Re: [PATCH 0/1] meson: Deprecate 32-bit host systems

[Daniel P . Berrangé]

On Tue, Jan 28, 2025 at 09:02:48AM +0000, Alex Bennée wrote:
> Thomas Huth <thuth@redhat.com> writes:
> 
> > On 28/01/2025 01.42, Richard Henderson wrote:
> >> Time for our biennial attempt to kill ancient hosts.
> >> I've been re-working the tcg code generator a bit over the holidays.
> >> One place that screams for a bit of cleanup is with 64-bit guest
> >> addresses on 32-bit hosts.  Of course the best "cleanup" is to not
> >> have to handle such silliness at all.
> >> Two years after Thomas' last attempt,
> >>    
> >> https://lore.kernel.org/qemu-devel/20230130114428.1297295-1-thuth@redhat.com/
> >> which resulted only in deprecation of i686 host for system
> >> emulation.
> >> By itself, this just isn't enough for large-scale cleanups.
> >> I'll note that we've separately deprecated mips32, set to expire
> >> with the end of Debian bookworm, set to enter LTS in June 2026.
> >> I'll note that there is *already* no Debian support for ppc32,
> >> and that I am currently unable to cross-compile that host at all.
> >
> > IIRC the biggest pushback that I got two years ago was with regards to
> > 32-bit arm: The recommended version of Raspberry Pi OS is still
> > 32-bit:
> >
> >  
> > https://lore.kernel.org/qemu-devel/F852C238-77B8-4E24-9494-8D060EB78F9F@livius.net/
> >
> > And looking at https://www.raspberrypi.com/software/operating-systems/
> > this still seems to be the case...
> >
> > So I guess the main question is now: Would it be ok to kill support
> > for 32-bit Raspberry Pi OS nowadays?
> 
> I would argue yes for a few reasons.
> 
>   - you can't buy 32 bit only Pi's AFAICT, even the Pi Zero 2W can work
>     with a 64 bit OS.
> 
>   - It's not like the versions shipping in bullseye and bookworm will
>     stop working.
> 
>   - Even if we deprecate now there will likely be one more Debian
>     release cycle that gets 32 bit host support.
> 
> >> Showing my hand a bit, I am willing to limit deprecation to
> >> 64-bit guests on 32-bit hosts.  But I'd prefer to go the whole hog:
> >> unconditional support for TCG_TYPE_I64 would remove a *lot* of
> >> 32-bit fallback code.
> 
> I support going the whole hog. I would be curious what use cases still
> exist for an up to date 32-on-32 QEMU based emulation?

Last time we discussed this, we distinguished between system emulation
and linux-user. I believe Richard is proposing to deprecated *both*,
but lets call that out explicitly in any deprecation message to avoid
mis-understandings.

With regards,
Daniel
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