From: tip-bot for H. Peter Anvin on 17 May 2010 19:00 Commit-ID: c59bd5688299cddb71183e156e7a3c1409b90df2 Gitweb: http://git.kernel.org/tip/c59bd5688299cddb71183e156e7a3c1409b90df2 Author: H. Peter Anvin <hpa(a)linux.intel.com> AuthorDate: Mon, 17 May 2010 15:13:23 -0700 Committer: H. Peter Anvin <hpa(a)linux.intel.com> CommitDate: Mon, 17 May 2010 15:17:16 -0700 x86, hweight: Use a 32-bit popcnt for __arch_hweight32() Use a 32-bit popcnt instruction for __arch_hweight32(), even on x86-64. Even though the input register will *usually* be zero-extended due to the standard operation of the hardware, it isn't necessarily so if the input value was the result of truncating a 64-bit operation. Note: the POPCNT32 variant used on x86-64 has a technically unnecessary REX prefix to make it five bytes long, the same as a CALL instruction, therefore avoiding an unnecessary NOP. Reported-by: Linus Torvalds <torvalds(a)linux-foundation.org> Signed-off-by: H. Peter Anvin <hpa(a)linux.intel.com> Cc: Borislav Petkov <borislav.petkov(a)amd.com> LKML-Reference: <alpine.LFD.2.00.1005171443060.4195(a)i5.linux-foundation.org> --- arch/x86/include/asm/arch_hweight.h | 10 ++++++---- 1 files changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h index d1fc3c2..9686c3d 100644 --- a/arch/x86/include/asm/arch_hweight.h +++ b/arch/x86/include/asm/arch_hweight.h @@ -2,13 +2,15 @@ #define _ASM_X86_HWEIGHT_H #ifdef CONFIG_64BIT +/* popcnt %edi, %eax -- redundant REX prefix for alignment */ +#define POPCNT32 ".byte 0xf3,0x40,0x0f,0xb8,0xc7" /* popcnt %rdi, %rax */ -#define POPCNT ".byte 0xf3,0x48,0x0f,0xb8,0xc7" +#define POPCNT64 ".byte 0xf3,0x48,0x0f,0xb8,0xc7" #define REG_IN "D" #define REG_OUT "a" #else /* popcnt %eax, %eax */ -#define POPCNT ".byte 0xf3,0x0f,0xb8,0xc0" +#define POPCNT32 ".byte 0xf3,0x0f,0xb8,0xc0" #define REG_IN "a" #define REG_OUT "a" #endif @@ -23,7 +25,7 @@ static inline unsigned int __arch_hweight32(unsigned int w) { unsigned int res = 0; - asm (ALTERNATIVE("call __sw_hweight32", POPCNT, X86_FEATURE_POPCNT) + asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT) : "="REG_OUT (res) : REG_IN (w)); @@ -48,7 +50,7 @@ static inline unsigned long __arch_hweight64(__u64 w) return __arch_hweight32((u32)w) + __arch_hweight32((u32)(w >> 32)); #else - asm (ALTERNATIVE("call __sw_hweight64", POPCNT, X86_FEATURE_POPCNT) + asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT) : "="REG_OUT (res) : REG_IN (w)); #endif /* CONFIG_X86_32 */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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