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From: "roger at nextmovesoftware dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug other/113336] New: libatomic (testsuite) regressions on
 armv6-linux-gnueabihf
Date: Thu, 11 Jan 2024 15:42:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113336

            Bug ID: 113336
           Summary: libatomic (testsuite) regressions on
                    armv6-linux-gnueabihf
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roger at nextmovesoftware dot com
  Target Milestone: ---

As suggested by Richard Earnshaw, this opens a bugzilla PR for tracking this
issue.  All the tests in libatomic currently fail on a raspberry pi running
raspbian, but passed back in December 2020.
https://gcc.gnu.org/pipermail/gcc-patches/2024-January/642168.html

The regression (which isn't really a regression) was caused by:
2023-09-26  Hans-Peter Nilsson  <hp@axis.com>

        PR target/107567
        PR target/109166
        * builtins.cc (expand_builtin) <case BUILT_IN_ATOMIC_TEST_AND_SET>:
        Handle failure from expand_builtin_atomic_test_and_set.
        * optabs.cc (expand_atomic_test_and_set): When all attempts fail to
        generate atomic code through target support, return NULL
        instead of emitting non-atomic code.  Also, for code handling
        targetm.atomic_test_and_set_trueval !=3D 1, gcc_assert result
        from calling emit_store_flag_force instead of returning NULL.


Prior to this, when -fno-sync-libcalls was specified on the command line, t=
he
__atomic_test_and_set built-in simply expanded to a non-atomic code sequenc=
e,
which then passed libatomic's configure tests for HAVE_ATOMIC_TAS.  Now that
this hole/bug/correctness issue has been fixed, and HAVE_ATOMIC_TAS is now
detected as false, the libatomics's tas_n.c can no longer implement tas_8_2=
_.o
without (a missing helper function) tas_1_2_.o.

Hence libatomic has (always?) been broken on armv6, but synchronization
primitives can now be supported with the above change. We've just not notic=
ed
that necessary pieces of the runtime were missing, until the above correctn=
ess
fix resulted in a link error.=