On Wed, 6 Apr 2016 12:13:00 +0200
Borislav Petkov <b...@suse.de> wrote:
> On Wed, Apr 06, 2016 at 05:14:45PM +0800, zengzhao...@163.com wrote:
> > From: Zhaoxiu Zeng <zhaoxiu.z...@gmail.com>
> >
> > Use alternatives, lifted from arch_hweight
> >
> > Signed-off-by: Zhaoxiu Zeng <zhaoxiu.z...@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
