ref: 3e94fbcf9c6caa7cde6051bec82cae3b1c8d3e11 dir: /sys/src/ape/lib/ap/386/tas.s/
TEXT tas(SB),$0 MOVL $0xdeadead,AX MOVL l+0(FP),BX XCHGL AX,(BX) RET