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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(3),  real-
       loc(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 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 to by __malloc_hook, __realloc_hook, __mema-
       lign_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  mal-
       loc(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.

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 3.25 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU                               2002-07-20                    MALLOC_HOOK(3)
 

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