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

[Thomas Huth]

On 27/02/2023 23.32, Philippe Mathieu-Daudé wrote:
> 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".

No, I think you misunderstood something here. x86 CPUs always start in 
16-bit mode, as far as I know, and the firmware / OS then has to switch to 
32-bit or 64-bit mode as desired.

 Thomas