[PATCH] [libstdc++] ensure mutex_pool survives _Safe_sequence_base

[Alexandre Oliva <oliva@adacore.com>]

On vxworks, after destroying the semaphore used to implement a mutex,
__gthread_mutex_lock fails and __gnu_cxx::__mutex::lock calls
__throw_concurrence_lock_error.  Nothing ensures the mutex_pool
mutexes survive init-once objects containing _Safe_sequence_base.  If
such an object completes construction before mutex_pool
initialization, it will be registered for atexit destruction after the
mutex_pool mutexes, so the _M_detach_all() call in the
_Safe_sequence_base dtor will use already-destructed mutexes, and
basic_string/requirements/citerators_cc fails calling terminate.

This patch fixes this problem by ensuring the mutex pool completes
construction before any _Safe_sequence_base-containing object, so that
the mutex pool survives them all.

Regstrapped on x86_64-linux-gnu.
Tested on arm-vxworks7 (gcc-12) and arm-eabi (trunk).  Ok to install?

for  libstdc++-v3/ChangeLog

	* include/debug/safe_base.h (_Safe_sequence_base): Ensure
	the mutex pool survives *this.
---
 libstdc++-v3/include/debug/safe_base.h |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/debug/safe_base.h b/libstdc++-v3/include/debug/safe_base.h
index 1dfa9f68b65b5..d4ba404cdac6e 100644
--- a/libstdc++-v3/include/debug/safe_base.h
+++ b/libstdc++-v3/include/debug/safe_base.h
@@ -203,7 +203,15 @@ namespace __gnu_debug
     // Initialize with a version number of 1 and no iterators
     _Safe_sequence_base() _GLIBCXX_NOEXCEPT
     : _M_iterators(0), _M_const_iterators(0), _M_version(1)
-    { }
+    {
+      // Make sure the mutex_pool machinery is initialized before any
+      // full object containing a _Safe_sequence_base completes
+      // construction, so that any local static mutexes in the mutex
+      // pool won't be destructed before our destructor runs;
+      // _M_detach_all could fail otherwise, on targets whose mutexes
+      // stop working after being destroyed.
+      (void)this->_M_get_mutex();
+    }
 
 #if __cplusplus >= 201103L
     _Safe_sequence_base(const _Safe_sequence_base&) noexcept

-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <https://stallmansupport.org>