[External] : RE: ClassFile.build() is loading result file
Chen Liang
chen.l.liang at oracle.com
Wed Jan 8 16:36:05 UTC 2025
So ClassHierarchyResolver.ofClassLoading loads system classes and inspect them with core reflection to determine their class hierarchy, based on the assumptions that the system classes are constant. However, such assumptions do not stand when agents are present, and agents do not wish system class loaded in the process of handling class files. As a result, we should inspect the class file resources instead, which is largely the same as agent-transformed classes (as agents don't usually change super classes or change classes to interfaces)
P.S. Forwarding this conversation to classfile-api-dev as this may be valuable to the public.
Regards, Chen
________________________________
From: Mark Roberts <markro at cs.washington.edu>
Sent: Wednesday, January 8, 2025 10:15 AM
To: Chen Liang <chen.l.liang at oracle.com>
Subject: RE: [External] : RE: ClassFile.build() is loading result file
Ok that worked – thank you.
Could you give me a little background on what’s going on and why the option is needed?
Thanks,
Mark
From: Chen Liang <chen.l.liang at oracle.com<mailto:chen.l.liang at oracle.com>>
Sent: Wednesday, January 8, 2025 8:05 AM
To: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>
Subject: Re: [External] : RE: ClassFile.build() is loading result file
Yep; for the loader, if you are just transforming system classes, ClassLoader.getSystemClassLoader() should be sufficient.
________________________________
From: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>
Sent: Wednesday, January 8, 2025 9:28 AM
To: Chen Liang <chen.l.liang at oracle.com<mailto:chen.l.liang at oracle.com>>
Subject: RE: [External] : RE: ClassFile.build() is loading result file
So would that be:
ClassFile classFile = ClassFile.of(ClassFile.ClassHierarchyResolverOption.of(ClassHierarchyResolver.ofResourceParsing(loader)));
From: Chen Liang <chen.l.liang at oracle.com<mailto:chen.l.liang at oracle.com>>
Sent: Wednesday, January 8, 2025 6:32 AM
To: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>; classfile-api-dev at openjdk.org<mailto:classfile-api-dev at openjdk.org>
Subject: Re: [External] : RE: ClassFile.build() is loading result file
Use ClassHierarchyResolver.ofResourceParsing instead.
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________________________________
From: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>
Sent: Wednesday, January 8, 2025 8:02:16 AM
To: Chen Liang <chen.l.liang at oracle.com<mailto:chen.l.liang at oracle.com>>
Subject: [External] : RE: ClassFile.build() is loading result file
I’m sorry but I don’t understand. A documentation note doesn’t solve my problem. What do I have to do to keep this from happening?
Mark
From: Chen Liang <chen.l.liang at oracle.com<mailto:chen.l.liang at oracle.com>>
Sent: Tuesday, January 7, 2025 7:14 PM
To: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>; 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
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<mailto:classfile-api-dev-retn at openjdk.org>> on behalf of Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>
Sent: Tuesday, January 7, 2025 8:13:03 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
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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