Add a page with hints about debugging Git

[phil-blain]

Could start with:
gitgitgadget/git#582 (comment)

Hi @ParthGala2k !

Also I'm having trouble running the program on gdb, is there any reference for that?

The CodingGuidelines document also has some guidance for using the system-installed GDB.

If you compiled GDB yourself you will need to invoke it like this:

GIT_DEBUGGER="/path/to/gdb --args" ./bin-wrappers/git <command> <args...>

I you are on macOS and want to use LLDB, that would be:

GIT_DEBUGGER="lldb --" ./bin-wrappers/git <command> <args...>

Sometimes Git command spawn other Git commands under the hood, using fork+exec. You will recognize this by a call to either run_command or more rarely directly to start_command.

If the code your are trying to debug is in an instance of git spawned (fork+exec) by the main git process, you will need to use the set detach-on-fork off option in GDB, which works on Linux but not on macOS (I don't know about anything about Windows). I had success doing that on Ubuntu 17.10 using a self-compiled GDB 8.3.1, but not with the system-installed GDB 7.1.2.

Another option is to put a call to sleep() just after the fork in start_command, then open another instance of GDB and attach to the new process, e.g. with

gdb -p $(pgrep -n git)

Then you can control both instances independently.

Addendum: there is also some interesting guidelines on the old wiki, that might still be useful for debugging tests: https://git.wiki.kernel.org/index.php/What_to_do_when_a_test_fails

maybe also add pointers to configure VScode for debugging.

also : gitgitgadget/git#582 (comment)

also of interest: https://github.com/git-for-windows/git/wiki/Debugging-Git

[chriscool]

You are welcome to start such a page! What is in your above comment is a good starting point, so I encourage you to contribute it!

[phil-blain]

thanks @chriscool. I might get to this some day. I guess another question is does it make sense to put some of that info in git.git somewhere...

[chriscool]

I started something, see:

• https://git.github.io/Hacking-Git/
• https://github.com/git/git.github.io/blob/master/Hacking-Git.md

[chriscool]

@phil-blain feel free to contribute to the above page :-)

[chriscool]

Let's close this for now and maybe open more specific issues to improve the above page.