Problem in overriding malloc

Question

I am trying to override malloc by doing this.

#define malloc(X) my_malloc((X))

void* my_malloc(size_t size)
{

    void *p = malloc(size);
    printf (\"All         


        

Answer 1

With Glibc, there exists malloc_hook(3) as the proper way to globally interpose your own malloc function.

#include 
#include 

static void *(*old_malloc_hook)(size_t, const void *);

static void *new_malloc_hook(size_t size, const void *caller) {
    void *mem;

    __malloc_hook = old_malloc_hook;
    mem = malloc(size);
    fprintf(stderr, "%p: malloc(%zu) = %p\n", caller, size, mem);
    __malloc_hook = new_malloc_hook;

    return mem;
}

static void init_my_hooks(void) {
    old_malloc_hook = __malloc_hook;
    __malloc_hook = new_malloc_hook;
}

void (*__malloc_initialize_hook)(void) = init_my_hooks;

$ cat >mem.c <<'EOF'
(the code above)
EOF
$ cat >main.c <<'EOF'
#include 
#include 
int main() {
    char *buf = malloc(50);
    sprintf(buf, "Hello, world!");
    puts(buf);
    free(buf);
    return 0;
}
EOF
$ cc mem.c main.c
$ ./a.out
0x40077e: malloc(50) = 0x22f7010
Hello, world!

(We could use __attribute__((constructor)), but that trick isn't necessary: Glibc handily provides __malloc_initialize_hook as another way to load run code before main.)