On Wed, May 29, 2013 at 03:41:09PM +0200, Paolo Bonzini wrote:
> Il 29/05/2013 15:24, Michael S. Tsirkin ha scritto:
> > You expect a compiler to pad this structure:
> >
> > struct foo {
> > uint8_t a;
> > uint8_t b;
> > uint16_t c;
> > uint32_t d;
> > };
> >
> > I'm guessing any compiler that decides to waste memory in this way
> > will quickly get dropped by users and then we won't worry
> > about building QEMU with it.
>
> You know the virtio-pci config structures are padded, but not all of
> them are. For example, virtio_balloon_stat is not padded and indeed has
> an __attribute__((__packed__)) in the spec.
>
> For this reason I prefer to have the attribute everywhere. So people
> don't have to wonder why it's here and not there.
>
> Paolo
FWIW I think it was a mistake to lay the balloon structure out like that.
We should have padded it manually.
__attribute__((__packed__)) is really easy to misuse.
If you get into such a situation, just use offset enums ...
--
MST
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