a bug for __builtin_offsetof operator ?

["Michael Gong" <mwgong@xxxxxxxxxxxxxx>]

Hi,

I have following program which is compiled successfully by gcc.

struct A {
  int a;
};

struct B {
struct A a1;
};

int main()  {

__builtin_offsetof(struct B, a1.a);    /* line 11 */

}


However, if I add "()" around the "a1.a" on line 11, ie. line 11 
becomes:
  __builtin_offsetof(struct B, (a1.a) );    /* line 11 */


gcc reports:
   foo.c: In function 'main':
   foo.c:11: error: syntax error before '(' token.


I am not sure whether it is a gcc bug.

Regards,

Mike