gistfile1.txt

#define DYLD_INTERPOSE(_replacement,_replacee) \
__attribute__((used)) static struct{ const void* replacement; const void* replacee; } _interpose_##_replacee \
__attribute__ ((section ("__DATA,__interpose"))) = { (const void*)(unsigned long)&_replacement, (const void*)(unsigned long)&_replacee };

DYLD_INTERPOSE(my_function_replacement, original_function);

int original_function() {
    return 5;
}

int my_function_replacement() {
    int result = original_function();
    printf("%i\n",result);
    return result;
}