1gdb(1) GNU Tools gdb(1)
2
6 gdb - The GNU Debugger
7
9 gdb [-help] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev]
10 [-s symfile] [-e prog] [-se prog] [-c core] [-x cmds] [-d dir]
11 [prog[core|procID]]
12
14 The purpose of a debugger such as GDB is to allow you to see what is
15 going on ``inside'' another program while it executes—or what another
16 program was doing at the moment it crashed.
17 GDB can do four main kinds of things (plus other things in support of
19 these) to help you catch bugs in the act:
20 · Start your program, specifying anything that might affect its
23 behavior.
24 · Make your program stop on specified conditions.
27 · Examine what has happened, when your program has stopped.
30 · Change things in your program, so you can experiment with cor‐
33 recting the effects of one bug and go on to learn about another.
34 You can use GDB to debug programs written in C, C++, and Modula-2.
36 Fortran support will be added when a GNU Fortran compiler is ready.
37 GDB is invoked with the shell command gdb. Once started, it reads com‐
39 mands from the terminal until you tell it to exit with the GDB command
40 quit. You can get online help from gdb itself by using the command
41 help.
42 You can run gdb with no arguments or options; but the most usual way to
44 start GDB is with one argument or two, specifying an executable program
45 as the argument:
46 gdb program
48 You can also start with both an executable program and a core file
51 specified:
52 gdb program core
54 You can, instead, specify a process ID as a second argument, if you
57 want to debug a running process:
58 gdb program 1234
60 would attach GDB to process 1234 (unless you also have a file named
63 `1234'; GDB does check for a core file first).
64 Here are some of the most frequently needed GDB commands:
66 break [file:]function
68 Set a breakpoint at function (in file).
69 run [arglist]
71 Start your program (with arglist, if specified).
72 bt Backtrace: display the program stack.
74 print expr
76 Display the value of an expression.
77 c Continue running your program (after stopping, e.g. at a break‐
79 point).
80 next Execute next program line (after stopping); step over any func‐
82 tion calls in the line.
83 edit [file:]function
85 look at the program line where it is presently stopped.
86 list [file:]function
88 type the text of the program in the vicinity of where it is
89 presently stopped.
90 step Execute next program line (after stopping); step into any func‐
92 tion calls in the line.
93 help [name]
95 Show information about GDB command name, or general information
96 about using GDB.
97 quit Exit from GDB.
99 For full details on GDB, see Using GDB: A Guide to the GNU Source-Level
101 Debugger, by Richard M. Stallman and Roland H. Pesch. The same text is
102 available online as the gdb entry in the info program.
103
105 Any arguments other than options specify an executable file and core
106 file (or process ID); that is, the first argument encountered with no
107 associated option flag is equivalent to a `-se' option, and the second,
108 if any, is equivalent to a `-c' option if it's the name of a file.
109 Many options have both long and short forms; both are shown here. The
110 long forms are also recognized if you truncate them, so long as enough
111 of the option is present to be unambiguous. (If you prefer, you can
112 flag option arguments with `+' rather than `-', though we illustrate
113 the more usual convention.)
114 All the options and command line arguments you give are processed in
116 sequential order. The order makes a difference when the `-x' option is
117 used.
118 -help
121 -h List all options, with brief explanations.
123 -symbols=file
126 -s file
128 Read symbol table from file file.
129 -write Enable writing into executable and core files.
132 -exec=file
135 -e file
137 Use file file as the executable file to execute when appropri‐
138 ate, and for examining pure data in conjunction with a core
139 dump.
140 -se=file
143 Read symbol table from file file and use it as the executable
144 file.
145 -core=file
148 -c file
150 Use file file as a core dump to examine.
151 -command=file
154 -x file
156 Execute GDB commands from file file.
157 -directory=directory
160 -d directory
162 Add directory to the path to search for source files.
163 -nx
165 -n Do not execute commands from any `.gdbinit' initialization
167 files. Normally, the commands in these files are executed after
168 all the command options and arguments have been processed.
169 -quiet
173 -q ``Quiet''. Do not print the introductory and copyright mes‐
175 sages. These messages are also suppressed in batch mode.
176 -batch Run in batch mode. Exit with status 0 after processing all the
179 command files specified with `-x' (and `.gdbinit', if not inhib‐
180 ited). Exit with nonzero status if an error occurs in executing
181 the GDB commands in the command files.
182 Batch mode may be useful for running GDB as a filter, for exam‐
184 ple to download and run a program on another computer; in order
185 to make this more useful, the message
186 Program exited normally.
188 (which is ordinarily issued whenever a program running under GDB
191 control terminates) is not issued when running in batch mode.
192 -cd=directory
195 Run GDB using directory as its working directory, instead of
196 the current directory.
197 -fullname
200 -f Emacs sets this option when it runs GDB as a subprocess. It
202 tells GDB to output the full file name and line number in a
203 standard, recognizable fashion each time a stack frame is dis‐
204 played (which includes each time the program stops). This rec‐
205 ognizable format looks like two ` 32' characters, followed by
206 the file name, line number and character position separated by
207 colons, and a newline. The Emacs-to-GDB interface program uses
208 the two ` 32' characters as a signal to display the source code
209 for the frame.
210 -b bps Set the line speed (baud rate or bits per second) of any serial
213 interface used by GDB for remote debugging.
214 -tty=device
217 Run using device for your program's standard input and output.
218
220 `gdb' entry in info; Using GDB: A Guide to the GNU Source-Level Debug‐
221 ger, Richard M. Stallman and Roland H. Pesch, July 1991.
222
224 Copyright (c) 1991 Free Software Foundation, Inc.
225 Permission is granted to make and distribute verbatim copies of this
227 manual provided the copyright notice and this permission notice are
228 preserved on all copies.
229 Permission is granted to copy and distribute modified versions of this
231 manual under the conditions for verbatim copying, provided that the
232 entire resulting derived work is distributed under the terms of a per‐
233 mission notice identical to this one.
234 Permission is granted to copy and distribute translations of this man‐
236 ual into another language, under the above conditions for modified ver‐
237 sions, except that this permission notice may be included in transla‐
238 tions approved by the Free Software Foundation instead of in the origi‐
239 nal English.
240GNU Tools 22may2002 gdb(1)