Re: DLL Base Address VTABLEs and COM

From:

"Alex Blekhman" <tkfx.N05P4M@yahoo.com>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 4 May 2006 15:38:34 +0300

Message-ID:

<#ePbqe3bGHA.3472@TK2MSFTNGP02.phx.gbl>

Tim Roberts wrote:

"Alex Blekhman" wrote:

I think that virtual function in that respect is not
different from regular exported function in DLL. When DLL
module is loading, then loader fixes IAT in main module
so IAT will contain correct addresses. At runtime all
calls (no matter virtual or regular) are routed through
IAT.

You have the right spirit, but the wrong details.
Virtual functions aren't imported and exported, because
they are never called by name. They're called through
function pointers, and don't get involved in the IAT.

I created simple Win32 DLL project and virtual functions
(along with vtable) are exported. Here's DUMPBIN output:

ordinal hint RVA name

      1 0 0001116D ??0CSimpleWin32Dll@@QAE@ABV0@@Z
      2 1 000110B9 ??0CSimpleWin32Dll@@QAE@XZ
      3 2 00011041 ??4CSimpleWin32Dll@@QAEAAV0@ABV0@@Z
      4 3 00015540 ??_7CSimpleWin32Dll@@6B@
      5 4 00011023 ?Foo@CSimpleWin32Dll@@UAEHXZ

Class declared like that:

class __declspec(dllexport) CSimpleWin32Dll
{
public:
    CSimpleWin32Dll(void);

    virtual int Foo();
};