gdb(1)
GDB(1) GNU Development Tools GDB(1)
NAME
gdb - The GNU Debugger
SYNOPSIS
gdb [-help] [-nh] [-nx] [-q] [-batch] [-cd=dir] [-f]
[-b bps]
[-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core]
[-p procID]
[-x cmds] [-d dir] [prog|prog procID|prog core]
DESCRIPTION
The purpose of a debugger such as GDB is to allow you to see
what is going on "inside" another program while it executes
-- or what another program was doing at the moment it
crashed.
GDB can do four main kinds of things (plus other things in
support of these) to help you catch bugs in the act:
o Start your program, specifying anything that might
affect its behavior.
o Make your program stop on specified conditions.
o Examine what has happened, when your program has
stopped.
o Change things in your program, so you can experiment
with correcting the effects of one bug and go on to
learn about another.
You can use GDB to debug programs written in C, C@t{++},
Fortran and Modula-2.
GDB is invoked with the shell command "gdb". Once started,
it reads commands from the terminal until you tell it to
exit with the GDB command "quit". You can get online help
from GDB itself by using the command "help".
You can run "gdb" with no arguments or options; but the most
usual way to start GDB is with one argument or two,
specifying an executable program as the argument:
gdb program
You can also start with both an executable program and a
core file specified:
gdb program core
You can, instead, specify a process ID as a second argument,
if you want to debug a running process:
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gdb program 1234
gdb -p 1234
would attach GDB to process 1234 (unless you also have a
file named 1234; GDB does check for a core file first).
With option -p you can omit the program filename.
Here are some of the most frequently needed GDB commands:
break [file:]function
Set a breakpoint at function (in file).
run [arglist]
Start your program (with arglist, if specified).
bt Backtrace: display the program stack.
print expr
Display the value of an expression.
c Continue running your program (after stopping, e.g. at a
breakpoint).
next
Execute next program line (after stopping); step over
any function calls in the line.
edit [file:]function
look at the program line where it is presently stopped.
list [file:]function
type the text of the program in the vicinity of where it
is presently stopped.
step
Execute next program line (after stopping); step into
any function calls in the line.
help [name]
Show information about GDB command name, or general
information about using GDB.
quit
Exit from GDB.
For full details on GDB, see Using GDB: A Guide to the GNU
Source-Level Debugger, by Richard M. Stallman and Roland H.
Pesch. The same text is available online as the "gdb" entry
in the "info" program.
OPTIONS
Any arguments other than options specify an executable file
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and core file (or process ID); that is, the first argument
encountered with no associated option flag is equivalent to
a -se option, and the second, if any, is equivalent to a -c
option if it's the name of a file. Many options have both
long and short forms; both are shown here. The long forms
are also recognized if you truncate them, so long as enough
of the option is present to be unambiguous. (If you prefer,
you can flag option arguments with + rather than -, though
we illustrate the more usual convention.)
All the options and command line arguments you give are
processed in sequential order. The order makes a difference
when the -x option is used.
-help
-h List all options, with brief explanations.
-symbols=file
-s file
Read symbol table from file file.
-write
Enable writing into executable and core files.
-exec=file
-e file
Use file file as the executable file to execute when
appropriate, and for examining pure data in conjunction
with a core dump.
-se=file
Read symbol table from file file and use it as the
executable file.
-core=file
-c file
Use file file as a core dump to examine.
-command=file
-x file
Execute GDB commands from file file.
-ex command
Execute given GDB command.
-directory=directory
-d directory
Add directory to the path to search for source files.
-nh Do not execute commands from ~/.gdbinit.
-nx
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-n Do not execute commands from any .gdbinit initialization
files.
-quiet
-q "Quiet". Do not print the introductory and copyright
messages. These messages are also suppressed in batch
mode.
-batch
Run in batch mode. Exit with status 0 after processing
all the command files specified with -x (and .gdbinit,
if not inhibited). Exit with nonzero status if an error
occurs in executing the GDB commands in the command
files.
Batch mode may be useful for running GDB as a filter,
for example to download and run a program on another
computer; in order to make this more useful, the message
Program exited normally.
(which is ordinarily issued whenever a program running
under GDB control terminates) is not issued when running
in batch mode.
-cd=directory
Run GDB using directory as its working directory,
instead of the current directory.
-fullname
-f Emacs sets this option when it runs GDB as a subprocess.
It tells GDB to output the full file name and line
number in a standard, recognizable fashion each time a
stack frame is displayed (which includes each time the
program stops). This recognizable format looks like two
\032 characters, followed by the file name, line number
and character position separated by colons, and a
newline. The Emacs-to-GDB interface program uses the
two \032 characters as a signal to display the source
code for the frame.
-b bps
Set the line speed (baud rate or bits per second) of any
serial interface used by GDB for remote debugging.
-tty=device
Run using device for your program's standard input and
output.
SEE ALSO
The full documentation for GDB is maintained as a Texinfo
manual. If the "info" and "gdb" programs and GDB's Texinfo
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documentation are properly installed at your site, the
command
info gdb
should give you access to the complete manual.
Using GDB: A Guide to the GNU Source-Level Debugger, Richard
M. Stallman and Roland H. Pesch, July 1991.
COPYRIGHT
Copyright (c) 1988-2018 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation
License, Version 1.3 or any later version published by the
Free Software Foundation; with the Invariant Sections being
"Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU
Manual," and with the Back-Cover Texts as in (a) below.
(a) The FSF's Back-Cover Text is: "You are free to copy and
modify this GNU Manual. Buying copies from GNU Press
supports the FSF in developing GNU and promoting software
freedom."
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