Re: [Xen-devel] [PATCH] xen: only clobber multicall elements without error

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 11/27/18 7:34 AM, Juergen Gross wrote:
> On 26/11/2018 17:51, Julien Grall wrote:
> > On 26/11/2018 16:17, Juergen Gross wrote:
> > > On 26/11/2018 17:01, Julien Grall wrote:
> > > > On 26/11/2018 15:29, Juergen Gross wrote:
> > > > > On 26/11/2018 15:58, Jan Beulich wrote:
> > > > > > > > > On 26.11.18 at 15:23, <jgross@xxxxxxxx> wrote:
> > > > > > > On 26/11/2018 15:01, Jan Beulich wrote:
> > > > > > > > > > > On 26.11.18 at 14:52, <jgross@xxxxxxxx> wrote:
> > Secondly, you are introducing an ABI change without explicitly telling
> > it. This should be clarified in the public interface and probably the
> > multicall code to avoid re-introducing the clobbering in the future.
> No, I don't think I'm introducing an ABI change. There is no guarantee
> Xen will clobber all multicall arguments. In fact a NDEBUG hypervisor
> never does. The guest must not rely on non-clobbered values, of course.
The last sentence is what the ABI promises you. The rest is a 
implementation decision to avoid performance impact.
If you don't change the ABI, then how the guest will be able to know the 
values are correct? Furthermore, as your change are not documented how 
do you guarantee that this will not be reverted in the future?
Cheers,

--
Julien Grall

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