Don't we not need this ifdef since x & CLONE_VFORK will always be 0?

incorporated ( removed CLONE_VFORKdefinition from prov_buffer.c )

Normally, pre-processor macros would be the right way to eliminate duplicated code.

In this particular case, the C code is generated from Python in generator/gen_libc_hooks.py, and there isn't a good way to emit code that calls the C preprocessor macros. It would be better to implement the logic directly in Python.

Therefore, for the above file, can you write out what it should be after expanding the pre-processor macros?

My concern is that in Linux, the shared library needs to define a function with the name we want to interpose (e.g., open), and load the real/underlying function with a new name (e.g., unwrapped_open) using dlsym.

In Mac, it seems that we define a function with the new name (e.g., my_open), and call the real/underlying function with the original name (open)

__attribute__ ((section ("__DATA,__interpose"))) = {
    (const void*)(unsigned long)&my_open,
    (const void*)(unsigned long)&open
};

The meaning of the name open is reversed: in Linux its the wrapper; in Mac it's the underlying function.

This is of course salvageable. We should always call unwrapped_open and wrapped_open to eliminate confusion, but alias one of them to the "original name" based on platform.

#ifdef linux
#define wrapped_open open
#else if apple
#define unwrapped_open open
#endif

We hardly ever call the wrapped versions, always the unwrapped, which are already called as unwrapped_ in our code.

But I wanted to confirm that this is the only way to interpose functions in Mac before doing that. So please let me know.

I think there may be a race if multiple threads try to init at the same. I think I specified the algorihtm incorrectly (slightly the first time). Here's what it should be:

if (is process inited) {
  if (test_and_set(is first thread)) {
      ... do your process initialization you have here
      is process initted = true;
   } else {
     // process is not initted, but someone else is already handling it.
     while (!process is inited) { sched_yield(); }
   }
}
// process is inited here. Yay!

test_and_set should be replaced __sync_bool_compare_and_swap