Add support for embedding runtime configuration (#6103)

Runtime configuration (e.g. whether to use server GC) can currently be provided either through environment variables at runtime, or through a RhConfig.ini file placed next to the executable. This adds another channel where we burn a blob similar to RhConfig.ini format into the executable. The order of precedence is environment variable > RhConfig.ini > embedded config.

The `ServerGarbageCollection` project property that is used to determine whether to link with a runtime that supports server GC will be also used to control whether to generate a configuration that enables server GC at runtime by default.

Fixes #6100.

4 files changed, 65 insertions, 0 deletions

diff --git a/src/ILCompiler.Compiler/src/Compiler/Compilation.cs b/src/ILCompiler.Compiler/src/Compiler/Compilation.cs
index 7df723cb5..6a307aac4 100644
--- a/src/ILCompiler.Compiler/src/Compiler/Compilation.cs
+++ b/src/ILCompiler.Compiler/src/Compiler/Compilation.cs
@@ -421,6 +421,11 @@ namespace ILCompiler
             {
                 _graph.AddRoot(_factory.ModuleMetadata(module), reason);
             }
+
+            public void RootReadOnlyDataBlob(byte[] data, int alignment, string reason, string exportName)
+            {
+                _graph.AddRoot(_factory.ReadOnlyDataBlob(exportName, data, alignment), reason);
+            }
         }
     }
 
diff --git a/src/ILCompiler.Compiler/src/Compiler/IRootingServiceProvider.cs b/src/ILCompiler.Compiler/src/Compiler/IRootingServiceProvider.cs
index 0895464cc..1a462e9fc 100644
--- a/src/ILCompiler.Compiler/src/Compiler/IRootingServiceProvider.cs
+++ b/src/ILCompiler.Compiler/src/Compiler/IRootingServiceProvider.cs
@@ -18,5 +18,6 @@ namespace ILCompiler
         void RootNonGCStaticBaseForType(TypeDesc type, string reason);
         void RootVirtualMethodForReflection(MethodDesc method, string reason);
         void RootModuleMetadata(ModuleDesc module, string reason);
+        void RootReadOnlyDataBlob(byte[] data, int alignment, string reason, string exportName);
     }
 }
diff --git a/src/ILCompiler.Compiler/src/Compiler/RuntimeConfigurationRootProvider.cs b/src/ILCompiler.Compiler/src/Compiler/RuntimeConfigurationRootProvider.cs
new file mode 100644
index 000000000..e4be79fc1
--- /dev/null
+++ b/src/ILCompiler.Compiler/src/Compiler/RuntimeConfigurationRootProvider.cs
@@ -0,0 +1,58 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+
+namespace ILCompiler
+{
+    /// <summary>
+    /// A root provider that provides a runtime configuration blob that influences runtime behaviors.
+    /// See RhConfigValues.h for allowed values.
+    /// </summary>
+    public class RuntimeConfigurationRootProvider : ICompilationRootProvider
+    {
+        private readonly IEnumerable<string> _runtimeOptions;
+
+        public RuntimeConfigurationRootProvider(IEnumerable<string> runtimeOptions)
+        {
+            _runtimeOptions = runtimeOptions;
+        }
+
+        void ICompilationRootProvider.AddCompilationRoots(IRootingServiceProvider rootProvider)
+        {
+            rootProvider.RootReadOnlyDataBlob(GetRuntimeOptionsBlob(), 4, "Runtime configuration information", "g_compilerEmbeddedSettingsBlob");
+        }
+
+        protected byte[] GetRuntimeOptionsBlob()
+        {
+            const int HeaderSize = 4;
+
+            ArrayBuilder<byte> options = new ArrayBuilder<byte>();
+
+            // Reserve space for the header
+            options.ZeroExtend(HeaderSize);
+
+            foreach (string option in _runtimeOptions)
+            {
+                byte[] optionBytes = System.Text.Encoding.ASCII.GetBytes(option);
+                options.Append(optionBytes);
+
+                // Emit a null to separate the next option
+                options.Add(0);
+            }
+
+            byte[] result = options.ToArray();
+
+            int length = options.Count - HeaderSize;
+
+            // Encode the size of the blob into the header
+            result[0] = (byte)length;
+            result[1] = (byte)(length >> 8);
+            result[2] = (byte)(length >> 0x10);
+            result[3] = (byte)(length >> 0x18);
+
+            return result;
+        }
+    }
+}
diff --git a/src/ILCompiler.Compiler/src/ILCompiler.Compiler.csproj b/src/ILCompiler.Compiler/src/ILCompiler.Compiler.csproj
index 7b86399ea..5c84847c2 100644
--- a/src/ILCompiler.Compiler/src/ILCompiler.Compiler.csproj
+++ b/src/ILCompiler.Compiler/src/ILCompiler.Compiler.csproj
@@ -333,6 +333,7 @@
     <Compile Include="Compiler\ExportsFileWriter.cs" />
     <Compile Include="Compiler\PrecomputedMetadataManager.cs" />
     <Compile Include="Compiler\ReadyToRun.cs" />
+    <Compile Include="Compiler\RuntimeConfigurationRootProvider.cs" />
     <Compile Include="Compiler\RyuJitCompilation.cs" />
     <Compile Include="Compiler\RyuJitCompilationBuilder.cs" />
     <Compile Include="Compiler\SingleFileCompilationModuleGroup.cs" />