Hide almost all the exported symbols

Author: grendello

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

@@ -90,11 +90,16 @@ void MakeArchiveItem (NativeRuntimeComponents.Archive archive, List<ITaskItem> a
 	{
 		foreach (ITaskItem resolvedArchive in ResolvedNativeArchives) {
 			string fileName = Path.GetFileName (resolvedArchive.ItemSpec);
-			if (String.Compare (fileName, archive.Name, StringComparison.OrdinalIgnoreCase) == 0) {
-				ITaskItem newItem = DoMakeItem ("_ResolvedNativeArchive", resolvedArchive, uniqueAbis);
-				newItem.SetMetadata (KnownMetadata.LinkWholeArchive, archive.WholeArchive.ToString ());
-				archives.Add (newItem);
+			if (String.Compare (fileName, archive.Name, StringComparison.OrdinalIgnoreCase) != 0) {
+				continue;
+			}
+
+			ITaskItem newItem = DoMakeItem ("_ResolvedNativeArchive", resolvedArchive, uniqueAbis);
+			newItem.SetMetadata (KnownMetadata.NativeLinkWholeArchive, archive.WholeArchive.ToString ());
+			if (archive.DontExportSymbols) {
+				newItem.SetMetadata (KnownMetadata.NativeDontExportSymbols, "true");
 			}
+			archives.Add (newItem);
 		}
 	}
 

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

@@ -3,6 +3,7 @@ namespace Xamarin.Android.Tasks;
 static class KnownMetadata
 {
 	public const string Abi = "Abi";
-	public const string LinkWholeArchive = "LinkWholeArchive";
+	public const string NativeLinkWholeArchive = "LinkWholeArchive";
 	public const string RuntimeIdentifier = "RuntimeIdentifier";
+	public const string NativeDontExportSymbols = "DontExportSymbols";
 }

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

@@ -114,31 +114,36 @@ public bool Link (ITaskItem outputLibraryPath, List<ITaskItem> objectFiles, List
 
 		string libBaseName = Path.GetFileNameWithoutExtension (outputLibraryPath.ItemSpec);
 		string respFilePath = Path.Combine (intermediateDir, $"ld.{libBaseName}.{abi}.rsp");
-		using (var sw = new StreamWriter (File.Open (respFilePath, FileMode.Create, FileAccess.Write, FileShare.Read), new UTF8Encoding (false))) {
-			foreach (string arg in standardArgs) {
-				sw.WriteLine (arg);
-			}
+		using var sw = new StreamWriter (File.Open (respFilePath, FileMode.Create, FileAccess.Write, FileShare.Read), new UTF8Encoding (false));
+		foreach (string arg in standardArgs) {
+			sw.WriteLine (arg);
+		}
 
-			foreach (string arg in extraArgs) {
-				sw.WriteLine (arg);
-			}
+		foreach (string arg in extraArgs) {
+			sw.WriteLine (arg);
+		}
 
-			if (StripDebugSymbols && !SaveDebugSymbols) {
-				sw.WriteLine ("-s");
-			}
+		if (StripDebugSymbols && !SaveDebugSymbols) {
+			sw.WriteLine ("-s");
+		}
 
-			WriteFilesToResponseFile (sw, linkStartFiles);
-			WriteFilesToResponseFile (sw, objectFiles);
-			WriteFilesToResponseFile (sw, archives);
+		var excludeExportsLibs = new List<string> ();
+		WriteFilesToResponseFile (sw, linkStartFiles);
+		WriteFilesToResponseFile (sw, objectFiles);
+		WriteFilesToResponseFile (sw, archives);
 
-			foreach (ITaskItem libItem in libraries) {
-				sw.WriteLine ($"-l{libItem.ItemSpec}");
-			}
+		if (excludeExportsLibs.Count > 0) {
+			string libs = String.Join (",", excludeExportsLibs);
+			sw.WriteLine ($"--exclude-libs={libs}");
+		}
 
-			WriteFilesToResponseFile (sw, linkEndFiles);
-			sw.Flush ();
+		foreach (ITaskItem libItem in libraries) {
+			sw.WriteLine ($"-l{libItem.ItemSpec}");
 		}
 
+		WriteFilesToResponseFile (sw, linkEndFiles);
+		sw.Flush ();
+
 		var ldArgs = new List<string> {
 			$"@{respFilePath}",
 			"-o",
@@ -163,6 +168,10 @@ void WriteFilesToResponseFile (StreamWriter sw, List<ITaskItem> files)
 			foreach (ITaskItem file in files) {
 				bool wholeArchive = IncludeWholeArchive (file);
 
+				if (ExcludeFromExports (file)) {
+					excludeExportsLibs.Add (Path.GetFileName (file.ItemSpec));
+				}
+
 				if (wholeArchive) {
 					sw.Write ("--whole-archive ");
 				}
@@ -178,15 +187,18 @@ void WriteFilesToResponseFile (StreamWriter sw, List<ITaskItem> files)
 			}
 		}
 
-		bool IncludeWholeArchive (ITaskItem item)
+		bool IncludeWholeArchive (ITaskItem item) => ParseBooleanMetadata (item, KnownMetadata.NativeLinkWholeArchive);
+		bool ExcludeFromExports (ITaskItem item) => ParseBooleanMetadata (item, KnownMetadata.NativeDontExportSymbols);
+
+		bool ParseBooleanMetadata (ITaskItem item, string metadata)
 		{
-			string? wholeArchive = item.GetMetadata (KnownMetadata.LinkWholeArchive);
-			if (String.IsNullOrEmpty (wholeArchive)) {
+			string? value = item.GetMetadata (metadata);
+			if (String.IsNullOrEmpty (value)) {
 				return false;
 			}
 
 			// Purposefully not calling TryParse, let it throw and let us know if the value isn't a boolean.
-			return Boolean.Parse (wholeArchive);
+			return Boolean.Parse (value);
 		}
 	}
 

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

@@ -12,6 +12,7 @@ internal class Archive
 		public readonly string Name;
 		public bool Include => shouldInclude (this);
 		public readonly bool WholeArchive;
+		public bool DontExportSymbols { get; set; }
 
 		Func<Archive, bool> shouldInclude;
 
@@ -31,6 +32,7 @@ public MonoComponentArchive (string name, string componentName, Func<Archive, bo
 			: base (name, include)
 		{
 			ComponentName = componentName;
+			DontExportSymbols = true;
 		}
 	}
 
@@ -52,7 +54,9 @@ sealed class BclArchive : Archive
 	{
 		public BclArchive (string name, bool wholeArchive = false)
 			: base (name, wholeArchive: wholeArchive)
-		{}
+		{
+			DontExportSymbols = true;
+		}
 	}
 
 	readonly ITaskItem[] monoComponents;
@@ -77,7 +81,9 @@ public NativeRuntimeComponents (ITaskItem[] monoComponents)
 			new MonoComponentArchive ("libmono-component-marshal-ilgen-stub-static.a",       "marshal-ilgen",       IncludeIfMonoComponentAbsent),
 
 			// MonoVM runtime + BCL
-			new Archive ("libmonosgen-2.0.a"),
+			new Archive ("libmonosgen-2.0.a") {
+				DontExportSymbols = true,
+			},
 			new BclArchive ("libSystem.Globalization.Native.a"),
 			new BclArchive ("libSystem.IO.Compression.Native.a"),
 			new BclArchive ("libSystem.Native.a"),