On Sat, Apr 04, 2015 at 10:36:11AM +0200, Quentin Casasnovas wrote:
> Since all of these are compile time constants, could we not use the safe
> variant on that same page? Not that I'm too worried about the signed right
> shift but heh that would be portable and should not impact performance
> anyway, so no added value in using the optimized version is there?
Seems to work with the experimental diff below. I need to do
-(-(x < y))
with the last term though as we're working with s32s.
---
diff --git a/arch/x86/include/asm/alternative-asm.h
b/arch/x86/include/asm/alternative-asm.h
index 44a1fc5439d3..2cb6da2716bf 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -53,14 +53,14 @@
* Shamelessly stolen and adapted from:
* http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
*/
-#define alt_max_short(a,b) (((a) - (((a) - (b)) & (((a) - (b)) >> 15))) &
0xffff)
+#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
140:
\oldinstr
141:
- .skip -((alt_max_short(new_len1, new_len2) - old_len) > 0) * \
- (alt_max_short(new_len1, new_len2) - old_len),0x90
+ .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
+ (alt_max_short(new_len1, new_len2) - (old_len)),0x90
142:
.pushsection .altinstructions,"a"
diff --git a/arch/x86/lib/memset_64.S b/arch/x86/lib/memset_64.S
index 93118fb23976..453b6a05a07e 100644
--- a/arch/x86/lib/memset_64.S
+++ b/arch/x86/lib/memset_64.S
@@ -29,6 +29,14 @@ ENTRY(__memset)
ALTERNATIVE_2 "jmp memset_orig", "", X86_FEATURE_REP_GOOD, \
"jmp memset_erms", X86_FEATURE_ERMS
+ ALTERNATIVE_2 \
+ ".byte 0xc3, 0xc3, 0xc3", \
+ ".byte 0x66, 0x66, 0x66, 0x90", \
+ X86_FEATURE_ALWAYS, \
+ ".byte 0x66, 0x66, 0x66, 0x66, 0xcc", \
+ X86_FEATURE_ALWAYS
+
+
movq %rdi,%r9
movq %rdx,%rcx
andl $7,%edx
> On the bonus side, you're getting rid of the double 'alt_end_marker' label
> in case of an alternative_2()!
>
> Looks good to me and I find it much easier to understand here :)
Cool. Please give it more critical staring as we're under time pressure
here.
Thanks!
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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