Understanding the ABI is helped by understanding how compilation
works and how information about the program's variables and functions 
(called, more generally, "symbols") is passed between the stages of the
compiler. 

GCC options to examine these stages, in a nutshell:
http://www.ouah.org/RevEng/x24.htm

Do the steps in Parts 1 and 2 of this article:
http://www.linuxjournal.com/content/examining-compilation-process-part-1
http://www.linuxjournal.com/content/examining-compilation-process-part-2
http://www.linuxjournal.com/content/examining-compilation-process-part-3

I recommend reading sections of 
      "Introduction to Reverse Engineering Software in Linux" 
             http://www.ouah.org/RevEng/t1.htm 
about tools you haven't yet encountered in your programming
experience. The "Understanding Assembly" chapter is also very useful
if you haven't done assembly before -- but nothing can replace playing
with the compiler ('gcc -S', 'objdump -d', etc.) on your own.