1  struct B;
       2  struct A
       3  {
       4    long a;
       5    struct B *foo;
       6    struct C *bar;
       7  };
       8  
       9  struct C
      10  {
      11    struct B *foo;
      12    int b;
      13  };
      14  
      15  static struct C *foo __attribute__((used));
      16  static struct A *bar __attribute__((used));