- fix some cases where we are using uninitialized memory

- fix some cases where we are using uninitialized memory
- use attribute 'no msan' on NativeEntry::ReturnValueIsError function
  as msan doesn't seem to track the return slot being set by a native
  function
- vsnprintf seems to have issues with msan so unpoison the allocated
  memory buffer everytime vsnprintf is used to suppress the error.

BUG=
R=fschneider@google.com

Committed: https://github.com/dart-lang/sdk/commit/42c58c5c2de9232efd05080631cca08813f206b7

[siva, 2016-10-01 01:02:14]

asiva@google.com changed reviewers:
+ fschneider@google.com

[Florian Schneider, 2016-10-04 21:02:02]

lgtm

https://codereview.chromium.org/2383293003/diff/20001/runtime/vm/native_entry.cc
File runtime/vm/native_entry.cc (right):

https://codereview.chromium.org/2383293003/diff/20001/runtime/vm/native_entry...
runtime/vm/native_entry.cc:102: NO_SANITIZE_MEMORY
Here, it would be nice to figure out why the unpoison that we have is not
enough. I wonder if there is some problem with msan itself?

[siva, 2016-10-05 20:38:07]

https://codereview.chromium.org/2383293003/diff/20001/runtime/vm/native_entry.cc
File runtime/vm/native_entry.cc (right):

https://codereview.chromium.org/2383293003/diff/20001/runtime/vm/native_entry...
runtime/vm/native_entry.cc:102: NO_SANITIZE_MEMORY
On 2016/10/04 21:02:02, Florian Schneider wrote:
> Here, it would be nice to figure out why the unpoison that we have is not
> enough. I wonder if there is some problem with msan itself?

Figured out what the problem was, we need to unpoison the contents
of the return value location also (see ArgAt and ReturnValue functions in class
NativeArguments).

I have removed this NO_SANITIZE_MEMORY from here.

[siva, 2016-10-05 23:54:21]

Description was changed from

==========
- fix some cases where we are using uninitialized memory
- use attribute 'no msan' on NativeEntry::ReturnValueIsError function
  as msan doesn't seem to track the return slot being set by a native
  function
- vsnprintf seems to have issues with msan so unpoison the allocated
  memory buffer everytime vsnprintf is used to suppress the error.

BUG=
==========

to

==========
- fix some cases where we are using uninitialized memory
- use attribute 'no msan' on NativeEntry::ReturnValueIsError function
  as msan doesn't seem to track the return slot being set by a native
  function
- vsnprintf seems to have issues with msan so unpoison the allocated
  memory buffer everytime vsnprintf is used to suppress the error.

BUG=
R=fschneider@google.com

Committed:
https://github.com/dart-lang/sdk/commit/42c58c5c2de9232efd05080631cca08813f206b7
==========

[siva, 2016-10-05 23:54:22]

Committed patchset #3 (id:40001) manually as
42c58c5c2de9232efd05080631cca08813f206b7 (presubmit successful).