How to Automate Exporting .NET Function to Unmanaged Programs

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Introduction

Exporting functions to unmanaged programs - why not? I don't want to change *.il files by hand. I need to automate this. So here we go...

Background

A few days ago, I was writing a program (Terminal Services addin). The first problem was that I couldn't write this in C# ... Ok. I started writing it in C++/CLI. But there was another problem - mstsc.exe doesn't like to load such a library. Ok. No problem. I started another project (in C++/CLI - the first I change to pure C++) which exports one function. The first library loaded the second one and everything worked. But for dependencies, I needed easy deployment without installing VC80 runtimes... So I tried to find a way to export the function from C#. And I found it. While I was working with a project, I compiled it often and changing *.il files by hand was really annoying. That's why I made this tool. (Anyway later I found that the first library can be written in C# but it is a topic for another article - "How to write Terminal Services addin in pure C#" .)

Using the Code

Well the code is just the code ... it's a home-grown parser with some other functionality... So I'll rather write how to use it (and sometimes how it works).

Beginning

What you need to use it:

• Framework 2.0 SDK
• Visual Studio 2005 (optional)

First you should download the code (there are two projects ExportDll.exe and ExportDllAttribute.dll) and build it.

Then you should know how to use it... After creating the library project in C# or VB.NET, you need to add dependency to ExportDllAttribute. "Oh no, not another dependency" - you'll say. Easy ... just wait ... This library contains an attribute which tells ExportDll.exe that some function needs to be exported.

How It Works

As I said, ExportDll.exe needs to know which functions need to be exported. So you'll write something like this:

public class SomeClassName
{
    //second parameter of attribute is calling convention,
    //default is StdCall but u can use others fx.:
    [ExportDllAttribute.ExportDll("ExportNameOfFunction",
    System.Runtime.InteropServices.CallingConvention.Cdecl)]
    public static void SomeFunctionName()
    {
        System.Console.WriteLine("I really do nothing");
    }
}

After compiling, you need to use ExportDll tool to export this:

ExportDll.exe full_path_to_yours_dll\yoursdll.dll [/Release|/Debug]

Note: /Release flag is default. What exactly does ExportDll do:

• Reads DLL as assembly and makes a dictionary of exported function
• Decompiles DLL
• Searches and replaces some stuff in IL code (If you want to know what, read the article that I mentioned in the "Background" section.)

• Deletes ExportDllAttribute dependency

  .assembly extern ExportDllAttribute
  {
    .ver x:x:x:x
  }

  and

  .custom instance void
      [ExportDllAttribute]ExportDllAttribute.ExportDllAttribute ...

• Compiles modified IL code again

Post-building in Visual Studio 2005

How? It's easy... Just add in Project property named "Post-build event command".

"path_to_tools\ExportDll.exe" "$(TargetPath)" /$(ConfigurationName)

OMG! It's Not Working

Hmm... Yes, forgot to mention about ExportDll.exe.cofig ...

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <sectionGroup name="applicationSettings" 
        type="System.Configuration.ApplicationSettingsGroup, 
        System, Version=2.0.0.0, Culture=neutral, 
        PublicKeyToken=b77a5c561934e089" >
            <section name="ExportDll.Properties.Settings"
        type="System.Configuration.ClientSettingsSection,
        System, Version=2.0.0.0, Culture=neutral,
        PublicKeyToken=b77a5c561934e089" requirePermission="false" />
        </sectionGroup>
    </configSections>
    <applicationSettings>
        <ExportDll.Properties.Settings>
            <setting name="ildasmpath" serializeAs="String">
                <value>C:\Program Files\
                Microsoft Visual Studio 8\SDK\v2.0\Bin\ildasm.exe</value>
            </setting>
            <setting name="ilasmpath" serializeAs="String">
                <value>C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\ilasm.exe
                </value>
            </setting>
        </ExportDll.Properties.Settings>
    </applicationSettings>
</configuration>

You need to configure path to ilasm and ildasm.

Updates

New version

• now accept MarshalAsAtrribute
• new commands in command line support: first had to be TargetPath then you can add:
  /release or /debug - /release id default
  /AnyCPU or /x64 - /AnyCPU is default its for 32/64 bit (for itanium add /PE64 /ITANIUM)
  ... any valid command for ildasm.exe
• support fo x64

  "path_to_tools\ExportDll.exe" "$(TargetPath)" /$(ConfigurationName) /$(PlatformName)

  if PlatformName == "AnyCPU" then compiles for 32 bit
  if PlatformName == "x64" then compiles for 64 bit
• now its compiled for runtime 4.0(ExportDll.exe) and 2.0 (ExportDllAttribut.dll) so it should be working for frameworks 2.0 - 4.0
• it can compile for 2.0 or 4.0 runtime (runtime its not framework - frm 3.0 and 3.5 are using 2.0 runtime)
  it can be change by changing ilasmpath setting so:
  2.0 => C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\ilasm.exe
  4.0 => C:\Windows\Microsoft.NET\Framework\v4.0.30319\ilasm.exe

References

• Unmanaged Code Can Wrap Managed Methods