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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) GNU 2002-07-20 MALLOC_HOOK(3)