hook.cpp

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <dlfcn.h>
#include <unistd.h>

extern "C" {
    void *malloc(std::size_t size) {
        using malloc_t = decltype(&std::malloc);
        static malloc_t native_malloc = reinterpret_cast<malloc_t>(dlsym(RTLD_NEXT, "malloc"));

        char buf[80];
        std::snprintf(buf, sizeof(buf), "malloc(%zu)\n", size);
        write(2, buf, strlen(buf));

        return native_malloc(size);
    }

    void free(void *ptr) {
        using free_t = decltype(&std::free);
        static free_t native_free = reinterpret_cast<free_t>(dlsym(RTLD_NEXT, "free"));

        char buf[80];
        std::snprintf(buf, sizeof(buf), "free(%p)\n", ptr);
        write(2, buf, strlen(buf));

        return native_free(ptr);
    }

    void *calloc(std::size_t num, std::size_t size) {
        using calloc_t = decltype(&std::calloc);
        static calloc_t native_calloc = reinterpret_cast<calloc_t>(dlsym(RTLD_NEXT, "calloc"));

        char buf[80];
        std::snprintf(buf, sizeof(buf), "calloc(%zu, %zu)\n", num, size);
        write(2, buf, strlen(buf));

        return native_calloc(num, size);
    }

    void *realloc(void *ptr, std::size_t size) {
        using realloc_t = decltype(&std::realloc);
        static realloc_t native_realloc = reinterpret_cast<realloc_t>(dlsym(RTLD_NEXT, "realloc"));

        char buf[80];
        std::snprintf(buf, sizeof(buf), "realloc(%p, %zu)\n", ptr, size);
        write(2, buf, strlen(buf));

        return native_realloc(ptr, size);
    }
}

g++ -fPIC -ldl lib.cpp -o lib.so
LD_PRELOAD=./lib.so ls