static volatile int done;
static void fn(union sigval v)
{
  sigset_t ss;
  printf("#1 mask all\n");
  sigfillset(&ss);  // 0xfffffffc7ffffffful
  sigprocmask(SIG_SETMASK, &ss, NULL); // unblock 32 33 34
  sleep(1);
  printf("#2 save & restore\n");
  sigprocmask(0, NULL, &ss); // ss &= ~0x380000000ULL
  sigprocmask(SIG_SETMASK, &ss, NULL); // unblock 32 33 34
  sleep(1);
  done = 1;
}

int main()
{
  timer_t t;
  struct sigevent sev = {
    .sigev_notify = SIGEV_THREAD,
    .sigev_notify_function = fn, 
  };
  struct itimerspec its = {
    .it_value = {0, 100000000},
    .it_interval = {0, 100000000}, 
  };
  timer_create(CLOCK_MONOTONIC, &sev, &t);
  timer_settime(t, 0, &its, NULL);
  while (done = 0) {
    usleep(10000);
  }
  timer_delete(t);
  return 0;
}