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

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 29/06/2020 09:28, Jan Beulich wrote:
> On 27.06.2020 11:55, 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.
> The added padding doesn't change the alignment. It's sizeof() which
> gets corrected this way.
I will update the commit message.

> > 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
> Nit: ... will be the same ...
Ok.

> > the all architectures. The potential breakage of compatibility is ought
> Nit: Drop "is".
Ok.

> > 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.
> Why is the other adjustment fine to make due to still being tech
> preview, but this one wouldn't be for the same reason?
This is mostly a left-over of the previous message. Although, I am not 
really inclined to address this myself any time soon.
Cheers,

--
Julien Grall