On Tue, Sep 1, 2020 at 9:16 PM Jason A. Donenfeld <Jason@xxxxxxxxx> 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@xxxxxxxxx>
> > Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> > ---
> > 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
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