https://gcc.gnu.org/g:4046caad61a0406e42cae0c38a6aa26f5975a197
commit r16-7357-g4046caad61a0406e42cae0c38a6aa26f5975a197 Author: Jonathan Wakely <[email protected]> Date: Tue Dec 9 21:02:56 2025 +0000 libstdc++: Prevent std::stacktrace from using atomics on arm-eabi [PR120567] The conftest.cc in GLIBCXX_ENABLE_BACKTRACE checks if calls to __atomic_load and __atomic_store result in libatomic calls. For arm-eabi those expand to normal loads with a call to __sync_synchronize to ensure correct ordering. That means the generated assembly does not match the grep pattern "__atomic_" and so configure incorrectly assumes we can use atomics in libbacktrace. The fix is to grep for "__atomic_|__sync_" instead of just "__atomic_". As explained in the bug comments, the similar grep for "__atomic_" in the GLIBCXX_ENABLE_ATOMIC_BUILTINS macro doesn't need the same change. That conftest.cc program does emit a call to a libatomic function that matches the grep pattern "__atomic_" so the test gives the right answer for arm-eabi. libstdc++-v3/ChangeLog: PR libstdc++/120567 * acinclude.m4 (GLIBCXX_ENABLE_BACKTRACE): Include "__sync_" in grep command to check for extern calls to libatomic. * configure: Regenerate. Reviewed-by: Tomasz Kamiński <[email protected]> Diff: --- libstdc++-v3/acinclude.m4 | 2 +- libstdc++-v3/configure | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 index 38030e432d81..8dc9e17b214c 100644 --- a/libstdc++-v3/acinclude.m4 +++ b/libstdc++-v3/acinclude.m4 @@ -5318,7 +5318,7 @@ EOF AC_MSG_CHECKING([for atomic builtins for libbacktrace]) if AC_TRY_EVAL(ac_compile); then - if grep __atomic_ conftest.s >/dev/null 2>&1 ; then + if grep -E '__atomic_|__sync_' conftest.s >/dev/null 2>&1 ; then glibcxx_cv_libbacktrace_atomics=no else glibcxx_cv_libbacktrace_atomics=yes diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure index 4f144382e1b1..6713e4504b1c 100755 --- a/libstdc++-v3/configure +++ b/libstdc++-v3/configure @@ -54172,7 +54172,7 @@ $as_echo_n "checking for atomic builtins for libbacktrace... " >&6; } ac_status=$? $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5 test $ac_status = 0; }; then - if grep __atomic_ conftest.s >/dev/null 2>&1 ; then + if grep -E '__atomic_|__sync_' conftest.s >/dev/null 2>&1 ; then glibcxx_cv_libbacktrace_atomics=no else glibcxx_cv_libbacktrace_atomics=yes
