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This article mainly introduces the relevant knowledge of "how to use the Linux program debugging tool gdb". The editor shows you the operation process through the actual case. The operation method is simple, fast and practical. I hope this article "how to use the Linux program debugging tool gdb" can help you solve the problem.

Gdb is a powerful program debugging tool under Linux released by GNU open source organization. It is mainly used to debug programs written in Cmax + language. Of course, you can also debug programs in other languages.

Name:

Gdb-gnu Debugger

Summary:

Gdb [- help] [- nx] [- Q] [- batch] [- cd=dir] [- f] [- b bps] [- tty=dev] [- s symfile] [- e prog] [- se prog] [- c core] [- x cmds] [- d dir] [prog [core | procID]]

Gdb [options]-args prog [arguments]

Gdbtui [options]

Description:

The main purpose of gdb is to let you know what code is running inside the program, or what code is executing when the program crashes.

There are four main things GDB can do to help you find bug:

Start your program and specify any parameters that can affect the program's behavior.

Let your program stop under the specified conditions.

Test what happens when your program stops.

Change the variables within the program to correct the errors in the program and continue to execute.

You can debug modula-2 + and modula-2 programs with gdb. Fortran compiler is required for fortran support.

Gdb uses the shell command gdb to call, once started, read the command from the terminal directly gdb exit, you can get help through the help command.

You can execute the gdb command without any arguments or options, but the most common way to start gdb is to take one or two parameters and specify an executable file as the parameter:

Gdb program (gdb+ executable name)

You can also specify the names of the executable and core files after the gdb file:

Gdb program core (gdb + executable + core file)

You can, instead, specify a process ID as a second argument, if you want to debug a running process:

You can also specify a process id as the second parameter, if you want to debug a running program:

Gdb program 1234 (gdb process name + process id)

Attach gdb to process 1234 (unless there is a file name "1234"; GDB first checks the core file)

Gdb debug commands:

Break [file:] function

Set a breakpoint in the function (in the file)

Run [arglist]

Start the program with the specified parameters

Bt Backtrace:

Show stack

Print expr

Display the value of the expression

C

Continue to execute your program (after the program stops, for example, stop at the breakpoint)

Next

Execute the next line of code of the program (after the program stops); cross the function call of any current line.

Edit [file:] function

See where the current program is parked.

List [file:] function

Displays the code near the line of code where the program is currently stopped

Step single step debugging

Execute the next line of the program (after the program stops) and enter the interior of the function call on the current line

Help [name]

Displays information about the gdb command.

Quit

Exit gdb

For detailed gdb instructions, check out using gdb: a guide to the gdb debugger, written by stallmain and roland, and the online documentation available as a gdb entry in the gdb project information.

Options:

By default, the first option is to execute the file name (equivalent to "- se"), and the second option is the core file name (equivalent to "- c"). Many options have full names and abbreviations, as follows:

The full name format is also for workers, and if you truncate them, you can use it as long as it is clear enough. You can mark options with "+" instead of "-" if you like, although "-" is more common.

All options and command-line arguments are processed sequentially, which is different when using the-x option.

-b bps

Set the speed of all serial interfaces for gdb remote debugging

-batch

Batch execution mode, after processing all command files specified by "- x" (and ".gdbinit", if not inhibited), exit with the return code 0, and return non-0 if there is an error. Batch mode is very useful when gdb is used as a filter to test downloads and execute programs on remote computers to make sure it is useful. The message that the program exits (when a program is posted to the control terminal in gdb mode) is not released when using batch mode.

-c FILE,-core=FILE

Use the file as a coredump file to test

-cd=directory

Specify the working directory, otherwise the current directory

-d DIRECTORY,-directory=DIRECTORY

Add directory to the path to search for source files.

-e FILE,-exec=FILE

Specify the name of the executable file

-f.-fullname.

Emacs sets these options when treating gdb as a child process, telling gdb to output the complete file name and line number in a standard and recognizable manner (including each program interruption) each time the stack is displayed, in a recognizable form that looks like the beginning of two '32' characters, followed by the file name, line number and character position and new line, which are separated by colons The emacs-to-gdb interface program uses two'32 'characters as signals to display the source code on a frame.

-h.-help.

Display help information

-n.-nx.

Do not execute from any initialization file that ends with ".gdbinit". Normally, commands for such files are executed after all command-line arguments and options have been processed.

-s FILE,-symbols=FILE

Read the symbol table from the file

-se=file

Read symbol table files and executable files

Q.-quiet

Exit, do not print introduction and copyright information, and these messages are not printed in batch mode

-tty=device

Use the device as your standard input and output

-args

Pass parameters after your program name when the program is executed.

-tui

Run gdb using the documentation (console) user interface.

-write

Allow writing to execution files and core files

-x FILE,-command=FILE

Execute the gdb command from a file

two。 Example 1. The simplest gdb debugging

File name: add.c

The code is very simple, implement an addition, add two numbers together, and output the result

# include

Int add (int x pencil int y)

{

Return Xeroy

}

Int main ()

{

Int x = 10

Int y = 20

Int num = add (xQuery y)

Printf ("num =% d\ n", num)

Return 0

}

Compile gcc-g add.c to generate a.out files (note that the-g option must be added when compiling to use the gdb debugger)

Gdb. / a.out

There is a warning message in the above picture, because I am installed in the source code, just copy the python library under gdb to the specified directory (the directory in the warning)

Enter help to view help information

Start startup program

You can run the entire program using the NMAS command, which is simple, and you can familiarize yourself with the various commands of gdb through this simple demo.

2.gdb multi-process debugging

Gdb commands to debug multiple processes:

Set follow-fork-mode mode sets the mode of the debugger

The mode parameter can be

After parent fork, the original process is debugged, and the child process is not affected. This is the default way.

The new process is debugged after child fork, and the parent process is not affected.

Show follow-fork-mode displays the mode of the current debugger

Set detach-on-fork mode sets whether gdb is one of the detach processes after fork, or remains in control of both processes

The on child process (or parent process, depending on the value of follow-fork-mode) will detach and then run independently, which is the default mode

Off both processes are controlled by gdb, one process (child or parent process, dependent on follow-fork-mode) is debugged, and the other process is suspended

Info inferiors displays all processes

Inferiors processid handover process

Detach inferiors processid detach a specified process and then remove it from the fork list. This process will be

Allow to continue to run independently.

Kill inferiors processid kills a specified process and then removes it from the fork list.

Catch fork causes the program to break when fork,vfork or exec is called

Example: fork.c

# include

# include

# include

# include

Int add (int x pencil int y)

{

Return Xeroy

}

Int test ()

{

Int num = 0

Pid_t pid = fork ()

If (pid = = 0)

{

While (1)

{

Num = add (1mai 2)

Printf ("child:pid:%d num =% d\ n", getpid (), num)

Sleep (1)

}

Exit (0)

}

While (1) {

Num = add (100.20)

Printf ("parent:pid:%d num =% d\ n", getpid (), num)

Sleep (1)

}

Return 0

}

Int main ()

{

Test ()

Return 0

}

Compile gcc-g fork.c

Set catch fork to check the default values for follow-fork-mode and detach-on-fork

Setting detach-on-fork to off,start launcher will stop at the fork breakpoint.

The add functions in the two processes set the endpoints respectively:

Continue to execute the program, and info inferiors displays the process

Inferiors 2 switchover process

Detach inferiors 2

Restart gdb to test kill inferiors 2, as shown in the following figure

3.gdb multithreading debugging

Gdb debug commands for multithreading:

Info threads query thread information

Thread threadno switch thread

Thread apply [threadno] [all] args executes commands on thread list

Set print thread-events controls printing information at the beginning and end of a thread

Show print thread-events displays the switch status of thread print information

Example: file name thread.c

The code is simple as follows:

# include

# include

# include

Int add (int x pencil int y)

{

Return Xeroy

}

Void* thread (void* args)

{

Int num = 0

While (1)

{

Num + = add (1Jue 2)

Sleep (1)

}

}

Int main ()

{

Pthread_t tid

Pthread_create (& tid, NULL, thread, NULL)

Int num = 0

While (1)

{

Num + = add (100.20)

Sleep (1)

}

Return 0

}

Compile gcc-g thread.c-lpthread (link to the pthread library)

Gdb debugging: gdb. / a.out

Set breakpoints at two locations in the thread where the add function is called

Start starts the program, c continues to execute the program until the breakpoint

Info threads displays threads in the current program

C continues to execute the program, arrives at the second program and then executes the info threads command, and finds that the current program has undergone a thread switch, from thread 2 to thread 1

Thread 2 manually switches threads to thread 2, and then executes info threads to view the current thread

Example of using the thread apply command:

Set print thread-events on/off is enabled by default.

Show print thread-events

This is the end of the introduction on "how to use gdb, a Linux program debugging tool". Thank you for reading. If you want to know more about the industry, you can follow the industry information channel. The editor will update different knowledge points for you every day.

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