[comex]

The C standard does not allow casting directly between function pointers and other pointers; they might not even be the same size. Using a union or memcpy will allow you to standards-compatibly reinterpret the bit pattern of a function pointer as a data pointer or vice versa (modulo size differences), but creating the resulting pointer, even without dereferencing it, might cause a crash if the bit pattern is a "trap representation", and in any case dereferencing it isn't guaranteed to do anything useful. ...Not that a portable program has any business trying to read instruction opcodes in the first place.