CODEWITHSUNDEEP
winapicrashdllexportrundll32
user272237
user272237

Reputation:

How to implement rundll2-callable function?

I'm trying to write an exe that also exports functions which can be called with rundll32. Is this possible and if so, why isn't it working like this?

I closely followed Microsoft's advice on this.

#define RUNDLL32(func) extern "C" __declspec(dllexport) void CALLBACK func(HWND hWnd, HINSTANCE hInst, LPSTR lpszCmdLine, int nCmdShow)

RUNDLL32(MyFunc)
{
  MessageBox(0, 0, 0, 0);
}

But when called with

rundll32 myprog.exe,_MyFunc@16

rundll32 crashes/DEP kicks in.

Upvotes: 2

Views: 388

Answers (1)

Hans Passant
Hans Passant

Reputation: 941635

Rundll32.exe uses LoadLibrary() to load the executable image. This is not likely to work out well for an EXE, it doesn't expect to get loaded on an address that's that not its default. Which is guaranteed to happen, rundll32.exe already occupies that default address. Not sure if you could tinker with the linker so that it doesn't omit the relocation records.

But don't bother with this approach, just create a DLL instead of an EXE. And pass real arguments to MessageBox(). And, yes, use a .def file to rename the exported function.

Upvotes: 2

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