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authorStefan Fritsch <sf@cvs.openbsd.org>2012-11-18 12:17:41 +0000
committerStefan Fritsch <sf@cvs.openbsd.org>2012-11-18 12:17:41 +0000
commit0e94671412c59a1bcf6f69279a1bea633ec682de (patch)
treea908d0a2164d4496baef91cb6130349dfd5223c3 /sys
parent0a199aba1829fff8571512d74a89b4b13ff57082 (diff)
Small memcpy optimizations
On x86, the xchg operation between reg and mem has an implicit lock prefix, i.e. on MP, it is a relatively expensive atomic operation. This is not needed here. Instead of swapping arguments on the stack, load them in reverse order and jump further into bcopy (idea by kettenis@). ok kettenis@
Diffstat (limited to 'sys')
-rw-r--r--sys/arch/i386/i386/locore.s15
1 files changed, 9 insertions, 6 deletions
diff --git a/sys/arch/i386/i386/locore.s b/sys/arch/i386/i386/locore.s
index f2f42b22202..ff1516df7cb 100644
--- a/sys/arch/i386/i386/locore.s
+++ b/sys/arch/i386/i386/locore.s
@@ -1,4 +1,4 @@
-/* $OpenBSD: locore.s,v 1.144 2012/11/10 09:45:05 mglocker Exp $ */
+/* $OpenBSD: locore.s,v 1.145 2012/11/18 12:17:40 sf Exp $ */
/* $NetBSD: locore.s,v 1.145 1996/05/03 19:41:19 christos Exp $ */
/*-
@@ -789,6 +789,7 @@ ENTRY(bcopy)
pushl %edi
movl 12(%esp),%esi
movl 16(%esp),%edi
+docopy:
movl 20(%esp),%ecx
movl %edi,%eax
subl %esi,%eax
@@ -827,13 +828,15 @@ ENTRY(bcopy)
ret
/*
- * Emulate memcpy() by swapping the first two arguments and calling bcopy()
+ * Emulate memcpy() by loading the first two arguments in reverse order
+ * and jumping into bcopy()
*/
ENTRY(memcpy)
- movl 4(%esp),%ecx
- xchg 8(%esp),%ecx
- movl %ecx,4(%esp)
- jmp _C_LABEL(bcopy)
+ pushl %esi
+ pushl %edi
+ movl 12(%esp),%edi
+ movl 16(%esp),%esi
+ jmp docopy
/*****************************************************************************/