Re: QEMU requires a 64-bit CPU host architecture?

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

On 25/3/26 11:24, Peter Maydell wrote:
> On Wed, 25 Mar 2026 at 09:19, Daniel P. Berrangé <berrange@redhat.com> wrote:
>>
>> On Wed, Mar 25, 2026 at 11:08:41AM +0300, Michael Tokarev wrote:
>>> On 20.03.2026 09:45, Michael Tokarev wrote:
>>>> Hi!
>>>>
>>>> Is it intentional that qemu does not build utilities on 32bit hosts
>>>> anymore?
>>>
>>> This is
>>>
>>> commit 372ec46b9f1215f48a4717f2b7ed969f65bfadc6
>>> Author: Richard Henderson <richard.henderson@linaro.org>
>>> Date:   Thu Dec 18 09:56:27 2025 +1100
>>>
>>>      meson: Reject 32-bit hosts
>>>
>>>      32-bit hosts have been deprecated since 10.0.
>>>
>>> How would one build qemu-img and especially qemu-guest-agent, say,
>>> on i386 or armhf?
>>>
>>> I tried removing this error message from meson.build (in $subject),
>>> but it fails to build even the qga due to errors in atomic.h, -
>>> even if these aren't used by qga.
>>>
>>> That smells like a bad decision, - to drop qga and qemu-img support
>>> on 32bit architectures.  Especially qga.
>>
>> IMHO dropping the block related tools is reasonable, as if you keep
>> that, the dependencies that need to remain 32-bit compatible ripple
>> out across a very large part of the codebase.
>>
>> Not having qga though feels like a pretty undesirable consequence,
>> given our message overall is that we were dropping host support but
>> keeping 32-bit emulation.
> 
> Yes, I'm not sure we quite realised that we would be no longer
> building QGA for 32-bits. How much effort would it be to
> reinstate that?

 From the commits in 5053e0a65db...90e2e8ada7c we'd need to (partially)
revert various of the buildsys ones (meson & configure).

Then we'd need to check if the Stat64 API (90e2e8ada7c) was used by
the block tools, and if so also revert the atomic64 patches (around
997d86a9bb1). If not some (sane) refactor is needed for some core
components (disentangle qdev from qom due to the atomic uses). Still
we rely heavily on atomic helpers for threads and co-routines used
by the block layer (and also to reference the QOM objects...).

How / where would we test that (and for how long)?