ref: 04066fe973c628476fbe9eb65bf62a67334987f7
parent: 7de7414e885c3fa3c52200c49528e1e8da5adcc9
author: cinap_lenrek <cinap_lenrek@felloff.net>
date: Thu May 7 19:27:27 EDT 2020
bcm64: fix kernels cmpswap() function spectacular bug. cmpswap() had a sign extension bug using sign extending MOV to load the old compare value and LDXRW using zero extension while the CMP instruction compared 64 bit registers. this caused cmpswap with negative old value always to fail. interestingly, libc's version of this function was fine.
--- a/sys/src/9/bcm64/l.s
+++ b/sys/src/9/bcm64/l.s
@@ -229,8 +229,8 @@
TEXT cas(SB), 1, $-4
TEXT cmpswap(SB), 1, $-4
- MOVW ov+8(FP), R1
- MOVW nv+16(FP), R2
+ MOVWU ov+8(FP), R1
+ MOVWU nv+16(FP), R2
_cas1:
LDXRW (R0), R3
CMP R3, R1