diff options
| author | Fenghua Yu <fenghua.yu@intel.com> | 2013-11-16 12:37:01 -0800 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2013-11-16 18:00:58 -0800 |
| commit | f4cb1cc18f364d761d5614eb6293cccc6647f259 (patch) | |
| tree | af6be6a073d887171d49401ba9dddaed9a537a99 /arch/x86/lib/copy_user_64.S | |
| parent | 1213959d4ad2f523290d0d7c94f712edef63852c (diff) | |
| download | op-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/copy_user_64.S')
| -rw-r--r-- | arch/x86/lib/copy_user_64.S | 8 |
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 |
