Re: [Embedded-pv-devel] [PATCH v9] xen: add para-virtual sound interface header files

[Artem Mygaiev <artem_mygaiev@xxxxxxxx>]

On 24.11.16 15:31, Jan Beulich wrote:
>>>> On 24.11.16 at 14:18, <artem_mygaiev@xxxxxxxx> wrote:
>> On 24.11.16 15:04, Jan Beulich wrote:
>>>> In my case I need it to at least define Linux specific __packed
>>>> attribute which is not supported by Win AFAIK.
>>> ... needs to avoid using platform specific constructs (or making
>>> other assumptions on the platform). I can only re-iterate: Please
>>> follow the model other PV protocols already present (without
>>> repeating their mistakes, if at all possible).
>> But if we don't pack (or enforce some specific alignment) data
>> structures used between domains they may have different alignment on
>> different domains, no?
> Let me repeat what I've said before: Please take a look at existing
> interface headers. By properly placing fields and adding explicit
> padding where needed, you can avoid such layout differences.

Don't get me wrong - I have checked the i/f headers before. My concern
is very generic: C standard defines alignment as an
*implementation-defined* integer, so current implementation is based
under two assumptions on the guest platforms: a) guest compiler does not
have "packing" enabled by default and b) alignment follows typical
values (1 byte for char, 2 bytes for short, ...). While this is true in
most cases, with some embedded RTOS this may become an issue.

This is not critical/important ATM, and completely disconnected from the
purpose of the patch, so I agree it has to be rewritten according to
current practices.

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