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

[Alex Bennée]

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? 

>
> Sound like a good alternative to me!
>
>  Thomas

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro