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C# for systems programming

These samples show how to compile C# to native code using a minimalist .NET runtime (CoreRT).

no-runtime is a rather pointless sample that demonstrates how to write code in C# that is directly runnable without a runtime. C# has value types and you can p/invoke into an unmanaged memory allocator, so you can do things with this, but you're so severily limited it's rather pointless. But Hello world ends up being about 4-5 kB native EXE, so that's rather cool.

with-runtime is something that can be actually useful. This includes the full managed and unmanaged runtime - GC, exception handling, and interface dispatch all work. Test.CoreLib used as the class library here is the same Test.CoreLib that you can find in the CoreRT repo. Don't look for things like Object.ToString() because being compatible with .NET is not the point. This sample comes down to about 400 kB, most of which is the C runtime library.

efi-no-runtime is an EFI boot application that lets you run C# on bare metal, without an OS. Similar restrictions to the no-runtime sample apply. Making a version of this sample with a runtime would require some porting work on the runtime side.

Building the samples

There are some prerequisites for running the build scripts:

  • A CoreRT drop
  • Visual Studio 2017 with C++ support and a Windows SDK

You can run these without building CoreRT yourself. Just point the DROPPATH environment variable to the ILCompiler package in your NuGet package cache (if you ever played with using CoreRT, it will be somewhere like C:\Users\{user}\.nuget\packages\\1.0.0-alpha-27402-01). If you haven't tried CoreRT for your normal .NET Core projects yet, go try it out, it's cool. Alternatively, clone the CoreRT GitHub project and build it yourself (more prerequisites apply - see that repo for instructions). Once you have a local build of CoreRT, the DROPPATH to use will be something like D:\git\rt\bin\Windows_NT.x64.Debug.

The build.cmd script needs to be executed from a "x64 Native Tools Command Prompt for VS 2017" - it's in your Start menu. Also make sure DROPPATH is set as above.

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