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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 28/1/25 10:02, 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?

Current maintainers don't have spare time to support the 32-on-32
emulation. If there is interest in the community for such niche,
someone needs to step forward, willing to maintain it.