Re: [PATCH] crypto/x86: Use XORL r32,32 in poly1305-x86_64-cryptogams.pl

["Jason A. Donenfeld" <Jason@zx2c4.com>]

Hi Uros,

Any benchmarks for this? Seems like it's all in initialization code,
right? I'm CC'ing Andy into this.

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
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