added presentation (and the used patch)

jrd-WeakPoint/01.markdown

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+# java-runtime-(de)compiler
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+https://github.com/judovana/java-runtime-decompiler
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+	* why? Because we can!
+		* binary blob reproducers
+			* obfuscated
+			* debuginfo
+		* swap lines
+		* oversee instrumetnations
+	* what!
+	* how? This talk!
+		* standard APIS only
+
+Jiri Vanek
+Red Hat
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jrd-WeakPoint/02.markdown

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+# Demo I
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+	* install
+	* overview
+	* list and read
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jrd-WeakPoint/03.markdown

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+# How - Agent attach I
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+https://docs.oracle.com/javase/8/docs/jdk/api/attach/spec/com/sun/tools/attach/VirtualMachine.html
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+```
+VirtualMachine vm = VirtualMachine.attach(Integer.toString(pid));
+vm.loadAgent(agentJar,”param1:value1,param:value2,…valueN”);
+vm.detach();
+```
+	* Agent is just bunch of classes which does nothing. No logic, no communication
+		* unless  you write that
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jrd-WeakPoint/04.markdown

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+# How - Agent attach II
+```
+public static void premain(String agentArgs, Instrumentation inst); 
+```
+	* Is  the launched start point after agent is loaded, and instrumentation is what matters
+	* For example you can open ServerSocket to receive commands
+	* Agents can not be unloaded. Can be just turned off in best effort
+	* And you can register transformer!
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jrd-WeakPoint/05.markdown

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+# Demo II
+.
+	* self modifications
+		* classes
+		* classloaders I
+		* desompilers/disassemblers/hex
+			* –-patch-module
+			* (keyword based) code completion
+			* inner classes
+			* additional sources/binaries/diffs
+		* back compile/assemble
+		* real changes
+		* bytecode level
+	* java.lang.Override
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jrd-WeakPoint/06.markdown

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+# How - Transformers
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+https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/Instrumentation.html
+https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/ClassFileTransformer.html
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+```
+Transformer transformer = new Transformer();
+inst.addTransformer(transformer, true);
+//repeat(work-earn-spend)until die
+instrumentation.removeTransformer(transformer);
+```
+	* Classes can NEVER EVER be unloaded
+		* Depends on JVM?
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jrd-WeakPoint/07.markdown

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+# Demo III
+.
+	* self modifications
+	* Class Redefinition - hotswap - limits
+		* No new methods, no new fields, no renaming, no signatures…
+			* even non used BYTECODE fieLds limits
+			* bytecode level!
+		* Generally you can only change content of methods bodies (including new variables)
+			* byteman and JRD apis
+			* not add jar/classes
+			* dcevm/jrebel
+	* global counter
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jrd-WeakPoint/08.markdown

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+# How - Trasnformer api
+```
+byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer)
+Byte[] -> byte[] //… can not be more simple
+```
+	* asm ow2	
+	* If the class was never used, it will not be reachable from there
+	* Calling Class.forName on it will then do the job
+...
+	* So what actually JRD simply does, is **Map<classname,Map<classloader,body[]>** where overrides are stored, ad transform returns  hit front hat map if found
+	* Similarly, if we require class, to send to client, we record it in this method
+	* You have to return the “modified” bytecode everytime class redefiniton happens (which is pretty often)
+	* Depends on VM, but on hotspot, one of the few places where it will not be picked up is during loop in method
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jrd-WeakPoint/09.markdown

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+# How - chaining of agents/transformers
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+	* agents are modyfying and non modyfying
+	* agents are processed in order of attach
+	* modyfing (with Transformer) agents processed in order of reistered Transformer
+	* original class definition (immutable) -> byte[] ->
+		* Transformer1 -> byte[] ->
+		* Transformer.. -> byte[] ->
+		* TransformerN.. -> byte[] ->
+		* final class definition usage
+	*the full chain is always called. 
+		* if you unregister, changes are gone
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jrd-WeakPoint/10.markdown

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+# Demo IV
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+	* byteman
+		* second agent!
+		* silent non sucess
+	* chaining of agents
+	* code coverage instrumentation
+	* multiple class defintions classloaders II
+		* no change in gui
+	* modules
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jrd-WeakPoint/11.markdown

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+# Demo V
+
+	* cli
+	* adding classes
+		* ServerImplNw
+	* patch
+		* not as simple
+		* split?
+		* full java files?
+		* full binary classes?
+	* Future - debugger attach
+		* source-codeless IDE
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jrd-WeakPoint/12.markdown

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+# More hardcore ways to overcome hotswap limitations
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+	* Class Redefinition - hotswap - limits
+		* No new methods, no new fields, no renaming…
+		* Generally you can only change content of methods bodies (including new variables)
+		* DCEVM JDK based on Phd these is removing those limits with (huge) cost of performance
+		* Take ages after JDK (jdk 17 not yet properly out, last udpate December 2022)
+	* Jetbrains took it recently over
+	* Jrebel JVMTI hacks
+	* Tricks
+		* In agent predefined map of objects to store fields/methods
+		* Bytemen do it behind the doors
+		* JRD offer sclumsy appi for it
+		* Add a new class with reimplementation and call it where needed
+		* inst.appendToSystem/BootClassLoader
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