I'm just trying to improve my poor C knowledge

Be careful what you wish for. :) I'm not sure studying large and complex C code bases is a good way to learn C. I started by reading The C Programming Language, aka K&R, from cover to cover.

Having slaved over many huge C code bases over the years, I can assure you they all rely heavily on static and dynamic code analysis tools to keep the code clean (e.g. Coverity, Valgrind, AddressSanitizer and many more). P5P is no different, as indicated by the EXTERNAL TOOLS FOR DEBUGGING PERL section at perlhack.

So, if you want to become a serious C coder, you must master these tools.