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MALLOC_HOOK(3)             Linux Programmer's Manual            MALLOC_HOOK(3)

       __malloc_hook,  __malloc_initialize_hook, __memalign_hook, __free_hook, __realloc_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

       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
           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.

       Hook  variables  are  not thread-safe so they are deprecated now.  Programmers should instead preempt callst to
       the relevant functions by defining and exporting functions like "malloc" and "free".

       These functions are GNU extensions.

       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
           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)

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

GNU                               2002-07-20                    MALLOC_HOOK(3)