From: Russ Cox <rsc@golang.org>
Date: Thu, 1 Aug 2013 04:16:31 +0000 (-0400)
Subject: runtime: fix arm preemption
X-Git-Tag: go1.2rc2~848
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=cba880e04a074806f0e948fbdee8e2fe31705f14;p=gostls13.git

runtime: fix arm preemption

Preemption during the software floating point code
could cause m (R9) to change, so that when the
original registers were restored at the end of the
floating point handler, the changed and correct m
would be replaced by the old and incorrect m.

TBR=dvyukov
CC=golang-dev
https://golang.org/cl/11883045
---

diff --git a/src/pkg/runtime/vlop_arm.s b/src/pkg/runtime/vlop_arm.s
index 02eb985f7b..cd56898dc6 100644
--- a/src/pkg/runtime/vlop_arm.s
+++ b/src/pkg/runtime/vlop_arm.s
@@ -59,7 +59,15 @@ TEXT _sfloat(SB), 7, $64-0 // 4 arg + 14*4 saved regs + cpsr
 	MOVW	64(R13), R1
 	WORD	$0xe128f001	// msr cpsr_f, r1
 	MOVW	$12(R13), R0
-	MOVM.IA.W	(R0), [R1-R12]
+	// Restore R1-R8 and R11-R12, but ignore the saved R9 (m) and R10 (g).
+	// Both are maintained by the runtime and always have correct values,
+	// so there is no need to restore old values here.
+	// The g should not have changed, but m may have, if we were preempted
+	// and restarted on a different thread, in which case restoring the old
+	// value is incorrect and will cause serious confusion in the runtime.
+	MOVM.IA.W	(R0), [R1-R8]
+	MOVW	$52(R13), R0
+	MOVM.IA.W	(R0), [R11-R12]
 	MOVW	8(R13), R0
 	RET