[Bug c++/101933] New: Unloaded dll with global std::mutex causes exe to crash on exit #38

[Bug c++/101933] New: Unloaded dll with global std::mutex causes exe to crash on exit #38

[mailnew4ster at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101933

            Bug ID: 101933
           Summary: Unloaded dll with global std::mutex causes exe to
                    crash on exit #38
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mailnew4ster at gmail dot com
  Target Milestone: ---

Reproduction on Windows:

Create and compile dll.cc as following:

```
#include <mutex>
std::mutex x;
```

g++.exe dll.cc -shared -o test.dll

Create and compile exe.cc as following:

```
#include <windows.h>
int main()
{
    auto x = LoadLibrary("test.dll");
    MessageBox(0,0,0,0);
    FreeLibrary(x);
    MessageBox(0,0,0,0);
    return 0;
}
```

g++.exe exe.cc -o test.exe

Run test.exe and observe a crash after seeing both message boxes.
The crash happens in msvcrt.doexit, which tries to call a cleanup function
inside the dll which was already freed.

I'm using TDM-GCC, and I also reported the issue there:
https://github.com/jmeubank/tdm-gcc/issues/38

I'm not sure whether it's specific to TDM-GCC, it applies some patches on GCC,
but they are very small and I think they probably don't affect this issue.

[Bug target/101933] Unloaded dll with global std::mutex causes exe to crash on exit #38

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101933

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect it is because __cxa_exit is not used such that deconstructors are not
called at unload of the dll time.

[Bug target/101933] Unloaded dll with global std::mutex causes exe to crash on exit #38

[mailnew4ster at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101933

--- Comment #2 from Paul Jackson <mailnew4ster at gmail dot com> ---
I tried to work around the problem, and it's even worse than I expected. You
can replace dll.cc with the following and observe the same crash.

That means that even if I want to do manual memory management with raw
pointers, I can't. Please, consider fixing at least this.

```
#include <vector>

struct {
    std::vector<int> v;
} *test;

void x()
{
    if (test) {
        test->v.push_back(2);
    }
}
```

[Bug target/101933] Unloaded dll with global std::mutex causes exe to crash on exit #38

[mailnew4ster at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101933

--- Comment #3 from Paul Jackson <mailnew4ster at gmail dot com> ---
Maybe I'm missing something, but even this dll crashes for me now. So it seems
like it has nothing to do with global variables or static storage. That sucks,
it means that I just can't use C++ in dlls. Or is it? How come nobody noticed
it before?

I hope that I'm missing something here.

```
#include <vector>

void x()
{
    std::vector<int> v;
    v.push_back(2);
}
```

[Bug target/101933] Unloaded dll with global std::mutex causes exe to crash on exit

[mailnew4ster at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101933

Paul Jackson <mailnew4ster at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Paul Jackson <mailnew4ster at gmail dot com> ---
I debugged it a bit more, and I found out that:
1. It's happening when exceptions are involved.
2. It's actually a bug of TDM-GCC.

For details, please see my second comment in the GitHub issue:
https://github.com/jmeubank/tdm-gcc/issues/38#issuecomment-912876481