When you compile a program for a 64-bit architecture, off_t is 64 bits long, so the *64() versions of functions (open64(), stat64(), etc.) aren't defined. If you're using a *64() function, switch to the normal one (e.g., s/open64/open/); to maintain source compatibility when you're compiling for a 32-bit architecture, add -D_FILE_OFFSET_BITS=64 to the command line, or define _LARGEFILE64_SOURCE to be 1.