bytecode

I need to change a call to a function inside another function during run-time. Consider the following code: def now(): print "Hello World!" class Sim: def __init__(self, arg, msg): self.msg = msg self.func = arg self.patch(self.func) def now(self): print self.msg def run(self): self.func() def patch(self, func): # Any references to the global now() in func # are replaced with the self.now() method. def myfunc(): now() Then ... >>> a = Sim(myfunc, "Hello Locals #1") >>> b = Sim(myfunc, "Hello Locals #2") >>> b.run() Hello Locals #2 >>> a.run() Hello Locals #1 One user has written code, myfunc()

There are several computer programming languages using JVM bytecode as, lets say, target language for their interpreter/compilers. It seems to me that many new programming languages (less than 15 years old) run over JVM and I wonder whether explicit memory deallocation is forbidden for all of them: Is it possible to explicitly allocate-deallocate memory using in bytecode through any instruction? Is, on de contrary, the garbage collector always resposible for memory liberation? The JVM abstracts away all memory management. There is no bytecode for memory deallocation, just as there is no

I was wondering if there's an obvious and quick way of when analyzing a constructor's bytecode, to determine where the super() code ends in. More concretely, and in sharp contrast to Java, where a call in the constructor to any super() constructor method is optional (or rather, when not present -- implicit), in the bytecode world it is always needed. For black magic purposes I'm in need of knowing just by bytecode analysis and by the simplest method available, what's the INVOKESPECIAL call that corresponds to the Java world's super() call. I'll leave you here with a hard example: public static

When decompiling a specific jar using java decompiler (http://java.decompiler.free.fr/) I got some strange code I cannot identify what is. can someone help me? the code is something like: Foo.access$004(Foo.this); or this Bar.access$006(Bar.this); or else Baz.access$102(Baz.this, true) What are these methods access$004 , access$006 and access$102 ? Synthetic methods like this get created to support acessing private methods of inner classes. Since inner classes were not part of the initial jvm version, the access modifiers could not really handle this case. The solution was to create additional

I am wondering why the Exception in the following bytecode (used to throw an Exception) is duplicated. NEW java/lang/IllegalArgumentException DUP INVOKESPECIAL java/lang/IllegalArgumentException <init> ()V ATHROW I'll analyze this line by line where [] = new stack after that op is used: NEW puts a new IllegalArgumentException onto the stack [SomeIllegalArgumentException] DUP duplicates it [SomeIllegalArgumentException, SomeIllegalArgumentException] INVOKESPECIAL pops off the top one and initializes it by calling it's <init> method [SomeIllegalArgumentException] (The init method will not return

Our project does some Java bytecode instrumentation. And we stumbled upon some strange behavior. Suppose the following code snippet: public void a() { new Integer(2); } Oracle's javac compiles the above into the following bytecode: 0: new #2; //class java/lang/Integer 3: dup 4: iconst_2 5: invokespecial #3; //Method java/lang/Integer."<init>":(I)V 8: pop 9: return and Eclipse's compiler into: 0: new #15; //class java/lang/Integer 3: iconst_2 4: invokespecial #17; //Method java/lang/Integer."<init>":(I)V 7: return As you can see, Oracle compiler produces "dup" after "new", whereas Eclipse doesn

I was asked the following question in an exam today. I still don't know the answer. Java uses stack for byte code in JVM. Each instruction is of one byte, so how many such instructions (per byte code) are possible in an operating system. All I know is that the stack is 32 bits wide. Can anybody help me (I am a beginner in JVM)? The expected answer was almost certainly 256, because there are 256 possible values of a byte. This of course has nothing to do with the actual JVM instruction set. The number of possible instructions can vary anywhere from a couple dozen to an exponentially large