BadImageFormatException encountered with WcfSvcHost and IIS WCF host

Question

Creating a WCF Service Library in Visual Studio 2008 on Vista x64 is troublesome when referencing an x86 DLL. A service that calls a 32-bit DLL is required to have a platform target of x86 to run on a 64-bit OS. When you do this, the WcfSvcHost throws a BadImageFormatException when you attempt to debug the service. There is a bug report on MS connect. The workaround I used was to coreflag WcfSvcHost as 32-bit.

Manifest Problem

The main issue I've run in to is this third-party native 32-bit DLL fails to load using certain WCF hosts. I receive the following error when a service operation is invoked that uses the third-party DLL:

System.TypeInitializationException: The type initializer for '' threw an exception.

.ModuleLoadExceptionHandlerException: A nested exception occurred after the primary exception that caused the C++ module to fail to load.

System.BadImageFormatException: The module was expected to contain an assembly manifest. (Exception from HRESULT: 0x80131018)

NestedException:

The handle is invalid. (Exception from HRESULT: 0x80070006 (E_HANDLE))

This exception is not raised when WcfSvcHost starts, it's raised when the a service operation is invoked that references the 32-bit DLL. What's very interesting, hosting this same service with the same app.config on a console app has no exceptions and works perfectly:

using (ServiceHost host = new ServiceHost (typeof (MsgBrokerService))) {
    host.Open ();
    Console.WriteLine ("running");
    Console.ReadLine ();

This exception occurs right after:

'WcfSvcHost.exe' (Managed): Loaded 'C:\Windows\WinSxS\x86_microsoft.vc80.crt_1fc8b3b9a1e18e3b_8.0.50727.3053_ none_d08d7bba442a9b36\msvcm80.dll'

Again, the console app does not have an exception and loads the same DLL:

'ConsoleApp.vshost.exe' (Managed): Loaded 'C:\Windows\WinSxS\x86_microsoft.vc80.crt_1fc8b3b9a1e18e3b_8.0.50727.3053_ none_d08d7bba442a9b36\msvcm80.dll'

See answer from Microsoft Product Support.

Update #1: Both the console application and the WcfSvcHost.exe host process runs under the same session and logged-in user (me). I've copied WcfSvcHost.exe to the directory of the service, manually launched and experienced the same result. I've also checked the Windows Event Log for additional information and used sxstrace, but nothing was logged.

Running Process Explorer, I've verified the following are the same between the two processes:

• Image: 32-bit
• Current Directory
• User/SID
• Session
• Security (groups denied, privileges disabled)

Running Process Monitor, and configuring symbols, I see WcfSvcHost looks for the following registry and files, while the console host does not. Process Monitor logs a lot of data and I'm not sure what I'm looking for :(.

HKLM\SOFTWARE\Microsoft\Fusion\PublisherPolicy\Default\policy.8.0.msvcm80__b03f5f7f11d50a3a C:\Windows\assembly\GAC_32\msvcm80\8.0.50727.3053__b03f5f7f11d50a3a C:\Windows\assembly\GAC_MSIL\msvcm80\8.0.50727.3053__b03f5f7f11d50a3a C:\Windows\assembly\GAC\msvcm80\8.0.50727.3053__b03f5f7f11d50a3a

Update #2: This same exception occurs when the service is hosted in production on IIS 6 / Windows Server 2003.

Update #3: The 3rd-party 32-bit .NET assembly is the StreamBase API:

• sbclient.dll (managed)
• monitor.netmodule (managed)
• dotnetapi.dll (unmanaged)
• pthreads-vc8.dll (unmanaged)

Update #4: Added manifests without success:

1. Verified that dotnetapi.dll and pthreads-vc8.dll have RT_MANIFEST. The sbclient.dll .NET assembly did not have a manifest
2. Removed sbclient.dll from the GAC
3. Registered sbclient.dll for verification skipping
4. Added a manifest via mt.exe to both sbclient.dll and monitor.netmodule
5. Verified manifest was added and that the expected files were loaded during testing (via Visual Studio - debug modules window)
6. The same BadImageFormatException is thrown under BackgroundWorker.OnDoWork(), and the call stack shows a call to dotnetapi.dll...DefaultDomain.Initalize().

I have verified that msvcm80.dll does not have a manifest, I believe this is the only file loaded that doesn't have a manifest :)

Interesting find

When I load monitor.netmodule in Reflector, it says:

'monitor.netmodule' does not contain an assembly manifest.

Even though it displays an error, Reflector is still able to disassemble the managed code.

Answer 1

a bit late but you can also change the app pool setting "Enable 32-bit Applications" to true in advanced settings.

Answer 2

Microsoft Product Support has resolved this question: It's by design. The unmanaged code is not loaded in the default AppDomain when using WcfSvcHost or the IIS WCF host.

A pure image will use a CLR version of the C run-time library. However, the CRT is not verifiable, so you cannot use the CRT when compiling with /clr:safe. For more information, see C Run-Time Libraries.

http://msdn.microsoft.com/en-us/library/k8d11d4s.aspx

Answer 3

I cannot provide an explanation for the error, only my initial suspicion that there is a permission difference between the context in which your code is run as a service and the context in which it is run when you place it in a console application. The E_HANDLE HRESULT is my clue here. Assuming that you run the console application as your logged-in user, you could try configuring the service to start as that user as well. If it works in that configuration, then you can attempt to narrow down what required resource is unavailable when it fails.

I can suggest a workaround. If there is an oddity of the DLL in question that prevents it from working in a hosted service, you can take the sacrificial process approach, so named because it is typically used to isolate a DLL that crashes often. Briefly, you create a proxy program whose only purpose is to load and call the DLL on behalf of your main process, using named pipes or some other IPC method to pass requests and results. If the DLL crashes, you start a new instance of the proxy program. In your case it would have the added benefit that only the wrapper program would need to be 32-bit.

Answer 4

Do you see anything special in the Event viewer?.
In Vista if there a manifest problem you will see traces of it in the Event Viewer, it will tell you to use SxsTrace.

Answer 5

Could you manually add a manifest to this DLL yourself, using the mt.exe file?

MSDN Article on using mt.exe

Answer 6

This may seem a bit dumb; but make sure your service is running in the correct application pool.

Answer 7

Ran into this issue myself. I found a helpful post. As noted in other posts, Microsoft stated this is by design. Basically you need to:

1. Locate your version of WcfSvcHost.exe. (for me and visual studio 2017: C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\Common7\IDE)

2. Launch developer command prompt

3. Execute cmd: copy C:\SourcePath\WcfSvcHost.exe C:\DestinationPath\WcfSvcHost32.exe (Destination doesn't matter)

4. cmd: corflags /32BIT+ /Force WcfSvcHost32.exe (may need to cd to DestinationPath

5. In visual studio open the WCF project properties > Debug tab > Start External program: C:\DestinationPath\WcfSvcHost32.exe

6. Also add your command line arguments:

   /service:MyWCFProjectName.dll /config:MyWCFProjectName.dll.config

   Note: You do not need to use ($ProjectDir) here

7. Launch the app. You are now free to launch WcfServiceHost.exe seperately.

8. Optionally go to solution > Set Startup Projects > Multiple Startup Projects > Choose the Wcf project and the client project.