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Loading a Cygwin based DLL and calling exported functions
- From: James Dickson <james dot dickson at gmail dot com>
- To: cygwin at cygwin dot com
- Date: Wed, 8 Dec 2010 08:57:42 +0000
- Subject: Loading a Cygwin based DLL and calling exported functions
- References: <AANLkTim2j17e_BiNicdwqyeSaGxxm7Ok6OX5oXpvbNGA@mail.gmail.com>
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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