__try_cmpxchg_user_asm
__try_cmpxchg_user_asm("q", "r", (_ptr), (_oldp), (_nval), _label)
case 1: __ret = __try_cmpxchg_user_asm("b", "q", \
case 2: __ret = __try_cmpxchg_user_asm("w", "r", \
case 4: __ret = __try_cmpxchg_user_asm("l", "r", \