[monodroid] Work around an Android 9 dlopen bug on x86 (#4914)

Fixes: #4893

The setup:

 1. App with `AndroidManifest.xml` which sets
    `/application/@android:extractNativeLibs` to `false`, e.g.:

        [assembly:Application (ExtractNativeLibs=false)]

 2. Build (1) as a *Release* app

 3. Run (2) on an Android 9.0 (API-28) *x86* emulator (32-bit!)

The result: app crash during process startup!

	E/mono(14126): Unhandled Exception:
	E/mono(14126): System.ArgumentNullException: Value cannot be null.
	E/mono(14126): Parameter name: key
	E/mono(14126):   at System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key)
	E/mono(14126):   at System.Collections.Generic.Dictionary`2[TKey,TValue].TryGetValue (TKey key, TValue& value)
	E/mono(14126):   at Java.Interop.TypeManager.RegisterType (System.String java_class, System.Type t)
	E/mono(14126):   at Android.Runtime.JNIEnv.RegisterJniNatives (System.IntPtr typeName_ptr, System.Int32 typeName_len, System.IntPtr jniClass, System.IntPtr methods_ptr, System.Int32 methods_len)

The cause of the crash is an apparent Android bionic bug, a'la:

	void* h1 = dlopen ("…path/to/libmonodroid.so", RTLD_LAZY);
	// time passses
	void* h2 = dlopen ("…path/to/libmonodroid.so", RTLD_LAZY);

"Normal"/expected semantics are that `h1` is the same as `h2`, with
the second `dlopen()` invocation effectively being a no-op, as the
library has already been loaded.

On 32-bit Android 9 -- but *only* when `extractNativeLibs`=false! --
what *instead* happens is that that native library is *re-loaded* such
that `h1` != `h2` (potentially?!), *and* the global state of `h1` is
cleared; the library is reinitialized.

Where this comes in is with P/Invokes to `__Internal`, which we
"redirect" to `libmonodroid.so`.  However, since `dlopen(NULL)`
has a history on Android of generating a SIGSEGV, we avoid the crash
by explicitly loading `libmonodroid.so` every time we need to satisfy
a request for `__Internal` (in `MonodroidRuntime::monodroid_dlopen()`
when `name` is `nullptr`).  As we re-load `libmonodroid.so` and
`dlopen()` potentially *clears* global data, what happens is that
certain class members initialized in `Runtime.initInternal()` become
`nullptr`.  In this particular case, `MonodroidRuntime::Class_getName`
became null, which meant that we couldn't lookup Java class names,
which caused the subsequent crash.

The fix is to introduce a new `libxa-internal-api.so` which contains
only three things of consequence:

 1. Explicit "init" and "shutdown" exports:

        MONO_API bool _monodroid_init_internal_api (MonoAndroidInternalCalls *api);
        MONO_API bool _monodroid_shutdown_internal_api (void);

 2. A pointer to a new `MonoAndroidInternalCalls` "interface",
    implemented in `libmonodroid.so`, and

 3. Other "C" exports that `__Internal` needs to invoke, which are
    implemented by delegating through `MonoAndroidInternalCalls`.

`libxa-internal-api.so` thus becomes the *only* library that we ever
`dlopen()` more than once, and as we control when it's loaded, we can
call `_monodroid_init_internal_api()` and
`_monodroid_shutdown_internal_api()` as appropriate, ensuring that
when we run on Android 9+x86+`extractNativeLibs`=false, the "damage"
from subsequent `dlopen()` invocations is minimized.

Author: grendello

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

@@ -38,6 +38,7 @@ projects that use the Microsoft.Android framework in .NET 5.
     <ItemGroup>
       <_AndroidRuntimePackAssets Include="$(XamarinAndroidSourcePath)bin\$(Configuration)\lib\xamarin.android\xbuild\Xamarin\Android\lib\$(AndroidABI)\libmono-android.debug.so" />
       <_AndroidRuntimePackAssets Include="$(XamarinAndroidSourcePath)bin\$(Configuration)\lib\xamarin.android\xbuild\Xamarin\Android\lib\$(AndroidABI)\libmono-android.release.so" />
+      <_AndroidRuntimePackAssets Include="$(XamarinAndroidSourcePath)bin\$(Configuration)\lib\xamarin.android\xbuild\Xamarin\Android\lib\$(AndroidABI)\libxa-internal-api.so" />
       <_AndroidRuntimePackAssets Include="$(XamarinAndroidSourcePath)bin\$(Configuration)\lib\xamarin.android\xbuild\Xamarin\Android\lib\$(AndroidABI)\libsqlite3_xamarin.so" />
       <_AndroidRuntimePackAssets Include="$(XamarinAndroidSourcePath)bin\$(Configuration)\lib\xamarin.android\xbuild\Xamarin\Android\lib\$(AndroidABI)\libxamarin-debug-app-helper.so" />
       <FrameworkListFileClass Include="@(_AndroidRuntimePackAssets->'%(Filename)%(Extension)')" Profile="Android" />

build-tools/installers/create-installers.targets

@@ -159,6 +159,7 @@
     <_MSBuildFiles Include="$(MSBuildSrcDir)\LayoutBinding.cs" />
     <_MSBuildFiles Include="@(AndroidSupportedTargetJitAbi->'$(MSBuildSrcDir)\lib\%(Identity)\libmono-android.debug.so')"       Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
     <_MSBuildFiles Include="@(AndroidSupportedTargetJitAbi->'$(MSBuildSrcDir)\lib\%(Identity)\libmono-android.release.so')"     Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
+    <_MSBuildFiles Include="@(AndroidSupportedTargetJitAbi->'$(MSBuildSrcDir)\lib\%(Identity)\libxa-internal-api.so')"          Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
     <_MSBuildFiles Include="@(AndroidSupportedTargetJitAbi->'$(MSBuildSrcDir)\lib\%(Identity)\libmono-btls-shared.so')"         Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
     <_MSBuildFiles Include="@(AndroidSupportedTargetJitAbi->'$(MSBuildSrcDir)\lib\%(Identity)\libmono-profiler-aot.so')"        Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
     <_MSBuildFiles Include="@(AndroidSupportedTargetJitAbi->'$(MSBuildSrcDir)\lib\%(Identity)\libmono-profiler-log.so')"        Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
@@ -294,6 +295,7 @@
     <_MSBuildLibHostFilesWin Include="$(MSBuildSrcDir)\lib\host-mxe-Win64\libMonoPosixHelper.dll" />
     <_MSBuildLibHostFilesWin Include="$(MSBuildSrcDir)\lib\host-mxe-Win64\libmonosgen-2.0.dll" />
     <_MSBuildLibHostFilesWin Include="$(MSBuildSrcDir)\lib\host-mxe-Win64\libxamarin-app.dll" Condition=" '$(HostOS)' != 'Windows' " />
+    <_MSBuildLibHostFilesWin Include="$(MSBuildSrcDir)\lib\host-mxe-Win64\libxa-internal-api.dll" Condition=" '$(HostOS)' != 'Windows' " />
   </ItemGroup>
   <ItemDefinitionGroup>
     <_MSBuildFilesUnixSign>
@@ -333,6 +335,7 @@
     <_MSBuildFilesUnixSign Include="$(MSBuildSrcDir)\lib\host-$(HostOS)\libMonoPosixHelper.$(LibExtension)"       Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
     <_MSBuildFilesUnixSign Include="$(MSBuildSrcDir)\lib\host-$(HostOS)\libmonosgen-2.0.$(LibExtension)"          Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
     <_MSBuildFilesUnixSign Include="$(MSBuildSrcDir)\lib\host-$(HostOS)\libxamarin-app.$(LibExtension)"           Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
+    <_MSBuildFilesUnixSign Include="$(MSBuildSrcDir)\lib\host-$(HostOS)\libxa-internal-api.$(LibExtension)"       Condition=" '$(PackageId)' != 'Microsoft.Android.Sdk' " />
     <_MSBuildFilesUnixSign Include="$(MSBuildSrcDir)\libzip.$(LibExtension)" />
     <_MSBuildFilesUnix Include="$(MSBuildSrcDir)\proguard\bin\proguard.sh" />
   </ItemGroup>

samples/HelloWorld/Properties/AndroidManifest.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" android:versionName="1.0" package="com.xamarin.android.helloworld">
 	<uses-sdk android:minSdkVersion="21" />
-	<application android:allowBackup="true" android:icon="@mipmap/icon" android:label="@string/app_name">
+	<application android:allowBackup="true" android:icon="@mipmap/icon" android:label="@string/app_name" android:extractNativeLibs="false">
 	</application>
 </manifest>

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

@@ -1890,6 +1890,7 @@ because xbuild doesn't support framework reference assemblies.
     <_AndroidNativeLibraryForFastDev Condition=" '$(_InstantRunEnabled)' == 'True' And '$(AndroidUseDebugRuntime)' == 'True' " Include="%(_TargetLibDir.Identity)\libxamarin-debug-app-helper.so" />
     <FrameworkNativeLibrary Include="%(_TargetLibDir.Identity)\libmono-android.debug.so" Condition=" '$(AndroidIncludeDebugSymbols)' == 'True' " ArchiveFileName="libmonodroid.so" />
     <FrameworkNativeLibrary Include="%(_TargetLibDir.Identity)\libmono-android.release.so" Condition=" '$(AndroidIncludeDebugSymbols)' != 'True' " ArchiveFileName="libmonodroid.so" />
+    <FrameworkNativeLibrary Include="%(_TargetLibInterpreterDir.Identity)\libxa-internal-api.so"  />
     <FrameworkNativeLibrary Include="%(_TargetLibInterpreterDir.Identity)\libmono-btls-shared.so"  />
     <FrameworkNativeLibrary Include="%(_TargetLibInterpreterDir.Identity)\libmono-profiler-aot.so" Condition=" @(_EmbedProfilers->Count()) > 0 and (@(_EmbedProfilers->AnyHaveMetadataValue('Identity', 'aot')) or @(_EmbedProfilers->AnyHaveMetadataValue('Identity', 'all'))) " />
     <FrameworkNativeLibrary Include="%(_TargetLibInterpreterDir.Identity)\libmono-profiler-log.so" Condition=" '$(AndroidIncludeDebugSymbols)' == 'True' or (@(_EmbedProfilers->Count()) > 0 and (@(_EmbedProfilers->AnyHaveMetadataValue('Identity', 'log')) or @(_EmbedProfilers->AnyHaveMetadataValue('Identity', 'all')))) " />

src/monodroid/CMakeLists.txt

@@ -228,6 +228,8 @@ else()
   endif()
 endif()
 
+string(STRIP "${EXTRA_LINKER_FLAGS}" EXTRA_LINKER_FLAGS)
+
 if (ENABLE_TIMING)
   add_definitions("-DMONODROID_TIMING=1")
 endif()
@@ -285,11 +287,10 @@ set(MONODROID_SOURCES
   ${SOURCES_DIR}/debug-constants.cc
   ${SOURCES_DIR}/embedded-assemblies.cc
   ${SOURCES_DIR}/embedded-assemblies-zip.cc
-  ${SOURCES_DIR}/external-api.cc
   ${SOURCES_DIR}/globals.cc
-  ${SOURCES_DIR}/jni.c
   ${SOURCES_DIR}/logger.cc
   ${SOURCES_DIR}/monodroid-glue.cc
+  ${SOURCES_DIR}/xa-internal-api.cc
   ${SOURCES_DIR}/osbridge.cc
   ${SOURCES_DIR}/shared-constants.cc
   ${SOURCES_DIR}/timezones.cc
@@ -299,6 +300,12 @@ set(MONODROID_SOURCES
   ${JAVA_INTEROP_SRC_PATH}/java-interop-util.cc
   )
 
+set(XA_INTERNAL_API_SOURCES
+  ${SOURCES_DIR}/jni.c
+  ${SOURCES_DIR}/internal-pinvoke-api.cc
+  ${JAVA_INTEROP_SRC_PATH}/java-interop-util.cc
+  )
+
 if(ENABLE_NDK)
   set(MONODROID_SOURCES
 	${MONODROID_SOURCES}
@@ -314,6 +321,15 @@ if(UNIX)
     )
 endif()
 
+add_library(xa-internal-api SHARED ${XA_INTERNAL_API_SOURCES})
+target_link_libraries(xa-internal-api ${EXTRA_LINKER_FLAGS})
+set_target_properties(
+  xa-internal-api
+  PROPERTIES
+  COMPILE_FLAGS -fvisibility=default
+  LINK_FLAGS -fvisibility=default
+  )
+
 set(XAMARIN_APP_STUB_SOURCES ${SOURCES_DIR}/application_dso_stub.cc)
 add_library(xamarin-app SHARED ${XAMARIN_APP_STUB_SOURCES})
 if (ENABLE_NDK)

src/monodroid/jni/cpu-arch-detect.cc

@@ -225,7 +225,7 @@ get_running_on_cpu (unsigned short *running_on_cpu)
 	*running_on_cpu = CPU_KIND_UNKNOWN;
 }
 
-MONO_API void
+void
 _monodroid_detect_cpu_and_architecture (unsigned short *built_for_cpu, unsigned short *running_on_cpu, unsigned char *is64bit)
 {
 	assert (built_for_cpu);

src/monodroid/jni/embedded-assemblies.cc

@@ -597,7 +597,7 @@ EmbeddedAssemblies::md_mmap_apk_file (int fd, uint32_t offset, uint32_t size, co
 	md_mmap_info file_info;
 	md_mmap_info mmap_info;
 
-	size_t pageSize       = static_cast<size_t>(monodroid_getpagesize());
+	size_t pageSize       = static_cast<size_t>(utils.monodroid_getpagesize ());
 	uint32_t offsetFromPage  = static_cast<uint32_t>(offset % pageSize);
 	uint32_t offsetPage      = offset - offsetFromPage;
 	uint32_t offsetSize      = size + offsetFromPage;