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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

> 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 ...

> the all architectures. The potential breakage of compatibility is ought

Nit: Drop "is".

> 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?

Jan