1GDB(1) GNU Development Tools GDB(1)
2
6 gdb - The GNU Debugger
7
9 gdb [-help] [-nh] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps]
10 [-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core] [-p procID]
11 [-x cmds] [-d dir] [prog|prog procID|prog core]
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
22 behavior.
23 · Make your program stop on specified conditions.
25 · Examine what has happened, when your program has stopped.
27 · Change things in your program, so you can experiment with
29 correcting the effects of one bug and go on to learn about another.
30 You can use GDB to debug programs written in C, C@t{++}, Fortran and
32 Modula-2.
33 GDB is invoked with the shell command "gdb". Once started, it reads
35 commands from the terminal until you tell it to exit with the GDB
36 command "quit". You can get online help from GDB itself by using the
37 command "help".
38 You can run "gdb" with no arguments or options; but the most usual way
40 to start GDB is with one argument or two, specifying an executable
41 program as the argument:
42 gdb program
44 You can also start with both an executable program and a core file
46 specified:
47 gdb program core
49 You can, instead, specify a process ID as a second argument, if you
51 want to debug a running process:
52 gdb program 1234
54 gdb -p 1234
55 would attach GDB to process 1234 (unless you also have a file named
57 1234; GDB does check for a core file first). With option -p you can
58 omit the program filename.
59 Here are some of the most frequently needed GDB commands:
61 break [file:]function
63 Set a breakpoint at function (in file).
64 run [arglist]
66 Start your program (with arglist, if specified).
67 bt Backtrace: display the program stack.
69 print expr
71 Display the value of an expression.
72 c Continue running your program (after stopping, e.g. at a
74 breakpoint).
75 next
77 Execute next program line (after stopping); step over any function
78 calls in the line.
79 edit [file:]function
81 look at the program line where it is presently stopped.
82 list [file:]function
84 type the text of the program in the vicinity of where it is
85 presently stopped.
86 step
88 Execute next program line (after stopping); step into any function
89 calls in the line.
90 help [name]
92 Show information about GDB command name, or general information
93 about using GDB.
94 quit
96 Exit from GDB.
97 For full details on GDB, see Using GDB: A Guide to the GNU Source-Level
99 Debugger, by Richard M. Stallman and Roland H. Pesch. The same text is
100 available online as the "gdb" entry in the "info" program.
101
103 Any arguments other than options specify an executable file and core
104 file (or process ID); that is, the first argument encountered with no
105 associated option flag is equivalent to a -se option, and the second,
106 if any, is equivalent to a -c option if it's the name of a file. Many
107 options have both long and short forms; both are shown here. The long
108 forms are also recognized if you truncate them, so long as enough of
109 the option is present to be unambiguous. (If you prefer, you can flag
110 option arguments with + rather than -, though we illustrate the more
111 usual convention.)
112 All the options and command line arguments you give are processed in
114 sequential order. The order makes a difference when the -x option is
115 used.
116 -help
118 -h List all options, with brief explanations.
119 -symbols=file
121 -s file
122 Read symbol table from file file.
123 -write
125 Enable writing into executable and core files.
126 -exec=file
128 -e file
129 Use file file as the executable file to execute when appropriate,
130 and for examining pure data in conjunction with a core dump.
131 -se=file
133 Read symbol table from file file and use it as the executable file.
134 -core=file
136 -c file
137 Use file file as a core dump to examine.
138 -command=file
140 -x file
141 Execute GDB commands from file file.
142 -ex command
144 Execute given GDB command.
145 -directory=directory
147 -d directory
148 Add directory to the path to search for source files.
149 -nh Do not execute commands from ~/.gdbinit.
151 -nx
153 -n Do not execute commands from any .gdbinit initialization files.
154 -quiet
156 -q "Quiet". Do not print the introductory and copyright messages.
157 These messages are also suppressed in batch mode.
158 -batch
160 Run in batch mode. Exit with status 0 after processing all the
161 command files specified with -x (and .gdbinit, if not inhibited).
162 Exit with nonzero status if an error occurs in executing the GDB
163 commands in the command files.
164 Batch mode may be useful for running GDB as a filter, for example
166 to download and run a program on another computer; in order to make
167 this more useful, the message
168 Program exited normally.
170 (which is ordinarily issued whenever a program running under GDB
172 control terminates) is not issued when running in batch mode.
173 -cd=directory
175 Run GDB using directory as its working directory, instead of the
176 current directory.
177 -fullname
179 -f Emacs sets this option when it runs GDB as a subprocess. It tells
180 GDB to output the full file name and line number in a standard,
181 recognizable fashion each time a stack frame is displayed (which
182 includes each time the program stops). This recognizable format
183 looks like two \032 characters, followed by the file name, line
184 number and character position separated by colons, and a newline.
185 The Emacs-to-GDB interface program uses the two \032 characters as
186 a signal to display the source code for the frame.
187 -b bps
189 Set the line speed (baud rate or bits per second) of any serial
190 interface used by GDB for remote debugging.
191 -tty=device
193 Run using device for your program's standard input and output.
194
196 The full documentation for GDB is maintained as a Texinfo manual. If
197 the "info" and "gdb" programs and GDB's Texinfo documentation are
198 properly installed at your site, the command
199 info gdb
201 should give you access to the complete manual.
203 Using GDB: A Guide to the GNU Source-Level Debugger, Richard M.
205 Stallman and Roland H. Pesch, July 1991.
206
208 Copyright (c) 1988-2018 Free Software Foundation, Inc.
209 Permission is granted to copy, distribute and/or modify this document
211 under the terms of the GNU Free Documentation License, Version 1.3 or
212 any later version published by the Free Software Foundation; with the
213 Invariant Sections being "Free Software" and "Free Software Needs Free
214 Documentation", with the Front-Cover Texts being "A GNU Manual," and
215 with the Back-Cover Texts as in (a) below.
216 (a) The FSF's Back-Cover Text is: "You are free to copy and modify this
218 GNU Manual. Buying copies from GNU Press supports the FSF in
219 developing GNU and promoting software freedom."
220gdb-8.1 2018-07-25 GDB(1)