From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id DEAC2385E037; Wed,  8 Jun 2022 09:19:05 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org DEAC2385E037
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/105880] eh_globals_init destructor not setting
 _M_init to false
Date: Wed, 08 Jun 2022 09:19:05 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 12.1.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-105880-4-bL1ke34vso@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-105880-4@http.gcc.gnu.org/bugzilla/>
References: <bug-105880-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Wed, 08 Jun 2022 09:19:06 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105880

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
As Andrew says, the problem here is that __cxa_get_globals is being used af=
ter
the global has been destroyed. Nothing done to the _M_init member in the
destructor can be changed to fix that, accessing an object after its destru=
ctor
runs is undefined, period.

What might "work" is to make the _M_init member a static data member, which
outlives the singleton instance of the class.

Something like this:

--- a/libstdc++-v3/libsupc++/eh_globals.cc
+++ b/libstdc++-v3/libsupc++/eh_globals.cc
@@ -90,29 +90,34 @@ eh_globals_dtor(void* ptr)
 struct __eh_globals_init
 {
   __gthread_key_t      _M_key;
-  bool                         _M_init;
+  static bool          _S_init;

-  __eh_globals_init() : _M_init(false)
-  {=20
+  __eh_globals_init()
+  {
     if (__gthread_active_p())
-      _M_init =3D __gthread_key_create(&_M_key, eh_globals_dtor) =3D=3D 0;=
=20
+      _S_init =3D __gthread_key_create(&_M_key, eh_globals_dtor) =3D=3D 0;
   }

   ~__eh_globals_init()
   {
-    if (_M_init)
+    if (_S_init)
       __gthread_key_delete(_M_key);
-    _M_init =3D false;
+    _S_init =3D false;
   }
+
+  __eh_globals_init(const __eh_globals_init&) =3D delete;
+  __eh_globals_init& operator=3D(const __eh_globals_init&) =3D delete;
 };

+bool __eh_globals_init::_S_init =3D false;
+
 static __eh_globals_init init;

 extern "C" __cxa_eh_globals*
 __cxxabiv1::__cxa_get_globals_fast() _GLIBCXX_NOTHROW
 {
   __cxa_eh_globals* g;
-  if (init._M_init)
+  if (init._S_init)
     g =3D static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_key=
));
   else
     g =3D &eh_globals;
@@ -123,7 +128,7 @@ extern "C" __cxa_eh_globals*
 __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
 {
   __cxa_eh_globals* g;
-  if (init._M_init)
+  if (init._S_init)
     {
       g =3D static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_k=
ey));
       if (!g)


This doesn't really seem correct though, as it just means we revert to the
eh_globals single-threaded fallback buffer after _S_init becomes false. But
that fallback buffer has also been destroyed at that point. So maybe we nee=
d to
make eh_globals immortal.=