dbgshim: activate cDAC via contract descriptor

[hoyosjs]

When servicing a data-access interface (IXCLRDataProcess / ISOSDacInterface), dbgshim now resolves the target runtime module's DotNetRuntimeContractDescriptor export itself and activates the cDAC through the universal binary's new DbgShimCreateInstanceFromContractDescriptor entry point (dotnet/runtime#131357), passing the descriptor address directly.

This is needed because dbgshim's data targets don't always implement ICLRContractLocator, so the existing CLRDataCreateInstance path can't source the descriptor on them.

Behavior:

• Descriptor not resolvable -> cDAC can't succeed, so it's skipped and we fall through to the legacy DAC.
• Descriptor resolvable but the cDAC binary predates the new export -> falls back to CLRDataCreateInstance on the same binary (temporary while cDAC gets updated in the tools).
• LegacyDacOnly policy and the public dbgshim API are unchanged; this is purely additive.
• On Windows-host targets the descriptor is read via a small PE export-directory walk (TryGetPEExportSymbol) that we already use in runtime; ELF/Mach-O use the existing TryGetSymbol.

[Copilot]

Pull request overview

This PR updates dbgshim’s cDAC activation path to resolve the runtime’s DotNetRuntimeContractDescriptor export directly (including via a Windows-host PE export-directory walk) and, when available, activate cDAC using the universal binary’s new DbgShimCreateInstanceFromContractDescriptor entry point. This improves compatibility with data targets that don’t implement ICLRContractLocator, while preserving the existing fallback behavior to the legacy DAC.

Changes:

• Introduces contract-descriptor resolution in dbgshim and routes cDAC activation through DbgShimCreateInstanceFromContractDescriptor with a fallback to CLRDataCreateInstance.
• Adds a Windows-host helper (TryGetPEExportSymbol) to resolve PE exports via the target data target (for Windows targets).
• Centralizes the contract-descriptor symbol name as CONTRACT_DESCRIPTOR_SYMBOL for reuse.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/SOS/Strike/platform/runtimeimpl.cpp	Switches contract descriptor lookup to use shared CONTRACT_DESCRIPTOR_SYMBOL.
src/shared/debug/inc/runtimeinfo.h	Defines CONTRACT_DESCRIPTOR_SYMBOL constant for cross-component use.
src/shared/debug/inc/dbgutil.h	Declares TryGetPEExportSymbol (Windows-host PE export resolution).
src/shared/debug/dbgutil/dbgutil.cpp	Implements TryGetPEExportSymbol by walking the PE export directory via the target.
src/dbgshim/debugshim.cpp	Adds contract-descriptor resolution + new cDAC activation path using the descriptor-address entry point.

Comments suppressed due to low confidence (1)

src/shared/debug/dbgutil/dbgutil.cpp:462

• The ordinal read from the name-ordinal table is untrusted data. Before using it to index into the export address table, validate it is within NumberOfFunctions; otherwise the code may read from an arbitrary RVA and return an invalid symbol address.

                // If the name matches, we should be able to get the ordinal
                uint16_t ordinalForNamedExport = 0;
                if (FAILED(ReadFromDataTarget(dataTarget, baseAddress + ordinalTableRVA + sizeof(uint16_t) * nameIndex, (BYTE*)&ordinalForNamedExport, sizeof(ordinalForNamedExport))))
                {
                    return false;
                }
                // If the name matches, we should be able to get the export

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