Re: [PATCH v2 0/3] target/i386: allow using named CPU modeles with user mode emulation

[Daniel P . Berrangé]

On Mon, Jun 26, 2023 at 11:27:54AM +0200, Paolo Bonzini wrote:
> On Mon, Jun 26, 2023 at 11:20 AM Daniel P. Berrangé <berrange@redhat.com> 
> wrote:
> > > - for qemu-i386, the issue is that this emulator is restricted to running
> > >   programs on a 32-bit processor, even though it is actually emulating
> > >   programs that use the 32-bit kernel ABI on any processor.  The behavior
> > >   the processor in compatibility (32-bit CS, EFER.LMA=1) mode is mostly
> > >   the same as when EFER.LMA=0 and the little code that is needed to handle
> > >   64-bit ring-0 is even present in the qemu-i386 binary, just hidden
> > >   behind checks for HF_LMA_MASK.  So, LM can also be treated as a feature
> > >   that is only relevant in kernel mode; not entirely, so this cannot yet
> > >   be extended to bsd-user, but the required changes are minimal.
> >
> > IMHO in this case we should hard block all named CPUs with
> > 'lm' set from qemu-i386. It only makes sense to use named CPU
> > models that were actually from the 32-bit era with qemu-i386.
> >
> > If someone wants Nehalem then they should be using qemu-x86_64.
> > If someone wants qemu-i386 then they should be using an older
> > named CPU model predating 'lm'.
> 
> What you write is true for qemu-system-*, but the problem is that
> qemu-user binaries are only able to run one ELF target. qemu-x86_64 is
> not able to run i386 binaries, unlike a 64-bit kernel; and that's
> really intrinsic in the design of qemu-user because implementing
> multiple ABIs (including multiple definitions of structs and syscall
> numbers) would require compiling the same files multiple times.

Oh, right, yes, ignore my comment.


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|