[NativeAOT] improve build logic, part 2 (#9631)

Context: 8d77130
Context: #9630

We're exploring how to get .NET for Android apps to build and run
using [Native AOT][0].

Default to `$(TrimMode)=Full` for NativeAOT, this enables trimmer
warnings and should be the default mode for NativeAOT.

Ensure the `_PrepareLinking` MSBuild target runs at the appropriate
time.  Failure to do so was causing
`Android.App.Activity.GetOnCreate_Landroid_os_Bundle_Handler()` to be
trimmed away.

Various fixes to avoid `java.lang.UnsatisfiedLinkError` errors:

  * Set `$(LinkerFlavor)=lld` by default to avoid:

        E AndroidRuntime: java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "__start___modules" referenced by
          "/data/app/~~_ggpMC4foLk_jUUycm0CfA==/net.dot.hellonativeaot-fvszIWroqgweLHYgULxVoQ==/split_config.arm64_v8a.apk!/lib/arm64-v8a/libNativeAOT.so"...

  * Include `libc++_shared.so` within the app, as Native AOT output
    requires C++:

        E AndroidRuntime: java.lang.UnsatisfiedLinkError: dlopen failed: library "libc++_shared.so" not found: needed by
          /data/app/~~_W0B9EE3hhajnFvCHyUKSg==/net.dot.hellonativeaot-zlXemqHdkbHaLu60oYPVQQ==/lib/arm64/libNativeAOT.so in namespace clns-6

Emit `JavaPeerStyle.JavaInterop1` java stubs for NativeAOT, as it is
easier to get working in place of `JavaPeerStyle.XAJavaInterop1`.
Specifically, we need to be able to avoid P/Invokes related to
typemaps/etc.  XAJavaInterop1 hits `JNIEnvInit.RegisterJniNatives()`,
which is full of P/Invokes such as `TypeManager.GetClassName()`,
while `JavaInterop1` hits `ManagedPeer.RegisterNativeMembers()` which
goes through `JniRuntime` abstractions, allowing for a P/Invoke-free
code path.

I updated `BuildTest2.NativeAOT()` to assert for these changes where
possible.

[0]: https://learn.microsoft.com/dotnet/core/deploying/native-aot/

Author: jonathanpeppers

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets

@@ -88,7 +88,7 @@
     <AndroidLinkMode Condition=" '$(AndroidLinkMode)' == '' and '$(PublishTrimmed)' == 'true' ">SdkOnly</AndroidLinkMode>
     <AndroidLinkMode Condition=" '$(AndroidLinkMode)' == '' ">None</AndroidLinkMode>
     <!-- For compat with user code not marked trimmable, only trim opt-in by default. -->
-    <TrimMode Condition=" '$(TrimMode)' == '' and '$(AndroidLinkMode)' == 'Full' ">full</TrimMode>
+    <TrimMode Condition=" '$(TrimMode)' == '' and ('$(AndroidLinkMode)' == 'Full' or '$(_AndroidNativeAot)' == 'true') ">full</TrimMode>
 		<TrimMode Condition="'$(TrimMode)' == ''">partial</TrimMode>
     <SuppressTrimAnalysisWarnings Condition=" '$(SuppressTrimAnalysisWarnings)' == '' and ('$(TrimMode)' == 'full' or '$(IsAotCompatible)' == 'true') ">false</SuppressTrimAnalysisWarnings>
     <SuppressTrimAnalysisWarnings Condition=" '$(SuppressTrimAnalysisWarnings)' == '' ">true</SuppressTrimAnalysisWarnings>

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.NativeAOT.targets

@@ -25,15 +25,17 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
     </IlcCompileDependsOn>
   </PropertyGroup>
 
-  <Target Name="_AndroidBeforeIlcCompile" BeforeTargets="SetupProperties">
+  <Target Name="_AndroidBeforeIlcCompile"
+      DependsOnTargets="_PrepareLinking"
+      BeforeTargets="SetupProperties">
     <!-- Example settings from: https://github.com/jonathanpeppers/Android-NativeAOT/blob/ea69d122cdc7de67aa6a5db14b7e560763c63cdd/DotNet/libdotnet.targets -->
     <PropertyGroup>
       <_NdkSysrootAbi>aarch64-linux-android</_NdkSysrootAbi>
       <_NdkClangPrefix>aarch64-linux-android21-</_NdkClangPrefix>
       <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('windows')) ">windows-x86_64</_NdkPrebuiltAbi>
       <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('osx')) ">darwin-x86_64</_NdkPrebuiltAbi>
       <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('linux')) ">linux-x86_64</_NdkPrebuiltAbi>
-      <_NdkSysrootDir>$(_AndroidNdkDirectory)toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/sysroot/usr/lib/$(_NdkSysrootAbi)</_NdkSysrootDir>
+      <_NdkSysrootDir>$(_AndroidNdkDirectory)toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/sysroot/usr/lib/$(_NdkSysrootAbi)/</_NdkSysrootDir>
       <_NdkBinDir>$(_AndroidNdkDirectory)toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/bin/</_NdkBinDir>
       <CppCompilerAndLinker>$(_NdkBinDir)$(_NdkClangPrefix)clang++</CppCompilerAndLinker>
       <CppLinker>$(CppCompilerAndLinker)</CppLinker>
@@ -56,6 +58,8 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
       <_targetOS>linux</_targetOS>
       <!-- HACK: prevents libSystem.Net.Security.Native.a from being added -->
       <_linuxLibcFlavor>bionic</_linuxLibcFlavor>
+      <!-- HACK: prevents: java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "__start___modules" -->
+      <LinkerFlavor Condition=" '$(LinkerFlavor)' == '' ">lld</LinkerFlavor>
     </PropertyGroup>
   </Target>
 
@@ -76,6 +80,8 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
       <IlcReference Include="@(_AndroidILLinkAssemblies)" />
       <!-- Passes linked assemblies to outer MSBuild tasks/targets -->
       <ResolvedFileToPublish Include="@(IlcCompileInput);@(_AndroidILLinkAssemblies)" RuntimeIdentifier="$(_OriginalRuntimeIdentifier)" />
+      <!-- Include libc++ -->
+      <ResolvedFileToPublish Include="$(_NdkSysrootDir)libc++_shared.so" RuntimeIdentifier="$(_OriginalRuntimeIdentifier)" />
     </ItemGroup>
   </Target>
 

src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaStubs.cs

@@ -387,7 +387,9 @@ IList<string> MergeManifest (NativeCodeGenState codeGenState, Dictionary<string,
 			var tdCache = new TypeDefinitionCache ();
 			(List<TypeDefinition> allJavaTypes, List<TypeDefinition> javaTypesForJCW) = ScanForJavaTypes (resolver, tdCache, assemblies, userAssemblies, useMarshalMethods);
 			var jcwContext = new JCWGeneratorContext (arch, resolver, assemblies.Values, javaTypesForJCW, tdCache, useMarshalMethods);
-			var jcwGenerator = new JCWGenerator (Log, jcwContext);
+			var jcwGenerator = new JCWGenerator (Log, jcwContext) {
+				NativeAot = NativeAot,
+			};
 			bool success;
 
 			if (generateJavaCode) {

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest2.cs

@@ -129,6 +129,7 @@ public void NativeAOT ()
 
 			using var b = CreateApkBuilder ();
 			Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
+			b.Output.AssertTargetIsNotSkipped ("_PrepareLinking");
 
 			string [] mono_classes = [
 				"Lmono/MonoRuntimeProvider;",
@@ -138,11 +139,23 @@ public void NativeAOT ()
 			];
 			string [] nativeaot_files = [
 				$"lib/arm64-v8a/lib{proj.ProjectName}.so",
+				"lib/arm64-v8a/libc++_shared.so",
 			];
 
 			var intermediate = Path.Combine (Root, b.ProjectDirectory, proj.IntermediateOutputPath, proj.RuntimeIdentifier);
 			var output = Path.Combine (Root, b.ProjectDirectory, proj.OutputPath, proj.RuntimeIdentifier);
 
+			var linkedMonoAndroidAssembly = Path.Combine (intermediate, "linked", "Mono.Android.dll");
+			FileAssert.Exists (linkedMonoAndroidAssembly);
+			using (var assembly = AssemblyDefinition.ReadAssembly (linkedMonoAndroidAssembly)) {
+				var typeName = "Android.App.Activity";
+				var methodName = "GetOnCreate_Landroid_os_Bundle_Handler";
+				var type = assembly.MainModule.GetType (typeName);
+				Assert.IsNotNull (type, $"{linkedMonoAndroidAssembly} should contain {typeName}");
+				var method = type.Methods.FirstOrDefault (m => m.Name == methodName);
+				Assert.IsNotNull (method, $"{linkedMonoAndroidAssembly} should contain {typeName}.{methodName}");
+			}
+
 			var dexFile = Path.Combine (intermediate, "android", "bin", "classes.dex");
 			FileAssert.Exists (dexFile);
 			foreach (var className in mono_classes) {

src/Xamarin.Android.Build.Tasks/Utilities/JCWGenerator.cs

@@ -44,6 +44,8 @@ class JCWGenerator
 	readonly TaskLoggingHelper log;
 	readonly JCWGeneratorContext context;
 
+	public bool NativeAot { get; set; }
+
 	public MarshalMethodsClassifier? Classifier { get; private set; }
 
 	public JCWGenerator (TaskLoggingHelper log, JCWGeneratorContext context)
@@ -125,7 +127,7 @@ bool GenerateCode (CallableWrapperType generator, TypeDefinition type, string ou
 		bool ok = true;
 		using var writer = MemoryStreamPool.Shared.CreateStreamWriter ();
 		var writer_options = new CallableWrapperWriterOptions {
-			CodeGenerationTarget    = JavaPeerStyle.XAJavaInterop1
+			CodeGenerationTarget    = NativeAot ? JavaPeerStyle.JavaInterop1 : JavaPeerStyle.XAJavaInterop1
 		};
 
 		try {