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

[BALATON Zoltan]

On Tue, 4 Apr 2023, Thomas Huth wrote:
> 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

Another issue I know is that mac99 behaves differently in qemu-system-ppc 
and qemu-system-ppc64. This is not only confusing users but makes it more 
difficult to get rid of qemu-system-ppc. I've tried to solve that and 
sumbitted a patch to start deprecating these but I could not get that 
merged. That thread ended here:

https://lists.nongnu.org/archive/html/qemu-ppc/2023-01/msg00406.html

Regards,
BALATON Zoltan