Add support in WASM for calling UnmanagedCallersOnly functions

[AaronRobinsonMSFT]

Fixes #121006

This provides an entry point, similar to P/Invokes thunks, for generated reverse P/Invoke stubs. A commented out example of the generated code was provided.

[dotnet-policy-service]

Tagging subscribers to this area: @mangod9
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull Request Overview

This PR adds support for UnmanagedCallersOnly methods in the WASM interpreter environment. It implements a thunk lookup mechanism for reverse P/Invoke scenarios and refactors some existing code for better organization.

Key changes:

• Implements GetUnmanagedCallersOnlyThunk function to look up thunks for methods with the UnmanagedCallersOnly attribute
• Adds caching infrastructure for reverse thunks using hash-based lookup
• Refactors ExecuteInterpretedMethodFromUnmanaged to consolidate interpreter method execution from unmanaged code
• Enables UnmanagedCallersOnly support in CreateDelegate for WASM by removing the blanket E_NOTIMPL error

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/coreclr/vm/wasm/helpers.cpp	Adds reverse thunk lookup infrastructure and GetUnmanagedCallersOnlyThunk implementation
src/coreclr/vm/wasm/callhelpers.hpp	Updates header guards and adds reverse thunk data structures
src/coreclr/vm/wasm/callhelpers.cpp	Adds reverse thunk map array definition with placeholder example
src/coreclr/vm/wasm/calldescrworkerwasm.cpp	Simplifies to use new ExecuteInterpretedMethodFromUnmanaged function
src/coreclr/vm/prestub.cpp	Refactors and renames function to ExecuteInterpretedMethodFromUnmanaged
src/coreclr/vm/precode_portable.hpp	Adds flags for tracking UnmanagedCallersOnly attribute
src/coreclr/vm/precode_portable.cpp	Implements HasUnmanagedCallersOnlyAttribute method with caching
src/coreclr/vm/method.cpp	Updates TryGetMultiCallableAddrOfCode to handle UnmanagedCallersOnly
src/coreclr/vm/interpexec.h	Adds forward declaration for ExecuteInterpretedMethodFromUnmanaged
src/coreclr/vm/corhost.cpp	Enables UnmanagedCallersOnly for WASM in CreateDelegate
src/coreclr/interpreter/compiler.cpp	Uses aggregate initialization instead of memset
src/coreclr/hosts/corerun/CMakeLists.txt	Conditionalizes WASM_BIGINT flag for browser-only scenarios

[AaronRobinsonMSFT]

Converting this to draft. The approach in this PR doesn't permit linking against exports. I will need to modify it.

[radekdoulik]

I have the reversed generator part nearly ported, current output looks like https://gist.github.com/radekdoulik/049236003eca75bc34fed6ee727d89fc

Take it just as a preview, didn't try to build the output yet. It also shouldn't have zero sized args arrays, etc.

[jkotas]

Thanks

[AaronRobinsonMSFT]

I have the reversed generator part nearly ported, current output looks like https://gist.github.com/radekdoulik/049236003eca75bc34fed6ee727d89fc

Take it just as a preview, didn't try to build the output yet. It also shouldn't have zero sized args arrays, etc.

Thanks @radekdoulik. I had to tweak them a bit, but they were close. See 0bf48e9. Note that the hashing logic doesn't match what is in this PR. That means this will only work for exports and not through ldftn calls using C# function pointers.

@pavelsavara Please checkout the above commit so you can see how to enable this for more.

[radekdoulik]

/ba-g unrelated timeouts

[radekdoulik]

I have the reversed generator part nearly ported, current output looks like https://gist.github.com/radekdoulik/049236003eca75bc34fed6ee727d89fc
Take it just as a preview, didn't try to build the output yet. It also shouldn't have zero sized args arrays, etc.

Thanks @radekdoulik. I had to tweak them a bit, but they were close. See 0bf48e9. Note that the hashing logic doesn't match what is in this PR. That means this will only work for exports and not through ldftn calls using C# function pointers.

That's great, thank you. I will finish the generator changes.

[pavelsavara]

So now, we don't need those anymore

runtime/src/coreclr/vm/corelib.h

Lines 757 to 761 in 6e1e6b1

	DEFINE_CLASS(TIMER_QUEUE, Threading, TimerQueue)
	DEFINE_METHOD(TIMER_QUEUE, TIMER_HANDLER, TimerHandler, SM_RetVoid)
	DEFINE_CLASS(THREAD_POOL, Threading, ThreadPool)
	DEFINE_METHOD(THREAD_POOL, BACKGROUND_JOB_HANDLER, BackgroundJobHandler, SM_RetVoid)

except they are keeping the IL from trimming.

Because #101434