Adding GetJitHelperFunctionName cDAC API

[rcj1]

• Adding AuxiliarySymbols cDAC contract with TryGetAuxiliarySymbolName API
• Looks up given IP in the set of code addresses that are patched at runtime (currently JIT write barriers); if match is found, return the human-friendly name
• Used in GetJitHelperFunctionName API to return a human-readable string for these during disasm
• Behavior change: Unmanaged symbols are resolved in fallback paths if present: https://github.com/dotnet/diagnostics/blob/3d151d818166737df8a248d1f7a14f958012ebd5/src/SOS/Strike/disasmX86.cpp#L436. However, we will not see human-readable names for other unmanaged JIT helpers if unmanaged symbols are not present. We had discussed this and decided it was fine.

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[Copilot]

Pull request overview

Adds a new cDAC contract (AuxiliarySymbols) to resolve names for dynamically-located JIT helper functions (notably write barriers) and wires it into the legacy SOS DAC GetJitHelperFunctionName API.

Changes:

• CoreCLR: export a global table/count of “interesting” JIT helper addresses + names and register write-barrier helpers into it.
• DataContractReader: introduce the IAuxiliarySymbols contract + JitHelperInfo data type and register the factory in the contract registry.
• Tests/docs: add unit tests for the new contract and a design doc for the contract.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/native/managed/cdac/tests/AuxiliarySymbolsTests.cs	New unit tests covering basic address→name resolution for the contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader/CachingContractRegistry.cs	Registers AuxiliarySymbolsFactory so the contract can be resolved from targets.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs	Routes GetJitHelperFunctionName through the new contract and writes UTF-8 to the output buffer.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/OutputBufferHelpers.cs	Adds a helper to copy UTF-8 strings into SOS DAC output buffers.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ISOSDacInterface.cs	Updates the managed signature for GetJitHelperFunctionName.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/JitHelperInfo.cs	New data reader for JitHelperInfo entries in the exported helper table.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/AuxiliarySymbols_1.cs	Contract implementation that scans the exported helper table for a matching code pointer.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/AuxiliarySymbolsFactory.cs	Factory that instantiates the v1 contract implementation.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Constants.cs	Adds global names for the helper table pointer and count.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/DataType.cs	Adds DataType.JitHelperInfo.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IAuxiliarySymbols.cs	New public contract interface and default “throws” implementation struct.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/ContractRegistry.cs	Exposes AuxiliarySymbols from the registry.
src/coreclr/vm/threads.cpp	Records dynamically-copied write-barrier addresses and their names into the new “interesting helpers” table.
src/coreclr/vm/jitinterface.h	Declares the new helper table/count and SetInterestingJitHelperFunction.
src/coreclr/vm/jitinterface.cpp	Provides DAC-accessible storage for the helper table/count under DACCESS_COMPILE.
src/coreclr/vm/jithelpers.cpp	Defines and populates the helper table/count and implements SetInterestingJitHelperFunction.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Adds the JitHelperInfo type + globals and declares the AuxiliarySymbols contract.
src/coreclr/inc/dacvars.h	Adds DAC vars for the exported helper table/count.
docs/design/datacontracts/AuxiliarySymbols.md	New design doc describing the contract, descriptors, globals, and algorithm.

[max-charlamb]

cDAC code looks good to me, do we have any testing that the helper names work end to end?

[rcj1]

cDAC code looks good to me, do we have any testing that the helper names work end to end?

There are unit tests, and I have tested locally in windbg.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated 4 comments.

[noahfalk]

This looks good to me assuming we complete the brittle-DAC side you were already following up on.

[Copilot]

Pull request overview

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