fd = open(argv[1], O_RDONLY);
  if (fd < 0) {
    perror(argv[1]);
    exit(1);
  }

  mapstart = (long *)mmap((void *)0, len, PROT_READ, MAP_PRIVATE, fd,
                          offset & ~MAP_MASK);
  if ((long)mapstart < 0) {
     perror("mapstart failed");
     exit(1);
  }
  close(fd);
  
  printf("Test values before second mmap:\n");
  testMap(mapstart);

  fd2 = open(argv[2], O_RDONLY);
  if (fd < 0) {
    perror(argv[2]);
    exit(1);
  }

  mapstart2 = (long *)mmap((void *)0, len, PROT_READ, MAP_PRIVATE, fd2,
                          offset & ~MAP_MASK);
  if ((long)mapstart2 < 0) {
     perror("mapstart2 failed");
     exit(1);
  }
  close(fd2);

  printf("Test values before second mmap:\n");
  testMap(mapstart);

  printf("Did the contents of the second mmap overwrite?\n");
  testMap(mapstart2);