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[R8] [Optimization] Public fields in bindings are not protected by proguard rules

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評価

難易度
4/5
見積もり時間
3〜5日
初心者へのやさしさ
22/100
issue の種類
バグ
明瞭さ
おおむね明確
活発さ
活発
技術スタック
android, csharp, java
領域
build-system, mobile

調査の方向性

Start with the generated proguard_project_references.cfg and compare its keep rules for com.facebook.LoggingBehavior and androidx.media3.exoplayer.ExoPlaybackException with the workaround rules in the issue. Then reproduce with TrimMode=full and AndroidLinkTool=r8 and check the R8 usage and proguard.map output for the removed enum value and the int to byte field change. Done means public fields and enum members used by bindings are kept, and the Type getter still matches the DEX field type.

索引モデルが issue の本文から書いたものです。

説明

Area: App+Library Build needs-triage
Android framework version

net11.0-android (Preview)

Affected platform version

.NET 11.0.100-rc2

Description

It seems like public/protected fields in Java classes and enums, which managed code is accessing via bingings, are not protected by the generated proguard rules. This issue seems to be related to the optimization from https://github.com/dotnet/android/issues/12270, although most likely not caused by it.

Here are details that we discovered in our project, which is using native Facebook SDK binding and Xamarin.AndroidX.Media3.ExoPlayer nuget. During the build the following rules are generated in proguard_project_references.cfg:

-keep class com.facebook.LoggingBehavior
-keepclassmembers class com.facebook.LoggingBehavior {
}
-keep class androidx.media3.exoplayer.ExoPlaybackException
-keepclassmembers class androidx.media3.exoplayer.ExoPlaybackException {
}

com.facebook.LoggingBehavior is actually an enum, which values we are using via bindings, specifically

FacebookSdk.AddLoggingBehavior(LoggingBehavior.AppEvents);
FacebookSdk.AddLoggingBehavior(LoggingBehavior.Cache);
FacebookSdk.AddLoggingBehavior(LoggingBehavior.DeveloperErrors);
FacebookSdk.AddLoggingBehavior(LoggingBehavior.GraphApiDebugInfo);
FacebookSdk.AddLoggingBehavior(LoggingBehavior.GraphApiDebugWarning);
FacebookSdk.AddLoggingBehavior(LoggingBehavior.IncludeAccessTokens);
FacebookSdk.AddLoggingBehavior(LoggingBehavior.IncludeRawResponses);
FacebookSdk.AddLoggingBehavior(LoggingBehavior.Requests);

But because none of the enum values are protected by the generated rules, and with optimization enabled R8 decided to remove one of the values (seems like the only value with no explicit internal usage in Facebook SDK, at least after trimming). In the R8 "print usage" output there's the following record:

com.facebook.LoggingBehavior:
    public static final enum com.facebook.LoggingBehavior CACHE

The case with androidx.media3.exoplayer.ExoPlaybackException is a bit different. We are using it's public Type field of type int like that:

if (exception is ExoPlaybackException error)
{
    switch (error.Type)
    {
       ... 
    }
}

In this case R8 does not remove the field completely, but performs another type of optimization (extracted from the proguard.map):

androidx.media3.exoplayer.ExoPlaybackException -> androidx.media3.exoplayer.ExoPlaybackException:
# {"id":"sourceFile","fileName":"ExoPlaybackException.java"}
    boolean isRecoverable -> g
    int type -> type
      # {"id":"com.android.tools.r8.residualsignature","signature":"B"}

So the type of the field was optimized to be byte instead of int in DEX, while the binding code is still expecting int:

public int Type {
    get {
        return _members.InstanceFields.GetInt32Value ("type.I", this);
    }
}

The issue probably become noticeable only after enabling R8 optimizations. We double-checked that with older .NET 10.0.200 same public fields are also not protected by default:

-keep class com.facebook.LoggingBehavior
-keepclassmembers class com.facebook.LoggingBehavior {
   *** valueOf(...);
   *** values(...);
}
-keep class androidx.media3.exoplayer.ExoPlaybackException
-keepclassmembers class androidx.media3.exoplayer.ExoPlaybackException {
   *** getRendererException(...);
   *** getSourceException(...);
   *** getUnexpectedException(...);
   *** createForRemote(...);
   *** createForRenderer(...);
   *** createForRenderer(...);
   *** createForSource(...);
   *** createForUnexpected(...);
   *** createForUnexpected(...);
}
Steps to Reproduce

Seems like the issue can be reproduced on any .NET and Android workload version, but may lead to runtime crashes only in setup with R8 optimization enabled (11.0.100-rc.2/10.0.402)

  1. Android project with TrimMode=full and AndroidLinkTool=r8
  2. Access any native public field (like enum value) via binding
  3. Build project and check generated proguard_project_references.cfg
Did you find any workaround?

Custom proguard rules file to protect public fields and enums:

-keepclassmembers enum * {
    *;
}

-keepclassmembers class * {
    public protected !static <fields>;
    public protected static !final <fields>;
    public protected static final ** *;
    public protected static final **[] *;
}
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