ClassFile.build() is loading result file

Wed Jan 8 03:14:23 UTC 2025

Thanks for this investigation. I should definitely add a note to tge class hierarchy resolver option about this side effect when this is used by instrumentation.

Chen

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________________________________
From: classfile-api-dev <classfile-api-dev-retn at openjdk.org> on behalf of Mark Roberts <markro at cs.washington.edu>
Sent: Tuesday, January 7, 2025 8:13:03 PM
To: Chen Liang <liangchenblue at gmail.com>
Cc: classfile-api-dev <classfile-api-dev at openjdk.org>
Subject: RE: ClassFile.build() is loading result file

OK – I build my own version of java.base so I could debug this issue.  It looks like the problem is that when StackMapGenerator wants to see if something is an interface, the code ends up doing a Class.forName and loads the class being built prematurely.

  Here is the interesting call stack:

  at java.base/jdk.internal.loader.URLClassPath$FileLoader.getResource(URLClassPath.java:1073)

    at java.base/jdk.internal.loader.URLClassPath.getResource(URLClassPath.java:315)

    at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:757)

    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)

    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)

    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)

    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:528)

    at java.base/java.lang.Class.forName0(Native Method)

    at java.base/java.lang.Class.forName(Class.java:582)

    at java.base/java.lang.Class.forName(Class.java:561)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl$ClassLoadingClassHierarchyResolver$1.apply(ClassHierarchyImpl.java:223)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl$ClassLoadingClassHierarchyResolver$1.apply(ClassHierarchyImpl.java:219)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl$ClassLoadingClassHierarchyResolver.getClassInfo(ClassHierarchyImpl.java:243)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl$CachedClassHierarchyResolver$1.apply(ClassHierarchyImpl.java:134)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl$CachedClassHierarchyResolver$1.apply(ClassHierarchyImpl.java:131)

    at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1229)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl$CachedClassHierarchyResolver.getClassInfo(ClassHierarchyImpl.java:142)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl.resolve(ClassHierarchyImpl.java:74)

    at java.base/jdk.internal.classfile.impl.ClassHierarchyImpl.isInterface(ClassHierarchyImpl.java:86)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator$Type.mergeReferenceFrom(StackMapGenerator.java:1547)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator$Type.mergeFrom(StackMapGenerator.java:1515)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator$Frame.merge(StackMapGenerator.java:1376)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator$Frame.checkAssignableTo(StackMapGenerator.java:1326)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator.processMethod(StackMapGenerator.java:433)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator.generate(StackMapGenerator.java:302)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator.<init>(StackMapGenerator.java:245)

    at java.base/jdk.internal.classfile.impl.StackMapGenerator.of(StackMapGenerator.java:156)

    at java.base/jdk.internal.classfile.impl.DirectCodeBuilder$4.generateStackMaps(DirectCodeBuilder.java:317)

    at java.base/jdk.internal.classfile.impl.DirectCodeBuilder$4.tryGenerateStackMaps(DirectCodeBuilder.java:325)

    at java.base/jdk.internal.classfile.impl.DirectCodeBuilder$4.writeBody(DirectCodeBuilder.java:360)

    at java.base/jdk.internal.classfile.impl.UnboundAttribute$AdHocAttribute.writeTo(UnboundAttribute.java:835)

    at java.base/jdk.internal.classfile.impl.Util.writeAttribute(Util.java:230)

    at java.base/jdk.internal.classfile.impl.AttributeHolder.writeTo(AttributeHolder.java:71)

    at java.base/jdk.internal.classfile.impl.DirectMethodBuilder.writeTo(DirectMethodBuilder.java:146)

    at java.base/jdk.internal.classfile.impl.Util.writeList(Util.java:247)

    at java.base/jdk.internal.classfile.impl.DirectClassBuilder.build(DirectClassBuilder.java:198)

    at java.base/jdk.internal.classfile.impl.ClassFileImpl.build(ClassFileImpl.java:146)

    at java.base/java.lang.classfile.ClassFile.build(ClassFile.java:333)

    at daikon.chicory.Instrument.transform(Instrument.java:295)

    at java.instrument/java.lang.instrument.ClassFileTransformer.transform(ClassFileTransformer.java:259)

    at java.instrument/sun.instrument.TransformerManager.transform(TransformerManager.java:188)

    at java.instrument/sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:611)

    at java.base/java.lang.ClassLoader.defineClass1(Native Method)

    at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1026)

    at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)

    at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862)

    at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)

    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)

    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)

    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)

    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:528)

    at java.base/java.lang.ClassLoader.defineClass1(Native Method)

    at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1026)

    at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)

    at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862)

    at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)

    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)

    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)

    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)

    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:528)

    at javautil.ArrayList17Test.main(ArrayList17Test.java:7)

Thank you,

Mark

From: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>
Sent: Monday, January 6, 2025 12:51 PM
To: 'Chen Liang' <liangchenblue at gmail.com<mailto:liangchenblue at gmail.com>>
Cc: 'classfile-api-dev' <classfile-api-dev at openjdk.org<mailto:classfile-api-dev at openjdk.org>>
Subject: RE: ClassFile.build() is loading result file

I modified the jvmti minst tool to capture java execution method enter and exit.  I have attached what I hope is the relevant part of the log file.  This section of the log file starts with:

daikon.chicory.Instrument.modifyClass exit

and ends with:

java.lang.LinkageError: loader 'app' attempted duplicate abstract class definition for javautil.AbstractList17.

Along the way you can see the load:

 [6.689s][info][class,load] javautil.AbstractList17 source: file:/scratch/markro/tests/scratch/markro/clones/mydaikon.24/tests/daikon-tests/ArrayList17/

Happening twice.  The second time is expected when the code exits the transform method.  This first seems like an error that occurs at some point while the DirectCodeBuilder is running.

Hope this helps to debug my problem.

Thank you,

Mark

From: Chen Liang <liangchenblue at gmail.com<mailto:liangchenblue at gmail.com>>
Sent: Sunday, January 5, 2025 2:06 PM
To: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>
Cc: classfile-api-dev <classfile-api-dev at openjdk.org<mailto:classfile-api-dev at openjdk.org>>
Subject: Re: ClassFile.build() is loading result file

Hi Mark,
why do you need to supply the ClassLoader to the modifyClass method? Class file transformation should have no dependency on the CHA process, and the only need is encapsulated within the ClassFile context object.

Can you post your modifyClass?

Chen

On Sun, Jan 5, 2025, 2:57 PM Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>> wrote:

I am using ClassFileTransformer.transform() to instrument class files as they are loaded.   Within my transform method I call

byte[] newBytes =  classFile.build(classModel.thisClass().asSymbol(),

                          classBuilder -> modifyClass(classBuilder, classModel, loader));

where modifyClass does all the instrumentation.

The problem is some where inside of classFile.build() the class is actually being loaded!  Thus, when I return newBytes from the transform method I get an error ‘attempted duplicate abstract class definition’. I have verified that the class has not be loaded prior to the return from modifyClass().

What is going on?

Thank you,

Mark
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