[Intel-gfx] [PATCH v2 2/7] drm/i915: Mark the ggtt_view structs as packed

[Chris Wilson]

On Fri, Jan 13, 2017 at 08:44:34AM +0000, Tvrtko Ursulin wrote:
> 
> On 12/01/2017 21:35, Chris Wilson wrote:
> >In the next few patches, we will depend upon there being no
> >uninitialised bits inside the ggtt_view. To ensure this we add the
> >__packed attribute and double check with a build on that gcc hasn't
> >expanded the struct to include some padding bytes.
> >
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >---
> > drivers/gpu/drm/i915/i915_gem_gtt.h | 14 ++++++++++++--
> > 1 file changed, 12 insertions(+), 2 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
> >index 5dd3755a5a45..57cbd532dae1 100644
> >--- a/drivers/gpu/drm/i915/i915_gem_gtt.h
> >+++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
> >@@ -156,12 +156,22 @@ struct intel_rotation_info {
> > 		/* tiles */
> > 		unsigned int width, height, stride, offset;
> > 	} plane[2];
> 
> Isn't packed theoretically needed on the intel_rotation_plane_info
> name in the previous patch as well? Otherwise there could be a hole
> between the array elements if the structure got changed in the
> future.

Possibly, not too sure on the inner details of __packed. The assert
below will catch accidental holes in future (and if they change the
struct without changing the assert, a nuisance).

> >+static inline void assert_intel_rotation_info_is_packed(void)
> >+{
> >+	BUILD_BUG_ON(sizeof(struct intel_rotation_info) != 8*sizeof(unsigned int));
> >+}

-- 
Chris Wilson, Intel Open Source Technology Centre