Re: [PATCH RFC 1/4] docs: add a table showing x86-64 ABI compatibility levels

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Feb 01, 2021 at 04:53:03PM +0000, Peter Maydell wrote:
> On Mon, 1 Feb 2021 at 15:39, Daniel P. Berrangé <berrange@redhat.com> wrote:
> >
> > It is useful to know which CPUs satisfy each x86-64 ABI
> > compatibility level, when dealing with guest OS that require
> > something newer than the baseline ABI.
> >
> > These ABI levels are defined in:
> >
> >   https://gitlab.com/x86-psABIs/x86-64-ABI/
> >
> > and supported by GCC, CLang, GLibC and more.
> >
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > +ABI compatibility levels for CPU models
> > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > +
> > +The x86_64 architecture has a number of `ABI compatibility levels`_
> > +defined. Traditionally most operating systems and toolchains would
> > +only target the original baseline ABI. It is expected that in
> > +future OS and toolchains are likely to target newer ABIs. The
> > +following table illustrates which ABI compatibility levels can be
> > +satisfied by the QEMU CPU models
> > +
> > +.. _ABI compatibility levels: https://gitlab.com/x86-psABIs/x86-64-ABI/
> > +
> > +.. csv-table:: x86-64 ABI compatibility levels
> > +   :file: cpu-models-x86-abi.csv
> > +   :widths: 40,15,15,15,15
> > +   :header-rows: 1
> 
> Apart from the QEMU/KVM specific CPU models, why is this something
> we should be documenting rather than, say, the people specifying
> what the ABI compatiblity levels are ?

QEMU's named CPU models are not a perfect match for features in the
real world silicon. So even if someone has a Skylake Server CPU with
feature X, this doesn't mean QEMU's definition of the Skylake-Server
CPU model is guaranteed to have feature X.  So we want to document
the compatibility of the exact CPU models that QEMU has defined.


Regards,
Daniel
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