ref: 85d0f0e1a2c05afee5a101c1e51a3ddd2ff2a5f6 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