linux-kernel - [RFC][PATCH] x86: add memory clobber in switch

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Date:	Sun, 14 Sep 2008 19:03:53 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org
Subject: [RFC][PATCH] x86: add memory clobber in switch_to()

There are more places which have segment register reloads without
adding memory clobbers. Should we fix them up? Here's one of them:

>From 5f135687f7730fbdd979b6fb408fd3ca08a0a678 Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@...il.com>
Date: Sun, 14 Sep 2008 18:53:22 +0200
Subject: [PATCH] x86: add memory clobber in switch_to()

Segment registers are reloaded, so we should add a memory clobber. The
generated assembly code is identical in my tests, but this doesn't mean
it is necessarily true for all configurations/compilers.

x86_64 already has the memory clobber.

Signed-off-by: Vegard Nossum <vegard.nossum@...il.com>
---
 include/asm-x86/system.h |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/include/asm-x86/system.h b/include/asm-x86/system.h
index 983ce37..fed6482 100644
--- a/include/asm-x86/system.h
+++ b/include/asm-x86/system.h
@@ -64,7 +64,10 @@ do {									\
 		       							\
 		       /* regparm parameters for __switch_to(): */	\
 		       [prev]     "a" (prev),				\
-		       [next]     "d" (next));				\
+		       [next]     "d" (next)				\
+									\
+		     : /* reloaded segment registers */			\
+			"memory");					\
 } while (0)
 
 /*
-- 
1.5.5.1

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