Messages in this thread | | | From | Stefan Schake <> | Date | Tue, 1 May 2018 02:11:37 +0200 | Subject | Re: [PATCH] drm/vc4: Add a pad field to align drm_vc4_submit_cl to 64 bits. |
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On Tue, May 1, 2018 at 1:59 AM, Eric Anholt <eric@anholt.net> 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@gmail.com>
Thanks, Stefan
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