Messages in this thread | | | Date | Wed, 6 Apr 2016 11:37:37 +0100 | From | One Thousand Gnomes <> | Subject | Re: [PATCH v2 10/30] Add x86-specific parity functions |
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On Wed, 6 Apr 2016 12:13:00 +0200 Borislav Petkov <bp@suse.de> wrote:
> On Wed, Apr 06, 2016 at 05:14:45PM +0800, zengzhaoxiu@163.com wrote: > > From: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com> > > > > Use alternatives, lifted from arch_hweight > > > > Signed-off-by: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com> > > --- > > arch/x86/include/asm/arch_hweight.h | 5 ++ > > arch/x86/include/asm/arch_parity.h | 102 ++++++++++++++++++++++++++++++++++++ > > arch/x86/include/asm/bitops.h | 4 +- > > arch/x86/lib/Makefile | 8 +++ > > arch/x86/lib/parity.c | 32 ++++++++++++ > > 5 files changed, 150 insertions(+), 1 deletion(-) > > create mode 100644 arch/x86/include/asm/arch_parity.h > > create mode 100644 arch/x86/lib/parity.c > > ... > > > +static __always_inline unsigned int __arch_parity32(unsigned int w) > > +{ > > + unsigned int res; > > + > > + asm(ALTERNATIVE("call __sw_parity32", POPCNT32 "; and $1, %0", X86_FEATURE_POPCNT) > > + : "="REG_OUT (res) > > + : REG_IN (w) > > + : "cc"); > > So why all that churn instead of simply doing: > > static __always_inline unsigned int __arch_parity32(unsigned int w) > { > return hweight32(w) & 1; > } > > Ditto for the 64-bit version.
Even that would still be wrong for the smaller parity values. The CPU supports 8bit parity directly going back to the 8086 so the implementation for 8bit and I think 16bit is still wrong.
Alan
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