| NAME | SYNOPSIS | DESCRIPTION | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
MALLOC_HOOK(3) Linux Programmer's Manual MALLOC_HOOK(3)
__malloc_hook, __malloc_initialize_hook, __memalign_hook, __free_hook, __real-
loc_hook, __after_morecore_hook - malloc debugging variables
#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);
The GNU C library lets you modify the behavior of malloc(3), realloc(3), and
free(3) 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(3),
realloc(3), memalign(3), free(3), respectively, except that they have a final
argument caller that gives the address of the caller of malloc(3), etc.
The variable __after_morecore_hook points at a function that is called each
time after sbrk(2) was asked for more memory.
These functions are GNU extensions.
The use of these hook functions is not safe in multithreaded programs, and
they are now deprecated. Programmers should instead preempt calls to the
relevant functions by defining and exporting functions such as "malloc" and
"free".
Here is a short example of 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 initializing 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\n",
(unsigned int) size, caller, result);
/* Restore our own hooks */
__malloc_hook = my_malloc_hook;
return result;
}
mallinfo(3), malloc(3), mcheck(3), mtrace(3)
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at http://www.kernel.org/doc/man-pages/.
GNU 2010-10-13 MALLOC_HOOK(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface