#define _GNU_SOURCE 1

#include <sys/types.h>

#include <unistd.h>

#include <sys/ptrace.h>

#include <linux/ptrace.h>

#include <sys/user.h>

#include <sys/debugreg.h>

#include <assert.h>

#include <unistd.h>

#include <errno.h>

#include <signal.h>

  fprintf (stderr,

           "babl_set_malloc:\n"

           " first_malloc_used: %p\n"

           " old malloc_f:      %p\n"

           " malloc_function:   %p\n",

           first_malloc_used, malloc_f, malloc_function);

  fprintf (stderr,

           "babl_set_free:\n"

           " first_free_used:   %p\n"

           " old free_f:        %p\n"

           " free_function:     %p\n",

           first_free_used, free_f, free_function);

static void set_watchpoint(void* addr) {

  /* Thanks to jankratochvil in #gdb@freenode who pointed this out:

     http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/tests/ptrace-tests/tests/watchpoint.c?cvsroot=systemtap

  */

  pid_t child;

  int status;

  unsigned long dr7;

  long l;

  child = fork ();

  switch (child)

    {

    case -1:

      assert (0);

    case 0:

      assert (ptrace (PTRACE_TRACEME, 0, NULL, NULL) == 0);

      assert (raise (SIGTRAP) == 0);

      return;

    default:

      break;

    }

  assert (waitpid (child, &status, 0) == child);

  assert (WIFSTOPPED (status));

  assert (WSTOPSIG (status) == SIGTRAP);

  errno = 0;

  l = ptrace (PTRACE_POKEUSER, child,

	      offsetof (struct user, u_debugreg[0]), (unsigned long) addr);

  assert_perror (errno);

  assert (l == 0);

  dr7 = (DR_RW_WRITE << DR_CONTROL_SHIFT);

#ifdef DR_LEN_8

  /*

   * For a 32-bit build, DR_LEN_8 might be defined by the header.

   * On a 64-bit kernel, we might even be able to use it.

   * But we can't tell, and we don't really need it, so just use DR_LEN_4.

   */

  if (sizeof (long) > 4)

    dr7 |= (DR_LEN_8 << DR_CONTROL_SHIFT);

  else

#endif

    dr7 |= (DR_LEN_4 << DR_CONTROL_SHIFT);

  dr7 |= (1UL << DR_LOCAL_ENABLE_SHIFT);

  dr7 |= (1UL << DR_GLOBAL_ENABLE_SHIFT);

  l = ptrace (PTRACE_POKEUSER, child, offsetof (struct user, u_debugreg[7]), dr7);

  assert_perror (errno);

  assert (l == 0);

  errno = 0;

  l = ptrace (PTRACE_CONT, child, 0l, 0l);

  assert_perror (errno);

  assert (l == 0);

  exit(0);

}

          fprintf (stderr,

                   "First use of malloc:\n"

                   " first_malloc_used: %p\n"

                   " malloc_f:          %p\n"

                   " first_free_used:   %p\n"

                   " free_f:            %p\n",

                   first_malloc_used, malloc_f, first_free_used, free_f);

          /*

          fprintf (stderr, "Please attach debugger to pid %lu and press enter",

                   (unsigned long)getpid());

          {

            char buf[30];

            fgets(buf, sizeof(buf), stdin);

          }

          */

          fprintf (stderr, "Watching for writes to %p\n", &malloc_f);

          set_watchpoint(&malloc_f);

          fprintf (stderr,

                   "babl memory function(s) attempted switched on the fly:\n"

                   " first_malloc_used: %p\n"

                   " malloc_f:          %p\n"

                   " first_free_used:   %p\n"

                   " free_f:            %p\n",

                   first_malloc_used, malloc_f, first_free_used, free_f);

          abort ();