ref: 74bcc2aa4c0b8e2d9915ae2cda6e4b2fabf56e95 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