ref: 42a0212d55360cdc703a2e496fe0e4cea2b32dc4 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