C# hostpolicy.dll Fatal Error

[erikw343]

Hi, in C# I’m trying to load a custom modified System.Private.CoreLib, I modified the Dictionary.cs generic class.

When I run my console application, I get:

A fatal error was encountered. The library 'hostpolicy.dll' required to execute the application was not found in 'C:\Program Files\dotnet'. Failed to run as a self-contained app.

The application was run as a self-contained app because 'C:\Users\erikw\source\repos\MainDict2\MainDict2\bin\x64\Debug\net9.0\MainDict2.runtimeconfig.json' did not specify a framework.
If this should be a framework-dependent app, specify the appropriate framework in 'C:\Users\erikw\source\repos\MainDict2\MainDict2\bin\x64\Debug\net9.0\MainDict2.runtimeconfig.json'.
This is my main project file:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
      <DisableImplicitFrameworkReferences>true</DisableImplicitFrameworkReferences>
      <Platforms>AnyCPU;x64</Platforms>
  </PropertyGroup>

  <ItemGroup>
    <Reference Include="Microsoft.Extensions.DotNetDeltaApplier">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\sdk\9.0.302\DotnetTools\dotnet-watch\9.0.302-servicing.25319.7\tools\net9.0\any\hotreload\Microsoft.Extensions.DotNetDeltaApplier.dll</HintPath>
    </Reference>
    <Reference Include="System.Collections">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Collections.dll</HintPath>
    </Reference>
    <Reference Include="System.Collections.Concurrent">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Collections.Concurrent.dll</HintPath>
    </Reference>
    <Reference Include="System.Console">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Console.dll</HintPath>
    </Reference>
    <Reference Include="System.IO.Pipes">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.IO.Pipes.dll</HintPath>
    </Reference>
    <Reference Include="System.Linq">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Linq.dll</HintPath>
    </Reference>
    <Reference Include="System.Net.Http">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Net.Http.dll</HintPath>
    </Reference>
    <Reference Include="System.Private.CoreLib">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Private.CoreLib.dll</HintPath>
    </Reference>
    <Reference Include="System.Runtime">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Runtime.dll</HintPath>
    </Reference>
    <Reference Include="System.Runtime.InteropServices">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Runtime.InteropServices.dll</HintPath>
    </Reference>
    <Reference Include="System.Text.Encoding.Extensions">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Text.Encoding.Extensions.dll</HintPath>
    </Reference>
    <Reference Include="System.Threading">
      <HintPath>..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Threading.dll</HintPath>
    </Reference>
  </ItemGroup>

</Project>

Notice that I loaded all of the required assemblies to make the code compile… such as System.Runtime.dll

Note that I disabled the Implicit Framework References/Assemblies... I did so because I have a custom System.Private.CoreLib with a modified Dictionary.cs generic class. This is all for messing around with an example in my O'Reilly Programming C# 10.0 book. I am just playing around with the code in order to learn...

I tried to import hostpolicy.dll, but it gave me an error:

The reference is invalid or unsupported.
Any suggestions? Thanks!

[jkotas]

You should use instructions at https://github.com/dotnet/runtime/blob/main/docs/workflow/testing/using-dev-shipping-packages.md#creating-and-running-the-app-with-your-build to test your app with your private build of the runtime.

There is no other reliable way to do that. (If there was one, we would have mentioned it in the repo docs.)

[jkotas]

Duplicate of #117575

[erikw343]

Thanks man :)

[erikw343]

Did I follow the instructions correctly, sorry?

C:\Users\erikw\OneDrive\Documents\HelloWorld\bin\Release\net9.0\win-x64\publish>dir
 Volume in drive C is Windows-SSD
 Volume Serial Number is 745E-1B48

 Directory of C:\Users\erikw\OneDrive\Documents\HelloWorld\bin\Release\net9.0\win-x64\publish

07/20/2025  07:52 PM    <DIR>          .
07/20/2025  07:52 PM    <DIR>          ..
07/20/2025  07:52 PM               475 HelloWorld.deps.json
07/20/2025  07:52 PM             4,608 HelloWorld.dll
07/20/2025  07:52 PM           155,136 HelloWorld.exe
07/20/2025  07:52 PM            10,680 HelloWorld.pdb
07/20/2025  07:52 PM               340 HelloWorld.runtimeconfig.json
               5 File(s)        171,239 bytes
               2 Dir(s)  3,790,656,286,720 bytes free

C:\Users\erikw\OneDrive\Documents\HelloWorld\bin\Release\net9.0\win-x64\publish>HelloWorld.exe
Hello World from .NET 9.0.7+3c298d9f00936d651cc47d221762474e25277672.
The location of System.Private.CoreLib.dll is 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.7\System.Private.CoreLib.dll'
Hello, World!

This is my Hello, World console app directory:

C:\Users\erikw\OneDrive\Documents\HelloWorld>dir
 Volume in drive C is Windows-SSD
 Volume Serial Number is 745E-1B48

 Directory of C:\Users\erikw\OneDrive\Documents\HelloWorld

07/20/2025  07:34 PM    <DIR>          .
07/20/2025  07:16 PM    <DIR>          ..
07/20/2025  07:35 PM    <DIR>          bin
07/20/2025  07:32 PM               475 HelloWorld.csproj
07/20/2025  07:18 PM    <DIR>          LocalNugetCache
07/20/2025  07:25 PM             1,013 nuget.config
07/20/2025  07:35 PM    <DIR>          obj
07/20/2025  07:34 PM               420 Program.cs
               3 File(s)          1,908 bytes
               5 Dir(s)  3,790,664,192,000 bytes free

C:\Users\erikw\OneDrive\Documents\HelloWorld>

Program.cs:

// See https://aka.ms/new-console-template for more information

using System.Diagnostics;

var coreAssemblyInfo = FileVersionInfo.GetVersionInfo(typeof(object).Assembly.Location);
Console.WriteLine($"Hello World from .NET {coreAssemblyInfo.ProductVersion}.");
Console.WriteLine($"The location of System.Private.CoreLib.dll is '{typeof(object).Assembly.Location}'");

Console.WriteLine("Hello, World!");

My runtime release I downloaded from github is from C:\rt2:

C:\rt2>dir
 Volume in drive C is Windows-SSD
 Volume Serial Number is 745E-1B48

 Directory of C:\rt2

07/20/2025  06:26 PM    <DIR>          .
07/20/2025  05:47 PM                20 .clang-format
07/20/2025  05:47 PM                38 .clang-tidy
07/20/2025  05:47 PM               576 .CodeQL.yml
07/20/2025  05:47 PM    <DIR>          .config
07/20/2025  05:47 PM    <DIR>          .devcontainer
07/20/2025  05:47 PM             5,041 .dockerignore
07/20/2025  06:27 PM    <DIR>          .dotnet
07/20/2025  05:47 PM             7,800 .editorconfig
07/20/2025  05:47 PM             2,067 .gitattributes
07/20/2025  05:47 PM    <DIR>          .github
07/20/2025  05:47 PM             5,556 .gitignore
07/20/2025  05:47 PM                71 .markdownlint.json
07/20/2025  05:47 PM             2,525 .vsconfig
07/20/2025  06:57 PM    <DIR>          artifacts
07/20/2025  05:47 PM               214 build.cmd
07/20/2025  05:47 PM               784 Build.proj
07/20/2025  05:47 PM               853 build.sh
07/20/2025  05:47 PM               258 CODE-OF-CONDUCT.md
07/20/2025  05:47 PM            14,787 CONTRIBUTING.md
07/20/2025  05:47 PM            40,122 Directory.Build.props
07/20/2025  05:47 PM                92 Directory.Build.rsp
07/20/2025  05:47 PM            15,065 Directory.Build.targets
07/20/2025  05:47 PM               234 Directory.Solution.props
07/20/2025  05:47 PM    <DIR>          docs
07/20/2025  05:47 PM               800 dotnet.cmd
07/20/2025  05:47 PM               867 dotnet.sh
07/20/2025  05:47 PM    <DIR>          eng
07/20/2025  05:47 PM             1,168 github-merge-flow.jsonc
07/20/2025  05:47 PM               480 global.json
07/20/2025  05:47 PM             1,116 LICENSE.TXT
07/20/2025  05:47 PM             2,455 NuGet.config
07/20/2025  05:47 PM             2,584 PATENTS.TXT
07/20/2025  05:47 PM             4,969 README.md
07/20/2025  05:47 PM             1,042 SECURITY.md
07/20/2025  05:59 PM    <DIR>          src
07/20/2025  05:47 PM            74,244 THIRD-PARTY-NOTICES.TXT
              28 File(s)        185,828 bytes
               9 Dir(s)  3,790,652,395,520 bytes free

C:\rt2>

This is my nuget.config file:

<?xml version="1.0" encoding="utf-8"?>
<configuration>

  <config>
    <!-- Set the "value" here to the folder you will be using for your local Nuget cache. -->
    <add key="globalPackagesFolder" value="C:/Users/erikw/OneDrive/Documents/HelloWorld/LocalNugetCache" />
  </config>

  <packageSources>
    <!--To inherit the global NuGet package sources remove the <clear/> line below -->
    <clear />

    <!-- Any packages that might be required, but not present in your build, will have to be taken from the latest NuGet feed. -->
    <!-- More info on: https://github.com/dotnet/sdk#installing-the-sdk -->
    <add key="dotnet9" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet9/nuget/v3/index.json" />

    <!-- Set this path to where your Shipping Artifacts are located. Note that we are assuming a 'Debug' build in this example. -->
    <add key="local runtime" value="C:/rt2/artifacts/packages/Debug/Shipping" />
  </packageSources>

</configuration>

The LocalNugetCache folder is empty...

C:\Users\erikw\OneDrive\Documents\HelloWorld\LocalNugetCache>dir
 Volume in drive C is Windows-SSD
 Volume Serial Number is 745E-1B48

 Directory of C:\Users\erikw\OneDrive\Documents\HelloWorld\LocalNugetCache

07/20/2025  07:18 PM    <DIR>          .
07/20/2025  07:34 PM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)  3,790,651,191,296 bytes free

This is my HelloWorld.csproj file:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

<ItemGroup>
  <!-- At the time of writing, '10.0.0-dev' is the version of the runtime repo's shipping packages. -->
  <FrameworkReference Update="Microsoft.NETCore.App" RuntimeFrameworkVersion="9.0.7" />
</ItemGroup>

</Project>

I don't know if I am using the newly compiled dotnet runtime (from github), or just the one that is installed by default with VS 2022?
Can you guys tell me if I setup all this stuff correctly or not?
I want to have the runtime from C:\rt2 to be installed!

Thanks,
Erik W.

[jkotas]

Directory of C:\Users\erikw\OneDrive\Documents\HelloWorld\bin\Release\net9.0\win-x64\publish

There should be a lot more files in this directory, including System.Private.CoreLib.dll with your changes.

The instructions have a bug. I have submitted a fix #117874 . Could you please re-run dotnet publish --self-contained to see whether it is going to fix the problem?

[erikw343]

Yes, I tried that, and I got some error messages!

C:\Users\erikw\OneDrive\Documents\HelloWorld>dotnet publish --self-contained
    C:\Users\erikw\OneDrive\Documents\HelloWorld\HelloWorld.csproj : error NU1102:
      Unable to find package Microsoft.WindowsDesktop.App.Runtime.win-x64 with version (= 9.0.7)
        - Found 597 version(s) in dotnet9 [ Nearest version: 10.0.0-alpha.1.24414.4 ]
        - Found 0 version(s) in C:\Program Files\dotnet\library-packs
        - Found 0 version(s) in local runtime
    C:\Users\erikw\OneDrive\Documents\HelloWorld\HelloWorld.csproj : error NU1102:
      Unable to find package Microsoft.AspNetCore.App.Runtime.win-x64 with version (= 9.0.7)
        - Found 1149 version(s) in dotnet9 [ Nearest version: 10.0.0-alpha.1.24416.1 ]
        - Found 0 version(s) in C:\Program Files\dotnet\library-packs
        - Found 0 version(s) in local runtime

Restore failed with 2 error(s) in 3.3s

This is my publish directory also:

C:\Users\erikw\OneDrive\Documents\HelloWorld\bin\Release\net9.0\win-x64\publish>dir
 Volume in drive C is Windows-SSD
 Volume Serial Number is 745E-1B48

 Directory of C:\Users\erikw\OneDrive\Documents\HelloWorld\bin\Release\net9.0\win-x64\publish

07/20/2025  07:52 PM    <DIR>          .
07/20/2025  07:52 PM    <DIR>          ..
07/20/2025  07:52 PM               475 HelloWorld.deps.json
07/20/2025  07:52 PM             4,608 HelloWorld.dll
07/20/2025  07:52 PM           155,136 HelloWorld.exe
07/20/2025  07:52 PM            10,680 HelloWorld.pdb
07/20/2025  07:52 PM               340 HelloWorld.runtimeconfig.json
               5 File(s)        171,239 bytes
               2 Dir(s)  3,761,493,147,648 bytes free

[jkotas]

Hmm, looks like these instructions are completely broken. There is a link to alternative instructions listed at the top of the doc:

https://github.com/dotnet/runtime/blob/main/docs/workflow/testing/using-your-build-with-installed-sdk.md#create-a-sample-self-contained-application

Could you please try those?

[erikw343]

Ok thanks I will try that :)