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authorFenghua Yu <fenghua.yu@intel.com>2013-11-16 12:37:01 -0800
committerH. Peter Anvin <hpa@linux.intel.com>2013-11-16 18:00:58 -0800
commitf4cb1cc18f364d761d5614eb6293cccc6647f259 (patch)
treeaf6be6a073d887171d49401ba9dddaed9a537a99 /arch/x86/lib
parent1213959d4ad2f523290d0d7c94f712edef63852c (diff)
downloadop-kernel-dev-f4cb1cc18f364d761d5614eb6293cccc6647f259.zip
op-kernel-dev-f4cb1cc18f364d761d5614eb6293cccc6647f259.tar.gz
x86-64, copy_user: Remove zero byte check before copy user buffer.
Operation of rep movsb instruction handles zero byte copy. As pointed out by Linus, there is no need to check zero size in kernel. Removing this redundant check saves a few cycles in copy user functions. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> Link: http://lkml.kernel.org/r/1384634221-6006-1-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/lib')
-rw-r--r--arch/x86/lib/copy_user_64.S8
1 files changed, 2 insertions, 6 deletions
diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index a30ca15..ffe4eb9 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -236,8 +236,6 @@ ENDPROC(copy_user_generic_unrolled)
ENTRY(copy_user_generic_string)
CFI_STARTPROC
ASM_STAC
- andl %edx,%edx
- jz 4f
cmpl $8,%edx
jb 2f /* less than 8 bytes, go to byte copy loop */
ALIGN_DESTINATION
@@ -249,7 +247,7 @@ ENTRY(copy_user_generic_string)
2: movl %edx,%ecx
3: rep
movsb
-4: xorl %eax,%eax
+ xorl %eax,%eax
ASM_CLAC
ret
@@ -279,12 +277,10 @@ ENDPROC(copy_user_generic_string)
ENTRY(copy_user_enhanced_fast_string)
CFI_STARTPROC
ASM_STAC
- andl %edx,%edx
- jz 2f
movl %edx,%ecx
1: rep
movsb
-2: xorl %eax,%eax
+ xorl %eax,%eax
ASM_CLAC
ret
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