[PATCH v10 7/9] powerpc64: Add optimized chacha20

[Adhemerval Zanella Netto]

On 15/07/22 16:48, Paul E Murphy wrote:
> 
> 
> On 7/14/22 6:28 AM, Adhemerval Zanella via Libc-alpha wrote:
>> From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
> 
>> +++ b/sysdeps/powerpc/powerpc64/be/multiarch/chacha20_arch.h
>> @@ -0,0 +1,42 @@
>> +/* PowerPC optimization for ChaCha20.
>> +   Copyright (C) 2022 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <http://www.gnu.org/licenses/>.  */
>> +
>> +#include <stdbool.h>
>> +#include <ldsodefs.h>
>> +
>> +unsigned int __chacha20_power8_blocks4 (uint32_t *state, uint8_t *dst,
>> +                    const uint8_t *src, size_t nblks)
>> +     attribute_hidden;
>> +
>> +static void
>> +chacha20_crypt (uint32_t *state, uint8_t *dst,
>> +        const uint8_t *src, size_t bytes)
>> +{
>> +  _Static_assert (CHACHA20_BUFSIZE % 4 == 0,
>> +          "CHACHA20_BUFSIZE not multiple of 4");
>> +  _Static_assert (CHACHA20_BUFSIZE >= CHACHA20_BLOCK_SIZE * 4,
>> +          "CHACHA20_BUFSIZE < CHACHA20_BLOCK_SIZE * 4");
>> +
>> +  unsigned long int hwcap = GLRO(dl_hwcap);
>> +  unsigned long int hwcap2 = GLRO(dl_hwcap2);
>> +  if (hwcap2 & PPC_FEATURE2_ARCH_2_07 && hwcap & PPC_FEATURE_HAS_ALTIVEC)
>> +    __chacha20_power8_blocks4 (state, dst, src,
>> +                   CHACHA20_BUFSIZE / CHACHA20_BLOCK_SIZE);
>> +  else
>> +    chacha20_crypt_generic (state, dst, src, bytes);
>> +}
> 
> I wonder if using libc_ifunc_hidden and such might simplify this a little.  I don't feel strongly about this.  I think this patch is OK as is.  LGTM.

I think we can reevaluate it for 2.37, although even a hidden ifunc requires
a PLT call and I think for powerpc it is way costly than global memory load
and a predictable branch. 

> 
> Reviewed-by: Paul E. Murphy <murphyp@linux.ibm.com>
> 

Thanks!