On Wed, May 29, 2013 at 09:27:02AM +0200, Paolo Bonzini wrote: > Il 29/05/2013 06:33, Rusty Russell ha scritto: > > Paolo Bonzini <pbonz...@redhat.com> writes: > >> Il 28/05/2013 19:32, Michael S. Tsirkin ha scritto: > >>>>>>> + > >>>>>>> + switch (addr) { > >>>>>>> + case offsetof(struct virtio_pci_common_cfg, > >>>>>>> device_feature_select): > >>>>>>> + return proxy->device_feature_select; > >>>>> > >>>>> Oh dear no... Please use defines like the rest of QEMU. > >>> Any good reason not to use offsetof? > >> > >> I'm not sure it's portable to use it in case labels. IIRC, the > >> definition ((int)&(((T *)0)->field)) is not a valid C integer constant > >> expression. Laszlo? > > > > It's defined to yield an integer constant expression in the ISO standard > > (and I think ANSI too, though that's not at hand): > > It's not in C89. The oldest compiler QEMU cares about is GCC 4.2. I > don't know if it has a builtin offsetof, probably it does.
Yes, I think __builtin_offsetof was added in 4.0: http://gcc.gnu.org/onlinedocs/gcc-4.0.0/gcc/Offsetof.html > But I'm not sure about other users of virtio headers. > > Paolo > > > > 7.19, para 3: > > > > ...offsetof(type, member-designator) > > which expands to an integer constant expression that has type > > size_t, ... > > > > The real question is whether compilers qemu cares about meet the > > standard (there's some evidence that older compilers fail this). If > > not, we'll have to define them as raw offsets... So I think the question is whether we care about GCC 3. We used to when mingw in debian stable was GCC 3, but not anymore ... > > > > Cheers, > > Rusty. > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html