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

[Mark Cave-Ayland]

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.


ATB,

Mark.