[RFC PATCH] docs/about/deprecated: Deprecate 32-bit host systems

[Thomas Huth]

On 05/02/2023 23.12, Mark Cave-Ayland wrote:
> On 30/01/2023 20:45, Alex Bennée wrote:
> 
>> Daniel P. Berrangé <berrange at redhat.com> writes:
>>
>>> On Mon, Jan 30, 2023 at 11:47:02AM +0000, Peter Maydell wrote:
>>>> On Mon, 30 Jan 2023 at 11:44, Thomas Huth <thuth at redhat.com> wrote:
>>>>>
>>>>> Testing 32-bit host OS support takes a lot of precious time during the 
>>>>> QEMU
>>>>> contiguous integration tests, and considering that many OS vendors stopped
>>>>> shipping 32-bit variants of their OS distributions and most hardware from
>>>>> the past >10 years is capable of 64-bit
>>>>
>>>> True for x86, not necessarily true for other architectures.
>>>> Are you proposing to deprecate x86 32-bit, or all 32-bit?
>>>> I'm not entirely sure about whether we're yet at a point where
>>>> I'd want to deprecate-and-drop 32-bit arm host support.
>>>
>>> Do we have a feeling on which aspects of 32-bit cause us the support
>>> burden ? The boring stuff like compiler errors from mismatched integer
>>> sizes is mostly quick & easy to detect simply through a cross compile.
>>>
>>> I vaguely recall someone mentioned problems with atomic ops in the past,
>>> or was it 128-bit ints, caused implications for the codebase ?
>>
>> Atomic operations on > TARGET_BIT_SIZE and cputlb when
>> TCG_OVERSIZED_GUEST is set. Also the core TCG code and a bunch of the
>> backends have TARGET_LONG_BITS > TCG_TARGET_REG_BITS ifdefs peppered
>> throughout.
> 
> I am one of an admittedly small group of people still interested in using 
> KVM-PR on ppc32 to boot MacOS, although there is some interest on using 
> 64-bit KVM-PR to run super-fast MacOS on modern Talos hardware.
> 
>  From my perspective losing the ability to run 64-bit guests on 32-bit 
> hardware with TCG wouldn't be an issue, as long as it were still possible to 
> use qemu-system-ppc on 32-bit hardware using both TCG and KVM to help debug 
> the remaining issues.

  Hi Mark!

Just out of curiosity (since we briefly talked about 32-bit KVM on ppc in 
today's QEMU/KVM call - in the context of whether qemu-system-ppc64 is a 
proper superset of qemu-system-ppc when it comes to building a unified 
qemu-system binary): What host machine are you using for running KVM-PR? And 
which QEMU machine are you using for running macOS? The mac99 or the g3beige 
machine?

Unrelated to KVM: Do you happen to know whether there are any problems when 
running 32-bit guests with TCG with the mac99 or g3beige machine while using 
qemu-system-ppc64 ?

  Thanks,
   Thomas