On Tue, May 1, 2018 at 1:59 AM, Eric Anholt <eric@xxxxxxxxxx> wrote: > I had originally asked Stefan Schake to drop the pad field from the > syncobj changes that just landed, because I couldn't come up with a > reason to align to 64 bits. > > Talking with Dave Airlie about the new v3d driver's submit ioctl, we > came up with a reason: sizeof() on 64-bit platforms may align to 64 > bits, in which case the userspace will be submitting the aligned size > and the final 32 bits won't be zero-padded by the kernel. If > userspace doesn't zero-fill, then a future ABI change adding a 32-bit > field at the end could potentially cause the kernel to read undefined > data from old userspace (our userspace happens to use structure > initialization that zero-fills, but as a general rule we try not to > rely on that in the kernel). > Did a quick sizeof check on arm64 and that indeed came to 176 mod 8 = 0, suggesting we need this additional pad. So fwiw Reviewed-by: Stefan Schake <stschake@xxxxxxxxx> Thanks, Stefan _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
