[NativeAOT] Enable workload-provided linker for NDK-free builds

build-tools/create-packs/Microsoft.Android.Runtime.proj

@@ -108,6 +108,22 @@ projects that use the Microsoft.Android.Runtimes framework in .NET 6+.
       <NativeRuntimeAsset Condition=" Exists('$(NativeRuntimeOutputRootDir)$(_RuntimeFlavorDirName)\$(AndroidRID)\libnaot-android.debug-static-debug.a') " Include="$(NativeRuntimeOutputRootDir)$(_RuntimeFlavorDirName)\$(AndroidRID)\libnaot-android.debug-static-debug.a" />
       <NativeRuntimeAsset Condition=" Exists('$(NativeRuntimeOutputRootDir)$(_RuntimeFlavorDirName)\$(AndroidRID)\libnaot-android.release-static-release.a') " Include="$(NativeRuntimeOutputRootDir)$(_RuntimeFlavorDirName)\$(AndroidRID)\libnaot-android.release-static-release.a" />
       <_AndroidRuntimePackAssemblies Include="$(_MonoAndroidNETOutputRoot)$(AndroidLatestStableApiLevel)\Microsoft.Android.Runtime.NativeAOT.dll" />
+
+      <!-- NativeAOT uses a separate redist directory with system lib stubs and CRT objects
+           at the higher API level required by dotnet/runtime's native libraries (API 24). -->
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)redist-nativeaot\$(AndroidRID)\crtbegin_so.o" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)redist-nativeaot\$(AndroidRID)\crtend_so.o" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)redist-nativeaot\$(AndroidRID)\libc.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)redist-nativeaot\$(AndroidRID)\libdl.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)redist-nativeaot\$(AndroidRID)\liblog.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)redist-nativeaot\$(AndroidRID)\libm.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)redist-nativeaot\$(AndroidRID)\libz.so" />
+
+      <!-- Toolchain libraries (API-level-agnostic, from common redist) -->
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libc++_static.a" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libc++abi.a" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libclang_rt.builtins-$(_ClangArch)-android.a" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libunwind.a" />
     </ItemGroup>
 
     <ItemGroup>

build-tools/xaprepare/xaprepare/Steps/Step_Android_SDK_NDK.cs

@@ -229,17 +229,29 @@ bool CopyRedistributableFiles (Context context)
 				foreach (string file in ClangArchFiles) {
 					CopyFile (abi, clangArchLibPath, file);
 				}
+
+				// NativeAOT only supports 64-bit ABIs and links against dotnet/runtime's
+				// libSystem.Native.a which was compiled targeting a higher API level. Copy a
+				// second set of CRT/system lib stubs from the higher API level sysroot for the
+				// NativeAOT runtime pack.
+				bool is64BitAbi = abi == "arm64-v8a" || abi == "x86_64";
+				if (is64BitAbi) {
+					string nativeAotCrtFilesPath = Path.Combine (abiDir, BuildAndroidPlatforms.NdkMinimumNonMonoAPI);
+					foreach (string file in CRTFiles) {
+						CopyFile (abi, nativeAotCrtFilesPath, file, redistDirName: "redist-nativeaot");
+					}
+				}
 			}
 
 			return true;
 
-			void CopyFile (string abi, string sourceDir, string fileName)
+			void CopyFile (string abi, string sourceDir, string fileName, string? redistDirName = null)
 			{
 				Log.StatusLine ($"  {context.Characters.Bullet} Copying NDK redistributable: ", $"{fileName} ({abi})", tailColor: ConsoleColor.White);
 				string rid = Configurables.Defaults.AbiToRID [abi];
 				string outputDir = Path.Combine (
 					context.Properties.GetRequiredValue (KnownProperties.NativeRuntimeOutputRootDir),
-					context.Properties.GetRequiredValue (KnownProperties.RuntimeRedistDirName),
+					redistDirName ?? context.Properties.GetRequiredValue (KnownProperties.RuntimeRedistDirName),
 					rid
 				);
 

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

@@ -83,7 +83,6 @@ They run in a context of an inner build with a single $(RuntimeIdentifier).
          runs in an inner build and `_RuntimePackLibraryDirectory` items aren't carried over to it.
     -->
     <ProcessRuntimePackLibraryDirectories
-        Condition=" '$(_AndroidRuntime)' != 'NativeAOT' "
         ResolvedFilesToPublish="@(ResolvedFileToPublish)">
       <Output TaskParameter="RuntimePackLibraryDirectories" ItemName="_RuntimePackLibraryDirectory" />
       <Output TaskParameter="NativeLibrariesToRemove" ItemName="_NativeLibraryToRemove" />

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

@@ -144,7 +144,6 @@ _ResolveAssemblies MSBuild target.
          are never taken into consideration in any context.
     -->
     <ProcessRuntimePackLibraryDirectories
-        Condition=" '$(_AndroidRuntime)' != 'NativeAOT' "
         ResolvedFilesToPublish="@(ResolvedFileToPublish)">
       <Output TaskParameter="RuntimePackLibraryDirectories" ItemName="_RuntimePackLibraryDirectory" />
       <Output TaskParameter="NativeLibrariesToRemove" ItemName="_NativeLibraryToRemove" />

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

@@ -307,49 +307,79 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
       Outputs="$(NativeOutputPath)$(NativeBinaryPrefix)$(TargetName).so">
     <PropertyGroup>
       <_AndroidNativeAotSharedLibrary>$(NativeOutputPath)$(NativeBinaryPrefix)$(TargetName).so</_AndroidNativeAotSharedLibrary>
-      <!-- NDK paths for CRT objects and compiler-rt -->
+      <_AndroidUseWorkloadNativeLinker Condition=" '$(_AndroidUseWorkloadNativeLinker)' == '' ">false</_AndroidUseWorkloadNativeLinker>
+    </PropertyGroup>
+
+    <!-- Resolve the runtime pack native directory for workload-provided linker dependencies.
+         _RuntimePackLibraryDirectory is not populated for NativeAOT, so derive the path from
+         the libnaot-android RuntimePackAsset item. -->
+    <ItemGroup Condition=" '$(_AndroidUseWorkloadNativeLinker)' == 'true' ">
+      <_NativeAotRuntimePackAsset Include="@(RuntimePackAsset->WithMetadataValue('Filename', 'libnaot-android.$(Configuration.ToLower())-static-$(Configuration.ToLower())'))" />
+    </ItemGroup>
+    <PropertyGroup Condition=" '$(_AndroidUseWorkloadNativeLinker)' == 'true' ">
+      <_NativeAotRuntimePackNativeDir>@(_NativeAotRuntimePackAsset->'%(RootDir)%(Directory)')</_NativeAotRuntimePackNativeDir>
+      <_NativeAotLinkerBinDir>$(AndroidBinUtilsDirectory)</_NativeAotLinkerBinDir>
+    </PropertyGroup>
+
+    <!-- NDK paths (default, when not using workload linker) -->
+    <PropertyGroup Condition=" '$(_AndroidUseWorkloadNativeLinker)' != 'true' ">
       <_NdkApiSysrootDir>$(_NdkSysrootDir)$(_NDKApiLevel)/</_NdkApiSysrootDir>
       <_NdkClangResourceDir>$(_AndroidNdkDirectory)toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/lib/clang</_NdkClangResourceDir>
+      <_NativeAotLinkerBinDir>$(_NdkBinDir)</_NativeAotLinkerBinDir>
     </PropertyGroup>
 
-    <ItemGroup>
-      <!-- CRT start file -->
-      <_NativeAotCrtStartFiles Include="$(_NdkApiSysrootDir)crtbegin_so.o">
+    <!-- CRT and toolchain items from workload runtime pack -->
+    <ItemGroup Condition=" '$(_AndroidUseWorkloadNativeLinker)' == 'true' ">
+      <_NativeAotCrtStartFiles Include="$(_NativeAotRuntimePackNativeDir)/crtbegin_so.o">
         <Abi>@(_PrivateBuildTargetAbi)</Abi>
       </_NativeAotCrtStartFiles>
+      <_NativeAotCrtEndFiles Include="$(_NativeAotRuntimePackNativeDir)/crtend_so.o">
+        <Abi>@(_PrivateBuildTargetAbi)</Abi>
+      </_NativeAotCrtEndFiles>
+      <_NativeAotLibSearchPaths Include="$(_NativeAotRuntimePackNativeDir)" />
+      <_NativeAotCompilerRtLibs Include="$(_NativeAotRuntimePackNativeDir)/libclang_rt.builtins-$(_NdkAbi)-android.a" />
+      <_NativeAotCompilerRtLibs Include="$(_NativeAotRuntimePackNativeDir)/libunwind.a" />
+    </ItemGroup>
 
-      <!-- CRT end file -->
+    <!-- CRT and toolchain items from NDK -->
+    <ItemGroup Condition=" '$(_AndroidUseWorkloadNativeLinker)' != 'true' ">
+      <_NativeAotCrtStartFiles Include="$(_NdkApiSysrootDir)crtbegin_so.o">
+        <Abi>@(_PrivateBuildTargetAbi)</Abi>
+      </_NativeAotCrtStartFiles>
       <_NativeAotCrtEndFiles Include="$(_NdkApiSysrootDir)crtend_so.o">
         <Abi>@(_PrivateBuildTargetAbi)</Abi>
       </_NativeAotCrtEndFiles>
-
-      <!-- Library search paths (matching what clang provides) -->
       <_NativeAotLibSearchPaths Include="$(_NdkApiSysrootDir)" />
       <_NativeAotLibSearchPaths Include="$(_NdkSysrootDir)" />
+      <_NativeAotCompilerRtLibs Include="$(_NdkClangResourceDir)/**/libclang_rt.builtins-$(_NdkAbi)-android.a" />
+      <_NativeAotCompilerRtLibs Include="$(_NdkClangResourceDir)/**/$(_NdkAbi)/libunwind.a" />
+    </ItemGroup>
 
-      <!-- ILC runtime .a files are already in @(NativeLibrary) from SetupOSSpecificProps -->
-      <!-- Android-added libraries from _AndroidComputeIlcCompileInputs are in @(_NdkLibs) -->
+    <!-- Common items (same regardless of linker source) -->
+    <ItemGroup>
       <_NativeAotLinkLibraries Include="@(NativeLibrary)" />
-      <_NativeAotLinkLibraries Include="@(_NdkLibs)" />
-
-      <!-- Additional .o files (jni_init, environment) -->
       <_NativeAotAdditionalObjects Include="@(_PrivateJniInitFuncsNativeObjectFile)" />
       <_NativeAotAdditionalObjects Include="@(_PrivateEnvironmentNativeObjectFile)" />
-
-      <!-- System libraries (resolved via -L search paths) -->
       <_NativeAotSystemLibraries Include="dl" />
       <_NativeAotSystemLibraries Include="z" />
       <_NativeAotSystemLibraries Include="log" />
       <_NativeAotSystemLibraries Include="m" />
       <_NativeAotSystemLibraries Include="c" />
+    </ItemGroup>
 
-      <!-- Compiler-rt builtins and unwinder (explicit paths from NDK) -->
-      <_NativeAotCompilerRtLibs Include="$(_NdkClangResourceDir)/**/libclang_rt.builtins-$(_NdkAbi)-android.a" />
-      <_NativeAotCompilerRtLibs Include="$(_NdkClangResourceDir)/**/$(_NdkAbi)/libunwind.a" />
+    <!-- When using workload linker, resolve libc++/libnaot from runtime pack dir.
+         When using NDK, @(_NdkLibs) already has the right NDK sysroot paths. -->
+    <ItemGroup Condition=" '$(_AndroidUseWorkloadNativeLinker)' == 'true' ">
+      <_NativeAotLinkLibraries Include="@(RuntimePackAsset->WithMetadataValue('Filename', 'libnaot-android.$(Configuration.ToLower())-static-$(Configuration.ToLower())'))" />
+      <_NativeAotLinkLibraries Include="$(_NativeAotRuntimePackNativeDir)libc++_static.a" />
+      <_NativeAotLinkLibraries Include="$(_NativeAotRuntimePackNativeDir)libc++abi.a" />
+    </ItemGroup>
+    <ItemGroup Condition=" '$(_AndroidUseWorkloadNativeLinker)' != 'true' ">
+      <_NativeAotLinkLibraries Include="@(_NdkLibs)" />
     </ItemGroup>
 
     <LinkNativeAotSharedLibrary
-        AndroidBinUtilsDirectory="$(_NdkBinDir)"
+        AndroidBinUtilsDirectory="$(_NativeAotLinkerBinDir)"
         IntermediateOutputPath="$(NativeIntermediateOutputPath)"
         RuntimePackLibraryDirectories="@(RuntimePackLibraryDirectories)"
         NativeObject="$(NativeObject)"
@@ -376,6 +406,7 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
         <RelativePath>$(NativeBinaryPrefix)$(TargetName).so</RelativePath>
         <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
       </ResolvedFileToPublish>
+
       <FileWrites Include="$(_AndroidNativeAotSharedLibrary)" />
       <FileWrites Include="$(_AndroidNativeAotSharedLibrary)$(NativeSymbolExt)" Condition=" '$(AndroidIncludeDebugSymbols)' != 'true' " />
       <FileWrites Include="$(NativeIntermediateOutputPath)sections.ld" />

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

@@ -131,7 +131,6 @@ bool LinkForAbi (string abi)
 			HashStyleBoth = true,
 			LittleEndian = true,
 			EntryPoint = "0x0",
-			CompressDebugSections = "zlib",
 		};
 
 		if (!ExportsFile.IsNullOrEmpty ()) {

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

@@ -95,6 +95,7 @@ bool IsInSupportedRuntimePack (ITaskItem item)
 		}
 
 		return NuGetPackageId.StartsWith ("Microsoft.Android.Runtime.CoreCLR.", StringComparison.OrdinalIgnoreCase) ||
-		       NuGetPackageId.StartsWith ("Microsoft.Android.Runtime.Mono.", StringComparison.OrdinalIgnoreCase);
+		       NuGetPackageId.StartsWith ("Microsoft.Android.Runtime.Mono.", StringComparison.OrdinalIgnoreCase) ||
+		       NuGetPackageId.StartsWith ("Microsoft.Android.Runtime.NativeAOT.", StringComparison.OrdinalIgnoreCase);
 	}
 }

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

@@ -0,0 +1,54 @@
+using NUnit.Framework;
+using Xamarin.Android.Tasks;
+using Xamarin.ProjectTools;
+
+namespace Xamarin.Android.Build.Tests
+{
+	/// <summary>
+	/// Build tests specific to the NativeAOT runtime.
+	/// </summary>
+	[TestFixture]
+	[Category ("Node-2")]
+	public class NativeAotBuildTests : BaseTest
+	{
+		[Test]
+		public void BuildNativeAot_WithoutNdk_Fails ()
+		{
+			var proj = new XamarinAndroidApplicationProject {
+				IsRelease = true,
+			};
+			proj.SetRuntime (AndroidRuntime.NativeAOT);
+
+			using var builder = CreateApkBuilder ();
+			builder.ThrowOnBuildFailure = false;
+			// Override _AndroidNdkDirectory (the internal resolved path) to simulate no NDK.
+			// Setting AndroidNdkDirectory alone is not sufficient because ResolveSdks has a
+			// fallback chain that discovers NDK from the SDK directory, environment variables,
+			// and other standard locations.  /p: has highest MSBuild precedence and cannot be
+			// overridden by task outputs.
+			Assert.IsFalse (
+				builder.Build (proj, parameters: new [] { "_AndroidNdkDirectory=" }),
+				"Build should have failed without NDK."
+			);
+		}
+
+		[Test]
+		public void BuildNativeAot_WithWorkloadLinker_WithoutNdk ()
+		{
+			var proj = new XamarinAndroidApplicationProject {
+				IsRelease = true,
+			};
+			proj.SetRuntime (AndroidRuntime.NativeAOT);
+
+			using var builder = CreateApkBuilder ();
+			// Use workload-provided linker and sysroot instead of NDK
+			Assert.IsTrue (
+				builder.Build (proj, parameters: new [] {
+					"_AndroidNdkDirectory=",
+					"_AndroidUseWorkloadNativeLinker=true",
+				}),
+				"Build should succeed with workload linker and no NDK."
+			);
+		}
+	}
+}

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/Builder.cs

@@ -104,6 +104,11 @@ public IEnumerable<string> LastBuildOutput {
 		/// </summary>
 		public bool AutomaticNuGetRestore { get; set; } = true;
 
+		/// <summary>
+		/// When true, skip emitting AndroidNdkDirectory into the test response file.
+		/// </summary>
+		public bool SkipNdkDirectory { get; set; } = false;
+
 		/// <summary>
 		/// Checks whether cross-compilers are available for the specified Android ABIs.
 		/// </summary>
@@ -276,7 +281,7 @@ protected bool BuildInternal (string projectOrSolution, string target, string []
 					sw.WriteLine ("/p:AndroidSdkDirectory=\"{0}\"", sdkPath);
 				}
 				string ndkPath = AndroidSdkResolver.GetAndroidNdkPath ();
-				if (Directory.Exists (ndkPath)) {
+				if (!SkipNdkDirectory && Directory.Exists (ndkPath)) {
 					sw.WriteLine ("/p:AndroidNdkDirectory=\"{0}\"", ndkPath);
 				}
 				string jdkPath = AndroidSdkResolver.GetJavaSdkPath ();

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

@@ -68,7 +68,8 @@ public static Config GetConfig (TaskLoggingHelper log, string androidBinUtilsDir
 
 			string stubPath = Path.Combine (packLibDir.ItemSpec, StubFileName);
 			if (!File.Exists (stubPath)) {
-				throw new InvalidOperationException ($"Internal error: archive DSO stub file '{stubPath}' does not exist in runtime pack at {packLibDir}");
+				log.LogDebugMessage ($"Archive DSO stub file '{stubPath}' not found in runtime pack directory, skipping");
+				continue;
 			}
 
 			AndroidTargetArch arch = MonoAndroidHelper.RidToArch (packRID);