Re: [PATCH 0/5] Reinstate ability to use Qemu on pre-SSE4.1 x86 hosts

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jun 12, 2024 at 01:55:20PM +0300, Alexander Monakov wrote:
> Hello,
> 
> I'm sending straightforward reverts to recent patches that bumped minimum
> required x86 instruction set to SSE4.2. The older chips did not stop working,
> and people still test and use new software on older hardware:
> https://sourceware.org/bugzilla/show_bug.cgi?id=31867
> 
> Considering the very minor gains from the baseline raise, I'm honestly not
> sure why it happened. It seems better to let distributions handle that.

Indeed distros are opinionated about the x86_64 baseline they want
to target.

While RHEL-9 switched to a x86_64-v2 baseline, Fedora has repeatedly
rejected the idea of moving to an x86_64-v2 baseline, wanting to retain
full backwards compat. So this assumption in QEMU is preventing the
distros from satisfying their chosen build target goals.

> Alexander Monakov (5):
>   Revert "host/i386: assume presence of POPCNT"
>   Revert "host/i386: assume presence of SSSE3"
>   Revert "host/i386: assume presence of SSE2"
>   Revert "host/i386: assume presence of CMOV"
>   Revert "meson: assume x86-64-v2 baseline ISA"
> 
>  host/include/i386/host/cpuinfo.h |  3 +++
>  meson.build                      | 10 +++-------
>  tcg/i386/tcg-target.c.inc        | 15 ++++++++++++++-
>  tcg/i386/tcg-target.h            |  5 +++--
>  util/bufferiszero.c              |  4 ++--
>  util/cpuinfo-i386.c              |  7 +++++--
>  6 files changed, 30 insertions(+), 14 deletions(-)
> 
> -- 
> 2.32.0
> 
> 

With regards,
Daniel
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