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x86/lib/memset_64.S: Convert to ALTERNATIVE_2 macro

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Make alternatives replace single JMPs instead of whole memset functions,
thus decreasing the amount of instructions copied during patching time
at boot.

While at it, make it use the REP_GOOD version by default which means
alternatives NOP out the JMP to the other versions, as REP_GOOD is set
by default on the majority of relevant x86 processors.

Signed-off-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Borislav Petkov 2015-02-04 08:57:00 +01:00
parent a930dc4543
commit 84d95ad4cb
1 changed files with 24 additions and 37 deletions
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61
arch/x86/lib/memset_64.S
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@ -5,19 +5,30 @@
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>
.weak memset
/*
* ISO C memset - set a memory block to a byte value. This function uses fast
* string to get better performance than the original function. The code is
* simpler and shorter than the orignal function as well.
*
*
* rdi destination
* rsi value (char)
* rdx count (bytes)
*
* rsi value (char)
* rdx count (bytes)
*
* rax original destination
*/
.section .altinstr_replacement, "ax", @progbits
.Lmemset_c:
*/
ENTRY(memset)
ENTRY(__memset)
/*
* Some CPUs support enhanced REP MOVSB/STOSB feature. It is recommended
* to use it when possible. If not available, use fast string instructions.
*
* Otherwise, use original memset function.
*/
ALTERNATIVE_2 "jmp memset_orig", "", X86_FEATURE_REP_GOOD, \
"jmp memset_erms", X86_FEATURE_ERMS
movq %rdi,%r9
movq %rdx,%rcx
andl $7,%edx
@ -31,8 +42,8 @@
rep stosb
movq %r9,%rax
ret
.Lmemset_e:
.previous
ENDPROC(memset)
ENDPROC(__memset)
/*
* ISO C memset - set a memory block to a byte value. This function uses
@ -45,21 +56,16 @@
*
* rax original destination
*/
.section .altinstr_replacement, "ax", @progbits
.Lmemset_c_e:
ENTRY(memset_erms)
movq %rdi,%r9
movb %sil,%al
movq %rdx,%rcx
rep stosb
movq %r9,%rax
ret
.Lmemset_e_e:
.previous
ENDPROC(memset_erms)
.weak memset
ENTRY(memset)
ENTRY(__memset)
ENTRY(memset_orig)
CFI_STARTPROC
movq %rdi,%r10
@ -134,23 +140,4 @@ ENTRY(__memset)
jmp .Lafter_bad_alignment
.Lfinal:
CFI_ENDPROC
ENDPROC(memset)
ENDPROC(__memset)
/* Some CPUs support enhanced REP MOVSB/STOSB feature.
* It is recommended to use this when possible.
*
* If enhanced REP MOVSB/STOSB feature is not available, use fast string
* instructions.
*
* Otherwise, use original memset function.
*
* In .altinstructions section, ERMS feature is placed after REG_GOOD
* feature to implement the right patch order.
*/
.section .altinstructions,"a"
altinstruction_entry __memset,.Lmemset_c,X86_FEATURE_REP_GOOD,\
.Lfinal-__memset,.Lmemset_e-.Lmemset_c,0
altinstruction_entry __memset,.Lmemset_c_e,X86_FEATURE_ERMS, \
.Lfinal-__memset,.Lmemset_e_e-.Lmemset_c_e,0
.previous
ENDPROC(memset_orig)