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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1259176706-5908-1-git-send-email-brgerst@gmail.com>
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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/