20011019-1.c

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

extern void exit (int);
extern void abort (void);

struct { int a; int b[5]; } x;
int *y;

int foo (void)
{
  return y - x.b;
}

int main (void)
{
  y = x.b;
  if (foo ())
    abort ();
  exit (0);
}