[Bug sanitizer/63627] New: thread sanitizer does not instrument __atomic_test_and_set or __atomic_clear

[rogero at howzatt dot demon.co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63627

            Bug ID: 63627
           Summary: thread sanitizer does not instrument
                    __atomic_test_and_set or __atomic_clear
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rogero at howzatt dot demon.co.uk
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org

Created attachment 33791
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33791&action=edit
EXample using __atomic_test_and_set that causes tsan positives

When compiling code using atomic instrinsics with -fsanitize=thread some of the
functions - in particular __atomic_test_and_set and __atomic_clear are not
instrumented.

Hence tsan reports false positives when spin-locking with
__atomic_test_and_set/__atomic_clear but not when using
__atomic_exchange_n/__atomic_store_n.

(This also affects std:atomic_flag as it uses the problematic operations in its
implementation.)