linux-kernel - [PATCH] x86: loadsegment() optimization

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Date:	Wed, 25 Nov 2009 14:18:26 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86: loadsegment() optimization

Zero the input register in the exception handler instead of using
an extra register to pass in a zero value.

Signed-off-by: Brian Gerst <brgerst@...il.com>
---
 arch/x86/include/asm/system.h |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index f08f973..18ac1ec 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -158,18 +158,19 @@ extern void native_load_gs_index(unsigned);
  * segment if something goes wrong..
  */
 #define loadsegment(seg, value)			\
+do {						\
+	unsigned short __val = value;		\
 	asm volatile("\n"			\
 		     "1:\t"			\
 		     "movl %k0,%%" #seg "\n"	\
-		     "2:\n"			\
 		     ".section .fixup,\"ax\"\n"	\
-		     "3:\t"			\
-		     "movl %k1, %%" #seg "\n\t"	\
-		     "jmp 2b\n"			\
+		     "2:\t"			\
+		     "xorl %k0,%k0\n\t"		\
+		     "jmp 1b\n"			\
 		     ".previous\n"		\
-		     _ASM_EXTABLE(1b,3b)	\
-		     : :"r" (value), "r" (0) : "memory")
-
+		     _ASM_EXTABLE(1b,2b)	\
+		     : "+r" (__val) : : "memory"); \
+} while (0)
 
 /*
  * Save a segment register away
-- 
1.6.5.2

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