[cDAC] Implement IsMatchingParentFrame for cDAC

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs

@@ -548,8 +548,31 @@ public int GetCountOfInternalFrames(ulong vmThread, uint* pRetVal)
     public int EnumerateInternalFrames(ulong vmThread, nint fpCallback, nint pUserData)
         => LegacyFallbackHelper.CanFallback() && _legacy is not null ? _legacy.EnumerateInternalFrames(vmThread, fpCallback, pUserData) : HResults.E_NOTIMPL;
 
+    // Match native: ExInfo::IsUnwoundToTargetParentFrame is just an equality check.
     public int IsMatchingParentFrame(ulong fpToCheck, ulong fpParent, Interop.BOOL* pResult)
-        => LegacyFallbackHelper.CanFallback() && _legacy is not null ? _legacy.IsMatchingParentFrame(fpToCheck, fpParent, pResult) : HResults.E_NOTIMPL;
+    {
+        *pResult = Interop.BOOL.FALSE;
+        int hr = HResults.S_OK;
+        try
+        {
+            *pResult = fpToCheck == fpParent ? Interop.BOOL.TRUE : Interop.BOOL.FALSE;
+        }
+        catch (System.Exception ex)
+        {
+            hr = ex.HResult;
+        }
+#if DEBUG
+        if (_legacy is not null)
+        {
+            Interop.BOOL resultLocal;
+            int hrLocal = _legacy.IsMatchingParentFrame(fpToCheck, fpParent, &resultLocal);
+            Debug.ValidateHResult(hr, hrLocal);
+            if (hr == HResults.S_OK)
+                Debug.Assert(*pResult == resultLocal, $"cDAC: {*pResult}, DAC: {resultLocal}");
+        }
+#endif
+        return hr;
+    }
 
     public int GetStackParameterSize(ulong controlPC, uint* pRetVal)
         => LegacyFallbackHelper.CanFallback() && _legacy is not null ? _legacy.GetStackParameterSize(controlPC, pRetVal) : HResults.E_NOTIMPL;

src/native/managed/cdac/tests/DacDbiImplTests.cs

@@ -0,0 +1,54 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Diagnostics.DataContractReader.Legacy;
+using Xunit;
+
+namespace Microsoft.Diagnostics.DataContractReader.Tests;
+
+public class DacDbiImplTests
+{
+    private static DacDbiImpl CreateDacDbi(MockTarget.Architecture arch)
+    {
+        var builder = new TestPlaceholderTarget.Builder(arch);
+        TestPlaceholderTarget target = builder.Build();
+        return new DacDbiImpl(target, legacyObj: null);
+    }
+
+    [Theory]
+    [ClassData(typeof(MockTarget.StdArch))]
+    public unsafe void IsMatchingParentFrame_EqualFramePointers_ReturnsTrue(MockTarget.Architecture arch)
+    {
+        DacDbiImpl dbi = CreateDacDbi(arch);
+
+        ulong[] testValues = [0x1000, 0, ulong.MaxValue, 0x7FFF_FFFF_FFFF_FFFFul];
+        foreach (ulong value in testValues)
+        {
+            Interop.BOOL result;
+            int hr = dbi.IsMatchingParentFrame(value, value, &result);
+            Assert.Equal(System.HResults.S_OK, hr);
+            Assert.Equal(Interop.BOOL.TRUE, result);
+        }
+    }
+
+    [Theory]
+    [ClassData(typeof(MockTarget.StdArch))]
+    public unsafe void IsMatchingParentFrame_DifferentFramePointers_ReturnsFalse(MockTarget.Architecture arch)
+    {
+        DacDbiImpl dbi = CreateDacDbi(arch);
+
+        (ulong fpToCheck, ulong fpParent)[] testCases =
+        [
+            (0x1000, 0x2000),
+            (0, 1),
+            (ulong.MaxValue, 0),
+        ];
+        foreach ((ulong fpToCheck, ulong fpParent) in testCases)
+        {
+            Interop.BOOL result;
+            int hr = dbi.IsMatchingParentFrame(fpToCheck, fpParent, &result);
+            Assert.Equal(System.HResults.S_OK, hr);
+            Assert.Equal(Interop.BOOL.FALSE, result);
+        }
+    }
+}