> > I'm not entirely convinced this is true; If we'll not enforce the > > alignment of this 64-bit field, it's possible there will be > > differences between 32-bit and 64-bit machines versions of this struct. > > You have to recall that this is going to be copied via DMA between PF > > and VF, so they must have the exact same representation of the structure. > > Then use properly sized types to fill in all the space in the structure, > that's how > you guarantee layout, not aligned_u64. Also, do not use the packed attribute. > > struct foo { > u32 x; > u32 y; > u64 z; > }; > > 'z' will always be 64-bit aligned.
Perhaps my bit-numeric is a bit weak - why is it so? I.e., what prevents `z' from only being 32-bit aligned on a 32-bit machine? Isn't it possible that (&x % 8) == 4, (&y % 8) == 0 and (&z % 8) == 4 on such a platform?