I log fine descriptions.

desc on realloc:
The C library function void *realloc(void *ptr, size_t size) attempts to
resize the memory block pointed to by ptr that was previously allocated
with a call to malloc or calloc, or realloc either.

paras: void *ptr, size_t size.

ptr − This is the pointer to a memory block previously allocated with malloc, calloc or realloc to be reallocated. If this is NULL, a new block is allocated and a pointer to it is returned by the function.

size − This is the new size for the memory block, in bytes. If it is 0 and ptr points to an existing block of memory, the memory block pointed by ptr is deallocated and a NULL pointer is returned.

atomic_forced_read macro:
# define atomic_forced_read(x) \
  ({ __typeof (x) __x; __asm ("" : "=r" (__x) : "0" (x)); __x; })

put `malloc_hook` into any one of registers , and retrieve it atomically..