diff options
| author | Jan Beulich <JBeulich@novell.com> | 2009-12-18 16:16:03 +0000 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-12-30 11:57:32 +0100 |
| commit | 7269e8812a59f74fb1ce134465d0bcf5683b93a1 (patch) | |
| tree | cfa0022a98907232edc8ffbe145926a272da14f1 /arch/x86/lib/memcpy_64.S | |
| parent | 1b1d9258181bae199dc940f4bd0298126b9a73d9 (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.S | 23 |
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 |