On 17-07-14 22:10:15, Ville Syrjälä wrote:
On Fri, Jul 14, 2017 at 11:41:49AM -0700, Ben Widawsky wrote:
On 17-06-29 22:49:44, Ville Syrjälä wrote:
[snip]
>
>... but here it's ALIGN(formats_offset+formats_size). I think we should
>be aligning the same thing in both cases, or we add a BUILD_BUG_ON to
>make sure the header size always stays a multiple of 8 bytes.
>
>That's mainly because the design of the structure seems geared towards
>expanding the header in the future (as in why else would you have the
>offsets?).
>
I guess I don't quite understand what you're asking for. The first thing is
determining a size, the second is finding an offset into the blob.
If I remember my thinking correctly, then what I was trying to say was
ALIGN(multiple_of_4, 8) + ALIGN(multiple_of_4, 8) != ALIGN(multiple_of_4 + multiple_of_4, 8)
but the code was assuming that it's true, or that at least one of those
things is a multiple of 8 already.
Going with this and calling it sufficient.
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 0da6707a8cf7..5c14beee52ff 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -96,6 +96,7 @@ static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane
/* Modifiers offset is a pointer to a struct with a 64 bit field so it
* should be naturally aligned to 8B.
*/
+ BUILD_BUG_ON(sizeof(struct drm_format_modifier_blob) % 8);
blob_size += ALIGN(formats_size, 8);
blob_size += modifiers_size;
I don't mind changing this, but tell me what you want.
BUILD_BUG_ON sounds good to me regardless.
[snip]
--
Ben Widawsky, Intel Open Source Technology Center
--
Ville Syrjälä
Intel OTC
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