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>hifive-unleashed-5.1
parent
4677d4a53e
commit
c59bd56882
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@ -2,13 +2,15 @@
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#define _ASM_X86_HWEIGHT_H
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#define _ASM_X86_HWEIGHT_H
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#ifdef CONFIG_64BIT
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#ifdef CONFIG_64BIT
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/* popcnt %edi, %eax -- redundant REX prefix for alignment */
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#define POPCNT32 ".byte 0xf3,0x40,0x0f,0xb8,0xc7"
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/* popcnt %rdi, %rax */
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/* popcnt %rdi, %rax */
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#define POPCNT ".byte 0xf3,0x48,0x0f,0xb8,0xc7"
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#define POPCNT64 ".byte 0xf3,0x48,0x0f,0xb8,0xc7"
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#define REG_IN "D"
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#define REG_IN "D"
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#define REG_OUT "a"
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#define REG_OUT "a"
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#else
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#else
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/* popcnt %eax, %eax */
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/* popcnt %eax, %eax */
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#define POPCNT ".byte 0xf3,0x0f,0xb8,0xc0"
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#define POPCNT32 ".byte 0xf3,0x0f,0xb8,0xc0"
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#define REG_IN "a"
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#define REG_IN "a"
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#define REG_OUT "a"
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#define REG_OUT "a"
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#endif
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#endif
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@ -23,7 +25,7 @@ static inline unsigned int __arch_hweight32(unsigned int w)
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{
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{
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unsigned int res = 0;
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unsigned int res = 0;
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asm (ALTERNATIVE("call __sw_hweight32", POPCNT, X86_FEATURE_POPCNT)
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asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT)
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: "="REG_OUT (res)
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: "="REG_OUT (res)
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: REG_IN (w));
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: REG_IN (w));
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@ -48,7 +50,7 @@ static inline unsigned long __arch_hweight64(__u64 w)
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return __arch_hweight32((u32)w) +
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return __arch_hweight32((u32)w) +
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__arch_hweight32((u32)(w >> 32));
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__arch_hweight32((u32)(w >> 32));
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#else
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#else
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asm (ALTERNATIVE("call __sw_hweight64", POPCNT, X86_FEATURE_POPCNT)
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asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
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: "="REG_OUT (res)
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: "="REG_OUT (res)
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: REG_IN (w));
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: REG_IN (w));
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#endif /* CONFIG_X86_32 */
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#endif /* CONFIG_X86_32 */
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