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authorJan Beulich <JBeulich@novell.com>2009-12-18 16:16:03 +0000
committerIngo Molnar <mingo@elte.hu>2009-12-30 11:57:32 +0100
commit7269e8812a59f74fb1ce134465d0bcf5683b93a1 (patch)
treecfa0022a98907232edc8ffbe145926a272da14f1 /arch/x86/lib/memcpy_64.S
parent1b1d9258181bae199dc940f4bd0298126b9a73d9 (diff)
x86-64: Modify memcpy()/memset() alternatives mechanism
In order to avoid unnecessary chains of branches, rather than implementing memcpy()/memset()'s access to their alternative implementations via a jump, patch the (larger) original function directly. The memcpy() part of this is slightly subtle: while alternative instruction patching does itself use memcpy(), with the replacement block being less than 64-bytes in size the main loop of the original function doesn't get used for copying memcpy_c() over memcpy(), and hence we can safely write over its beginning. Also note that the CFI annotations are fine for both variants of each of the functions. Signed-off-by: Jan Beulich <jbeulich@novell.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> LKML-Reference: <4B2BB8D30200007800026AF2@vpn.id2.novell.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/lib/memcpy_64.S')
-rw-r--r--arch/x86/lib/memcpy_64.S23
1 files changed, 8 insertions, 15 deletions
diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
index ad5441ed1b5..f82e884928a 100644
--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -20,12 +20,11 @@
/*
* memcpy_c() - fast string ops (REP MOVSQ) based variant.
*
- * Calls to this get patched into the kernel image via the
+ * This gets patched over the unrolled variant (below) via the
* alternative instructions framework:
*/
- ALIGN
-memcpy_c:
- CFI_STARTPROC
+ .section .altinstr_replacement, "ax", @progbits
+.Lmemcpy_c:
movq %rdi, %rax
movl %edx, %ecx
@@ -35,8 +34,8 @@ memcpy_c:
movl %edx, %ecx
rep movsb
ret
- CFI_ENDPROC
-ENDPROC(memcpy_c)
+.Lmemcpy_e:
+ .previous
ENTRY(__memcpy)
ENTRY(memcpy)
@@ -128,16 +127,10 @@ ENDPROC(__memcpy)
* It is also a lot simpler. Use this when possible:
*/
- .section .altinstr_replacement, "ax"
-1: .byte 0xeb /* jmp <disp8> */
- .byte (memcpy_c - memcpy) - (2f - 1b) /* offset */
-2:
- .previous
-
.section .altinstructions, "a"
.align 8
.quad memcpy
- .quad 1b
+ .quad .Lmemcpy_c
.byte X86_FEATURE_REP_GOOD
/*
@@ -145,6 +138,6 @@ ENDPROC(__memcpy)
* so it is silly to overwrite itself with nops - reboot is the
* only outcome...
*/
- .byte 2b - 1b
- .byte 2b - 1b
+ .byte .Lmemcpy_e - .Lmemcpy_c
+ .byte .Lmemcpy_e - .Lmemcpy_c
.previous