[Mono.Android] Don't use __Internal in our P/Invoke calls (#4757)

Context: #4914
Context: d583b7c

Context: mono/mono#20295 (comment)

Context? mono/mono#17369
Context? mono/mono@d5b6cf3

As a runtime extension, Mono long supported `[DllImport("__Internal")]`
as a synonym for [`dlopen(NULL, 0)`][0].  Unfortunately, this
[did not work on Android][1] -- Bionic would SIGSEGV when the
filename parameter was `NULL` -- and as "fallout" of this change the
`loader_func` that Xamarin.Android registers with mono via
`mono_dl_fallback_register()` would be invoked *instead of*
`dlopen(NULL)` when loading `__Internal`…but *only* on Android.

Use of this feature remains widely used in Xamarin.Android, e.g.
[`java-interop` is mapped to `__Internal`][2], avoiding the need to
build and ship a separate `libjava-interop.so` library.

Unfortunately, as part of .NET 5, MonoVM will be overhauling the
semantics of `[DllImport("__Internal")]`, preventing `loader_func`
from being invoked on Android to resolve `__Internal`.

Consequently, we need to begin moving away from use of `__Internal`.

Begin this process, and remove all P/Invokes to `__Internal` within
`Mono.Android.dll` with P/Invokes to `xa-internal-api` (d583b7c).

[0]: https://linux.die.net/man/3/dlopen
[1]: mono/mono@9b73cd9
[2]: https://github.com/xamarin/xamarin-android/blob/faf1d16692ead1115d34fdf7b84c256c94a321da/src/monodroid/config.xml#L2

Author: grendello

src/Mono.Android/Android.Runtime/AndroidEnvironment.cs

@@ -280,7 +280,7 @@ static string GetDefaultTimeZone ()
 			}
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		static extern IntPtr _monodroid_timezone_get_default_id ();
 
 		// This is invoked by
@@ -301,7 +301,7 @@ static string GetDefaultTimeZone ()
 		// These are invoked by
 		// System.dll!System.AndroidPlatform.getifaddrs
 		// DO NOT REMOVE
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		static extern int _monodroid_getifaddrs (out IntPtr ifap);
 
 		static int GetInterfaceAddresses (out IntPtr ifap)
@@ -312,15 +312,15 @@ static int GetInterfaceAddresses (out IntPtr ifap)
 		// These are invoked by
 		// System.dll!System.AndroidPlatform.freeifaddrs
 		// DO NOT REMOVE
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
                 static extern void _monodroid_freeifaddrs (IntPtr ifap);
 
 		static void FreeInterfaceAddresses (IntPtr ifap)
 		{
 			_monodroid_freeifaddrs (ifap);
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		static extern void _monodroid_detect_cpu_and_architecture (ref ushort built_for_cpu, ref ushort running_on_cpu, ref byte is64bit);
 
 		static void DetectCPUAndArchitecture (out ushort builtForCPU, out ushort runningOnCPU, out bool is64bit)

src/Mono.Android/Android.Runtime/AndroidRuntime.cs

@@ -16,6 +16,8 @@ namespace Android.Runtime {
 
 	class AndroidRuntime : JniRuntime {
 
+		public const string InternalDllName = "xa-internal-api";
+
 		internal AndroidRuntime (IntPtr jnienv,
 				IntPtr vm,
 				bool allocNewObjectSupported,
@@ -100,7 +102,7 @@ public AndroidRuntimeOptions (IntPtr jnienv,
 
 	class AndroidObjectReferenceManager : JniRuntime.JniObjectReferenceManager {
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		static extern int _monodroid_gref_get ();
 
 		public override int GlobalReferenceCount {

src/Mono.Android/Android.Runtime/JNIEnv.cs

@@ -66,16 +66,16 @@ public static partial class JNIEnv {
 
 		internal    static      AndroidValueManager? AndroidValueManager;
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		extern static void monodroid_log (LogLevel level, LogCategories category, string message);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal extern static IntPtr monodroid_timing_start (string? message);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal extern static void monodroid_timing_stop (IntPtr sequence, string? message);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal extern static void monodroid_free (IntPtr ptr);
 
 		public static IntPtr Handle {
@@ -296,7 +296,7 @@ internal static void PropagateUncaughtException (IntPtr env, IntPtr javaThreadPt
 			}
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		extern static void _monodroid_gc_wait_for_bridge_processing ();
 
 #pragma warning disable CS0649 // Field is never assigned to.  This field is assigned from monodroid-glue.cc.
@@ -310,7 +310,7 @@ public static void WaitForBridgeProcessing ()
 			_monodroid_gc_wait_for_bridge_processing ();
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		extern static IntPtr _monodroid_get_identity_hash_code (IntPtr env, IntPtr value);
 
 		internal static Func<IntPtr, IntPtr>? IdentityHash;
@@ -597,25 +597,25 @@ internal static void DeleteRef (IntPtr handle, JniHandleOwnership transfer)
 			}
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern int _monodroid_gref_log (string message);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern int _monodroid_gref_log_new (IntPtr curHandle, byte curType, IntPtr newHandle, byte newType, string? threadName, int threadId, [In] StringBuilder? from, int from_writable);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern void _monodroid_gref_log_delete (IntPtr handle, byte type, string? threadName, int threadId, [In] StringBuilder? from, int from_writable);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern void _monodroid_weak_gref_new (IntPtr curHandle, byte curType, IntPtr newHandle, byte newType, string? threadName, int threadId, [In] StringBuilder? from, int from_writable);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern void _monodroid_weak_gref_delete (IntPtr handle, byte type, string? threadName, int threadId, [In] StringBuilder? from, int from_writable);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern int _monodroid_lref_log_new (int lrefc, IntPtr handle, byte type, string? threadName, int threadId, [In] StringBuilder from, int from_writable);
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern void _monodroid_lref_log_delete (int lrefc, IntPtr handle, byte type, string? threadName, int threadId, [In] StringBuilder from, int from_writable);
 
 		public static IntPtr NewGlobalRef (IntPtr jobject)

src/Mono.Android/Android.Runtime/Logger.cs

@@ -60,7 +60,7 @@ public static void Log (LogLevel level, string appname, string? log) {
 			}
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		extern static uint monodroid_get_log_categories ();
 
 		static Logger ()

src/Mono.Android/Java.Interop/Runtime.cs

@@ -20,14 +20,14 @@ public static List<WeakReference> GetSurfacedObjects ()
 			return r;
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		static extern int _monodroid_max_gref_get ();
 
 		public static int MaxGlobalReferenceCount {
 			get {return _monodroid_max_gref_get ();}
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		static extern int _monodroid_gref_get ();
 
 		public static int GlobalReferenceCount {

src/Mono.Android/Java.Interop/TypeManager.cs

@@ -38,7 +38,7 @@ public static Dictionary<Type, string> ManagedToJni {
 	}
 
 	public static partial class TypeManager {
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
+		[DllImport (AndroidRuntime.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		extern static IntPtr monodroid_TypeManager_get_java_class_name (IntPtr klass);
 
 		internal static string GetClassName (IntPtr class_ptr)

src/monodroid/jni/monodroid-glue-internal.hh

@@ -139,7 +139,7 @@ namespace xamarin::android::internal
 	private:
 		unsigned int convert_dl_flags (int flags);
 #if defined (WINDOWS) || defined (APPLE_OS_X)
-		static const char* get_my_location ();
+		static const char* get_my_location (bool remove_file_name = true);
 #endif  // defined(WINDOWS) || defined(APPLE_OS_X)
 		static void* monodroid_dlopen (const char *name, int flags, char **err, void *user_data);
 		static void* monodroid_dlsym (void *handle, const char *name, char **err, void *user_data);

src/monodroid/jni/monodroid-glue.cc

@@ -1151,27 +1151,92 @@ MonodroidRuntime::monodroid_dlopen (const char *name, int flags, char **err, [[m
 {
 	unsigned int dl_flags = monodroidRuntime.convert_dl_flags (flags);
 	bool libmonodroid_fallback = false;
-
+	bool name_is_full_path = false;
+	bool name_needs_free = false;
 	/* name is nullptr when we're P/Invoking __Internal, so remap to libxa-internal-api */
-	if (name == nullptr) {
+	if (name == nullptr || strstr (name, "xa-internal-api") != nullptr) {
+#if defined (WINDOWS)
+		char *tmp_name = nullptr;
+
+		auto probe_dll_at = [&](const char *the_path) -> bool {
+			if (the_path == nullptr) {
+				return false;
+			}
+
+			const char *last_sep = strrchr (the_path, MONODROID_PATH_SEPARATOR_CHAR);
+			if (last_sep != nullptr) {
+				char *dir = utils.strdup_new (the_path, last_sep - the_path);
+				tmp_name = utils.string_concat (dir, MONODROID_PATH_SEPARATOR, API_DSO_NAME);
+				delete[] dir;
+				if (!utils.file_exists (tmp_name)) {
+					delete[] tmp_name;
+					tmp_name = nullptr;
+					return false;
+				}
+
+				return true;
+			}
+
+			return false;
+		};
+
+		//
+		// First try to see if it exist at the path pointed to by `name`. With p/invokes, currently (Sep 2020), we can't
+		// really trust the path since it consists of *some* directory path + p/invoke library name and it does not
+		// point to the location where the native library is. However, we still need to check the location first, should
+		// it point to the right place in the future.
+		//
+		// Context: https://github.com/mono/mono/issues/20295#issuecomment-679271621
+		//
+		bool found = probe_dll_at (name);
+		if (!found) {
+			// Next lets try the location of the XA runtime DLL, libxa-internal-api.dll should be next to it.
+			const char *path = get_my_location (false);
+			found = probe_dll_at (path);
+			if (path != nullptr) {
+				free (reinterpret_cast<void*>(const_cast<char*>(path)));
+			}
+
+			if (!found) {
+				log_warn (LOG_DEFAULT, "Failed to locate %s, using file name without the path", API_DSO_NAME);
+				name = API_DSO_NAME;
+			} else {
+				name = tmp_name;
+				name_is_full_path = true;
+				name_needs_free = true;
+			}
+		}
+#else // ndef WINDOWS
 		name = API_DSO_NAME;
+#endif // WINDOWS
 		libmonodroid_fallback = true;
 	}
 
-	void *h = androidSystem.load_dso_from_any_directories (name, dl_flags);
+	void *h = nullptr;
+	if (!name_is_full_path)
+		h = androidSystem.load_dso_from_any_directories (name, dl_flags);
 
 	if (h != nullptr) {
-		return monodroid_dlopen_log_and_return (h, err, name, false, libmonodroid_fallback);
+		return monodroid_dlopen_log_and_return (h, err, name, name_needs_free, libmonodroid_fallback);
 	}
 
 	if (libmonodroid_fallback) {
-		char *full_name = utils.path_combine (AndroidSystem::SYSTEM_LIB_PATH, API_DSO_NAME);
+		const char *full_name;
+		if (name_is_full_path) {
+			full_name = name;
+		} else {
+			if (name_needs_free) {
+				delete[] name;
+			}
+			full_name = utils.path_combine (AndroidSystem::SYSTEM_LIB_PATH, API_DSO_NAME);
+			name_needs_free = true;
+		}
 		h = androidSystem.load_dso (full_name, dl_flags, false);
-		return monodroid_dlopen_log_and_return (h, err, full_name, true, true);
+		return monodroid_dlopen_log_and_return (h, err, full_name, name_needs_free, true);
 	}
 
 	if (!utils.ends_with (name, ".dll.so") && !utils.ends_with (name, ".exe.so")) {
-		return monodroid_dlopen_log_and_return (h, err, name, false);
+		return monodroid_dlopen_log_and_return (h, err, name, name_needs_free);
 	}
 
 	char *basename_part = const_cast<char*> (strrchr (name, '/'));
@@ -1186,6 +1251,10 @@ MonodroidRuntime::monodroid_dlopen (const char *name, int flags, char **err, [[m
 	if (h != nullptr && XA_UNLIKELY (utils.should_log (LOG_ASSEMBLY)))
 		log_info_nocheck (LOG_ASSEMBLY, "Loaded AOT image '%s'", static_cast<const char*>(basename));
 
+	if (name_needs_free) {
+		delete[] name;
+	}
+
 	return h;
 }
 
@@ -1489,7 +1558,7 @@ MonodroidRuntime::typemap_managed_to_java (MonoReflectionType *type, const uint8
 
 #if defined (WINDOWS)
 const char*
-MonodroidRuntime::get_my_location ()
+MonodroidRuntime::get_my_location (bool remove_file_name)
 {
 	HMODULE hm = NULL;
 
@@ -1507,21 +1576,24 @@ MonodroidRuntime::get_my_location ()
 		return nullptr;
 	}
 
-	PathRemoveFileSpecW (path);
+	if (remove_file_name)
+		PathRemoveFileSpecW (path);
 
 	return utils.utf16_to_utf8 (path);
 }
 #elif defined (APPLE_OS_X)
 const char*
-MonodroidRuntime::get_my_location ()
+MonodroidRuntime::get_my_location (bool remove_file_name)
 {
 	Dl_info info;
 	if (dladdr (reinterpret_cast<const void*>(&MonodroidRuntime::get_my_location), &info) == 0) {
 		log_warn (LOG_DEFAULT, "Could not lookup library containing `MonodroidRuntime::get_my_location()`; dladdr failed: %s", dlerror ());
 		return nullptr;
 	}
 
-	return utils.strdup_new (dirname (const_cast<char*>(info.dli_fname)));
+	if (remove_file_name)
+		return utils.strdup_new (dirname (const_cast<char*>(info.dli_fname)));
+	return utils.strdup_new (info.dli_fname);
 }
 #endif  // defined(WINDOWS)
 

tests/MSBuildDeviceIntegration/Tests/XASdkDeployTests.cs

@@ -55,11 +55,7 @@ public void DotNetDebug ()
 			AssertHasDevices ();
 
 			XASdkProject proj;
-			proj = new XASdkProject {
-				//TODO: targetSdkVersion="30" causes a crash on startup in .NET 5
-				MinSdkVersion = null,
-				TargetSdkVersion = null,
-			};
+			proj = new XASdkProject ();
 			proj.SetRuntimeIdentifier (DeviceAbi);
 
 			var relativeProjDir = Path.Combine ("temp", TestName);