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

[Julien Grall <julien.grall@xxxxxxx>]

On 24/11/16 15:50, Artem Mygaiev wrote:
> On 24.11.16 17:09, Julien Grall wrote:
> > Hi Artem,
> >
> > On 24/11/16 14:58, Artem Mygaiev wrote:
> > > 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.
> > I am not sure why you mentioned embedded RTOS, this is specific to the
> > compiler and not an OS.
> Indeed, my statement is not quite correct. It is just that there are
> proprietary RTOSes bundled with IDEs with own or customized tools,
> compilers, etc.
And their own ABI? It sounds crazy to me that someone may decide to use 
padding even when field are naturally aligned.
Regards,

--
Julien Grall

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