Add breaking change version DAC API (ISOSDacInterface9 interface)

[mikem8361]

GetBreakingChangeVersion(int* version)

Used in SOS to check if any of the runtime data structures it depends on has changed.

Issue: #27309

[ghost]

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[jkotas]

Are you doing any breaking changes together with this? I would love to delete https://github.com/dotnet/runtime/search?q=TlsIdx_ThreadType that I had to keep to avoid breaking SOS.

[noahfalk]

LGTM

[mikem8361]

This is for future breaking changes in the runtime that affect SOS. I’m not planning any in 5.0. As far as TlsIdx_ThreadType are you asking if could add another method on a DAC interface to return the ThreadType for a managed thread?

[noahfalk]

I don't know if @mikem8361 had any breaking changes on deck? My hope would be that we wouldn't take any breaking changes immediately because most of our customers would still be using old versions of SOS that don't have a check for the version number. We don't have great usage telemetry, but we do have NuGet download numbers and likely some windbg metrics to give us a clue how quickly new SOS versions are being adopted.

[mikem8361]

@jkotas, I'm not sure how to write the DAC API to get the ThreadType since it is in thread_local variable (t_ThreadType). Maybe it is simple but I haven't seem another example in existing DAC code.

[ghost]

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[jkotas]

I'm not sure how to write the DAC API to get the ThreadType since it is in thread_local variable

DI has the code to do that (CordbUnmanagedThread::GetEEThreadPtr). It needs NT_TIB* pointer to start from. The DAC API can take this pointer. Or it can take some other form of thread-id and get NT_TIB* from it.