Loading a Cygwin based DLL

[James Dickson]

Hey,

I just posted (apologies if I have the wrong mailing list) to see if
anyone could help me with the following problem.

I have successfully managed to load a cygwin based DLL through
LoadLibrary into a VC++ 10.0 (as an aside I have also tried 8.0 and
9.0 compiler versions) compiled application, ensuring I have 4k of
scratch space as per FAQ 6.16 and the example
http://cygwin.com/cgi-bin/cvsweb.cgi/src/winsup/testsuite/cygload/Attic/cygload.cc?cvsroot=src.

However, if I then proceed to call any function internal or exported
from the DLL which makes stack allocations through local variables,
the application hangs\crashes. I hope the below example is sufficient
to demonstrate the problem and no amount of googling seems to yield
the answer, that or I haven't found the right combination of search
words.

VC++ 10.0 client application:

int main(int argc, char ** argv)
{
    // 4k scratch space.
    char *stackbase;
    __asm
    {
        mov eax, fs:[4];
        mov stackbase, eax;
    }

    // Load cygwin dll.
    HMODULE cygwin_ptr = LoadLibrary(L"cygwin1.dll");

    // error checks omitted....

    init_ptr init = (init_ptr)GetProcAddress(cygwin_ptr, "cygwin_dll_init");

    // error checks omitted....

    init();

    // Load plugin
    HMODULE plugin_ptr = LoadLibrary(L"plugin.dll");

    // error checks omitted....

    plugin_ptr exp_test = (plugin_ptr)GetProcAddress(plugin_ptr,
"plugin_example");

    // error checks omitted....

    exp_test(); // This call hangs the application.
}

Cygwin based DLL:

extern "C" __declspec(dllexport) void plugin_example(void)
{
   std::wstring tmp(L"some string");  // This for some reason causes
the application to hang.
   std::wcerr << tmp << std::endl;
}

I have found I can make it work sometimes, but when I start using more
stack allocated local variables the hanging reoccurs. Am I missing
something simple? I really hope so.

Thank you for any help you can give me.

--
James Dickson

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