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From:   Uros Bizjak <ubizjak@gmail.com>
Date:   Wed, 2 Sep 2020 07:52:26 +0200
Message-ID: <CAFULd4YFPFsuZuQRCq1A4u1azNrdtfSxymYA=nM1X=6neycT-g@mail.gmail.com>
Subject: Re: [PATCH] crypto/x86: Use XORL r32,32 in poly1305-x86_64-cryptogams.pl
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Andy Polyakov <appro@cryptogams.org>,
        Linux Crypto List <linux-crypto@vger.kernel.org>,
        X86 ML <x86@kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>
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On Tue, Sep 1, 2020 at 9:16 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> Hi Uros,
>
> Any benchmarks for this? Seems like it's all in initialization code,
> right? I'm CC'ing Andy into this.

This patch should have no performance effect, it saves REX prefix byte
when the optimization is applied to legacy registers.

Uros.

> Jason
>
> On Thu, Aug 27, 2020 at 07:38:31PM +0200, Uros Bizjak wrote:
> > x86_64 zero extends 32bit operations, so for 64bit operands,
> > XORL r32,r32 is functionally equal to XORQ r64,r64, but avoids
> > a REX prefix byte when legacy registers are used.
> >
> > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> > Cc: Herbert Xu <herbert@gondor.apana.org.au>
> > Cc: "David S. Miller" <davem@davemloft.net>
> > ---
> >  arch/x86/crypto/poly1305-x86_64-cryptogams.pl | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/crypto/poly1305-x86_64-cryptogams.pl b/arch/x86/crypto/poly1305-x86_64-cryptogams.pl
> > index 137edcf038cb..7d568012cc15 100644
> > --- a/arch/x86/crypto/poly1305-x86_64-cryptogams.pl
> > +++ b/arch/x86/crypto/poly1305-x86_64-cryptogams.pl
> > @@ -246,7 +246,7 @@ $code.=<<___ if (!$kernel);
> >  ___
> >  &declare_function("poly1305_init_x86_64", 32, 3);
> >  $code.=<<___;
> > -     xor     %rax,%rax
> > +     xor     %eax,%eax
> >       mov     %rax,0($ctx)            # initialize hash value
> >       mov     %rax,8($ctx)
> >       mov     %rax,16($ctx)
> > @@ -2853,7 +2853,7 @@ $code.=<<___;
> >  .type        poly1305_init_base2_44,\@function,3
> >  .align       32
> >  poly1305_init_base2_44:
> > -     xor     %rax,%rax
> > +     xor     %eax,%eax
> >       mov     %rax,0($ctx)            # initialize hash value
> >       mov     %rax,8($ctx)
> >       mov     %rax,16($ctx)
> > @@ -3947,7 +3947,7 @@ xor128_decrypt_n_pad:
> >       mov     \$16,$len
> >       sub     %r10,$len
> >       xor     %eax,%eax
> > -     xor     %r11,%r11
> > +     xor     %r11d,%r11d
> >  .Loop_dec_byte:
> >       mov     ($inp,$otp),%r11b
> >       mov     ($otp),%al
> > @@ -4085,7 +4085,7 @@ avx_handler:
> >       .long   0xa548f3fc              # cld; rep movsq
> >
> >       mov     $disp,%rsi
> > -     xor     %rcx,%rcx               # arg1, UNW_FLAG_NHANDLER
> > +     xor     %ecx,%ecx               # arg1, UNW_FLAG_NHANDLER
> >       mov     8(%rsi),%rdx            # arg2, disp->ImageBase
> >       mov     0(%rsi),%r8             # arg3, disp->ControlPc
> >       mov     16(%rsi),%r9            # arg4, disp->FunctionEntry
> > --
> > 2.26.2
> >
>
> --
> Jason A. Donenfeld
> Deep Space Explorer
> fr: +33 6 51 90 82 66
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> www.jasondonenfeld.com
> www.zx2c4.com
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