On 12 August 2017 at 12:04, Samuel Thibault <samuel.thiba...@gnu.org> wrote: > Peter Maydell, on sam. 12 août 2017 11:53:20 +0100, wrote: >> The utility of the warning is that it means you get told >> about stuff that might break on other architectures. > > Sure, I understand that. But here all fields are aligned on their size > inside the packed structure. So there can't be alignment issues, and the > compiler should be able to determine that.
Alignment is architecture-dependent, and the compiler can't know the alignment requirements for every architecture. There's no rule in C that says that uint16_t only needs 2 byte alignment and not 4 on some hosts. (Also I just noticed 'struct ip6' uses bitfields: that's badly non-portable if it's trying to match an on-the-wire layout.) thanks -- PMM
