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

[Tvrtko Ursulin]

On 13/01/2017 08:47, Chris Wilson wrote:
> 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));
>>> +}
>

Somehow I only saw the assert for partial info.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko