[Bug libstdc++/67791] New: Crash using std::thread and iostream with dynamic loading of a shared library

[nexyon at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67791

            Bug ID: 67791
           Summary: Crash using std::thread and iostream with dynamic
                    loading of a shared library
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nexyon at gmail dot com
  Target Milestone: ---

Created attachment 36430
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36430&action=edit
the source of the shared library

If you think the summary of this bug is long/strange: yes, to me this seems
like the most weird bug, I have ever found.

What I am doing is the following:

* I have a main program (main.cpp) that loads a dynamic library thread.so and
calls a function in there.
* main.cpp also includes <iostream> without actually using this library.
(sounds weird, eh?)
* The function in thread.so creates a std::thread and runs it.
* The application crashes when the thread should be started.

Let me show you what happens (or: how to reproduce):

--------------

% g++ -g -fPIC -shared -o thread.so thread.cpp -std=c++11 -lpthread
% g++ -g -ldl -o main main.cpp
%  gdb main
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Reading symbols from main...done.
(gdb) r
Starting program: /data/Work/Computer/Programming/Audaspace/bug/main 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt full
#0  0x0000000000000000 in ?? ()
No symbol table info available.
#1  0x00007ffff790e493 in __gthread_create (__args=<optimized out>,
__func=0x7ffff790e330 <std::(anonymous
namespace)::execute_native_thread_routine(void*)>, __threadid=0x7fffffffdd60)
    at
/build/gcc-multilib/src/gcc-build/x86_64-unknown-linux-gnu/libstdc++-v3/include/x86_64-unknown-linux-gnu/bits/gthr-default.h:662
No locals.
#2  std::thread::_M_start_thread (this=0x7fffffffdd60, __b=...) at
/build/gcc-multilib/src/gcc-5.2.0/libstdc++-v3/src/c++11/thread.cc:149
No locals.
#3  0x00007ffff6d99826 in std::thread::thread<void (&)(int, unsigned long
long*), int, unsigned long long*&>(void (&)(int, unsigned long long*), int&&,
unsigned long long*&) (this=0x7fffffffdd60, __f=
    @0x7ffff6d993e2: {void (int, unsigned long long *)} 0x7ffff6d993e2
<factorial(int, unsigned long long*)>) at /usr/include/c++/5.2.0/thread:137
No locals.
#4  0x00007ffff6d99463 in run () at thread.cpp:17
        a = 4196233
        c = 0x7fffffffdd70
        t1 = {_M_id = {_M_thread = 0}}
#5  0x0000000000400793 in main (argc=1, argv=0x7fffffffdea8) at main.cpp:9
        handle = 0x612c40
        run_func = 0x7ffff6d99430 <run()>
(gdb)

--------------

Now why is this weird/funny?

There are two ways you can get rid of the crash:

* the first is to add -lpthread to the second g++ line (the one that compiles
main.cpp and links the main program) OR
* you remove the line #include <iostream> in main.cpp

I found this bug in a way bigger code base as you can imagine and I already
spent a lot of time to get it down to this minimal example. I hope you can
find, what is the problem here! Thanks!