Verify alignment of shared libraries

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

@@ -107,6 +107,8 @@ public class BuildApk : AndroidTask
 
 		public string ZipFlushSizeLimit { get; set; }
 
+		public int ZipAlignmentPages { get; set; } = AndroidZipAlign.DefaultZipAlignment64Bit;
+
 		[Required]
 		public string ProjectFullPath { get; set; }
 
@@ -683,14 +685,15 @@ sealed class LibInfo
 			public string Link;
 			public string Abi;
 			public string ArchiveFileName;
+			public ITaskItem Item;
 		}
 
 		CompressionMethod GetCompressionMethod (string fileName)
 		{
 			return uncompressedFileExtensions.Contains (Path.GetExtension (fileName)) ? UncompressedMethod : CompressionMethod.Default;
 		}
 
-		void AddNativeLibraryToArchive (ZipArchiveEx apk, string abi, string filesystemPath, string inArchiveFileName)
+		void AddNativeLibraryToArchive (ZipArchiveEx apk, string abi, string filesystemPath, string inArchiveFileName, ITaskItem taskItem)
 		{
 			string archivePath = MakeArchiveLibPath (abi, inArchiveFileName);
 			existingEntries.Remove (archivePath);
@@ -700,6 +703,7 @@ void AddNativeLibraryToArchive (ZipArchiveEx apk, string abi, string filesystemP
 				return;
 			}
 			Log.LogDebugMessage ($"Adding native library: {filesystemPath} (APK path: {archivePath})");
+			ELFHelper.AssertValidLibraryAlignment (Log, ZipAlignmentPages, filesystemPath, taskItem);
 			apk.AddEntryAndFlush (archivePath, File.OpenRead (filesystemPath), compressionMethod);
 		}
 
@@ -709,7 +713,7 @@ void AddRuntimeLibraries (ZipArchiveEx apk, string [] supportedAbis)
 				foreach (ITaskItem item in ApplicationSharedLibraries) {
 					if (String.Compare (abi, item.GetMetadata ("abi"), StringComparison.Ordinal) != 0)
 						continue;
-					AddNativeLibraryToArchive (apk, abi, item.ItemSpec, Path.GetFileName (item.ItemSpec));
+					AddNativeLibraryToArchive (apk, abi, item.ItemSpec, Path.GetFileName (item.ItemSpec), item);
 				}
 			}
 		}
@@ -762,7 +766,8 @@ private void AddNativeLibraries (ArchiveFileList files, string [] supportedAbis)
 				Path = v.ItemSpec,
 				Link = v.GetMetadata ("Link"),
 				Abi = GetNativeLibraryAbi (v),
-				ArchiveFileName = GetArchiveFileName (v)
+				ArchiveFileName = GetArchiveFileName (v),
+				Item = v,
 			});
 
 			AddNativeLibraries (files, supportedAbis, frameworkLibs);
@@ -773,7 +778,8 @@ private void AddNativeLibraries (ArchiveFileList files, string [] supportedAbis)
 						Path = v.ItemSpec,
 						Link = v.GetMetadata ("Link"),
 						Abi = GetNativeLibraryAbi (v),
-						ArchiveFileName = GetArchiveFileName (v)
+						ArchiveFileName = GetArchiveFileName (v),
+						Item = v,
 					}
 				);
 
@@ -854,8 +860,9 @@ void AddNativeLibraries (ArchiveFileList files, string [] supportedAbis, System.
 						string.Join (", ", libs.Where (lib => lib.Abi == null).Select (lib => lib.Path)));
 			libs = libs.Where (lib => lib.Abi != null);
 			libs = libs.Where (lib => supportedAbis.Contains (lib.Abi));
-			foreach (var info in libs)
-				AddNativeLibrary (files, info.Path, info.Abi, info.ArchiveFileName);
+			foreach (var info in libs) {
+				AddNativeLibrary (files, info.Path, info.Abi, info.ArchiveFileName, info.Item);
+			}
 		}
 
 		private void AddAdditionalNativeLibraries (ArchiveFileList files, string [] supportedAbis)
@@ -868,12 +875,13 @@ private void AddAdditionalNativeLibraries (ArchiveFileList files, string [] supp
 					Path = l.ItemSpec,
 					Abi = AndroidRidAbiHelper.GetNativeLibraryAbi (l),
 					ArchiveFileName = l.GetMetadata ("ArchiveFileName"),
+					Item = l,
 				});
 
 			AddNativeLibraries (files, supportedAbis, libs);
 		}
 
-		void AddNativeLibrary (ArchiveFileList files, string path, string abi, string archiveFileName)
+		void AddNativeLibrary (ArchiveFileList files, string path, string abi, string archiveFileName, ITaskItem? taskItem = null)
 		{
 			string fileName = string.IsNullOrEmpty (archiveFileName) ? Path.GetFileName (path) : archiveFileName;
 			var item = (filePath: path, archivePath: MakeArchiveLibPath (abi, fileName));
@@ -882,6 +890,7 @@ void AddNativeLibrary (ArchiveFileList files, string path, string abi, string ar
 				return;
 			}
 
+			ELFHelper.AssertValidLibraryAlignment (Log, ZipAlignmentPages, path, taskItem);
 			if (!ELFHelper.IsEmptyAOTLibrary (Log, item.filePath)) {
 				files.Add (item);
 			} else {

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

@@ -1,11 +1,14 @@
 using System;
 using System.Collections.Concurrent;
 using System.IO;
+using System.Text;
 
 using ELFSharp;
 using ELFSharp.ELF;
 using ELFSharp.ELF.Sections;
+using ELFSharp.ELF.Segments;
 using Microsoft.Android.Build.Tasks;
+using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
 
 using ELFSymbolType = global::ELFSharp.ELF.Sections.SymbolType;
@@ -15,6 +18,85 @@ namespace Xamarin.Android.Tasks
 {
 	static class ELFHelper
 	{
+		public static void AssertValidLibraryAlignment (TaskLoggingHelper log, int alignmentInPages, string path, ITaskItem? item)
+		{
+			if (String.IsNullOrEmpty (path) || !File.Exists (path)) {
+				return;
+			}
+
+			log.LogDebugMessage ($"Checking alignment to {alignmentInPages}k page boundary in shared library {path}");
+			try {
+				AssertValidLibraryAlignment (log, MonoAndroidHelper.ZipAlignmentToPageSize (alignmentInPages), path, ELFReader.Load (path), item);
+			} catch (Exception ex) {
+				log.LogWarning ($"Attempt to check whether '{path}' is a correctly aligned ELF file failed with exception, ignoring alignment check for the file.");
+				log.LogWarningFromException (ex, showStackTrace: true);
+			}
+		}
+
+		static void AssertValidLibraryAlignment (TaskLoggingHelper log, uint pageSize, string path, IELF elf, ITaskItem? item)
+		{
+			if (elf.Class == Class.Bit32 || elf.Class == Class.NotELF) {
+				log.LogDebugMessage ($"  Not a 64-bit ELF image.  Ignored.");
+				return;
+			}
+
+			var elf64 = elf as ELF<ulong>;
+			if (elf64 == null) {
+				throw new InvalidOperationException ($"Internal error: {elf} is not ELF<ulong>");
+			}
+
+			// We need to find all segments of Load type and make sure their alignment is as expected.
+			foreach (ISegment segment in elf64.Segments) {
+				if (segment.Type != SegmentType.Load) {
+					continue;
+				}
+
+				var segment64 = segment as Segment<ulong>;
+				if (segment64 == null) {
+					throw new InvalidOperationException ($"Internal error: {segment} is not Segment<ulong>");
+				}
+
+				// TODO: what happens if the library is aligned at, say, 64k while 16k is required? Should we erorr out?
+				//       We will need more info about that, have to wait till Google formally announce the requirement.
+				//       At this moment the script https://developer.android.com/guide/practices/page-sizes#test they
+				//       provide suggests it's a strict requirement, so we test for equality below.
+				if (segment64.Alignment == pageSize) {
+					continue;
+				}
+				log.LogDebugMessage ($"    expected segment alignment of 0x{pageSize:x}, found 0x{segment64.Alignment:x}");
+
+				// TODO: turn into a coded warning and, eventually, error. Need better wording.
+				//       Until dotnet runtime produces properly aligned libraries, this should be a plain message as a warning
+				//       would break all the tests that require no warnings to be produced during build.
+				log.LogMessage ($"Native {elf64.Machine} shared library '{Path.GetFileName (path)}', from NuGet package {GetNugetPackageInfo ()} isn't properly aligned.");
+				break;
+			}
+
+			string GetNugetPackageInfo ()
+			{
+				const string Unknown = "<unknown>";
+
+				if (item == null) {
+					return Unknown;
+				}
+
+				var sb = new StringBuilder ();
+				string? metaValue = item.GetMetadata ("NuGetPackageId");
+				if (String.IsNullOrEmpty (metaValue)) {
+					return Unknown;
+				}
+
+				sb.Append (metaValue);
+				metaValue = item.GetMetadata ("NuGetPackageVersion");
+				if (!String.IsNullOrEmpty (metaValue)) {
+					sb.Append (" version ");
+					sb.Append (metaValue);
+				}
+
+				return sb.ToString ();
+			}
+		}
+
 		public static bool IsEmptyAOTLibrary (TaskLoggingHelper log, string path)
 		{
 			if (String.IsNullOrEmpty (path) || !File.Exists (path)) {

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -2092,6 +2092,7 @@ because xbuild doesn't support framework reference assemblies.
     IncludeFiles="@(AndroidPackagingOptionsInclude)"
     ZipFlushFilesLimit="$(_ZipFlushFilesLimit)"
     ZipFlushSizeLimit="$(_ZipFlushSizeLimit)"
+    ZipAlignmentPages="$(AndroidZipAlignment)"
     UseAssemblyStore="$(AndroidUseAssemblyStore)">
     <Output TaskParameter="OutputFiles" ItemName="ApkFiles" />
   </BuildApk>
@@ -2129,6 +2130,7 @@ because xbuild doesn't support framework reference assemblies.
       IncludeFiles="@(AndroidPackagingOptionsInclude)"
       ZipFlushFilesLimit="$(_ZipFlushFilesLimit)"
       ZipFlushSizeLimit="$(_ZipFlushSizeLimit)"
+      ZipAlignmentPages="$(AndroidZipAlignment)"
       UseAssemblyStore="$(AndroidUseAssemblyStore)">
     <Output TaskParameter="OutputFiles" ItemName="BaseZipFile" />
   </BuildBaseAppBundle>