_hurd_id.aux.gids[0] = _hurd_id.aux.gids[1] = gid;
newaux[0] = newaux[1] = gid;
DEFUN(__setgid, (gid), gid_t gid){  auth_t newauth;  error_t err;  HURD_CRITICAL_BEGIN;  __mutex_lock (&_hurd_id.lock);  err = _hurd_check_ids ();  if (!err)    {      /* Make a new auth handle which has GID as the real gid,	 and as the first element in the list of effective gids.  */      gid_t *newgen, *newaux, auxbuf[2];      size_t ngen, naux;      newaux = _hurd_id.aux.gids;      naux = _hurd_id.aux.ngids;      if (_hurd_id.gen.ngids == 0)	{	  /* No effective gids now.  The new set will be just GID.  */	  newgen = &gid;	  ngen = 1;	}      else if (_hurd_id.gen.gids[0] == 0)	{	  /* We are root; set the effective, real, and saved to GID.  */	  _hurd_id.gen.gids[0] = gid;	  _hurd_id.valid = 0;	  newgen = _hurd_id.gen.gids;	  ngen = _hurd_id.gen.ngids;	  if (_hurd_id.aux.ngids < 2)	    {	      newaux = auxbuf;	      naux = 2;	    }	  _hurd_id.aux.gids[0] = _hurd_id.aux.gids[1] = gid;	}      else	{	  /* We are not root; just change the effective GID.  */	  _hurd_id.gen.gids[0] = gid;	  _hurd_id.valid = 0;	  newgen = _hurd_id.gen.gids;	  ngen = _hurd_id.gen.ngids;	}      err = __USEPORT (AUTH, __auth_makeauth		       (port, NULL, MACH_MSG_TYPE_COPY_SEND, 0,			newgen, ngen, newaux, naux,			_hurd_id.gen.gids, _hurd_id.gen.ngids,			_hurd_id.aux.gids, _hurd_id.aux.ngids,			&newauth));    }  __mutex_unlock (&_hurd_id.lock);  HURD_CRITICAL_END;  if (err)    return __hurd_fail (err);  /* Install the new handle and reauthenticate everything.  */  err = __setauth (newauth);  __mach_port_deallocate (__mach_task_self (), newauth);  return err;}