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

[Mark Cave-Ayland]

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.