malloc_hook

MALLOC_HOOK(3)             Linux Programmer's Manual            MALLOC_HOOK(3)



NAME
       __malloc_hook,  __malloc_initialize_hook, __memalign_hook, __free_hook,
       __realloc_hook, __after_morecore_hook - malloc debugging variables

SYNOPSIS
       #include <malloc.h>

       void *(*__malloc_hook)(size_t size, const void *caller);

       void *(*__realloc_hook)(void *ptr, size_t size, const void *caller);

       void *(*__memalign_hook)(size_t  alignment,  size_t  size,  const  void
       *caller);

       void (*__free_hook)(void *ptr, const void *caller);

       void (*__malloc_initialize_hook)(void);

       void (*__after_morecore_hook)(void);

DESCRIPTION
       The  GNU C library lets you modify the behavior of malloc(), realloc(),
       and free() by specifying appropriate hook functions.  You can use these
       hooks  to  help  you debug programs that use dynamic memory allocation,
       for example.

       The variable __malloc_initialize_hook points  at  a  function  that  is
       called  once  when the malloc implementation is initialized.  This is a
       weak variable, so it can be overridden in the application with a  defi-
       nition like the following:
           void (*__malloc_initialize_hook)(void) = my_init_hook;
       Now the function my_init_hook() can do the initialization of all hooks.

       The four functions pointed at by __malloc_hook, __realloc_hook, __mema-
       lign_hook,  __free_hook  have  a prototype like the functions malloc(),
       realloc(), memalign(), free(), respectively, except that  they  have  a
       final argument caller that gives the address of the caller of malloc(),
       etc.

       The variable __after_morecore_hook points at a function that is  called
       each time after sbrk() was asked for more core.

EXAMPLE
       Here a short example how to use these variables.

       #include <stdio.h>
       #include <malloc.h>

       /* Prototypes for our hooks.  */
       static void my_init_hook(void);
       static void *my_malloc_hook(size_t, const void *);

       /* Variables to save original hooks. */
       static void *(*old_malloc_hook)(size_t, const void *);

       /* Override initialising hook from the C library. */
       void (*__malloc_initialize_hook) (void) = my_init_hook;

       static void
       my_init_hook(void) {
           old_malloc_hook = __malloc_hook;
           __malloc_hook = my_malloc_hook;
       }

       static void *
       my_malloc_hook (size_t size, const void *caller) {
           void *result;

           /* Restore all old hooks */
           __malloc_hook = old_malloc_hook;

           /* Call recursively */
           result = malloc (size);

           /* Save underlying hooks */
           old_malloc_hook = __malloc_hook;

           /* `printf' might call `malloc', so protect it too. */
           printf ("malloc(%u) called from %p returns %p0,
               (unsigned int) size, caller, result);

           /* Restore our own hooks */
           __malloc_hook = my_malloc_hook;

           return result;
       }

SEE ALSO
       mallinfo(3), malloc(3), mtrace(3), mcheck(3)



GNU                               2002-07-20                    MALLOC_HOOK(3)