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 04:09:29PM +0100, Daniel P. Berrangé wrote:
> On Wed, Jun 12, 2024 at 01:21:26PM +0100, Daniel P. Berrangé wrote:
> > On Wed, Jun 12, 2024 at 01:51:31PM +0200, Paolo Bonzini wrote:
> > > On Wed, Jun 12, 2024 at 1:38 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
> > > > This isn't anything to do with the distro installer. The use case is that
> > > > the distro wants all its software to be able to run on the x86_64 baseline
> > > > it has chosen to build with.
> > > 
> > > Sure, and they can patch the packages if their wish is not shared by
> > > upstream. Alternatively they can live with the fact that not all users
> > > will be able to use all packages, which is probably already the case.
> > 
> > Yep, there's almost certainly scientific packages that have done
> > optimizations in their builds. QEMU is slightly more special
> > though because it is classed as a "critical path" package for
> > the distro. Even the QEMU linux-user pieces are now critical path,
> > since they're leveraged by docker & podman for running foreign arch
> > containers.
> > 
> > > Or drop QEMU, I guess. Has FeSCO ever expressed how strict they are
> > > and which of the three options they'd pick?
> > 
> > I don't know - i'm going to raise this question to find out if
> > there's any guidance.
> 
> I learnt that FESCo approved a surprisingly loose rule saying
> 
>   "Libraries packaged in Fedora may require ISA extensions,
>    however any packaged application must not crash on any
>    officially supported architecture, either by providing
>    a generic fallback implementation OR by cleanly exiting
>    when the requisite hardware support is unavailable."
>

..snip..

I queried the looseness of this wording, and it is suggested
it wasn't intended to apply to existing packages, just newly
added ones. By that interpretation it wouldn't be valid for
QEMU, and we'd be pushed towards the revert downstream, to
retain a runtime check for the feature. I really hate the
idea of keeping a revert of these patches downstream though,
as it would be an indefinite rebase headache.

With regards,
Daniel
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