Re: [PATCH v4 for-4.14 2/2] pvcalls: Document correctly and explicitely the padding for all arches

[Julien Grall <julien@xxxxxxx>]

Hi,

Gentle ping.

Is the new commit message fine?

Cheers,

On 04/07/2020 16:29, Julien Grall wrote:
> Hi,
>
> On 27/06/2020 10:55, Julien Grall wrote:
> > From: Julien Grall <jgrall@xxxxxxxxxx>
> >
> > The specification of pvcalls suggests there is padding for 32-bit x86
> > at the end of most the structure. However, they are not described in
> > in the public header.
> >
> > Because of that all the structures would be 32-bit aligned and not
> > 64-bit aligned for 32-bit x86.
> >
> > For all the other architectures supported (Arm and 64-bit x86), the
> > structure are aligned to 64-bit because they contain uint64_t field.
> > Therefore all the structures contain implicit padding.
> >
> > Given the specification is authoriitative, the padding will the same for
> > the all architectures. The potential breakage of compatibility is ought
> > to be fine as pvcalls is still a tech preview.
> >
> > As an aside, the padding sadly cannot be mandated to be 0 as they are
> > already present. So it is not going to be possible to use the padding
> > for extending a command in the future.
> >
> > Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> It looks like most of the comments are on the commit message. So rather 
> than sending the series again, below a new version of the commit message:
> "
> The specification of pvcalls suggests there is padding for 32-bit x86
> at the end of most the structure. However, they are not described in
> in the public header.
>
> Because of that all the structures would have a different size between 
> 32-bit x86 and 64-bit x86.
> For all the other architectures supported (Arm and 64-bit x86), the
> structure have the sames sizes because they contain implicit padding 
> thanks to the 64-bit alinment of the field uint64_t field.
> Given the specification is authoritative, the padding will now be the 
> same for all architectures. The potential breakage of compatibility is 
> ought to be fine as pvcalls is still a tech preview.
> "
>
> Cheers,
--
Julien Grall