CreateThread in 64bit DLL won't work

Question

I have a 32 bit and a 64 bit executable. Both load a DLL that is of the same bit, as in the 64 bit executable loads a 64bit dll. Anyway, the 32 bit DLL works perfectly, it creates a thread and pops a hello world messagebox. The 64bit DLL however, that piece of code never executes. It's like the createthread fails.

    case DLL_PROCESS_ATTACH:
        myFunc();
        break;
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

void myFunc()
{

    HANDLE hThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)&MyThread, NULL, 0, NULL);
}

DWORD WINAPI MyThread(LPVOID param)
{
    MessageBoxA(0, "HELLO 64", 0,0);
    ExitThread(0);
}

Those are the some snippets from the DLL. I've googeled and all I can come up with is that it's the stack alignment failing? If that is the reason, how do I properly call CreateThread to make it work? If that isnt the reason, does anyone know what might be wrong?

I'd be outmost grateful for any help, thanks in advance!

possible duplicate of [DLL_PROCESS_ATTACH failing to execute on Windows 7 C++](http://stackoverflow.com/questions/8556782/dll-process-attach-failing-to-execute-on-windows-7-c) — GSerg, Aug 17 '12 at 22:54

tinman · Answer 1 · 2012-08-17T23:22:59.227

3

You have the wrong signature for MyThread. You should not cast it you should make sure your function matches the signature. The correct code would be:

CreateThread(NULL, 0, MyThread, NULL, 0, NULL);

DWORD WINAPI MyThread(LPVOID param)
{
    // etc
}

Apart from that you should not do anything in your DllMain as @GSerg comments because there is a lock that is held while you are in there. By doing anything complex you can inadvertently load another DLL causing a deadlock.

Instead you would usually have a separate initialization function in your DLL that your calling code can call after it has loaded the DLL.

edited Aug 17 '12 at 23:22

answered Aug 17 '12 at 23:16

tinman

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5

As a general rule, if you're casting a pointer to a function for any purpose other than to cast it back to the exact same type it originally was, you're probably doing something fundamentally broken. – David Schwartz Aug 17 '12 at 23:22

score 0 · Answer 2 · answered Aug 19 '12 at 07:02

0

Ok the solve was simple, the thread exited too early. Adding WaitForSingleObject(hThread, INFINITE); solved the issue. Wasn't necessary in 32bit for some reason. :)

answered Aug 19 '12 at 07:02

John Reues

1
3

Or maybe it is but it was just a coincidence that your 32-bit piece of program did not exit too early? You should add that `Wait..` to your 32-bit piece of program, too. – xQuare Aug 19 '12 at 07:08
I can't understand your answer, unless I assume that you mean the main program exited early and killed the thread before it could show the message box. albert – Albert van der Horst Jul 12 '18 at 12:17

CreateThread in 64bit DLL won't work

2 Answers2