@luqunl, looks like a corefx update is needed to match a coreclr change?

System\Runtime\InteropServices\WindowsRuntime\MarshalingHelpers.cs(313,65): error CS1061: 'EventRegistrationTokenTable<NotifyCollectionChangedEventHandler>' does not contain a definition for 'ExtractHandler' and no extension method 'ExtractHandler' accepting a first argument of type 'EventRegistrationTokenTable<NotifyCollectionChangedEventHandler>' could be found (are you missing a using directive or an assembly reference?) [D:\j\workspace\windows-TGrou---74aa877a\src\System.Runtime.WindowsRuntime\src\System.Runtime.WindowsRuntime.csproj]
System\Runtime\InteropServices\WindowsRuntime\MarshalingHelpers.cs(395,57): error CS1061: 'EventRegistrationTokenTable<PropertyChangedEventHandler>' does not contain a definition for 'ExtractHandler' and no extension method 'ExtractHandler' accepting a first argument of type 'EventRegistrationTokenTable<PropertyChangedEventHandler>' could be found (are you missing a using directive or an assembly reference?) [D:\j\workspace\windows-TGrou---74aa877a\src\System.Runtime.WindowsRuntime\src\System.Runtime.WindowsRuntime.csproj]
System\Runtime\InteropServices\WindowsRuntime\MarshalingHelpers.cs(503,42): error CS1061: 'EventRegistrationTokenTable<EventHandler>' does not contain a definition for 'ExtractHandler' and no extension method 'ExtractHandler' accepting a first argument of type 'EventRegistrationTokenTable<EventHandler>' could be found (are you missing a using directive or an assembly reference?) [D:\j\workspace\windows-TGrou---74aa877a\src\System.Runtime.WindowsRuntime\src\System.Runtime.WindowsRuntime.csproj]

@stephentoub, I am working on it.

These testcase failures are likely not related to my change.
https://mc.dot.net/#/user/dotnet-maestro-bot/pr~2Fjenkins~2Fdotnet~2Fcorefx~2Fmaster~2F/test~2Ffunctional~2Fcli~2F/0065a74f91d150e9af649e4d927de27ceca0397d

@AndyAyersMS Microsoft.CSharp.Tests are failing on Unix. dotnet/coreclr#18563 looks like the most likely source of the regression. Could you please take a look?

The failing test case has struct like this:

private struct ImplementingStruct : IInterface
{
}

Couldn't update this pull request: Head commit author 'luqunl' is not 'dotnet-maestro-bot'
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Sure, I'll take a look.

Still working on getting a repro...

Couldn't update this pull request: Head commit author 'luqunl' is not 'dotnet-maestro-bot'
Would have applied 'Update BuildTools, CoreClr, CoreFx, CoreSetup, ProjectNTfs, ProjectNTfsTestILC to preview1-02928-02, preview1-26629-01, preview1-26628-03, preview1-26628-03, beta-26628-00, beta-26628-00, respectively'

Still no luck with a repro ... will keep trying.

• Built both CoreCLR & CoreFX on OSX and swapped in the new jit and ran the CSharp Tests
• Extracted the failing tests into a standalone app and they likewise pass under corerun on OSX
• MC repro tool creation fails for me with assert so no luck trying that that yet
• Am rebuilding my Ubuntu environment now

Couldn't update this pull request: Head commit author 'luqunl' is not 'dotnet-maestro-bot'
Would have applied 'Update BuildTools, CoreClr, CoreFx, CoreSetup, ProjectNTfs, ProjectNTfsTestILC to preview1-02929-01, preview1-26629-01, preview1-26628-03, preview1-26628-03, beta-26628-00, beta-26628-00, respectively'

Looks like I finally have a repro on ubuntu now. Will update when I know more.

Couldn't update this pull request: Head commit author 'luqunl' is not 'dotnet-maestro-bot'
Would have applied 'Update BuildTools, CoreClr, CoreFx, CoreSetup, ProjectNTfs, ProjectNTfsTestILC to preview1-02929-01, preview1-26629-01, preview1-26628-03, preview1-26628-03, beta-26629-00, beta-26629-00, respectively'

Looks like the issue is that a struct with no fields (and hence has nominal size 1 byte) is classified as something that can't be returned in registers by ClassifyEightBytesWithManagedLayout

https://github.com/dotnet/coreclr/blob/1ad9c94ef5e541e9c8ac29606515d6f54e0e445c/src/vm/methodtable.cpp#L2323-L2328

The changes in #18563 introduced a preference for size-based return classification and so now return that struct in a register. So we have a calling convention mismatch. This impacts the CSharp tests as they have a struct with no fields; the codegen diverges in CallSite.Target.

It's probably best to fix this in the jit as it appears there are other cases where the calling convention we use can disagree with a sized-based approach.

Couldn't update this pull request: Head commit author 'luqunl' is not 'dotnet-maestro-bot'
Would have applied 'Update BuildTools, CoreClr, CoreFx, CoreSetup, ProjectNTfs, ProjectNTfsTestILC to preview1-02929-01, preview1-26629-04, preview1-26628-03, preview1-26629-02, beta-26629-00, beta-26629-00, respectively'

@jkotas, Will we start a new PR to include AndyAyersMS coreclr fix?

Right