[release/6.0-preview7] Fix UMEntryThunkCache::GetUMEntryThunk #55847
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The function was initializing UMThunkMarshInfo allocated from Stub heap without using the ExecutableWriterHolder. That causes a crash when a hosting application calls coreclr_create_delegate. This was discovered in .NET 6 Preview 6 when running a xamarin app that uses a special host. This code path is exercised only by coreclr_create_delegate.
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jkotas
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Jul 16, 2021
janvorli
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Backport of #55834 to release/6.0-preview7
/cc @janvorli
Customer Impact
Customers trying to run applications that use special hosts like xamarin on Apple Silicon or on any platform with W^X enabled experience hard crash during the startup (bus error on Apple Silicon). Standard hosts like dotnet or apphost are not affected.
Testing
Testing with customer provided testing application. With this fix the application runs fine.
Risk
Low, the code path is exercised only from coreclr_create_delegate called from special hosts and without this fix, it always just crashes.
Regression
Yes, it has regressed in preview 6, in preview 5 it worked fine.