ref: ce72cab0e49c08c71888c57cf616563b90d7497a dir: /sys/src/ape/lib/ap/arm64/tas.s/
TEXT tas(SB), 1, $-4 MOVW $1, R2 _tas1: LDXRW (R0), R1 STXRW R2, (R0), R3 CBNZ R3, _tas1 MOVW R1, R0 TEXT _barrier(SB), 1, $-4 DMB $0xB // ISH RETURN