Re: [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@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@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