Re: [PATCH] drm/tegra: Remove gratuitous pad field

From: Thierry Reding <thierry.reding@gmail.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: "Terje Bergström" <tbergstrom@nvidia.com>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] drm/tegra: Remove gratuitous pad field
Date: Wed, 9 Apr 2014 15:11:29 +0200	[thread overview]
Message-ID: <20140409131127.GA24799@ulmo> (raw)
In-Reply-To: <CAKMK7uEYgj0=mjByVxG8u=_tpTxjEORRc1x4os+000p-71kXwQ@mail.gmail.com>

[-- Attachment #1.1: Type: text/plain, Size: 2259 bytes --]

On Wed, Apr 09, 2014 at 02:44:42PM +0200, Daniel Vetter wrote:
> cc: stable to make sure that even once you release userspace you won't
> get angry bug reports?

Yes, good point. I was just pondering whether doing that would be smart
or not. But I came to the same conclusion.

Thierry

> -Daniel
> 
> On Wed, Apr 9, 2014 at 2:39 PM, Thierry Reding <thierry.reding@gmail.com> wrote:
> > From: Thierry Reding <treding@nvidia.com>
> >
> > 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@nvidia.com>
> > ---
> >  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;
> > --
> > 1.9.1
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

[-- Attachment #1.2: Type: application/pgp-signature, Size: 836 bytes --]

[-- Attachment #2: Type: text/plain, Size: 159 bytes --]

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/dri-devel