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From: "michalz at nvidia dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99613] New: Static variable destruction order race condition
Date: Tue, 16 Mar 2021 10:58:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99613

            Bug ID: 99613
           Summary: Static variable destruction order race condition
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: michalz at nvidia dot com
  Target Milestone: ---

Created attachment 50394
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50394&action=3Dedit
Race condition demo

Function static variables should be destroyed in the reverse order of
initialization. However, the lock is released before calling atexit to regi=
ster
the destructor, allowing for a race condition to occur if multiple threads =
are
accessing static variables for the first time.

The bug affects all versions of GCC that I've tried (6.4, 7.3, 8.2, 9.3, 10=
.2)
on multiple platforms.

The error in output assembly can be seen when compiling the following code:

struct S{
   S();
   ~S();
};

S& foo(){
    static S s;
    return s;
}

The attached file contains a working example that triggers the race conditi=
on
(it's a race condition, so sometimes it succeeds).=