On 09.04.2014 15:39, Thierry Reding wrote:
> From: Thierry Reding <treding@xxxxxxxxxx>
>
> The version of the drm_tegra_submit structure that was merged all the
> way back in 3.10 contains a pad field that was originally intended to
> properly pad the following __u64 field. Unfortunately it seems like a
> different field was dropped during review that caused this padding to
> become unnecessary, but the pad field wasn't removed at that time.
>
> One possible side-effect of this is that since the __u64 following the
> pad is now no longer properly aligned, the compiler may (or may not)
> introduce padding itself, which results in no predictable ABI.
>
> Rectify this by removing the pad field so that all fields are again
> naturally aligned. Technically this is breaking existing userspace ABI,
> but given that there aren't any (released) userspace drivers that make
> use of this yet, the fallout should be minimal.
>
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
> ---
> include/uapi/drm/tegra_drm.h | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/include/uapi/drm/tegra_drm.h b/include/uapi/drm/tegra_drm.h
> index b042b48495d9..b75482112428 100644
> --- a/include/uapi/drm/tegra_drm.h
> +++ b/include/uapi/drm/tegra_drm.h
> @@ -120,7 +120,6 @@ struct drm_tegra_submit {
> __u32 num_waitchks;
> __u32 waitchk_mask;
> __u32 timeout;
> - __u32 pad;
> __u64 syncpts;
> __u64 cmdbufs;
> __u64 relocs;
>
The padding is hilarious. I added it to remove the possibility for
compiler to add implicit padding, but it does completely the opposite.
If we'd care about binary compatibility, we could have also just added
__packed to the definition. But as this is in staging, I don't think
that's necessary.
Acked-By: tbergstrom@xxxxxxxxxx <tbergstrom@xxxxxxxxxx>
-----------------------------------------------------------------------------------
This email message is for the sole use of the intended recipient(s) and may contain
confidential information. Any unauthorized review, use, disclosure or distribution
is prohibited. If you are not the intended recipient, please contact the sender by
reply email and destroy all copies of the original message.
-----------------------------------------------------------------------------------
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/dri-devel
