Override the GNU C library -- painlessly

Learn a quick way to debug glibc functions by overriding the GNU C library. What do you do if you don't have the source for your application and it's failing because a GNU Library for C (glibc) function is returning something bad to the application? Because glibc is open-source, you can of course get the source code, make your changes, rebuild, and install. This is not for the faint of heart, however, because although the API is well documented, the internal organization of the GNU C library is not. Finding the correct function prototypes is only the first of many challenges.