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Re: [PATCH 0/2] target/ppc: Fix vextu[bhw][lr]x on big endian hosts


From: Matheus K. Ferst
Subject: Re: [PATCH 0/2] target/ppc: Fix vextu[bhw][lr]x on big endian hosts
Date: Wed, 25 Aug 2021 22:28:13 -0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 25/08/2021 09:55, Mark Cave-Ayland wrote:
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On 24/08/2021 21:11, matheus.ferst@eldorado.org.br wrote:

From: Matheus Ferst <matheus.ferst@eldorado.org.br>

The definition of struct Int128 is currently independent of the host
endianness, causing different results when using the member s128 of
union ppc_vsr_t in big-endian builds with CONFIG_INT128 or
!CONFIG_INT128.

The only PPC instructions that seem to be affected by this issue are the
"Vector Extract Unsigned Byte/Halfword/Word to GPR using GPR-specified
Left/Right-Index." Even on builds with Int128 support, however, their
helpers give the wrong result on big-endian hosts.

The first patch in this series changes the definition of struct Int128
to allow its use in the ppc_vsr_t union. The second patch fixes the
helper definition.

Matheus Ferst (2):
   include/qemu/int128.h: define struct Int128 according to the host
     endianness
   target/ppc: fix vextu[bhw][lr]x helpers

  include/qemu/int128.h   | 19 ++++++++++++-------
  target/ppc/int_helper.c | 38 ++++++++++----------------------------
  2 files changed, 22 insertions(+), 35 deletions(-)

Hi Matheus,

Slightly unrelated to this patchset, however I see you've managed to make some good efforts in consolidating the functionality between big-endian and little-endian host
systems.

When I first worked on adding host vector support for PPC I noticed there were some further places in target/ppc/int_helper.c that could be improved from accessing ppc_avr_t fields such as u64 directly and instead using the relevant Vsr*() macros.

If you feel suitably motivated, it would be amazing to see more patches to help this further along: basically look in target/ppc/int_helper.c for individual elements such as u64 (and also the VECTOR_FOR_INORDER_I macro) and determine which ones are better
replaced by the relevant Vsr*() macro.


ATB,

Mark.

Hi Mark,

That would be a nice change. Our efforts are currently on PowerISA v3.1 instructions, but I'll try to change that in helpers of things we move to decodetree. After completing the new instructions, I can give a shot in a Vsr*() patchset.

--
Matheus K. Ferst
Instituto de Pesquisas ELDORADO <http://www.eldorado.org.br/>
Analista de Software Júnior
Aviso Legal - Disclaimer <https://www.eldorado.org.br/disclaimer.html>



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