Use android-native-tools for NativeAOT linking instead of Android NDK

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

@@ -105,6 +105,20 @@ projects that use the Microsoft.Android.Runtimes framework in .NET 6+.
     </ItemGroup>
 
     <ItemGroup Condition=" '$(AndroidRuntime)' == 'NativeAOT' ">
+      <!-- Include sysroot libraries for NativeAOT linking -->
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libc.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libdl.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\liblog.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libm.so" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\libz.so" />
+      <!-- C++ runtime and compiler builtins for NativeAOT -->
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\crtbegin_so.o" />
+      <NativeRuntimeAsset Include="$(NativeRuntimeOutputRootDir)$(_RuntimeRedistDirName)\$(AndroidRID)\crtend_so.o" />
+      <NativeRuntimeAsset Include="$(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" />
+      <!-- NativeAOT runtime libraries -->
       <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" />

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

@@ -32,8 +32,11 @@ _ResolveAssemblies MSBuild target.
   </PropertyGroup>
 
   <PropertyGroup>
-    <!-- When marshal methods are enabled, AOT needs to run after the GenerateJavaStubs task -->
-    <_RunAotMaybe Condition=" '$(_AndroidUseMarshalMethods)' != 'True' ">_AndroidAot</_RunAotMaybe>
+    <!--
+      When marshal methods are enabled, AOT needs to run after the GenerateJavaStubs task.
+      For NativeAOT, _RunAotMaybe is set in Microsoft.Android.Sdk.NativeAOT.targets.
+    -->
+    <_RunAotMaybe Condition=" '$(_AndroidUseMarshalMethods)' != 'True' and '$(_AndroidRuntime)' != 'NativeAOT' ">_AndroidAot</_RunAotMaybe>
   </PropertyGroup>
 
   <Target Name="_ComputeFilesToPublishForRuntimeIdentifiers"
@@ -123,7 +126,6 @@ _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/Tasks/LinkNativeAotLibrary.cs

@@ -0,0 +1,242 @@
+#nullable enable
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+using Microsoft.Android.Build.Tasks;
+
+namespace Xamarin.Android.Tasks;
+
+/// <summary>
+/// Links NativeAOT-compiled object files into a shared library (.so) for Android.
+/// Uses android-native-tools (our custom LLVM build) instead of the Android NDK.
+/// </summary>
+public class LinkNativeAotLibrary : AndroidTask
+{
+	public override string TaskPrefix => "LNA";
+
+	[Required]
+	public string AndroidBinUtilsDirectory { get; set; } = "";
+
+	[Required]
+	public string IntermediateOutputPath { get; set; } = "";
+
+	/// <summary>
+	/// The main object file produced by ILC ($(NativeObject)).
+	/// </summary>
+	[Required]
+	public string NativeObject { get; set; } = "";
+
+	/// <summary>
+	/// Additional object files (e.g., generated assembler sources).
+	/// </summary>
+	public ITaskItem[] NativeObjectFiles { get; set; } = [];
+
+	/// <summary>
+	/// Static archives from ILC SDK and runtime packs.
+	/// </summary>
+	[Required]
+	public ITaskItem[] NativeArchives { get; set; } = [];
+
+	[Required]
+	public string OutputLibrary { get; set; } = "";
+
+	[Required]
+	public string RuntimeIdentifier { get; set; } = "";
+
+	[Required]
+	public ITaskItem[] RuntimePackLibraryDirectories { get; set; } = [];
+
+	public bool StripDebugSymbols { get; set; } = true;
+	public bool SaveDebugSymbols { get; set; } = true;
+
+	public override bool RunTask ()
+	{
+		string abi = GetAbiFromRuntimeIdentifier (RuntimeIdentifier);
+		string clangArch = GetClangArchFromRuntimeIdentifier (RuntimeIdentifier);
+
+		// Use the full filename as soname (e.g., "libMyApp.so") following ELF/Android conventions
+		string soname = Path.GetFileName (OutputLibrary);
+
+		// Find the sysroot directory from runtime pack library directories
+		string? sysrootDir = FindSysrootDirectory ();
+		if (sysrootDir == null) {
+			Log.LogError ("Could not find sysroot directory containing C++ runtime libraries in runtime pack");
+			return false;
+		}
+
+		var linker = new NativeLinker (Log, abi, soname, AndroidBinUtilsDirectory, IntermediateOutputPath, RuntimePackLibraryDirectories) {
+			StripDebugSymbols = StripDebugSymbols,
+			SaveDebugSymbols = SaveDebugSymbols,
+			AllowUndefinedSymbols = false,
+			UseNdkLibraries = false,
+			TargetsCLR = false, // NativeAOT uses its own runtime, not CoreCLR
+			UseSymbolic = true,
+			IsNativeAOT = true, // Enable NativeAOT-specific linker flags
+		};
+
+		List<ITaskItem> linkItems = OrganizeCommandLineItems (abi, sysrootDir, clangArch);
+		List<ITaskItem> linkStartFiles = GetCrtStartFiles (abi, sysrootDir);
+		List<ITaskItem> linkEndFiles = GetCrtEndFiles (abi, sysrootDir);
+
+		// If required files were missing (errors logged above), don't invoke the linker
+		// with incomplete inputs — it would produce confusing secondary errors.
+		if (Log.HasLoggedErrors) {
+			return false;
+		}
+
+		bool success = linker.Link (
+			CreateItemWithAbi (OutputLibrary, abi),
+			linkItems,
+			linkStartFiles,
+			linkEndFiles,
+			exportDynamicSymbols: null
+		);
+
+		if (!success) {
+			Log.LogError ($"Failed to link NativeAOT library: {OutputLibrary}");
+		}
+
+		return success;
+	}
+
+	string GetAbiFromRuntimeIdentifier (string rid)
+	{
+		return rid switch {
+			"android-arm64" => "arm64-v8a",
+			"android-x64" => "x86_64",
+			_ => throw new NotSupportedException ($"Unsupported RuntimeIdentifier for NativeAOT: {rid}")
+		};
+	}
+
+	string GetClangArchFromRuntimeIdentifier (string rid)
+	{
+		return rid switch {
+			"android-arm64" => "aarch64",
+			"android-x64" => "x86_64",
+			_ => throw new NotSupportedException ($"Unsupported RuntimeIdentifier for NativeAOT: {rid}")
+		};
+	}
+
+	/// <summary>
+	/// Finds the sysroot directory containing C++ runtime libraries.
+	/// </summary>
+	string? FindSysrootDirectory ()
+	{
+		foreach (var dir in RuntimePackLibraryDirectories) {
+			string libcppPath = Path.Combine (dir.ItemSpec, "libc++_static.a");
+			if (File.Exists (libcppPath)) {
+				return dir.ItemSpec;
+			}
+		}
+		return null;
+	}
+
+	/// <summary>
+	/// Get CRT start files (crtbegin_so.o).
+	/// </summary>
+	List<ITaskItem> GetCrtStartFiles (string abi, string sysrootDir)
+	{
+		var items = new List<ITaskItem> ();
+		string crtbegin = Path.Combine (sysrootDir, "crtbegin_so.o");
+		if (File.Exists (crtbegin)) {
+			items.Add (CreateItemWithAbi (crtbegin, abi));
+		} else {
+			Log.LogError ($"Required CRT file 'crtbegin_so.o' not found in {sysrootDir}. The NativeAOT runtime pack may be incomplete.");
+		}
+		return items;
+	}
+
+	/// <summary>
+	/// Get CRT end files (crtend_so.o).
+	/// </summary>
+	List<ITaskItem> GetCrtEndFiles (string abi, string sysrootDir)
+	{
+		var items = new List<ITaskItem> ();
+		string crtend = Path.Combine (sysrootDir, "crtend_so.o");
+		if (File.Exists (crtend)) {
+			items.Add (CreateItemWithAbi (crtend, abi));
+		} else {
+			Log.LogError ($"Required CRT file 'crtend_so.o' not found in {sysrootDir}. The NativeAOT runtime pack may be incomplete.");
+		}
+		return items;
+	}
+
+	/// <summary>
+	/// Organizes link items in the correct order for the native linker.
+	/// Order matters for static linking!
+	/// </summary>
+	List<ITaskItem> OrganizeCommandLineItems (string abi, string sysrootDir, string clangArch)
+	{
+		var items = new List<ITaskItem> ();
+
+		// First: ILC's main object file
+		items.Add (CreateItemWithAbi (NativeObject, abi));
+
+		// Then: additional object files (generated assembler sources)
+		foreach (ITaskItem objFile in NativeObjectFiles) {
+			items.Add (CreateItemWithAbi (objFile.ItemSpec, abi));
+		}
+
+		// Then: static archives from ILC SDK and runtime packs
+		foreach (ITaskItem archive in NativeArchives) {
+			var item = CreateItemWithAbi (archive.ItemSpec, abi);
+			// Check if this archive should be included with --whole-archive
+			string? wholeArchive = archive.GetMetadata (KnownMetadata.NativeLinkWholeArchive);
+			if (!wholeArchive.IsNullOrEmpty () && Boolean.Parse (wholeArchive)) {
+				item.SetMetadata (KnownMetadata.NativeLinkWholeArchive, "true");
+			}
+			items.Add (item);
+		}
+
+		// C++ standard library (required by NativeAOT runtime for std::nothrow, operator new/delete, etc.)
+		string libcppStatic = Path.Combine (sysrootDir, "libc++_static.a");
+		if (File.Exists (libcppStatic)) {
+			items.Add (CreateItemWithAbi (libcppStatic, abi));
+		} else {
+			Log.LogError ($"Required library 'libc++_static.a' not found in {sysrootDir}. The NativeAOT runtime pack may be incomplete.");
+		}
+
+		string libcppabi = Path.Combine (sysrootDir, "libc++abi.a");
+		if (File.Exists (libcppabi)) {
+			items.Add (CreateItemWithAbi (libcppabi, abi));
+		} else {
+			Log.LogError ($"Required library 'libc++abi.a' not found in {sysrootDir}. The NativeAOT runtime pack may be incomplete.");
+		}
+
+		// Unwinding support
+		string libunwind = Path.Combine (sysrootDir, "libunwind.a");
+		if (File.Exists (libunwind)) {
+			items.Add (CreateItemWithAbi (libunwind, abi));
+		} else {
+			Log.LogError ($"Required library 'libunwind.a' not found in {sysrootDir}. The NativeAOT runtime pack may be incomplete.");
+		}
+
+		// Compiler runtime builtins (required for atomic intrinsics and TLS emulation)
+		string libclangBuiltins = Path.Combine (sysrootDir, $"libclang_rt.builtins-{clangArch}-android.a");
+		if (File.Exists (libclangBuiltins)) {
+			items.Add (CreateItemWithAbi (libclangBuiltins, abi));
+		} else {
+			Log.LogError ($"Required library 'libclang_rt.builtins-{clangArch}-android.a' not found in {sysrootDir}. The NativeAOT runtime pack may be incomplete.");
+		}
+
+		// Add required system libraries (linked dynamically)
+		items.Add (NativeLinker.MakeLibraryItem ("log", abi));  // Android logging
+		items.Add (NativeLinker.MakeLibraryItem ("z", abi));    // zlib compression
+		items.Add (NativeLinker.MakeLibraryItem ("m", abi));    // math library
+		items.Add (NativeLinker.MakeLibraryItem ("dl", abi));   // dynamic linking
+		items.Add (NativeLinker.MakeLibraryItem ("c", abi));    // C library (must be last)
+
+		return items;
+	}
+
+	ITaskItem CreateItemWithAbi (string path, string abi)
+	{
+		var item = new TaskItem (path);
+		item.SetMetadata (KnownMetadata.Abi, abi);
+		return item;
+	}
+}

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.ProjectTools/Resources/Base/BuildReleaseArm64SimpleDotNet.NativeAOT.apkdesc

@@ -5,13 +5,13 @@
       "Size": 3124
     },
     "classes.dex": {
-      "Size": 24224
+      "Size": 25320
     },
     "lib/arm64-v8a/libUnnamedProject.so": {
-      "Size": 4968680
+      "Size": 5424528
     },
     "META-INF/BNDLTOOL.RSA": {
-      "Size": 1211
+      "Size": 1213
     },
     "META-INF/BNDLTOOL.SF": {
       "Size": 1211
@@ -44,5 +44,5 @@
       "Size": 1904
     }
   },
-  "PackageSize": 2094050
+  "PackageSize": 2225122
 }

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Resources/Base/BuildReleaseArm64XFormsDotNet.NativeAOT.apkdesc

@@ -5,7 +5,7 @@
       "Size": 6740
     },
     "classes.dex": {
-      "Size": 9136980
+      "Size": 9132020
     },
     "kotlin/annotation/annotation.kotlin_builtins": {
       "Size": 928
@@ -29,7 +29,7 @@
       "Size": 2396
     },
     "lib/arm64-v8a/libUnnamedProject.so": {
-      "Size": 21592848
+      "Size": 22047616
     },
     "META-INF/androidx.activity_activity.version": {
       "Size": 6
@@ -182,7 +182,7 @@
       "Size": 6
     },
     "META-INF/BNDLTOOL.RSA": {
-      "Size": 1223
+      "Size": 1213
     },
     "META-INF/BNDLTOOL.SF": {
       "Size": 89178
@@ -2252,5 +2252,5 @@
       "Size": 812848
     }
   },
-  "PackageSize": 12521545
+  "PackageSize": 12652617
 }

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

@@ -68,6 +68,14 @@ public static Config GetConfig (TaskLoggingHelper log, string androidBinUtilsDir
 
 			string stubPath = Path.Combine (packLibDir.ItemSpec, StubFileName);
 			if (!File.Exists (stubPath)) {
+				// NativeAOT runtime packs don't include the DSO stub because they don't need
+				// DSO wrapping. Skip them gracefully instead of failing the build.
+				string? packageId = packLibDir.GetMetadata ("NuGetPackageId");
+				if (!String.IsNullOrEmpty (packageId) && packageId.StartsWith ("Microsoft.Android.Runtime.NativeAOT.", StringComparison.OrdinalIgnoreCase)) {
+					log.LogDebugMessage ($"Skipping NativeAOT runtime pack directory '{packLibDir.ItemSpec}': no DSO stub needed");
+					continue;
+				}
+
 				throw new InvalidOperationException ($"Internal error: archive DSO stub file '{stubPath}' does not exist in runtime pack at {packLibDir}");
 			}