Java Community | Help. Code. Learn.•2mo ago

Java agent throws UnsupportedClassVersionError when Instrumentation#retransformClasses is called.

I need to dump who invokes a setCancelled(boolean cancelled) method in a running jar (Spigot 1.8). I decided to do this via dumping the caller using StackWalker by using a javaagent to add a method call which dumps the caller, the item field which is of type org.bukkit.inventory.ItemStack, & the cancelled argument. The only issue currently, is that when i call retransformClasses the whole thing comes burning down. Target class: org.bukkit.event.player.PlayerInteractEvent The agent is compiled under Java 17.0.12 the JVM is 17.0.12 The spigot jar is java 8 (i think) Ran via the -javaagent command line option

53 Replies

JavaBot•2mo ago

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cireOP•2mo ago

Transformer:

ClassReader classReader = new ClassReader(byteCode);
ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);

ClassNode classNode = new ClassNode();
classReader.accept(classNode, 0);

MethodNode methodNode_isCancelled = null;
for (MethodNode mn : classNode.methods) {
  if ("setCancelled".equals(mn.name)) {
    methodNode_isCancelled = mn;
    break;
  }
}

if (methodNode_isCancelled == null)
   return byteCode;

InsnList insnList = new InsnList();
insnList.add(new VarInsnNode(Opcodes.ALOAD, 0));
insnList.add(new FieldInsnNode(Opcodes.GETSTATIC, "java/lang/StackWalker$Option", "RETAIN_CLASS_REFERENCE", "Ljava/lang/StackWalker$Option"));
insnList.add(new MethodInsnNode(INVOKESTATIC, "java/lang/StackWalker", "getInstance", "(Ljava/lang/StackWalker$Option;)Ljava/lang/StackWalker", false));
insnList.add(new MethodInsnNode(INVOKEVIRTUAL, "java/lang/StackWalker", "getCallerClass", "()Ljava/lang/Class", false));
insnList.add(new VarInsnNode(Opcodes.ALOAD, 0));
insnList.add(new FieldInsnNode(Opcodes.GETFIELD, "org/bukkit/event/player/PlayerInteractEvent", "item", "Lorg/bukkit/inventory/ItemStack"));
insnList.add(new VarInsnNode(Opcodes.ILOAD, 1));

insnList.add(new MethodInsnNode(INVOKESTATIC, "me/cire3/sfbf/SFBFTransformer", "dump", "(Ljava/lang/Class;Ljava/lang/Object;Z)V", false));

            methodNode_isCancelled.instructions.insertBefore(methodNode_isCancelled.instructions.getFirst(), insnList);

byteCode = classWriter.toByteArray();

ClassReader classReader = new ClassReader(byteCode);
ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);

ClassNode classNode = new ClassNode();
classReader.accept(classNode, 0);

MethodNode methodNode_isCancelled = null;
for (MethodNode mn : classNode.methods) {
  if ("setCancelled".equals(mn.name)) {
    methodNode_isCancelled = mn;
    break;
  }
}

if (methodNode_isCancelled == null)
   return byteCode;

InsnList insnList = new InsnList();
insnList.add(new VarInsnNode(Opcodes.ALOAD, 0));
insnList.add(new FieldInsnNode(Opcodes.GETSTATIC, "java/lang/StackWalker$Option", "RETAIN_CLASS_REFERENCE", "Ljava/lang/StackWalker$Option"));
insnList.add(new MethodInsnNode(INVOKESTATIC, "java/lang/StackWalker", "getInstance", "(Ljava/lang/StackWalker$Option;)Ljava/lang/StackWalker", false));
insnList.add(new MethodInsnNode(INVOKEVIRTUAL, "java/lang/StackWalker", "getCallerClass", "()Ljava/lang/Class", false));
insnList.add(new VarInsnNode(Opcodes.ALOAD, 0));
insnList.add(new FieldInsnNode(Opcodes.GETFIELD, "org/bukkit/event/player/PlayerInteractEvent", "item", "Lorg/bukkit/inventory/ItemStack"));
insnList.add(new VarInsnNode(Opcodes.ILOAD, 1));

insnList.add(new MethodInsnNode(INVOKESTATIC, "me/cire3/sfbf/SFBFTransformer", "dump", "(Ljava/lang/Class;Ljava/lang/Object;Z)V", false));

            methodNode_isCancelled.instructions.insertBefore(methodNode_isCancelled.instructions.getFirst(), insnList);

byteCode = classWriter.toByteArray();

Only ran on target class obviously

dan1st•2mo ago

Can you show the stack trace?

cireOP•2mo ago

Stacktrace:

Exception in thread "main" java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:568)
        at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:491)
        at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:503)
Caused by: java.lang.UnsupportedClassVersionError
        at java.instrument/sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
        at java.instrument/sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:169)
        at me.cire3.sfbf.SFBFAgentEntryPoint.transform(SFBFAgentEntryPoint.java:39)
        at me.cire3.sfbf.SFBFAgentEntryPoint.premain(SFBFAgentEntryPoint.java:17)
        ... 6 more
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message Outstanding error when calling method in invokeJavaAgentMainMethod at s\src\java.instrument\share\native\libinstrument\JPLISAgent.c line: 619
*** java.lang.instrument ASSERTION FAILED ***: "success" with message invokeJavaAgentMainMethod failed at s\src\java.instrument\share\native\libinstrument\JPLISAgent.c line: 459
*** java.lang.instrument ASSERTION FAILED ***: "result" with message agent load/premain call failed at s\src\java.instrument\share\native\libinstrument\JPLISAgent.c line: 422
FATAL ERROR in native method: processing of -javaagent failed, processJavaStart failed

Exception in thread "main" java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:568)
        at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:491)
        at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:503)
Caused by: java.lang.UnsupportedClassVersionError
        at java.instrument/sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
        at java.instrument/sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:169)
        at me.cire3.sfbf.SFBFAgentEntryPoint.transform(SFBFAgentEntryPoint.java:39)
        at me.cire3.sfbf.SFBFAgentEntryPoint.premain(SFBFAgentEntryPoint.java:17)
        ... 6 more
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message Outstanding error when calling method in invokeJavaAgentMainMethod at s\src\java.instrument\share\native\libinstrument\JPLISAgent.c line: 619
*** java.lang.instrument ASSERTION FAILED ***: "success" with message invokeJavaAgentMainMethod failed at s\src\java.instrument\share\native\libinstrument\JPLISAgent.c line: 459
*** java.lang.instrument ASSERTION FAILED ***: "result" with message agent load/premain call failed at s\src\java.instrument\share\native\libinstrument\JPLISAgent.c line: 422
FATAL ERROR in native method: processing of -javaagent failed, processJavaStart failed

dan1st•2mo ago

Are you ure you are running it with java 17? How exactly are you running the application?

cireOP•2mo ago

yep javaw -javaagent:path/to/java/agent spigot-1.8.8.jar [server options here] ASM version 9.6 btw

dan1st•2mo ago

Does javaw -version show you any output?

cireOP•2mo ago

nvm, im actually running java -javaagent:path/to/agent -Xmx1G -Xms1G -jar spigot-1.8.8.jar java --version is openjdk 17.0.12

dan1st•2mo ago

Can you set the bytecode version with ClassWriter?

cireOP•2mo ago

i don't think so but im new to asm

dan1st•2mo ago

Where are you adding the instructions to the classWriter?

cireOP•2mo ago

Adding to the classNode which affects the classwriter

cireOP•2mo ago

cireOP•2mo ago

oh i forgot cn.accept(cw) brb i'll test if that fixes

JavaBot•2mo ago

When compiling Java applications to .class files, javac adds an integer representing the version it has been compiled for to the class file. Each Java version has a class file (major) version associated with it. A list with Java versions and the matching class file major version numbers can be found in this Stack Overflow question. In order to use a class, the JVM must be of a newer or equal version to the one specified in the class file.

dan1st•2mo ago

try cn.version = 52 before the cn.accept(cw)

cireOP•2mo ago

got it should i bother with minor version?

dan1st•2mo ago

cireOP•2mo ago

i dont think jdk cares k

dan1st•2mo ago

though maybe you need some bit magic

cireOP•2mo ago

oh yeah its like 16 msb is minor and 16 lsb is major right

dan1st•2mo ago

I think it might be ok just using 52 might be the less significant part

JavaBot•2mo ago

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cireOP•2mo ago

Okay, i downgraded to JVM 1.8

cireOP•2mo ago

to access sun.reflect

dan1st•2mo ago

If you are using Java 8 to run it, your agent needs to be compiled with that as well Why do you need that?

cireOP•2mo ago

yup i changed my gradle #getCallerClass my vm that needs the debugging runs jvm8 so StackWalker doesn't exist

dan1st•2mo ago

? If the target uses Java 8 then you'd need to compile your agent with java 8 anyways, yes

cireOP•2mo ago

i need to figure out whats calling the setCancelled method yup agent is now built with jvm8

dan1st•2mo ago

Can't you just set a breakpoint?

cireOP•2mo ago

3rd party jar on a vm not really

dan1st•2mo ago

What about just getting/printing the stack trace?

cireOP•2mo ago

im waiting for the vm to shutdown the server and reboot with new agent

dan1st•2mo ago

You can still do that

cireOP•2mo ago

i heavily dislike bytecode, getCallerClass is the easiest with bytecode huh

dan1st•2mo ago

You can attach a debugger and set breakpoints even for code that isn't yours as long as you can control the JVM in question

cireOP•2mo ago

ill take a look at that thanks

JavaBot•2mo ago

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cireOP•2mo ago

[SavageFactionsBugFixAgent] Transforming class PlayerInteractEvent
Exception in thread "main" java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:386)
        at sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:401)
Caused by: java.lang.ClassFormatError
        at sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
        at sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:144)
        at me.cire3.sfbf.SFBFAgentEntryPoint.transform(SFBFAgentEntryPoint.java:41)
        at me.cire3.sfbf.SFBFAgentEntryPoint.premain(SFBFAgentEntryPoint.java:19)
        ... 6 more
FATAL ERROR in native method: processing of -javaagent failed

[SavageFactionsBugFixAgent] Transforming class PlayerInteractEvent
Exception in thread "main" java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:386)
        at sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:401)
Caused by: java.lang.ClassFormatError
        at sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
        at sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:144)
        at me.cire3.sfbf.SFBFAgentEntryPoint.transform(SFBFAgentEntryPoint.java:41)
        at me.cire3.sfbf.SFBFAgentEntryPoint.premain(SFBFAgentEntryPoint.java:19)
        ... 6 more
FATAL ERROR in native method: processing of -javaagent failed

buh 😒

dan1st•2mo ago

What does it have to do with that?

cireOP•2mo ago

i have to write the dumping in bytecode

dan1st•2mo ago

It's pretty much new Exception("THIS IS INSERTED FOR DEBUGGING").printStackTrace()

cireOP•2mo ago

ohhhhhh shit

dan1st•2mo ago

and you can do the same in bytecode

cireOP•2mo ago

wait i'm stupid 💀

dan1st•2mo ago

or you could use Thread.getStackTrace() to get the current stack trace as a StackTraceElement[]

cireOP•2mo ago

i dont even need to printStackTrace i can just throw the exception and check console omg im stupid

dan1st•2mo ago

or that but that has a significant side effect but as I said, there's also the option of attaching a debugger and setting a breakpoint

cireOP•2mo ago

i'm only running this for debugging to figure out which plugin is cancelling the event i think i'll just throw an exception if cancelled param is true and check logs

dan1st•2mo ago

Note that the code calling the method could catch the exception

JavaBot•2mo ago

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Java agent throws UnsupportedClassVersionError when Instrumentation#retransformClasses is called.