Proguard replaces Methodref to InterfaceMethodref, but does not change instructions

[xxDark]

Hello.
We are using this awesome framework for our needs (https://github.com/SpongePowered/Mixin) and everything works fine.

However, Proguard breaks valid bytecode after obfuscation.
Before Proguard:

00000000 : aload_0
00000001 : invokevirtual       java.util.List hh.a()
00000004 : areturn

After Proguard:

We will attempt to fix that issue in Mixin framework, however, can Proguard:
a) Also change instructions?
b) Don't touch constant pool in that case?
Thanks.

P.S The problem is that INVOKEVIRTUAL requires Methodref, not InterfaceMethodref. That change triggers JVM's verifier.

 java.lang.VerifyError: Illegal type at constant pool entry 6 in class hh
             Exception Details:
                Location:
                  hh.appendSibling(Lhh;)Lhh; @2: invokevirtual
                Reason:
                  Constant pool index 6 is invalid
                Bytecode:
                  0x0000000: 2a2b b600 06b0                         
                  	at qs.a(Unknown Source)
                  	at vi$a.<init>(Unknown Source)
                  	at vi.a(Unknown Source)
                  	at vi.c(Unknown Source)
                  	at ni.c(Unknown Source)
                  	at bib.<init>(Unknown Source)

[xxDark]

SpongePowered/Mixin#413

[ingdas]

Thanks for taking the time to report this to us. Would it be possible for you to provide us with a (minimal) example jar or source file to start from?

[xxDark]

proguard.zip
java -cp . Test

[ingdas]

Thanks for that. Can you also give us the same classes in a version which isn't processed by ProGuard (and thus working?). That way we can trace the execution and find out where it goes wrong.

[xxDark]

Sure.
proguard.zip

[ingdas]

I'll need to bother you once more. I can't replicate your error.

• Are you sure you are using Proguard 7.0.0?
• Have you set any extra configuration options for this sample? I tried the following standalone configuration:

-injars ./pre
-outjars ./output.jar

-libraryjars <java.home>/lib/rt.jar

-keep class Test {
	<methods>;
}

[xxDark]

I guess that I provided not transformed class files, sorry.
Try on these:
dist.zip

[xxDark]

Configuration:

-injars app-merged.jar
-outjars dist/app-proguard.jar

-libraryjars libs
-libraryjars <java.home>/lib/rt.jar

-dontshrink
-dontobfuscate
-optimizations class/marking/*,method/marking/*,method/inlining/tailrecursion,code/*
-optimizationpasses 1
-allowaccessmodification
-printmapping roguard.map
-overloadaggressively
-repackageclasses ''
-keepattributes *Annotations*,*Signature*,LineNumberTable,SourceFile
-verbose

-keepclassmembers enum  * {
    <fields>;
    <methods>;
}

-keep class App {
    void main(java.lang.String[]);
}

# Keep - Native method names. Keep all native class/method names.
-keepclasseswithmembers,includedescriptorclasses,allowshrinking class * {
    native <methods>;
}