diff options
| author | H. Peter Anvin <hpa@linux.intel.com> | 2010-05-17 15:13:23 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2010-05-17 15:17:16 -0700 |
| commit | c59bd5688299cddb71183e156e7a3c1409b90df2 (patch) | |
| tree | d7b99407367b30aa7766219083ad0262c8edbab8 /arch | |
| parent | 4677d4a53e0d565742277e8913e91c821453e63e (diff) | |
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@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <alpine.LFD.2.00.1005171443060.4195@i5.linux-foundation.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | 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 d1fc3c219ae..9686c3d9ff7 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 */ |