Re: [PATCH 1/2] docs/about: Deprecate 32-bit x86 hosts and qemu-system-i386

[Philippe Mathieu-Daudé]

On 27/2/23 21:12, Michael S. Tsirkin wrote:
> On Mon, Feb 27, 2023 at 11:50:07AM +0000, Daniel P. Berrangé wrote:
> > I feel like we should have separate deprecation entries for the
> > i686 host support, and for qemu-system-i386 emulator binary, as
> > although they're related they are independant features with
> > differing impact. eg removing qemu-system-i386 affects all
> > host architectures, not merely 32-bit x86 host, so I think we
> > can explain the impact more clearly if we separate them.
>
> Removing qemu-system-i386 seems ok to me - I think qemu-system-x86_64 is
> a superset.

Doesn't qemu-system-i386 start the CPU in a different mode that
qemu-system-x86_64? Last time we discussed it, we mention adding
-32 and -64 CLI flags to maintain compat, and IIRC this flag would
add boot code to switch the CPU in 32-b. But then maybe I misunderstood.
Thomas said, "CPUs must start in the same mode they start in HW".

> Removing support for building on 32 bit systems seems like a pity - it's
> one of a small number of ways to run 64 bit binaries on 32 bit systems,
> and the maintainance overhead is quite small.
>
> In fact, keeping this support around forces correct use of
> posix APIs such as e.g. PRIx64 which makes the code base
> more future-proof.