[x64/Linux] Crossgen fails loading 'System.Runtime, Version=4.2.1.0'

[kterhorst]

(0.) Delete ~/.dotnet and ~/.nuget to get a fresh linux .NET Core environment.

1. Download a .NET Core build (3.0.100 preview in this case); same problem with 2.1 and 2.2 in the past. Extract to "~/Downloads/dotnet-sdk-3.0.100".
2. Create a simple application. Run "~/Downloads/dotnet-sdk-3.0.100/dotnet new console" in some directory. Here it is ~/tmp/crossgentest.
3. Publish the app:
   ~/tmp/crossgentest/bin/Debug/netcoreapp3.0/linux-x64>$ ~/Downloads/dotnet-sdk-3.0.100/dotnet publish --self-contained --runtime linux-x64
   Now the resulting linux-x64 directory should contain all binaries to run/crossgen the app.
4. Copy crossgen from "/home/klaus/.nuget/packages/runtime.linux-x64.microsoft.netcore.app/3.0.0-preview-27122-01/tools" to the linux-x64 directory.
   (Running crossgen directly from this directory results in "System.Private.CoreLib.dll not found".)
5. Run
   ~/tmp/crossgentest/bin/Debug/netcoreapp3.0/linux-x64>$ ./crossgen crossgentest.dll
   Error: Could not load file or assembly 'System.Runtime, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
   (Exception from HRESULT: 0x80070002)
   Error compiling crossgentest.dll: Could not find or load a specific file. (Exception from HRESULT: 0x80131621)
   Error: compilation failed for "crossgentest.dll" (0x80131621)

In my case it always fails at this point. I even compiled a custom CoreCLR build but still get the same error. My aim is to crossgen the .NET core binaries to improve the startup time.

My linux build is: Linux anarchy 4.18.16-arch1-1-ARCH dotnet/coreclr#1 SMP PREEMPT Sat Oct 20 22:06:45 UTC 2018 x86_64 GNU/Linux

[jkotas]

crossgen expects references to all assemblies to be passed on the command line explicitly. Adding -Platform_Assemblies_Paths argument that points to the directory with System.Runtime and other assemblies should help.

Related to: #11022

cc @zamont

[kterhorst]

Thank you very much! I wished I had known this earlier (before copying around various versions of System.Runtime.dll and building CoreCLR).