[cDAC] Add RuntimeSignatureDecoder for ELEMENT_TYPE_INTERNAL support

Custom signature decoder handling runtime-internal type codes
(ELEMENT_TYPE_INTERNAL 0x21, ELEMENT_TYPE_CMOD_INTERNAL 0x22) which
SRM's SignatureDecoder cannot parse. Replaces SRM in PromoteCallerStack.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Max Charlamb

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/FrameHandling/FrameIterator.cs

@@ -580,9 +580,10 @@ private void PromoteCallerStack(
             return;
 
         ReadOnlySpan<byte> signature;
+        MetadataReader? metadataReader;
         try
         {
-            signature = GetMethodSignatureBytes(methodDescPtr);
+            signature = GetMethodSignatureBytes(methodDescPtr, out metadataReader);
         }
         catch (System.Exception)
         {
@@ -595,20 +596,14 @@ private void PromoteCallerStack(
         MethodSignature<GcTypeKind> methodSig;
         try
         {
-            unsafe
-            {
-                fixed (byte* pSig = signature)
-                {
-                    BlobReader blobReader = new(pSig, signature.Length);
-                    SignatureDecoder<GcTypeKind, object?> decoder = new(
-                        GcSignatureTypeProvider.Instance, metadataReader: null!, genericContext: null);
-                    methodSig = decoder.DecodeMethodSignature(ref blobReader);
-                }
-            }
+            RuntimeSignatureDecoder<GcTypeKind, object?, SpanSignatureReader> decoder = new(
+                GcSignatureTypeProvider.Instance, target, genericContext: null,
+                new SpanSignatureReader(signature, target.IsLittleEndian), metadataReader);
+            methodSig = decoder.DecodeMethodSignature();
         }
         catch (System.Exception)
         {
-            // If signature decoding fails (e.g., ELEMENT_TYPE_INTERNAL), skip this frame.
+            // If signature decoding fails for any reason, skip this frame.
             // The GCRefMap path handles these cases when available.
             return;
         }
@@ -707,8 +702,9 @@ private void PromoteCallerStackHelper(
         }
     }
 
-    private ReadOnlySpan<byte> GetMethodSignatureBytes(TargetPointer methodDescPtr)
+    private ReadOnlySpan<byte> GetMethodSignatureBytes(TargetPointer methodDescPtr, out MetadataReader? metadataReader)
     {
+        metadataReader = null;
         IRuntimeTypeSystem rts = target.Contracts.RuntimeTypeSystem;
         MethodDescHandle mdh = rts.GetMethodDescHandle(methodDescPtr);
 
@@ -727,13 +723,13 @@ private ReadOnlySpan<byte> GetMethodSignatureBytes(TargetPointer methodDescPtr)
         ModuleHandle moduleHandle = loader.GetModuleHandleFromModulePtr(modulePtr);
 
         IEcmaMetadata ecmaMetadata = target.Contracts.EcmaMetadata;
-        MetadataReader? mdReader = ecmaMetadata.GetMetadata(moduleHandle);
-        if (mdReader is null)
+        metadataReader = ecmaMetadata.GetMetadata(moduleHandle);
+        if (metadataReader is null)
             return default;
 
         MethodDefinitionHandle methodDefHandle = MetadataTokens.MethodDefinitionHandle((int)(methodToken & 0x00FFFFFF));
-        MethodDefinition methodDef = mdReader.GetMethodDefinition(methodDefHandle);
-        BlobReader blobReader = mdReader.GetBlobReader(methodDef.Signature);
+        MethodDefinition methodDef = metadataReader.GetMethodDefinition(methodDefHandle);
+        BlobReader blobReader = metadataReader.GetBlobReader(methodDef.Signature);
         return blobReader.ReadBytes(blobReader.Length);
     }
 

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/GC/GcSignatureTypeProvider.cs

@@ -23,11 +23,12 @@ internal enum GcTypeKind
 
 /// <summary>
 /// Classifies signature types for GC scanning purposes.
-/// Implements <see cref="ISignatureTypeProvider{TType, TGenericContext}"/> for use
-/// with SRM's <see cref="SignatureDecoder{TType, TGenericContext}"/>.
+/// Implements <see cref="IRuntimeSignatureTypeProvider{TType, TGenericContext}"/> which
+/// is a superset of SRM's <see cref="ISignatureTypeProvider{TType, TGenericContext}"/>,
+/// adding support for <c>ELEMENT_TYPE_INTERNAL</c>.
 /// </summary>
 internal sealed class GcSignatureTypeProvider
-    : ISignatureTypeProvider<GcTypeKind, object?>
+    : IRuntimeSignatureTypeProvider<GcTypeKind, object?>
 {
     public static readonly GcSignatureTypeProvider Instance = new();
 
@@ -60,5 +61,41 @@ public GcTypeKind GetGenericInstantiation(GcTypeKind genericType, ImmutableArray
     public GcTypeKind GetGenericTypeParameter(object? genericContext, int index) => GcTypeKind.Ref;
     public GcTypeKind GetFunctionPointerType(MethodSignature<GcTypeKind> signature) => GcTypeKind.None;
     public GcTypeKind GetModifiedType(GcTypeKind modifier, GcTypeKind unmodifiedType, bool isRequired) => unmodifiedType;
+    public GcTypeKind GetInternalModifiedType(Target target, TargetPointer typeHandlePointer, GcTypeKind unmodifiedType, bool isRequired) => unmodifiedType;
     public GcTypeKind GetPinnedType(GcTypeKind elementType) => elementType;
+
+    public GcTypeKind GetInternalType(Target target, TargetPointer typeHandlePointer)
+    {
+        if (typeHandlePointer == TargetPointer.Null)
+            return GcTypeKind.None;
+
+        try
+        {
+            IRuntimeTypeSystem rts = target.Contracts.RuntimeTypeSystem;
+            TypeHandle th = rts.GetTypeHandle(typeHandlePointer);
+            CorElementType corType = rts.GetSignatureCorElementType(th);
+
+            return corType switch
+            {
+                CorElementType.Void or CorElementType.Boolean or CorElementType.Char
+                    or CorElementType.I1 or CorElementType.U1
+                    or CorElementType.I2 or CorElementType.U2
+                    or CorElementType.I4 or CorElementType.U4
+                    or CorElementType.I8 or CorElementType.U8
+                    or CorElementType.R4 or CorElementType.R8
+                    or CorElementType.I or CorElementType.U
+                    or CorElementType.FnPtr or CorElementType.Ptr
+                    => GcTypeKind.None,
+
+                CorElementType.Byref => GcTypeKind.Interior,
+                CorElementType.ValueType => GcTypeKind.Other,
+
+                _ => GcTypeKind.Ref,
+            };
+        }
+        catch
+        {
+            return GcTypeKind.Ref;
+        }
+    }
 }