AppletTalk.com Java discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Adding constructor by bytecode instrumentation          AppletTalk.com Forum Index -> JVM, native methods and hardware View previous topic :: View next topic   Author Message Moritz Hammer Guest Posted: Tue Mar 20, 2007 10:31 am    Post subject: Adding constructor by bytecode instrumentation Hello, I am trying to use JVMTI to instrument the bytecode of all classes up to java.lang.Object. I need this so I can have a plain constructor (with some special signature) that does not do anything besides calling a superclass constructor that also does nothing (I want to simulate the effect of the actual constructor later). Right now, that does not sound too complicated to me: add another <init> method in the constant pool and a method block later. However, before I start, I wanted to ask people who know whether it can really be done: adding another constructor to java.lang.Object (or, at least, any direct subclass). Any pitfalls I am currently heading to? Is there any framework I can use (I do not want to permanently instrument all Java classes, so unless I am mistaken, I need to do it with JVMTI and implement it in C to get a grasp on java.lang.Object). Any hints are greatly appreciated, Moritz Back to top Chris Uppal Guest Posted: Wed Mar 21, 2007 3:59 am    Post subject: Re: Adding constructor by bytecode instrumentation Moritz Hammer wrote: Quote: However, before I start, I wanted to ask people who know whether it can really be done: adding another constructor to java.lang.Object (or, at least, any direct subclass). Yes it can be done. I've just tried it with JDK 1.6.0 and it seems to work fine. -- chris Back to top Moritz Hammer Guest Posted: Fri Mar 23, 2007 10:18 am    Post subject: Re: Adding constructor by bytecode instrumentation On Tue, 20 Mar 2007 22:59:01 +0000, Chris Uppal wrote: Quote: Yes it can be done. I've just tried it with JDK 1.6.0 and it seems to work fine. Just for the record: Indeed it works, and it only takes some minor modification to the java_crw_demo sources supplied with JDK 1.6 (persumably with 1.5 also) to get things working. There is a minor issue with obtaining a unique constructor signature, which I first attempted to get with a unique class reference; but this leads to problems, since the class loader cannot load the class it has been instrumented with... I would have to add that class to the bootstrap class loader, but then I just went with a very obscure combination of primitive types as the signature; it will be fun to see when I get clashes with existing constructors ;-) Thank you for your reply, Moritz Back to top Moritz Hammer Guest Posted: Mon Mar 26, 2007 12:24 pm    Post subject: Re: Adding constructor by bytecode instrumentation On Mon, 26 Mar 2007 11:36:05 +0100, Chris Uppal wrote: Quote: I used [D[D[D as the signature in my test. Now I come to think about it, I can't see why the double[] array doesn't suffer from the same problem (double[] is a subclass of Object after all). But, since it doesn't (at least with a Sun 1.6 JVM), a neat way of getting a unique signature is to use something like not.defined.Anywhere[] as the parameter type (pass a null if you want to invoke it, of course). Well, I am not entirely sure, but I think it is a bootstrap class loading issue. java.lang.Object gets loaded anyway, but not.defined.Anywhere requires a genuine ClassLoader to be loaded, unless put into the bootstrap classpath. I just checked, if you put it in the bootstrap classpath, things are working ok. Maybe a cleaner solution than using an "unlikely" signature - I used "DIFFZIFF" If not.defined.Anywhere is not put into the bootstrap classpath, the instrumented ClassLoader subclass gets screwed, since it requires a loaded instance of not.defined.Anywhere to get started, and this leads to very strange errors. Regards, Moritz Back to top Chris Uppal Guest Posted: Mon Mar 26, 2007 3:36 pm    Post subject: Re: Adding constructor by bytecode instrumentation Moritz Hammer wrote: Quote: There is a minor issue with obtaining a unique constructor signature, which I first attempted to get with a unique class reference; but this leads to problems, since the class loader cannot load the class it has been instrumented with... I used [D[D[D as the signature in my test. Now I come to think about it, I can't see why the double[] array doesn't suffer from the same problem (double[] is a subclass of Object after all). But, since it doesn't (at least with a Sun 1.6 JVM), a neat way of getting a unique signature is to use something like not.defined.Anywhere[] as the parameter type (pass a null if you want to invoke it, of course). -- chris Back to top Chris Uppal Guest Posted: Tue Mar 27, 2007 7:11 am    Post subject: Re: Adding constructor by bytecode instrumentation Moritz Hammer wrote: Quote: Maybe a cleaner solution than using an "unlikely" signature - I used "DIFFZIFF" If not.defined.Anywhere is not put into the bootstrap classpath, the instrumented ClassLoader subclass gets screwed, since it requires a loaded instance of not.defined.Anywhere to get started, and this leads to very strange errors. I'm probably misunderstanding you, but I don't see why you'd have to load class not.defined.Anywhere at all -- there's no need to create an instance just to call a method with that signature. I was able to call my additional Object constuctor with bytecode: new java/lang/Object aconst_null invokespecial java/lang/Object/<init> ([Lnot/defined/Anywhere;)V Which worked, in that my constuctor was called, but of course I had nothing comparable to your custom classloader in my test settup. -- chris Back to top Moritz Hammer Guest Posted: Tue Mar 27, 2007 8:58 am    Post subject: Re: Adding constructor by bytecode instrumentation On Tue, 27 Mar 2007 06:30:04 +0100, Chris Uppal wrote: Quote: I'm probably misunderstanding you, but I don't see why you'd have to load class not.defined.Anywhere at all -- there's no need to create an instance just to call a method with that signature. I was able to call my additional Object constuctor with bytecode: new java/lang/Object aconst_null invokespecial java/lang/Object/<init> ([Lnot/defined/Anywhere;)V Which worked, in that my constuctor was called, but of course I had nothing comparable to your custom classloader in my test settup. I instrument every class with the additional constructor, and if not.defined.Anywhere is not in the bootclasspath, I get the exception: Error occurred during initialization of VM java.lang.NullPointerException at java.util.Hashtable.put(Hashtable.java:394) at java.lang.System.initProperties(Native Method) at java.lang.System.initializeSystemClass(System.java:1072) This is independent on whether not.defined.Anywhere is in the classpath or not. I excluded various classes from instrumentation, and eventually found that if I exclude the ClassLoader subclasses and some classes from sun.* packages (apparently related to reading the actual bytecode), thinks work ok. Therefore I suspect that the ClassLoader cannot be instrumented. If I instrument java.lang.Object only, things are ok even if not.defined.Anywhere is indeed not defined anywhere. But then I get a ClassNotFoundException when I use reflection to see the constructors. I have not tried assembling the bytecode to invoke the special java.lang.Object constructor. That might work. I assume you are right, and not.defined.Anywhere needs not be loaded if it is used for the signature of a constructor invoked directly. If reflection is used to get the constructor, and I guess this is the case with the ClassLoader subclasses, then not.defined.Anywhere needs to be loaded. Regards, Moritz Back to top Cyril Shelest Guest Posted: Fri Mar 30, 2007 1:23 am    Post subject: Re: Adding constructor by bytecode instrumentation Hi, I did the same you mentioned. In my product that written with pure C++ I developed a code that parses Java bytecode, decomposes it into a syntax tree. The syntax tree is modified to add new methods/constructors. And then from this syntax tree I generate a new Java bytecode. The products that include this algorithm are avalable at http://www.simtel.net/product.php[id]94368[SiteID]simtel.net and http://www.simtel.net/product.php[id]93174[SiteID]simtel.net "Moritz Hammer" <newsgroup001@hammer-tour.com> wrote in message news:etod6b$7f1$1 (AT) news (DOT) lrz-muenchen.de... Quote: Hello, I am trying to use JVMTI to instrument the bytecode of all classes up to java.lang.Object. I need this so I can have a plain constructor (with some special signature) that does not do anything besides calling a superclass constructor that also does nothing (I want to simulate the effect of the actual constructor later). Right now, that does not sound too complicated to me: add another <init> method in the constant pool and a method block later. However, before I start, I wanted to ask people who know whether it can really be done: adding another constructor to java.lang.Object (or, at least, any direct subclass). Any pitfalls I am currently heading to? Is there any framework I can use (I do not want to permanently instrument all Java classes, so unless I am mistaken, I need to do it with JVMTI and implement it in C to get a grasp on java.lang.Object). Any hints are greatly appreciated, Moritz Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         AppletTalk.com Forum Index -> JVM, native methods and hardware All times are GMT Page 1 of 1   Jump to: Select a forum Java Newsgroups----------------Java DiscussionsWeb-based java games comp.lang.java 3D Graphics API's for Java Java: Support and criticism Java System Announcements comp.lang.java.api JavaBeans Java and CORBA Java and Databases comp.lang.java.developer Java GUI Toolkits Java Help comp.lang.java.javascript JVM, native methods and hardware comp.lang.java.misc Java Language Programming Security and Java comp.lang.java.setup Java Software Tools comp.lang.java.tech ibm.software.java.linux  Non-English Java Newsgroups----------------Java Language (German)Language Java (Français)Java (Italian)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.