Windows DLLs and TLS

[Regan Heath]

On Mon, 08 Oct 2012 12:26:29 +0100, Jakob Ovrum <jakobovrum at gmail.com>  
wrote:

> I have a bug in one of my programs that I find particularly hard to  
> reduce.
>
> I am writing a Windows DLL plugin for the IRC chat client HexChat (aka  
> XChat). Problem is, all TLS variables, regardless of type, appear to be  
> initialized to complete rubbish values. Reading them does not cause an  
> access violation or anything, but the initial values are garbage. I am  
> initializing the runtime using the helpers found in core.sys.windows.dll  
> [1].
>
> I wrote a dummy host application in C mimicking the loading behaviour of  
> HexChat - the TLS variables are initialized correctly in this case, even  
> though the DLL file is exactly the same.
>
> What is it that a host application can do to break the TLS of a D plugin  
> it loads?
>
> [1] http://pastebin.com/rg9uUQMe

Could XChat be loading your dll using:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms684179(v=vs.85).aspx

and the flag DONT_RESOLVE_DLL_REFERENCES, or similar.

To debug, I would write a debug file using *C* IO functions from DllMain,  
check it loads/runs/outputs to the file from your dummy C host  
application, then try again with XChat and see what you get.

You could also alter the dummy C host application to call LoadLibraryEx  
and pass DONT_RESOLVE_DLL_REFERENCES and see what happens.

R

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