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 <ch...@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.ursu...@intel.com>

Regards,

Tvrtko
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