ref: fd8a2d81c3ddf6584d2b47f1b8efe30b66beb7b5 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