__malloc_hook(3) -- Linux man page
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 definition 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 to by
__malloc_hook,
__realloc_hook,
__memalign_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 %p,
(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)
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