From 540feaae470ad4cf838b0c1bd5a74bdde096a082 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Mon, 2 May 2011 10:49:19 -0400
Subject: runtime, sync/atomic: fix arm cas

Works around bug in kernel implementation on old ARM5 kernels.
Bug was fixed on 26 Nov 2007 (between 2.6.23 and 2.6.24) but
old kernels persist.

Fixes #1750.

R=dfc, golang-dev
CC=golang-dev
https://golang.org/cl/4436072
---
 src/pkg/runtime/linux/arm/sys.s | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

(limited to 'src/pkg/runtime/linux')

diff --git a/src/pkg/runtime/linux/arm/sys.s b/src/pkg/runtime/linux/arm/sys.s
index d866b0e220..2b5365bd86 100644
--- a/src/pkg/runtime/linux/arm/sys.s
+++ b/src/pkg/runtime/linux/arm/sys.s
@@ -258,11 +258,22 @@ TEXT cas<>(SB),7,$0
 TEXT runtime·cas(SB),7,$0
 	MOVW	valptr+0(FP), R2
 	MOVW	old+4(FP), R0
+casagain:
 	MOVW	new+8(FP), R1
 	BL	cas<>(SB)
-	MOVW	$0, R0
-	MOVW.CS	$1, R0
+	BCC	cascheck
+	MOVW $1, R0
 	RET
+cascheck:
+	// Kernel lies; double-check.
+	MOVW	valptr+0(FP), R2
+	MOVW	old+4(FP), R0
+	MOVW	0(R2), R3
+	CMP	R0, R3
+	BEQ	casagain
+	MOVW $0, R0
+	RET
+
 
 TEXT runtime·casp(SB),7,$0
 	B	runtime·cas(SB)
-- 
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