[cDAC] Add GetApproxTypeHandle DacDbi API by Copilot · Pull Request #128921 · dotnet/runtime

Copilot · 2026-06-02T22:45:40Z

Add this API using a port of the native type-walk logic and a slight tweak to the RuntimeTypeSystem API that determines if something is a reference type.

Co-authored-by: rcj1 <77995559+rcj1@users.noreply.github.com>

dotnet-policy-service · 2026-06-02T22:47:04Z

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…y+metadataToken Co-authored-by: rcj1 <77995559+rcj1@users.noreply.github.com>

Copilot

Pull request overview

This PR adds dump-based coverage for DacDbiImpl.GetApproxTypeHandle by mirroring the existing exact-type-handle dump tests: it enumerates heap objects reachable from GC handles in the ExactTypeHandle debuggee, constructs the flattened DebuggerIPCE_TypeArgData[] tree (a managed port of CordbType::GatherTypeData), round-trips that through GetApproxTypeHandle, and asserts the returned vmTypeHandle matches an independently canonicalized expected MethodTable. To support this, it also adds a managed TypeDataWalk implementation and refactors some type lookup logic into a helper.

Changes:

Add a new dump test suite DacDbiApproxTypeHandleDumpTests implementing the right-side “gather type data” flattening and expected-handle canonicalization.
Implement managed GetApproxTypeHandle support via a new TypeDataWalk port and supporting helper types.
Replace IsObjRef(TypeHandle) usage with a new IsCorElementTypeObjRef(CorElementType) helper across tests, the contract, and documentation.

Show a summary per file

File	Description
src/native/managed/cdac/tests/MethodTableTests.cs	Updates objref classification assertions to use `IsCorElementTypeObjRef(GetInternalCorElementType(...))`.
src/native/managed/cdac/tests/DumpTests/RuntimeTypeSystemDumpTests.cs	Updates dump-based RTS “objref consistency” test to use the new helper.
src/native/managed/cdac/tests/DumpTests/DacDbi/DacDbiObjectDumpTests.cs	Updates reference-type offset logic to use the new helper.
src/native/managed/cdac/tests/DumpTests/DacDbi/DacDbiApproxTypeHandleDumpTests.cs	New dump test covering round-trip behavior for `GetApproxTypeHandle` across reachable handle objects.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/TypeDataWalk.cs	New managed port of the native flattened-type-data walker used by `GetApproxTypeHandle`.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/IDacDbiInterface.cs	Adds `DebuggerIPCE_TypeArgData` / `TypeInfoList` and tightens `GetApproxTypeHandle` signature to a typed pointer.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DbiHelpers.cs	New helper for resolving typeDef/typeRef MethodTables from an assembly+token via loader lookup tables.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs	Implements managed `GetApproxTypeHandle` and switches some ref-type checks to `IsCorElementTypeObjRef`.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs	Replaces `IsObjRef` with `IsCorElementTypeObjRef` implementation used by the contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeTypeSystem.cs	Changes the contract surface by removing `IsObjRef(TypeHandle)` and adding `IsCorElementTypeObjRef(CorElementType)`.
docs/design/datacontracts/RuntimeTypeSystem.md	Updates contract documentation to match the new helper.

Copilot's findings

Files reviewed: 11/11 changed files
Comments generated: 5

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Copilot's findings

Files reviewed: 11/11 changed files
Comments generated: 7

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Copilot's findings

Files reviewed: 11/11 changed files
Comments generated: 4

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot · 2026-06-08T00:22:16Z

@copilot please fix the cDAC dump tests.

Fixed the CdacDumpTests build break. The failure was a set of CS0246/CS0103 errors in DacDbiApproxTypeHandleDumpTests.cs (DumpTestBase, TestConfiguration, TestConfigurations not found). Those types were relocated to the Microsoft.Diagnostics.DataContractReader.TestInfrastructure namespace by the test-harness refactor (#128863) that landed via the merge, and the new test file was missing that using. Added the directive to match the sibling DacDbiExactTypeHandleDumpTests.cs.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Copilot's findings

Files reviewed: 11/11 changed files
Comments generated: 1

Copilot

Copilot's findings

Files reviewed: 11/11 changed files
Comments generated: 2

Copilot

Copilot's findings

Files reviewed: 10/10 changed files
Comments generated: 2

+    // True if the CorElementType represents a GC-collectable object reference.
+    bool IsCorElementTypeObjRef(CorElementType elementType) => throw new NotImplementedException();
    // Returns the address of one of the runtime's well-known singleton MethodTables,
    // or TargetPointer.Null if the runtime has not yet initialized that global.
    TargetPointer GetWellKnownMethodTable(WellKnownMethodTable kind) => throw new NotImplementedException();
-    bool IsObjRef(TypeHandle typeHandle) => throw new NotImplementedException();
    // True if the MethodTable represents a type that contains managed references


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Copilot

Copilot's findings

Files reviewed: 10/10 changed files
Comments generated: 5

+        Assert.True(contract.IsCorElementTypeObjRef(contract.GetInternalCorElementType(contract.GetTypeHandle(objectTypePtr))));
+        Assert.True(contract.IsCorElementTypeObjRef(contract.GetInternalCorElementType(contract.GetTypeHandle(stringTypePtr))));
+        Assert.True(contract.IsCorElementTypeObjRef(contract.GetInternalCorElementType(contract.GetTypeHandle(szArrayTypePtr))));
+        Assert.False(contract.IsCorElementTypeObjRef(contract.GetInternalCorElementType(contract.GetTypeHandle(truePrimitiveTypePtr))));


+///   - Top-level Class / ValueType keeps the typeDef; only its type-args are canonicalized.
+///   - Reference-typed generic args collapse to <c>System.__Canon</c>.
+///   - Value-type args are recursively approximated (with the same rules applied to their args).
+///   - Array / Ptr / Byref: outer shape preserved; the inner type goes through the
+///     type-arg canonicalization rules.
+/// </para>


+            IRuntimeTypeSystem rts = _target.Contracts.RuntimeTypeSystem;
+
+            TargetPointer canonMtPtr = _target.ReadPointer(_target.ReadGlobalPointer(Constants.Globals.CanonMethodTable));
+            TypeHandle canonTh = rts.GetTypeHandle(canonMtPtr);
+


+using System;
+using System.Collections.Immutable;
+using System.Runtime.InteropServices;
+using Microsoft.Diagnostics.DataContractReader.Contracts;


    // True if the MethodTable is the System.Object MethodTable (g_pObjectClass)
    bool IsObject(TypeHandle typeHandle) => throw new NotImplementedException();
    bool IsString(TypeHandle typeHandle) => throw new NotImplementedException();
+    // True if the CorElementType represents a GC-collectable object reference.
+    bool IsCorElementTypeObjRef(CorElementType elementType) => throw new NotImplementedException();
    // Returns the address of one of the runtime's well-known singleton MethodTables,
    // or TargetPointer.Null if the runtime has not yet initialized that global.
    TargetPointer GetWellKnownMethodTable(WellKnownMethodTable kind) => throw new NotImplementedException();
-    bool IsObjRef(TypeHandle typeHandle) => throw new NotImplementedException();
    // True if the MethodTable represents a type that contains managed references


Copilot AI and others added 2 commits June 2, 2026 15:30

Implement DacDbiImpl.GetApproxTypeHandle in cDAC

9e0b5cd

Co-authored-by: rcj1 <77995559+rcj1@users.noreply.github.com>

Add DacDbiApproxTypeHandle dump tests

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Copilot AI assigned Copilot and rcj1 Jun 2, 2026

Copilot AI requested review from Copilot and removed request for Copilot June 2, 2026 22:45

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Fix InstantiationApprox to look up open generic typeDef via vmAssembl…

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Copilot AI requested review from Copilot and removed request for Copilot June 3, 2026 00:35

Copilot AI changed the title ~~Add DacDbi approximate type handle dump tests~~ Add GetApproxTypeHandle dump tests Jun 3, 2026

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Update DacDbiApproxTypeHandleDumpTests.cs

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rcj1 and others added 2 commits June 2, 2026 23:05

Update RuntimeTypeSystem_1.cs

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Copilot finished work on behalf of rcj1 June 8, 2026 00:22

rcj1 changed the title ~~Add GetApproxTypeHandle dump tests~~ [cDAC] Add GetApproxTypeHandle DacDbi API Jun 8, 2026

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[ci-scan] Build break: crosscomp.h CONTEXT_UNWOUND_TO_CALL macro redefinition in runtime-diagnostics #129111

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Comment thread ...d/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeTypeSystem.cs

Merge branch 'main' into copilot/implement-getapproxtypehandle

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Update DacDbiImpl.cs

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Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. dotnet/dnceng#5922

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refactor

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Copilot AI commented Jun 2, 2026 •

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