malloc_interposer.c

/* Example of a library interposer: interpose on malloc().
 * gcc -D_GNU_SOURCE -fPIC -O2 -Wall -o malloc_interposer.so -shared malloc_interposer.c -ldl
 * setenv LD_PRELOAD $cwd/malloc_interposer.so
 * run the app
 */

#include <stdio.h>
#include <dlfcn.h>
#include <string.h>

void *malloc(size_t size) {
    static void * (*func)();

    if(!func)
        func = (void *(*)()) dlsym(RTLD_NEXT, "malloc");

    void *mem = func(size);

    if (mem)
        memset(mem, 0, size);
    return mem;
}