Question

64-bit code calls 32-bit DLL through ATL COM adapter but gets 64-bit version, not 32-bit

Asked by: EdAtCertFirst

My 64-bit code needs to call 32-bit DLL code that cannot be recompiled in 64-bit (bought DLL, not the source). I wrote an adapter using ATL/COM out of process server. I am using Visual Studio 2008, C++.
My 64-bit client works with the adapter compiled in 64-bit mode and when both are compiled in 32-bit mode, they work. I am looking for the magic function call, parameter, or registry modification to make the 64-to-32-bit combination work. The two articles in MSDN about 64-bit to 32-bit calls do not help.
The adapter is an out of process COM server, an EXE written with ATL.
I have a .zip file of my code but even the .sln file is not allowed in a .zip by exp-xch.

// Client2.cpp				2009-08-06
//
//		Test driver for COM Adapter3 to access the Calculator DLL
//
#include <windows.h>
#include <objbase.h>
#include <iostream>
#include <iomanip>
using namespace std;
 
#include <atlbase.h>
#include <atldef.h>
#include <windef.h>
#include "ComAdapter3_i.h"
 
///////////////////////////// Interface code for accessing the COM Adapter ///////////////////////////////////////
 
int main()
{
	// Initialize COM
 
	HRESULT hr = 0;
	LPUNKNOWN pServer = 0;
	ICoCalc* calc = 0;
 
	::CoInitialize(NULL);
 
// Tried this:
	//PVOID sv = 0;
	//Wow64DisableWow64FsRedirection(&sv);
 
	hr = CoCreateInstance(CLSID_CoCalc, NULL, CLSCTX_LOCAL_SERVER, IID_IUnknown, (LPVOID*) &pServer);
	if (FAILED(hr))
	{
		cout << "Failed to load server\n";
		goto cleanup;
	}
 
	hr = pServer->QueryInterface(IID_ICoCalc, (LPVOID*)&calc);
	if (FAILED(hr))
	{
		cout << "ICalc not found" << endl;
		goto cleanup;
	}
 
	////////////////////////// Normal Application Code //////////////////////////////
 
	cout << "\n\tCalcTest\n\n\n";
 
	long a = 0, b = 0, c = 0;
 
	while (cout << "Enter two integers or Q to quit: ", cin >> a >> b)
	{
		// COM keeps the function addresses in the VTable, makes virtual function calls
		c = calc->Add(a, b);		// a proxy layer could hide calc pointer
		cout << "Sum = " << c << endl;
///  I modified Add to just:   return 8 * sizeof(size_t);
///  It returns 32 or 64 to show what version of code is running in the "COM server"
		cout << "\nClient calc: " << calc << endl;
		cout << "Add: a: " << a << "  &a: " << &a << endl;
		cout << "     b: " << b << "  &b: " << &b << endl;
		cout << "     c: " << c << "  &c: " << &c <<endl;
	}
 
cleanup:		// Cannot build a new ComServer until its usage count is zero.
	if (calc) 
		hr = calc->Release();
	if (pServer)
		hr = pServer->Release();
	CoUninitialize();
	return hr;
}
 
 
 
// CoCalc.cpp : Implementation of CCoCalc
//
//	Test program with local Add function representing code that would be in 32-bit DLL.
//	Calling the DLL will be easy after the 64-32 barrier is fixed.
//
//  When launching Visual Studio, run as Administrator so that various build steps will work.
//  Build ComAdapter3. Then build ComAdapter3PS by right-clicking on that Project name and selecting
//  Project only > Rebuild on ComAdapter3PS.
//
//  Next, go to Client3 directory and run COPY.BAT from a command line window. It copies some generated files.
//  I like keeping the client and server separated.
//  Then build the client3 program and run it.
//  Be careful to check that client is 64-bits and Adapter is 32-bits. Test shows 64-bit Adapter is loaded, matching the
//  bit-ness of the client. I need to turn off the direct matching and access the 32-bit version.
//  The code is basically correct, just missing the magic instructions to override that mapping.
//  Building both Client and Adapter in 32 or 64-bit mode shows correct 32 or 64 output.
 
#include "stdafx.h"
#include "CoCalc.h"
#include <cstddef>
#include <cstdlib>
 
// CCoCalc
 
STDMETHODIMP CCoCalc::Add(LONG a, LONG b)
{
	long c = a + b;
 
	c = sizeof(size_t) * 8;		// report 32-bit or 64-bit version instead of sum to prove the 64 to 32 call works
 
	return c;
}

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Asked On: 2009-08-09 at 22:30:28ID24639043
Tags: COM
,; ATL
,; 64-bit
,; x64
Topics: Microsoft Visual C++
,; Windows ATL / WTL / COM Programming
,; Windows 64-bit
Participating Experts: 1
Points: 400
Comments: 10

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Answers

by: Gideon7Posted on 2009-08-10 at 05:14:58ID: 25059163

There is no magic call. The choice of COM process server is determined solely by the registry (HKEY_CURRENT_USER\CLSID and HKEY_LOCAL_MACHINE\CLSID). You might be running into some confusion because multiple 32-bit and 64-bit proxy server DLLs for the same CLSID might be registered different hives of HKEY_CLASSES_ROOT with registry reflection in coming into play.

Registry reflection occurs on on W2K3 x64, Vista x64 and W2K8 x64. It copies the LocalServer32 entry between the 64-bit and 32-bit registry hives. It uses a last-writer-wins policy. So whichever side (32-bit or 64-bit) last wrote the LocalServer32 value will get reflected into the other hive and 'win'. See http://msdn.microsoft.com/en-us/library/aa384182.aspx and http://msdn.microsoft.com/en-us/library/aa384182.aspx

To add to the confusion HKEY_CURRENT_USER\CLSID can also be reflected and can override HKLM keys.

(Registry reflection is a confusing hack. It has been removed from WIndows 7 x64 and W2K8R2 x64.)

Carefully check HKEY_LOCAL_MACHINE\Software\CLSID\{GUID} and HKEY_LOCAL_MACHINE\Software\Wow6432Node\CLSID\{GUID}. Verify that the both point to the desired target server path. Also check under HKEY_CURRENT_USER. If you are using a custom proxy DLL also check its GUID for InprocServer32 to make sure it is pointing to the right DLL.

Good luck!

by: EdAtCertFirstPosted on 2009-08-10 at 06:33:31ID: 25059741

That sounds good. I will check it out. The "last-writer-wins" policy does not seem to be in effect because I can just recompile the client in 32 or 64-bit mode and it always calls the matching bit-ness version of the COM EXE.

I will make sure there is no 64-bit COM adapter with that name/CLSID/GUID and see what happens.

Thanks!

Ed

by: EdAtCertFirstPosted on 2009-08-10 at 21:41:00ID: 25066182

Gideon7:
I cleaned up the registry, renamed the programs, built ComServer32b in 32-bit mode only and Client64 in 64-bit mode. I now get E_NOINTERFACE from the QueryInterface call.

I am building in separate Solutions, copying some generated files from server to client directory and adding the existing files to the project:

copy ..\ComServer32b\ComServer32b_i.c .
copy ..\ComServer32b\ComServer32b_i.h .
copy ..\ComServer32b\Debug\ComServer32b.tlb .
copy ..\ComServer32b\Resource.h .

I could E-mail a zip file of the VS2000 code, if you want it. Are there App Wizard or Class Wizard settings I am doing wrong?

Thanks,

Ed

// Client64b.cpp		2009-08-10
//
//		Test program for ComServer32b
//
// Notes:
//			Run Visual Studio in Administrator mode (right click on icon, choose Run as Administrator).
//			After building companion ComServer32b, run copy.bat script file from command line to pull some files to here.
//			Answer "yes" to messages about reloading files that have been changed outside of VS.
//			Then build and run Client64b. Enter two arbitary integers to test the Add function.
//
#include <windows.h>
#include <objbase.h>
#include <iostream>
#include <iomanip>
using namespace std;
 
#include <atlbase.h>
#include <atldef.h>
#include <windef.h>
#include "ComServer32b_i.h"
	
#include <iostream>
#include <iomanip>
using namespace std;
 
// Interface code for accessing the COM Adapter 
 
int main()
{
	HRESULT hr = 0;
	LPUNKNOWN pServer = 0;
	ICalc* calc = 0;
 
	hr = ::CoInitialize(NULL);
 
	hr = CoGetClassObject(CLSID_Calc, CLSCTX_LOCAL_SERVER, NULL, IID_IClassFactory, (LPVOID*) &pServer);
 
	if (FAILED(hr))
	{
		cout << "Failed to load server\n";
		goto cleanup;
	}
 
	hr = pServer->QueryInterface(IID_ICalc, (LPVOID*)&calc);
	if (FAILED(hr))
	{
		cout << "ICalc not found: " << hex << hr << endl;
		goto cleanup;
	}
 
// Normal Application Code
 
	cout << "\n\tCalcTest\n\n\n";
 
	long a = 0, b = 0, c = 0;
 
	while (cout << "Enter two integers or Q to quit: ", cin >> a >> b)
	{
		// COM keeps the function addresses in the VTable, makes virtual function calls
		hr = calc->Add(a, b, &c);		// a proxy layer could hide calc pointer
		cout << "Sum = " << c << endl;
 
		cout << "\nClient calc: " << calc << endl;
		cout << "Add: a: " << a << "  &a: " << &a << endl;
		cout << "     b: " << b << "  &b: " << &b << endl;
		cout << "     c: " << c << "  &c: " << &c <<endl;
	}
 
cleanup:	// Cannot build a new ComServer until its usage count is zero.
	if (calc) 
		hr = calc->Release();
 
	if (pServer)
		hr = pServer->Release();
 
	CoUninitialize();
 
	return hr;
}
 
 
=============================== ComServer32b =========================
 
// Calc.cpp : Implementation of CCalc
 
#include "stdafx.h"
#include "Calc.h"
 
 
// CCalc
 
 
STDMETHODIMP CCalc::Add(LONG a, LONG b, LONG* c)
{
	*c = a + b;
 
	return S_OK;
}
 
////////////////////////ComServer32b_i.h//////////////////////
 
/* this ALWAYS GENERATED file contains the definitions for the interfaces */
 
 
 /* File created by MIDL compiler version 7.00.0500 */
/* at Tue Aug 11 00:16:39 2009
 */
/* Compiler settings for .\ComServer32b.idl:
    Oicf, W1, Zp8, env=Win32 (32b run)
    protocol : dce , ms_ext, c_ext, robust
    error checks: stub_data 
    VC __declspec() decoration level: 
         __declspec(uuid()), __declspec(selectany), __declspec(novtable)
         DECLSPEC_UUID(), MIDL_INTERFACE()
*/
//@@MIDL_FILE_HEADING(  )
 
#pragma warning( disable: 4049 )  /* more than 64k source lines */
 
 
/* verify that the <rpcndr.h> version is high enough to compile this file*/
#ifndef __REQUIRED_RPCNDR_H_VERSION__
#define __REQUIRED_RPCNDR_H_VERSION__ 475
#endif
 
#include "rpc.h"
#include "rpcndr.h"
 
#ifndef __RPCNDR_H_VERSION__
#error this stub requires an updated version of <rpcndr.h>
#endif // __RPCNDR_H_VERSION__
 
#ifndef COM_NO_WINDOWS_H
#include "windows.h"
#include "ole2.h"
#endif /*COM_NO_WINDOWS_H*/
 
#ifndef __ComServer32b_i_h__
#define __ComServer32b_i_h__
 
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
#pragma once
#endif
 
/* Forward Declarations */ 
 
#ifndef __ICalc_FWD_DEFINED__
#define __ICalc_FWD_DEFINED__
typedef interface ICalc ICalc;
#endif 	/* __ICalc_FWD_DEFINED__ */
 
 
#ifndef __Calc_FWD_DEFINED__
#define __Calc_FWD_DEFINED__
 
#ifdef __cplusplus
typedef class Calc Calc;
#else
typedef struct Calc Calc;
#endif /* __cplusplus */
 
#endif 	/* __Calc_FWD_DEFINED__ */
 
 
/* header files for imported files */
#include "oaidl.h"
#include "ocidl.h"
 
#ifdef __cplusplus
extern "C"{
#endif 
 
 
#ifndef __ICalc_INTERFACE_DEFINED__
#define __ICalc_INTERFACE_DEFINED__
 
/* interface ICalc */
/* [unique][helpstring][uuid][object] */ 
 
 
EXTERN_C const IID IID_ICalc;
 
#if defined(__cplusplus) && !defined(CINTERFACE)
    
    MIDL_INTERFACE("FA9C0E6C-2E58-42DD-B7AF-349988D0F34A")
    ICalc : public IUnknown
    {
    public:
        virtual /* [local][helpstring] */ HRESULT STDMETHODCALLTYPE Add( 
            /* [in] */ LONG a,
            /* [in] */ LONG b,
            /* [out] */ LONG *c) = 0;
        
    };
    
#else 	/* C style interface */
 
    typedef struct ICalcVtbl
    {
        BEGIN_INTERFACE
        
        HRESULT ( STDMETHODCALLTYPE *QueryInterface )( 
            ICalc * This,
            /* [in] */ REFIID riid,
            /* [iid_is][out] */ 
            __RPC__deref_out  void **ppvObject);
        
        ULONG ( STDMETHODCALLTYPE *AddRef )( 
            ICalc * This);
        
        ULONG ( STDMETHODCALLTYPE *Release )( 
            ICalc * This);
        
        /* [local][helpstring] */ HRESULT ( STDMETHODCALLTYPE *Add )( 
            ICalc * This,
            /* [in] */ LONG a,
            /* [in] */ LONG b,
            /* [out] */ LONG *c);
        
        END_INTERFACE
    } ICalcVtbl;
 
    interface ICalc
    {
        CONST_VTBL struct ICalcVtbl *lpVtbl;
    };
 
    
 
#ifdef COBJMACROS
 
 
#define ICalc_QueryInterface(This,riid,ppvObject)	\
    ( (This)->lpVtbl -> QueryInterface(This,riid,ppvObject) ) 
 
#define ICalc_AddRef(This)	\
    ( (This)->lpVtbl -> AddRef(This) ) 
 
#define ICalc_Release(This)	\
    ( (This)->lpVtbl -> Release(This) ) 
 
 
#define ICalc_Add(This,a,b,c)	\
    ( (This)->lpVtbl -> Add(This,a,b,c) ) 
 
#endif /* COBJMACROS */
 
 
#endif 	/* C style interface */
 
 
 
 
#endif 	/* __ICalc_INTERFACE_DEFINED__ */
 
 
 
#ifndef __ComServer32bLib_LIBRARY_DEFINED__
#define __ComServer32bLib_LIBRARY_DEFINED__
 
/* library ComServer32bLib */
/* [helpstring][version][uuid] */ 
 
 
EXTERN_C const IID LIBID_ComServer32bLib;
 
EXTERN_C const CLSID CLSID_Calc;
 
#ifdef __cplusplus
 
class DECLSPEC_UUID("06BEAE5A-BE01-438B-A2A4-DB4B6B8621FA")
Calc;
#endif
#endif /* __ComServer32bLib_LIBRARY_DEFINED__ */
 
/* Additional Prototypes for ALL interfaces */
 
/* end of Additional Prototypes */
 
#ifdef __cplusplus
}
#endif
 
#endif
 
///////////////// Calc.h ///////////////////////
 
// Calc.h : Declaration of the CCalc
 
#pragma once
#include "resource.h"       // main symbols
 
#include "ComServer32b_i.h"
 
 
#if defined(_WIN32_WCE) && !defined(_CE_DCOM) && !defined(_CE_ALLOW_SINGLE_THREADED_OBJECTS_IN_MTA)
#error "Single-threaded COM objects are not properly supported on Windows CE platform, such as the Windows Mobile platforms that do not include full DCOM support. Define _CE_ALLOW_SINGLE_THREADED_OBJECTS_IN_MTA to force ATL to support creating single-thread COM object's and allow use of it's single-threaded COM object implementations. The threading model in your rgs file was set to 'Free' as that is the only threading model supported in non DCOM Windows CE platforms."
#endif
 
 
 
// CCalc
 
class ATL_NO_VTABLE CCalc :
	public CComObjectRootEx<CComSingleThreadModel>,
	public CComCoClass<CCalc, &CLSID_Calc>,
	public ICalc
{
public:
	CCalc()
	{
	}
 
DECLARE_REGISTRY_RESOURCEID(IDR_CALC)
 
DECLARE_NOT_AGGREGATABLE(CCalc)
 
BEGIN_COM_MAP(CCalc)
	COM_INTERFACE_ENTRY(ICalc)
END_COM_MAP()
 
 
 
	DECLARE_PROTECT_FINAL_CONSTRUCT()
 
	HRESULT FinalConstruct()
	{
		return S_OK;
	}
 
	void FinalRelease()
	{
	}
 
public:
 
	STDMETHOD(Add)(LONG a, LONG b, LONG* c);
};
 
OBJECT_ENTRY_AUTO(__uuidof(Calc), CCalc)

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by: EdAtCertFirstPosted on 2009-08-16 at 18:54:55ID: 25111264

A couple articles on the internet have code examples that do not work. VS2008 has different support for COM and ATL from the old VS 6.0 examples. There has to be a way of calling 32-bit code from 64-bit code. Does Microsoft have any documentation concerning this? MSDN does not seem to have a coherent discussion of this topic. Does anyone do this using Vista, Visual Studio 2008, unmanaged C++, COM, ATL?

Thanks,

Ed

by: EdAtCertFirstPosted on 2009-08-19 at 03:04:00ID: 25130982

Do the implementers at Microsoft in the Vista, WOW64, COM, registry, development areas monitor EE or does anyone know them and could send them a message to look at this question? Windows7 dropped the registry reflection mechanism, perhaps because of problems such as this one.

I have conferred with various COM experts who have written books, courses and taught COM/ATL and they have all moved on to .NET for the last 6 years or so and did not have any 64-bit experience with COM. One remembered a similar issue when the transition was from 16-bit to 32-bit.

I called MS support and they could not answer my questions and they said they do not have a way of sending issues into the developers. They did not charge my credit card the $79.

Since my out-of-process calls work 32-to-32 and 64-to-64, I figure this is a Microsoft bug or a documentation problem if there is a special call or parameter that would make this work.

If someone could get the Microsoft developers to look at this, maybe I can get a definitive answer.

Thanks,

Ed

by: EdAtCertFirstPosted on 2009-08-21 at 07:26:03ID: 25152114

The solution to this problem is at:

http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Windows/Windows_64-bit/Q_24664818.html#a25149007

by: EdAtCertFirstPosted on 2009-08-21 at 07:33:32ID: 25152194

COM/ATL books and course materials I used did not have the latest Visual Studio nuances. They also did not have the relatively new CLSCTX_ACTIVATE_32_BIT_SERVER parameter for CoCreateInstance and other methods:

hr = CoCreateInstance(CLSID_AAServe, NULL, CLSCTX_LOCAL_SERVER | CLSCTX_ACTIVATE_32_BIT_SERVER, IID_IAAGetSet, (LPVOID*) &pGetSet);

Documenting this issue and solution here in EE and on MSDN C++ forum should help.

20120131-EE-VQP-002

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64-bit code calls 32-bit DLL through ATL COM adapter but gets 64-bit version, not 32-bit

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COM

ATL

64-bit

x64

Microsoft Visual C++

Windows ATL / WTL / COM Programming

Windows 64-bit

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