[cDAC] Stack walk GC reference scanning and bug fixes (1/5) by max-charlamb · Pull Request #127395 · dotnet/runtime

max-charlamb · 2026-04-24T18:35:02Z

Summary

Part 1 of 5 stacked PRs splitting #126408 into reviewable pieces.

What this PR contains

Stack walker fixes (IsFirst preserved for skipped frames, UpdateState refactor)
PromoteCallerStack / PromoteCallerStackUsingGCRefMap for transition frames
GCRefMapDecoder + FindGCRefMap with ReadyToRun import section resolution
SOSDacImpl.GetStackReferences using cDAC contract
GCInfoDecoder.EnumerateLiveSlots goto removal
GcSignatureTypeProvider for GC type classification
Data descriptor additions (TransitionBlock, ExceptionInfo, frame types)
RequiresInstArg, IsAsyncMethod, HasRetBuffArg on IRuntimeTypeSystem

Stack overview

PR	Content	Status
→ This PR	Stack walk fixes + GC scanning	🔄
PR 2	RuntimeSignatureDecoder (ELEMENT_TYPE_INTERNAL)	Pending
PR 3	ArgIterator port from crossgen2	Pending
PR 4	Native stress framework (cdacstress.cpp)	Pending
PR 5	Managed stress tests + CI pipeline	Pending

Testing

1707/1707 unit tests pass ✅
Dump tests (StackWalkDumpTests, StackReferenceDumpTests) validate end-to-end

Note

This PR description was created with AI assistance from Copilot.

Implement GC reference scanning for stub/transition frames and fix stack walker state machine bugs: - PromoteCallerStack/PromoteCallerStackUsingGCRefMap for transition frames - GCRefMap decoder for ReadyToRun import section resolution - FindGCRefMap with FindReadyToRunModule fallback - SOSDacImpl.GetStackReferences using cDAC contract - Fix IsFirst preserved for skipped frames - Fix skipped frame handling moved to UpdateState - GCInfoDecoder goto removal (ReportUntrackedAndSucceed local function) - RequiresInstArg, IsAsyncMethod, HasRetBuffArg on IRuntimeTypeSystem - ExceptionInfo ClauseForCatch fields for catch handler detection - Data descriptor additions for frame types and TransitionBlock layout Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-04-24T18:36:37Z

Tagging subscribers to this area: @steveisok, @tommcdon, @dotnet/dotnet-diag
See info in area-owners.md if you want to be subscribed.

Copilot

Pull request overview

Implements the first slice of cDAC stack-walk GC reference scanning, extending data descriptors/contracts and wiring SOSDacImpl.GetStackReferences to use the cDAC StackWalk contract (including transition-frame root scanning via GCRefMap and signature-based fallback).

Changes:

Add/extend cDAC data descriptors and contract data types for transition frames, ReadyToRun import sections, and exception clause ranges needed for stack GC root enumeration.
Refactor StackWalk filtering/state transitions and implement managed/live-slot + frame-based GC root scanning paths.
Extend contract APIs (ExecutionManager/GCInfo/RuntimeTypeSystem) and update solution/test project structure to include StressTests.

Reviewed changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.ExecutionManager.cs	Updates mock ReadyToRunInfo descriptor layout with import section fields.
src/native/managed/cdac/tests/Microsoft.Diagnostics.DataContractReader.Tests.csproj	Treats StressTests as a separate test project and excludes it from unit-test compilation.
src/native/managed/cdac/cdac.slnx	Adds StressTests project to the cdac solution filter.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs	Implements `GetStackReferences` using cDAC StackWalk contract, with DEBUG cross-check.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/ReadyToRunInfo.cs	Reads/imports R2R import section pointer + count into the contract data.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/TransitionBlock.cs	Exposes descriptor-provided layout offsets used for GCRefMap/arg-reg scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/StubDispatchFrame.cs	Adds GCRefMap + lazy-resolution fields for stub dispatch frame root scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/ExternalMethodFrame.cs	New contract data type for ExternalMethodFrame GCRefMap-based scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/DynamicHelperFrame.cs	New contract data type for DynamicHelperFrame flag-based scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/ExceptionInfo.cs	Adds catch-handler clause range fields for interruptible-offset override logic.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/StackWalk_1.cs	Refactors stack-walk filtering/Next integration and adds GC root enumeration behaviors.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/GC/GcSignatureTypeProvider.cs	Adds signature-type classifier used by signature decoding for GC scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/GC/GCRefMapDecoder.cs	Adds managed decoder for the compact GCRefMap bitstream.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/FrameHandling/FrameIterator.cs	Adds return-address retrieval and frame-type-specific GC root scanning (GCRefMap/MetaSig paths).
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs	Implements `RequiresInstArg` and `IsAsyncMethod` for TransitionFrame argument layout decisions.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/IGCInfoDecoder.cs	Extends decoder surface to expose interruptible ranges.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/GCInfo_1.cs	Plumbs `GetInterruptibleRanges` through the GCInfo contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/GCInfoDecoder.cs	Removes `goto`, fixes untracked-slot reporting behavior, and keeps decoding accessible.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/ExecutionManager/ExecutionManager_2.cs	Exposes `FindReadyToRunModule` in ExecutionManager v2 contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/ExecutionManager/ExecutionManager_1.cs	Exposes `FindReadyToRunModule` in ExecutionManager v1 contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/ExecutionManager/ExecutionManagerCore.cs	Implements R2R module resolution via RangeSection lookup.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/DataType.cs	Adds DataType entries for new frame data types.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeTypeSystem.cs	Adds `RequiresInstArg` and `IsAsyncMethod` to abstractions interface.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IGCInfo.cs	Adds `InterruptibleRange` and `GetInterruptibleRanges` to the public abstraction contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IExecutionManager.cs	Adds `FindReadyToRunModule` to the abstraction contract.
src/coreclr/vm/readytoruninfo.h	Adds cdac_data offsets for import sections in ReadyToRunInfo.
src/coreclr/vm/frames.h	Adds cdac_data for ExternalMethodFrame/DynamicHelperFrame and fields for StubDispatchFrame GCRefMap resolution.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Adds/extends descriptors for new frame fields, transition block offsets, and catch clause ranges.
docs/design/datacontracts/StackWalk.md	Documents new descriptors used by stack walking + GC reference scanning.
docs/design/datacontracts/RuntimeTypeSystem.md	Documents new RuntimeTypeSystem contract methods.
docs/design/datacontracts/GCInfo.md	Documents new GCInfo contract API for interruptible ranges.

jkotas · 2026-04-25T00:43:40Z

+
+    /// <summary>
+    /// Finds the R2R module that contains the given address.
+    /// Used by FindGCRefMap to resolve m_pZapModule when it's null.


Can we do this unconditionally and drop ZapModule from the constract? ZapModule seems to be a nice-to-have cache.

(Also, ZapModule can be renamed to Module or ReadyToRunModule. Zap is a very old codename name for crossgen/ngen that we have almost eradicated from the codebase.)

Copilot

Pull request overview

Copilot reviewed 32 out of 32 changed files in this pull request and generated 4 comments.

- Use ex.HResult instead of E_FAIL in GetStackReferences catch block - Remove ZapModule references from StackWalk.md documentation - Replace magic 0x11 with (byte)SignatureTypeKind.ValueType - Remove StressTests csproj reference from cdac.slnx (PR5 only) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

davidwrighton

In general this looks good, but there are LOTS of details missing their contract documentation.

davidwrighton · 2026-04-28T20:06:40Z

 | `StubDispatchFrame` | `MethodDescPtr` | Pointer to Frame's method desc |
 | `StubDispatchFrame` | `RepresentativeMTPtr` | Pointer to Frame's method table pointer |
 | `StubDispatchFrame` | `RepresentativeSlot` | Frame's method table slot |
+| `StubDispatchFrame` | `GCRefMap` | Cached pointer to GC reference map blob for caller stack promotion |


Where is the description of how the GCRefMap works, and its layout?

davidwrighton · 2026-04-28T20:08:27Z

+    /// Returns TargetPointer.Null if the Frame has no return address (e.g., non-active ICF,
+    /// base Frame types, FuncEvalFrame during exception eval).
+    /// </summary>
+    public TargetPointer GetReturnAddress()


This needs documentation.

Copilot

Pull request overview

Copilot reviewed 31 out of 31 changed files in this pull request and generated 3 comments.

Copilot · 2026-04-28T21:03:59Z


        GC_SPBASE_FIRST = GC_CALLER_SP_REL,
        GC_SPBASE_LAST = GC_FRAMEREG_REL,
    }

-    public readonly record struct InterruptibleRange(uint StartOffset, uint EndOffset);
-
    public readonly record struct GcSlotDesc
    {


InterruptibleRange was moved out of this file, but GcInfoDecoder<TTraits> still references InterruptibleRange (e.g., List<InterruptibleRange>). Since this file is in ...Contracts.GCInfoHelpers and the type now lives in Microsoft.Diagnostics.DataContractReader.Contracts, the simple name won’t resolve without adding a using Microsoft.Diagnostics.DataContractReader.Contracts; (or fully-qualifying the type). As-is, this should fail to compile.

Copilot · 2026-04-28T21:04:00Z

+                        _ => throw new InvalidOperationException($"Unknown stack slot base: {spBase}"),
+                    };
+
+                    TargetPointer addr = new(baseAddr.Value + (ulong)(long)spOffset);


When computing the stack slot address, baseAddr.Value + (ulong)(long)spOffset relies on unsigned wraparound for negative offsets. That can produce incorrect addresses on 32-bit targets (high bits become set) and is generally fragile. Prefer computing with signed arithmetic (e.g., cast baseAddr.Value to long, add spOffset, then cast back to ulong) so negative offsets subtract correctly without wrap issues.

Suggested change

TargetPointer addr = new(baseAddr.Value + (ulong)(long)spOffset);

TargetPointer addr = new((ulong)((long)baseAddr.Value + spOffset));

Copilot · 2026-04-28T21:04:00Z

+            // InlinedCallFrame: returns 0 if inactive, else m_pCallerReturnAddress
+            case FrameType.InlinedCallFrame:
+                Data.InlinedCallFrame icf = target.ProcessedData.GetOrAdd<Data.InlinedCallFrame>(currentFramePointer);
+                return InlinedCallFrameHasActiveCall(icf) ? new TargetPointer(icf.CallerReturnAddress) : TargetPointer.Null;


In GetReturnAddress(), the InlinedCallFrame case wraps an existing TargetPointer in new TargetPointer(icf.CallerReturnAddress). Since CallerReturnAddress is already a TargetPointer, this extra conversion is unnecessary; returning icf.CallerReturnAddress directly would be simpler and avoids implicit conversions.

Suggested change

return InlinedCallFrameHasActiveCall(icf) ? new TargetPointer(icf.CallerReturnAddress) : TargetPointer.Null;

return InlinedCallFrameHasActiveCall(icf) ? icf.CallerReturnAddress : TargetPointer.Null;

jkotas · 2026-04-28T23:03:22Z

 CDAC_TYPE_FIELD(StubDispatchFrame, T_POINTER, MethodDescPtr, cdac_data<FramedMethodFrame>::MethodDescPtr)
 CDAC_TYPE_FIELD(StubDispatchFrame, T_UINT32, RepresentativeSlot, cdac_data<StubDispatchFrame>::RepresentativeSlot)
+CDAC_TYPE_FIELD(StubDispatchFrame, T_POINTER, GCRefMap, cdac_data<StubDispatchFrame>::GCRefMap)
+CDAC_TYPE_FIELD(StubDispatchFrame, T_POINTER, ZapModule, cdac_data<StubDispatchFrame>::ZapModule)


Can we delete ZapModule from the cdac contracts?

I see my comment about this got resolved, but it is still here - is it needed for some reason?

Sorry Claude resolved that. I'm planning to push another iteration. I'll include this and the gcrefmap removal

jkotas · 2026-04-28T23:05:04Z

 CDAC_TYPE_FIELD(StubDispatchFrame, T_POINTER, RepresentativeMTPtr, cdac_data<StubDispatchFrame>::RepresentativeMTPtr)
 CDAC_TYPE_FIELD(StubDispatchFrame, T_POINTER, MethodDescPtr, cdac_data<FramedMethodFrame>::MethodDescPtr)
 CDAC_TYPE_FIELD(StubDispatchFrame, T_UINT32, RepresentativeSlot, cdac_data<StubDispatchFrame>::RepresentativeSlot)
+CDAC_TYPE_FIELD(StubDispatchFrame, T_POINTER, GCRefMap, cdac_data<StubDispatchFrame>::GCRefMap)


GCRefMap field can be deleted too. It is a nice to have cache as well. It should be fine to do the full lookup in cdac.

Copilot AI review requested due to automatic review settings April 24, 2026 18:35

github-actions Bot added the area-Diagnostics-coreclr label Apr 24, 2026

dotnet-policy-service Bot assigned max-charlamb Apr 24, 2026

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max-charlamb marked this pull request as ready for review April 24, 2026 18:44

max-charlamb requested review from noahfalk and rcj1 April 24, 2026 18:44

jkotas reviewed Apr 25, 2026

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max-charlamb force-pushed the cdac-stackrefs-pr1 branch from 7c419ec to 6c234d9 Compare April 27, 2026 20:52

Copilot AI review requested due to automatic review settings April 27, 2026 21:21

max-charlamb force-pushed the cdac-stackrefs-pr1 branch from 6c234d9 to 0ee4452 Compare April 27, 2026 21:21

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max-charlamb requested a review from davidwrighton April 28, 2026 13:07

davidwrighton requested changes Apr 28, 2026

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Max Charlamb added 2 commits April 28, 2026 16:46

add docs for FindReadyToRunModule

3b8bd21

add docs for GCInfo parsing (including InterruptibleRanges

762145c

max-charlamb force-pushed the cdac-stackrefs-pr1 branch from 0ee4452 to d9d8bb7 Compare April 28, 2026 20:49

Copilot AI review requested due to automatic review settings April 28, 2026 20:56

max-charlamb force-pushed the cdac-stackrefs-pr1 branch from d9d8bb7 to 762145c Compare April 28, 2026 20:56

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jkotas reviewed Apr 28, 2026

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	TargetPointer addr = new(baseAddr.Value + (ulong)(long)spOffset);
	TargetPointer addr = new((ulong)((long)baseAddr.Value + spOffset));

	return InlinedCallFrameHasActiveCall(icf) ? new TargetPointer(icf.CallerReturnAddress) : TargetPointer.Null;
	return InlinedCallFrameHasActiveCall(icf) ? icf.CallerReturnAddress : TargetPointer.Null;

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max-charlamb commented Apr 24, 2026

Summary

What this PR contains

Stack overview

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jkotas Apr 25, 2026 •

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