Mesa (master): isl: Mark enum isl_channel_select packed so it becomes 1 byte.

[GitLab Mirror]

Module: Mesa
Branch: master
Commit: d5d2fb5c4c100300f17976dbc4cf4c7045a2b688
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=d5d2fb5c4c100300f17976dbc4cf4c7045a2b688

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Thu Jun  6 17:36:09 2019 -0700

isl: Mark enum isl_channel_select packed so it becomes 1 byte.

I recently discovered that the following code lead to valgrind errors:

   struct isl_swizzle swizzle = ISL_SWIZZLE_IDENTITY;
   VALGRIND_CHECK_MEM_IS_DEFINED(&swizzle, sizeof(swizzle));

which is surprising, because struct isl_swizzle is simply:

   struct isl_swizzle {
      enum isl_channel_select r:4;
      enum isl_channel_select g:4;
      enum isl_channel_select b:4;
      enum isl_channel_select a:4;
   };

and the above code initializes all of them with a C99 initializer.
Iván Briano reminded me that C99 initializers don't necessarily zero
padding.  A quick inspection revealed that sizeof(struct isl_swizzle)
was 4 (rather than the expected 2).  Ian Romanick suggested changing
it to uint16_t, since this is essentially dicing up an unsigned, and
that worked.

This patch marks enum isl_channel_select packed, changing its size
from 4 bytes to 1 byte.  This then makes struct isl_swizzle 2 bytes,
with no bogus padding fields.  This eliminates valgrind undefined
memory warnings.

These isl_swizzle values become part of our BLORP blit program keys,
which are then hashed.  This undefined padding was being included in
the hashing, possibly leading to issues.  I originally saw this error
when running KHR-GL45.texture_size_promotion.functional in iris under
valgrind.

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

---

 src/intel/isl/isl.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/intel/isl/isl.h b/src/intel/isl/isl.h
index 6790ba002ad..0218f05d175 100644
--- a/src/intel/isl/isl.h
+++ b/src/intel/isl/isl.h
@@ -861,7 +861,7 @@ typedef uint8_t isl_channel_mask_t;
 /**
  * @brief A channel select (also known as texture swizzle) value
  */
-enum isl_channel_select {
+enum PACKED isl_channel_select {
    ISL_CHANNEL_SELECT_ZERO = 0,
    ISL_CHANNEL_SELECT_ONE = 1,
    ISL_CHANNEL_SELECT_RED = 4,