void bt() {
  enum { BT_SIZE = 10 }; // Whatever big enough.
  int i;
  void *btbuf[BT_SIZE];
  int btsize = backtrace(btbuf, BT_SIZE);
  printf("Backtrace entries: %d\n", btsize);
  for(i=0; i<btsize; i++) {
    printf("%d: %p\n", i, btbuf[i]);
  }
}