Implement ISOSDacInterface12::GetGlobalAllocationContext in cDAC SOSDacImpl

[Copilot]

Description

Implements GetGlobalAllocationContext in the cDAC SOSDacImpl, matching the native ClrDataAccess::GetGlobalAllocationContext in request.cpp. The implementation is routed through the GC contract layer. Adds a dump test using the GCRoots debuggee.

Changes

• VM data descriptor (datadescriptor.inc): Expose g_global_alloc_context as CDAC_GLOBAL_POINTER(GlobalAllocContext, ...)
• Constants.cs: Add GlobalAllocContext global name constant
• IGC.cs: Add GetGlobalAllocationContext(out TargetPointer allocPtr, out TargetPointer allocLimit) to the IGC contract interface
• GC_1.cs: Implement GetGlobalAllocationContext using EEAllocContext/GCAllocContext Data types via ProcessedData.GetOrAdd
• SOSDacImpl.cs: Replace legacy-only delegation with cDAC implementation that calls _target.Contracts.GC.GetGlobalAllocationContext(), using ArgumentException for null parameter validation inside the try block and #if DEBUG legacy comparison with default-initialized locals
• GC.md: Document the EEAllocContext data descriptor type, GlobalAllocContext global variable, new API signature, and pseudocode implementation
• WorkstationGCDumpTests.cs: Add WorkstationGC_GlobalAllocationContextIsReadable test validating the global is readable via the contract layer and allocPtr <= allocLimit

The implementation reads the global pointer through the GC contract, which navigates EEAllocContext → GCAllocContext using the internal Data types, then extracts Pointer and Limit — mirroring how the native DAC dereferences ((ee_alloc_context)g_global_alloc_context).m_GCAllocContext.

Fixes #124824

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[max-charlamb]

@copilot, You should update the GC.md contract to add the new datadescriptor. Additionally, this should be accessed through the contract layer.

[Copilot]

@copilot, You should update the GC.md contract to add the new datadescriptor. Additionally, this should be accessed through the contract layer.

Done in e9b1e15. Added GetGlobalAllocationContext to the IGC contract interface, implemented it in GC_1.cs using EEAllocContext/GCAllocContext Data types, updated SOSDacImpl.cs to call through _target.Contracts.GC, documented the new EEAllocContext type descriptor, GlobalAllocContext global, and API in GC.md, and updated the dump test to use the contract layer.

[max-charlamb]

@copilot, address feedback

[max-charlamb]

lgtm

[Copilot]

Pull request overview

This PR implements ISOSDacInterface12::GetGlobalAllocationContext in the cDAC SOSDacImpl, providing access to the global allocation context pointer and limit through the GC contract. The implementation mirrors the native ClrDataAccess::GetGlobalAllocationContext in request.cpp by exposing the g_global_alloc_context global variable and routing calls through the GC contract layer.

Changes:

• Exposes g_global_alloc_context as a global pointer and implements the GC contract method to read it
• Implements cDAC SOSDacImpl method with proper error handling and DEBUG legacy comparison
• Adds dump test to verify the global allocation context is readable with valid pointer invariants

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreclr/vm/datadescriptor/datadescriptor.inc	Exposes g_global_alloc_context as GlobalAllocContext global pointer
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Constants.cs	Adds GlobalAllocContext constant for the global name
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IGC.cs	Adds GetGlobalAllocationContext method signature to the IGC contract interface
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GC/GC_1.cs	Implements GetGlobalAllocationContext using ProcessedData.GetOrAdd to traverse EEAllocContext → GCAllocContext
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs	Replaces legacy delegation with cDAC implementation including parameter validation, error handling, and DEBUG comparison
docs/design/datacontracts/GC.md	Documents the EEAllocContext data type, GlobalAllocContext global, API signature, and implementation pseudocode
src/native/managed/cdac/tests/DumpTests/WorkstationGCDumpTests.cs	Adds test validating global allocation context readability and pointer invariant (allocPtr <= allocLimit)

Comments suppressed due to low confidence (1)

src/native/managed/cdac/tests/DumpTests/WorkstationGCDumpTests.cs:92

• The test is missing the [SkipOnVersion("net10.0", "GC contract is not available in .NET 10 dumps")] attribute that all other GC contract tests in this file have. This attribute should be added to ensure the test is skipped on .NET 10 dumps where the GC contract is not available, maintaining consistency with the other tests in this file.

    [ConditionalTheory]
    [MemberData(nameof(TestConfigurations))]

[Copilot]

@copilot, You should update the GC.md contract to add the new datadescriptor. Additionally, this should be accessed through the contract layer.

This was already addressed in e9b1e15 — GC.md was updated with the EEAllocContext data descriptor and all access goes through the contract layer via IGC.GetGlobalAllocationContext.