mesa: Disable support for loading libtxc_dxtn.so if msan is enabled.

mesa: Disable support for loading libtxc_dxtn.so if msan is enabled.

The libtxc_dxtn.so library supports loading textures in S3TC
format. This change disables code in mesa that loads libtxc_dxtn.so
if msan is enabled, as the library will be loaded from a system
directory, which may cause spurious msan reports because msan expects
most libraries in the process to be compiled with msan.

For some reason, msan only appears to break when compiling with -Os,
as revealed by a recent attempt [0] to enable -Os on Linux and Mac.

[0] https://codereview.chromium.org/2864383003/

BUG=660216
R=senorblanco@chromium.org,thakis@chromium.org

Review-Url: https://codereview.chromium.org/2876693003
Cr-Commit-Position: refs/heads/master@{#471045}
Committed: https://chromium.googlesource.com/chromium/src/+/97b99808511f8918d00add266a8555ba5e21813c

[pcc1, 2017-05-11 05:22:43]

The CQ bit was checked by pcc@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-05-11 05:23:35]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-11 08:05:47]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-11 08:05:47]

Dry run: This issue passed the CQ dry run.

[Stephen White, 2017-05-11 15:01:46]

LGTM

[Nico, 2017-05-11 15:05:33]

lgtm, but:

https://codereview.chromium.org/2876693003/diff/1/third_party/mesa/BUILD.gn
File third_party/mesa/BUILD.gn (right):

https://codereview.chromium.org/2876693003/diff/1/third_party/mesa/BUILD.gn#n...
third_party/mesa/BUILD.gn:118: defines += [ "USE_EXTERNAL_DXTN_LIB=0" ]
Add comment for as to why. Also, we could probably just add this to the prebuilt
libs so that msan tests what we actually ship. (But I think the plan is for us
to no longer depend on mesa eventually. Then again, those plans sometimes take a
long time to materialize and might change in the future.)

[pcc1, 2017-05-11 17:18:41]

The CQ bit was checked by pcc@chromium.org

[pcc1, 2017-05-11 17:18:41]

The patchset sent to the CQ was uploaded after l-g-t-m from thakis@chromium.org,
senorblanco@chromium.org
Link to the patchset: https://codereview.chromium.org/2876693003/#ps20001
(title: "Add comment")

[commit-bot: I haz the power, 2017-05-11 17:19:15]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-11 19:35:30]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1494523121368570,
"parent_rev": "67d309c494ff65745c436e46e4ed7c3095b07d8a", "commit_rev":
"97b99808511f8918d00add266a8555ba5e21813c"}

[commit-bot: I haz the power, 2017-05-11 19:35:41]

Description was changed from

==========
mesa: Disable support for loading libtxc_dxtn.so if msan is enabled.

The libtxc_dxtn.so library supports loading textures in S3TC
format. This change disables code in mesa that loads libtxc_dxtn.so
if msan is enabled, as the library will be loaded from a system
directory, which may cause spurious msan reports because msan expects
most libraries in the process to be compiled with msan.

For some reason, msan only appears to break when compiling with -Os,
as revealed by a recent attempt [0] to enable -Os on Linux and Mac.

[0] https://codereview.chromium.org/2864383003/

BUG=660216
R=senorblanco@chromium.org,thakis@chromium.org
==========

to

==========
mesa: Disable support for loading libtxc_dxtn.so if msan is enabled.

The libtxc_dxtn.so library supports loading textures in S3TC
format. This change disables code in mesa that loads libtxc_dxtn.so
if msan is enabled, as the library will be loaded from a system
directory, which may cause spurious msan reports because msan expects
most libraries in the process to be compiled with msan.

For some reason, msan only appears to break when compiling with -Os,
as revealed by a recent attempt [0] to enable -Os on Linux and Mac.

[0] https://codereview.chromium.org/2864383003/

BUG=660216
R=senorblanco@chromium.org,thakis@chromium.org

Review-Url: https://codereview.chromium.org/2876693003
Cr-Commit-Position: refs/heads/master@{#471045}
Committed:
https://chromium.googlesource.com/chromium/src/+/97b99808511f8918d00add266a85...
==========

[commit-bot: I haz the power, 2017-05-11 19:35:42]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/chromium/src/+/97b99808511f8918d00add266a85...

[pcc1, 2017-05-15 19:56:09]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/2879373002/ by pcc@chromium.org.

The reason for reverting is: Large number of perf regressions on mac.

BUG=722473.