ref: 7faa0a6225f7f6d3b4a5b9c0b0ce919a8d7056a2 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