Linux Kernel Module Cheat

While step debugging any complex program, you always end up feeling the need to step in reverse to reach the last call to some function that was called before the failure point, in order to trace back the problem to the actual bug source.

While GDB "has" this feature, it is just too broken to be usable, and so we expose the amazing Mozilla RR tool conveniently in this repo: https://stackoverflow.com/questions/1470434/how-does-reverse-debugging-work/53063242#53063242

Before the first usage setup rr with:

Then use it with your content of interest, for example:

This will:

From there, run the program until your point of interest, e.g.:

and you can now reliably use reverse debugging commands such as reverse-continue, reverse-finish and reverse-next!

To restart debugging again after quitting rr, simply run on your host terminal:

The use case of rr is often to go to the final crash and then walk back from there, so you often want to automate running until the end after record with --debug-vm-args as in:

Programs often tend to blow up in very low frames that use values passed in from higher frames. In those cases, remember that just like with forward debugging, you can’t just go:

but rather, you must: