20021127-1.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

long long a = -1;
long long llabs (long long);
void abort (void);
int
main()
{
  if (llabs (a) != 1)
    abort ();
  return 0;
}
long long llabs (long long b)
{
	abort ();
}