[Bug libc/17404] New: atomic_exchange_rel lacking a barrier on MIPS16, GCC before 4.7?

[triegel at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17404

            Bug ID: 17404
           Summary: atomic_exchange_rel lacking a barrier on MIPS16, GCC
                    before 4.7?
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: triegel at redhat dot com
                CC: drepper.fsp at gmail dot com

MIPS16 on GCC before 4.7 implements atomic_exchange_acq using
__sync_lock_test_and_set (which has only acquire semantics) yet does not define
atomic_exchange_rel.  This will lead to atomic_exchange_rel having only acquire
semantics and not release semantics.

__sync_lock_test_and_set might be stronger on MIPS16, but Joseph reports that
he did not see anything special there to give a stronger barrier.

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