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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

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@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.

Regards,

Tvrtko

> -};
> +} __packed;
> +
> +static inline void assert_intel_rotation_info_is_packed(void)
> +{
> +	BUILD_BUG_ON(sizeof(struct intel_rotation_info) != 8*sizeof(unsigned int));
> +}
>
>  struct intel_partial_info {
>  	u64 offset;
>  	unsigned int size;
> -};
> +} __packed;
> +
> +static inline void assert_intel_partial_info_is_packed(void)
> +{
> +	BUILD_BUG_ON(sizeof(struct intel_partial_info) != sizeof(u64) + sizeof(unsigned int));
> +}
>
>  struct i915_ggtt_view {
>  	enum i915_ggtt_view_type type;
>
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