is kept
3693 in a register called the @dfn{frame pointer register} while execution is
3694 going on in that frame.
3696 @cindex frame number
3697 @value{GDBN} assigns numbers to all existing stack frames, starting with
3698 zero for the innermost frame, one for the frame that called it,
3699 and so on upward. These numbers do not really exist in your program;
3700 they are assigned by @value{GDBN} to give you a way of designating stack
3701 frames in @value{GDBN} commands.
3703 @c The -fomit-frame-pointer below perennially causes hbox overflow
3704 @c underflow problems.
3705 @cindex frameless execution
3706 Some compilers provide a way to compile functions so that they operate
3707 without stack frames. (For example, the @value{GCC} option
3709 @samp{-fomit-frame-pointer}
3711 generates functions without a frame.)
3712 This is occasionally done with heavily used library functions to save
3713 the frame setup time. @value{GDBN} has limited facilities for dealing
3714 with these function invocations. If the innermost function invocation
3715 has no stack frame, @value{GDBN} nevertheless regards it as though
3716 it had a separate frame, which is numbered zero as usual, allowing
3717 correct tracing of the function call chain. However, @value{GDBN} has
3718 no provision for frameless functions elsewhere in the stack.
3721 @kindex frame@r{, command}
3722 @cindex current stack frame
3723 @item frame @var{args}
3724 The @code{frame} command allows you to move from one stack frame to another,
3725 and to print the stack frame you select. @var{args} may be either the
3726 address of the frame or the stack frame number. Without an argument,
3727 @code{frame} prints the current stack frame.
3729 @kindex select-frame
3730 @cindex selecting frame silently
3732 The @code{select-frame} command allows you to move from one stack frame
3733 to another without printing the frame. This is the silent version of
3742 @cindex stack traces
3743 A backtrace is a summary of how your program got where it is. It shows one
3744 line per frame, for many frames, starting with the currently executing
3745 frame (frame zero), followed by its caller (frame one), and on up the
3750 @kindex bt @r{(@code{backtrace})}
3753 Print a backtrace of the entire stack: one line per frame for all
3754 frames in the stack.
3756 You can stop the backtrace at any time by typing the system interrupt
3757 character, normally @kbd{C-c}.
3759 @item backtrace @var{n}
3761 Similar, but print only the innermost @var{n} frames.
3763 @item backtrace -@var{n}
3765 Similar, but print only the outermost @var{n} frames.
3770 @kindex info s @r{(@code{info stack})}
3771 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3772 are additional aliases for @code{backtrace}.
3774 Each line in the backtrace shows the frame number and the function name.
3775 The program counter value is also shown---unless you use @code{set
3776 print address off}. The backtrace also shows the source file name and
3777 line number, as well as the arguments to the function. The program
3778 counter value is omitted if it is at the beginning of the code for that
3781 Here is an example of a backtrace. It was made with the command
3782 @samp{bt 3}, so it shows the innermost three frames.
3786 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3788 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3789 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3791 (More stack frames follow...)
3796 The display for frame zero does not begin with a program counter
3797 value, indicating that your program has stopped at the beginning of the
3798 code for line @code{993} of @code{builtin.c}.
3801 @section Selecting a frame
3803 Most commands for examining the stack and other data in your program work on
3804 whichever stack frame is selected at the moment. Here are the commands for
3805 selecting a stack frame; all of them finish by printing a brief description
3806 of the stack frame just selected.
3809 @kindex frame@r{, selecting}
3810 @kindex f @r{(@code{frame})}
3813 Select frame number @var{n}. Recall that frame zero is the innermost
3814 (currently executing) frame, frame one is the frame that called the
3815 innermost one, and so on. The highest-numbered frame is the one for
3818 @item frame @var{addr}
3820 Select the frame at address @var{addr}. This is useful mainly if the
3821 chaining of stack frames has been damaged by a bug, making it
3822 impossible for @value{GDBN} to assign numbers properly to all frames. In
3823 addition, this can be useful when your program has multiple stacks and
3824 switches between them.
3826 On the SPARC architecture, @code{frame} needs two addresses to
3827 select an arbitrary frame: a frame pointer and a stack pointer.
3829 On the MIPS and Alpha architecture, it needs two addresses: a stack
3830 pointer and a program counter.
3832 On the 29k architecture, it needs three addresses: a register stack
3833 pointer, a program counter, and a memory stack pointer.
3834 @c note to future updaters: this is conditioned on a flag
3835 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3836 @c as of 27 Jan 1994.
3840 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3841 advances toward the outermost frame, to higher frame numbers, to frames
3842 that have existed longer. @var{n} defaults to one.
3845 @kindex do @r{(@code{down})}
3847 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3848 advances toward the innermost frame, to lower frame numbers, to frames
3849 that were created more recently. @var{n} defaults to one. You may
3850 abbreviate @code{down} as @code{do}.
3853 All of these commands end by printing two lines of output describing the
3854 frame. The first line shows the frame number, the function name, the
3855 arguments, and the source file and line number of execution in that
3856 frame. The second line shows the text of that source line.
3864 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3866 10 read_input_file (argv[i]);
3870 After such a printout, the @code{list} command with no arguments
3871 prints ten lines centered on the point of execution in the frame.
3872 @xref{List, ,Printing source lines}.
3875 @kindex down-silently
3877 @item up-silently @var{n}
3878 @itemx down-silently @var{n}
3879 These two commands are variants of @code{up} and @code{down},
3880 respectively; they differ in that they do their work silently, without
3881 causing display of the new frame. They are intended primarily for use
3882 in @value{GDBN} command scripts, where the output might be unnecessary and
3887 @section Information about a frame
3889 There are several other commands to print information about the selected
3895 When used without any argument, this command does not change which
3896 frame is selected, but prints a brief description of the currently
3897 selected stack frame. It can be abbreviated @code{f}. With an
3898 argument, this command is used to select a stack frame.
3899 @xref{Selection, ,Selecting a frame}.
3902 @kindex info f @r{(@code{info frame})}
3905 This command prints a verbose description of the selected stack frame,
3910 the address of the frame
3912 the address of the next frame down (called by this frame)
3914 the address of the next frame up (caller of this frame)
3916 the language in which the source code corresponding to this frame is written
3918 the address of the frame's arguments
3920 the address of the frame's local variables
3922 the program counter saved in it (the address of execution in the caller frame)
3924 which registers were saved in the frame
3927 @noindent The verbose description is useful when
3928 something has gone wrong that has made the stack format fail to fit
3929 the usual conventions.
3931 @item info frame @var{addr}
3932 @itemx info f @var{addr}
3933 Print a verbose description of the frame at address @var{addr}, without
3934 selecting that frame. The selected frame remains unchanged by this
3935 command. This requires the same kind of address (more than one for some
3936 architectures) that you specify in the @code{frame} command.
3937 @xref{Selection, ,Selecting a frame}.
3941 Print the arguments of the selected frame, each on a separate line.
3945 Print the local variables of the selected frame, each on a separate
3946 line. These are all variables (declared either static or automatic)
3947 accessible at the point of execution of the selected frame.
3950 @cindex catch exceptions, list active handlers
3951 @cindex exception handlers, how to list
3953 Print a list of all the exception handlers that are active in the
3954 current stack frame at the current point of execution. To see other
3955 exception handlers, visit the associated frame (using the @code{up},
3956 @code{down}, or @code{frame} commands); then type @code{info catch}.
3957 @xref{Set Catchpoints, , Setting catchpoints}.
3963 @chapter Examining Source Files
3965 @value{GDBN} can print parts of your program's source, since the debugging
3966 information recorded in the program tells @value{GDBN} what source files were
3967 used to build it. When your program stops, @value{GDBN} spontaneously prints
3968 the line where it stopped. Likewise, when you select a stack frame
3969 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3970 execution in that frame has stopped. You can print other portions of
3971 source files by explicit command.
3973 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3974 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3975 @value{GDBN} under @sc{gnu} Emacs}.
3978 * List:: Printing source lines
3979 * Search:: Searching source files
3980 * Source Path:: Specifying source directories
3981 * Machine Code:: Source and machine code
3985 @section Printing source lines
3988 @kindex l @r{(@code{list})}
3989 To print lines from a source file, use the @code{list} command
3990 (abbreviated @code{l}). By default, ten lines are printed.
3991 There are several ways to specify what part of the file you want to print.
3993 Here are the forms of the @code{list} command most commonly used:
3996 @item list @var{linenum}
3997 Print lines centered around line number @var{linenum} in the
3998 current source file.
4000 @item list @var{function}
4001 Print lines centered around the beginning of function
4005 Print more lines. If the last lines printed were printed with a
4006 @code{list} command, this prints lines following the last lines
4007 printed; however, if the last line printed was a solitary line printed
4008 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4009 Stack}), this prints lines centered around that line.
4012 Print lines just before the lines last printed.
4015 By default, @value{GDBN} prints ten source lines with any of these forms of
4016 the @code{list} command. You can change this using @code{set listsize}:
4019 @kindex set listsize
4020 @item set listsize @var{count}
4021 Make the @code{list} command display @var{count} source lines (unless
4022 the @code{list} argument explicitly specifies some other number).
4024 @kindex show listsize
4026 Display the number of lines that @code{list} prints.
4029 Repeating a @code{list} command with @key{RET} discards the argument,
4030 so it is equivalent to typing just @code{list}. This is more useful
4031 than listing the same lines again. An exception is made for an
4032 argument of @samp{-}; that argument is preserved in repetition so that
4033 each repetition moves up in the source file.
4036 In general, the @code{list} command expects you to supply zero, one or two
4037 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4038 of writing them, but the effect is always to specify some source line.
4039 Here is a complete description of the possible arguments for @code{list}:
4042 @item list @var{linespec}
4043 Print lines centered around the line specified by @var{linespec}.
4045 @item list @var{first},@var{last}
4046 Print lines from @var{first} to @var{last}. Both arguments are
4049 @item list ,@var{last}
4050 Print lines ending with @var{last}.
4052 @item list @var{first},
4053 Print lines starting with @var{first}.
4056 Print lines just after the lines last printed.
4059 Print lines just before the lines last printed.
4062 As described in the preceding table.
4065 Here are the ways of specifying a single source line---all the
4070 Specifies line @var{number} of the current source file.
4071 When a @code{list} command has two linespecs, this refers to
4072 the same source file as the first linespec.
4075 Specifies the line @var{offset} lines after the last line printed.
4076 When used as the second linespec in a @code{list} command that has
4077 two, this specifies the line @var{offset} lines down from the
4081 Specifies the line @var{offset} lines before the last line printed.
4083 @item @var{filename}:@var{number}
4084 Specifies line @var{number} in the source file @var{filename}.
4086 @item @var{function}
4087 Specifies the line that begins the body of the function @var{function}.
4088 For example: in C, this is the line with the open brace.
4090 @item @var{filename}:@var{function}
4091 Specifies the line of the open-brace that begins the body of the
4092 function @var{function} in the file @var{filename}. You only need the
4093 file name with a function name to avoid ambiguity when there are
4094 identically named functions in different source files.
4096 @item *@var{address}
4097 Specifies the line containing the program address @var{address}.
4098 @var{address} may be any expression.
4102 @section Searching source files
4104 @kindex reverse-search
4106 There are two commands for searching through the current source file for a
4111 @kindex forward-search
4112 @item forward-search @var{regexp}
4113 @itemx search @var{regexp}
4114 The command @samp{forward-search @var{regexp}} checks each line,
4115 starting with the one following the last line listed, for a match for
4116 @var{regexp}. It lists the line that is found. You can use the
4117 synonym @samp{search @var{regexp}} or abbreviate the command name as
4120 @item reverse-search @var{regexp}
4121 The command @samp{reverse-search @var{regexp}} checks each line, starting
4122 with the one before the last line listed and going backward, for a match
4123 for @var{regexp}. It lists the line that is found. You can abbreviate
4124 this command as @code{rev}.
4128 @section Specifying source directories
4131 @cindex directories for source files
4132 Executable programs sometimes do not record the directories of the source
4133 files from which they were compiled, just the names. Even when they do,
4134 the directories could be moved between the compilation and your debugging
4135 session. @value{GDBN} has a list of directories to search for source files;
4136 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4137 it tries all the directories in the list, in the order they are present
4138 in the list, until it finds a file with the desired name. Note that
4139 the executable search path is @emph{not} used for this purpose. Neither is
4140 the current working directory, unless it happens to be in the source
4143 If @value{GDBN} cannot find a source file in the source path, and the
4144 object program records a directory, @value{GDBN} tries that directory
4145 too. If the source path is empty, and there is no record of the
4146 compilation directory, @value{GDBN} looks in the current directory as a
4149 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4150 any information it has cached about where source files are found and where
4151 each line is in the file.
4155 When you start @value{GDBN}, its source path includes only @samp{cdir}
4156 and @samp{cwd}, in that order.
4157 To add other directories, use the @code{directory} command.
4160 @item directory @var{dirname} @dots{}
4161 @item dir @var{dirname} @dots{}
4162 Add directory @var{dirname} to the front of the source path. Several
4163 directory names may be given to this command, separated by @samp{:}
4164 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4165 part of absolute file names) or
4166 whitespace. You may specify a directory that is already in the source
4167 path; this moves it forward, so @value{GDBN} searches it sooner.
4171 @vindex $cdir@r{, convenience variable}
4172 @vindex $cwdr@r{, convenience variable}
4173 @cindex compilation directory
4174 @cindex current directory
4175 @cindex working directory
4176 @cindex directory, current
4177 @cindex directory, compilation
4178 You can use the string @samp{$cdir} to refer to the compilation
4179 directory (if one is recorded), and @samp{$cwd} to refer to the current
4180 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4181 tracks the current working directory as it changes during your @value{GDBN}
4182 session, while the latter is immediately expanded to the current
4183 directory at the time you add an entry to the source path.
4186 Reset the source path to empty again. This requires confirmation.
4188 @c RET-repeat for @code{directory} is explicitly disabled, but since
4189 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4191 @item show directories
4192 @kindex show directories
4193 Print the source path: show which directories it contains.
4196 If your source path is cluttered with directories that are no longer of
4197 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4198 versions of source. You can correct the situation as follows:
4202 Use @code{directory} with no argument to reset the source path to empty.
4205 Use @code{directory} with suitable arguments to reinstall the
4206 directories you want in the source path. You can add all the
4207 directories in one command.
4211 @section Source and machine code
4213 You can use the command @code{info line} to map source lines to program
4214 addresses (and vice versa), and the command @code{disassemble} to display
4215 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4216 mode, the @code{info line} command causes the arrow to point to the
4217 line specified. Also, @code{info line} prints addresses in symbolic form as
4222 @item info line @var{linespec}
4223 Print the starting and ending addresses of the compiled code for
4224 source line @var{linespec}. You can specify source lines in any of
4225 the ways understood by the @code{list} command (@pxref{List, ,Printing
4229 For example, we can use @code{info line} to discover the location of
4230 the object code for the first line of function
4231 @code{m4_changequote}:
4233 @c FIXME: I think this example should also show the addresses in
4234 @c symbolic form, as they usually would be displayed.
4236 (@value{GDBP}) info line m4_changequote
4237 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4241 We can also inquire (using @code{*@var{addr}} as the form for
4242 @var{linespec}) what source line covers a particular address:
4244 (@value{GDBP}) info line *0x63ff
4245 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4248 @cindex @code{$_} and @code{info line}
4249 @kindex x@r{(examine), and} info line
4250 After @code{info line}, the default address for the @code{x} command
4251 is changed to the starting address of the line, so that @samp{x/i} is
4252 sufficient to begin examining the machine code (@pxref{Memory,
4253 ,Examining memory}). Also, this address is saved as the value of the
4254 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4259 @cindex assembly instructions
4260 @cindex instructions, assembly
4261 @cindex machine instructions
4262 @cindex listing machine instructions
4264 This specialized command dumps a range of memory as machine
4265 instructions. The default memory range is the function surrounding the
4266 program counter of the selected frame. A single argument to this
4267 command is a program counter value; @value{GDBN} dumps the function
4268 surrounding this value. Two arguments specify a range of addresses
4269 (first inclusive, second exclusive) to dump.
4272 The following example shows the disassembly of a range of addresses of
4273 HP PA-RISC 2.0 code:
4276 (@value{GDBP}) disas 0x32c4 0x32e4
4277 Dump of assembler code from 0x32c4 to 0x32e4:
4278 0x32c4 <main+204>: addil 0,dp
4279 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4280 0x32cc <main+212>: ldil 0x3000,r31
4281 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4282 0x32d4 <main+220>: ldo 0(r31),rp
4283 0x32d8 <main+224>: addil -0x800,dp
4284 0x32dc <main+228>: ldo 0x588(r1),r26
4285 0x32e0 <main+232>: ldil 0x3000,r31
4286 End of assembler dump.
4289 Some architectures have more than one commonly-used set of instruction
4290 mnemonics or other syntax.
4293 @kindex set disassembly-flavor
4294 @cindex assembly instructions
4295 @cindex instructions, assembly
4296 @cindex machine instructions
4297 @cindex listing machine instructions
4298 @cindex Intel disassembly flavor
4299 @cindex AT&T disassembly flavor
4300 @item set disassembly-flavor @var{instruction-set}
4301 Select the instruction set to use when disassembling the
4302 program via the @code{disassemble} or @code{x/i} commands.
4304 Currently this command is only defined for the Intel x86 family. You
4305 can set @var{instruction-set} to either @code{intel} or @code{att}.
4306 The default is @code{att}, the AT&T flavor used by default by Unix
4307 assemblers for x86-based targets.
4312 @chapter Examining Data
4314 @cindex printing data
4315 @cindex examining data
4318 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4319 @c document because it is nonstandard... Under Epoch it displays in a
4320 @c different window or something like that.
4321 The usual way to examine data in your program is with the @code{print}
4322 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4323 evaluates and prints the value of an expression of the language your
4324 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4325 Different Languages}).
4328 @item print @var{expr}
4329 @itemx print /@var{f} @var{expr}
4330 @var{expr} is an expression (in the source language). By default the
4331 value of @var{expr} is printed in a format appropriate to its data type;
4332 you can choose a different format by specifying @samp{/@var{f}}, where
4333 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4337 @itemx print /@var{f}
4338 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4339 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4340 conveniently inspect the same value in an alternative format.
4343 A more low-level way of examining data is with the @code{x} command.
4344 It examines data in memory at a specified address and prints it in a
4345 specified format. @xref{Memory, ,Examining memory}.
4347 If you are interested in information about types, or about how the
4348 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4349 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4353 * Expressions:: Expressions
4354 * Variables:: Program variables
4355 * Arrays:: Artificial arrays
4356 * Output Formats:: Output formats
4357 * Memory:: Examining memory
4358 * Auto Display:: Automatic display
4359 * Print Settings:: Print settings
4360 * Value History:: Value history
4361 * Convenience Vars:: Convenience variables
4362 * Registers:: Registers
4363 * Floating Point Hardware:: Floating point hardware
4364 * Memory Region Attributes:: Memory region attributes
4368 @section Expressions
4371 @code{print} and many other @value{GDBN} commands accept an expression and
4372 compute its value. Any kind of constant, variable or operator defined
4373 by the programming language you are using is valid in an expression in
4374 @value{GDBN}. This includes conditional expressions, function calls, casts
4375 and string constants. It unfortunately does not include symbols defined
4376 by preprocessor @code{#define} commands.
4378 @value{GDBN} supports array constants in expressions input by
4379 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4380 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4381 memory that is @code{malloc}ed in the target program.
4383 Because C is so widespread, most of the expressions shown in examples in
4384 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4385 Languages}, for information on how to use expressions in other
4388 In this section, we discuss operators that you can use in @value{GDBN}
4389 expressions regardless of your programming language.
4391 Casts are supported in all languages, not just in C, because it is so
4392 useful to cast a number into a pointer in order to examine a structure
4393 at that address in memory.
4394 @c FIXME: casts supported---Mod2 true?
4396 @value{GDBN} supports these operators, in addition to those common
4397 to programming languages:
4401 @samp{@@} is a binary operator for treating parts of memory as arrays.
4402 @xref{Arrays, ,Artificial arrays}, for more information.
4405 @samp{::} allows you to specify a variable in terms of the file or
4406 function where it is defined. @xref{Variables, ,Program variables}.
4408 @cindex @{@var{type}@}
4409 @cindex type casting memory
4410 @cindex memory, viewing as typed object
4411 @cindex casts, to view memory
4412 @item @{@var{type}@} @var{addr}
4413 Refers to an object of type @var{type} stored at address @var{addr} in
4414 memory. @var{addr} may be any expression whose value is an integer or
4415 pointer (but parentheses are required around binary operators, just as in
4416 a cast). This construct is allowed regardless of what kind of data is
4417 normally supposed to reside at @var{addr}.
4421 @section Program variables
4423 The most common kind of expression to use is the name of a variable
4426 Variables in expressions are understood in the selected stack frame
4427 (@pxref{Selection, ,Selecting a frame}); they must be either:
4431 global (or file-static)
4438 visible according to the scope rules of the
4439 programming language from the point of execution in that frame
4442 @noindent This means that in the function
4457 you can examine and use the variable @code{a} whenever your program is
4458 executing within the function @code{foo}, but you can only use or
4459 examine the variable @code{b} while your program is executing inside
4460 the block where @code{b} is declared.
4462 @cindex variable name conflict
4463 There is an exception: you can refer to a variable or function whose
4464 scope is a single source file even if the current execution point is not
4465 in this file. But it is possible to have more than one such variable or
4466 function with the same name (in different source files). If that
4467 happens, referring to that name has unpredictable effects. If you wish,
4468 you can specify a static variable in a particular function or file,
4469 using the colon-colon notation:
4471 @cindex colon-colon, context for variables/functions
4473 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4474 @cindex @code{::}, context for variables/functions
4477 @var{file}::@var{variable}
4478 @var{function}::@var{variable}
4482 Here @var{file} or @var{function} is the name of the context for the
4483 static @var{variable}. In the case of file names, you can use quotes to
4484 make sure @value{GDBN} parses the file name as a single word---for example,
4485 to print a global value of @code{x} defined in @file{f2.c}:
4488 (@value{GDBP}) p 'f2.c'::x
4491 @cindex C@t{++} scope resolution
4492 This use of @samp{::} is very rarely in conflict with the very similar
4493 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4494 scope resolution operator in @value{GDBN} expressions.
4495 @c FIXME: Um, so what happens in one of those rare cases where it's in
4498 @cindex wrong values
4499 @cindex variable values, wrong
4501 @emph{Warning:} Occasionally, a local variable may appear to have the
4502 wrong value at certain points in a function---just after entry to a new
4503 scope, and just before exit.
4505 You may see this problem when you are stepping by machine instructions.
4506 This is because, on most machines, it takes more than one instruction to
4507 set up a stack frame (including local variable definitions); if you are
4508 stepping by machine instructions, variables may appear to have the wrong
4509 values until the stack frame is completely built. On exit, it usually
4510 also takes more than one machine instruction to destroy a stack frame;
4511 after you begin stepping through that group of instructions, local
4512 variable definitions may be gone.
4514 This may also happen when the compiler does significant optimizations.
4515 To be sure of always seeing accurate values, turn off all optimization
4518 @cindex ``No symbol "foo" in current context''
4519 Another possible effect of compiler optimizations is to optimize
4520 unused variables out of existence, or assign variables to registers (as
4521 opposed to memory addresses). Depending on the support for such cases
4522 offered by the debug info format used by the compiler, @value{GDBN}
4523 might not be able to display values for such local variables. If that
4524 happens, @value{GDBN} will print a message like this:
4527 No symbol "foo" in current context.
4530 To solve such problems, either recompile without optimizations, or use a
4531 different debug info format, if the compiler supports several such
4532 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4533 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4534 in a format that is superior to formats such as COFF. You may be able
4535 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4536 debug info. See @ref{Debugging Options,,Options for Debugging Your
4537 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4542 @section Artificial arrays
4544 @cindex artificial array
4545 @kindex @@@r{, referencing memory as an array}
4546 It is often useful to print out several successive objects of the
4547 same type in memory; a section of an array, or an array of
4548 dynamically determined size for which only a pointer exists in the
4551 You can do this by referring to a contiguous span of memory as an
4552 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4553 operand of @samp{@@} should be the first element of the desired array
4554 and be an individual object. The right operand should be the desired length
4555 of the array. The result is an array value whose elements are all of
4556 the type of the left argument. The first element is actually the left
4557 argument; the second element comes from bytes of memory immediately
4558 following those that hold the first element, and so on. Here is an
4559 example. If a program says
4562 int *array = (int *) malloc (len * sizeof (int));
4566 you can print the contents of @code{array} with
4572 The left operand of @samp{@@} must reside in memory. Array values made
4573 with @samp{@@} in this way behave just like other arrays in terms of
4574 subscripting, and are coerced to pointers when used in expressions.
4575 Artificial arrays most often appear in expressions via the value history
4576 (@pxref{Value History, ,Value history}), after printing one out.
4578 Another way to create an artificial array is to use a cast.
4579 This re-interprets a value as if it were an array.
4580 The value need not be in memory:
4582 (@value{GDBP}) p/x (short[2])0x12345678
4583 $1 = @{0x1234, 0x5678@}
4586 As a convenience, if you leave the array length out (as in
4587 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4588 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4590 (@value{GDBP}) p/x (short[])0x12345678
4591 $2 = @{0x1234, 0x5678@}
4594 Sometimes the artificial array mechanism is not quite enough; in
4595 moderately complex data structures, the elements of interest may not
4596 actually be adjacent---for example, if you are interested in the values
4597 of pointers in an array. One useful work-around in this situation is
4598 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4599 variables}) as a counter in an expression that prints the first
4600 interesting value, and then repeat that expression via @key{RET}. For
4601 instance, suppose you have an array @code{dtab} of pointers to
4602 structures, and you are interested in the values of a field @code{fv}
4603 in each structure. Here is an example of what you might type:
4613 @node Output Formats
4614 @section Output formats
4616 @cindex formatted output
4617 @cindex output formats
4618 By default, @value{GDBN} prints a value according to its data type. Sometimes
4619 this is not what you want. For example, you might want to print a number
4620 in hex, or a pointer in decimal. Or you might want to view data in memory
4621 at a certain address as a character string or as an instruction. To do
4622 these things, specify an @dfn{output format} when you print a value.
4624 The simplest use of output formats is to say how to print a value
4625 already computed. This is done by starting the arguments of the
4626 @code{print} command with a slash and a format letter. The format
4627 letters supported are:
4631 Regard the bits of the value as an integer, and print the integer in
4635 Print as integer in signed decimal.
4638 Print as integer in unsigned decimal.
4641 Print as integer in octal.
4644 Print as integer in binary. The letter @samp{t} stands for ``two''.
4645 @footnote{@samp{b} cannot be used because these format letters are also
4646 used with the @code{x} command, where @samp{b} stands for ``byte'';
4647 see @ref{Memory,,Examining memory}.}
4650 @cindex unknown address, locating
4651 @cindex locate address
4652 Print as an address, both absolute in hexadecimal and as an offset from
4653 the nearest preceding symbol. You can use this format used to discover
4654 where (in what function) an unknown address is located:
4657 (@value{GDBP}) p/a 0x54320
4658 $3 = 0x54320 <_initialize_vx+396>
4662 The command @code{info symbol 0x54320} yields similar results.
4663 @xref{Symbols, info symbol}.
4666 Regard as an integer and print it as a character constant.
4669 Regard the bits of the value as a floating point number and print
4670 using typical floating point syntax.
4673 For example, to print the program counter in hex (@pxref{Registers}), type
4680 Note that no space is required before the slash; this is because command
4681 names in @value{GDBN} cannot contain a slash.
4683 To reprint the last value in the value history with a different format,
4684 you can use the @code{print} command with just a format and no
4685 expression. For example, @samp{p/x} reprints the last value in hex.
4688 @section Examining memory
4690 You can use the command @code{x} (for ``examine'') to examine memory in
4691 any of several formats, independently of your program's data types.
4693 @cindex examining memory
4695 @kindex x @r{(examine memory)}
4696 @item x/@var{nfu} @var{addr}
4699 Use the @code{x} command to examine memory.
4702 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4703 much memory to display and how to format it; @var{addr} is an
4704 expression giving the address where you want to start displaying memory.
4705 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4706 Several commands set convenient defaults for @var{addr}.
4709 @item @var{n}, the repeat count
4710 The repeat count is a decimal integer; the default is 1. It specifies
4711 how much memory (counting by units @var{u}) to display.
4712 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4715 @item @var{f}, the display format
4716 The display format is one of the formats used by @code{print},
4717 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4718 The default is @samp{x} (hexadecimal) initially.
4719 The default changes each time you use either @code{x} or @code{print}.
4721 @item @var{u}, the unit size
4722 The unit size is any of
4728 Halfwords (two bytes).
4730 Words (four bytes). This is the initial default.
4732 Giant words (eight bytes).
4735 Each time you specify a unit size with @code{x}, that size becomes the
4736 default unit the next time you use @code{x}. (For the @samp{s} and
4737 @samp{i} formats, the unit size is ignored and is normally not written.)
4739 @item @var{addr}, starting display address
4740 @var{addr} is the address where you want @value{GDBN} to begin displaying
4741 memory. The expression need not have a pointer value (though it may);
4742 it is always interpreted as an integer address of a byte of memory.
4743 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4744 @var{addr} is usually just after the last address examined---but several
4745 other commands also set the default address: @code{info breakpoints} (to
4746 the address of the last breakpoint listed), @code{info line} (to the
4747 starting address of a line), and @code{print} (if you use it to display
4748 a value from memory).
4751 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4752 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4753 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4754 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4755 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4757 Since the letters indicating unit sizes are all distinct from the
4758 letters specifying output formats, you do not have to remember whether
4759 unit size or format comes first; either order works. The output
4760 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4761 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4763 Even though the unit size @var{u} is ignored for the formats @samp{s}
4764 and @samp{i}, you might still want to use a count @var{n}; for example,
4765 @samp{3i} specifies that you want to see three machine instructions,
4766 including any operands. The command @code{disassemble} gives an
4767 alternative way of inspecting machine instructions; see @ref{Machine
4768 Code,,Source and machine code}.
4770 All the defaults for the arguments to @code{x} are designed to make it
4771 easy to continue scanning memory with minimal specifications each time
4772 you use @code{x}. For example, after you have inspected three machine
4773 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4774 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4775 the repeat count @var{n} is used again; the other arguments default as
4776 for successive uses of @code{x}.
4778 @cindex @code{$_}, @code{$__}, and value history
4779 The addresses and contents printed by the @code{x} command are not saved
4780 in the value history because there is often too much of them and they
4781 would get in the way. Instead, @value{GDBN} makes these values available for
4782 subsequent use in expressions as values of the convenience variables
4783 @code{$_} and @code{$__}. After an @code{x} command, the last address
4784 examined is available for use in expressions in the convenience variable
4785 @code{$_}. The contents of that address, as examined, are available in
4786 the convenience variable @code{$__}.
4788 If the @code{x} command has a repeat count, the address and contents saved
4789 are from the last memory unit printed; this is not the same as the last
4790 address printed if several units were printed on the last line of output.
4793 @section Automatic display
4794 @cindex automatic display
4795 @cindex display of expressions
4797 If you find that you want to print the value of an expression frequently
4798 (to see how it changes), you might want to add it to the @dfn{automatic
4799 display list} so that @value{GDBN} prints its value each time your program stops.
4800 Each expression added to the list is given a number to identify it;
4801 to remove an expression from the list, you specify that number.
4802 The automatic display looks like this:
4806 3: bar[5] = (struct hack *) 0x3804
4810 This display shows item numbers, expressions and their current values. As with
4811 displays you request manually using @code{x} or @code{print}, you can
4812 specify the output format you prefer; in fact, @code{display} decides
4813 whether to use @code{print} or @code{x} depending on how elaborate your
4814 format specification is---it uses @code{x} if you specify a unit size,
4815 or one of the two formats (@samp{i} and @samp{s}) that are only
4816 supported by @code{x}; otherwise it uses @code{print}.
4820 @item display @var{expr}
4821 Add the expression @var{expr} to the list of expressions to display
4822 each time your program stops. @xref{Expressions, ,Expressions}.
4824 @code{display} does not repeat if you press @key{RET} again after using it.
4826 @item display/@var{fmt} @var{expr}
4827 For @var{fmt} specifying only a display format and not a size or
4828 count, add the expression @var{expr} to the auto-display list but
4829 arrange to display it each time in the specified format @var{fmt}.
4830 @xref{Output Formats,,Output formats}.
4832 @item display/@var{fmt} @var{addr}
4833 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4834 number of units, add the expression @var{addr} as a memory address to
4835 be examined each time your program stops. Examining means in effect
4836 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4839 For example, @samp{display/i $pc} can be helpful, to see the machine
4840 instruction about to be executed each time execution stops (@samp{$pc}
4841 is a common name for the program counter; @pxref{Registers, ,Registers}).
4844 @kindex delete display
4846 @item undisplay @var{dnums}@dots{}
4847 @itemx delete display @var{dnums}@dots{}
4848 Remove item numbers @var{dnums} from the list of expressions to display.
4850 @code{undisplay} does not repeat if you press @key{RET} after using it.
4851 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4853 @kindex disable display
4854 @item disable display @var{dnums}@dots{}
4855 Disable the display of item numbers @var{dnums}. A disabled display
4856 item is not printed automatically, but is not forgotten. It may be
4857 enabled again later.
4859 @kindex enable display
4860 @item enable display @var{dnums}@dots{}
4861 Enable display of item numbers @var{dnums}. It becomes effective once
4862 again in auto display of its expression, until you specify otherwise.
4865 Display the current values of the expressions on the list, just as is
4866 done when your program stops.
4868 @kindex info display
4870 Print the list of expressions previously set up to display
4871 automatically, each one with its item number, but without showing the
4872 values. This includes disabled expressions, which are marked as such.
4873 It also includes expressions which would not be displayed right now
4874 because they refer to automatic variables not currently available.
4877 If a display expression refers to local variables, then it does not make
4878 sense outside the lexical context for which it was set up. Such an
4879 expression is disabled when execution enters a context where one of its
4880 variables is not defined. For example, if you give the command
4881 @code{display last_char} while inside a function with an argument
4882 @code{last_char}, @value{GDBN} displays this argument while your program
4883 continues to stop inside that function. When it stops elsewhere---where
4884 there is no variable @code{last_char}---the display is disabled
4885 automatically. The next time your program stops where @code{last_char}
4886 is meaningful, you can enable the display expression once again.
4888 @node Print Settings
4889 @section Print settings
4891 @cindex format options
4892 @cindex print settings
4893 @value{GDBN} provides the following ways to control how arrays, structures,
4894 and symbols are printed.
4897 These settings are useful for debugging programs in any language:
4900 @kindex set print address
4901 @item set print address
4902 @itemx set print address on
4903 @value{GDBN} prints memory addresses showing the location of stack
4904 traces, structure values, pointer values, breakpoints, and so forth,
4905 even when it also displays the contents of those addresses. The default
4906 is @code{on}. For example, this is what a stack frame display looks like with
4907 @code{set print address on}:
4912 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4914 530 if (lquote != def_lquote)
4918 @item set print address off
4919 Do not print addresses when displaying their contents. For example,
4920 this is the same stack frame displayed with @code{set print address off}:
4924 (@value{GDBP}) set print addr off
4926 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4927 530 if (lquote != def_lquote)
4931 You can use @samp{set print address off} to eliminate all machine
4932 dependent displays from the @value{GDBN} interface. For example, with
4933 @code{print address off}, you should get the same text for backtraces on
4934 all machines---whether or not they involve pointer arguments.
4936 @kindex show print address
4937 @item show print address
4938 Show whether or not addresses are to be printed.
4941 When @value{GDBN} prints a symbolic address, it normally prints the
4942 closest earlier symbol plus an offset. If that symbol does not uniquely
4943 identify the address (for example, it is a name whose scope is a single
4944 source file), you may need to clarify. One way to do this is with
4945 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4946 you can set @value{GDBN} to print the source file and line number when
4947 it prints a symbolic address:
4950 @kindex set print symbol-filename
4951 @item set print symbol-filename on
4952 Tell @value{GDBN} to print the source file name and line number of a
4953 symbol in the symbolic form of an address.
4955 @item set print symbol-filename off
4956 Do not print source file name and line number of a symbol. This is the
4959 @kindex show print symbol-filename
4960 @item show print symbol-filename
4961 Show whether or not @value{GDBN} will print the source file name and
4962 line number of a symbol in the symbolic form of an address.
4965 Another situation where it is helpful to show symbol filenames and line
4966 numbers is when disassembling code; @value{GDBN} shows you the line
4967 number and source file that corresponds to each instruction.
4969 Also, you may wish to see the symbolic form only if the address being
4970 printed is reasonably close to the closest earlier symbol:
4973 @kindex set print max-symbolic-offset
4974 @item set print max-symbolic-offset @var{max-offset}
4975 Tell @value{GDBN} to only display the symbolic form of an address if the
4976 offset between the closest earlier symbol and the address is less than
4977 @var{max-offset}. The default is 0, which tells @value{GDBN}
4978 to always print the symbolic form of an address if any symbol precedes it.
4980 @kindex show print max-symbolic-offset
4981 @item show print max-symbolic-offset
4982 Ask how large the maximum offset is that @value{GDBN} prints in a
4986 @cindex wild pointer, interpreting
4987 @cindex pointer, finding referent
4988 If you have a pointer and you are not sure where it points, try
4989 @samp{set print symbol-filename on}. Then you can determine the name
4990 and source file location of the variable where it points, using
4991 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4992 For example, here @value{GDBN} shows that a variable @code{ptt} points
4993 at another variable @code{t}, defined in @file{hi2.c}:
4996 (@value{GDBP}) set print symbol-filename on
4997 (@value{GDBP}) p/a ptt
4998 $4 = 0xe008 <t in hi2.c>
5002 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5003 does not show the symbol name and filename of the referent, even with
5004 the appropriate @code{set print} options turned on.
5007 Other settings control how different kinds of objects are printed:
5010 @kindex set print array
5011 @item set print array
5012 @itemx set print array on
5013 Pretty print arrays. This format is more convenient to read,
5014 but uses more space. The default is off.
5016 @item set print array off
5017 Return to compressed format for arrays.
5019 @kindex show print array
5020 @item show print array
5021 Show whether compressed or pretty format is selected for displaying
5024 @kindex set print elements
5025 @item set print elements @var{number-of-elements}
5026 Set a limit on how many elements of an array @value{GDBN} will print.
5027 If @value{GDBN} is printing a large array, it stops printing after it has
5028 printed the number of elements set by the @code{set print elements} command.
5029 This limit also applies to the display of strings.
5030 When @value{GDBN} starts, this limit is set to 200.
5031 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5033 @kindex show print elements
5034 @item show print elements
5035 Display the number of elements of a large array that @value{GDBN} will print.
5036 If the number is 0, then the printing is unlimited.
5038 @kindex set print null-stop
5039 @item set print null-stop
5040 Cause @value{GDBN} to stop printing the characters of an array when the first
5041 @sc{null} is encountered. This is useful when large arrays actually
5042 contain only short strings.
5045 @kindex set print pretty
5046 @item set print pretty on
5047 Cause @value{GDBN} to print structures in an indented format with one member
5048 per line, like this:
5063 @item set print pretty off
5064 Cause @value{GDBN} to print structures in a compact format, like this:
5068 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5069 meat = 0x54 "Pork"@}
5074 This is the default format.
5076 @kindex show print pretty
5077 @item show print pretty
5078 Show which format @value{GDBN} is using to print structures.
5080 @kindex set print sevenbit-strings
5081 @item set print sevenbit-strings on
5082 Print using only seven-bit characters; if this option is set,
5083 @value{GDBN} displays any eight-bit characters (in strings or
5084 character values) using the notation @code{\}@var{nnn}. This setting is
5085 best if you are working in English (@sc{ascii}) and you use the
5086 high-order bit of characters as a marker or ``meta'' bit.
5088 @item set print sevenbit-strings off
5089 Print full eight-bit characters. This allows the use of more
5090 international character sets, and is the default.
5092 @kindex show print sevenbit-strings
5093 @item show print sevenbit-strings
5094 Show whether or not @value{GDBN} is printing only seven-bit characters.
5096 @kindex set print union
5097 @item set print union on
5098 Tell @value{GDBN} to print unions which are contained in structures. This
5099 is the default setting.
5101 @item set print union off
5102 Tell @value{GDBN} not to print unions which are contained in structures.
5104 @kindex show print union
5105 @item show print union
5106 Ask @value{GDBN} whether or not it will print unions which are contained in
5109 For example, given the declarations
5112 typedef enum @{Tree, Bug@} Species;
5113 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5114 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5125 struct thing foo = @{Tree, @{Acorn@}@};
5129 with @code{set print union on} in effect @samp{p foo} would print
5132 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5136 and with @code{set print union off} in effect it would print
5139 $1 = @{it = Tree, form = @{...@}@}
5145 These settings are of interest when debugging C@t{++} programs:
5149 @kindex set print demangle
5150 @item set print demangle
5151 @itemx set print demangle on
5152 Print C@t{++} names in their source form rather than in the encoded
5153 (``mangled'') form passed to the assembler and linker for type-safe
5154 linkage. The default is on.
5156 @kindex show print demangle
5157 @item show print demangle
5158 Show whether C@t{++} names are printed in mangled or demangled form.
5160 @kindex set print asm-demangle
5161 @item set print asm-demangle
5162 @itemx set print asm-demangle on
5163 Print C@t{++} names in their source form rather than their mangled form, even
5164 in assembler code printouts such as instruction disassemblies.
5167 @kindex show print asm-demangle
5168 @item show print asm-demangle
5169 Show whether C@t{++} names in assembly listings are printed in mangled
5172 @kindex set demangle-style
5173 @cindex C@t{++} symbol decoding style
5174 @cindex symbol decoding style, C@t{++}
5175 @item set demangle-style @var{style}
5176 Choose among several encoding schemes used by different compilers to
5177 represent C@t{++} names. The choices for @var{style} are currently:
5181 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5184 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5185 This is the default.
5188 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5191 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5194 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5195 @strong{Warning:} this setting alone is not sufficient to allow
5196 debugging @code{cfront}-generated executables. @value{GDBN} would
5197 require further enhancement to permit that.
5200 If you omit @var{style}, you will see a list of possible formats.
5202 @kindex show demangle-style
5203 @item show demangle-style
5204 Display the encoding style currently in use for decoding C@t{++} symbols.
5206 @kindex set print object
5207 @item set print object
5208 @itemx set print object on
5209 When displaying a pointer to an object, identify the @emph{actual}
5210 (derived) type of the object rather than the @emph{declared} type, using
5211 the virtual function table.
5213 @item set print object off
5214 Display only the declared type of objects, without reference to the
5215 virtual function table. This is the default setting.
5217 @kindex show print object
5218 @item show print object
5219 Show whether actual, or declared, object types are displayed.
5221 @kindex set print static-members
5222 @item set print static-members
5223 @itemx set print static-members on
5224 Print static members when displaying a C@t{++} object. The default is on.
5226 @item set print static-members off
5227 Do not print static members when displaying a C@t{++} object.
5229 @kindex show print static-members
5230 @item show print static-members
5231 Show whether C@t{++} static members are printed, or not.
5233 @c These don't work with HP ANSI C++ yet.
5234 @kindex set print vtbl
5235 @item set print vtbl
5236 @itemx set print vtbl on
5237 Pretty print C@t{++} virtual function tables. The default is off.
5238 (The @code{vtbl} commands do not work on programs compiled with the HP
5239 ANSI C@t{++} compiler (@code{aCC}).)
5241 @item set print vtbl off
5242 Do not pretty print C@t{++} virtual function tables.
5244 @kindex show print vtbl
5245 @item show print vtbl
5246 Show whether C@t{++} virtual function tables are pretty printed, or not.
5250 @section Value history
5252 @cindex value history
5253 Values printed by the @code{print} command are saved in the @value{GDBN}
5254 @dfn{value history}. This allows you to refer to them in other expressions.
5255 Values are kept until the symbol table is re-read or discarded
5256 (for example with the @code{file} or @code{symbol-file} commands).
5257 When the symbol table changes, the value history is discarded,
5258 since the values may contain pointers back to the types defined in the
5263 @cindex history number
5264 The values printed are given @dfn{history numbers} by which you can
5265 refer to them. These are successive integers starting with one.
5266 @code{print} shows you the history number assigned to a value by
5267 printing @samp{$@var{num} = } before the value; here @var{num} is the
5270 To refer to any previous value, use @samp{$} followed by the value's
5271 history number. The way @code{print} labels its output is designed to
5272 remind you of this. Just @code{$} refers to the most recent value in
5273 the history, and @code{$$} refers to the value before that.
5274 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5275 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5276 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5278 For example, suppose you have just printed a pointer to a structure and
5279 want to see the contents of the structure. It suffices to type
5285 If you have a chain of structures where the component @code{next} points
5286 to the next one, you can print the contents of the next one with this:
5293 You can print successive links in the chain by repeating this
5294 command---which you can do by just typing @key{RET}.
5296 Note that the history records values, not expressions. If the value of
5297 @code{x} is 4 and you type these commands:
5305 then the value recorded in the value history by the @code{print} command
5306 remains 4 even though the value of @code{x} has changed.
5311 Print the last ten values in the value history, with their item numbers.
5312 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5313 values} does not change the history.
5315 @item show values @var{n}
5316 Print ten history values centered on history item number @var{n}.
5319 Print ten history values just after the values last printed. If no more
5320 values are available, @code{show values +} produces no display.
5323 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5324 same effect as @samp{show values +}.
5326 @node Convenience Vars
5327 @section Convenience variables
5329 @cindex convenience variables
5330 @value{GDBN} provides @dfn{convenience variables} that you can use within
5331 @value{GDBN} to hold on to a value and refer to it later. These variables
5332 exist entirely within @value{GDBN}; they are not part of your program, and
5333 setting a convenience variable has no direct effect on further execution
5334 of your program. That is why you can use them freely.
5336 Convenience variables are prefixed with @samp{$}. Any name preceded by
5337 @samp{$} can be used for a convenience variable, unless it is one of
5338 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5339 (Value history references, in contrast, are @emph{numbers} preceded
5340 by @samp{$}. @xref{Value History, ,Value history}.)
5342 You can save a value in a convenience variable with an assignment
5343 expression, just as you would set a variable in your program.
5347 set $foo = *object_ptr
5351 would save in @code{$foo} the value contained in the object pointed to by
5354 Using a convenience variable for the first time creates it, but its
5355 value is @code{void} until you assign a new value. You can alter the
5356 value with another assignment at any time.
5358 Convenience variables have no fixed types. You can assign a convenience
5359 variable any type of value, including structures and arrays, even if
5360 that variable already has a value of a different type. The convenience
5361 variable, when used as an expression, has the type of its current value.
5364 @kindex show convenience
5365 @item show convenience
5366 Print a list of convenience variables used so far, and their values.
5367 Abbreviated @code{show conv}.
5370 One of the ways to use a convenience variable is as a counter to be
5371 incremented or a pointer to be advanced. For example, to print
5372 a field from successive elements of an array of structures:
5376 print bar[$i++]->contents
5380 Repeat that command by typing @key{RET}.
5382 Some convenience variables are created automatically by @value{GDBN} and given
5383 values likely to be useful.
5386 @vindex $_@r{, convenience variable}
5388 The variable @code{$_} is automatically set by the @code{x} command to
5389 the last address examined (@pxref{Memory, ,Examining memory}). Other
5390 commands which provide a default address for @code{x} to examine also
5391 set @code{$_} to that address; these commands include @code{info line}
5392 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5393 except when set by the @code{x} command, in which case it is a pointer
5394 to the type of @code{$__}.
5396 @vindex $__@r{, convenience variable}
5398 The variable @code{$__} is automatically set by the @code{x} command
5399 to the value found in the last address examined. Its type is chosen
5400 to match the format in which the data was printed.
5403 @vindex $_exitcode@r{, convenience variable}
5404 The variable @code{$_exitcode} is automatically set to the exit code when
5405 the program being debugged terminates.
5408 On HP-UX systems, if you refer to a function or variable name that
5409 begins with a dollar sign, @value{GDBN} searches for a user or system
5410 name first, before it searches for a convenience variable.
5416 You can refer to machine register contents, in expressions, as variables
5417 with names starting with @samp{$}. The names of registers are different
5418 for each machine; use @code{info registers} to see the names used on
5422 @kindex info registers
5423 @item info registers
5424 Print the names and values of all registers except floating-point
5425 registers (in the selected stack frame).
5427 @kindex info all-registers
5428 @cindex floating point registers
5429 @item info all-registers
5430 Print the names and values of all registers, including floating-point
5433 @item info registers @var{regname} @dots{}
5434 Print the @dfn{relativized} value of each specified register @var{regname}.
5435 As discussed in detail below, register values are normally relative to
5436 the selected stack frame. @var{regname} may be any register name valid on
5437 the machine you are using, with or without the initial @samp{$}.
5440 @value{GDBN} has four ``standard'' register names that are available (in
5441 expressions) on most machines---whenever they do not conflict with an
5442 architecture's canonical mnemonics for registers. The register names
5443 @code{$pc} and @code{$sp} are used for the program counter register and
5444 the stack pointer. @code{$fp} is used for a register that contains a
5445 pointer to the current stack frame, and @code{$ps} is used for a
5446 register that contains the processor status. For example,
5447 you could print the program counter in hex with
5454 or print the instruction to be executed next with
5461 or add four to the stack pointer@footnote{This is a way of removing
5462 one word from the stack, on machines where stacks grow downward in
5463 memory (most machines, nowadays). This assumes that the innermost
5464 stack frame is selected; setting @code{$sp} is not allowed when other
5465 stack frames are selected. To pop entire frames off the stack,
5466 regardless of machine architecture, use @code{return};
5467 see @ref{Returning, ,Returning from a function}.} with
5473 Whenever possible, these four standard register names are available on
5474 your machine even though the machine has different canonical mnemonics,
5475 so long as there is no conflict. The @code{info registers} command
5476 shows the canonical names. For example, on the SPARC, @code{info
5477 registers} displays the processor status register as @code{$psr} but you
5478 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5479 is an alias for the @sc{eflags} register.
5481 @value{GDBN} always considers the contents of an ordinary register as an
5482 integer when the register is examined in this way. Some machines have
5483 special registers which can hold nothing but floating point; these
5484 registers are considered to have floating point values. There is no way
5485 to refer to the contents of an ordinary register as floating point value
5486 (although you can @emph{print} it as a floating point value with
5487 @samp{print/f $@var{regname}}).
5489 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5490 means that the data format in which the register contents are saved by
5491 the operating system is not the same one that your program normally
5492 sees. For example, the registers of the 68881 floating point
5493 coprocessor are always saved in ``extended'' (raw) format, but all C
5494 programs expect to work with ``double'' (virtual) format. In such
5495 cases, @value{GDBN} normally works with the virtual format only (the format
5496 that makes sense for your program), but the @code{info registers} command
5497 prints the data in both formats.
5499 Normally, register values are relative to the selected stack frame
5500 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5501 value that the register would contain if all stack frames farther in
5502 were exited and their saved registers restored. In order to see the
5503 true contents of hardware registers, you must select the innermost
5504 frame (with @samp{frame 0}).
5506 However, @value{GDBN} must deduce where registers are saved, from the machine
5507 code generated by your compiler. If some registers are not saved, or if
5508 @value{GDBN} is unable to locate the saved registers, the selected stack
5509 frame makes no difference.
5511 @node Floating Point Hardware
5512 @section Floating point hardware
5513 @cindex floating point
5515 Depending on the configuration, @value{GDBN} may be able to give
5516 you more information about the status of the floating point hardware.
5521 Display hardware-dependent information about the floating
5522 point unit. The exact contents and layout vary depending on the
5523 floating point chip. Currently, @samp{info float} is supported on
5524 the ARM and x86 machines.
5527 @node Memory Region Attributes
5528 @section Memory Region Attributes
5529 @cindex memory region attributes
5531 @dfn{Memory region attributes} allow you to describe special handling
5532 required by regions of your target's memory. @value{GDBN} uses attributes
5533 to determine whether to allow certain types of memory accesses; whether to
5534 use specific width accesses; and whether to cache target memory.
5536 Defined memory regions can be individually enabled and disabled. When a
5537 memory region is disabled, @value{GDBN} uses the default attributes when
5538 accessing memory in that region. Similarly, if no memory regions have
5539 been defined, @value{GDBN} uses the default attributes when accessing
5542 When a memory region is defined, it is given a number to identify it;
5543 to enable, disable, or remove a memory region, you specify that number.
5547 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5548 Define memory region bounded by @var{address1} and @var{address2}
5549 with attributes @var{attributes}@dots{}.
5552 @item delete mem @var{nums}@dots{}
5553 Remove memory region numbers @var{nums}.
5556 @item disable mem @var{nums}@dots{}
5557 Disable memory region numbers @var{nums}.
5558 A disabled memory region is not forgotten.
5559 It may be enabled again later.
5562 @item enable mem @var{nums}@dots{}
5563 Enable memory region numbers @var{nums}.
5567 Print a table of all defined memory regions, with the following columns
5571 @item Memory Region Number
5572 @item Enabled or Disabled.
5573 Enabled memory regions are marked with @samp{y}.
5574 Disabled memory regions are marked with @samp{n}.
5577 The address defining the inclusive lower bound of the memory region.
5580 The address defining the exclusive upper bound of the memory region.
5583 The list of attributes set for this memory region.
5588 @subsection Attributes
5590 @subsubsection Memory Access Mode
5591 The access mode attributes set whether @value{GDBN} may make read or
5592 write accesses to a memory region.
5594 While these attributes prevent @value{GDBN} from performing invalid
5595 memory accesses, they do nothing to prevent the target system, I/O DMA,
5596 etc. from accessing memory.
5600 Memory is read only.
5602 Memory is write only.
5604 Memory is read/write (default).
5607 @subsubsection Memory Access Size
5608 The acccess size attributes tells @value{GDBN} to use specific sized
5609 accesses in the memory region. Often memory mapped device registers
5610 require specific sized accesses. If no access size attribute is
5611 specified, @value{GDBN} may use accesses of any size.
5615 Use 8 bit memory accesses.
5617 Use 16 bit memory accesses.
5619 Use 32 bit memory accesses.
5621 Use 64 bit memory accesses.
5624 @c @subsubsection Hardware/Software Breakpoints
5625 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5626 @c will use hardware or software breakpoints for the internal breakpoints
5627 @c used by the step, next, finish, until, etc. commands.
5631 @c Always use hardware breakpoints
5632 @c @item swbreak (default)
5635 @subsubsection Data Cache
5636 The data cache attributes set whether @value{GDBN} will cache target
5637 memory. While this generally improves performance by reducing debug
5638 protocol overhead, it can lead to incorrect results because @value{GDBN}
5639 does not know about volatile variables or memory mapped device
5644 Enable @value{GDBN} to cache target memory.
5645 @item nocache (default)
5646 Disable @value{GDBN} from caching target memory.
5649 @c @subsubsection Memory Write Verification
5650 @c The memory write verification attributes set whether @value{GDBN}
5651 @c will re-reads data after each write to verify the write was successful.
5655 @c @item noverify (default)
5659 @chapter Tracepoints
5660 @c This chapter is based on the documentation written by Michael
5661 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
5664 In some applications, it is not feasible for the debugger to interrupt
5665 the program's execution long enough for the developer to learn
5666 anything helpful about its behavior. If the program's correctness
5667 depends on its real-time behavior, delays introduced by a debugger
5668 might cause the program to change its behavior drastically, or perhaps
5669 fail, even when the code itself is correct. It is useful to be able
5670 to observe the program's behavior without interrupting it.
5672 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
5673 specify locations in the program, called @dfn{tracepoints}, and
5674 arbitrary expressions to evaluate when those tracepoints are reached.
5675 Later, using the @code{tfind} command, you can examine the values
5676 those expressions had when the program hit the tracepoints. The
5677 expressions may also denote objects in memory---structures or arrays,
5678 for example---whose values @value{GDBN} should record; while visiting
5679 a particular tracepoint, you may inspect those objects as if they were
5680 in memory at that moment. However, because @value{GDBN} records these
5681 values without interacting with you, it can do so quickly and
5682 unobtrusively, hopefully not disturbing the program's behavior.
5684 The tracepoint facility is currently available only for remote
5685 targets. @xref{Targets}.
5687 This chapter describes the tracepoint commands and features.
5691 * Analyze Collected Data::
5692 * Tracepoint Variables::
5695 @node Set Tracepoints
5696 @section Commands to Set Tracepoints
5698 Before running such a @dfn{trace experiment}, an arbitrary number of
5699 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
5700 tracepoint has a number assigned to it by @value{GDBN}. Like with
5701 breakpoints, tracepoint numbers are successive integers starting from
5702 one. Many of the commands associated with tracepoints take the
5703 tracepoint number as their argument, to identify which tracepoint to
5706 For each tracepoint, you can specify, in advance, some arbitrary set
5707 of data that you want the target to collect in the trace buffer when
5708 it hits that tracepoint. The collected data can include registers,
5709 local variables, or global data. Later, you can use @value{GDBN}
5710 commands to examine the values these data had at the time the
5713 This section describes commands to set tracepoints and associated
5714 conditions and actions.
5717 * Create and Delete Tracepoints::
5718 * Enable and Disable Tracepoints::
5719 * Tracepoint Passcounts::
5720 * Tracepoint Actions::
5721 * Listing Tracepoints::
5722 * Starting and Stopping Trace Experiment::
5725 @node Create and Delete Tracepoints
5726 @subsection Create and Delete Tracepoints
5729 @cindex set tracepoint
5732 The @code{trace} command is very similar to the @code{break} command.
5733 Its argument can be a source line, a function name, or an address in
5734 the target program. @xref{Set Breaks}. The @code{trace} command
5735 defines a tracepoint, which is a point in the target program where the
5736 debugger will briefly stop, collect some data, and then allow the
5737 program to continue. Setting a tracepoint or changing its commands
5738 doesn't take effect until the next @code{tstart} command; thus, you
5739 cannot change the tracepoint attributes once a trace experiment is
5742 Here are some examples of using the @code{trace} command:
5745 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
5747 (@value{GDBP}) @b{trace +2} // 2 lines forward
5749 (@value{GDBP}) @b{trace my_function} // first source line of function
5751 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
5753 (@value{GDBP}) @b{trace *0x2117c4} // an address
5757 You can abbreviate @code{trace} as @code{tr}.
5760 @cindex last tracepoint number
5761 @cindex recent tracepoint number
5762 @cindex tracepoint number
5763 The convenience variable @code{$tpnum} records the tracepoint number
5764 of the most recently set tracepoint.
5766 @kindex delete tracepoint
5767 @cindex tracepoint deletion
5768 @item delete tracepoint @r{[}@var{num}@r{]}
5769 Permanently delete one or more tracepoints. With no argument, the
5770 default is to delete all tracepoints.
5775 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
5777 (@value{GDBP}) @b{delete trace} // remove all tracepoints
5781 You can abbreviate this command as @code{del tr}.
5784 @node Enable and Disable Tracepoints
5785 @subsection Enable and Disable Tracepoints
5788 @kindex disable tracepoint
5789 @item disable tracepoint @r{[}@var{num}@r{]}
5790 Disable tracepoint @var{num}, or all tracepoints if no argument
5791 @var{num} is given. A disabled tracepoint will have no effect during
5792 the next trace experiment, but it is not forgotten. You can re-enable
5793 a disabled tracepoint using the @code{enable tracepoint} command.
5795 @kindex enable tracepoint
5796 @item enable tracepoint @r{[}@var{num}@r{]}
5797 Enable tracepoint @var{num}, or all tracepoints. The enabled
5798 tracepoints will become effective the next time a trace experiment is
5802 @node Tracepoint Passcounts
5803 @subsection Tracepoint Passcounts
5807 @cindex tracepoint pass count
5808 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
5809 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
5810 automatically stop a trace experiment. If a tracepoint's passcount is
5811 @var{n}, then the trace experiment will be automatically stopped on
5812 the @var{n}'th time that tracepoint is hit. If the tracepoint number
5813 @var{num} is not specified, the @code{passcount} command sets the
5814 passcount of the most recently defined tracepoint. If no passcount is
5815 given, the trace experiment will run until stopped explicitly by the
5821 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of tracepoint 2
5823 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
5824 // most recently defined tracepoint.
5825 (@value{GDBP}) @b{trace foo}
5826 (@value{GDBP}) @b{pass 3}
5827 (@value{GDBP}) @b{trace bar}
5828 (@value{GDBP}) @b{pass 2}
5829 (@value{GDBP}) @b{trace baz}
5830 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
5831 // executed 3 times OR when bar has
5832 // been executed 2 times
5833 // OR when baz has been executed 1 time.
5837 @node Tracepoint Actions
5838 @subsection Tracepoint Action Lists
5842 @cindex tracepoint actions
5843 @item actions @r{[}@var{num}@r{]}
5844 This command will prompt for a list of actions to be taken when the
5845 tracepoint is hit. If the tracepoint number @var{num} is not
5846 specified, this command sets the actions for the one that was most
5847 recently defined (so that you can define a tracepoint and then say
5848 @code{actions} without bothering about its number). You specify the
5849 actions themselves on the following lines, one action at a time, and
5850 terminate the actions list with a line containing just @code{end}. So
5851 far, the only defined actions are @code{collect} and
5852 @code{while-stepping}.
5854 @cindex remove actions from a tracepoint
5855 To remove all actions from a tracepoint, type @samp{actions @var{num}}
5856 and follow it immediately with @samp{end}.
5859 (@value{GDBP}) @b{collect @var{data}} // collect some data
5861 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times and collect data
5863 (@value{GDBP}) @b{end} // signals the end of actions.
5866 In the following example, the action list begins with @code{collect}
5867 commands indicating the things to be collected when the tracepoint is
5868 hit. Then, in order to single-step and collect additional data
5869 following the tracepoint, a @code{while-stepping} command is used,
5870 followed by the list of things to be collected while stepping. The
5871 @code{while-stepping} command is terminated by its own separate
5872 @code{end} command. Lastly, the action list is terminated by an
5876 (@value{GDBP}) @b{trace foo}
5877 (@value{GDBP}) @b{actions}
5878 Enter actions for tracepoint 1, one per line:
5887 @kindex collect @r{(tracepoints)}
5888 @item collect @var{expr1}, @var{expr2}, @dots{}
5889 Collect values of the given expressions when the tracepoint is hit.
5890 This command accepts a comma-separated list of any valid expressions.
5891 In addition to global, static, or local variables, the following
5892 special arguments are supported:
5896 collect all registers
5899 collect all function arguments
5902 collect all local variables.
5905 You can give several consecutive @code{collect} commands, each one
5906 with a single argument, or one @code{collect} command with several
5907 arguments separated by commas: the effect is the same.
5909 The command @code{info scope} (@pxref{Symbols, info scope}) is
5910 particularly useful for figuring out what data to collect.
5912 @kindex while-stepping @r{(tracepoints)}
5913 @item while-stepping @var{n}
5914 Perform @var{n} single-step traces after the tracepoint, collecting
5915 new data at each step. The @code{while-stepping} command is
5916 followed by the list of what to collect while stepping (followed by
5917 its own @code{end} command):
5921 > collect $regs, myglobal
5927 You may abbreviate @code{while-stepping} as @code{ws} or
5931 @node Listing Tracepoints
5932 @subsection Listing Tracepoints
5935 @kindex info tracepoints
5936 @cindex information about tracepoints
5937 @item info tracepoints @r{[}@var{num}@r{]}
5938 Display information the tracepoint @var{num}. If you don't specify a
5939 tracepoint number displays information about all the tracepoints
5940 defined so far. For each tracepoint, the following information is
5947 whether it is enabled or disabled
5951 its passcount as given by the @code{passcount @var{n}} command
5953 its step count as given by the @code{while-stepping @var{n}} command
5955 where in the source files is the tracepoint set
5957 its action list as given by the @code{actions} command
5961 (@value{GDBP}) @b{info trace}
5962 Num Enb Address PassC StepC What
5963 1 y 0x002117c4 0 0 <gdb_asm>
5964 2 y 0x0020dc64 0 0 in gdb_test at gdb_test.c:375
5965 3 y 0x0020b1f4 0 0 in collect_data at ../foo.c:1741
5970 This command can be abbreviated @code{info tp}.
5973 @node Starting and Stopping Trace Experiment
5974 @subsection Starting and Stopping Trace Experiment
5978 @cindex start a new trace experiment
5979 @cindex collected data discarded
5981 This command takes no arguments. It starts the trace experiment, and
5982 begins collecting data. This has the side effect of discarding all
5983 the data collected in the trace buffer during the previous trace
5987 @cindex stop a running trace experiment
5989 This command takes no arguments. It ends the trace experiment, and
5990 stops collecting data.
5992 @strong{Note:} a trace experiment and data collection may stop
5993 automatically if any tracepoint's passcount is reached
5994 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
5997 @cindex status of trace data collection
5998 @cindex trace experiment, status of
6000 This command displays the status of the current trace data
6004 Here is an example of the commands we described so far:
6007 (@value{GDBP}) @b{trace gdb_c_test}
6008 (@value{GDBP}) @b{actions}
6009 Enter actions for tracepoint #1, one per line.
6010 > collect $regs,$locals,$args
6015 (@value{GDBP}) @b{tstart}
6016 [time passes @dots{}]
6017 (@value{GDBP}) @b{tstop}
6021 @node Analyze Collected Data
6022 @section Using the collected data
6024 After the tracepoint experiment ends, you use @value{GDBN} commands
6025 for examining the trace data. The basic idea is that each tracepoint
6026 collects a trace @dfn{snapshot} every time it is hit and another
6027 snapshot every time it single-steps. All these snapshots are
6028 consecutively numbered from zero and go into a buffer, and you can
6029 examine them later. The way you examine them is to @dfn{focus} on a
6030 specific trace snapshot. When the remote stub is focused on a trace
6031 snapshot, it will respond to all @value{GDBN} requests for memory and
6032 registers by reading from the buffer which belongs to that snapshot,
6033 rather than from @emph{real} memory or registers of the program being
6034 debugged. This means that @strong{all} @value{GDBN} commands
6035 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6036 behave as if we were currently debugging the program state as it was
6037 when the tracepoint occurred. Any requests for data that are not in
6038 the buffer will fail.
6041 * tfind:: How to select a trace snapshot
6042 * tdump:: How to display all data for a snapshot
6043 * save-tracepoints:: How to save tracepoints for a future run
6047 @subsection @code{tfind @var{n}}
6050 @cindex select trace snapshot
6051 @cindex find trace snapshot
6052 The basic command for selecting a trace snapshot from the buffer is
6053 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6054 counting from zero. If no argument @var{n} is given, the next
6055 snapshot is selected.
6057 Here are the various forms of using the @code{tfind} command.
6061 Find the first snapshot in the buffer. This is a synonym for
6062 @code{tfind 0} (since 0 is the number of the first snapshot).
6065 Stop debugging trace snapshots, resume @emph{live} debugging.
6068 Same as @samp{tfind none}.
6071 No argument means find the next trace snapshot.
6074 Find the previous trace snapshot before the current one. This permits
6075 retracing earlier steps.
6077 @item tfind tracepoint @var{num}
6078 Find the next snapshot associated with tracepoint @var{num}. Search
6079 proceeds forward from the last examined trace snapshot. If no
6080 argument @var{num} is given, it means find the next snapshot collected
6081 for the same tracepoint as the current snapshot.
6083 @item tfind pc @var{addr}
6084 Find the next snapshot associated with the value @var{addr} of the
6085 program counter. Search proceeds forward from the last examined trace
6086 snapshot. If no argument @var{addr} is given, it means find the next
6087 snapshot with the same value of PC as the current snapshot.
6089 @item tfind outside @var{addr1}, @var{addr2}
6090 Find the next snapshot whose PC is outside the given range of
6093 @item tfind range @var{addr1}, @var{addr2}
6094 Find the next snapshot whose PC is between @var{addr1} and
6095 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6097 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6098 Find the next snapshot associated with the source line @var{n}. If
6099 the optional argument @var{file} is given, refer to line @var{n} in
6100 that source file. Search proceeds forward from the last examined
6101 trace snapshot. If no argument @var{n} is given, it means find the
6102 next line other than the one currently being examined; thus saying
6103 @code{tfind line} repeatedly can appear to have the same effect as
6104 stepping from line to line in a @emph{live} debugging session.
6107 The default arguments for the @code{tfind} commands are specifically
6108 designed to make it easy to scan through the trace buffer. For
6109 instance, @code{tfind} with no argument selects the next trace
6110 snapshot, and @code{tfind -} with no argument selects the previous
6111 trace snapshot. So, by giving one @code{tfind} command, and then
6112 simply hitting @key{RET} repeatedly you can examine all the trace
6113 snapshots in order. Or, by saying @code{tfind -} and then hitting
6114 @key{RET} repeatedly you can examine the snapshots in reverse order.
6115 The @code{tfind line} command with no argument selects the snapshot
6116 for the next source line executed. The @code{tfind pc} command with
6117 no argument selects the next snapshot with the same program counter
6118 (PC) as the current frame. The @code{tfind tracepoint} command with
6119 no argument selects the next trace snapshot collected by the same
6120 tracepoint as the current one.
6122 In addition to letting you scan through the trace buffer manually,
6123 these commands make it easy to construct @value{GDBN} scripts that
6124 scan through the trace buffer and print out whatever collected data
6125 you are interested in. Thus, if we want to examine the PC, FP, and SP
6126 registers from each trace frame in the buffer, we can say this:
6129 (@value{GDBP}) @b{tfind start}
6130 (@value{GDBP}) @b{while ($trace_frame != -1)}
6131 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6132 $trace_frame, $pc, $sp, $fp
6136 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6137 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6138 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6139 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6140 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6141 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6142 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6143 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6144 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6145 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6146 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6149 Or, if we want to examine the variable @code{X} at each source line in
6153 (@value{GDBP}) @b{tfind start}
6154 (@value{GDBP}) @b{while ($trace_frame != -1)}
6155 > printf "Frame %d, X == %d\n", $trace_frame, X
6165 @subsection @code{tdump}
6167 @cindex dump all data collected at tracepoint
6168 @cindex tracepoint data, display
6170 This command takes no arguments. It prints all the data collected at
6171 the current trace snapshot.
6174 (@value{GDBP}) @b{trace 444}
6175 (@value{GDBP}) @b{actions}
6176 Enter actions for tracepoint #2, one per line:
6177 > collect $regs, $locals, $args, gdb_long_test
6180 (@value{GDBP}) @b{tstart}
6182 (@value{GDBP}) @b{tfind line 444}
6183 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6185 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6187 (@value{GDBP}) @b{tdump}
6188 Data collected at tracepoint 2, trace frame 1:
6189 d0 0xc4aa0085 -995491707
6193 d4 0x71aea3d 119204413
6198 a1 0x3000668 50333288
6201 a4 0x3000698 50333336
6203 fp 0x30bf3c 0x30bf3c
6204 sp 0x30bf34 0x30bf34
6206 pc 0x20b2c8 0x20b2c8
6210 p = 0x20e5b4 "gdb-test"
6217 gdb_long_test = 17 '\021'
6222 @node save-tracepoints
6223 @subsection @code{save-tracepoints @var{filename}}
6224 @kindex save-tracepoints
6225 @cindex save tracepoints for future sessions
6227 This command saves all current tracepoint definitions together with
6228 their actions and passcounts, into a file @file{@var{filename}}
6229 suitable for use in a later debugging session. To read the saved
6230 tracepoint definitions, use the @code{source} command (@pxref{Command
6233 @node Tracepoint Variables
6234 @section Convenience Variables for Tracepoints
6235 @cindex tracepoint variables
6236 @cindex convenience variables for tracepoints
6239 @vindex $trace_frame
6240 @item (int) $trace_frame
6241 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6242 snapshot is selected.
6245 @item (int) $tracepoint
6246 The tracepoint for the current trace snapshot.
6249 @item (int) $trace_line
6250 The line number for the current trace snapshot.
6253 @item (char []) $trace_file
6254 The source file for the current trace snapshot.
6257 @item (char []) $trace_func
6258 The name of the function containing @code{$tracepoint}.
6261 Note: @code{$trace_file} is not suitable for use in @code{printf},
6262 use @code{output} instead.
6264 Here's a simple example of using these convenience variables for
6265 stepping through all the trace snapshots and printing some of their
6269 (@value{GDBP}) @b{tfind start}
6271 (@value{GDBP}) @b{while $trace_frame != -1}
6272 > output $trace_file
6273 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6279 @chapter Using @value{GDBN} with Different Languages
6282 Although programming languages generally have common aspects, they are
6283 rarely expressed in the same manner. For instance, in ANSI C,
6284 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6285 Modula-2, it is accomplished by @code{p^}. Values can also be
6286 represented (and displayed) differently. Hex numbers in C appear as
6287 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6289 @cindex working language
6290 Language-specific information is built into @value{GDBN} for some languages,
6291 allowing you to express operations like the above in your program's
6292 native language, and allowing @value{GDBN} to output values in a manner
6293 consistent with the syntax of your program's native language. The
6294 language you use to build expressions is called the @dfn{working
6298 * Setting:: Switching between source languages
6299 * Show:: Displaying the language
6300 * Checks:: Type and range checks
6301 * Support:: Supported languages
6305 @section Switching between source languages
6307 There are two ways to control the working language---either have @value{GDBN}
6308 set it automatically, or select it manually yourself. You can use the
6309 @code{set language} command for either purpose. On startup, @value{GDBN}
6310 defaults to setting the language automatically. The working language is
6311 used to determine how expressions you type are interpreted, how values
6314 In addition to the working language, every source file that
6315 @value{GDBN} knows about has its own working language. For some object
6316 file formats, the compiler might indicate which language a particular
6317 source file is in. However, most of the time @value{GDBN} infers the
6318 language from the name of the file. The language of a source file
6319 controls whether C@t{++} names are demangled---this way @code{backtrace} can
6320 show each frame appropriately for its own language. There is no way to
6321 set the language of a source file from within @value{GDBN}, but you can
6322 set the language associated with a filename extension. @xref{Show, ,
6323 Displaying the language}.
6325 This is most commonly a problem when you use a program, such
6326 as @code{cfront} or @code{f2c}, that generates C but is written in
6327 another language. In that case, make the
6328 program use @code{#line} directives in its C output; that way
6329 @value{GDBN} will know the correct language of the source code of the original
6330 program, and will display that source code, not the generated C code.
6333 * Filenames:: Filename extensions and languages.
6334 * Manually:: Setting the working language manually
6335 * Automatically:: Having @value{GDBN} infer the source language
6339 @subsection List of filename extensions and languages
6341 If a source file name ends in one of the following extensions, then
6342 @value{GDBN} infers that its language is the one indicated.
6367 Modula-2 source file
6371 Assembler source file. This actually behaves almost like C, but
6372 @value{GDBN} does not skip over function prologues when stepping.
6375 In addition, you may set the language associated with a filename
6376 extension. @xref{Show, , Displaying the language}.
6379 @subsection Setting the working language
6381 If you allow @value{GDBN} to set the language automatically,
6382 expressions are interpreted the same way in your debugging session and
6385 @kindex set language
6386 If you wish, you may set the language manually. To do this, issue the
6387 command @samp{set language @var{lang}}, where @var{lang} is the name of
6389 @code{c} or @code{modula-2}.
6390 For a list of the supported languages, type @samp{set language}.
6392 Setting the language manually prevents @value{GDBN} from updating the working
6393 language automatically. This can lead to confusion if you try
6394 to debug a program when the working language is not the same as the
6395 source language, when an expression is acceptable to both
6396 languages---but means different things. For instance, if the current
6397 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6405 might not have the effect you intended. In C, this means to add
6406 @code{b} and @code{c} and place the result in @code{a}. The result
6407 printed would be the value of @code{a}. In Modula-2, this means to compare
6408 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6411 @subsection Having @value{GDBN} infer the source language
6413 To have @value{GDBN} set the working language automatically, use
6414 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6415 then infers the working language. That is, when your program stops in a
6416 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6417 working language to the language recorded for the function in that
6418 frame. If the language for a frame is unknown (that is, if the function
6419 or block corresponding to the frame was defined in a source file that
6420 does not have a recognized extension), the current working language is
6421 not changed, and @value{GDBN} issues a warning.
6423 This may not seem necessary for most programs, which are written
6424 entirely in one source language. However, program modules and libraries
6425 written in one source language can be used by a main program written in
6426 a different source language. Using @samp{set language auto} in this
6427 case frees you from having to set the working language manually.
6430 @section Displaying the language
6432 The following commands help you find out which language is the
6433 working language, and also what language source files were written in.
6435 @kindex show language
6436 @kindex info frame@r{, show the source language}
6437 @kindex info source@r{, show the source language}
6440 Display the current working language. This is the
6441 language you can use with commands such as @code{print} to
6442 build and compute expressions that may involve variables in your program.
6445 Display the source language for this frame. This language becomes the
6446 working language if you use an identifier from this frame.
6447 @xref{Frame Info, ,Information about a frame}, to identify the other
6448 information listed here.
6451 Display the source language of this source file.
6452 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6453 information listed here.
6456 In unusual circumstances, you may have source files with extensions
6457 not in the standard list. You can then set the extension associated
6458 with a language explicitly:
6460 @kindex set extension-language
6461 @kindex info extensions
6463 @item set extension-language @var{.ext} @var{language}
6464 Set source files with extension @var{.ext} to be assumed to be in
6465 the source language @var{language}.
6467 @item info extensions
6468 List all the filename extensions and the associated languages.
6472 @section Type and range checking
6475 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6476 checking are included, but they do not yet have any effect. This
6477 section documents the intended facilities.
6479 @c FIXME remove warning when type/range code added
6481 Some languages are designed to guard you against making seemingly common
6482 errors through a series of compile- and run-time checks. These include
6483 checking the type of arguments to functions and operators, and making
6484 sure mathematical overflows are caught at run time. Checks such as
6485 these help to ensure a program's correctness once it has been compiled
6486 by eliminating type mismatches, and providing active checks for range
6487 errors when your program is running.
6489 @value{GDBN} can check for conditions like the above if you wish.
6490 Although @value{GDBN} does not check the statements in your program, it
6491 can check expressions entered directly into @value{GDBN} for evaluation via
6492 the @code{print} command, for example. As with the working language,
6493 @value{GDBN} can also decide whether or not to check automatically based on
6494 your program's source language. @xref{Support, ,Supported languages},
6495 for the default settings of supported languages.
6498 * Type Checking:: An overview of type checking
6499 * Range Checking:: An overview of range checking
6502 @cindex type checking
6503 @cindex checks, type
6505 @subsection An overview of type checking
6507 Some languages, such as Modula-2, are strongly typed, meaning that the
6508 arguments to operators and functions have to be of the correct type,
6509 otherwise an error occurs. These checks prevent type mismatch
6510 errors from ever causing any run-time problems. For example,
6518 The second example fails because the @code{CARDINAL} 1 is not
6519 type-compatible with the @code{REAL} 2.3.
6521 For the expressions you use in @value{GDBN} commands, you can tell the
6522 @value{GDBN} type checker to skip checking;
6523 to treat any mismatches as errors and abandon the expression;
6524 or to only issue warnings when type mismatches occur,
6525 but evaluate the expression anyway. When you choose the last of
6526 these, @value{GDBN} evaluates expressions like the second example above, but
6527 also issues a warning.
6529 Even if you turn type checking off, there may be other reasons
6530 related to type that prevent @value{GDBN} from evaluating an expression.
6531 For instance, @value{GDBN} does not know how to add an @code{int} and
6532 a @code{struct foo}. These particular type errors have nothing to do
6533 with the language in use, and usually arise from expressions, such as
6534 the one described above, which make little sense to evaluate anyway.
6536 Each language defines to what degree it is strict about type. For
6537 instance, both Modula-2 and C require the arguments to arithmetical
6538 operators to be numbers. In C, enumerated types and pointers can be
6539 represented as numbers, so that they are valid arguments to mathematical
6540 operators. @xref{Support, ,Supported languages}, for further
6541 details on specific languages.
6543 @value{GDBN} provides some additional commands for controlling the type checker:
6545 @kindex set check@r{, type}
6546 @kindex set check type
6547 @kindex show check type
6549 @item set check type auto
6550 Set type checking on or off based on the current working language.
6551 @xref{Support, ,Supported languages}, for the default settings for
6554 @item set check type on
6555 @itemx set check type off
6556 Set type checking on or off, overriding the default setting for the
6557 current working language. Issue a warning if the setting does not
6558 match the language default. If any type mismatches occur in
6559 evaluating an expression while type checking is on, @value{GDBN} prints a
6560 message and aborts evaluation of the expression.
6562 @item set check type warn
6563 Cause the type checker to issue warnings, but to always attempt to
6564 evaluate the expression. Evaluating the expression may still
6565 be impossible for other reasons. For example, @value{GDBN} cannot add
6566 numbers and structures.
6569 Show the current setting of the type checker, and whether or not @value{GDBN}
6570 is setting it automatically.
6573 @cindex range checking
6574 @cindex checks, range
6575 @node Range Checking
6576 @subsection An overview of range checking
6578 In some languages (such as Modula-2), it is an error to exceed the
6579 bounds of a type; this is enforced with run-time checks. Such range
6580 checking is meant to ensure program correctness by making sure
6581 computations do not overflow, or indices on an array element access do
6582 not exceed the bounds of the array.
6584 For expressions you use in @value{GDBN} commands, you can tell
6585 @value{GDBN} to treat range errors in one of three ways: ignore them,
6586 always treat them as errors and abandon the expression, or issue
6587 warnings but evaluate the expression anyway.
6589 A range error can result from numerical overflow, from exceeding an
6590 array index bound, or when you type a constant that is not a member
6591 of any type. Some languages, however, do not treat overflows as an
6592 error. In many implementations of C, mathematical overflow causes the
6593 result to ``wrap around'' to lower values---for example, if @var{m} is
6594 the largest integer value, and @var{s} is the smallest, then
6597 @var{m} + 1 @result{} @var{s}
6600 This, too, is specific to individual languages, and in some cases
6601 specific to individual compilers or machines. @xref{Support, ,
6602 Supported languages}, for further details on specific languages.
6604 @value{GDBN} provides some additional commands for controlling the range checker:
6606 @kindex set check@r{, range}
6607 @kindex set check range
6608 @kindex show check range
6610 @item set check range auto
6611 Set range checking on or off based on the current working language.
6612 @xref{Support, ,Supported languages}, for the default settings for
6615 @item set check range on
6616 @itemx set check range off
6617 Set range checking on or off, overriding the default setting for the
6618 current working language. A warning is issued if the setting does not
6619 match the language default. If a range error occurs and range checking is on,
6620 then a message is printed and evaluation of the expression is aborted.
6622 @item set check range warn
6623 Output messages when the @value{GDBN} range checker detects a range error,
6624 but attempt to evaluate the expression anyway. Evaluating the
6625 expression may still be impossible for other reasons, such as accessing
6626 memory that the process does not own (a typical example from many Unix
6630 Show the current setting of the range checker, and whether or not it is
6631 being set automatically by @value{GDBN}.
6635 @section Supported languages
6637 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
6638 @c This is false ...
6639 Some @value{GDBN} features may be used in expressions regardless of the
6640 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6641 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6642 ,Expressions}) can be used with the constructs of any supported
6645 The following sections detail to what degree each source language is
6646 supported by @value{GDBN}. These sections are not meant to be language
6647 tutorials or references, but serve only as a reference guide to what the
6648 @value{GDBN} expression parser accepts, and what input and output
6649 formats should look like for different languages. There are many good
6650 books written on each of these languages; please look to these for a
6651 language reference or tutorial.
6655 * Modula-2:: Modula-2
6660 @subsection C and C@t{++}
6662 @cindex C and C@t{++}
6663 @cindex expressions in C or C@t{++}
6665 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
6666 to both languages. Whenever this is the case, we discuss those languages
6670 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
6671 @cindex @sc{gnu} C@t{++}
6672 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
6673 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
6674 effectively, you must compile your C@t{++} programs with a supported
6675 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
6676 compiler (@code{aCC}).
6678 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
6679 format. You can select that format explicitly with the @code{g++}
6680 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6681 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
6682 CC, gcc.info, Using @sc{gnu} CC}, for more information.
6685 * C Operators:: C and C@t{++} operators
6686 * C Constants:: C and C@t{++} constants
6687 * C plus plus expressions:: C@t{++} expressions
6688 * C Defaults:: Default settings for C and C@t{++}
6689 * C Checks:: C and C@t{++} type and range checks
6690 * Debugging C:: @value{GDBN} and C
6691 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
6695 @subsubsection C and C@t{++} operators
6697 @cindex C and C@t{++} operators
6699 Operators must be defined on values of specific types. For instance,
6700 @code{+} is defined on numbers, but not on structures. Operators are
6701 often defined on groups of types.
6703 For the purposes of C and C@t{++}, the following definitions hold:
6708 @emph{Integral types} include @code{int} with any of its storage-class
6709 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
6712 @emph{Floating-point types} include @code{float}, @code{double}, and
6713 @code{long double} (if supported by the target platform).
6716 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
6719 @emph{Scalar types} include all of the above.
6724 The following operators are supported. They are listed here
6725 in order of increasing precedence:
6729 The comma or sequencing operator. Expressions in a comma-separated list
6730 are evaluated from left to right, with the result of the entire
6731 expression being the last expression evaluated.
6734 Assignment. The value of an assignment expression is the value
6735 assigned. Defined on scalar types.
6738 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6739 and translated to @w{@code{@var{a} = @var{a op b}}}.
6740 @w{@code{@var{op}=}} and @code{=} have the same precedence.
6741 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6742 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6745 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6746 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6750 Logical @sc{or}. Defined on integral types.
6753 Logical @sc{and}. Defined on integral types.
6756 Bitwise @sc{or}. Defined on integral types.
6759 Bitwise exclusive-@sc{or}. Defined on integral types.
6762 Bitwise @sc{and}. Defined on integral types.
6765 Equality and inequality. Defined on scalar types. The value of these
6766 expressions is 0 for false and non-zero for true.
6768 @item <@r{, }>@r{, }<=@r{, }>=
6769 Less than, greater than, less than or equal, greater than or equal.
6770 Defined on scalar types. The value of these expressions is 0 for false
6771 and non-zero for true.
6774 left shift, and right shift. Defined on integral types.
6777 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6780 Addition and subtraction. Defined on integral types, floating-point types and
6783 @item *@r{, }/@r{, }%
6784 Multiplication, division, and modulus. Multiplication and division are
6785 defined on integral and floating-point types. Modulus is defined on
6789 Increment and decrement. When appearing before a variable, the
6790 operation is performed before the variable is used in an expression;
6791 when appearing after it, the variable's value is used before the
6792 operation takes place.
6795 Pointer dereferencing. Defined on pointer types. Same precedence as
6799 Address operator. Defined on variables. Same precedence as @code{++}.
6801 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
6802 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
6803 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6804 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
6808 Negative. Defined on integral and floating-point types. Same
6809 precedence as @code{++}.
6812 Logical negation. Defined on integral types. Same precedence as
6816 Bitwise complement operator. Defined on integral types. Same precedence as
6821 Structure member, and pointer-to-structure member. For convenience,
6822 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6823 pointer based on the stored type information.
6824 Defined on @code{struct} and @code{union} data.
6827 Dereferences of pointers to members.
6830 Array indexing. @code{@var{a}[@var{i}]} is defined as
6831 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6834 Function parameter list. Same precedence as @code{->}.
6837 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
6838 and @code{class} types.
6841 Doubled colons also represent the @value{GDBN} scope operator
6842 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6846 If an operator is redefined in the user code, @value{GDBN} usually
6847 attempts to invoke the redefined version instead of using the operator's
6855 @subsubsection C and C@t{++} constants
6857 @cindex C and C@t{++} constants
6859 @value{GDBN} allows you to express the constants of C and C@t{++} in the
6864 Integer constants are a sequence of digits. Octal constants are
6865 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6866 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6867 @samp{l}, specifying that the constant should be treated as a
6871 Floating point constants are a sequence of digits, followed by a decimal
6872 point, followed by a sequence of digits, and optionally followed by an
6873 exponent. An exponent is of the form:
6874 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6875 sequence of digits. The @samp{+} is optional for positive exponents.
6876 A floating-point constant may also end with a letter @samp{f} or
6877 @samp{F}, specifying that the constant should be treated as being of
6878 the @code{float} (as opposed to the default @code{double}) type; or with
6879 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6883 Enumerated constants consist of enumerated identifiers, or their
6884 integral equivalents.
6887 Character constants are a single character surrounded by single quotes
6888 (@code{'}), or a number---the ordinal value of the corresponding character
6889 (usually its @sc{ascii} value). Within quotes, the single character may
6890 be represented by a letter or by @dfn{escape sequences}, which are of
6891 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6892 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6893 @samp{@var{x}} is a predefined special character---for example,
6894 @samp{\n} for newline.
6897 String constants are a sequence of character constants surrounded by
6898 double quotes (@code{"}). Any valid character constant (as described
6899 above) may appear. Double quotes within the string must be preceded by
6900 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6904 Pointer constants are an integral value. You can also write pointers
6905 to constants using the C operator @samp{&}.
6908 Array constants are comma-separated lists surrounded by braces @samp{@{}
6909 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6910 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6911 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6915 * C plus plus expressions::
6922 @node C plus plus expressions
6923 @subsubsection C@t{++} expressions
6925 @cindex expressions in C@t{++}
6926 @value{GDBN} expression handling can interpret most C@t{++} expressions.
6928 @cindex C@t{++} support, not in @sc{coff}
6929 @cindex @sc{coff} versus C@t{++}
6930 @cindex C@t{++} and object formats
6931 @cindex object formats and C@t{++}
6932 @cindex a.out and C@t{++}
6933 @cindex @sc{ecoff} and C@t{++}
6934 @cindex @sc{xcoff} and C@t{++}
6935 @cindex @sc{elf}/stabs and C@t{++}
6936 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
6937 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6938 @c periodically whether this has happened...
6940 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
6941 proper compiler. Typically, C@t{++} debugging depends on the use of
6942 additional debugging information in the symbol table, and thus requires
6943 special support. In particular, if your compiler generates a.out, MIPS
6944 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6945 symbol table, these facilities are all available. (With @sc{gnu} CC,
6946 you can use the @samp{-gstabs} option to request stabs debugging
6947 extensions explicitly.) Where the object code format is standard
6948 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
6949 support in @value{GDBN} does @emph{not} work.
6954 @cindex member functions
6956 Member function calls are allowed; you can use expressions like
6959 count = aml->GetOriginal(x, y)
6962 @vindex this@r{, inside C@t{++} member functions}
6963 @cindex namespace in C@t{++}
6965 While a member function is active (in the selected stack frame), your
6966 expressions have the same namespace available as the member function;
6967 that is, @value{GDBN} allows implicit references to the class instance
6968 pointer @code{this} following the same rules as C@t{++}.
6970 @cindex call overloaded functions
6971 @cindex overloaded functions, calling
6972 @cindex type conversions in C@t{++}
6974 You can call overloaded functions; @value{GDBN} resolves the function
6975 call to the right definition, with some restrictions. @value{GDBN} does not
6976 perform overload resolution involving user-defined type conversions,
6977 calls to constructors, or instantiations of templates that do not exist
6978 in the program. It also cannot handle ellipsis argument lists or
6981 It does perform integral conversions and promotions, floating-point
6982 promotions, arithmetic conversions, pointer conversions, conversions of
6983 class objects to base classes, and standard conversions such as those of
6984 functions or arrays to pointers; it requires an exact match on the
6985 number of function arguments.
6987 Overload resolution is always performed, unless you have specified
6988 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6989 ,@value{GDBN} features for C@t{++}}.
6991 You must specify @code{set overload-resolution off} in order to use an
6992 explicit function signature to call an overloaded function, as in
6994 p 'foo(char,int)'('x', 13)
6997 The @value{GDBN} command-completion facility can simplify this;
6998 see @ref{Completion, ,Command completion}.
7000 @cindex reference declarations
7002 @value{GDBN} understands variables declared as C@t{++} references; you can use
7003 them in expressions just as you do in C@t{++} source---they are automatically
7006 In the parameter list shown when @value{GDBN} displays a frame, the values of
7007 reference variables are not displayed (unlike other variables); this
7008 avoids clutter, since references are often used for large structures.
7009 The @emph{address} of a reference variable is always shown, unless
7010 you have specified @samp{set print address off}.
7013 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7014 expressions can use it just as expressions in your program do. Since
7015 one scope may be defined in another, you can use @code{::} repeatedly if
7016 necessary, for example in an expression like
7017 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7018 resolving name scope by reference to source files, in both C and C@t{++}
7019 debugging (@pxref{Variables, ,Program variables}).
7022 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7023 calling virtual functions correctly, printing out virtual bases of
7024 objects, calling functions in a base subobject, casting objects, and
7025 invoking user-defined operators.
7028 @subsubsection C and C@t{++} defaults
7030 @cindex C and C@t{++} defaults
7032 If you allow @value{GDBN} to set type and range checking automatically, they
7033 both default to @code{off} whenever the working language changes to
7034 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7035 selects the working language.
7037 If you allow @value{GDBN} to set the language automatically, it
7038 recognizes source files whose names end with @file{.c}, @file{.C}, or
7039 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7040 these files, it sets the working language to C or C@t{++}.
7041 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7042 for further details.
7044 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7045 @c unimplemented. If (b) changes, it might make sense to let this node
7046 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7049 @subsubsection C and C@t{++} type and range checks
7051 @cindex C and C@t{++} checks
7053 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7054 is not used. However, if you turn type checking on, @value{GDBN}
7055 considers two variables type equivalent if:
7059 The two variables are structured and have the same structure, union, or
7063 The two variables have the same type name, or types that have been
7064 declared equivalent through @code{typedef}.
7067 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7070 The two @code{struct}, @code{union}, or @code{enum} variables are
7071 declared in the same declaration. (Note: this may not be true for all C
7076 Range checking, if turned on, is done on mathematical operations. Array
7077 indices are not checked, since they are often used to index a pointer
7078 that is not itself an array.
7081 @subsubsection @value{GDBN} and C
7083 The @code{set print union} and @code{show print union} commands apply to
7084 the @code{union} type. When set to @samp{on}, any @code{union} that is
7085 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7086 appears as @samp{@{...@}}.
7088 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7089 with pointers and a memory allocation function. @xref{Expressions,
7093 * Debugging C plus plus::
7096 @node Debugging C plus plus
7097 @subsubsection @value{GDBN} features for C@t{++}
7099 @cindex commands for C@t{++}
7101 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7102 designed specifically for use with C@t{++}. Here is a summary:
7105 @cindex break in overloaded functions
7106 @item @r{breakpoint menus}
7107 When you want a breakpoint in a function whose name is overloaded,
7108 @value{GDBN} breakpoint menus help you specify which function definition
7109 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7111 @cindex overloading in C@t{++}
7112 @item rbreak @var{regex}
7113 Setting breakpoints using regular expressions is helpful for setting
7114 breakpoints on overloaded functions that are not members of any special
7116 @xref{Set Breaks, ,Setting breakpoints}.
7118 @cindex C@t{++} exception handling
7121 Debug C@t{++} exception handling using these commands. @xref{Set
7122 Catchpoints, , Setting catchpoints}.
7125 @item ptype @var{typename}
7126 Print inheritance relationships as well as other information for type
7128 @xref{Symbols, ,Examining the Symbol Table}.
7130 @cindex C@t{++} symbol display
7131 @item set print demangle
7132 @itemx show print demangle
7133 @itemx set print asm-demangle
7134 @itemx show print asm-demangle
7135 Control whether C@t{++} symbols display in their source form, both when
7136 displaying code as C@t{++} source and when displaying disassemblies.
7137 @xref{Print Settings, ,Print settings}.
7139 @item set print object
7140 @itemx show print object
7141 Choose whether to print derived (actual) or declared types of objects.
7142 @xref{Print Settings, ,Print settings}.
7144 @item set print vtbl
7145 @itemx show print vtbl
7146 Control the format for printing virtual function tables.
7147 @xref{Print Settings, ,Print settings}.
7148 (The @code{vtbl} commands do not work on programs compiled with the HP
7149 ANSI C@t{++} compiler (@code{aCC}).)
7151 @kindex set overload-resolution
7152 @cindex overloaded functions, overload resolution
7153 @item set overload-resolution on
7154 Enable overload resolution for C@t{++} expression evaluation. The default
7155 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7156 and searches for a function whose signature matches the argument types,
7157 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7158 expressions}, for details). If it cannot find a match, it emits a
7161 @item set overload-resolution off
7162 Disable overload resolution for C@t{++} expression evaluation. For
7163 overloaded functions that are not class member functions, @value{GDBN}
7164 chooses the first function of the specified name that it finds in the
7165 symbol table, whether or not its arguments are of the correct type. For
7166 overloaded functions that are class member functions, @value{GDBN}
7167 searches for a function whose signature @emph{exactly} matches the
7170 @item @r{Overloaded symbol names}
7171 You can specify a particular definition of an overloaded symbol, using
7172 the same notation that is used to declare such symbols in C@t{++}: type
7173 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7174 also use the @value{GDBN} command-line word completion facilities to list the
7175 available choices, or to finish the type list for you.
7176 @xref{Completion,, Command completion}, for details on how to do this.
7180 @subsection Modula-2
7182 @cindex Modula-2, @value{GDBN} support
7184 The extensions made to @value{GDBN} to support Modula-2 only support
7185 output from the @sc{gnu} Modula-2 compiler (which is currently being
7186 developed). Other Modula-2 compilers are not currently supported, and
7187 attempting to debug executables produced by them is most likely
7188 to give an error as @value{GDBN} reads in the executable's symbol
7191 @cindex expressions in Modula-2
7193 * M2 Operators:: Built-in operators
7194 * Built-In Func/Proc:: Built-in functions and procedures
7195 * M2 Constants:: Modula-2 constants
7196 * M2 Defaults:: Default settings for Modula-2
7197 * Deviations:: Deviations from standard Modula-2
7198 * M2 Checks:: Modula-2 type and range checks
7199 * M2 Scope:: The scope operators @code{::} and @code{.}
7200 * GDB/M2:: @value{GDBN} and Modula-2
7204 @subsubsection Operators
7205 @cindex Modula-2 operators
7207 Operators must be defined on values of specific types. For instance,
7208 @code{+} is defined on numbers, but not on structures. Operators are
7209 often defined on groups of types. For the purposes of Modula-2, the
7210 following definitions hold:
7215 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7219 @emph{Character types} consist of @code{CHAR} and its subranges.
7222 @emph{Floating-point types} consist of @code{REAL}.
7225 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7229 @emph{Scalar types} consist of all of the above.
7232 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7235 @emph{Boolean types} consist of @code{BOOLEAN}.
7239 The following operators are supported, and appear in order of
7240 increasing precedence:
7244 Function argument or array index separator.
7247 Assignment. The value of @var{var} @code{:=} @var{value} is
7251 Less than, greater than on integral, floating-point, or enumerated
7255 Less than or equal to, greater than or equal to
7256 on integral, floating-point and enumerated types, or set inclusion on
7257 set types. Same precedence as @code{<}.
7259 @item =@r{, }<>@r{, }#
7260 Equality and two ways of expressing inequality, valid on scalar types.
7261 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7262 available for inequality, since @code{#} conflicts with the script
7266 Set membership. Defined on set types and the types of their members.
7267 Same precedence as @code{<}.
7270 Boolean disjunction. Defined on boolean types.
7273 Boolean conjunction. Defined on boolean types.
7276 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7279 Addition and subtraction on integral and floating-point types, or union
7280 and difference on set types.
7283 Multiplication on integral and floating-point types, or set intersection
7287 Division on floating-point types, or symmetric set difference on set
7288 types. Same precedence as @code{*}.
7291 Integer division and remainder. Defined on integral types. Same
7292 precedence as @code{*}.
7295 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7298 Pointer dereferencing. Defined on pointer types.
7301 Boolean negation. Defined on boolean types. Same precedence as
7305 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7306 precedence as @code{^}.
7309 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7312 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7316 @value{GDBN} and Modula-2 scope operators.
7320 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7321 treats the use of the operator @code{IN}, or the use of operators
7322 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7323 @code{<=}, and @code{>=} on sets as an error.
7327 @node Built-In Func/Proc
7328 @subsubsection Built-in functions and procedures
7329 @cindex Modula-2 built-ins
7331 Modula-2 also makes available several built-in procedures and functions.
7332 In describing these, the following metavariables are used:
7337 represents an @code{ARRAY} variable.
7340 represents a @code{CHAR} constant or variable.
7343 represents a variable or constant of integral type.
7346 represents an identifier that belongs to a set. Generally used in the
7347 same function with the metavariable @var{s}. The type of @var{s} should
7348 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7351 represents a variable or constant of integral or floating-point type.
7354 represents a variable or constant of floating-point type.
7360 represents a variable.
7363 represents a variable or constant of one of many types. See the
7364 explanation of the function for details.
7367 All Modula-2 built-in procedures also return a result, described below.
7371 Returns the absolute value of @var{n}.
7374 If @var{c} is a lower case letter, it returns its upper case
7375 equivalent, otherwise it returns its argument.
7378 Returns the character whose ordinal value is @var{i}.
7381 Decrements the value in the variable @var{v} by one. Returns the new value.
7383 @item DEC(@var{v},@var{i})
7384 Decrements the value in the variable @var{v} by @var{i}. Returns the
7387 @item EXCL(@var{m},@var{s})
7388 Removes the element @var{m} from the set @var{s}. Returns the new
7391 @item FLOAT(@var{i})
7392 Returns the floating point equivalent of the integer @var{i}.
7395 Returns the index of the last member of @var{a}.
7398 Increments the value in the variable @var{v} by one. Returns the new value.
7400 @item INC(@var{v},@var{i})
7401 Increments the value in the variable @var{v} by @var{i}. Returns the
7404 @item INCL(@var{m},@var{s})
7405 Adds the element @var{m} to the set @var{s} if it is not already
7406 there. Returns the new set.
7409 Returns the maximum value of the type @var{t}.
7412 Returns the minimum value of the type @var{t}.
7415 Returns boolean TRUE if @var{i} is an odd number.
7418 Returns the ordinal value of its argument. For example, the ordinal
7419 value of a character is its @sc{ascii} value (on machines supporting the
7420 @sc{ascii} character set). @var{x} must be of an ordered type, which include
7421 integral, character and enumerated types.
7424 Returns the size of its argument. @var{x} can be a variable or a type.
7426 @item TRUNC(@var{r})
7427 Returns the integral part of @var{r}.
7429 @item VAL(@var{t},@var{i})
7430 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7434 @emph{Warning:} Sets and their operations are not yet supported, so
7435 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7439 @cindex Modula-2 constants
7441 @subsubsection Constants
7443 @value{GDBN} allows you to express the constants of Modula-2 in the following
7449 Integer constants are simply a sequence of digits. When used in an
7450 expression, a constant is interpreted to be type-compatible with the
7451 rest of the expression. Hexadecimal integers are specified by a
7452 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7455 Floating point constants appear as a sequence of digits, followed by a
7456 decimal point and another sequence of digits. An optional exponent can
7457 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7458 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7459 digits of the floating point constant must be valid decimal (base 10)
7463 Character constants consist of a single character enclosed by a pair of
7464 like quotes, either single (@code{'}) or double (@code{"}). They may
7465 also be expressed by their ordinal value (their @sc{ascii} value, usually)
7466 followed by a @samp{C}.
7469 String constants consist of a sequence of characters enclosed by a
7470 pair of like quotes, either single (@code{'}) or double (@code{"}).
7471 Escape sequences in the style of C are also allowed. @xref{C
7472 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
7476 Enumerated constants consist of an enumerated identifier.
7479 Boolean constants consist of the identifiers @code{TRUE} and
7483 Pointer constants consist of integral values only.
7486 Set constants are not yet supported.
7490 @subsubsection Modula-2 defaults
7491 @cindex Modula-2 defaults
7493 If type and range checking are set automatically by @value{GDBN}, they
7494 both default to @code{on} whenever the working language changes to
7495 Modula-2. This happens regardless of whether you or @value{GDBN}
7496 selected the working language.
7498 If you allow @value{GDBN} to set the language automatically, then entering
7499 code compiled from a file whose name ends with @file{.mod} sets the
7500 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
7501 the language automatically}, for further details.
7504 @subsubsection Deviations from standard Modula-2
7505 @cindex Modula-2, deviations from
7507 A few changes have been made to make Modula-2 programs easier to debug.
7508 This is done primarily via loosening its type strictness:
7512 Unlike in standard Modula-2, pointer constants can be formed by
7513 integers. This allows you to modify pointer variables during
7514 debugging. (In standard Modula-2, the actual address contained in a
7515 pointer variable is hidden from you; it can only be modified
7516 through direct assignment to another pointer variable or expression that
7517 returned a pointer.)
7520 C escape sequences can be used in strings and characters to represent
7521 non-printable characters. @value{GDBN} prints out strings with these
7522 escape sequences embedded. Single non-printable characters are
7523 printed using the @samp{CHR(@var{nnn})} format.
7526 The assignment operator (@code{:=}) returns the value of its right-hand
7530 All built-in procedures both modify @emph{and} return their argument.
7534 @subsubsection Modula-2 type and range checks
7535 @cindex Modula-2 checks
7538 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
7541 @c FIXME remove warning when type/range checks added
7543 @value{GDBN} considers two Modula-2 variables type equivalent if:
7547 They are of types that have been declared equivalent via a @code{TYPE
7548 @var{t1} = @var{t2}} statement
7551 They have been declared on the same line. (Note: This is true of the
7552 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
7555 As long as type checking is enabled, any attempt to combine variables
7556 whose types are not equivalent is an error.
7558 Range checking is done on all mathematical operations, assignment, array
7559 index bounds, and all built-in functions and procedures.
7562 @subsubsection The scope operators @code{::} and @code{.}
7564 @cindex @code{.}, Modula-2 scope operator
7565 @cindex colon, doubled as scope operator
7567 @vindex colon-colon@r{, in Modula-2}
7568 @c Info cannot handle :: but TeX can.
7571 @vindex ::@r{, in Modula-2}
7574 There are a few subtle differences between the Modula-2 scope operator
7575 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
7580 @var{module} . @var{id}
7581 @var{scope} :: @var{id}
7585 where @var{scope} is the name of a module or a procedure,
7586 @var{module} the name of a module, and @var{id} is any declared
7587 identifier within your program, except another module.
7589 Using the @code{::} operator makes @value{GDBN} search the scope
7590 specified by @var{scope} for the identifier @var{id}. If it is not
7591 found in the specified scope, then @value{GDBN} searches all scopes
7592 enclosing the one specified by @var{scope}.
7594 Using the @code{.} operator makes @value{GDBN} search the current scope for
7595 the identifier specified by @var{id} that was imported from the
7596 definition module specified by @var{module}. With this operator, it is
7597 an error if the identifier @var{id} was not imported from definition
7598 module @var{module}, or if @var{id} is not an identifier in
7602 @subsubsection @value{GDBN} and Modula-2
7604 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
7605 Five subcommands of @code{set print} and @code{show print} apply
7606 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
7607 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
7608 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
7609 analogue in Modula-2.
7611 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
7612 with any language, is not useful with Modula-2. Its
7613 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
7614 created in Modula-2 as they can in C or C@t{++}. However, because an
7615 address can be specified by an integral constant, the construct
7616 @samp{@{@var{type}@}@var{adrexp}} is still useful.
7618 @cindex @code{#} in Modula-2
7619 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
7620 interpreted as the beginning of a comment. Use @code{<>} instead.
7625 The extensions made to @value{GDBN} to support Chill only support output
7626 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
7627 supported, and attempting to debug executables produced by them is most
7628 likely to give an error as @value{GDBN} reads in the executable's symbol
7631 @c This used to say "... following Chill related topics ...", but since
7632 @c menus are not shown in the printed manual, it would look awkward.
7633 This section covers the Chill related topics and the features
7634 of @value{GDBN} which support these topics.
7637 * How modes are displayed:: How modes are displayed
7638 * Locations:: Locations and their accesses
7639 * Values and their Operations:: Values and their Operations
7640 * Chill type and range checks::
7644 @node How modes are displayed
7645 @subsubsection How modes are displayed
7647 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
7648 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
7649 slightly from the standard specification of the Chill language. The
7652 @c FIXME: this @table's contents effectively disable @code by using @r
7653 @c on every @item. So why does it need @code?
7655 @item @r{@emph{Discrete modes:}}
7658 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
7661 @emph{Boolean Mode} which is predefined by @code{BOOL},
7663 @emph{Character Mode} which is predefined by @code{CHAR},
7665 @emph{Set Mode} which is displayed by the keyword @code{SET}.
7667 (@value{GDBP}) ptype x
7668 type = SET (karli = 10, susi = 20, fritzi = 100)
7670 If the type is an unnumbered set the set element values are omitted.
7672 @emph{Range Mode} which is displayed by
7674 @code{type = <basemode>(<lower bound> : <upper bound>)}
7676 where @code{<lower bound>, <upper bound>} can be of any discrete literal
7677 expression (e.g. set element names).
7680 @item @r{@emph{Powerset Mode:}}
7681 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7682 the member mode of the powerset. The member mode can be any discrete mode.
7684 (@value{GDBP}) ptype x
7685 type = POWERSET SET (egon, hugo, otto)
7688 @item @r{@emph{Reference Modes:}}
7691 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
7692 followed by the mode name to which the reference is bound.
7694 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7697 @item @r{@emph{Procedure mode}}
7698 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7699 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7700 list>} is a list of the parameter modes. @code{<return mode>} indicates
7701 the mode of the result of the procedure if any. The exceptionlist lists
7702 all possible exceptions which can be raised by the procedure.
7705 @item @r{@emph{Instance mode}}
7706 The instance mode is represented by a structure, which has a static
7707 type, and is therefore not really of interest.
7710 @item @r{@emph{Synchronization Modes:}}
7713 @emph{Event Mode} which is displayed by
7715 @code{EVENT (<event length>)}
7717 where @code{(<event length>)} is optional.
7719 @emph{Buffer Mode} which is displayed by
7721 @code{BUFFER (<buffer length>)<buffer element mode>}
7723 where @code{(<buffer length>)} is optional.
7726 @item @r{@emph{Timing Modes:}}
7729 @emph{Duration Mode} which is predefined by @code{DURATION}
7731 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7734 @item @r{@emph{Real Modes:}}
7735 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7737 @item @r{@emph{String Modes:}}
7740 @emph{Character String Mode} which is displayed by
7742 @code{CHARS(<string length>)}
7744 followed by the keyword @code{VARYING} if the String Mode is a varying
7747 @emph{Bit String Mode} which is displayed by
7754 @item @r{@emph{Array Mode:}}
7755 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7756 followed by the element mode (which may in turn be an array mode).
7758 (@value{GDBP}) ptype x
7761 SET (karli = 10, susi = 20, fritzi = 100)
7764 @item @r{@emph{Structure Mode}}
7765 The Structure mode is displayed by the keyword @code{STRUCT(<field
7766 list>)}. The @code{<field list>} consists of names and modes of fields
7767 of the structure. Variant structures have the keyword @code{CASE <field>
7768 OF <variant fields> ESAC} in their field list. Since the current version
7769 of the GNU Chill compiler doesn't implement tag processing (no runtime
7770 checks of variant fields, and therefore no debugging info), the output
7771 always displays all variant fields.
7773 (@value{GDBP}) ptype str
7788 @subsubsection Locations and their accesses
7790 A location in Chill is an object which can contain values.
7792 A value of a location is generally accessed by the (declared) name of
7793 the location. The output conforms to the specification of values in
7794 Chill programs. How values are specified
7795 is the topic of the next section, @ref{Values and their Operations}.
7797 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7798 display or change the result of a currently-active procedure:
7805 This does the same as the Chill action @code{RESULT EXPR} (which
7806 is not available in @value{GDBN}).
7808 Values of reference mode locations are printed by @code{PTR(<hex
7809 value>)} in case of a free reference mode, and by @code{(REF <reference
7810 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7811 represents the address where the reference points to. To access the
7812 value of the location referenced by the pointer, use the dereference
7815 Values of procedure mode locations are displayed by
7818 (<argument modes> ) <return mode> @} <address> <name of procedure
7821 @code{<argument modes>} is a list of modes according to the parameter
7822 specification of the procedure and @code{<address>} shows the address of
7826 Locations of instance modes are displayed just like a structure with two
7827 fields specifying the @emph{process type} and the @emph{copy number} of
7828 the investigated instance location@footnote{This comes from the current
7829 implementation of instances. They are implemented as a structure (no
7830 na). The output should be something like @code{[<name of the process>;
7831 <instance number>]}.}. The field names are @code{__proc_type} and
7834 Locations of synchronization modes are displayed like a structure with
7835 the field name @code{__event_data} in case of a event mode location, and
7836 like a structure with the field @code{__buffer_data} in case of a buffer
7837 mode location (refer to previous paragraph).
7839 Structure Mode locations are printed by @code{[.<field name>: <value>,
7840 ...]}. The @code{<field name>} corresponds to the structure mode
7841 definition and the layout of @code{<value>} varies depending of the mode
7842 of the field. If the investigated structure mode location is of variant
7843 structure mode, the variant parts of the structure are enclosed in curled
7844 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
7845 on the same memory location and represent the current values of the
7846 memory location in their specific modes. Since no tag processing is done
7847 all variants are displayed. A variant field is printed by
7848 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7851 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7852 [.cs: []], (susi) = [.ds: susi]}]
7856 Substructures of string mode-, array mode- or structure mode-values
7857 (e.g. array slices, fields of structure locations) are accessed using
7858 certain operations which are described in the next section, @ref{Values
7859 and their Operations}.
7861 A location value may be interpreted as having a different mode using the
7862 location conversion. This mode conversion is written as @code{<mode
7863 name>(<location>)}. The user has to consider that the sizes of the modes
7864 have to be equal otherwise an error occurs. Furthermore, no range
7865 checking of the location against the destination mode is performed, and
7866 therefore the result can be quite confusing.
7869 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7872 @node Values and their Operations
7873 @subsubsection Values and their Operations
7875 Values are used to alter locations, to investigate complex structures in
7876 more detail or to filter relevant information out of a large amount of
7877 data. There are several (mode dependent) operations defined which enable
7878 such investigations. These operations are not only applicable to
7879 constant values but also to locations, which can become quite useful
7880 when debugging complex structures. During parsing the command line
7881 (e.g. evaluating an expression) @value{GDBN} treats location names as
7882 the values behind these locations.
7884 This section describes how values have to be specified and which
7885 operations are legal to be used with such values.
7888 @item Literal Values
7889 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7890 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7892 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7893 @c be converted to a @ref.
7898 @emph{Integer Literals} are specified in the same manner as in Chill
7899 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7901 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7903 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7906 @emph{Set Literals} are defined by a name which was specified in a set
7907 mode. The value delivered by a Set Literal is the set value. This is
7908 comparable to an enumeration in C/C@t{++} language.
7910 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7911 emptiness literal delivers either the empty reference value, the empty
7912 procedure value or the empty instance value.
7915 @emph{Character String Literals} are defined by a sequence of characters
7916 enclosed in single- or double quotes. If a single- or double quote has
7917 to be part of the string literal it has to be stuffed (specified twice).
7919 @emph{Bitstring Literals} are specified in the same manner as in Chill
7920 programs (refer z200/88 chpt 5.2.4.8).
7922 @emph{Floating point literals} are specified in the same manner as in
7923 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7928 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7929 name>} can be omitted if the mode of the tuple is unambiguous. This
7930 unambiguity is derived from the context of a evaluated expression.
7931 @code{<tuple>} can be one of the following:
7934 @item @emph{Powerset Tuple}
7935 @item @emph{Array Tuple}
7936 @item @emph{Structure Tuple}
7937 Powerset tuples, array tuples and structure tuples are specified in the
7938 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7941 @item String Element Value
7942 A string element value is specified by
7944 @code{<string value>(<index>)}
7946 where @code{<index>} is a integer expression. It delivers a character
7947 value which is equivalent to the character indexed by @code{<index>} in
7950 @item String Slice Value
7951 A string slice value is specified by @code{<string value>(<slice
7952 spec>)}, where @code{<slice spec>} can be either a range of integer
7953 expressions or specified by @code{<start expr> up <size>}.
7954 @code{<size>} denotes the number of elements which the slice contains.
7955 The delivered value is a string value, which is part of the specified
7958 @item Array Element Values
7959 An array element value is specified by @code{<array value>(<expr>)} and
7960 delivers a array element value of the mode of the specified array.
7962 @item Array Slice Values
7963 An array slice is specified by @code{<array value>(<slice spec>)}, where
7964 @code{<slice spec>} can be either a range specified by expressions or by
7965 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7966 arrayelements the slice contains. The delivered value is an array value
7967 which is part of the specified array.
7969 @item Structure Field Values
7970 A structure field value is derived by @code{<structure value>.<field
7971 name>}, where @code{<field name>} indicates the name of a field specified
7972 in the mode definition of the structure. The mode of the delivered value
7973 corresponds to this mode definition in the structure definition.
7975 @item Procedure Call Value
7976 The procedure call value is derived from the return value of the
7977 procedure@footnote{If a procedure call is used for instance in an
7978 expression, then this procedure is called with all its side
7979 effects. This can lead to confusing results if used carelessly.}.
7981 Values of duration mode locations are represented by @code{ULONG} literals.
7983 Values of time mode locations appear as
7985 @code{TIME(<secs>:<nsecs>)}
7990 This is not implemented yet:
7991 @item Built-in Value
7993 The following built in functions are provided:
8005 @item @code{UPPER()}
8006 @item @code{LOWER()}
8007 @item @code{LENGTH()}
8011 @item @code{ARCSIN()}
8012 @item @code{ARCCOS()}
8013 @item @code{ARCTAN()}
8020 For a detailed description refer to the GNU Chill implementation manual
8024 @item Zero-adic Operator Value
8025 The zero-adic operator value is derived from the instance value for the
8026 current active process.
8028 @item Expression Values
8029 The value delivered by an expression is the result of the evaluation of
8030 the specified expression. If there are error conditions (mode
8031 incompatibility, etc.) the evaluation of expressions is aborted with a
8032 corresponding error message. Expressions may be parenthesised which
8033 causes the evaluation of this expression before any other expression
8034 which uses the result of the parenthesised expression. The following
8035 operators are supported by @value{GDBN}:
8038 @item @code{OR, ORIF, XOR}
8039 @itemx @code{AND, ANDIF}
8041 Logical operators defined over operands of boolean mode.
8044 Equality and inequality operators defined over all modes.
8048 Relational operators defined over predefined modes.
8051 @itemx @code{*, /, MOD, REM}
8052 Arithmetic operators defined over predefined modes.
8055 Change sign operator.
8058 String concatenation operator.
8061 String repetition operator.
8064 Referenced location operator which can be used either to take the
8065 address of a location (@code{->loc}), or to dereference a reference
8066 location (@code{loc->}).
8068 @item @code{OR, XOR}
8071 Powerset and bitstring operators.
8075 Powerset inclusion operators.
8078 Membership operator.
8082 @node Chill type and range checks
8083 @subsubsection Chill type and range checks
8085 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8086 of the two modes are equal. This rule applies recursively to more
8087 complex datatypes which means that complex modes are treated
8088 equivalent if all element modes (which also can be complex modes like
8089 structures, arrays, etc.) have the same size.
8091 Range checking is done on all mathematical operations, assignment, array
8092 index bounds and all built in procedures.
8094 Strong type checks are forced using the @value{GDBN} command @code{set
8095 check strong}. This enforces strong type and range checks on all
8096 operations where Chill constructs are used (expressions, built in
8097 functions, etc.) in respect to the semantics as defined in the z.200
8098 language specification.
8100 All checks can be disabled by the @value{GDBN} command @code{set check
8104 @c Deviations from the Chill Standard Z200/88
8105 see last paragraph ?
8108 @node Chill defaults
8109 @subsubsection Chill defaults
8111 If type and range checking are set automatically by @value{GDBN}, they
8112 both default to @code{on} whenever the working language changes to
8113 Chill. This happens regardless of whether you or @value{GDBN}
8114 selected the working language.
8116 If you allow @value{GDBN} to set the language automatically, then entering
8117 code compiled from a file whose name ends with @file{.ch} sets the
8118 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8119 the language automatically}, for further details.
8122 @chapter Examining the Symbol Table
8124 The commands described in this chapter allow you to inquire about the
8125 symbols (names of variables, functions and types) defined in your
8126 program. This information is inherent in the text of your program and
8127 does not change as your program executes. @value{GDBN} finds it in your
8128 program's symbol table, in the file indicated when you started @value{GDBN}
8129 (@pxref{File Options, ,Choosing files}), or by one of the
8130 file-management commands (@pxref{Files, ,Commands to specify files}).
8132 @cindex symbol names
8133 @cindex names of symbols
8134 @cindex quoting names
8135 Occasionally, you may need to refer to symbols that contain unusual
8136 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8137 most frequent case is in referring to static variables in other
8138 source files (@pxref{Variables,,Program variables}). File names
8139 are recorded in object files as debugging symbols, but @value{GDBN} would
8140 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8141 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8142 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8149 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8152 @kindex info address
8153 @cindex address of a symbol
8154 @item info address @var{symbol}
8155 Describe where the data for @var{symbol} is stored. For a register
8156 variable, this says which register it is kept in. For a non-register
8157 local variable, this prints the stack-frame offset at which the variable
8160 Note the contrast with @samp{print &@var{symbol}}, which does not work
8161 at all for a register variable, and for a stack local variable prints
8162 the exact address of the current instantiation of the variable.
8165 @cindex symbol from address
8166 @item info symbol @var{addr}
8167 Print the name of a symbol which is stored at the address @var{addr}.
8168 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8169 nearest symbol and an offset from it:
8172 (@value{GDBP}) info symbol 0x54320
8173 _initialize_vx + 396 in section .text
8177 This is the opposite of the @code{info address} command. You can use
8178 it to find out the name of a variable or a function given its address.
8181 @item whatis @var{expr}
8182 Print the data type of expression @var{expr}. @var{expr} is not
8183 actually evaluated, and any side-effecting operations (such as
8184 assignments or function calls) inside it do not take place.
8185 @xref{Expressions, ,Expressions}.
8188 Print the data type of @code{$}, the last value in the value history.
8191 @item ptype @var{typename}
8192 Print a description of data type @var{typename}. @var{typename} may be
8193 the name of a type, or for C code it may have the form @samp{class
8194 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8195 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8197 @item ptype @var{expr}
8199 Print a description of the type of expression @var{expr}. @code{ptype}
8200 differs from @code{whatis} by printing a detailed description, instead
8201 of just the name of the type.
8203 For example, for this variable declaration:
8206 struct complex @{double real; double imag;@} v;
8210 the two commands give this output:
8214 (@value{GDBP}) whatis v
8215 type = struct complex
8216 (@value{GDBP}) ptype v
8217 type = struct complex @{
8225 As with @code{whatis}, using @code{ptype} without an argument refers to
8226 the type of @code{$}, the last value in the value history.
8229 @item info types @var{regexp}
8231 Print a brief description of all types whose names match @var{regexp}
8232 (or all types in your program, if you supply no argument). Each
8233 complete typename is matched as though it were a complete line; thus,
8234 @samp{i type value} gives information on all types in your program whose
8235 names include the string @code{value}, but @samp{i type ^value$} gives
8236 information only on types whose complete name is @code{value}.
8238 This command differs from @code{ptype} in two ways: first, like
8239 @code{whatis}, it does not print a detailed description; second, it
8240 lists all source files where a type is defined.
8243 @cindex local variables
8244 @item info scope @var{addr}
8245 List all the variables local to a particular scope. This command
8246 accepts a location---a function name, a source line, or an address
8247 preceded by a @samp{*}, and prints all the variables local to the
8248 scope defined by that location. For example:
8251 (@value{GDBP}) @b{info scope command_line_handler}
8252 Scope for command_line_handler:
8253 Symbol rl is an argument at stack/frame offset 8, length 4.
8254 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8255 Symbol linelength is in static storage at address 0x150a1c, length 4.
8256 Symbol p is a local variable in register $esi, length 4.
8257 Symbol p1 is a local variable in register $ebx, length 4.
8258 Symbol nline is a local variable in register $edx, length 4.
8259 Symbol repeat is a local variable at frame offset -8, length 4.
8263 This command is especially useful for determining what data to collect
8264 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8269 Show the name of the current source file---that is, the source file for
8270 the function containing the current point of execution---and the language
8273 @kindex info sources
8275 Print the names of all source files in your program for which there is
8276 debugging information, organized into two lists: files whose symbols
8277 have already been read, and files whose symbols will be read when needed.
8279 @kindex info functions
8280 @item info functions
8281 Print the names and data types of all defined functions.
8283 @item info functions @var{regexp}
8284 Print the names and data types of all defined functions
8285 whose names contain a match for regular expression @var{regexp}.
8286 Thus, @samp{info fun step} finds all functions whose names
8287 include @code{step}; @samp{info fun ^step} finds those whose names
8288 start with @code{step}.
8290 @kindex info variables
8291 @item info variables
8292 Print the names and data types of all variables that are declared
8293 outside of functions (i.e., excluding local variables).
8295 @item info variables @var{regexp}
8296 Print the names and data types of all variables (except for local
8297 variables) whose names contain a match for regular expression
8301 This was never implemented.
8302 @kindex info methods
8304 @itemx info methods @var{regexp}
8305 The @code{info methods} command permits the user to examine all defined
8306 methods within C@t{++} program, or (with the @var{regexp} argument) a
8307 specific set of methods found in the various C@t{++} classes. Many
8308 C@t{++} classes provide a large number of methods. Thus, the output
8309 from the @code{ptype} command can be overwhelming and hard to use. The
8310 @code{info-methods} command filters the methods, printing only those
8311 which match the regular-expression @var{regexp}.
8314 @cindex reloading symbols
8315 Some systems allow individual object files that make up your program to
8316 be replaced without stopping and restarting your program. For example,
8317 in VxWorks you can simply recompile a defective object file and keep on
8318 running. If you are running on one of these systems, you can allow
8319 @value{GDBN} to reload the symbols for automatically relinked modules:
8322 @kindex set symbol-reloading
8323 @item set symbol-reloading on
8324 Replace symbol definitions for the corresponding source file when an
8325 object file with a particular name is seen again.
8327 @item set symbol-reloading off
8328 Do not replace symbol definitions when encountering object files of the
8329 same name more than once. This is the default state; if you are not
8330 running on a system that permits automatic relinking of modules, you
8331 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8332 may discard symbols when linking large programs, that may contain
8333 several modules (from different directories or libraries) with the same
8336 @kindex show symbol-reloading
8337 @item show symbol-reloading
8338 Show the current @code{on} or @code{off} setting.
8341 @kindex set opaque-type-resolution
8342 @item set opaque-type-resolution on
8343 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8344 declared as a pointer to a @code{struct}, @code{class}, or
8345 @code{union}---for example, @code{struct MyType *}---that is used in one
8346 source file although the full declaration of @code{struct MyType} is in
8347 another source file. The default is on.
8349 A change in the setting of this subcommand will not take effect until
8350 the next time symbols for a file are loaded.
8352 @item set opaque-type-resolution off
8353 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8354 is printed as follows:
8356 @{<no data fields>@}
8359 @kindex show opaque-type-resolution
8360 @item show opaque-type-resolution
8361 Show whether opaque types are resolved or not.
8363 @kindex maint print symbols
8365 @kindex maint print psymbols
8366 @cindex partial symbol dump
8367 @item maint print symbols @var{filename}
8368 @itemx maint print psymbols @var{filename}
8369 @itemx maint print msymbols @var{filename}
8370 Write a dump of debugging symbol data into the file @var{filename}.
8371 These commands are used to debug the @value{GDBN} symbol-reading code. Only
8372 symbols with debugging data are included. If you use @samp{maint print
8373 symbols}, @value{GDBN} includes all the symbols for which it has already
8374 collected full details: that is, @var{filename} reflects symbols for
8375 only those files whose symbols @value{GDBN} has read. You can use the
8376 command @code{info sources} to find out which files these are. If you
8377 use @samp{maint print psymbols} instead, the dump shows information about
8378 symbols that @value{GDBN} only knows partially---that is, symbols defined in
8379 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
8380 @samp{maint print msymbols} dumps just the minimal symbol information
8381 required for each object file from which @value{GDBN} has read some symbols.
8382 @xref{Files, ,Commands to specify files}, for a discussion of how
8383 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
8387 @chapter Altering Execution
8389 Once you think you have found an error in your program, you might want to
8390 find out for certain whether correcting the apparent error would lead to
8391 correct results in the rest of the run. You can find the answer by
8392 experiment, using the @value{GDBN} features for altering execution of the
8395 For example, you can store new values into variables or memory
8396 locations, give your program a signal, restart it at a different
8397 address, or even return prematurely from a function.
8400 * Assignment:: Assignment to variables
8401 * Jumping:: Continuing at a different address
8402 * Signaling:: Giving your program a signal
8403 * Returning:: Returning from a function
8404 * Calling:: Calling your program's functions
8405 * Patching:: Patching your program
8409 @section Assignment to variables
8412 @cindex setting variables
8413 To alter the value of a variable, evaluate an assignment expression.
8414 @xref{Expressions, ,Expressions}. For example,
8421 stores the value 4 into the variable @code{x}, and then prints the
8422 value of the assignment expression (which is 4).
8423 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
8424 information on operators in supported languages.
8426 @kindex set variable
8427 @cindex variables, setting
8428 If you are not interested in seeing the value of the assignment, use the
8429 @code{set} command instead of the @code{print} command. @code{set} is
8430 really the same as @code{print} except that the expression's value is
8431 not printed and is not put in the value history (@pxref{Value History,
8432 ,Value history}). The expression is evaluated only for its effects.
8434 If the beginning of the argument string of the @code{set} command
8435 appears identical to a @code{set} subcommand, use the @code{set
8436 variable} command instead of just @code{set}. This command is identical
8437 to @code{set} except for its lack of subcommands. For example, if your
8438 program has a variable @code{width}, you get an error if you try to set
8439 a new value with just @samp{set width=13}, because @value{GDBN} has the
8440 command @code{set width}:
8443 (@value{GDBP}) whatis width
8445 (@value{GDBP}) p width
8447 (@value{GDBP}) set width=47
8448 Invalid syntax in expression.
8452 The invalid expression, of course, is @samp{=47}. In
8453 order to actually set the program's variable @code{width}, use
8456 (@value{GDBP}) set var width=47
8459 Because the @code{set} command has many subcommands that can conflict
8460 with the names of program variables, it is a good idea to use the
8461 @code{set variable} command instead of just @code{set}. For example, if
8462 your program has a variable @code{g}, you run into problems if you try
8463 to set a new value with just @samp{set g=4}, because @value{GDBN} has
8464 the command @code{set gnutarget}, abbreviated @code{set g}:
8468 (@value{GDBP}) whatis g
8472 (@value{GDBP}) set g=4
8476 The program being debugged has been started already.
8477 Start it from the beginning? (y or n) y
8478 Starting program: /home/smith/cc_progs/a.out
8479 "/home/smith/cc_progs/a.out": can't open to read symbols:
8481 (@value{GDBP}) show g
8482 The current BFD target is "=4".
8487 The program variable @code{g} did not change, and you silently set the
8488 @code{gnutarget} to an invalid value. In order to set the variable
8492 (@value{GDBP}) set var g=4
8495 @value{GDBN} allows more implicit conversions in assignments than C; you can
8496 freely store an integer value into a pointer variable or vice versa,
8497 and you can convert any structure to any other structure that is the
8498 same length or shorter.
8499 @comment FIXME: how do structs align/pad in these conversions?
8500 @comment /doc@cygnus.com 18dec1990
8502 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
8503 construct to generate a value of specified type at a specified address
8504 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
8505 to memory location @code{0x83040} as an integer (which implies a certain size
8506 and representation in memory), and
8509 set @{int@}0x83040 = 4
8513 stores the value 4 into that memory location.
8516 @section Continuing at a different address
8518 Ordinarily, when you continue your program, you do so at the place where
8519 it stopped, with the @code{continue} command. You can instead continue at
8520 an address of your own choosing, with the following commands:
8524 @item jump @var{linespec}
8525 Resume execution at line @var{linespec}. Execution stops again
8526 immediately if there is a breakpoint there. @xref{List, ,Printing
8527 source lines}, for a description of the different forms of
8528 @var{linespec}. It is common practice to use the @code{tbreak} command
8529 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
8532 The @code{jump} command does not change the current stack frame, or
8533 the stack pointer, or the contents of any memory location or any
8534 register other than the program counter. If line @var{linespec} is in
8535 a different function from the one currently executing, the results may
8536 be bizarre if the two functions expect different patterns of arguments or
8537 of local variables. For this reason, the @code{jump} command requests
8538 confirmation if the specified line is not in the function currently
8539 executing. However, even bizarre results are predictable if you are
8540 well acquainted with the machine-language code of your program.
8542 @item jump *@var{address}
8543 Resume execution at the instruction at address @var{address}.
8546 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
8547 On many systems, you can get much the same effect as the @code{jump}
8548 command by storing a new value into the register @code{$pc}. The
8549 difference is that this does not start your program running; it only
8550 changes the address of where it @emph{will} run when you continue. For
8558 makes the next @code{continue} command or stepping command execute at
8559 address @code{0x485}, rather than at the address where your program stopped.
8560 @xref{Continuing and Stepping, ,Continuing and stepping}.
8562 The most common occasion to use the @code{jump} command is to back
8563 up---perhaps with more breakpoints set---over a portion of a program
8564 that has already executed, in order to examine its execution in more
8569 @section Giving your program a signal
8573 @item signal @var{signal}
8574 Resume execution where your program stopped, but immediately give it the
8575 signal @var{signal}. @var{signal} can be the name or the number of a
8576 signal. For example, on many systems @code{signal 2} and @code{signal
8577 SIGINT} are both ways of sending an interrupt signal.
8579 Alternatively, if @var{signal} is zero, continue execution without
8580 giving a signal. This is useful when your program stopped on account of
8581 a signal and would ordinary see the signal when resumed with the
8582 @code{continue} command; @samp{signal 0} causes it to resume without a
8585 @code{signal} does not repeat when you press @key{RET} a second time
8586 after executing the command.
8590 Invoking the @code{signal} command is not the same as invoking the
8591 @code{kill} utility from the shell. Sending a signal with @code{kill}
8592 causes @value{GDBN} to decide what to do with the signal depending on
8593 the signal handling tables (@pxref{Signals}). The @code{signal} command
8594 passes the signal directly to your program.
8598 @section Returning from a function
8601 @cindex returning from a function
8604 @itemx return @var{expression}
8605 You can cancel execution of a function call with the @code{return}
8606 command. If you give an
8607 @var{expression} argument, its value is used as the function's return
8611 When you use @code{return}, @value{GDBN} discards the selected stack frame
8612 (and all frames within it). You can think of this as making the
8613 discarded frame return prematurely. If you wish to specify a value to
8614 be returned, give that value as the argument to @code{return}.
8616 This pops the selected stack frame (@pxref{Selection, ,Selecting a
8617 frame}), and any other frames inside of it, leaving its caller as the
8618 innermost remaining frame. That frame becomes selected. The
8619 specified value is stored in the registers used for returning values
8622 The @code{return} command does not resume execution; it leaves the
8623 program stopped in the state that would exist if the function had just
8624 returned. In contrast, the @code{finish} command (@pxref{Continuing
8625 and Stepping, ,Continuing and stepping}) resumes execution until the
8626 selected stack frame returns naturally.
8629 @section Calling program functions
8631 @cindex calling functions
8634 @item call @var{expr}
8635 Evaluate the expression @var{expr} without displaying @code{void}
8639 You can use this variant of the @code{print} command if you want to
8640 execute a function from your program, but without cluttering the output
8641 with @code{void} returned values. If the result is not void, it
8642 is printed and saved in the value history.
8644 For the A29K, a user-controlled variable @code{call_scratch_address},
8645 specifies the location of a scratch area to be used when @value{GDBN}
8646 calls a function in the target. This is necessary because the usual
8647 method of putting the scratch area on the stack does not work in systems
8648 that have separate instruction and data spaces.
8651 @section Patching programs
8653 @cindex patching binaries
8654 @cindex writing into executables
8655 @cindex writing into corefiles
8657 By default, @value{GDBN} opens the file containing your program's
8658 executable code (or the corefile) read-only. This prevents accidental
8659 alterations to machine code; but it also prevents you from intentionally
8660 patching your program's binary.
8662 If you'd like to be able to patch the binary, you can specify that
8663 explicitly with the @code{set write} command. For example, you might
8664 want to turn on internal debugging flags, or even to make emergency
8670 @itemx set write off
8671 If you specify @samp{set write on}, @value{GDBN} opens executable and
8672 core files for both reading and writing; if you specify @samp{set write
8673 off} (the default), @value{GDBN} opens them read-only.
8675 If you have already loaded a file, you must load it again (using the
8676 @code{exec-file} or @code{core-file} command) after changing @code{set
8677 write}, for your new setting to take effect.
8681 Display whether executable files and core files are opened for writing
8686 @chapter @value{GDBN} Files
8688 @value{GDBN} needs to know the file name of the program to be debugged,
8689 both in order to read its symbol table and in order to start your
8690 program. To debug a core dump of a previous run, you must also tell
8691 @value{GDBN} the name of the core dump file.
8694 * Files:: Commands to specify files
8695 * Symbol Errors:: Errors reading symbol files
8699 @section Commands to specify files
8701 @cindex symbol table
8702 @cindex core dump file
8704 You may want to specify executable and core dump file names. The usual
8705 way to do this is at start-up time, using the arguments to
8706 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
8707 Out of @value{GDBN}}).
8709 Occasionally it is necessary to change to a different file during a
8710 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8711 a file you want to use. In these situations the @value{GDBN} commands
8712 to specify new files are useful.
8715 @cindex executable file
8717 @item file @var{filename}
8718 Use @var{filename} as the program to be debugged. It is read for its
8719 symbols and for the contents of pure memory. It is also the program
8720 executed when you use the @code{run} command. If you do not specify a
8721 directory and the file is not found in the @value{GDBN} working directory,
8722 @value{GDBN} uses the environment variable @code{PATH} as a list of
8723 directories to search, just as the shell does when looking for a program
8724 to run. You can change the value of this variable, for both @value{GDBN}
8725 and your program, using the @code{path} command.
8727 On systems with memory-mapped files, an auxiliary file named
8728 @file{@var{filename}.syms} may hold symbol table information for
8729 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8730 @file{@var{filename}.syms}, starting up more quickly. See the
8731 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8732 (available on the command line, and with the commands @code{file},
8733 @code{symbol-file}, or @code{add-symbol-file}, described below),
8734 for more information.
8737 @code{file} with no argument makes @value{GDBN} discard any information it
8738 has on both executable file and the symbol table.
8741 @item exec-file @r{[} @var{filename} @r{]}
8742 Specify that the program to be run (but not the symbol table) is found
8743 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8744 if necessary to locate your program. Omitting @var{filename} means to
8745 discard information on the executable file.
8748 @item symbol-file @r{[} @var{filename} @r{]}
8749 Read symbol table information from file @var{filename}. @code{PATH} is
8750 searched when necessary. Use the @code{file} command to get both symbol
8751 table and program to run from the same file.
8753 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8754 program's symbol table.
8756 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8757 of its convenience variables, the value history, and all breakpoints and
8758 auto-display expressions. This is because they may contain pointers to
8759 the internal data recording symbols and data types, which are part of
8760 the old symbol table data being discarded inside @value{GDBN}.
8762 @code{symbol-file} does not repeat if you press @key{RET} again after
8765 When @value{GDBN} is configured for a particular environment, it
8766 understands debugging information in whatever format is the standard
8767 generated for that environment; you may use either a @sc{gnu} compiler, or
8768 other compilers that adhere to the local conventions.
8769 Best results are usually obtained from @sc{gnu} compilers; for example,
8770 using @code{@value{GCC}} you can generate debugging information for
8773 For most kinds of object files, with the exception of old SVR3 systems
8774 using COFF, the @code{symbol-file} command does not normally read the
8775 symbol table in full right away. Instead, it scans the symbol table
8776 quickly to find which source files and which symbols are present. The
8777 details are read later, one source file at a time, as they are needed.
8779 The purpose of this two-stage reading strategy is to make @value{GDBN}
8780 start up faster. For the most part, it is invisible except for
8781 occasional pauses while the symbol table details for a particular source
8782 file are being read. (The @code{set verbose} command can turn these
8783 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8784 warnings and messages}.)
8786 We have not implemented the two-stage strategy for COFF yet. When the
8787 symbol table is stored in COFF format, @code{symbol-file} reads the
8788 symbol table data in full right away. Note that ``stabs-in-COFF''
8789 still does the two-stage strategy, since the debug info is actually
8793 @cindex reading symbols immediately
8794 @cindex symbols, reading immediately
8796 @cindex memory-mapped symbol file
8797 @cindex saving symbol table
8798 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8799 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8800 You can override the @value{GDBN} two-stage strategy for reading symbol
8801 tables by using the @samp{-readnow} option with any of the commands that
8802 load symbol table information, if you want to be sure @value{GDBN} has the
8803 entire symbol table available.
8805 If memory-mapped files are available on your system through the
8806 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8807 cause @value{GDBN} to write the symbols for your program into a reusable
8808 file. Future @value{GDBN} debugging sessions map in symbol information
8809 from this auxiliary symbol file (if the program has not changed), rather
8810 than spending time reading the symbol table from the executable
8811 program. Using the @samp{-mapped} option has the same effect as
8812 starting @value{GDBN} with the @samp{-mapped} command-line option.
8814 You can use both options together, to make sure the auxiliary symbol
8815 file has all the symbol information for your program.
8817 The auxiliary symbol file for a program called @var{myprog} is called
8818 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8819 than the corresponding executable), @value{GDBN} always attempts to use
8820 it when you debug @var{myprog}; no special options or commands are
8823 The @file{.syms} file is specific to the host machine where you run
8824 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8825 symbol table. It cannot be shared across multiple host platforms.
8827 @c FIXME: for now no mention of directories, since this seems to be in
8828 @c flux. 13mar1992 status is that in theory GDB would look either in
8829 @c current dir or in same dir as myprog; but issues like competing
8830 @c GDB's, or clutter in system dirs, mean that in practice right now
8831 @c only current dir is used. FFish says maybe a special GDB hierarchy
8832 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8837 @item core-file @r{[} @var{filename} @r{]}
8838 Specify the whereabouts of a core dump file to be used as the ``contents
8839 of memory''. Traditionally, core files contain only some parts of the
8840 address space of the process that generated them; @value{GDBN} can access the
8841 executable file itself for other parts.
8843 @code{core-file} with no argument specifies that no core file is
8846 Note that the core file is ignored when your program is actually running
8847 under @value{GDBN}. So, if you have been running your program and you
8848 wish to debug a core file instead, you must kill the subprocess in which
8849 the program is running. To do this, use the @code{kill} command
8850 (@pxref{Kill Process, ,Killing the child process}).
8852 @kindex add-symbol-file
8853 @cindex dynamic linking
8854 @item add-symbol-file @var{filename} @var{address}
8855 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8856 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address}
8857 The @code{add-symbol-file} command reads additional symbol table
8858 information from the file @var{filename}. You would use this command
8859 when @var{filename} has been dynamically loaded (by some other means)
8860 into the program that is running. @var{address} should be the memory
8861 address at which the file has been loaded; @value{GDBN} cannot figure
8862 this out for itself. You can additionally specify an arbitrary number
8863 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
8864 section name and base address for that section. You can specify any
8865 @var{address} as an expression.
8867 The symbol table of the file @var{filename} is added to the symbol table
8868 originally read with the @code{symbol-file} command. You can use the
8869 @code{add-symbol-file} command any number of times; the new symbol data
8870 thus read keeps adding to the old. To discard all old symbol data
8871 instead, use the @code{symbol-file} command without any arguments.
8873 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8875 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8876 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8877 table information for @var{filename}.
8879 @kindex add-shared-symbol-file
8880 @item add-shared-symbol-file
8881 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8882 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8883 shared libraries, however if @value{GDBN} does not find yours, you can run
8884 @code{add-shared-symbol-file}. It takes no arguments.
8888 The @code{section} command changes the base address of section SECTION of
8889 the exec file to ADDR. This can be used if the exec file does not contain
8890 section addresses, (such as in the a.out format), or when the addresses
8891 specified in the file itself are wrong. Each section must be changed
8892 separately. The @code{info files} command, described below, lists all
8893 the sections and their addresses.
8899 @code{info files} and @code{info target} are synonymous; both print the
8900 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8901 including the names of the executable and core dump files currently in
8902 use by @value{GDBN}, and the files from which symbols were loaded. The
8903 command @code{help target} lists all possible targets rather than
8908 All file-specifying commands allow both absolute and relative file names
8909 as arguments. @value{GDBN} always converts the file name to an absolute file
8910 name and remembers it that way.
8912 @cindex shared libraries
8913 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8916 @value{GDBN} automatically loads symbol definitions from shared libraries
8917 when you use the @code{run} command, or when you examine a core file.
8918 (Before you issue the @code{run} command, @value{GDBN} does not understand
8919 references to a function in a shared library, however---unless you are
8920 debugging a core file).
8922 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8923 automatically loads the symbols at the time of the @code{shl_load} call.
8925 @c FIXME: some @value{GDBN} release may permit some refs to undef
8926 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8927 @c FIXME...lib; check this from time to time when updating manual
8930 @kindex info sharedlibrary
8933 @itemx info sharedlibrary
8934 Print the names of the shared libraries which are currently loaded.
8936 @kindex sharedlibrary
8938 @item sharedlibrary @var{regex}
8939 @itemx share @var{regex}
8940 Load shared object library symbols for files matching a
8941 Unix regular expression.
8942 As with files loaded automatically, it only loads shared libraries
8943 required by your program for a core file or after typing @code{run}. If
8944 @var{regex} is omitted all shared libraries required by your program are
8948 On HP-UX systems, @value{GDBN} detects the loading of a shared library
8949 and automatically reads in symbols from the newly loaded library, up to
8950 a threshold that is initially set but that you can modify if you wish.
8952 Beyond that threshold, symbols from shared libraries must be explicitly
8953 loaded. To load these symbols, use the command @code{sharedlibrary
8954 @var{filename}}. The base address of the shared library is determined
8955 automatically by @value{GDBN} and need not be specified.
8957 To display or set the threshold, use the commands:
8960 @kindex set auto-solib-add
8961 @item set auto-solib-add @var{threshold}
8962 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8963 nonzero, symbols from all shared object libraries will be loaded
8964 automatically when the inferior begins execution or when the dynamic
8965 linker informs @value{GDBN} that a new library has been loaded, until
8966 the symbol table of the program and libraries exceeds this threshold.
8967 Otherwise, symbols must be loaded manually, using the
8968 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8970 @kindex show auto-solib-add
8971 @item show auto-solib-add
8972 Display the current autoloading size threshold, in megabytes.
8976 @section Errors reading symbol files
8978 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8979 such as symbol types it does not recognize, or known bugs in compiler
8980 output. By default, @value{GDBN} does not notify you of such problems, since
8981 they are relatively common and primarily of interest to people
8982 debugging compilers. If you are interested in seeing information
8983 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8984 only one message about each such type of problem, no matter how many
8985 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8986 to see how many times the problems occur, with the @code{set
8987 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8990 The messages currently printed, and their meanings, include:
8993 @item inner block not inside outer block in @var{symbol}
8995 The symbol information shows where symbol scopes begin and end
8996 (such as at the start of a function or a block of statements). This
8997 error indicates that an inner scope block is not fully contained
8998 in its outer scope blocks.
9000 @value{GDBN} circumvents the problem by treating the inner block as if it had
9001 the same scope as the outer block. In the error message, @var{symbol}
9002 may be shown as ``@code{(don't know)}'' if the outer block is not a
9005 @item block at @var{address} out of order
9007 The symbol information for symbol scope blocks should occur in
9008 order of increasing addresses. This error indicates that it does not
9011 @value{GDBN} does not circumvent this problem, and has trouble
9012 locating symbols in the source file whose symbols it is reading. (You
9013 can often determine what source file is affected by specifying
9014 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9017 @item bad block start address patched
9019 The symbol information for a symbol scope block has a start address
9020 smaller than the address of the preceding source line. This is known
9021 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9023 @value{GDBN} circumvents the problem by treating the symbol scope block as
9024 starting on the previous source line.
9026 @item bad string table offset in symbol @var{n}
9029 Symbol number @var{n} contains a pointer into the string table which is
9030 larger than the size of the string table.
9032 @value{GDBN} circumvents the problem by considering the symbol to have the
9033 name @code{foo}, which may cause other problems if many symbols end up
9036 @item unknown symbol type @code{0x@var{nn}}
9038 The symbol information contains new data types that @value{GDBN} does
9039 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9040 uncomprehended information, in hexadecimal.
9042 @value{GDBN} circumvents the error by ignoring this symbol information.
9043 This usually allows you to debug your program, though certain symbols
9044 are not accessible. If you encounter such a problem and feel like
9045 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9046 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9047 and examine @code{*bufp} to see the symbol.
9049 @item stub type has NULL name
9051 @value{GDBN} could not find the full definition for a struct or class.
9053 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9054 The symbol information for a C@t{++} member function is missing some
9055 information that recent versions of the compiler should have output for
9058 @item info mismatch between compiler and debugger
9060 @value{GDBN} could not parse a type specification output by the compiler.
9065 @chapter Specifying a Debugging Target
9067 @cindex debugging target
9070 A @dfn{target} is the execution environment occupied by your program.
9072 Often, @value{GDBN} runs in the same host environment as your program;
9073 in that case, the debugging target is specified as a side effect when
9074 you use the @code{file} or @code{core} commands. When you need more
9075 flexibility---for example, running @value{GDBN} on a physically separate
9076 host, or controlling a standalone system over a serial port or a
9077 realtime system over a TCP/IP connection---you can use the @code{target}
9078 command to specify one of the target types configured for @value{GDBN}
9079 (@pxref{Target Commands, ,Commands for managing targets}).
9082 * Active Targets:: Active targets
9083 * Target Commands:: Commands for managing targets
9084 * Byte Order:: Choosing target byte order
9085 * Remote:: Remote debugging
9086 * KOD:: Kernel Object Display
9090 @node Active Targets
9091 @section Active targets
9093 @cindex stacking targets
9094 @cindex active targets
9095 @cindex multiple targets
9097 There are three classes of targets: processes, core files, and
9098 executable files. @value{GDBN} can work concurrently on up to three
9099 active targets, one in each class. This allows you to (for example)
9100 start a process and inspect its activity without abandoning your work on
9103 For example, if you execute @samp{gdb a.out}, then the executable file
9104 @code{a.out} is the only active target. If you designate a core file as
9105 well---presumably from a prior run that crashed and coredumped---then
9106 @value{GDBN} has two active targets and uses them in tandem, looking
9107 first in the corefile target, then in the executable file, to satisfy
9108 requests for memory addresses. (Typically, these two classes of target
9109 are complementary, since core files contain only a program's
9110 read-write memory---variables and so on---plus machine status, while
9111 executable files contain only the program text and initialized data.)
9113 When you type @code{run}, your executable file becomes an active process
9114 target as well. When a process target is active, all @value{GDBN}
9115 commands requesting memory addresses refer to that target; addresses in
9116 an active core file or executable file target are obscured while the
9117 process target is active.
9119 Use the @code{core-file} and @code{exec-file} commands to select a new
9120 core file or executable target (@pxref{Files, ,Commands to specify
9121 files}). To specify as a target a process that is already running, use
9122 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9125 @node Target Commands
9126 @section Commands for managing targets
9129 @item target @var{type} @var{parameters}
9130 Connects the @value{GDBN} host environment to a target machine or
9131 process. A target is typically a protocol for talking to debugging
9132 facilities. You use the argument @var{type} to specify the type or
9133 protocol of the target machine.
9135 Further @var{parameters} are interpreted by the target protocol, but
9136 typically include things like device names or host names to connect
9137 with, process numbers, and baud rates.
9139 The @code{target} command does not repeat if you press @key{RET} again
9140 after executing the command.
9144 Displays the names of all targets available. To display targets
9145 currently selected, use either @code{info target} or @code{info files}
9146 (@pxref{Files, ,Commands to specify files}).
9148 @item help target @var{name}
9149 Describe a particular target, including any parameters necessary to
9152 @kindex set gnutarget
9153 @item set gnutarget @var{args}
9154 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9155 knows whether it is reading an @dfn{executable},
9156 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9157 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9158 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9161 @emph{Warning:} To specify a file format with @code{set gnutarget},
9162 you must know the actual BFD name.
9166 @xref{Files, , Commands to specify files}.
9168 @kindex show gnutarget
9169 @item show gnutarget
9170 Use the @code{show gnutarget} command to display what file format
9171 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9172 @value{GDBN} will determine the file format for each file automatically,
9173 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9176 Here are some common targets (available, or not, depending on the GDB
9181 @item target exec @var{program}
9182 An executable file. @samp{target exec @var{program}} is the same as
9183 @samp{exec-file @var{program}}.
9186 @item target core @var{filename}
9187 A core dump file. @samp{target core @var{filename}} is the same as
9188 @samp{core-file @var{filename}}.
9190 @kindex target remote
9191 @item target remote @var{dev}
9192 Remote serial target in GDB-specific protocol. The argument @var{dev}
9193 specifies what serial device to use for the connection (e.g.
9194 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9195 supports the @code{load} command. This is only useful if you have
9196 some other way of getting the stub to the target system, and you can put
9197 it somewhere in memory where it won't get clobbered by the download.
9201 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9209 works; however, you cannot assume that a specific memory map, device
9210 drivers, or even basic I/O is available, although some simulators do
9211 provide these. For info about any processor-specific simulator details,
9212 see the appropriate section in @ref{Embedded Processors, ,Embedded
9217 Some configurations may include these targets as well:
9222 @item target nrom @var{dev}
9223 NetROM ROM emulator. This target only supports downloading.
9227 Different targets are available on different configurations of @value{GDBN};
9228 your configuration may have more or fewer targets.
9230 Many remote targets require you to download the executable's code
9231 once you've successfully established a connection.
9235 @kindex load @var{filename}
9236 @item load @var{filename}
9237 Depending on what remote debugging facilities are configured into
9238 @value{GDBN}, the @code{load} command may be available. Where it exists, it
9239 is meant to make @var{filename} (an executable) available for debugging
9240 on the remote system---by downloading, or dynamic linking, for example.
9241 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
9242 the @code{add-symbol-file} command.
9244 If your @value{GDBN} does not have a @code{load} command, attempting to
9245 execute it gets the error message ``@code{You can't do that when your
9246 target is @dots{}}''
9248 The file is loaded at whatever address is specified in the executable.
9249 For some object file formats, you can specify the load address when you
9250 link the program; for other formats, like a.out, the object file format
9251 specifies a fixed address.
9252 @c FIXME! This would be a good place for an xref to the GNU linker doc.
9254 @code{load} does not repeat if you press @key{RET} again after using it.
9258 @section Choosing target byte order
9260 @cindex choosing target byte order
9261 @cindex target byte order
9263 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
9264 offer the ability to run either big-endian or little-endian byte
9265 orders. Usually the executable or symbol will include a bit to
9266 designate the endian-ness, and you will not need to worry about
9267 which to use. However, you may still find it useful to adjust
9268 @value{GDBN}'s idea of processor endian-ness manually.
9271 @kindex set endian big
9272 @item set endian big
9273 Instruct @value{GDBN} to assume the target is big-endian.
9275 @kindex set endian little
9276 @item set endian little
9277 Instruct @value{GDBN} to assume the target is little-endian.
9279 @kindex set endian auto
9280 @item set endian auto
9281 Instruct @value{GDBN} to use the byte order associated with the
9285 Display @value{GDBN}'s current idea of the target byte order.
9289 Note that these commands merely adjust interpretation of symbolic
9290 data on the host, and that they have absolutely no effect on the
9294 @section Remote debugging
9295 @cindex remote debugging
9297 If you are trying to debug a program running on a machine that cannot run
9298 @value{GDBN} in the usual way, it is often useful to use remote debugging.
9299 For example, you might use remote debugging on an operating system kernel,
9300 or on a small system which does not have a general purpose operating system
9301 powerful enough to run a full-featured debugger.
9303 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
9304 to make this work with particular debugging targets. In addition,
9305 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
9306 but not specific to any particular target system) which you can use if you
9307 write the remote stubs---the code that runs on the remote system to
9308 communicate with @value{GDBN}.
9310 Other remote targets may be available in your
9311 configuration of @value{GDBN}; use @code{help target} to list them.
9314 * Remote Serial:: @value{GDBN} remote serial protocol
9318 @subsection The @value{GDBN} remote serial protocol
9320 @cindex remote serial debugging, overview
9321 To debug a program running on another machine (the debugging
9322 @dfn{target} machine), you must first arrange for all the usual
9323 prerequisites for the program to run by itself. For example, for a C
9328 A startup routine to set up the C runtime environment; these usually
9329 have a name like @file{crt0}. The startup routine may be supplied by
9330 your hardware supplier, or you may have to write your own.
9333 A C subroutine library to support your program's
9334 subroutine calls, notably managing input and output.
9337 A way of getting your program to the other machine---for example, a
9338 download program. These are often supplied by the hardware
9339 manufacturer, but you may have to write your own from hardware
9343 The next step is to arrange for your program to use a serial port to
9344 communicate with the machine where @value{GDBN} is running (the @dfn{host}
9345 machine). In general terms, the scheme looks like this:
9349 @value{GDBN} already understands how to use this protocol; when everything
9350 else is set up, you can simply use the @samp{target remote} command
9351 (@pxref{Targets,,Specifying a Debugging Target}).
9353 @item On the target,
9354 you must link with your program a few special-purpose subroutines that
9355 implement the @value{GDBN} remote serial protocol. The file containing these
9356 subroutines is called a @dfn{debugging stub}.
9358 On certain remote targets, you can use an auxiliary program
9359 @code{gdbserver} instead of linking a stub into your program.
9360 @xref{Server,,Using the @code{gdbserver} program}, for details.
9363 The debugging stub is specific to the architecture of the remote
9364 machine; for example, use @file{sparc-stub.c} to debug programs on
9367 @cindex remote serial stub list
9368 These working remote stubs are distributed with @value{GDBN}:
9373 @cindex @file{i386-stub.c}
9376 For Intel 386 and compatible architectures.
9379 @cindex @file{m68k-stub.c}
9380 @cindex Motorola 680x0
9382 For Motorola 680x0 architectures.
9385 @cindex @file{sh-stub.c}
9388 For Hitachi SH architectures.
9391 @cindex @file{sparc-stub.c}
9393 For @sc{sparc} architectures.
9396 @cindex @file{sparcl-stub.c}
9399 For Fujitsu @sc{sparclite} architectures.
9403 The @file{README} file in the @value{GDBN} distribution may list other
9404 recently added stubs.
9407 * Stub Contents:: What the stub can do for you
9408 * Bootstrapping:: What you must do for the stub
9409 * Debug Session:: Putting it all together
9410 * Protocol:: Definition of the communication protocol
9411 * Server:: Using the `gdbserver' program
9412 * NetWare:: Using the `gdbserve.nlm' program
9416 @subsubsection What the stub can do for you
9418 @cindex remote serial stub
9419 The debugging stub for your architecture supplies these three
9423 @item set_debug_traps
9424 @kindex set_debug_traps
9425 @cindex remote serial stub, initialization
9426 This routine arranges for @code{handle_exception} to run when your
9427 program stops. You must call this subroutine explicitly near the
9428 beginning of your program.
9430 @item handle_exception
9431 @kindex handle_exception
9432 @cindex remote serial stub, main routine
9433 This is the central workhorse, but your program never calls it
9434 explicitly---the setup code arranges for @code{handle_exception} to
9435 run when a trap is triggered.
9437 @code{handle_exception} takes control when your program stops during
9438 execution (for example, on a breakpoint), and mediates communications
9439 with @value{GDBN} on the host machine. This is where the communications
9440 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
9441 representative on the target machine. It begins by sending summary
9442 information on the state of your program, then continues to execute,
9443 retrieving and transmitting any information @value{GDBN} needs, until you
9444 execute a @value{GDBN} command that makes your program resume; at that point,
9445 @code{handle_exception} returns control to your own code on the target
9449 @cindex @code{breakpoint} subroutine, remote
9450 Use this auxiliary subroutine to make your program contain a
9451 breakpoint. Depending on the particular situation, this may be the only
9452 way for @value{GDBN} to get control. For instance, if your target
9453 machine has some sort of interrupt button, you won't need to call this;
9454 pressing the interrupt button transfers control to
9455 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
9456 simply receiving characters on the serial port may also trigger a trap;
9457 again, in that situation, you don't need to call @code{breakpoint} from
9458 your own program---simply running @samp{target remote} from the host
9459 @value{GDBN} session gets control.
9461 Call @code{breakpoint} if none of these is true, or if you simply want
9462 to make certain your program stops at a predetermined point for the
9463 start of your debugging session.
9467 @subsubsection What you must do for the stub
9469 @cindex remote stub, support routines
9470 The debugging stubs that come with @value{GDBN} are set up for a particular
9471 chip architecture, but they have no information about the rest of your
9472 debugging target machine.
9474 First of all you need to tell the stub how to communicate with the
9478 @item int getDebugChar()
9479 @kindex getDebugChar
9480 Write this subroutine to read a single character from the serial port.
9481 It may be identical to @code{getchar} for your target system; a
9482 different name is used to allow you to distinguish the two if you wish.
9484 @item void putDebugChar(int)
9485 @kindex putDebugChar
9486 Write this subroutine to write a single character to the serial port.
9487 It may be identical to @code{putchar} for your target system; a
9488 different name is used to allow you to distinguish the two if you wish.
9491 @cindex control C, and remote debugging
9492 @cindex interrupting remote targets
9493 If you want @value{GDBN} to be able to stop your program while it is
9494 running, you need to use an interrupt-driven serial driver, and arrange
9495 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
9496 character). That is the character which @value{GDBN} uses to tell the
9497 remote system to stop.
9499 Getting the debugging target to return the proper status to @value{GDBN}
9500 probably requires changes to the standard stub; one quick and dirty way
9501 is to just execute a breakpoint instruction (the ``dirty'' part is that
9502 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
9504 Other routines you need to supply are:
9507 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
9508 @kindex exceptionHandler
9509 Write this function to install @var{exception_address} in the exception
9510 handling tables. You need to do this because the stub does not have any
9511 way of knowing what the exception handling tables on your target system
9512 are like (for example, the processor's table might be in @sc{rom},
9513 containing entries which point to a table in @sc{ram}).
9514 @var{exception_number} is the exception number which should be changed;
9515 its meaning is architecture-dependent (for example, different numbers
9516 might represent divide by zero, misaligned access, etc). When this
9517 exception occurs, control should be transferred directly to
9518 @var{exception_address}, and the processor state (stack, registers,
9519 and so on) should be just as it is when a processor exception occurs. So if
9520 you want to use a jump instruction to reach @var{exception_address}, it
9521 should be a simple jump, not a jump to subroutine.
9523 For the 386, @var{exception_address} should be installed as an interrupt
9524 gate so that interrupts are masked while the handler runs. The gate
9525 should be at privilege level 0 (the most privileged level). The
9526 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
9527 help from @code{exceptionHandler}.
9529 @item void flush_i_cache()
9530 @kindex flush_i_cache
9531 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
9532 instruction cache, if any, on your target machine. If there is no
9533 instruction cache, this subroutine may be a no-op.
9535 On target machines that have instruction caches, @value{GDBN} requires this
9536 function to make certain that the state of your program is stable.
9540 You must also make sure this library routine is available:
9543 @item void *memset(void *, int, int)
9545 This is the standard library function @code{memset} that sets an area of
9546 memory to a known value. If you have one of the free versions of
9547 @code{libc.a}, @code{memset} can be found there; otherwise, you must
9548 either obtain it from your hardware manufacturer, or write your own.
9551 If you do not use the GNU C compiler, you may need other standard
9552 library subroutines as well; this varies from one stub to another,
9553 but in general the stubs are likely to use any of the common library
9554 subroutines which @code{@value{GCC}} generates as inline code.
9558 @subsubsection Putting it all together
9560 @cindex remote serial debugging summary
9561 In summary, when your program is ready to debug, you must follow these
9566 Make sure you have defined the supporting low-level routines
9567 (@pxref{Bootstrapping,,What you must do for the stub}):
9569 @code{getDebugChar}, @code{putDebugChar},
9570 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
9574 Insert these lines near the top of your program:
9582 For the 680x0 stub only, you need to provide a variable called
9583 @code{exceptionHook}. Normally you just use:
9586 void (*exceptionHook)() = 0;
9590 but if before calling @code{set_debug_traps}, you set it to point to a
9591 function in your program, that function is called when
9592 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
9593 error). The function indicated by @code{exceptionHook} is called with
9594 one parameter: an @code{int} which is the exception number.
9597 Compile and link together: your program, the @value{GDBN} debugging stub for
9598 your target architecture, and the supporting subroutines.
9601 Make sure you have a serial connection between your target machine and
9602 the @value{GDBN} host, and identify the serial port on the host.
9605 @c The "remote" target now provides a `load' command, so we should
9606 @c document that. FIXME.
9607 Download your program to your target machine (or get it there by
9608 whatever means the manufacturer provides), and start it.
9611 To start remote debugging, run @value{GDBN} on the host machine, and specify
9612 as an executable file the program that is running in the remote machine.
9613 This tells @value{GDBN} how to find your program's symbols and the contents
9617 @cindex serial line, @code{target remote}
9618 Establish communication using the @code{target remote} command.
9619 Its argument specifies how to communicate with the target
9620 machine---either via a devicename attached to a direct serial line, or a
9621 TCP port (usually to a terminal server which in turn has a serial line
9622 to the target). For example, to use a serial line connected to the
9623 device named @file{/dev/ttyb}:
9626 target remote /dev/ttyb
9629 @cindex TCP port, @code{target remote}
9630 To use a TCP connection, use an argument of the form
9631 @code{@var{host}:port}. For example, to connect to port 2828 on a
9632 terminal server named @code{manyfarms}:
9635 target remote manyfarms:2828
9639 Now you can use all the usual commands to examine and change data and to
9640 step and continue the remote program.
9642 To resume the remote program and stop debugging it, use the @code{detach}
9645 @cindex interrupting remote programs
9646 @cindex remote programs, interrupting
9647 Whenever @value{GDBN} is waiting for the remote program, if you type the
9648 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
9649 program. This may or may not succeed, depending in part on the hardware
9650 and the serial drivers the remote system uses. If you type the
9651 interrupt character once again, @value{GDBN} displays this prompt:
9654 Interrupted while waiting for the program.
9655 Give up (and stop debugging it)? (y or n)
9658 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
9659 (If you decide you want to try again later, you can use @samp{target
9660 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
9661 goes back to waiting.
9664 @subsubsection Communication protocol
9666 @cindex debugging stub, example
9667 @cindex remote stub, example
9668 @cindex stub example, remote debugging
9669 The stub files provided with @value{GDBN} implement the target side of the
9670 communication protocol, and the @value{GDBN} side is implemented in the
9671 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
9672 these subroutines to communicate, and ignore the details. (If you're
9673 implementing your own stub file, you can still ignore the details: start
9674 with one of the existing stub files. @file{sparc-stub.c} is the best
9675 organized, and therefore the easiest to read.)
9677 However, there may be occasions when you need to know something about
9678 the protocol---for example, if there is only one serial port to your
9679 target machine, you might want your program to do something special if
9680 it recognizes a packet meant for @value{GDBN}.
9682 In the examples below, @samp{<-} and @samp{->} are used to indicate
9683 transmitted and received data respectfully.
9685 @cindex protocol, @value{GDBN} remote serial
9686 @cindex serial protocol, @value{GDBN} remote
9687 @cindex remote serial protocol
9688 All @value{GDBN} commands and responses (other than acknowledgments) are
9689 sent as a @var{packet}. A @var{packet} is introduced with the character
9690 @samp{$}, the actual @var{packet-data}, and the terminating character
9691 @samp{#} followed by a two-digit @var{checksum}:
9694 @code{$}@var{packet-data}@code{#}@var{checksum}
9698 @cindex checksum, for @value{GDBN} remote
9700 The two-digit @var{checksum} is computed as the modulo 256 sum of all
9701 characters between the leading @samp{$} and the trailing @samp{#} (an
9702 eight bit unsigned checksum).
9704 Implementors should note that prior to @value{GDBN} 5.0 the protocol
9705 specification also included an optional two-digit @var{sequence-id}:
9708 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
9711 @cindex sequence-id, for @value{GDBN} remote
9713 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
9714 has never output @var{sequence-id}s. Stubs that handle packets added
9715 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
9717 @cindex acknowledgment, for @value{GDBN} remote
9718 When either the host or the target machine receives a packet, the first
9719 response expected is an acknowledgment: either @samp{+} (to indicate
9720 the package was received correctly) or @samp{-} (to request
9724 <- @code{$}@var{packet-data}@code{#}@var{checksum}
9729 The host (@value{GDBN}) sends @var{command}s, and the target (the
9730 debugging stub incorporated in your program) sends a @var{response}. In
9731 the case of step and continue @var{command}s, the response is only sent
9732 when the operation has completed (the target has again stopped).
9734 @var{packet-data} consists of a sequence of characters with the
9735 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
9738 Fields within the packet should be separated using @samp{,} @samp{;} or
9739 @samp{:}. Except where otherwise noted all numbers are represented in
9740 HEX with leading zeros suppressed.
9742 Implementors should note that prior to @value{GDBN} 5.0, the character
9743 @samp{:} could not appear as the third character in a packet (as it
9744 would potentially conflict with the @var{sequence-id}).
9746 Response @var{data} can be run-length encoded to save space. A @samp{*}
9747 means that the next character is an @sc{ascii} encoding giving a repeat count
9748 which stands for that many repetitions of the character preceding the
9749 @samp{*}. The encoding is @code{n+29}, yielding a printable character
9750 where @code{n >=3} (which is where rle starts to win). The printable
9751 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
9752 value greater than 126 should not be used.
9754 Some remote systems have used a different run-length encoding mechanism
9755 loosely refered to as the cisco encoding. Following the @samp{*}
9756 character are two hex digits that indicate the size of the packet.
9763 means the same as "0000".
9765 The error response returned for some packets includes a two character
9766 error number. That number is not well defined.
9768 For any @var{command} not supported by the stub, an empty response
9769 (@samp{$#00}) should be returned. That way it is possible to extend the
9770 protocol. A newer @value{GDBN} can tell if a packet is supported based
9773 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
9774 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
9777 Below is a complete list of all currently defined @var{command}s and
9778 their corresponding response @var{data}:
9780 @multitable @columnfractions .30 .30 .40
9788 Enable extended mode. In extended mode, the remote server is made
9789 persistent. The @samp{R} packet is used to restart the program being
9792 @tab reply @samp{OK}
9794 The remote target both supports and has enabled extended mode.
9799 Indicate the reason the target halted. The reply is the same as for step
9808 @tab Reserved for future use
9810 @item set program arguments @strong{(reserved)}
9811 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
9816 Initialized @samp{argv[]} array passed into program. @var{arglen}
9817 specifies the number of bytes in the hex encoded byte stream @var{arg}.
9818 See @file{gdbserver} for more details.
9820 @tab reply @code{OK}
9822 @tab reply @code{E}@var{NN}
9824 @item set baud @strong{(deprecated)}
9825 @tab @code{b}@var{baud}
9827 Change the serial line speed to @var{baud}. JTC: @emph{When does the
9828 transport layer state change? When it's received, or after the ACK is
9829 transmitted. In either case, there are problems if the command or the
9830 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
9831 to add something like this, and get it working for the first time, they
9832 ought to modify ser-unix.c to send some kind of out-of-band message to a
9833 specially-setup stub and have the switch happen "in between" packets, so
9834 that from remote protocol's point of view, nothing actually
9837 @item set breakpoint @strong{(deprecated)}
9838 @tab @code{B}@var{addr},@var{mode}
9840 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
9841 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
9845 @tab @code{c}@var{addr}
9847 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9853 @item continue with signal
9854 @tab @code{C}@var{sig}@code{;}@var{addr}
9856 Continue with signal @var{sig} (hex signal number). If
9857 @code{;}@var{addr} is omitted, resume at same address.
9862 @item toggle debug @strong{(deprecated)}
9870 Detach @value{GDBN} from the remote system. Sent to the remote target before
9871 @value{GDBN} disconnects.
9873 @tab reply @emph{no response}
9875 @value{GDBN} does not check for any response after sending this packet.
9879 @tab Reserved for future use
9883 @tab Reserved for future use
9887 @tab Reserved for future use
9891 @tab Reserved for future use
9893 @item read registers
9895 @tab Read general registers.
9897 @tab reply @var{XX...}
9899 Each byte of register data is described by two hex digits. The bytes
9900 with the register are transmitted in target byte order. The size of
9901 each register and their position within the @samp{g} @var{packet} are
9902 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
9903 @var{REGISTER_NAME} macros. The specification of several standard
9904 @code{g} packets is specified below.
9906 @tab @code{E}@var{NN}
9910 @tab @code{G}@var{XX...}
9912 See @samp{g} for a description of the @var{XX...} data.
9914 @tab reply @code{OK}
9917 @tab reply @code{E}@var{NN}
9922 @tab Reserved for future use
9925 @tab @code{H}@var{c}@var{t...}
9927 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
9928 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
9929 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
9930 thread used in other operations. If zero, pick a thread, any thread.
9932 @tab reply @code{OK}
9935 @tab reply @code{E}@var{NN}
9939 @c 'H': How restrictive (or permissive) is the thread model. If a
9940 @c thread is selected and stopped, are other threads allowed
9941 @c to continue to execute? As I mentioned above, I think the
9942 @c semantics of each command when a thread is selected must be
9943 @c described. For example:
9945 @c 'g': If the stub supports threads and a specific thread is
9946 @c selected, returns the register block from that thread;
9947 @c otherwise returns current registers.
9949 @c 'G' If the stub supports threads and a specific thread is
9950 @c selected, sets the registers of the register block of
9951 @c that thread; otherwise sets current registers.
9953 @item cycle step @strong{(draft)}
9954 @tab @code{i}@var{addr}@code{,}@var{nnn}
9956 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
9957 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
9958 step starting at that address.
9960 @item signal then cycle step @strong{(reserved)}
9963 See @samp{i} and @samp{S} for likely syntax and semantics.
9967 @tab Reserved for future use
9971 @tab Reserved for future use
9976 FIXME: @emph{There is no description of how operate when a specific
9977 thread context has been selected (ie. does 'k' kill only that thread?)}.
9981 @tab Reserved for future use
9985 @tab Reserved for future use
9988 @tab @code{m}@var{addr}@code{,}@var{length}
9990 Read @var{length} bytes of memory starting at address @var{addr}.
9991 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
9992 using word alligned accesses. FIXME: @emph{A word aligned memory
9993 transfer mechanism is needed.}
9995 @tab reply @var{XX...}
9997 @var{XX...} is mem contents. Can be fewer bytes than requested if able
9998 to read only part of the data. Neither @value{GDBN} nor the stub assume that
9999 sized memory transfers are assumed using word alligned accesses. FIXME:
10000 @emph{A word aligned memory transfer mechanism is needed.}
10002 @tab reply @code{E}@var{NN}
10003 @tab @var{NN} is errno
10006 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
10008 Write @var{length} bytes of memory starting at address @var{addr}.
10009 @var{XX...} is the data.
10011 @tab reply @code{OK}
10014 @tab reply @code{E}@var{NN}
10016 for an error (this includes the case where only part of the data was
10021 @tab Reserved for future use
10025 @tab Reserved for future use
10029 @tab Reserved for future use
10033 @tab Reserved for future use
10035 @item read reg @strong{(reserved)}
10036 @tab @code{p}@var{n...}
10038 See write register.
10040 @tab return @var{r....}
10041 @tab The hex encoded value of the register in target byte order.
10044 @tab @code{P}@var{n...}@code{=}@var{r...}
10046 Write register @var{n...} with value @var{r...}, which contains two hex
10047 digits for each byte in the register (target byte order).
10049 @tab reply @code{OK}
10052 @tab reply @code{E}@var{NN}
10055 @item general query
10056 @tab @code{q}@var{query}
10058 Request info about @var{query}. In general @value{GDBN} queries
10059 have a leading upper case letter. Custom vendor queries should use a
10060 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
10061 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
10062 must ensure that they match the full @var{query} name.
10064 @tab reply @code{XX...}
10065 @tab Hex encoded data from query. The reply can not be empty.
10067 @tab reply @code{E}@var{NN}
10071 @tab Indicating an unrecognized @var{query}.
10074 @tab @code{Q}@var{var}@code{=}@var{val}
10076 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
10077 naming conventions.
10079 @item reset @strong{(deprecated)}
10082 Reset the entire system.
10084 @item remote restart
10085 @tab @code{R}@var{XX}
10087 Restart the program being debugged. @var{XX}, while needed, is ignored.
10088 This packet is only available in extended mode.
10093 The @samp{R} packet has no reply.
10096 @tab @code{s}@var{addr}
10098 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10104 @item step with signal
10105 @tab @code{S}@var{sig}@code{;}@var{addr}
10107 Like @samp{C} but step not continue.
10113 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
10115 Search backwards starting at address @var{addr} for a match with pattern
10116 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
10117 bytes. @var{addr} must be at least 3 digits.
10120 @tab @code{T}@var{XX}
10121 @tab Find out if the thread XX is alive.
10123 @tab reply @code{OK}
10124 @tab thread is still alive
10126 @tab reply @code{E}@var{NN}
10127 @tab thread is dead
10131 @tab Reserved for future use
10135 @tab Reserved for future use
10139 @tab Reserved for future use
10143 @tab Reserved for future use
10147 @tab Reserved for future use
10151 @tab Reserved for future use
10155 @tab Reserved for future use
10157 @item write mem (binary)
10158 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
10160 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
10161 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
10162 escaped using @code{0x7d}.
10164 @tab reply @code{OK}
10167 @tab reply @code{E}@var{NN}
10172 @tab Reserved for future use
10176 @tab Reserved for future use
10178 @item remove break or watchpoint @strong{(draft)}
10179 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10183 @item insert break or watchpoint @strong{(draft)}
10184 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10186 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
10187 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
10188 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
10189 bytes. For a software breakpoint, @var{length} specifies the size of
10190 the instruction to be patched. For hardware breakpoints and watchpoints
10191 @var{length} specifies the memory region to be monitored. To avoid
10192 potential problems with duplicate packets, the operations should be
10193 implemented in an idempotent way.
10195 @tab reply @code{E}@var{NN}
10198 @tab reply @code{OK}
10202 @tab If not supported.
10206 @tab Reserved for future use
10210 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
10211 receive any of the below as a reply. In the case of the @samp{C},
10212 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
10213 when the target halts. In the below the exact meaning of @samp{signal
10214 number} is poorly defined. In general one of the UNIX signal numbering
10215 conventions is used.
10217 @multitable @columnfractions .4 .6
10219 @item @code{S}@var{AA}
10220 @tab @var{AA} is the signal number
10222 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
10224 @var{AA} = two hex digit signal number; @var{n...} = register number
10225 (hex), @var{r...} = target byte ordered register contents, size defined
10226 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
10227 thread process ID, this is a hex integer; @var{n...} = other string not
10228 starting with valid hex digit. @value{GDBN} should ignore this
10229 @var{n...}, @var{r...} pair and go on to the next. This way we can
10230 extend the protocol.
10232 @item @code{W}@var{AA}
10234 The process exited, and @var{AA} is the exit status. This is only
10235 applicable for certains sorts of targets.
10237 @item @code{X}@var{AA}
10239 The process terminated with signal @var{AA}.
10241 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
10243 @var{AA} = signal number; @var{t...} = address of symbol "_start";
10244 @var{d...} = base of data section; @var{b...} = base of bss section.
10245 @emph{Note: only used by Cisco Systems targets. The difference between
10246 this reply and the "qOffsets" query is that the 'N' packet may arrive
10247 spontaneously whereas the 'qOffsets' is a query initiated by the host
10250 @item @code{O}@var{XX...}
10252 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
10253 while the program is running and the debugger should continue to wait
10258 The following set and query packets have already been defined.
10260 @multitable @columnfractions .2 .2 .6
10262 @item current thread
10263 @tab @code{q}@code{C}
10264 @tab Return the current thread id.
10266 @tab reply @code{QC}@var{pid}
10268 Where @var{pid} is a HEX encoded 16 bit process id.
10271 @tab Any other reply implies the old pid.
10273 @item all thread ids
10274 @tab @code{q}@code{fThreadInfo}
10276 @tab @code{q}@code{sThreadInfo}
10278 Obtain a list of active thread ids from the target (OS). Since there
10279 may be too many active threads to fit into one reply packet, this query
10280 works iteratively: it may require more than one query/reply sequence to
10281 obtain the entire list of threads. The first query of the sequence will
10282 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
10283 sequence will be the @code{qs}@code{ThreadInfo} query.
10286 @tab NOTE: replaces the @code{qL} query (see below).
10288 @tab reply @code{m}@var{<id>}
10289 @tab A single thread id
10291 @tab reply @code{m}@var{<id>},@var{<id>...}
10292 @tab a comma-separated list of thread ids
10294 @tab reply @code{l}
10295 @tab (lower case 'el') denotes end of list.
10299 In response to each query, the target will reply with a list of one
10300 or more thread ids, in big-endian hex, separated by commas. GDB will
10301 respond to each reply with a request for more thread ids (using the
10302 @code{qs} form of the query), until the target responds with @code{l}
10303 (lower-case el, for @code{'last'}).
10305 @item extra thread info
10306 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
10311 Where @var{<id>} is a thread-id in big-endian hex.
10312 Obtain a printable string description of a thread's attributes from
10313 the target OS. This string may contain anything that the target OS
10314 thinks is interesting for @value{GDBN} to tell the user about the thread.
10315 The string is displayed in @value{GDBN}'s @samp{info threads} display.
10316 Some examples of possible thread extra info strings are "Runnable", or
10317 "Blocked on Mutex".
10319 @tab reply @var{XX...}
10321 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
10322 printable string containing the extra information about the thread's
10325 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
10326 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
10331 Obtain thread information from RTOS. Where: @var{startflag} (one hex
10332 digit) is one to indicate the first query and zero to indicate a
10333 subsequent query; @var{threadcount} (two hex digits) is the maximum
10334 number of threads the response packet can contain; and @var{nextthread}
10335 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
10336 returned in the response as @var{argthread}.
10339 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
10342 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
10347 Where: @var{count} (two hex digits) is the number of threads being
10348 returned; @var{done} (one hex digit) is zero to indicate more threads
10349 and one indicates no further threads; @var{argthreadid} (eight hex
10350 digits) is @var{nextthread} from the request packet; @var{thread...} is
10351 a sequence of thread IDs from the target. @var{threadid} (eight hex
10352 digits). See @code{remote.c:parse_threadlist_response()}.
10354 @item compute CRC of memory block
10355 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
10358 @tab reply @code{E}@var{NN}
10359 @tab An error (such as memory fault)
10361 @tab reply @code{C}@var{CRC32}
10362 @tab A 32 bit cyclic redundancy check of the specified memory region.
10364 @item query sect offs
10365 @tab @code{q}@code{Offsets}
10367 Get section offsets that the target used when re-locating the downloaded
10368 image. @emph{Note: while a @code{Bss} offset is included in the
10369 response, @value{GDBN} ignores this and instead applies the @code{Data}
10370 offset to the @code{Bss} section.}
10372 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
10374 @item thread info request
10375 @tab @code{q}@code{P}@var{mode}@var{threadid}
10380 Returns information on @var{threadid}. Where: @var{mode} is a hex
10381 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
10385 See @code{remote.c:remote_unpack_thread_info_response()}.
10387 @item remote command
10388 @tab @code{q}@code{Rcmd,}@var{COMMAND}
10393 @var{COMMAND} (hex encoded) is passed to the local interpreter for
10394 execution. Invalid commands should be reported using the output string.
10395 Before the final result packet, the target may also respond with a
10396 number of intermediate @code{O}@var{OUTPUT} console output
10397 packets. @emph{Implementors should note that providing access to a
10398 stubs's interpreter may have security implications}.
10400 @tab reply @code{OK}
10402 A command response with no output.
10404 @tab reply @var{OUTPUT}
10406 A command response with the hex encoded output string @var{OUTPUT}.
10408 @tab reply @code{E}@var{NN}
10410 Indicate a badly formed request.
10415 When @samp{q}@samp{Rcmd} is not recognized.
10417 @item symbol lookup
10418 @tab @code{qSymbol::}
10420 Notify the target that @value{GDBN} is prepared to serve symbol lookup
10421 requests. Accept requests from the target for the values of symbols.
10426 @tab reply @code{OK}
10428 The target does not need to look up any (more) symbols.
10430 @tab reply @code{qSymbol:}@var{sym_name}
10432 The target requests the value of symbol @var{sym_name} (hex encoded).
10433 @value{GDBN} may provide the value by using the
10434 @code{qSymbol:}@var{sym_value}:@var{sym_name}
10435 message, described below.
10438 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
10440 Set the value of SYM_NAME to SYM_VALUE.
10444 @var{sym_name} (hex encoded) is the name of a symbol whose value
10445 the target has previously requested.
10449 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
10450 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
10451 field will be empty.
10453 @tab reply @code{OK}
10455 The target does not need to look up any (more) symbols.
10457 @tab reply @code{qSymbol:}@var{sym_name}
10459 The target requests the value of a new symbol @var{sym_name} (hex encoded).
10460 @value{GDBN} will continue to supply the values of symbols (if available),
10461 until the target ceases to request them.
10465 The following @samp{g}/@samp{G} packets have previously been defined.
10466 In the below, some thirty-two bit registers are transferred as sixty-four
10467 bits. Those registers should be zero/sign extended (which?) to fill the
10468 space allocated. Register bytes are transfered in target byte order.
10469 The two nibbles within a register byte are transfered most-significant -
10472 @multitable @columnfractions .5 .5
10476 All registers are transfered as thirty-two bit quantities in the order:
10477 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
10478 registers; fsr; fir; fp.
10482 All registers are transfered as sixty-four bit quantities (including
10483 thirty-two bit registers such as @code{sr}). The ordering is the same
10488 Example sequence of a target being re-started. Notice how the restart
10489 does not get any direct output:
10494 @emph{target restarts}
10497 -> @code{T001:1234123412341234}
10501 Example sequence of a target being stepped by a single instruction:
10509 -> @code{T001:1234123412341234}
10518 @subsubsection Using the @code{gdbserver} program
10521 @cindex remote connection without stubs
10522 @code{gdbserver} is a control program for Unix-like systems, which
10523 allows you to connect your program with a remote @value{GDBN} via
10524 @code{target remote}---but without linking in the usual debugging stub.
10526 @code{gdbserver} is not a complete replacement for the debugging stubs,
10527 because it requires essentially the same operating-system facilities
10528 that @value{GDBN} itself does. In fact, a system that can run
10529 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10530 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10531 because it is a much smaller program than @value{GDBN} itself. It is
10532 also easier to port than all of @value{GDBN}, so you may be able to get
10533 started more quickly on a new system by using @code{gdbserver}.
10534 Finally, if you develop code for real-time systems, you may find that
10535 the tradeoffs involved in real-time operation make it more convenient to
10536 do as much development work as possible on another system, for example
10537 by cross-compiling. You can use @code{gdbserver} to make a similar
10538 choice for debugging.
10540 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10541 or a TCP connection, using the standard @value{GDBN} remote serial
10545 @item On the target machine,
10546 you need to have a copy of the program you want to debug.
10547 @code{gdbserver} does not need your program's symbol table, so you can
10548 strip the program if necessary to save space. @value{GDBN} on the host
10549 system does all the symbol handling.
10551 To use the server, you must tell it how to communicate with @value{GDBN};
10552 the name of your program; and the arguments for your program. The
10556 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10559 @var{comm} is either a device name (to use a serial line) or a TCP
10560 hostname and portnumber. For example, to debug Emacs with the argument
10561 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10565 target> gdbserver /dev/com1 emacs foo.txt
10568 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10571 To use a TCP connection instead of a serial line:
10574 target> gdbserver host:2345 emacs foo.txt
10577 The only difference from the previous example is the first argument,
10578 specifying that you are communicating with the host @value{GDBN} via
10579 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10580 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10581 (Currently, the @samp{host} part is ignored.) You can choose any number
10582 you want for the port number as long as it does not conflict with any
10583 TCP ports already in use on the target system (for example, @code{23} is
10584 reserved for @code{telnet}).@footnote{If you choose a port number that
10585 conflicts with another service, @code{gdbserver} prints an error message
10586 and exits.} You must use the same port number with the host @value{GDBN}
10587 @code{target remote} command.
10589 @item On the @value{GDBN} host machine,
10590 you need an unstripped copy of your program, since @value{GDBN} needs
10591 symbols and debugging information. Start up @value{GDBN} as usual,
10592 using the name of the local copy of your program as the first argument.
10593 (You may also need the @w{@samp{--baud}} option if the serial line is
10594 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10595 remote} to establish communications with @code{gdbserver}. Its argument
10596 is either a device name (usually a serial device, like
10597 @file{/dev/ttyb}), or a TCP port descriptor in the form
10598 @code{@var{host}:@var{PORT}}. For example:
10601 (@value{GDBP}) target remote /dev/ttyb
10605 communicates with the server via serial line @file{/dev/ttyb}, and
10608 (@value{GDBP}) target remote the-target:2345
10612 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10613 For TCP connections, you must start up @code{gdbserver} prior to using
10614 the @code{target remote} command. Otherwise you may get an error whose
10615 text depends on the host system, but which usually looks something like
10616 @samp{Connection refused}.
10620 @subsubsection Using the @code{gdbserve.nlm} program
10622 @kindex gdbserve.nlm
10623 @code{gdbserve.nlm} is a control program for NetWare systems, which
10624 allows you to connect your program with a remote @value{GDBN} via
10625 @code{target remote}.
10627 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10628 using the standard @value{GDBN} remote serial protocol.
10631 @item On the target machine,
10632 you need to have a copy of the program you want to debug.
10633 @code{gdbserve.nlm} does not need your program's symbol table, so you
10634 can strip the program if necessary to save space. @value{GDBN} on the
10635 host system does all the symbol handling.
10637 To use the server, you must tell it how to communicate with
10638 @value{GDBN}; the name of your program; and the arguments for your
10639 program. The syntax is:
10642 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10643 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10646 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10647 the baud rate used by the connection. @var{port} and @var{node} default
10648 to 0, @var{baud} defaults to 9600@dmn{bps}.
10650 For example, to debug Emacs with the argument @samp{foo.txt}and
10651 communicate with @value{GDBN} over serial port number 2 or board 1
10652 using a 19200@dmn{bps} connection:
10655 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10658 @item On the @value{GDBN} host machine,
10659 you need an unstripped copy of your program, since @value{GDBN} needs
10660 symbols and debugging information. Start up @value{GDBN} as usual,
10661 using the name of the local copy of your program as the first argument.
10662 (You may also need the @w{@samp{--baud}} option if the serial line is
10663 running at anything other than 9600@dmn{bps}. After that, use @code{target
10664 remote} to establish communications with @code{gdbserve.nlm}. Its
10665 argument is a device name (usually a serial device, like
10666 @file{/dev/ttyb}). For example:
10669 (@value{GDBP}) target remote /dev/ttyb
10673 communications with the server via serial line @file{/dev/ttyb}.
10677 @section Kernel Object Display
10679 @cindex kernel object display
10680 @cindex kernel object
10683 Some targets support kernel object display. Using this facility,
10684 @value{GDBN} communicates specially with the underlying operating system
10685 and can display information about operating system-level objects such as
10686 mutexes and other synchronization objects. Exactly which objects can be
10687 displayed is determined on a per-OS basis.
10689 Use the @code{set os} command to set the operating system. This tells
10690 @value{GDBN} which kernel object display module to initialize:
10693 (@value{GDBP}) set os cisco
10696 If @code{set os} succeeds, @value{GDBN} will display some information
10697 about the operating system, and will create a new @code{info} command
10698 which can be used to query the target. The @code{info} command is named
10699 after the operating system:
10702 (@value{GDBP}) info cisco
10703 List of Cisco Kernel Objects
10705 any Any and all objects
10708 Further subcommands can be used to query about particular objects known
10711 There is currently no way to determine whether a given operating system
10712 is supported other than to try it.
10715 @node Configurations
10716 @chapter Configuration-Specific Information
10718 While nearly all @value{GDBN} commands are available for all native and
10719 cross versions of the debugger, there are some exceptions. This chapter
10720 describes things that are only available in certain configurations.
10722 There are three major categories of configurations: native
10723 configurations, where the host and target are the same, embedded
10724 operating system configurations, which are usually the same for several
10725 different processor architectures, and bare embedded processors, which
10726 are quite different from each other.
10731 * Embedded Processors::
10738 This section describes details specific to particular native
10743 * SVR4 Process Information:: SVR4 process information
10744 * DJGPP Native:: Features specific to the DJGPP port
10750 On HP-UX systems, if you refer to a function or variable name that
10751 begins with a dollar sign, @value{GDBN} searches for a user or system
10752 name first, before it searches for a convenience variable.
10754 @node SVR4 Process Information
10755 @subsection SVR4 process information
10758 @cindex process image
10760 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10761 used to examine the image of a running process using file-system
10762 subroutines. If @value{GDBN} is configured for an operating system with
10763 this facility, the command @code{info proc} is available to report on
10764 several kinds of information about the process running your program.
10765 @code{info proc} works only on SVR4 systems that include the
10766 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10767 and Unixware, but not HP-UX or Linux, for example.
10772 Summarize available information about the process.
10774 @kindex info proc mappings
10775 @item info proc mappings
10776 Report on the address ranges accessible in the program, with information
10777 on whether your program may read, write, or execute each range.
10779 @kindex info proc times
10780 @item info proc times
10781 Starting time, user CPU time, and system CPU time for your program and
10784 @kindex info proc id
10786 Report on the process IDs related to your program: its own process ID,
10787 the ID of its parent, the process group ID, and the session ID.
10789 @kindex info proc status
10790 @item info proc status
10791 General information on the state of the process. If the process is
10792 stopped, this report includes the reason for stopping, and any signal
10795 @item info proc all
10796 Show all the above information about the process.
10800 @subsection Features for Debugging @sc{djgpp} Programs
10801 @cindex @sc{djgpp} debugging
10802 @cindex native @sc{djgpp} debugging
10803 @cindex MS-DOS-specific commands
10805 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10806 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10807 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10808 top of real-mode DOS systems and their emulations.
10810 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10811 defines a few commands specific to the @sc{djgpp} port. This
10812 subsection describes those commands.
10817 This is a prefix of @sc{djgpp}-specific commands which print
10818 information about the target system and important OS structures.
10821 @cindex MS-DOS system info
10822 @cindex free memory information (MS-DOS)
10823 @item info dos sysinfo
10824 This command displays assorted information about the underlying
10825 platform: the CPU type and features, the OS version and flavor, the
10826 DPMI version, and the available conventional and DPMI memory.
10831 @cindex segment descriptor tables
10832 @cindex descriptor tables display
10834 @itemx info dos ldt
10835 @itemx info dos idt
10836 These 3 commands display entries from, respectively, Global, Local,
10837 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10838 tables are data structures which store a descriptor for each segment
10839 that is currently in use. The segment's selector is an index into a
10840 descriptor table; the table entry for that index holds the
10841 descriptor's base address and limit, and its attributes and access
10844 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10845 segment (used for both data and the stack), and a DOS segment (which
10846 allows access to DOS/BIOS data structures and absolute addresses in
10847 conventional memory). However, the DPMI host will usually define
10848 additional segments in order to support the DPMI environment.
10850 @cindex garbled pointers
10851 These commands allow to display entries from the descriptor tables.
10852 Without an argument, all entries from the specified table are
10853 displayed. An argument, which should be an integer expression, means
10854 display a single entry whose index is given by the argument. For
10855 example, here's a convenient way to display information about the
10856 debugged program's data segment:
10859 (@value{GDBP}) info dos ldt $ds
10860 0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
10864 This comes in handy when you want to see whether a pointer is outside
10865 the data segment's limit (i.e.@: @dfn{garbled}).
10867 @cindex page tables display (MS-DOS)
10869 @itemx info dos pte
10870 These two commands display entries from, respectively, the Page
10871 Directory and the Page Tables. Page Directories and Page Tables are
10872 data structures which control how virtual memory addresses are mapped
10873 into physical addresses. A Page Table includes an entry for every
10874 page of memory that is mapped into the program's address space; there
10875 may be several Page Tables, each one holding up to 4096 entries. A
10876 Page Directory has up to 4096 entries, one each for every Page Table
10877 that is currently in use.
10879 Without an argument, @kbd{info dos pde} displays the entire Page
10880 Directory, and @kbd{info dos pte} displays all the entries in all of
10881 the Page Tables. An argument, an integer expression, given to the
10882 @kbd{info dos pde} command means display only that entry from the Page
10883 Directory table. An argument given to the @kbd{info dos pte} command
10884 means display entries from a single Page Table, the one pointed to by
10885 the specified entry in the Page Directory.
10887 These commands are useful when your program uses @dfn{DMA} (Direct
10888 Memory Access), which needs physical addresses to program the DMA
10891 These commands are supported only with some DPMI servers.
10893 @cindex physical address from linear address
10894 @item info dos address-pte
10895 This command displays the Page Table entry for a specified linear
10896 address. The argument linear address should already have the
10897 appropriate segment's base address added to it, because this command
10898 accepts addresses which may belong to @emph{any} segment. For
10899 example, here's how to display the Page Table entry for the page where
10900 the variable @code{i} is stored:
10903 (@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i
10904 Page Table entry for address 0x11a00d30:
10905 Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
10909 This says that @code{i} is stored at offset @code{0xd30} from the page
10910 whose physical base address is @code{0x02698000}, and prints all the
10911 attributes of that page.
10913 Note that you must cast the addresses of variables to a @code{char *},
10914 since otherwise the value of @code{__djgpp_base_address}, the base
10915 address of all variables and functions in a @sc{djgpp} program, will
10916 be added using the rules of C pointer arithmetics: if @code{i} is
10917 declared an @code{int}, @value{GDBN} will add 4 times the value of
10918 @code{__djgpp_base_address} to the address of @code{i}.
10920 Here's another example, it displays the Page Table entry for the
10924 (@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)
10925 Page Table entry for address 0x29110:
10926 Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
10930 (The @code{+ 3} offset is because the transfer buffer's address is the
10931 3rd member of the @code{_go32_info_block} structure.) The output of
10932 this command clearly shows that addresses in conventional memory are
10933 mapped 1:1, i.e.@: the physical and linear addresses are identical.
10935 This command is supported only with some DPMI servers.
10939 @section Embedded Operating Systems
10941 This section describes configurations involving the debugging of
10942 embedded operating systems that are available for several different
10946 * VxWorks:: Using @value{GDBN} with VxWorks
10949 @value{GDBN} includes the ability to debug programs running on
10950 various real-time operating systems.
10953 @subsection Using @value{GDBN} with VxWorks
10959 @kindex target vxworks
10960 @item target vxworks @var{machinename}
10961 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
10962 is the target system's machine name or IP address.
10966 On VxWorks, @code{load} links @var{filename} dynamically on the
10967 current target system as well as adding its symbols in @value{GDBN}.
10969 @value{GDBN} enables developers to spawn and debug tasks running on networked
10970 VxWorks targets from a Unix host. Already-running tasks spawned from
10971 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
10972 both the Unix host and on the VxWorks target. The program
10973 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
10974 installed with the name @code{vxgdb}, to distinguish it from a
10975 @value{GDBN} for debugging programs on the host itself.)
10978 @item VxWorks-timeout @var{args}
10979 @kindex vxworks-timeout
10980 All VxWorks-based targets now support the option @code{vxworks-timeout}.
10981 This option is set by the user, and @var{args} represents the number of
10982 seconds @value{GDBN} waits for responses to rpc's. You might use this if
10983 your VxWorks target is a slow software simulator or is on the far side
10984 of a thin network line.
10987 The following information on connecting to VxWorks was current when
10988 this manual was produced; newer releases of VxWorks may use revised
10991 @kindex INCLUDE_RDB
10992 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
10993 to include the remote debugging interface routines in the VxWorks
10994 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
10995 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
10996 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
10997 source debugging task @code{tRdbTask} when VxWorks is booted. For more
10998 information on configuring and remaking VxWorks, see the manufacturer's
11000 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11002 Once you have included @file{rdb.a} in your VxWorks system image and set
11003 your Unix execution search path to find @value{GDBN}, you are ready to
11004 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11005 @code{vxgdb}, depending on your installation).
11007 @value{GDBN} comes up showing the prompt:
11014 * VxWorks Connection:: Connecting to VxWorks
11015 * VxWorks Download:: VxWorks download
11016 * VxWorks Attach:: Running tasks
11019 @node VxWorks Connection
11020 @subsubsection Connecting to VxWorks
11022 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11023 network. To connect to a target whose host name is ``@code{tt}'', type:
11026 (vxgdb) target vxworks tt
11030 @value{GDBN} displays messages like these:
11033 Attaching remote machine across net...
11038 @value{GDBN} then attempts to read the symbol tables of any object modules
11039 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11040 these files by searching the directories listed in the command search
11041 path (@pxref{Environment, ,Your program's environment}); if it fails
11042 to find an object file, it displays a message such as:
11045 prog.o: No such file or directory.
11048 When this happens, add the appropriate directory to the search path with
11049 the @value{GDBN} command @code{path}, and execute the @code{target}
11052 @node VxWorks Download
11053 @subsubsection VxWorks download
11055 @cindex download to VxWorks
11056 If you have connected to the VxWorks target and you want to debug an
11057 object that has not yet been loaded, you can use the @value{GDBN}
11058 @code{load} command to download a file from Unix to VxWorks
11059 incrementally. The object file given as an argument to the @code{load}
11060 command is actually opened twice: first by the VxWorks target in order
11061 to download the code, then by @value{GDBN} in order to read the symbol
11062 table. This can lead to problems if the current working directories on
11063 the two systems differ. If both systems have NFS mounted the same
11064 filesystems, you can avoid these problems by using absolute paths.
11065 Otherwise, it is simplest to set the working directory on both systems
11066 to the directory in which the object file resides, and then to reference
11067 the file by its name, without any path. For instance, a program
11068 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11069 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11070 program, type this on VxWorks:
11073 -> cd "@var{vxpath}/vw/demo/rdb"
11077 Then, in @value{GDBN}, type:
11080 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11081 (vxgdb) load prog.o
11084 @value{GDBN} displays a response similar to this:
11087 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11090 You can also use the @code{load} command to reload an object module
11091 after editing and recompiling the corresponding source file. Note that
11092 this makes @value{GDBN} delete all currently-defined breakpoints,
11093 auto-displays, and convenience variables, and to clear the value
11094 history. (This is necessary in order to preserve the integrity of
11095 debugger's data structures that reference the target system's symbol
11098 @node VxWorks Attach
11099 @subsubsection Running tasks
11101 @cindex running VxWorks tasks
11102 You can also attach to an existing task using the @code{attach} command as
11106 (vxgdb) attach @var{task}
11110 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11111 or suspended when you attach to it. Running tasks are suspended at
11112 the time of attachment.
11114 @node Embedded Processors
11115 @section Embedded Processors
11117 This section goes into details specific to particular embedded
11121 * A29K Embedded:: AMD A29K Embedded
11123 * H8/300:: Hitachi H8/300
11124 * H8/500:: Hitachi H8/500
11125 * i960:: Intel i960
11126 * M32R/D:: Mitsubishi M32R/D
11127 * M68K:: Motorola M68K
11128 * M88K:: Motorola M88K
11129 * MIPS Embedded:: MIPS Embedded
11130 * PA:: HP PA Embedded
11133 * Sparclet:: Tsqware Sparclet
11134 * Sparclite:: Fujitsu Sparclite
11135 * ST2000:: Tandem ST2000
11136 * Z8000:: Zilog Z8000
11139 @node A29K Embedded
11140 @subsection AMD A29K Embedded
11145 * Comms (EB29K):: Communications setup
11146 * gdb-EB29K:: EB29K cross-debugging
11147 * Remote Log:: Remote log
11152 @kindex target adapt
11153 @item target adapt @var{dev}
11154 Adapt monitor for A29K.
11156 @kindex target amd-eb
11157 @item target amd-eb @var{dev} @var{speed} @var{PROG}
11159 Remote PC-resident AMD EB29K board, attached over serial lines.
11160 @var{dev} is the serial device, as for @code{target remote};
11161 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
11162 name of the program to be debugged, as it appears to DOS on the PC.
11163 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
11168 @subsubsection A29K UDI
11171 @cindex AMD29K via UDI
11173 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
11174 protocol for debugging the a29k processor family. To use this
11175 configuration with AMD targets running the MiniMON monitor, you need the
11176 program @code{MONTIP}, available from AMD at no charge. You can also
11177 use @value{GDBN} with the UDI-conformant a29k simulator program
11178 @code{ISSTIP}, also available from AMD.
11181 @item target udi @var{keyword}
11183 Select the UDI interface to a remote a29k board or simulator, where
11184 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
11185 This file contains keyword entries which specify parameters used to
11186 connect to a29k targets. If the @file{udi_soc} file is not in your
11187 working directory, you must set the environment variable @samp{UDICONF}
11192 @subsubsection EBMON protocol for AMD29K
11194 @cindex EB29K board
11195 @cindex running 29K programs
11197 AMD distributes a 29K development board meant to fit in a PC, together
11198 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
11199 term, this development system is called the ``EB29K''. To use
11200 @value{GDBN} from a Unix system to run programs on the EB29K board, you
11201 must first connect a serial cable between the PC (which hosts the EB29K
11202 board) and a serial port on the Unix system. In the following, we
11203 assume you've hooked the cable between the PC's @file{COM1} port and
11204 @file{/dev/ttya} on the Unix system.
11206 @node Comms (EB29K)
11207 @subsubsection Communications setup
11209 The next step is to set up the PC's port, by doing something like this
11213 C:\> MODE com1:9600,n,8,1,none
11217 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
11218 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
11219 you must match the communications parameters when establishing the Unix
11220 end of the connection as well.
11221 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
11222 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
11224 @c It's optional, but it's unwise to omit it: who knows what is the
11225 @c default value set when the DOS machines boots? "No retry" means that
11226 @c the DOS serial device driver won't retry the operation if it fails;
11227 @c I understand that this is needed because the GDB serial protocol
11228 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
11230 To give control of the PC to the Unix side of the serial line, type
11231 the following at the DOS console:
11238 (Later, if you wish to return control to the DOS console, you can use
11239 the command @code{CTTY con}---but you must send it over the device that
11240 had control, in our example over the @file{COM1} serial line.)
11242 From the Unix host, use a communications program such as @code{tip} or
11243 @code{cu} to communicate with the PC; for example,
11246 cu -s 9600 -l /dev/ttya
11250 The @code{cu} options shown specify, respectively, the linespeed and the
11251 serial port to use. If you use @code{tip} instead, your command line
11252 may look something like the following:
11255 tip -9600 /dev/ttya
11259 Your system may require a different name where we show
11260 @file{/dev/ttya} as the argument to @code{tip}. The communications
11261 parameters, including which port to use, are associated with the
11262 @code{tip} argument in the ``remote'' descriptions file---normally the
11263 system table @file{/etc/remote}.
11264 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
11265 @c the DOS side's comms setup? cu can support -o (odd
11266 @c parity), -e (even parity)---apparently no settings for no parity or
11267 @c for character size. Taken from stty maybe...? John points out tip
11268 @c can set these as internal variables, eg ~s parity=none; man stty
11269 @c suggests that it *might* work to stty these options with stdin or
11270 @c stdout redirected... ---doc@cygnus.com, 25feb91
11272 @c There's nothing to be done for the "none" part of the DOS MODE
11273 @c command. The rest of the parameters should be matched by the
11274 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
11277 Using the @code{tip} or @code{cu} connection, change the DOS working
11278 directory to the directory containing a copy of your 29K program, then
11279 start the PC program @code{EBMON} (an EB29K control program supplied
11280 with your board by AMD). You should see an initial display from
11281 @code{EBMON} similar to the one that follows, ending with the
11282 @code{EBMON} prompt @samp{#}---
11287 G:\> CD \usr\joe\work29k
11289 G:\USR\JOE\WORK29K> EBMON
11290 Am29000 PC Coprocessor Board Monitor, version 3.0-18
11291 Copyright 1990 Advanced Micro Devices, Inc.
11292 Written by Gibbons and Associates, Inc.
11294 Enter '?' or 'H' for help
11296 PC Coprocessor Type = EB29K
11298 Memory Base = 0xd0000
11300 Data Memory Size = 2048KB
11301 Available I-RAM Range = 0x8000 to 0x1fffff
11302 Available D-RAM Range = 0x80002000 to 0x801fffff
11305 Register Stack Size = 0x800
11306 Memory Stack Size = 0x1800
11309 Am29027 Available = No
11310 Byte Write Available = Yes
11315 Then exit the @code{cu} or @code{tip} program (done in the example by
11316 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
11317 running, ready for @value{GDBN} to take over.
11319 For this example, we've assumed what is probably the most convenient
11320 way to make sure the same 29K program is on both the PC and the Unix
11321 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
11322 PC as a file system on the Unix host. If you do not have PC/NFS or
11323 something similar connecting the two systems, you must arrange some
11324 other way---perhaps floppy-disk transfer---of getting the 29K program
11325 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
11329 @subsubsection EB29K cross-debugging
11331 Finally, @code{cd} to the directory containing an image of your 29K
11332 program on the Unix system, and start @value{GDBN}---specifying as argument the
11333 name of your 29K program:
11336 cd /usr/joe/work29k
11341 Now you can use the @code{target} command:
11344 target amd-eb /dev/ttya 9600 MYFOO
11345 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
11346 @c emphasize that this is the name as seen by DOS (since I think DOS is
11347 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
11351 In this example, we've assumed your program is in a file called
11352 @file{myfoo}. Note that the filename given as the last argument to
11353 @code{target amd-eb} should be the name of the program as it appears to DOS.
11354 In our example this is simply @code{MYFOO}, but in general it can include
11355 a DOS path, and depending on your transfer mechanism may not resemble
11356 the name on the Unix side.
11358 At this point, you can set any breakpoints you wish; when you are ready
11359 to see your program run on the 29K board, use the @value{GDBN} command
11362 To stop debugging the remote program, use the @value{GDBN} @code{detach}
11365 To return control of the PC to its console, use @code{tip} or @code{cu}
11366 once again, after your @value{GDBN} session has concluded, to attach to
11367 @code{EBMON}. You can then type the command @code{q} to shut down
11368 @code{EBMON}, returning control to the DOS command-line interpreter.
11369 Type @kbd{CTTY con} to return command input to the main DOS console,
11370 and type @kbd{~.} to leave @code{tip} or @code{cu}.
11373 @subsubsection Remote log
11374 @cindex @file{eb.log}, a log file for EB29K
11375 @cindex log file for EB29K
11377 The @code{target amd-eb} command creates a file @file{eb.log} in the
11378 current working directory, to help debug problems with the connection.
11379 @file{eb.log} records all the output from @code{EBMON}, including echoes
11380 of the commands sent to it. Running @samp{tail -f} on this file in
11381 another window often helps to understand trouble with @code{EBMON}, or
11382 unexpected events on the PC side of the connection.
11390 @item target rdi @var{dev}
11391 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11392 use this target to communicate with both boards running the Angel
11393 monitor, or with the EmbeddedICE JTAG debug device.
11396 @item target rdp @var{dev}
11402 @subsection Hitachi H8/300
11406 @kindex target hms@r{, with H8/300}
11407 @item target hms @var{dev}
11408 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11409 Use special commands @code{device} and @code{speed} to control the serial
11410 line and the communications speed used.
11412 @kindex target e7000@r{, with H8/300}
11413 @item target e7000 @var{dev}
11414 E7000 emulator for Hitachi H8 and SH.
11416 @kindex target sh3@r{, with H8/300}
11417 @kindex target sh3e@r{, with H8/300}
11418 @item target sh3 @var{dev}
11419 @itemx target sh3e @var{dev}
11420 Hitachi SH-3 and SH-3E target systems.
11424 @cindex download to H8/300 or H8/500
11425 @cindex H8/300 or H8/500 download
11426 @cindex download to Hitachi SH
11427 @cindex Hitachi SH download
11428 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11429 board, the @code{load} command downloads your program to the Hitachi
11430 board and also opens it as the current executable target for
11431 @value{GDBN} on your host (like the @code{file} command).
11433 @value{GDBN} needs to know these things to talk to your
11434 Hitachi SH, H8/300, or H8/500:
11438 that you want to use @samp{target hms}, the remote debugging interface
11439 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11440 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11441 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11442 H8/300, or H8/500.)
11445 what serial device connects your host to your Hitachi board (the first
11446 serial device available on your host is the default).
11449 what speed to use over the serial device.
11453 * Hitachi Boards:: Connecting to Hitachi boards.
11454 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11455 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11458 @node Hitachi Boards
11459 @subsubsection Connecting to Hitachi boards
11461 @c only for Unix hosts
11463 @cindex serial device, Hitachi micros
11464 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11465 need to explicitly set the serial device. The default @var{port} is the
11466 first available port on your host. This is only necessary on Unix
11467 hosts, where it is typically something like @file{/dev/ttya}.
11470 @cindex serial line speed, Hitachi micros
11471 @code{@value{GDBN}} has another special command to set the communications
11472 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11473 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11474 the DOS @code{mode} command (for instance,
11475 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11477 The @samp{device} and @samp{speed} commands are available only when you
11478 use a Unix host to debug your Hitachi microprocessor programs. If you
11480 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11481 called @code{asynctsr} to communicate with the development board
11482 through a PC serial port. You must also use the DOS @code{mode} command
11483 to set up the serial port on the DOS side.
11485 The following sample session illustrates the steps needed to start a
11486 program under @value{GDBN} control on an H8/300. The example uses a
11487 sample H8/300 program called @file{t.x}. The procedure is the same for
11488 the Hitachi SH and the H8/500.
11490 First hook up your development board. In this example, we use a
11491 board attached to serial port @code{COM2}; if you use a different serial
11492 port, substitute its name in the argument of the @code{mode} command.
11493 When you call @code{asynctsr}, the auxiliary comms program used by the
11494 debugger, you give it just the numeric part of the serial port's name;
11495 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11499 C:\H8300\TEST> asynctsr 2
11500 C:\H8300\TEST> mode com2:9600,n,8,1,p
11502 Resident portion of MODE loaded
11504 COM2: 9600, n, 8, 1, p
11509 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11510 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11511 disable it, or even boot without it, to use @code{asynctsr} to control
11512 your development board.
11515 @kindex target hms@r{, and serial protocol}
11516 Now that serial communications are set up, and the development board is
11517 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11518 the name of your program as the argument. @code{@value{GDBN}} prompts
11519 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11520 commands to begin your debugging session: @samp{target hms} to specify
11521 cross-debugging to the Hitachi board, and the @code{load} command to
11522 download your program to the board. @code{load} displays the names of
11523 the program's sections, and a @samp{*} for each 2K of data downloaded.
11524 (If you want to refresh @value{GDBN} data on symbols or on the
11525 executable file without downloading, use the @value{GDBN} commands
11526 @code{file} or @code{symbol-file}. These commands, and @code{load}
11527 itself, are described in @ref{Files,,Commands to specify files}.)
11530 (eg-C:\H8300\TEST) @value{GDBP} t.x
11531 @value{GDBN} is free software and you are welcome to distribute copies
11532 of it under certain conditions; type "show copying" to see
11534 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11536 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11537 (@value{GDBP}) target hms
11538 Connected to remote H8/300 HMS system.
11539 (@value{GDBP}) load t.x
11540 .text : 0x8000 .. 0xabde ***********
11541 .data : 0xabde .. 0xad30 *
11542 .stack : 0xf000 .. 0xf014 *
11545 At this point, you're ready to run or debug your program. From here on,
11546 you can use all the usual @value{GDBN} commands. The @code{break} command
11547 sets breakpoints; the @code{run} command starts your program;
11548 @code{print} or @code{x} display data; the @code{continue} command
11549 resumes execution after stopping at a breakpoint. You can use the
11550 @code{help} command at any time to find out more about @value{GDBN} commands.
11552 Remember, however, that @emph{operating system} facilities aren't
11553 available on your development board; for example, if your program hangs,
11554 you can't send an interrupt---but you can press the @sc{reset} switch!
11556 Use the @sc{reset} button on the development board
11559 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11560 no way to pass an interrupt signal to the development board); and
11563 to return to the @value{GDBN} command prompt after your program finishes
11564 normally. The communications protocol provides no other way for @value{GDBN}
11565 to detect program completion.
11568 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11569 development board as a ``normal exit'' of your program.
11572 @subsubsection Using the E7000 in-circuit emulator
11574 @kindex target e7000@r{, with Hitachi ICE}
11575 You can use the E7000 in-circuit emulator to develop code for either the
11576 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11577 e7000} command to connect @value{GDBN} to your E7000:
11580 @item target e7000 @var{port} @var{speed}
11581 Use this form if your E7000 is connected to a serial port. The
11582 @var{port} argument identifies what serial port to use (for example,
11583 @samp{com2}). The third argument is the line speed in bits per second
11584 (for example, @samp{9600}).
11586 @item target e7000 @var{hostname}
11587 If your E7000 is installed as a host on a TCP/IP network, you can just
11588 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11591 @node Hitachi Special
11592 @subsubsection Special @value{GDBN} commands for Hitachi micros
11594 Some @value{GDBN} commands are available only for the H8/300:
11598 @kindex set machine
11599 @kindex show machine
11600 @item set machine h8300
11601 @itemx set machine h8300h
11602 Condition @value{GDBN} for one of the two variants of the H8/300
11603 architecture with @samp{set machine}. You can use @samp{show machine}
11604 to check which variant is currently in effect.
11613 @kindex set memory @var{mod}
11614 @cindex memory models, H8/500
11615 @item set memory @var{mod}
11617 Specify which H8/500 memory model (@var{mod}) you are using with
11618 @samp{set memory}; check which memory model is in effect with @samp{show
11619 memory}. The accepted values for @var{mod} are @code{small},
11620 @code{big}, @code{medium}, and @code{compact}.
11625 @subsection Intel i960
11629 @kindex target mon960
11630 @item target mon960 @var{dev}
11631 MON960 monitor for Intel i960.
11633 @kindex target nindy
11634 @item target nindy @var{devicename}
11635 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11636 the name of the serial device to use for the connection, e.g.
11643 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11644 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11645 tell @value{GDBN} how to connect to the 960 in several ways:
11649 Through command line options specifying serial port, version of the
11650 Nindy protocol, and communications speed;
11653 By responding to a prompt on startup;
11656 By using the @code{target} command at any point during your @value{GDBN}
11657 session. @xref{Target Commands, ,Commands for managing targets}.
11661 @cindex download to Nindy-960
11662 With the Nindy interface to an Intel 960 board, @code{load}
11663 downloads @var{filename} to the 960 as well as adding its symbols in
11667 * Nindy Startup:: Startup with Nindy
11668 * Nindy Options:: Options for Nindy
11669 * Nindy Reset:: Nindy reset command
11672 @node Nindy Startup
11673 @subsubsection Startup with Nindy
11675 If you simply start @code{@value{GDBP}} without using any command-line
11676 options, you are prompted for what serial port to use, @emph{before} you
11677 reach the ordinary @value{GDBN} prompt:
11680 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11684 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11685 identifies the serial port you want to use. You can, if you choose,
11686 simply start up with no Nindy connection by responding to the prompt
11687 with an empty line. If you do this and later wish to attach to Nindy,
11688 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11690 @node Nindy Options
11691 @subsubsection Options for Nindy
11693 These are the startup options for beginning your @value{GDBN} session with a
11694 Nindy-960 board attached:
11697 @item -r @var{port}
11698 Specify the serial port name of a serial interface to be used to connect
11699 to the target system. This option is only available when @value{GDBN} is
11700 configured for the Intel 960 target architecture. You may specify
11701 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11702 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11703 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11706 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11707 the ``old'' Nindy monitor protocol to connect to the target system.
11708 This option is only available when @value{GDBN} is configured for the Intel 960
11709 target architecture.
11712 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11713 connect to a target system that expects the newer protocol, the connection
11714 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11715 attempts to reconnect at several different line speeds. You can abort
11716 this process with an interrupt.
11720 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11721 system, in an attempt to reset it, before connecting to a Nindy target.
11724 @emph{Warning:} Many target systems do not have the hardware that this
11725 requires; it only works with a few boards.
11729 The standard @samp{-b} option controls the line speed used on the serial
11734 @subsubsection Nindy reset command
11739 For a Nindy target, this command sends a ``break'' to the remote target
11740 system; this is only useful if the target has been equipped with a
11741 circuit to perform a hard reset (or some other interesting action) when
11742 a break is detected.
11747 @subsection Mitsubishi M32R/D
11751 @kindex target m32r
11752 @item target m32r @var{dev}
11753 Mitsubishi M32R/D ROM monitor.
11760 The Motorola m68k configuration includes ColdFire support, and
11761 target command for the following ROM monitors.
11765 @kindex target abug
11766 @item target abug @var{dev}
11767 ABug ROM monitor for M68K.
11769 @kindex target cpu32bug
11770 @item target cpu32bug @var{dev}
11771 CPU32BUG monitor, running on a CPU32 (M68K) board.
11773 @kindex target dbug
11774 @item target dbug @var{dev}
11775 dBUG ROM monitor for Motorola ColdFire.
11778 @item target est @var{dev}
11779 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11781 @kindex target rom68k
11782 @item target rom68k @var{dev}
11783 ROM 68K monitor, running on an M68K IDP board.
11787 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11788 instead have only a single special target command:
11792 @kindex target es1800
11793 @item target es1800 @var{dev}
11794 ES-1800 emulator for M68K.
11802 @kindex target rombug
11803 @item target rombug @var{dev}
11804 ROMBUG ROM monitor for OS/9000.
11814 @item target bug @var{dev}
11815 BUG monitor, running on a MVME187 (m88k) board.
11819 @node MIPS Embedded
11820 @subsection MIPS Embedded
11822 @cindex MIPS boards
11823 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11824 MIPS board attached to a serial line. This is available when
11825 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11828 Use these @value{GDBN} commands to specify the connection to your target board:
11831 @item target mips @var{port}
11832 @kindex target mips @var{port}
11833 To run a program on the board, start up @code{@value{GDBP}} with the
11834 name of your program as the argument. To connect to the board, use the
11835 command @samp{target mips @var{port}}, where @var{port} is the name of
11836 the serial port connected to the board. If the program has not already
11837 been downloaded to the board, you may use the @code{load} command to
11838 download it. You can then use all the usual @value{GDBN} commands.
11840 For example, this sequence connects to the target board through a serial
11841 port, and loads and runs a program called @var{prog} through the
11845 host$ @value{GDBP} @var{prog}
11846 @value{GDBN} is free software and @dots{}
11847 (@value{GDBP}) target mips /dev/ttyb
11848 (@value{GDBP}) load @var{prog}
11852 @item target mips @var{hostname}:@var{portnumber}
11853 On some @value{GDBN} host configurations, you can specify a TCP
11854 connection (for instance, to a serial line managed by a terminal
11855 concentrator) instead of a serial port, using the syntax
11856 @samp{@var{hostname}:@var{portnumber}}.
11858 @item target pmon @var{port}
11859 @kindex target pmon @var{port}
11862 @item target ddb @var{port}
11863 @kindex target ddb @var{port}
11864 NEC's DDB variant of PMON for Vr4300.
11866 @item target lsi @var{port}
11867 @kindex target lsi @var{port}
11868 LSI variant of PMON.
11870 @kindex target r3900
11871 @item target r3900 @var{dev}
11872 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11874 @kindex target array
11875 @item target array @var{dev}
11876 Array Tech LSI33K RAID controller board.
11882 @value{GDBN} also supports these special commands for MIPS targets:
11885 @item set processor @var{args}
11886 @itemx show processor
11887 @kindex set processor @var{args}
11888 @kindex show processor
11889 Use the @code{set processor} command to set the type of MIPS
11890 processor when you want to access processor-type-specific registers.
11891 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11892 to use the CPU registers appropriate for the 3041 chip.
11893 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11894 is using. Use the @code{info reg} command to see what registers
11895 @value{GDBN} is using.
11897 @item set mipsfpu double
11898 @itemx set mipsfpu single
11899 @itemx set mipsfpu none
11900 @itemx show mipsfpu
11901 @kindex set mipsfpu
11902 @kindex show mipsfpu
11903 @cindex MIPS remote floating point
11904 @cindex floating point, MIPS remote
11905 If your target board does not support the MIPS floating point
11906 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11907 need this, you may wish to put the command in your @value{GDBN} init
11908 file). This tells @value{GDBN} how to find the return value of
11909 functions which return floating point values. It also allows
11910 @value{GDBN} to avoid saving the floating point registers when calling
11911 functions on the board. If you are using a floating point coprocessor
11912 with only single precision floating point support, as on the @sc{r4650}
11913 processor, use the command @samp{set mipsfpu single}. The default
11914 double precision floating point coprocessor may be selected using
11915 @samp{set mipsfpu double}.
11917 In previous versions the only choices were double precision or no
11918 floating point, so @samp{set mipsfpu on} will select double precision
11919 and @samp{set mipsfpu off} will select no floating point.
11921 As usual, you can inquire about the @code{mipsfpu} variable with
11922 @samp{show mipsfpu}.
11924 @item set remotedebug @var{n}
11925 @itemx show remotedebug
11926 @kindex set remotedebug@r{, MIPS protocol}
11927 @kindex show remotedebug@r{, MIPS protocol}
11928 @cindex @code{remotedebug}, MIPS protocol
11929 @cindex MIPS @code{remotedebug} protocol
11930 @c FIXME! For this to be useful, you must know something about the MIPS
11931 @c FIXME...protocol. Where is it described?
11932 You can see some debugging information about communications with the board
11933 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11934 @samp{set remotedebug 1}, every packet is displayed. If you set it
11935 to @code{2}, every character is displayed. You can check the current value
11936 at any time with the command @samp{show remotedebug}.
11938 @item set timeout @var{seconds}
11939 @itemx set retransmit-timeout @var{seconds}
11940 @itemx show timeout
11941 @itemx show retransmit-timeout
11942 @cindex @code{timeout}, MIPS protocol
11943 @cindex @code{retransmit-timeout}, MIPS protocol
11944 @kindex set timeout
11945 @kindex show timeout
11946 @kindex set retransmit-timeout
11947 @kindex show retransmit-timeout
11948 You can control the timeout used while waiting for a packet, in the MIPS
11949 remote protocol, with the @code{set timeout @var{seconds}} command. The
11950 default is 5 seconds. Similarly, you can control the timeout used while
11951 waiting for an acknowledgement of a packet with the @code{set
11952 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11953 You can inspect both values with @code{show timeout} and @code{show
11954 retransmit-timeout}. (These commands are @emph{only} available when
11955 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11957 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11958 is waiting for your program to stop. In that case, @value{GDBN} waits
11959 forever because it has no way of knowing how long the program is going
11960 to run before stopping.
11964 @subsection PowerPC
11968 @kindex target dink32
11969 @item target dink32 @var{dev}
11970 DINK32 ROM monitor.
11972 @kindex target ppcbug
11973 @item target ppcbug @var{dev}
11974 @kindex target ppcbug1
11975 @item target ppcbug1 @var{dev}
11976 PPCBUG ROM monitor for PowerPC.
11979 @item target sds @var{dev}
11980 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11985 @subsection HP PA Embedded
11989 @kindex target op50n
11990 @item target op50n @var{dev}
11991 OP50N monitor, running on an OKI HPPA board.
11993 @kindex target w89k
11994 @item target w89k @var{dev}
11995 W89K monitor, running on a Winbond HPPA board.
12000 @subsection Hitachi SH
12004 @kindex target hms@r{, with Hitachi SH}
12005 @item target hms @var{dev}
12006 A Hitachi SH board attached via serial line to your host. Use special
12007 commands @code{device} and @code{speed} to control the serial line and
12008 the communications speed used.
12010 @kindex target e7000@r{, with Hitachi SH}
12011 @item target e7000 @var{dev}
12012 E7000 emulator for Hitachi SH.
12014 @kindex target sh3@r{, with SH}
12015 @kindex target sh3e@r{, with SH}
12016 @item target sh3 @var{dev}
12017 @item target sh3e @var{dev}
12018 Hitachi SH-3 and SH-3E target systems.
12023 @subsection Tsqware Sparclet
12027 @value{GDBN} enables developers to debug tasks running on
12028 Sparclet targets from a Unix host.
12029 @value{GDBN} uses code that runs on
12030 both the Unix host and on the Sparclet target. The program
12031 @code{@value{GDBP}} is installed and executed on the Unix host.
12034 @item remotetimeout @var{args}
12035 @kindex remotetimeout
12036 @value{GDBN} supports the option @code{remotetimeout}.
12037 This option is set by the user, and @var{args} represents the number of
12038 seconds @value{GDBN} waits for responses.
12041 @cindex compiling, on Sparclet
12042 When compiling for debugging, include the options @samp{-g} to get debug
12043 information and @samp{-Ttext} to relocate the program to where you wish to
12044 load it on the target. You may also want to add the options @samp{-n} or
12045 @samp{-N} in order to reduce the size of the sections. Example:
12048 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12051 You can use @code{objdump} to verify that the addresses are what you intended:
12054 sparclet-aout-objdump --headers --syms prog
12057 @cindex running, on Sparclet
12059 your Unix execution search path to find @value{GDBN}, you are ready to
12060 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12061 (or @code{sparclet-aout-gdb}, depending on your installation).
12063 @value{GDBN} comes up showing the prompt:
12070 * Sparclet File:: Setting the file to debug
12071 * Sparclet Connection:: Connecting to Sparclet
12072 * Sparclet Download:: Sparclet download
12073 * Sparclet Execution:: Running and debugging
12076 @node Sparclet File
12077 @subsubsection Setting file to debug
12079 The @value{GDBN} command @code{file} lets you choose with program to debug.
12082 (gdbslet) file prog
12086 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12087 @value{GDBN} locates
12088 the file by searching the directories listed in the command search
12090 If the file was compiled with debug information (option "-g"), source
12091 files will be searched as well.
12092 @value{GDBN} locates
12093 the source files by searching the directories listed in the directory search
12094 path (@pxref{Environment, ,Your program's environment}).
12096 to find a file, it displays a message such as:
12099 prog: No such file or directory.
12102 When this happens, add the appropriate directories to the search paths with
12103 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12104 @code{target} command again.
12106 @node Sparclet Connection
12107 @subsubsection Connecting to Sparclet
12109 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12110 To connect to a target on serial port ``@code{ttya}'', type:
12113 (gdbslet) target sparclet /dev/ttya
12114 Remote target sparclet connected to /dev/ttya
12115 main () at ../prog.c:3
12119 @value{GDBN} displays messages like these:
12125 @node Sparclet Download
12126 @subsubsection Sparclet download
12128 @cindex download to Sparclet
12129 Once connected to the Sparclet target,
12130 you can use the @value{GDBN}
12131 @code{load} command to download the file from the host to the target.
12132 The file name and load offset should be given as arguments to the @code{load}
12134 Since the file format is aout, the program must be loaded to the starting
12135 address. You can use @code{objdump} to find out what this value is. The load
12136 offset is an offset which is added to the VMA (virtual memory address)
12137 of each of the file's sections.
12138 For instance, if the program
12139 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12140 and bss at 0x12010170, in @value{GDBN}, type:
12143 (gdbslet) load prog 0x12010000
12144 Loading section .text, size 0xdb0 vma 0x12010000
12147 If the code is loaded at a different address then what the program was linked
12148 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12149 to tell @value{GDBN} where to map the symbol table.
12151 @node Sparclet Execution
12152 @subsubsection Running and debugging
12154 @cindex running and debugging Sparclet programs
12155 You can now begin debugging the task using @value{GDBN}'s execution control
12156 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12157 manual for the list of commands.
12161 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12163 Starting program: prog
12164 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12165 3 char *symarg = 0;
12167 4 char *execarg = "hello!";
12172 @subsection Fujitsu Sparclite
12176 @kindex target sparclite
12177 @item target sparclite @var{dev}
12178 Fujitsu sparclite boards, used only for the purpose of loading.
12179 You must use an additional command to debug the program.
12180 For example: target remote @var{dev} using @value{GDBN} standard
12186 @subsection Tandem ST2000
12188 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12191 To connect your ST2000 to the host system, see the manufacturer's
12192 manual. Once the ST2000 is physically attached, you can run:
12195 target st2000 @var{dev} @var{speed}
12199 to establish it as your debugging environment. @var{dev} is normally
12200 the name of a serial device, such as @file{/dev/ttya}, connected to the
12201 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12202 connection (for example, to a serial line attached via a terminal
12203 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12205 The @code{load} and @code{attach} commands are @emph{not} defined for
12206 this target; you must load your program into the ST2000 as you normally
12207 would for standalone operation. @value{GDBN} reads debugging information
12208 (such as symbols) from a separate, debugging version of the program
12209 available on your host computer.
12210 @c FIXME!! This is terribly vague; what little content is here is
12211 @c basically hearsay.
12213 @cindex ST2000 auxiliary commands
12214 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12218 @item st2000 @var{command}
12219 @kindex st2000 @var{cmd}
12220 @cindex STDBUG commands (ST2000)
12221 @cindex commands to STDBUG (ST2000)
12222 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12223 manual for available commands.
12226 @cindex connect (to STDBUG)
12227 Connect the controlling terminal to the STDBUG command monitor. When
12228 you are done interacting with STDBUG, typing either of two character
12229 sequences gets you back to the @value{GDBN} command prompt:
12230 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12231 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12235 @subsection Zilog Z8000
12238 @cindex simulator, Z8000
12239 @cindex Zilog Z8000 simulator
12241 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12244 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12245 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12246 segmented variant). The simulator recognizes which architecture is
12247 appropriate by inspecting the object code.
12250 @item target sim @var{args}
12252 @kindex target sim@r{, with Z8000}
12253 Debug programs on a simulated CPU. If the simulator supports setup
12254 options, specify them via @var{args}.
12258 After specifying this target, you can debug programs for the simulated
12259 CPU in the same style as programs for your host computer; use the
12260 @code{file} command to load a new program image, the @code{run} command
12261 to run your program, and so on.
12263 As well as making available all the usual machine registers
12264 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12265 additional items of information as specially named registers:
12270 Counts clock-ticks in the simulator.
12273 Counts instructions run in the simulator.
12276 Execution time in 60ths of a second.
12280 You can refer to these values in @value{GDBN} expressions with the usual
12281 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12282 conditional breakpoint that suspends only after at least 5000
12283 simulated clock ticks.
12285 @node Architectures
12286 @section Architectures
12288 This section describes characteristics of architectures that affect
12289 all uses of @value{GDBN} with the architecture, both native and cross.
12302 @kindex set rstack_high_address
12303 @cindex AMD 29K register stack
12304 @cindex register stack, AMD29K
12305 @item set rstack_high_address @var{address}
12306 On AMD 29000 family processors, registers are saved in a separate
12307 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12308 extent of this stack. Normally, @value{GDBN} just assumes that the
12309 stack is ``large enough''. This may result in @value{GDBN} referencing
12310 memory locations that do not exist. If necessary, you can get around
12311 this problem by specifying the ending address of the register stack with
12312 the @code{set rstack_high_address} command. The argument should be an
12313 address, which you probably want to precede with @samp{0x} to specify in
12316 @kindex show rstack_high_address
12317 @item show rstack_high_address
12318 Display the current limit of the register stack, on AMD 29000 family
12326 See the following section.
12331 @cindex stack on Alpha
12332 @cindex stack on MIPS
12333 @cindex Alpha stack
12335 Alpha- and MIPS-based computers use an unusual stack frame, which
12336 sometimes requires @value{GDBN} to search backward in the object code to
12337 find the beginning of a function.
12339 @cindex response time, MIPS debugging
12340 To improve response time (especially for embedded applications, where
12341 @value{GDBN} may be restricted to a slow serial line for this search)
12342 you may want to limit the size of this search, using one of these
12346 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12347 @item set heuristic-fence-post @var{limit}
12348 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12349 search for the beginning of a function. A value of @var{0} (the
12350 default) means there is no limit. However, except for @var{0}, the
12351 larger the limit the more bytes @code{heuristic-fence-post} must search
12352 and therefore the longer it takes to run.
12354 @item show heuristic-fence-post
12355 Display the current limit.
12359 These commands are available @emph{only} when @value{GDBN} is configured
12360 for debugging programs on Alpha or MIPS processors.
12363 @node Controlling GDB
12364 @chapter Controlling @value{GDBN}
12366 You can alter the way @value{GDBN} interacts with you by using the
12367 @code{set} command. For commands controlling how @value{GDBN} displays
12368 data, see @ref{Print Settings, ,Print settings}. Other settings are
12373 * Editing:: Command editing
12374 * History:: Command history
12375 * Screen Size:: Screen size
12376 * Numbers:: Numbers
12377 * Messages/Warnings:: Optional warnings and messages
12378 * Debugging Output:: Optional messages about internal happenings
12386 @value{GDBN} indicates its readiness to read a command by printing a string
12387 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12388 can change the prompt string with the @code{set prompt} command. For
12389 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12390 the prompt in one of the @value{GDBN} sessions so that you can always tell
12391 which one you are talking to.
12393 @emph{Note:} @code{set prompt} does not add a space for you after the
12394 prompt you set. This allows you to set a prompt which ends in a space
12395 or a prompt that does not.
12399 @item set prompt @var{newprompt}
12400 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12402 @kindex show prompt
12404 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12408 @section Command editing
12410 @cindex command line editing
12412 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12413 @sc{gnu} library provides consistent behavior for programs which provide a
12414 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12415 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12416 substitution, and a storage and recall of command history across
12417 debugging sessions.
12419 You may control the behavior of command line editing in @value{GDBN} with the
12420 command @code{set}.
12423 @kindex set editing
12426 @itemx set editing on
12427 Enable command line editing (enabled by default).
12429 @item set editing off
12430 Disable command line editing.
12432 @kindex show editing
12434 Show whether command line editing is enabled.
12438 @section Command history
12440 @value{GDBN} can keep track of the commands you type during your
12441 debugging sessions, so that you can be certain of precisely what
12442 happened. Use these commands to manage the @value{GDBN} command
12446 @cindex history substitution
12447 @cindex history file
12448 @kindex set history filename
12449 @kindex GDBHISTFILE
12450 @item set history filename @var{fname}
12451 Set the name of the @value{GDBN} command history file to @var{fname}.
12452 This is the file where @value{GDBN} reads an initial command history
12453 list, and where it writes the command history from this session when it
12454 exits. You can access this list through history expansion or through
12455 the history command editing characters listed below. This file defaults
12456 to the value of the environment variable @code{GDBHISTFILE}, or to
12457 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12460 @cindex history save
12461 @kindex set history save
12462 @item set history save
12463 @itemx set history save on
12464 Record command history in a file, whose name may be specified with the
12465 @code{set history filename} command. By default, this option is disabled.
12467 @item set history save off
12468 Stop recording command history in a file.
12470 @cindex history size
12471 @kindex set history size
12472 @item set history size @var{size}
12473 Set the number of commands which @value{GDBN} keeps in its history list.
12474 This defaults to the value of the environment variable
12475 @code{HISTSIZE}, or to 256 if this variable is not set.
12478 @cindex history expansion
12479 History expansion assigns special meaning to the character @kbd{!}.
12480 @ifset have-readline-appendices
12481 @xref{Event Designators}.
12484 Since @kbd{!} is also the logical not operator in C, history expansion
12485 is off by default. If you decide to enable history expansion with the
12486 @code{set history expansion on} command, you may sometimes need to
12487 follow @kbd{!} (when it is used as logical not, in an expression) with
12488 a space or a tab to prevent it from being expanded. The readline
12489 history facilities do not attempt substitution on the strings
12490 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12492 The commands to control history expansion are:
12495 @kindex set history expansion
12496 @item set history expansion on
12497 @itemx set history expansion
12498 Enable history expansion. History expansion is off by default.
12500 @item set history expansion off
12501 Disable history expansion.
12503 The readline code comes with more complete documentation of
12504 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12505 or @code{vi} may wish to read it.
12506 @ifset have-readline-appendices
12507 @xref{Command Line Editing}.
12511 @kindex show history
12513 @itemx show history filename
12514 @itemx show history save
12515 @itemx show history size
12516 @itemx show history expansion
12517 These commands display the state of the @value{GDBN} history parameters.
12518 @code{show history} by itself displays all four states.
12524 @item show commands
12525 Display the last ten commands in the command history.
12527 @item show commands @var{n}
12528 Print ten commands centered on command number @var{n}.
12530 @item show commands +
12531 Print ten commands just after the commands last printed.
12535 @section Screen size
12536 @cindex size of screen
12537 @cindex pauses in output
12539 Certain commands to @value{GDBN} may produce large amounts of
12540 information output to the screen. To help you read all of it,
12541 @value{GDBN} pauses and asks you for input at the end of each page of
12542 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12543 to discard the remaining output. Also, the screen width setting
12544 determines when to wrap lines of output. Depending on what is being
12545 printed, @value{GDBN} tries to break the line at a readable place,
12546 rather than simply letting it overflow onto the following line.
12548 Normally @value{GDBN} knows the size of the screen from the terminal
12549 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12550 together with the value of the @code{TERM} environment variable and the
12551 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12552 you can override it with the @code{set height} and @code{set
12559 @kindex show height
12560 @item set height @var{lpp}
12562 @itemx set width @var{cpl}
12564 These @code{set} commands specify a screen height of @var{lpp} lines and
12565 a screen width of @var{cpl} characters. The associated @code{show}
12566 commands display the current settings.
12568 If you specify a height of zero lines, @value{GDBN} does not pause during
12569 output no matter how long the output is. This is useful if output is to a
12570 file or to an editor buffer.
12572 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12573 from wrapping its output.
12578 @cindex number representation
12579 @cindex entering numbers
12581 You can always enter numbers in octal, decimal, or hexadecimal in
12582 @value{GDBN} by the usual conventions: octal numbers begin with
12583 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12584 begin with @samp{0x}. Numbers that begin with none of these are, by
12585 default, entered in base 10; likewise, the default display for
12586 numbers---when no particular format is specified---is base 10. You can
12587 change the default base for both input and output with the @code{set
12591 @kindex set input-radix
12592 @item set input-radix @var{base}
12593 Set the default base for numeric input. Supported choices
12594 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12595 specified either unambiguously or using the current default radix; for
12605 sets the base to decimal. On the other hand, @samp{set radix 10}
12606 leaves the radix unchanged no matter what it was.
12608 @kindex set output-radix
12609 @item set output-radix @var{base}
12610 Set the default base for numeric display. Supported choices
12611 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12612 specified either unambiguously or using the current default radix.
12614 @kindex show input-radix
12615 @item show input-radix
12616 Display the current default base for numeric input.
12618 @kindex show output-radix
12619 @item show output-radix
12620 Display the current default base for numeric display.
12623 @node Messages/Warnings
12624 @section Optional warnings and messages
12626 By default, @value{GDBN} is silent about its inner workings. If you are
12627 running on a slow machine, you may want to use the @code{set verbose}
12628 command. This makes @value{GDBN} tell you when it does a lengthy
12629 internal operation, so you will not think it has crashed.
12631 Currently, the messages controlled by @code{set verbose} are those
12632 which announce that the symbol table for a source file is being read;
12633 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12636 @kindex set verbose
12637 @item set verbose on
12638 Enables @value{GDBN} output of certain informational messages.
12640 @item set verbose off
12641 Disables @value{GDBN} output of certain informational messages.
12643 @kindex show verbose
12645 Displays whether @code{set verbose} is on or off.
12648 By default, if @value{GDBN} encounters bugs in the symbol table of an
12649 object file, it is silent; but if you are debugging a compiler, you may
12650 find this information useful (@pxref{Symbol Errors, ,Errors reading
12655 @kindex set complaints
12656 @item set complaints @var{limit}
12657 Permits @value{GDBN} to output @var{limit} complaints about each type of
12658 unusual symbols before becoming silent about the problem. Set
12659 @var{limit} to zero to suppress all complaints; set it to a large number
12660 to prevent complaints from being suppressed.
12662 @kindex show complaints
12663 @item show complaints
12664 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12668 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12669 lot of stupid questions to confirm certain commands. For example, if
12670 you try to run a program which is already running:
12674 The program being debugged has been started already.
12675 Start it from the beginning? (y or n)
12678 If you are willing to unflinchingly face the consequences of your own
12679 commands, you can disable this ``feature'':
12683 @kindex set confirm
12685 @cindex confirmation
12686 @cindex stupid questions
12687 @item set confirm off
12688 Disables confirmation requests.
12690 @item set confirm on
12691 Enables confirmation requests (the default).
12693 @kindex show confirm
12695 Displays state of confirmation requests.
12699 @node Debugging Output
12700 @section Optional messages about internal happenings
12702 @kindex set debug arch
12703 @item set debug arch
12704 Turns on or off display of gdbarch debugging info. The default is off
12705 @kindex show debug arch
12706 @item show debug arch
12707 Displays the current state of displaying gdbarch debugging info.
12708 @kindex set debug event
12709 @item set debug event
12710 Turns on or off display of @value{GDBN} event debugging info. The
12712 @kindex show debug event
12713 @item show debug event
12714 Displays the current state of displaying @value{GDBN} event debugging
12716 @kindex set debug expression
12717 @item set debug expression
12718 Turns on or off display of @value{GDBN} expression debugging info. The
12720 @kindex show debug expression
12721 @item show debug expression
12722 Displays the current state of displaying @value{GDBN} expression
12724 @kindex set debug overload
12725 @item set debug overload
12726 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12727 info. This includes info such as ranking of functions, etc. The default
12729 @kindex show debug overload
12730 @item show debug overload
12731 Displays the current state of displaying @value{GDBN} C@t{++} overload
12733 @kindex set debug remote
12734 @cindex packets, reporting on stdout
12735 @cindex serial connections, debugging
12736 @item set debug remote
12737 Turns on or off display of reports on all packets sent back and forth across
12738 the serial line to the remote machine. The info is printed on the
12739 @value{GDBN} standard output stream. The default is off.
12740 @kindex show debug remote
12741 @item show debug remote
12742 Displays the state of display of remote packets.
12743 @kindex set debug serial
12744 @item set debug serial
12745 Turns on or off display of @value{GDBN} serial debugging info. The
12747 @kindex show debug serial
12748 @item show debug serial
12749 Displays the current state of displaying @value{GDBN} serial debugging
12751 @kindex set debug target
12752 @item set debug target
12753 Turns on or off display of @value{GDBN} target debugging info. This info
12754 includes what is going on at the target level of GDB, as it happens. The
12756 @kindex show debug target
12757 @item show debug target
12758 Displays the current state of displaying @value{GDBN} target debugging
12760 @kindex set debug varobj
12761 @item set debug varobj
12762 Turns on or off display of @value{GDBN} variable object debugging
12763 info. The default is off.
12764 @kindex show debug varobj
12765 @item show debug varobj
12766 Displays the current state of displaying @value{GDBN} variable object
12771 @chapter Canned Sequences of Commands
12773 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12774 command lists}), @value{GDBN} provides two ways to store sequences of
12775 commands for execution as a unit: user-defined commands and command
12779 * Define:: User-defined commands
12780 * Hooks:: User-defined command hooks
12781 * Command Files:: Command files
12782 * Output:: Commands for controlled output
12786 @section User-defined commands
12788 @cindex user-defined command
12789 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12790 which you assign a new name as a command. This is done with the
12791 @code{define} command. User commands may accept up to 10 arguments
12792 separated by whitespace. Arguments are accessed within the user command
12793 via @var{$arg0@dots{}$arg9}. A trivial example:
12797 print $arg0 + $arg1 + $arg2
12801 To execute the command use:
12808 This defines the command @code{adder}, which prints the sum of
12809 its three arguments. Note the arguments are text substitutions, so they may
12810 reference variables, use complex expressions, or even perform inferior
12816 @item define @var{commandname}
12817 Define a command named @var{commandname}. If there is already a command
12818 by that name, you are asked to confirm that you want to redefine it.
12820 The definition of the command is made up of other @value{GDBN} command lines,
12821 which are given following the @code{define} command. The end of these
12822 commands is marked by a line containing @code{end}.
12827 Takes a single argument, which is an expression to evaluate.
12828 It is followed by a series of commands that are executed
12829 only if the expression is true (nonzero).
12830 There can then optionally be a line @code{else}, followed
12831 by a series of commands that are only executed if the expression
12832 was false. The end of the list is marked by a line containing @code{end}.
12836 The syntax is similar to @code{if}: the command takes a single argument,
12837 which is an expression to evaluate, and must be followed by the commands to
12838 execute, one per line, terminated by an @code{end}.
12839 The commands are executed repeatedly as long as the expression
12843 @item document @var{commandname}
12844 Document the user-defined command @var{commandname}, so that it can be
12845 accessed by @code{help}. The command @var{commandname} must already be
12846 defined. This command reads lines of documentation just as @code{define}
12847 reads the lines of the command definition, ending with @code{end}.
12848 After the @code{document} command is finished, @code{help} on command
12849 @var{commandname} displays the documentation you have written.
12851 You may use the @code{document} command again to change the
12852 documentation of a command. Redefining the command with @code{define}
12853 does not change the documentation.
12855 @kindex help user-defined
12856 @item help user-defined
12857 List all user-defined commands, with the first line of the documentation
12862 @itemx show user @var{commandname}
12863 Display the @value{GDBN} commands used to define @var{commandname} (but
12864 not its documentation). If no @var{commandname} is given, display the
12865 definitions for all user-defined commands.
12869 When user-defined commands are executed, the
12870 commands of the definition are not printed. An error in any command
12871 stops execution of the user-defined command.
12873 If used interactively, commands that would ask for confirmation proceed
12874 without asking when used inside a user-defined command. Many @value{GDBN}
12875 commands that normally print messages to say what they are doing omit the
12876 messages when used in a user-defined command.
12879 @section User-defined command hooks
12880 @cindex command hooks
12881 @cindex hooks, for commands
12882 @cindex hooks, pre-command
12886 You may define @dfn{hooks}, which are a special kind of user-defined
12887 command. Whenever you run the command @samp{foo}, if the user-defined
12888 command @samp{hook-foo} exists, it is executed (with no arguments)
12889 before that command.
12891 @cindex hooks, post-command
12894 A hook may also be defined which is run after the command you executed.
12895 Whenever you run the command @samp{foo}, if the user-defined command
12896 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12897 that command. Post-execution hooks may exist simultaneously with
12898 pre-execution hooks, for the same command.
12900 It is valid for a hook to call the command which it hooks. If this
12901 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12903 @c It would be nice if hookpost could be passed a parameter indicating
12904 @c if the command it hooks executed properly or not. FIXME!
12906 @kindex stop@r{, a pseudo-command}
12907 In addition, a pseudo-command, @samp{stop} exists. Defining
12908 (@samp{hook-stop}) makes the associated commands execute every time
12909 execution stops in your program: before breakpoint commands are run,
12910 displays are printed, or the stack frame is printed.
12912 For example, to ignore @code{SIGALRM} signals while
12913 single-stepping, but treat them normally during normal execution,
12918 handle SIGALRM nopass
12922 handle SIGALRM pass
12925 define hook-continue
12926 handle SIGLARM pass
12930 As a further example, to hook at the begining and end of the @code{echo}
12931 command, and to add extra text to the beginning and end of the message,
12939 define hookpost-echo
12943 (@value{GDBP}) echo Hello World
12944 <<<---Hello World--->>>
12949 You can define a hook for any single-word command in @value{GDBN}, but
12950 not for command aliases; you should define a hook for the basic command
12951 name, e.g. @code{backtrace} rather than @code{bt}.
12952 @c FIXME! So how does Joe User discover whether a command is an alias
12954 If an error occurs during the execution of your hook, execution of
12955 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12956 (before the command that you actually typed had a chance to run).
12958 If you try to define a hook which does not match any known command, you
12959 get a warning from the @code{define} command.
12961 @node Command Files
12962 @section Command files
12964 @cindex command files
12965 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12966 commands. Comments (lines starting with @kbd{#}) may also be included.
12967 An empty line in a command file does nothing; it does not mean to repeat
12968 the last command, as it would from the terminal.
12971 @cindex @file{.gdbinit}
12972 @cindex @file{gdb.ini}
12973 When you start @value{GDBN}, it automatically executes commands from its
12974 @dfn{init files}. These are files named @file{.gdbinit} on Unix and
12975 @file{gdb.ini} on DOS/Windows. During startup, @value{GDBN} does the
12980 Reads the init file (if any) in your home directory@footnote{On
12981 DOS/Windows systems, the home directory is the one pointed to by the
12982 @code{HOME} environment variable.}.
12985 Processes command line options and operands.
12988 Reads the init file (if any) in the current working directory.
12991 Reads command files specified by the @samp{-x} option.
12994 The init file in your home directory can set options (such as @samp{set
12995 complaints}) that affect subsequent processing of command line options
12996 and operands. Init files are not executed if you use the @samp{-nx}
12997 option (@pxref{Mode Options, ,Choosing modes}).
12999 @cindex init file name
13000 On some configurations of @value{GDBN}, the init file is known by a
13001 different name (these are typically environments where a specialized
13002 form of @value{GDBN} may need to coexist with other forms, hence a
13003 different name for the specialized version's init file). These are the
13004 environments with special init file names:
13006 @cindex @file{.vxgdbinit}
13009 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13011 @cindex @file{.os68gdbinit}
13013 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13015 @cindex @file{.esgdbinit}
13017 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13020 You can also request the execution of a command file with the
13021 @code{source} command:
13025 @item source @var{filename}
13026 Execute the command file @var{filename}.
13029 The lines in a command file are executed sequentially. They are not
13030 printed as they are executed. An error in any command terminates execution
13031 of the command file.
13033 Commands that would ask for confirmation if used interactively proceed
13034 without asking when used in a command file. Many @value{GDBN} commands that
13035 normally print messages to say what they are doing omit the messages
13036 when called from command files.
13039 @section Commands for controlled output
13041 During the execution of a command file or a user-defined command, normal
13042 @value{GDBN} output is suppressed; the only output that appears is what is
13043 explicitly printed by the commands in the definition. This section
13044 describes three commands useful for generating exactly the output you
13049 @item echo @var{text}
13050 @c I do not consider backslash-space a standard C escape sequence
13051 @c because it is not in ANSI.
13052 Print @var{text}. Nonprinting characters can be included in
13053 @var{text} using C escape sequences, such as @samp{\n} to print a
13054 newline. @strong{No newline is printed unless you specify one.}
13055 In addition to the standard C escape sequences, a backslash followed
13056 by a space stands for a space. This is useful for displaying a
13057 string with spaces at the beginning or the end, since leading and
13058 trailing spaces are otherwise trimmed from all arguments.
13059 To print @samp{@w{ }and foo =@w{ }}, use the command
13060 @samp{echo \@w{ }and foo = \@w{ }}.
13062 A backslash at the end of @var{text} can be used, as in C, to continue
13063 the command onto subsequent lines. For example,
13066 echo This is some text\n\
13067 which is continued\n\
13068 onto several lines.\n
13071 produces the same output as
13074 echo This is some text\n
13075 echo which is continued\n
13076 echo onto several lines.\n
13080 @item output @var{expression}
13081 Print the value of @var{expression} and nothing but that value: no
13082 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13083 value history either. @xref{Expressions, ,Expressions}, for more information
13086 @item output/@var{fmt} @var{expression}
13087 Print the value of @var{expression} in format @var{fmt}. You can use
13088 the same formats as for @code{print}. @xref{Output Formats,,Output
13089 formats}, for more information.
13092 @item printf @var{string}, @var{expressions}@dots{}
13093 Print the values of the @var{expressions} under the control of
13094 @var{string}. The @var{expressions} are separated by commas and may be
13095 either numbers or pointers. Their values are printed as specified by
13096 @var{string}, exactly as if your program were to execute the C
13098 @c FIXME: the above implies that at least all ANSI C formats are
13099 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13100 @c Either this is a bug, or the manual should document what formats are
13104 printf (@var{string}, @var{expressions}@dots{});
13107 For example, you can print two values in hex like this:
13110 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13113 The only backslash-escape sequences that you can use in the format
13114 string are the simple ones that consist of backslash followed by a
13119 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13122 @cindex @sc{gnu} Emacs
13123 A special interface allows you to use @sc{gnu} Emacs to view (and
13124 edit) the source files for the program you are debugging with
13127 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13128 executable file you want to debug as an argument. This command starts
13129 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13130 created Emacs buffer.
13131 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13133 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13138 All ``terminal'' input and output goes through the Emacs buffer.
13141 This applies both to @value{GDBN} commands and their output, and to the input
13142 and output done by the program you are debugging.
13144 This is useful because it means that you can copy the text of previous
13145 commands and input them again; you can even use parts of the output
13148 All the facilities of Emacs' Shell mode are available for interacting
13149 with your program. In particular, you can send signals the usual
13150 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13155 @value{GDBN} displays source code through Emacs.
13158 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13159 source file for that frame and puts an arrow (@samp{=>}) at the
13160 left margin of the current line. Emacs uses a separate buffer for
13161 source display, and splits the screen to show both your @value{GDBN} session
13164 Explicit @value{GDBN} @code{list} or search commands still produce output as
13165 usual, but you probably have no reason to use them from Emacs.
13168 @emph{Warning:} If the directory where your program resides is not your
13169 current directory, it can be easy to confuse Emacs about the location of
13170 the source files, in which case the auxiliary display buffer does not
13171 appear to show your source. @value{GDBN} can find programs by searching your
13172 environment's @code{PATH} variable, so the @value{GDBN} input and output
13173 session proceeds normally; but Emacs does not get enough information
13174 back from @value{GDBN} to locate the source files in this situation. To
13175 avoid this problem, either start @value{GDBN} mode from the directory where
13176 your program resides, or specify an absolute file name when prompted for the
13177 @kbd{M-x gdb} argument.
13179 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13180 switch to debugging a program in some other location, from an existing
13181 @value{GDBN} buffer in Emacs.
13184 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13185 you need to call @value{GDBN} by a different name (for example, if you keep
13186 several configurations around, with different names) you can set the
13187 Emacs variable @code{gdb-command-name}; for example,
13190 (setq gdb-command-name "mygdb")
13194 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13195 in your @file{.emacs} file) makes Emacs call the program named
13196 ``@code{mygdb}'' instead.
13198 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13199 addition to the standard Shell mode commands:
13203 Describe the features of Emacs' @value{GDBN} Mode.
13206 Execute to another source line, like the @value{GDBN} @code{step} command; also
13207 update the display window to show the current file and location.
13210 Execute to next source line in this function, skipping all function
13211 calls, like the @value{GDBN} @code{next} command. Then update the display window
13212 to show the current file and location.
13215 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13216 display window accordingly.
13218 @item M-x gdb-nexti
13219 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13220 display window accordingly.
13223 Execute until exit from the selected stack frame, like the @value{GDBN}
13224 @code{finish} command.
13227 Continue execution of your program, like the @value{GDBN} @code{continue}
13230 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13233 Go up the number of frames indicated by the numeric argument
13234 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13235 like the @value{GDBN} @code{up} command.
13237 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13240 Go down the number of frames indicated by the numeric argument, like the
13241 @value{GDBN} @code{down} command.
13243 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13246 Read the number where the cursor is positioned, and insert it at the end
13247 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13248 around an address that was displayed earlier, type @kbd{disassemble};
13249 then move the cursor to the address display, and pick up the
13250 argument for @code{disassemble} by typing @kbd{C-x &}.
13252 You can customize this further by defining elements of the list
13253 @code{gdb-print-command}; once it is defined, you can format or
13254 otherwise process numbers picked up by @kbd{C-x &} before they are
13255 inserted. A numeric argument to @kbd{C-x &} indicates that you
13256 wish special formatting, and also acts as an index to pick an element of the
13257 list. If the list element is a string, the number to be inserted is
13258 formatted using the Emacs function @code{format}; otherwise the number
13259 is passed as an argument to the corresponding list element.
13262 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13263 tells @value{GDBN} to set a breakpoint on the source line point is on.
13265 If you accidentally delete the source-display buffer, an easy way to get
13266 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13267 request a frame display; when you run under Emacs, this recreates
13268 the source buffer if necessary to show you the context of the current
13271 The source files displayed in Emacs are in ordinary Emacs buffers
13272 which are visiting the source files in the usual way. You can edit
13273 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13274 communicates with Emacs in terms of line numbers. If you add or
13275 delete lines from the text, the line numbers that @value{GDBN} knows cease
13276 to correspond properly with the code.
13278 @c The following dropped because Epoch is nonstandard. Reactivate
13279 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13281 @kindex Emacs Epoch environment
13285 Version 18 of @sc{gnu} Emacs has a built-in window system
13286 called the @code{epoch}
13287 environment. Users of this environment can use a new command,
13288 @code{inspect} which performs identically to @code{print} except that
13289 each value is printed in its own window.
13292 @include annotate.texi
13293 @include gdbmi.texinfo
13296 @chapter Reporting Bugs in @value{GDBN}
13297 @cindex bugs in @value{GDBN}
13298 @cindex reporting bugs in @value{GDBN}
13300 Your bug reports play an essential role in making @value{GDBN} reliable.
13302 Reporting a bug may help you by bringing a solution to your problem, or it
13303 may not. But in any case the principal function of a bug report is to help
13304 the entire community by making the next version of @value{GDBN} work better. Bug
13305 reports are your contribution to the maintenance of @value{GDBN}.
13307 In order for a bug report to serve its purpose, you must include the
13308 information that enables us to fix the bug.
13311 * Bug Criteria:: Have you found a bug?
13312 * Bug Reporting:: How to report bugs
13316 @section Have you found a bug?
13317 @cindex bug criteria
13319 If you are not sure whether you have found a bug, here are some guidelines:
13322 @cindex fatal signal
13323 @cindex debugger crash
13324 @cindex crash of debugger
13326 If the debugger gets a fatal signal, for any input whatever, that is a
13327 @value{GDBN} bug. Reliable debuggers never crash.
13329 @cindex error on valid input
13331 If @value{GDBN} produces an error message for valid input, that is a
13332 bug. (Note that if you're cross debugging, the problem may also be
13333 somewhere in the connection to the target.)
13335 @cindex invalid input
13337 If @value{GDBN} does not produce an error message for invalid input,
13338 that is a bug. However, you should note that your idea of
13339 ``invalid input'' might be our idea of ``an extension'' or ``support
13340 for traditional practice''.
13343 If you are an experienced user of debugging tools, your suggestions
13344 for improvement of @value{GDBN} are welcome in any case.
13347 @node Bug Reporting
13348 @section How to report bugs
13349 @cindex bug reports
13350 @cindex @value{GDBN} bugs, reporting
13352 A number of companies and individuals offer support for @sc{gnu} products.
13353 If you obtained @value{GDBN} from a support organization, we recommend you
13354 contact that organization first.
13356 You can find contact information for many support companies and
13357 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13359 @c should add a web page ref...
13361 In any event, we also recommend that you send bug reports for
13362 @value{GDBN} to this addresses:
13368 @strong{Do not send bug reports to @samp{info-gdb}, or to
13369 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13370 not want to receive bug reports. Those that do have arranged to receive
13373 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13374 serves as a repeater. The mailing list and the newsgroup carry exactly
13375 the same messages. Often people think of posting bug reports to the
13376 newsgroup instead of mailing them. This appears to work, but it has one
13377 problem which can be crucial: a newsgroup posting often lacks a mail
13378 path back to the sender. Thus, if we need to ask for more information,
13379 we may be unable to reach you. For this reason, it is better to send
13380 bug reports to the mailing list.
13382 As a last resort, send bug reports on paper to:
13385 @sc{gnu} Debugger Bugs
13386 Free Software Foundation Inc.
13387 59 Temple Place - Suite 330
13388 Boston, MA 02111-1307
13392 The fundamental principle of reporting bugs usefully is this:
13393 @strong{report all the facts}. If you are not sure whether to state a
13394 fact or leave it out, state it!
13396 Often people omit facts because they think they know what causes the
13397 problem and assume that some details do not matter. Thus, you might
13398 assume that the name of the variable you use in an example does not matter.
13399 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13400 stray memory reference which happens to fetch from the location where that
13401 name is stored in memory; perhaps, if the name were different, the contents
13402 of that location would fool the debugger into doing the right thing despite
13403 the bug. Play it safe and give a specific, complete example. That is the
13404 easiest thing for you to do, and the most helpful.
13406 Keep in mind that the purpose of a bug report is to enable us to fix the
13407 bug. It may be that the bug has been reported previously, but neither
13408 you nor we can know that unless your bug report is complete and
13411 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13412 bell?'' Those bug reports are useless, and we urge everyone to
13413 @emph{refuse to respond to them} except to chide the sender to report
13416 To enable us to fix the bug, you should include all these things:
13420 The version of @value{GDBN}. @value{GDBN} announces it if you start
13421 with no arguments; you can also print it at any time using @code{show
13424 Without this, we will not know whether there is any point in looking for
13425 the bug in the current version of @value{GDBN}.
13428 The type of machine you are using, and the operating system name and
13432 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13433 ``@value{GCC}--2.8.1''.
13436 What compiler (and its version) was used to compile the program you are
13437 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13438 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13439 information; for other compilers, see the documentation for those
13443 The command arguments you gave the compiler to compile your example and
13444 observe the bug. For example, did you use @samp{-O}? To guarantee
13445 you will not omit something important, list them all. A copy of the
13446 Makefile (or the output from make) is sufficient.
13448 If we were to try to guess the arguments, we would probably guess wrong
13449 and then we might not encounter the bug.
13452 A complete input script, and all necessary source files, that will
13456 A description of what behavior you observe that you believe is
13457 incorrect. For example, ``It gets a fatal signal.''
13459 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13460 will certainly notice it. But if the bug is incorrect output, we might
13461 not notice unless it is glaringly wrong. You might as well not give us
13462 a chance to make a mistake.
13464 Even if the problem you experience is a fatal signal, you should still
13465 say so explicitly. Suppose something strange is going on, such as, your
13466 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13467 the C library on your system. (This has happened!) Your copy might
13468 crash and ours would not. If you told us to expect a crash, then when
13469 ours fails to crash, we would know that the bug was not happening for
13470 us. If you had not told us to expect a crash, then we would not be able
13471 to draw any conclusion from our observations.
13474 If you wish to suggest changes to the @value{GDBN} source, send us context
13475 diffs. If you even discuss something in the @value{GDBN} source, refer to
13476 it by context, not by line number.
13478 The line numbers in our development sources will not match those in your
13479 sources. Your line numbers would convey no useful information to us.
13483 Here are some things that are not necessary:
13487 A description of the envelope of the bug.
13489 Often people who encounter a bug spend a lot of time investigating
13490 which changes to the input file will make the bug go away and which
13491 changes will not affect it.
13493 This is often time consuming and not very useful, because the way we
13494 will find the bug is by running a single example under the debugger
13495 with breakpoints, not by pure deduction from a series of examples.
13496 We recommend that you save your time for something else.
13498 Of course, if you can find a simpler example to report @emph{instead}
13499 of the original one, that is a convenience for us. Errors in the
13500 output will be easier to spot, running under the debugger will take
13501 less time, and so on.
13503 However, simplification is not vital; if you do not want to do this,
13504 report the bug anyway and send us the entire test case you used.
13507 A patch for the bug.
13509 A patch for the bug does help us if it is a good one. But do not omit
13510 the necessary information, such as the test case, on the assumption that
13511 a patch is all we need. We might see problems with your patch and decide
13512 to fix the problem another way, or we might not understand it at all.
13514 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13515 construct an example that will make the program follow a certain path
13516 through the code. If you do not send us the example, we will not be able
13517 to construct one, so we will not be able to verify that the bug is fixed.
13519 And if we cannot understand what bug you are trying to fix, or why your
13520 patch should be an improvement, we will not install it. A test case will
13521 help us to understand.
13524 A guess about what the bug is or what it depends on.
13526 Such guesses are usually wrong. Even we cannot guess right about such
13527 things without first using the debugger to find the facts.
13530 @c The readline documentation is distributed with the readline code
13531 @c and consists of the two following files:
13533 @c inc-hist.texinfo
13534 @c Use -I with makeinfo to point to the appropriate directory,
13535 @c environment var TEXINPUTS with TeX.
13536 @include rluser.texinfo
13537 @include inc-hist.texinfo
13540 @node Formatting Documentation
13541 @appendix Formatting Documentation
13543 @cindex @value{GDBN} reference card
13544 @cindex reference card
13545 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13546 for printing with PostScript or Ghostscript, in the @file{gdb}
13547 subdirectory of the main source directory@footnote{In
13548 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13549 release.}. If you can use PostScript or Ghostscript with your printer,
13550 you can print the reference card immediately with @file{refcard.ps}.
13552 The release also includes the source for the reference card. You
13553 can format it, using @TeX{}, by typing:
13559 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13560 mode on US ``letter'' size paper;
13561 that is, on a sheet 11 inches wide by 8.5 inches
13562 high. You will need to specify this form of printing as an option to
13563 your @sc{dvi} output program.
13565 @cindex documentation
13567 All the documentation for @value{GDBN} comes as part of the machine-readable
13568 distribution. The documentation is written in Texinfo format, which is
13569 a documentation system that uses a single source file to produce both
13570 on-line information and a printed manual. You can use one of the Info
13571 formatting commands to create the on-line version of the documentation
13572 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13574 @value{GDBN} includes an already formatted copy of the on-line Info
13575 version of this manual in the @file{gdb} subdirectory. The main Info
13576 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13577 subordinate files matching @samp{gdb.info*} in the same directory. If
13578 necessary, you can print out these files, or read them with any editor;
13579 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13580 Emacs or the standalone @code{info} program, available as part of the
13581 @sc{gnu} Texinfo distribution.
13583 If you want to format these Info files yourself, you need one of the
13584 Info formatting programs, such as @code{texinfo-format-buffer} or
13587 If you have @code{makeinfo} installed, and are in the top level
13588 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13589 version @value{GDBVN}), you can make the Info file by typing:
13596 If you want to typeset and print copies of this manual, you need @TeX{},
13597 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13598 Texinfo definitions file.
13600 @TeX{} is a typesetting program; it does not print files directly, but
13601 produces output files called @sc{dvi} files. To print a typeset
13602 document, you need a program to print @sc{dvi} files. If your system
13603 has @TeX{} installed, chances are it has such a program. The precise
13604 command to use depends on your system; @kbd{lpr -d} is common; another
13605 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
13606 require a file name without any extension or a @samp{.dvi} extension.
13608 @TeX{} also requires a macro definitions file called
13609 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
13610 written in Texinfo format. On its own, @TeX{} cannot either read or
13611 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
13612 and is located in the @file{gdb-@var{version-number}/texinfo}
13615 If you have @TeX{} and a @sc{dvi} printer program installed, you can
13616 typeset and print this manual. First switch to the the @file{gdb}
13617 subdirectory of the main source directory (for example, to
13618 @file{gdb-@value{GDBVN}/gdb}) and type:
13624 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
13626 @node Installing GDB
13627 @appendix Installing @value{GDBN}
13628 @cindex configuring @value{GDBN}
13629 @cindex installation
13631 @value{GDBN} comes with a @code{configure} script that automates the process
13632 of preparing @value{GDBN} for installation; you can then use @code{make} to
13633 build the @code{gdb} program.
13635 @c irrelevant in info file; it's as current as the code it lives with.
13636 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
13637 look at the @file{README} file in the sources; we may have improved the
13638 installation procedures since publishing this manual.}
13641 The @value{GDBN} distribution includes all the source code you need for
13642 @value{GDBN} in a single directory, whose name is usually composed by
13643 appending the version number to @samp{gdb}.
13645 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
13646 @file{gdb-@value{GDBVN}} directory. That directory contains:
13649 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
13650 script for configuring @value{GDBN} and all its supporting libraries
13652 @item gdb-@value{GDBVN}/gdb
13653 the source specific to @value{GDBN} itself
13655 @item gdb-@value{GDBVN}/bfd
13656 source for the Binary File Descriptor library
13658 @item gdb-@value{GDBVN}/include
13659 @sc{gnu} include files
13661 @item gdb-@value{GDBVN}/libiberty
13662 source for the @samp{-liberty} free software library
13664 @item gdb-@value{GDBVN}/opcodes
13665 source for the library of opcode tables and disassemblers
13667 @item gdb-@value{GDBVN}/readline
13668 source for the @sc{gnu} command-line interface
13670 @item gdb-@value{GDBVN}/glob
13671 source for the @sc{gnu} filename pattern-matching subroutine
13673 @item gdb-@value{GDBVN}/mmalloc
13674 source for the @sc{gnu} memory-mapped malloc package
13677 The simplest way to configure and build @value{GDBN} is to run @code{configure}
13678 from the @file{gdb-@var{version-number}} source directory, which in
13679 this example is the @file{gdb-@value{GDBVN}} directory.
13681 First switch to the @file{gdb-@var{version-number}} source directory
13682 if you are not already in it; then run @code{configure}. Pass the
13683 identifier for the platform on which @value{GDBN} will run as an
13689 cd gdb-@value{GDBVN}
13690 ./configure @var{host}
13695 where @var{host} is an identifier such as @samp{sun4} or
13696 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
13697 (You can often leave off @var{host}; @code{configure} tries to guess the
13698 correct value by examining your system.)
13700 Running @samp{configure @var{host}} and then running @code{make} builds the
13701 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
13702 libraries, then @code{gdb} itself. The configured source files, and the
13703 binaries, are left in the corresponding source directories.
13706 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
13707 system does not recognize this automatically when you run a different
13708 shell, you may need to run @code{sh} on it explicitly:
13711 sh configure @var{host}
13714 If you run @code{configure} from a directory that contains source
13715 directories for multiple libraries or programs, such as the
13716 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
13717 creates configuration files for every directory level underneath (unless
13718 you tell it not to, with the @samp{--norecursion} option).
13720 You can run the @code{configure} script from any of the
13721 subordinate directories in the @value{GDBN} distribution if you only want to
13722 configure that subdirectory, but be sure to specify a path to it.
13724 For example, with version @value{GDBVN}, type the following to configure only
13725 the @code{bfd} subdirectory:
13729 cd gdb-@value{GDBVN}/bfd
13730 ../configure @var{host}
13734 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
13735 However, you should make sure that the shell on your path (named by
13736 the @samp{SHELL} environment variable) is publicly readable. Remember
13737 that @value{GDBN} uses the shell to start your program---some systems refuse to
13738 let @value{GDBN} debug child processes whose programs are not readable.
13741 * Separate Objdir:: Compiling @value{GDBN} in another directory
13742 * Config Names:: Specifying names for hosts and targets
13743 * Configure Options:: Summary of options for configure
13746 @node Separate Objdir
13747 @section Compiling @value{GDBN} in another directory
13749 If you want to run @value{GDBN} versions for several host or target machines,
13750 you need a different @code{gdb} compiled for each combination of
13751 host and target. @code{configure} is designed to make this easy by
13752 allowing you to generate each configuration in a separate subdirectory,
13753 rather than in the source directory. If your @code{make} program
13754 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
13755 @code{make} in each of these directories builds the @code{gdb}
13756 program specified there.
13758 To build @code{gdb} in a separate directory, run @code{configure}
13759 with the @samp{--srcdir} option to specify where to find the source.
13760 (You also need to specify a path to find @code{configure}
13761 itself from your working directory. If the path to @code{configure}
13762 would be the same as the argument to @samp{--srcdir}, you can leave out
13763 the @samp{--srcdir} option; it is assumed.)
13765 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
13766 separate directory for a Sun 4 like this:
13770 cd gdb-@value{GDBVN}
13773 ../gdb-@value{GDBVN}/configure sun4
13778 When @code{configure} builds a configuration using a remote source
13779 directory, it creates a tree for the binaries with the same structure
13780 (and using the same names) as the tree under the source directory. In
13781 the example, you'd find the Sun 4 library @file{libiberty.a} in the
13782 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
13783 @file{gdb-sun4/gdb}.
13785 One popular reason to build several @value{GDBN} configurations in separate
13786 directories is to configure @value{GDBN} for cross-compiling (where
13787 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
13788 programs that run on another machine---the @dfn{target}).
13789 You specify a cross-debugging target by
13790 giving the @samp{--target=@var{target}} option to @code{configure}.
13792 When you run @code{make} to build a program or library, you must run
13793 it in a configured directory---whatever directory you were in when you
13794 called @code{configure} (or one of its subdirectories).
13796 The @code{Makefile} that @code{configure} generates in each source
13797 directory also runs recursively. If you type @code{make} in a source
13798 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
13799 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
13800 will build all the required libraries, and then build GDB.
13802 When you have multiple hosts or targets configured in separate
13803 directories, you can run @code{make} on them in parallel (for example,
13804 if they are NFS-mounted on each of the hosts); they will not interfere
13808 @section Specifying names for hosts and targets
13810 The specifications used for hosts and targets in the @code{configure}
13811 script are based on a three-part naming scheme, but some short predefined
13812 aliases are also supported. The full naming scheme encodes three pieces
13813 of information in the following pattern:
13816 @var{architecture}-@var{vendor}-@var{os}
13819 For example, you can use the alias @code{sun4} as a @var{host} argument,
13820 or as the value for @var{target} in a @code{--target=@var{target}}
13821 option. The equivalent full name is @samp{sparc-sun-sunos4}.
13823 The @code{configure} script accompanying @value{GDBN} does not provide
13824 any query facility to list all supported host and target names or
13825 aliases. @code{configure} calls the Bourne shell script
13826 @code{config.sub} to map abbreviations to full names; you can read the
13827 script, if you wish, or you can use it to test your guesses on
13828 abbreviations---for example:
13831 % sh config.sub i386-linux
13833 % sh config.sub alpha-linux
13834 alpha-unknown-linux-gnu
13835 % sh config.sub hp9k700
13837 % sh config.sub sun4
13838 sparc-sun-sunos4.1.1
13839 % sh config.sub sun3
13840 m68k-sun-sunos4.1.1
13841 % sh config.sub i986v
13842 Invalid configuration `i986v': machine `i986v' not recognized
13846 @code{config.sub} is also distributed in the @value{GDBN} source
13847 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
13849 @node Configure Options
13850 @section @code{configure} options
13852 Here is a summary of the @code{configure} options and arguments that
13853 are most often useful for building @value{GDBN}. @code{configure} also has
13854 several other options not listed here. @inforef{What Configure
13855 Does,,configure.info}, for a full explanation of @code{configure}.
13858 configure @r{[}--help@r{]}
13859 @r{[}--prefix=@var{dir}@r{]}
13860 @r{[}--exec-prefix=@var{dir}@r{]}
13861 @r{[}--srcdir=@var{dirname}@r{]}
13862 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
13863 @r{[}--target=@var{target}@r{]}
13868 You may introduce options with a single @samp{-} rather than
13869 @samp{--} if you prefer; but you may abbreviate option names if you use
13874 Display a quick summary of how to invoke @code{configure}.
13876 @item --prefix=@var{dir}
13877 Configure the source to install programs and files under directory
13880 @item --exec-prefix=@var{dir}
13881 Configure the source to install programs under directory
13884 @c avoid splitting the warning from the explanation:
13886 @item --srcdir=@var{dirname}
13887 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
13888 @code{make} that implements the @code{VPATH} feature.}@*
13889 Use this option to make configurations in directories separate from the
13890 @value{GDBN} source directories. Among other things, you can use this to
13891 build (or maintain) several configurations simultaneously, in separate
13892 directories. @code{configure} writes configuration specific files in
13893 the current directory, but arranges for them to use the source in the
13894 directory @var{dirname}. @code{configure} creates directories under
13895 the working directory in parallel to the source directories below
13898 @item --norecursion
13899 Configure only the directory level where @code{configure} is executed; do not
13900 propagate configuration to subdirectories.
13902 @item --target=@var{target}
13903 Configure @value{GDBN} for cross-debugging programs running on the specified
13904 @var{target}. Without this option, @value{GDBN} is configured to debug
13905 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
13907 There is no convenient way to generate a list of all available targets.
13909 @item @var{host} @dots{}
13910 Configure @value{GDBN} to run on the specified @var{host}.
13912 There is no convenient way to generate a list of all available hosts.
13915 There are many other options available as well, but they are generally
13916 needed for special purposes only.
13924 % I think something like @colophon should be in texinfo. In the
13926 \long\def\colophon{\hbox to0pt{}\vfill
13927 \centerline{The body of this manual is set in}
13928 \centerline{\fontname\tenrm,}
13929 \centerline{with headings in {\bf\fontname\tenbf}}
13930 \centerline{and examples in {\tt\fontname\tentt}.}
13931 \centerline{{\it\fontname\tenit\/},}
13932 \centerline{{\bf\fontname\tenbf}, and}
13933 \centerline{{\sl\fontname\tensl\/}}
13934 \centerline{are used for emphasis.}\vfill}
13936 % Blame: doc@cygnus.com, 1991.
13939 @c TeX can handle the contents at the start but makeinfo 3.12 can not