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.
---
Cross-built for arm-eabi and manually verified the config output is
correct. Testing now on aarch64-linux and x86_64-linux.
I'll wait for the CI results from linaro before pushing this.
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
--
2.52.0
