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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | STANDARDS | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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__malloc_hook(3) Library Functions Manual __malloc_hook(3)
__malloc_hook, __malloc_initialize_hook, __memalign_hook,
__free_hook, __realloc_hook, __after_morecore_hook - malloc
debugging variables (DEPRECATED)
Standard C library (libc, -lc)
#include <malloc.h>
typeof(void *(size_t size, const void *caller))
*volatile __malloc_hook;
typeof(void *(void *p, size_t size, const void *caller))
*volatile __realloc_hook;
typeof(void *(size_t align, size_t size, const void *caller))
*volatile __memalign_hook;
typeof(void *(void *p, const void *caller))
*volatile __free_hook;
typeof(void (void)) *__malloc_initialize_hook;
typeof(void (void)) *volatile __after_mrecore_hook;
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:
typeof(void (void)) *__malloc_initialize_hook = 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.
GNU.
The use of these hook functions is not safe in multithreaded
programs, and they are now deprecated. From glibc 2.24 onwards,
the __malloc_initialize_hook variable has been removed from the
API, and from glibc 2.34 onwards, all the hook variables have been
removed from the API. Programmers should instead preempt calls to
the relevant functions by defining and exporting malloc(), free(),
realloc(), and calloc().
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 typeof(void *(size_t, const void *)) *old_malloc_hook;
/* Override initializing hook from the C library */
typeof(void (void)) *__malloc_initialize_hook = 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(%zu) called from %p returns %p\n",
size, caller, result);
/* Restore our own hooks */
__malloc_hook = my_malloc_hook;
return result;
}
mallinfo(3), malloc(3), mcheck(3), mtrace(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.10.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.10 2025-01-05 __malloc_hook(3)
Pages that refer to this page: malloc_get_state(3), mallopt(3), mtrace(3)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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