On 1/22/19 12:18 PM, Peter Maydell wrote: > Various ipv6 structs in the slirp headers are marked QEMU_PACKED, > but they are actually naturally aligned and will have no padding > in them. Instead of marking them with the 'packed' attribute, > assert at compile time that they are the size we expect. This > allows us to take the address of fields within the structs > without risking undefined behaviour, and suppresses clang > -Waddress-of-packed-member warnings. > > Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > --- > slirp/ip6.h | 12 ++++++++++-- > slirp/ip6_icmp.h | 20 +++++++++++++++----- > 2 files changed, 25 insertions(+), 7 deletions(-) >
> +/* > + * We don't want to mark these ip6 structs as packed as they are naturally > + * correctly aligned; instead assert that there is no stray padding. > + * If we marked the struct as packed then we would be unable to take > + * the address of any of the fields in it. > + */ > +QEMU_BUILD_BUG_ON(sizeof(struct ip6) != 40); > +QEMU_BUILD_BUG_ON(sizeof(struct ip6_pseudohdr) != 40); Nice. (And IIRC, the IPv6 designers tried to pick natural alignments on purpose) Reviewed-by: Eric Blake <ebl...@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
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