GCC: --wrap option

GNU linker provides an --wrap option which can help developer replace symbols easily.

In man ld:

--wrap=symbol
    Use a wrapper function for symbol.  Any undefined reference to symbol will be resolved to
    "__wrap_symbol".  Any undefined reference to "__real_symbol" will be resolved to symbol.

    This can be used to provide a wrapper for a system function.  The wrapper function should
    be called "__wrap_symbol".  If it wishes to call the system function, it should call
    "__real_symbol".

One of user scenario is when developer is trying to analyze heap usage with customized malloc and free(i.e. using memory pool):

void * __wrap_malloc (size_t size)
{
  printf ("malloc called with %zu\n", size);
  return memory_pool_malloc(size);
}
//Same for free, realloc and calloc

Then link with option --wrap,malloc --wrap,free --wrap,realloc --wrap,calloc. If user want to mix customized malloc and system malloc, they can call __real_malloc when they want to call the system malloc.