[PATCH] x86/copy_user.S: Remove zero byte check before copy user buffer.

[Fenghua Yu]

From: Fenghua Yu <fenghua.yu@xxxxxxxxx>

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.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 arch/x86/lib/copy_user_64.S | 8 ++------
 1 file 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
 
-- 
1.8.0.1

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