ref: a05f1d6ea1a7f7c26f9e17ba41274081f2b9b7b3 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