/* Exception handling.
 */
#define	X_ACV			501	/* access violation		*/
#define	X_ARITH			502	/* arithmetic error		*/
#define	X_INT			503	/* keyboard interrupt		*/
#define	X_IPC			504	/* write to IPC with no reader	*/
#define	X_IGNORE		NULL	/* ignore exception		*/
#define	X_FIRST_EXCEPTION	501

#define	D_xwhen