iOS: Attempting to JIT compile method '(wrapper dynamic-method) void object:WriteArrayOfintToXml (System.Runtime.Serialization.XmlWriterDelegator,object,System.Runtime.Serialization.XmlObjectSerializerWriteContext,System.Runtime.Serialization.CollectionDataContract)' while running in aot-only mode.

[rolfbjarne]

Description

The following code throws an exception at runtime when running on an iOS device:

var ds = new DataContractSerializer (typeof (IEnumerable<int>));
using (var xw = XmlWriter.Create (System.IO.Stream.Null))
	ds.WriteObject (xw, new int [] { 1, 2, 3 });

Exception:

System.ExecutionEngineException: Attempting to JIT compile method '(wrapper dynamic-method) void object:WriteArrayOfintToXml (System.Runtime.Serialization.XmlWriterDelegator,object,System.Runtime.Serialization.XmlObjectSerializerWriteContext,System.Runtime.Serialization.CollectionDataContract)' while running in aot-only mode. See https://docs.microsoft.com/xamarin/ios/internals/limitations for more information.
    at System.Delegate.CreateDelegate(Type type, Object firstArgument, MethodInfo method, Boolean throwOnBindFailure, Boolean allowClosed)
    at System.Delegate.CreateDelegate(Type type, Object firstArgument, MethodInfo method, Boolean throwOnBindFailure)
    at System.Delegate.CreateDelegate(Type type, Object firstArgument, MethodInfo method)
    at System.Reflection.Emit.DynamicMethod.CreateDelegate(Type delegateType)
    at System.Runtime.Serialization.CodeGenerator.EndMethod()
    at System.Runtime.Serialization.XmlFormatWriterGenerator.CriticalHelper.GenerateCollectionWriter(CollectionDataContract collectionContract)
    at System.Runtime.Serialization.XmlFormatWriterGenerator.GenerateCollectionWriter(CollectionDataContract collectionContract)
    at System.Runtime.Serialization.CollectionDataContract.CreateXmlFormatWriterDelegate()
    at System.Runtime.Serialization.CollectionDataContract.get_XmlFormatWriterDelegate()
    at System.Runtime.Serialization.CollectionDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context)
    at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle)
    at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeAndVerifyType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, Boolean verifyKnownType, RuntimeTypeHandle declaredTypeHandle, Type declaredType)
    at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithXsiTypeAtTopLevel(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle originalDeclaredTypeHandle, Type graphType)
    at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver)
    at System.Runtime.Serialization.DataContractSerializer.InternalWriteObject(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver)
    at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectHandleExceptions(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver)
    at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectHandleExceptions(XmlWriterDelegator writer, Object graph)
    at System.Runtime.Serialization.DataContractSerializer.WriteObject(XmlWriter writer, Object graph)
    at MySingleView.AppDelegate.FinishedLaunching(UIApplication app, NSDictionary options) in /Users/rolf/work/maccore/onedotnet/xamarin-macios/tests/dotnet/MySingleView/AppDelegate.cs:line 45

Repro:

git clone https://github.com/rolfbjarne/xamarin-macios
cd xamarin-macios
git checkout dotnet-attempting-to-jit-compile-method-WriteArrayOfintToXml
./configure --enable-dotnet
make reset
make all -j8
make install -j8
make singleview -C tests/dotnet

Complete output

Configuration

.NET 6.0.100-alpha.1.21060.3

Binlog:
MySingleView.binlog.zip

Regression?

No (new feature)

[steveisok]

@vargaz should this work?

[vargaz]

Not likely, dynamic methods will only work with the interpreter.

[rolfbjarne]

@vargaz should this work?

The test case is C# code that works in current versions of Xamarin.iOS, so one possibility is that it's the BCL that has changed.

[steveisok]

I suspect we may want to hit this code path instead

runtime/src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/XmlFormatWriterGenerator.cs

Lines 109 to 112 in 39e8a6e

	if (DataContractSerializer.Option == SerializationOption.ReflectionOnly)
	{
	return CreateReflectionXmlFormatCollectionWriterDelegate();
	}

Which may mean setting this to be ReflectionOnly for iOS/tvOS/MacCatalyst

runtime/src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/DataContractSerializer.cs

Line 37 in 39e8a6e

private static SerializationOption _option = IsReflectionBackupAllowed() ? SerializationOption.ReflectionAsBackup : SerializationOption.CodeGenOnly;

@danmoseley who would be the best person to help us confirm this is the right approach? For iOS devices, we basically can't generate any IL on the fly.

[rolfbjarne]

Which may mean setting this to be ReflectionOnly for iOS/tvOS/MacCatalyst

Maybe make it depend on RuntimeFeature.IsDynamicCodeSupported?

https://docs.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.runtimefeature.isdynamiccodesupported?view=net-5.0

[MaximLipnin]

It's reproducible against the simulator when executing

1. ./build.sh -os iOSSimulator -arch x64 -c Release -s mono+libs
2. ./dotnet.sh build /t:Test /p:TargetOS=iOSSimulator /p:TargetArchitecture=x64 /p:Configuration=Release /p:RunAOTCompilation=true  /p:EnableAggressiveTrimming=true src/tests/FunctionalTests/iOS/Simulator/AOT/iOS.Simulator.Aot.Test.csproj

and using the code from the issue description as a functional test