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gdb man

gdb man

gdb [OPTIONS] [prog|prog procID|prog core]

The purpose of a debugger such as ROCGDB 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.

ROCGDB can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:

You can use ROCGDB to debug programs written in C, C++, Fortran and Modula-2.

ROCGDB is invoked with the shell command gdb. Once started, it reads commands from the terminal until you tell it to exit with the ROCGDB command quit or exit. You can get online help from ROCGDB itself by using the command help.

You can run gdb with no arguments or options; but the most usual way to start ROCGDB 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 or use option -p, if you want to debug a running process:

gdb program 1234
gdb -p 1234

would attach ROCGDB to process 1234. With option -p you can omit the program filename.

Here are some of the most frequently needed ROCGDB commands:

break [file:][function|line]

Set a breakpoint at function or line (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 ROCGDB command name, or general information about using ROCGDB.

quit
exit

Exit from ROCGDB.

Any arguments other than options specify an executable file 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 abbreviated 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.

The abbreviated forms are shown here with ‘-’ and long forms are shown with ‘--’ to reflect how they are shown in --help. However, ROCGDB recognizes all of the following conventions for most options:

--option=value
--option value
-option=value
-option value
--o=value
--o value
-o=value
-o value

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.

--write

Enable writing into executable and core files.

--exec=file
-e file

Use 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 and use it as the executable file.

--core=file
-c file

Use file as a core dump to examine.

--command=file
-x file

Execute ROCGDB commands from file.

--eval-command=command
-ex command

Execute given ROCGDB command.

--init-eval-command=command
-iex

Execute ROCGDB command before loading the inferior.

--directory=directory
-d directory

Add directory to the path to search for source files.

--nh

Do not execute commands from ~/.config/gdb/gdbinit, ~/.gdbinit, ~/.config/gdb/gdbearlyinit, or ~/.gdbearlyinit

--nx
-n

Do not execute commands from any .gdbinit or .gdbearlyinit initialization files.

--quiet
--silent
-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 ROCGDB commands in the command files.

Batch mode may be useful for running ROCGDB 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 ROCGDB control terminates) is not issued when running in batch mode.

--batch-silent

Run in batch mode, just like --batch, but totally silent. All ROCGDB output is supressed (stderr is unaffected). This is much quieter than --silent and would be useless for an interactive session.

This is particularly useful when using targets that give ‘Loading section’ messages, for example.

Note that targets that give their output via ROCGDB, as opposed to writing directly to stdout, will also be made silent.

--args prog [arglist]

Change interpretation of command line so that arguments following this option are passed as arguments to the inferior. As an example, take the following command:

gdb ./a.out -q

It would start ROCGDB with -q, not printing the introductory message. On the other hand, using:

gdb --args ./a.out -q

starts ROCGDB with the introductory message, and passes the option to the inferior.

--pid=pid

Attach ROCGDB to an already running program, with the PID pid.

--tui

Open the terminal user interface.

--readnow

Read all symbols from the given symfile on the first access.

--readnever

Do not read symbol files.

--return-child-result

ROCGDB’s exit code will be the same as the child’s exit code.

--configuration

Print details about GDB configuration and then exit.

--version

Print version information and then exit.

--cd=directory

Run ROCGDB using directory as its working directory, instead of the current directory.

--data-directory=directory
-D

Run ROCGDB using directory as its data directory. The data directory is where ROCGDB searches for its auxiliary files.

--fullname
-f

Emacs sets this option when it runs ROCGDB as a subprocess. It tells ROCGDB 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-ROCGDB interface program uses the two ‘\032’ characters as a signal to display the source code for the frame.

-b baudrate

Set the line speed (baud rate or bits per second) of any serial interface used by ROCGDB for remote debugging.

-l timeout

Set timeout, in seconds, for remote debugging.

--tty=device

Run using device for your program’s standard input and output.


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