The issue is that it is a C program, and according to the C standard, dereferencing (void * )0 is undefined behaviour. If you actually want to get at memory address 0 in a C program, you need to use some other mechanism or use a compiler that explicitly defines dereferencing NULL.

I believe the other mechanism could be as simple as pointer arithmetic, and not involve any compiler specific construct, but I would want to check the spec carefully before assuming that. Also, I would yell at whoever thought it was a good idea to store data at 0.