關於LD_PRELOAD的用法

轉自： http://blog.linuxeden.com/index.php/196616/viewspace-8082.html

$ make run

LD_LIBRARY_PATH=./ LD_PRELOAD=libleak.so ./main
malloc 0x893b008, size 1
free 0x893b008
$ cat main.c
#include <stdlib.h>

int
main (int argc, char *argv[])
{
  void *ptr;

  ptr = malloc (1);
  free (ptr);
  exit (EXIT_SUCCESS);
}
$ cat leak.c
#define _GNU_SOURCE
#include <stdio.h>
#include <dlfcn.h>

static void *(*real_malloc) (size_t size) = NULL;
static void (*real_free) (void *ptr) = NULL;

void *
malloc (size_t size)
{
  void *addr;

  if (!real_malloc) {
    real_malloc = dlsym (RTLD_NEXT, "malloc");
  }
  addr = real_malloc (size);
  printf ("malloc %p, size %d\n", addr, size);
  return addr;
}

void
free (void *ptr)
{
  if (!real_free) {
    real_free = dlsym (RTLD_NEXT, "free");
  }
  printf ("free %p\n", ptr);
  real_free (ptr);
}