How to tell which library a function is from

dlmalloc.c

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

int main(int argc, char **argv)
{
    void *sym;
    Dl_info_t dlip;

    sym = dlsym(RTLD_PROBE, "malloc");
    if (sym == NULL) {
	perror("dlsym failed");
	exit(1);
    }

    if (dladdr(sym, &dlip) == 0) {
	perror("dladdr failed");
	exit(1);
    }

    printf("malloc: 0x%x in %s\n", sym, dlip.dli_fname);
    exit(0);
}