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x86, alternatives: Use 16-bit numbers for cpufeature index

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We already have cpufeature indicies above 255, so use a 16-bit number
for the alternatives index.  This consumes a padding field and so
doesn't add any size, but it means that abusing the padding field to
create assembly errors on overflow no longer works.  We can retain the
test simply by redirecting it to the .discard section, however.

[ v3: updated to include open-coded locations ]

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <tip-f88731e3068f9d1392ba71cc9f50f035d26a0d4f@git.kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin
2010-06-10 00:10:43 +00:00
committed by H. Peter Anvin
parent 140236b4b1
commit 83a7a2ad2a
7 changed files with 17 additions and 14 deletions
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7
arch/x86/include/asm/alternative.h
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@@ -45,10 +45,9 @@
struct alt_instr {
u8 *instr; /* original instruction */
u8 *replacement;
u8 cpuid; /* cpuid bit set for replacement */
u16 cpuid; /* cpuid bit set for replacement */
u8 instrlen; /* length of original instruction */
u8 replacementlen; /* length of new instruction, <= instrlen */
u8 pad1;
#ifdef CONFIG_X86_64
u32 pad2;
#endif
@@ -86,9 +85,11 @@ static inline int alternatives_text_reserved(void *start, void *end)
_ASM_ALIGN "\n" \
_ASM_PTR "661b\n" /* label */ \
_ASM_PTR "663f\n" /* new instruction */ \
" .byte " __stringify(feature) "\n" /* feature bit */ \
" .word " __stringify(feature) "\n" /* feature bit */ \
" .byte 662b-661b\n" /* sourcelen */ \
" .byte 664f-663f\n" /* replacementlen */ \
".previous\n" \
".section .discard,\"aw\",@progbits\n" \
" .byte 0xff + (664f-663f) - (662b-661b)\n" /* rlen <= slen */ \
".previous\n" \
".section .altinstr_replacement, \"ax\"\n" \