Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

[Mono.Android] handle exceptions in RegisterNativeMembers #6672

Merged

Conversation

jonathanpeppers
Copy link
Member

@jonathanpeppers jonathanpeppers commented Jan 26, 2022

Context: dotnet/maui#4262

dotnet new maui-blazor crashes at runtime, if you do:

dotnet build -t:Run -c Release

You can turn off the linker to solve this issue:

dotnet build -t:Run -c Release -p:AndroidLinkMode=None

(or PublishTrimmed=false)

The app crashes in way that you get a native crash:

backtrace:
#00 pc 000000000065d8fc  /apex/com.android.art/lib64/libart.so (void art::StackVisitor::WalkStack<(art::StackVisitor::CountTransitions)0>(bool)+156) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
#01 pc 000000000069b25d  /apex/com.android.art/lib64/libart.so (art::Thread::GetCurrentMethod(unsigned int*, bool, bool) const+157) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
#02 pc 0000000000430fed  /apex/com.android.art/lib64/libart.so (art::JNI<false>::FindClass(_JNIEnv*, char const*)+765) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
#03 pc 0000000000047e5a  /data/app/~~0Qm6D1S0sO3f1lwfakN0PA==/com.companyname.mauiapp2-08UokVCH5k_PlbZEH_hhkA==/split_config.x86_64.apk!libmono-android.release.so (offset 0x11e000) (java_interop_jnienv_find_class+26) (BuildId: 3d04f8b946590175e97b89aee2e3b19ceed4b524)
#04 pc 00000000000128ac  <anonymous:41640000>

After much investigation... We found that
Java.IO.InputStream.GetReadHandler() was linked away.

This is because:

  1. Mono.Android.dll has it's Java stubs precompiled into
    mono.android.jar and mono.android.dex.

  2. Since Mono.Android.dll doesn't go through GenerateJavaStubs,
    the linker has no way to know if the missing method is used -- it
    is only called from Java in the crashing app.

To make the crash better, we need to try-catch all exceptions in
RegisterNativeMembers() and pass them to
AndroidRuntime.RaisePendingException(). This is because
RegisterNativeMembers() is called directly from Java.

Now the crash shows:

01-26 12:20:20.290 29264 29264 I MonoDroid: Android.Runtime.JavaProxyThrowable: Exception_WasThrown, Android.Runtime.JavaProxyThrowable
01-26 12:20:20.290 29264 29264 I MonoDroid:
01-26 12:20:20.290 29264 29264 I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
01-26 12:20:20.290 29264 29264 I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
01-26 12:20:20.290 29264 29264 I MonoDroid: --- End of stack trace from previous location ---
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)
01-26 12:20:20.290 29264 29264 I MonoDroid:
01-26 12:20:20.290 29264 29264 I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
01-26 12:20:20.290 29264 29264 I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
01-26 12:20:20.290 29264 29264 I MonoDroid: --- End of stack trace from previous location ---
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
01-26 12:20:20.290 29264 29264 I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)

This is much easier to reason about, and will save us time in the future.

A fix to the actual linker problem will be coming in another PR.

Context: dotnet/maui#4262

`dotnet new maui-blazor` crashes at runtime, if you do:

    dotnet build -t:Run -c Release

You can turn *off* the linker to solve this issue:

    dotnet build -t:Run -c Release -p:AndroidLinkMode=None

(or `PublishTrimmed=false`)

The app crashes in way that you get a native crash:

    backtrace:
    #00 pc 000000000065d8fc  /apex/com.android.art/lib64/libart.so (void art::StackVisitor::WalkStack<(art::StackVisitor::CountTransitions)0>(bool)+156) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
    #1 pc 000000000069b25d  /apex/com.android.art/lib64/libart.so (art::Thread::GetCurrentMethod(unsigned int*, bool, bool) const+157) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
    #2 pc 0000000000430fed  /apex/com.android.art/lib64/libart.so (art::JNI<false>::FindClass(_JNIEnv*, char const*)+765) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
    #3 pc 0000000000047e5a  /data/app/~~0Qm6D1S0sO3f1lwfakN0PA==/com.companyname.mauiapp2-08UokVCH5k_PlbZEH_hhkA==/split_config.x86_64.apk!libmono-android.release.so (offset 0x11e000) (java_interop_jnienv_find_class+26) (BuildId: 3d04f8b946590175e97b89aee2e3b19ceed4b524)
    #4 pc 00000000000128ac  <anonymous:41640000>

After much investigation... We found that
`Java.IO.InputStreamHandler.GetReadHandler()` was linked away.

This is because:

1. `Mono.Android.dll` has it's Java stubs precompiled into
   `mono.android.jar` and `mono.android.dex`.

2. Since `Mono.Android.dll` doesn't go through `GenerateJavaStubs`,
   the linker has no way to know if the missing method is used -- it
   is only called from Java in the crashing app.

To make the crash better, we need to `try-catch` *all* exceptions in
`RegisterNativeMembers()` and pass them to
`AndroidRuntime.RaisePendingException()`. This is because
`RegisterNativeMembers()` is called directly from Java.

Now the crash shows:

    01-26 12:20:20.290 29264 29264 I MonoDroid: Android.Runtime.JavaProxyThrowable: Exception_WasThrown, Android.Runtime.JavaProxyThrowable
    01-26 12:20:20.290 29264 29264 I MonoDroid:
    01-26 12:20:20.290 29264 29264 I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
    01-26 12:20:20.290 29264 29264 I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
    01-26 12:20:20.290 29264 29264 I MonoDroid: --- End of stack trace from previous location ---
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)
    01-26 12:20:20.290 29264 29264 I MonoDroid:
    01-26 12:20:20.290 29264 29264 I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
    01-26 12:20:20.290 29264 29264 I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
    01-26 12:20:20.290 29264 29264 I MonoDroid: --- End of stack trace from previous location ---
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
    01-26 12:20:20.290 29264 29264 I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
    01-26 12:20:20.290 29264 29264 I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)

This is much easier to reason about, and will save us time in the future.

A fix to the actual linker problem will be coming in another PR.
@jonathanpeppers
Copy link
Member Author

The diff is easier to view if you hide whitespace:

https://github.com/xamarin/xamarin-android/pull/6672/files?w=1

@jonpryor
Copy link
Member

Context: https://github.com/dotnet/maui/issues/4262
Context: https://github.com/xamarin/xamarin-android/pull/6675

If you run the `maui-blazor` template in a Release build:

	dotnet build -t:Run -c Release

it crashes at runtime:

	D monodroid-assembly: typemap: type with token 33555274 (0x200034a) in module {C7B4CC8F-7A03-4A3F-A34A-DC66EDC548B9} (Mono.Android) corresponds to Java type 'android/runtime/JavaProxyThrowable'
	
	F DEBUG   : backtrace:
	F DEBUG   : #00 pc 000000000065d8fc  /apex/com.android.art/lib64/libart.so (void art::StackVisitor::WalkStack<(art::StackVisitor::CountTransitions)0>(bool)+156) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #01 pc 000000000069b25d  /apex/com.android.art/lib64/libart.so (art::Thread::GetCurrentMethod(unsigned int*, bool, bool) const+157) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #02 pc 0000000000430fed  /apex/com.android.art/lib64/libart.so (art::JNI<false>::FindClass(_JNIEnv*, char const*)+765) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #03 pc 0000000000047e5a  /data/app/~~0Qm6D1S0sO3f1lwfakN0PA==/com.companyname.mauiapp2-08UokVCH5k_PlbZEH_hhkA==/split_config.x86_64.apk!libmono-android.release.so (offset 0x11e000) (java_interop_jnienv_find_class+26) (BuildId: 3d04f8b946590175e97b89aee2e3b19ceed4b524)
	F DEBUG   : #04 pc 00000000000128ac  <anonymous:41640000>

The crash can be avoided by disabling the linker:

	dotnet build -t:Run -c Release -p:AndroidLinkMode=None
	# -or-
	dotnet build -t:Run -c Release -p:PublishTrimmed=false

However, let us return to the crash: *why* is it crashing?
This isn't a "good debugging experience"; we have no useful context.

Lots of investigation later -- all hail printf debugging -- and we
found that the cause of the crash was an unhandled exception:

 1. `Mono.Android.dll` has it's Java Callable Wrappers generated
    from the *unlinked* assembly, into `mono.android.jar` and
    `mono.android.dex` files.  The Java Callable Wrapper for
    `Android.Runtime.InputStreamAdapter` thus includes *all*
    `Read()` method overloads.

 2. When the app is built in Release configuration, linking is
    enabled, and *some* of the `InputStreamAdapter.Read()` methods
    are removed by the linker, along with the
    `Java.IO.InputStream.Read()` methods that were overridden.

 3. At runtime, we perform [Java Type Registration][0] for the
    `Android.Runtime.InputStreamAdapter` type, which eventually calls
    `AndroidTypeManager.RegisterNativeMembers()`, which eventually
    attempts to *effectively* do:

        Delegate.CreateDelegate (
	        typeof(Func<Delegate>),
	        typeof(InputStreamAdapter),
	        "GetReadHandler");

 4. Because of (2), `Java.IO.InputStream.GetReadHandler()`
    *does not exist*, and thus `Delegate.CreateDelegate()` throws an
    `ArgumentException`.

So far, so reasonable, but…

 5. `AndroidTypeManager.RegisterNativeMembers()` didn't catch any
    exceptions, nor did any other method between the original Java
    `Runtime.register()` invocation and
    `AndroidTypeManager.RegisterNativeMembers()`.  The result is that
    a C# exception was "in flight", and Mono then proceeded to
    *tear down the stack frame* as it unwound the callstack looking
    for `catch` handlers.

At this point, the process is toast: the runtime stack is FUBAR.

This is also why the `backtrace:` is "rooted" in
`JNIEnv::FindClass()`: `JNIEnv::FindClass()` invokes Java static
constructors before returning, which is how the static constructor in
the Java Callable Wrapper for `InputStreamAdapter` called
`Runtime.register()` in the first place.

All of this makes for a miserable debugging experience.

Fixing the "original" linker issue will be done in
xamarin/xamarin-android#6675.

What we want to do *here* is improve this debugging experience, by
"wrapping" `AndroidTypeManager.RegisterNativeMembers()` in a
`try`/`catch` block, which can then *marshal the thrown exception*
back to Java.  This *prevents* Mono from unwinding the callstack past
a JNI boundary, and avoids the annoying-to-debug app crash.

After this change, we get a much friendlier unhandled exception crash:

	I MonoDroid: Android.Runtime.JavaProxyThrowable: Exception_WasThrown, Android.Runtime.JavaProxyThrowable
	I MonoDroid:
	I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
	I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
	I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
	I MonoDroid: --- End of stack trace from previous location ---
	I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
	I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
	I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
	I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
	I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
	I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
	I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)
	I MonoDroid:
	I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
	I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
	I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
	I MonoDroid: --- End of stack trace from previous location ---
	I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
	I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
	I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
	I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
	I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
	I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
	I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)

This is much easier to reason about, and will save us time in
the future.

[0]: https://github.com/xamarin/xamarin-android/wiki/Blueprint#java-type-registration

@jonpryor jonpryor merged commit b7a368a into dotnet:main Jan 27, 2022
jonathanpeppers added a commit that referenced this pull request Jan 27, 2022
Context: dotnet/maui#4262
Context: #6675

If you run the `maui-blazor` template in a Release build:

	dotnet build -t:Run -c Release

it crashes at runtime:

	D monodroid-assembly: typemap: type with token 33555274 (0x200034a) in module {C7B4CC8F-7A03-4A3F-A34A-DC66EDC548B9} (Mono.Android) corresponds to Java type 'android/runtime/JavaProxyThrowable'
	…
	F DEBUG   : backtrace:
	F DEBUG   : #00 pc 000000000065d8fc  /apex/com.android.art/lib64/libart.so (void art::StackVisitor::WalkStack<(art::StackVisitor::CountTransitions)0>(bool)+156) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #1 pc 000000000069b25d  /apex/com.android.art/lib64/libart.so (art::Thread::GetCurrentMethod(unsigned int*, bool, bool) const+157) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #2 pc 0000000000430fed  /apex/com.android.art/lib64/libart.so (art::JNI<false>::FindClass(_JNIEnv*, char const*)+765) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #3 pc 0000000000047e5a  /data/app/~~0Qm6D1S0sO3f1lwfakN0PA==/com.companyname.mauiapp2-08UokVCH5k_PlbZEH_hhkA==/split_config.x86_64.apk!libmono-android.release.so (offset 0x11e000) (java_interop_jnienv_find_class+26) (BuildId: 3d04f8b946590175e97b89aee2e3b19ceed4b524)
	F DEBUG   : #4 pc 00000000000128ac  <anonymous:41640000>

The crash can be avoided by disabling the linker:

	dotnet build -t:Run -c Release -p:AndroidLinkMode=None
	# -or-
	dotnet build -t:Run -c Release -p:PublishTrimmed=false

However, let us return to the crash: *why* is it crashing?
This isn't a "good debugging experience"; we have no useful context.

Lots of investigation later -- all hail printf debugging -- and we
found that the cause of the crash was an unhandled exception:

 1. `Mono.Android.dll` has it's Java Callable Wrappers generated
    from the *unlinked* assembly, into `mono.android.jar` and
    `mono.android.dex` files.  The Java Callable Wrapper for
    `Android.Runtime.InputStreamAdapter` thus includes *all*
    `Read()` method overloads.

 2. When the app is built in Release configuration, linking is
    enabled, and *some* of the `InputStreamAdapter.Read()` methods
    are removed by the linker, along with the
    `Java.IO.InputStream.Read()` methods that were overridden.

 3. At runtime, we perform [Java Type Registration][0] for the
    `Android.Runtime.InputStreamAdapter` type, which eventually calls
    `AndroidTypeManager.RegisterNativeMembers()`, which eventually
    attempts to *effectively* do:

        Delegate.CreateDelegate (
	        typeof(Func<Delegate>),
	        typeof(InputStreamAdapter),
	        "GetReadHandler");

 4. Because of (2), `Java.IO.InputStream.GetReadHandler()`
    *does not exist*, and thus `Delegate.CreateDelegate()` throws an
    `ArgumentException`.

So far, so reasonable, but…

 5. `AndroidTypeManager.RegisterNativeMembers()` didn't catch any
    exceptions, nor did any other method between the original Java
    `Runtime.register()` invocation and
    `AndroidTypeManager.RegisterNativeMembers()`.  The result is that
    a C# exception was "in flight", and Mono then proceeded to
    *tear down the stack frame* as it unwound the callstack looking
    for `catch` handlers.

At this point, the process is toast: the runtime stack is FUBAR.

This is also why the `backtrace:` is "rooted" in
`JNIEnv::FindClass()`: `JNIEnv::FindClass()` invokes Java static
constructors before returning, which is how the static constructor in
the Java Callable Wrapper for `InputStreamAdapter` called
`Runtime.register()` in the first place.

All of this makes for a miserable debugging experience.

Fixing the "original" linker issue will be done in
#6675.

This hasn't been an issue in "Classic" Xamarin.Android, presumably
because the classic linker isn't as good as the net6 linker.

What we want to do *here* is improve this debugging experience, by
"wrapping" `AndroidTypeManager.RegisterNativeMembers()` in a
`try`/`catch` block, which can then *marshal the thrown exception*
back to Java.  This *prevents* Mono from unwinding the callstack past
a JNI boundary, and avoids the annoying-to-debug app crash.

After this change, we get a much friendlier unhandled exception crash:

	I MonoDroid: Android.Runtime.JavaProxyThrowable: Exception_WasThrown, Android.Runtime.JavaProxyThrowable
	I MonoDroid:
	I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
	I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
	I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
	I MonoDroid: --- End of stack trace from previous location ---
	I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
	I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
	I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
	I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
	I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
	I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
	I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)
	I MonoDroid:
	I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
	I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
	I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
	I MonoDroid: --- End of stack trace from previous location ---
	I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
	I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
	I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
	I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
	I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
	I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
	I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)

This is much easier to reason about, and will save us time in
the future.

[0]: https://github.com/xamarin/xamarin-android/wiki/Blueprint#java-type-registration
@jonathanpeppers jonathanpeppers deleted the registernativemembers-handleexceptions branch January 27, 2022 20:35
@github-actions github-actions bot locked and limited conversation to collaborators Jan 24, 2024
Sign up for free to subscribe to this conversation on GitHub. Already have an account? Sign in.
Labels
None yet
Projects
None yet
Development

Successfully merging this pull request may close these issues.

2 participants