References to missing Types or Methods in referenced DLL

Ever wonder what happens if you have a binary reference to an external .dll and decide not to recompile the application or library that references/depends on it? You can get some strange errors depending on the changes that have been made. Ever experienced a BadImageFormatException, ExecutionEngineException, TypeLoadException, or MissingMethodException?

Firstly, the manifest file for the dependent app/library is not updated pointing to the new version. This can cause mismatched assembly version errors (BadImageFormatException).

Here are the results from some tests with the removal of types and/or methods on a referenced assembly (hereinafter referred to as ‘Bad Assembly’). All tests were done with x86 Console App/Library in separate solutions with a “static hardcoded” path reference to Bad Assembly (x64 shouldn’t matter):

1. Results were always the same for Release/Debug builds.
2. The bad assembly was always successfully loaded. ‘fuslogvw’ (.NET Assembly Load Viewer) confirmed this.
3. Setting the reference to Bad Assembly as “Specific Version” (using v1.0.0.0) and changing the version on Bad Assembly to v1.1.0.0 had no effect. However, I didn’t try defining Bad Assembly in the “assemblies” section of the app.config. It is possible that would have given a different result.
4. References to a missing Type OR calls to a missing Method from Bad Assembly in "static void Main()" resulted in a "System.ExecutionEngineException" (fatal error as shown below). This exception cannot be caught by any means: Assembly events, AppDomain events, try/catch block in "static void Main()". I confirmed this thru WinDbg. This is because it is the first method that the EE (CLR Execution Engine) tells the JIT to compile. Since JIT happens on a method-by-method basis and "static void Main()" is the entry point for the app, there is no place “upstream” where an exception can be caught. The error in the Event Viewer is completely cryptic and provides no indication what went wrong.
5. If the reference to a missing Type OR calls to a missing Method from Bad Assembly occurred “downstream” of "static void Main()" AND there WAS NOT exception handling upstream, OR there WAS exception handling upstream but the exception was rethrown so that is was never caught again, then results were same as #4.  (i.e. unhandled exception)
6. If the reference to a missing Type OR calls to a missing Method from Bad Assembly occurred “downstream” of "static void Main()" AND there WAS exception handling upstream, then the exception was caught as either a "System.TypeLoadException" or "System.MissingMethodException" respectively.  The exceptions were thrown from the JIT as the Type or Method was accessed.

HTH

Referencing platform-specific (x86/x64) assemblies in Visual Studio projects

CodeProjectRecently I've been thinking about how to make Assembly References dependent on the Platform Architecture for a given compiled application/library. A solution for this problem is necessary as you begin to move your apps to the x64 platform.

There are 2 solutions: one method is for "project-references"; the other is for "path-hardcoded dll references". Unfortunately, both involve manually editing the .csproj file yuk... AFAIK, there is no way to do this within the VisualStudio 2008 UI - I don't know about VS 2010. Note that it is NOT necessary to modify any of the references to the .NET dlls.

One quick note about these solutions is that they are independent of the Platform Architecture of the machine that is compiling the projects!

After opening the .csproj file in a text-editor (or as a .xml file within VisualStudio), do either of the following depending on your needs. Note that valid platform values are either: x86, x64, or ia64.

Platform-Specific Project References:

<ProjectReference Include="..\SomeLibrary.csproj" Condition="'$(Platform)' == 'x64'">

    <Project>{GUID of existing proj ref goes here...}</Project>

    <Name>SomeLibrary</Name>

</ProjectReference>

Platform-Specific Binary (.dll) References:

<Reference Include="SomeDll, Version=..., Culture=..., PublicKeyToken=..., processorArchitecture=x86" Condition="'$(Platform)' == 'x86'" />

    <SpecificVersion>False</SpecificVersion>

    <HintPath>C:\MyAppReferences\x86\SomeLibrary.dll</HintPath>

</Reference>

<Reference Include="SomeDll, Version=..., Culture=..., PublicKeyToken=..., processorArchitecture=x64" Condition="'$(Platform)' == 'x64'" />

    <SpecificVersion>False</SpecificVersion>

    <HintPath>C:\MyAppReferences\x64\SomeLibrary.dll</HintPath>

</Reference>