glibc的malloc钩子

Posted 2021-01-21 encode

调试C程序内存泄露，在腾讯游戏的分享中也是用的这个方法

__malloc_hook(3) - Linux man page

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 ",
(unsigned int) size, caller, result);
/ Restore our own hooks */
__malloc_hook = my_malloc_hook;
return result;
}