https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91910
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:4a2766ed00a47904dc8b85bf0538aa116d8e658b commit r14-3846-g4a2766ed00a47904dc8b85bf0538aa116d8e658b Author: Jonathan Wakely <jwak...@redhat.com> Date: Mon Sep 11 16:42:54 2023 +0100 libstdc++: Remove unconditional use of atomics in Debug Mode The fix for PR 91910 (r10-3426-gf7a3a382279585) introduced unconditional uses of atomics into src/c++11/debug.cc, which causes linker errors for arm4t where GCC emits an unresolved reference to __sync_synchronize. By making the uses of atomics depend on _GLIBCXX_HAS_GTHREADS we can avoid those unconditional references to __sync_synchronize for targets where the atomics are unnecessary. As a minor performance optimization we can also check the __gnu_cxx::__is_single_threaded function to avoid atomics for single-threaded programs even where they don't cause linker errors. libstdc++-v3/ChangeLog: * src/c++11/debug.cc (acquire_sequence_ptr_for_lock): New function. (reset_sequence_ptr): New function. (_Safe_iterator_base::_M_detach) (_Safe_local_iterator_base::_M_detach): Replace bare atomic_load with acquire_sequence_ptr_for_lock. (_Safe_iterator_base::_M_reset): Replace bare atomic_store with reset_sequence_ptr.
