[cDAC] Implement GetArgumentByIndex and GetLocalVariableByIndex on ClrDataFrame

[max-charlamb]

[cDAC] Implement GetArgumentByIndex and GetLocalVariableByIndex on ClrDataFrame

Builds on #125064 (GetContext/GetAppDomain) to add variable inspection support to the managed cDAC.

What this PR does

DebugInfo contract (variable location resolution):

• GetMethodVarInfo on IDebugInfo for resolving native variable locations from JIT debug info
• NativeVarInfo types (internal) with DoVars nibble decoder
• DebugVarInfo/DebugVarLocKind (public stable API in Abstractions)
• Register mapping for x64/x86/ARM64/ARM including REGNUM_AMBIENT_SP
• Documented in DebugInfo.md (Version 2 section with VarLocType constants and encoding format)

SignatureDecoder contract (type resolution):

• DecodeMethodSignature -- decodes full method signature resolving all parameter/return types including generic instantiations (VAR, MVAR, GENERICINST)
• DecodeLocalSignature -- reads IL method body header, finds local signature token, decodes all local variable types
• SignatureTypeProvider updated to resolve class-level generic params (VAR) via MethodDescHandle context
• Documented in SignatureDecoder.md

RuntimeTypeSystem contract:

• IsEnum(TypeHandle) -- detects enum types via GetSignatureCorElementType(ValueType) + InternalCorElementType != ValueType
• GetPrimitiveType(CorElementType) -- returns TypeHandle for a primitive/well-known CorElementType
• Documented in RuntimeTypeSystem.md (API section + Version 1 pseudocode)

ClrDataFrame.GetArgumentByIndex / GetLocalVariableByIndex:

• Parameter name resolution from metadata, this handling for instance methods
• Type resolution via ISignatureDecoder contracts (DecodeMethodSignature/DecodeLocalSignature)
• Variable location resolution via GetMethodVarInfo + local register/stack resolution
• MapCorElementTypeToFlags matches native DAC's GetTypeFieldValueFlags: IS_PRIMITIVE, IS_VALUE_TYPE, IS_REFERENCE, IS_STRING, IS_ARRAY, IS_ENUM, IS_POINTER
• ByRef unwrapping for underlying type flag resolution
• Function pointer types mapped to IntPtr matching native DAC behavior (ELEMENT_TYPE_FNPTR under #ifndef DACCESS_COMPILE -> IntPtr)
• Primitive size adjustment (NativeVarLocations always reports pointer-sized; shrink for actual primitive sizes)
• Legacy verification with AllowCdacSuccess validation mode

ClrDataValue (new, implements IXCLRDataValue):

• GetFlags, GetSize, GetBytes, GetAddress, GetNumLocations, GetLocationByIndex
• Legacy verification on all implemented methods
• ClrDataValueFlag and ClrDataVLocFlag made public for test access

Native DAC fix:

• REGNUM_AMBIENT_SP handling in GetRegOffsInCONTEXT on AMD64 (util.cpp)

Known Gaps (tracked as issues)

• [cDAC] ClrDataFrame.GetContext should use contextFlags to compute required context size #125791 -- ClrDataFrame.GetContext should use contextFlags to compute required context size (currently always returns full platform context)
• [cDAC] GetConstructedType cannot resolve cross-module pointer TypeDescs #125792 -- GetConstructedType cannot resolve cross-module pointer TypeDescs (pointer variables like int* return DEFAULT flags instead of IS_POINTER)

Dump test scenarios

LocalVariables debuggee with 13 frames exercising type coverage from simple to complex:

Frame	Arguments	Locals	Types Tested	Expected Flags
PrimitiveVars	int, double, bool, char, byte, short, long, float	int, double	I4, R8, BOOLEAN, CHAR, U1, I2, I8, R4	IS_PRIMITIVE
NativeIntVars	nint, nuint	nint, nuint	I, U	IS_PRIMITIVE (pointer-sized)
StructVars	TinyStruct(1B), SmallStruct(8B), LargeStruct(32B)	SmallStruct	VALUETYPE	IS_VALUE_TYPE
ReferenceTypeVars	string, class, enum, object, int[]	--	STRING, CLASS, VALUETYPE(enum), OBJECT, SZARRAY	IS_REFERENCE, IS_ENUM
GenericInstAndByRefVars	List<int>, KeyValuePair<int,string>, ref int	List<int>	GENERICINST+CLASS, GENERICINST+VALUETYPE, BYREF	IS_REFERENCE, IS_VALUE_TYPE, IS_PRIMITIVE (unwrapped)
InstanceMethodOnStruct	SmallStruct	--	VALUETYPE (static helper)	IS_VALUE_TYPE
InstanceMethodVars	this (SimpleClass), int	int	CLASS (this), I4	IS_REFERENCE, IS_PRIMITIVE
ClassGenericVars	T (class-level VAR)	T	VAR -> instantiated type	IS_REFERENCE
MethodGenericVars	T1, T2 (method-level MVAR)	T1	MVAR -> instantiated type	IS_PRIMITIVE, IS_REFERENCE
SingleDimArrayVars	int[]	int[]	SZARRAY	IS_REFERENCE
MultiDimArrayVars	int[,]	int[,]	ARRAY	IS_REFERENCE
PointerVars	int*, delegate*<int,int>	--	PTR, FNPTR	IS_POINTER (gap: #125792), IS_PRIMITIVE
Crash	--	--	(triggers dump)	--

IXCLRDataValueDumpTests -- validates GetSize, GetFlags, GetBytes, GetNumLocations, GetLocationByIndex across all frames above.

IXCLRDataFrameDumpTests -- validates GetArgumentByIndex, GetLocalVariableByIndex, GetNumArguments, GetNumLocalVariables, GetContext, GetAppDomain, GetMethodInstance.

Validation

• All dump tests pass (local runtime)
• SOS tests: non-GetContext tests pass; GetContext failures are pre-existing from [cDAC] Implement GetContext and GetAppDomain on ClrDataFrame #125064
• cdb comparison: zero assertion failures between cDAC and legacy DAC

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[Copilot]

Pull request overview

Implements cDAC-backed IXCLRDataFrame.GetArgumentByIndex / GetLocalVariableByIndex and introduces supporting DebugInfo/StackWalk contract APIs plus a new managed IXCLRDataValue implementation, with dump-based integration tests to validate behavior against the legacy DAC.

Changes:

• Extend DebugInfo contract v2 to decode/resolve native variable locations (vars section) and StackWalk contract to expose frame instruction pointers.
• Implement ClrDataFrame.GetArgumentByIndex / GetLocalVariableByIndex using cDAC debug info, and add a new managed ClrDataValue (IXCLRDataValue) for returned argument/local values.
• Add new dump debuggee (LocalVariables) and dump-based integration tests for IXCLRDataFrame, IXCLRDataValue, and IXCLRDataAppDomain.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
src/native/managed/cdac/tests/DumpTests/IXCLRDataValueDumpTests.cs	New dump tests validating IXCLRDataValue returned from arg/local APIs
src/native/managed/cdac/tests/DumpTests/IXCLRDataFrameDumpTests.cs	New dump tests covering IXCLRDataFrame APIs including arg/local retrieval
src/native/managed/cdac/tests/DumpTests/IXCLRDataAppDomainDumpTests.cs	New dump tests for IXCLRDataAppDomain behavior via frame GetAppDomain
src/native/managed/cdac/tests/DumpTests/DumpTestBase.cs	Adds overload to initialize dump tests with per-test debuggee + dump type
src/native/managed/cdac/tests/DumpTests/Debuggees/StackWalk/Program.cs	Adjusts debuggee to ensure locals/args exist for stack inspection
src/native/managed/cdac/tests/DumpTests/Debuggees/LocalVariables/Program.cs	New debuggee producing known args/locals for value inspection
src/native/managed/cdac/tests/DumpTests/Debuggees/LocalVariables/LocalVariables.csproj	New debuggee project enabling full dumps
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/IXCLRData.cs	Updates COM signatures to use DacComNullableByRef for AppDomain methods
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataValue.cs	New managed IXCLRDataValue implementation with legacy cross-validation
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataTask.cs	Updates ClrDataAppDomain construction to include Target
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataFrame.cs	Implements cDAC versions of GetAppDomain, arg/local-by-index, and helper parsing
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataAppDomain.cs	Implements cDAC AppDomain methods (GetName, GetUniqueID, GetFlags)
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/StackWalk_1.cs	Adds GetInstructionPointer for frame IP retrieval
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/Loader_1.cs	Returns "DefaultDomain" when FriendlyName is null
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/DebugInfo/NativeVarInfo.cs	Adds internal var-loc types/struct mirroring runtime encoding
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/DebugInfo/DebugInfo_2.cs	Implements GetMethodVarInfo + GetVariableLocations for v2
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/DebugInfo/DebugInfoHelpers.cs	Adds vars nibble-decoder and var-loc resolution across architectures
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IStackWalk.cs	Extends abstraction with GetInstructionPointer
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IDebugInfo.cs	Adds public stable DebugVarInfo/NativeVarLocation APIs
docs/design/datacontracts/Loader.md	Documents "DefaultDomain" fallback behavior
docs/design/datacontracts/DebugInfo.md	Documents DebugInfo v2 vars decoding + new APIs

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 26 out of 26 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 20 out of 20 changed files in this pull request and generated 5 comments.

[Copilot]

Pull request overview

Copilot reviewed 20 out of 20 changed files in this pull request and generated 3 comments.

[noahfalk]

max-charlamb force-pushed the cdac-dataframe-value-apis branch from 8325e2d to fb9d865

The force push re-writing commit history makes it harder to compare what changed from the last time I reviewed. I'd prefer if we keep the history intact while reviews are happening and then squash at the end.

[Copilot]

Pull request overview

Copilot reviewed 20 out of 20 changed files in this pull request and generated 1 comment.

[max-charlamb]

/ba-g test failures unrelated to cDAC change