Emacs C debug help function?

[Shenli Zhu]

Hi Emacs hackers.

I have tried to understand function (debug) on elisp level, and find some details on C level(e.g. debugger-step-after-exit). 
So, I attach emacs process to gdb. 

Backtrace is like:
...
#14 0x0818f78b in Ffuncall (nargs=1, args=0xbfa63a00) at eval.c:3021
#15 0x081c8d21 in Fbyte_code (bytestr=154800713, vector=166927821, maxdepth=16)
    at bytecode.c:680
#16 0x081911b2 in Feval (form=165809550) at eval.c:2352
...

Is there any help function to display form, etc? And is there any instruction files on hacking C files?

Thanks,
Davy