红帽全球峰会3.2.7. Debugging forking or threaded programs with GDB
Some programs use forking or threads to achieve parallel code execution. To debug multiple simultaneous execution paths, you can use a variety of commands based on your use case.
- Debugging forked programs with GDB
Forking is a situation when a program (parent) creates an independent copy of itself (child). Use the following settings and commands to affect what GDB does when a fork occurs:
The
follow-fork-modesetting controls whether GDB follows the parent or the child after the fork.set follow-fork-mode parent- After a fork, debug the parent process. This is the default.
set follow-fork-mode child- After a fork, debug the child process.
show follow-fork-mode-
Display the current setting of
follow-fork-mode.
The
set detach-on-forksetting controls whether the GDB keeps control of the other (not followed) process or leaves it to run.set detach-on-fork on-
The process which is not followed (depending on the value of
follow-fork-mode) is detached and runs independently. This is the default. set detach-on-fork off-
GDB keeps control of both processes. The process which is followed (depending on the value of
follow-fork-mode) is debugged as usual, while the other is suspended. show detach-on-fork-
Display the current setting of
detach-on-fork.
- Debugging Threaded Programs with GDB
-
GDB has the ability to debug individual threads, and to manipulate and examine them independently. To make GDB stop only the thread that is examined, use the commands
set non-stop onandset target-async on. You can add these commands to the.gdbinitfile. After that functionality is turned on, GDB is ready to conduct thread debugging.
GDB uses a concept of current thread. By default, commands apply to the current thread only.
info threads-
Display a list of threads with their
idandgidnumbers, indicating the current thread. thread id-
Set the thread with the specified
idas the current thread. thread apply ids command-
Apply the command
commandto all threads listed byids. Theidsoption is a space-separated list of thread ids. A special valueallapplies the command to all threads. break location thread id if condition-
Set a breakpoint at a certain
locationwith a certainconditiononly for the thread numberid. watch expression thread id-
Set a watchpoint defined by
expressiononly for the thread numberid. command&-
Run command
commandand return immediately to the gdb prompt(gdb), continuing any code execution in the background. interrupt- Halt execution in the background.
Additional resources
'%20d='M201.5%20305.5c-13.8%200-24.9-11.1-24.9-24.6%200-13.8%2011.1-24.9%2024.9-24.9%2013.6%200%2024.6%2011.1%2024.6%2024.9%200%2013.6-11.1%2024.6-24.6%2024.6zM504%20256c0%20137-111%20248-248%20248S8%20393%208%20256%20119%208%20256%208s248%20111%20248%20248zm-132.3-41.2c-9.4%200-17.7%203.9-23.8%2010-22.4-15.5-52.6-25.5-86.1-26.6l17.4-78.3%2055.4%2012.5c0%2013.6%2011.1%2024.6%2024.6%2024.6%2013.8%200%2024.9-11.3%2024.9-24.9s-11.1-24.9-24.9-24.9c-9.7%200-18%205.8-22.1%2013.8l-61.2-13.6c-3-.8-6.1%201.4-6.9%204.4l-19.1%2086.4c-33.2%201.4-63.1%2011.3-85.5%2026.8-6.1-6.4-14.7-10.2-24.1-10.2-34.9%200-46.3%2046.9-14.4%2062.8-1.1%205-1.7%2010.2-1.7%2015.5%200%2052.6%2059.2%2095.2%20132%2095.2%2073.1%200%20132.3-42.6%20132.3-95.2%200-5.3-.6-10.8-1.9-15.8%2031.3-16%2019.8-62.5-14.9-62.5zM302.8%20331c-18.2%2018.2-76.1%2017.9-93.6%200-2.2-2.2-6.1-2.2-8.3%200-2.5%202.5-2.5%206.4%200%208.6%2022.8%2022.8%2087.3%2022.8%20110.2%200%202.5-2.2%202.5-6.1%200-8.6-2.2-2.2-6.1-2.2-8.3%200zm7.7-75c-13.6%200-24.6%2011.1-24.6%2024.9%200%2013.6%2011.1%2024.6%2024.6%2024.6%2013.8%200%2024.9-11.1%2024.9-24.6%200-13.8-11-24.9-24.9-24.9z'/%3e%3c/svg%3e){kind=small}