MALLOC_HOOK
MALLOC_HOOK
NAMESYNOPSIS
DESCRIPTION
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO
COLOPHON
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(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.
CONFORMING TO
These functions are GNU extensions.
NOTES
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".
EXAMPLE
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;
}
SEE ALSO
mallinfo(3), malloc(3), mcheck(3), mtrace(3)
COLOPHON
This page is part of release 3.69 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man−pages/.
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