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

[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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[Bug libc/17404] 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

Torvald Riegel <triegel at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |joseph at codesourcery dot com

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

[jsm28 at gcc dot gnu.org]

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

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |2.23

--- Comment #2 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.23 by requiring GCC >= 4.7 to build glibc and removing the code in
question as dead.

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

[cvs-commit at gcc dot gnu.org]

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

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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The branch, master has been updated
       via  8f82f28bbaa6ca503e6296b2d26ecf213bceff88 (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=8f82f28bbaa6ca503e6296b2d26ecf213bceff88

commit 8f82f28bbaa6ca503e6296b2d26ecf213bceff88
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Oct 27 23:47:56 2015 +0000

    Remove MIPS16 atomics using __sync_* (bug 17404).

    MIPS16 atomics used __sync_* with GCC before 4.7, which as noted in
    bug 17404 is missing the required barrier semantics for
    atomic_exchange_rel.  This patch removes the code in question as dead
    now GCC before 4.7 is no longer supported for building glibc.

    Sanity tested with builds for MIPS.

        [BZ #17404]
        * sysdeps/mips/atomic-machine.h
        [__GNUC_PREREQ (4, 8) || (__mips16 && __GNUC_PREREQ (4, 7))]:
        Change conditional to [__GNUC_PREREQ (4, 8) || __mips16].
        [__mips16 && !__GNUC_PREREQ (4, 7)]: Remove conditional code.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                     |    6 ++++++
 NEWS                          |   20 ++++++++++----------
 sysdeps/mips/atomic-machine.h |   27 +--------------------------
 3 files changed, 17 insertions(+), 36 deletions(-)

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