LD_PRELOAD example for the closed-source fglrx driver.

ppinitialize.c

#define _GNU_SOURCE 1
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <dlfcn.h>

long PP_Initialize(void) {
    fp = fopen("/dev/stderr", "a");
    fprintf(fp, "DEBUG: entering PP_Initialize.\n");
    close(fp);

    // Call the original function but return a different value:
    long (*orig)(void) = dlsym(RTLD_NEXT, "PP_Initialize");
    orig();

    return 0;
}