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

static void *(*__real_malloc)(size_t);

static int mode = 0;

static void fin(void) {
    if (mode > 0) fprintf(stderr, "intercept: stopped\n");
    mode = 0;
}

static void init(void) {
    if (mode) return;
    mode = -1;
    if (((__real_malloc) = dlsym(RTLD_NEXT, "malloc")) == NULL) {
        fprintf(stderr, "intercept: unable to load symbol '%s': %s",
            "malloc", strerror(errno));
        return;
    }
    atexit(fin);
    fprintf(stderr, "intercept: intercepting function calls\n");
    mode = 1;
}

void *malloc(size_t size) {
    init();
    // before call to malloc
    void *ret = __real_malloc(size);
    // after call to malloc
    return ret;
}