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POHow to statically analyze reference types passed to each bytecode instruction?
 

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  1. POHow to statically analyze reference types passed to each bytecode instruction?
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    <p>I have rewritten the question (the question remains the same, just with less background noise) in hopes of creating less confusion directed at all the wrong things - due to this, some of the comments below may seem out of context.</p> <p>Analyzing Java bytecode, what is the easiest way to find all the possible reference types given as parameters for a given Java bytecode instruction? I'm interested in the type of the reference, that is, that a given putfield instruction will receive an Integer, or that it might receive an Integer or a Float, etc.</p> <p>For example, consider this code block:</p> <pre><code> 0: aload_1 1: invokestatic #21; //Method java/lang/Integer.valueOf:(Ljava/lang/String;)Ljava/lang/Integer; 4: astore_2 5: aload_2 6: ifnull 17 9: aload_0 10: aload_2 11: putfield #27; //Field value:Ljava/lang/Number; 14: goto 25 17: aload_0 18: iconst_0 19: invokestatic #29; //Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer; 22: putfield #27; //Field value:Ljava/lang/Number; 25: return </code></pre> <p>We can deduce that the putfield instruction at pc 11 will receive a ref type of <strong>Integer</strong>.</p> <pre><code>0: aload pushes ref type of String (the method param) 1: invokestatic pops the ref type and pushes a ref type of Integer (invoked method return type) 4: astore pops the ref type of Integer and stores it in local variable 2 5: aload pushes the ref type of Integer from local variable 2 6: ifnull pops the ref type of Integer and conditionally jumps to pc 17 9: aload pushes "this" 10: aload pushes the ref type of Integer 11: putfield: we know we have a ref type of Integer that the instruction will put in field </code></pre> <p>Do any of the bytecode/code analysis libraries do this for me, or do I have to write this myself? The <a href="http://asm.ow2.org/" rel="nofollow">ASM project</a> has an <a href="http://asm.ow2.org/asm33/javadoc/user/org/objectweb/asm/tree/analysis/Analyzer.html" rel="nofollow">Analyzer</a>, which seems like it might do part of the work for me, but really not enough to justify switching to using it.</p> <p>EDIT: I have done my homework and have studied the <a href="http://java.sun.com/docs/books/jvms/second_edition/html/VMSpecTOC.doc.html" rel="nofollow">Java VM Spec</a>.</p>
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    1. COYou want to compile .java-files. You don't have the dependencies. You extract the signatures from the compiled (.class) versions of the .java files.... uhm, why did you want to compile the java-files in the first place, if you had the .class to do the analysis on?
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    2. CO@aioobe: OK, a valid question (duly upvoted), there are several scenarios. One is, I lost the .java file, and I want to change the class. Another one is that I may have never had the .java in the first place (decompilation). Yet another one I described in the question itself, when I'm creating a new class and I need the dependencies of a set of compiled classes just for the compiler.
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    3. COI'm not really looking to validate the idea, that's what my PoC was for and it validated the idea for me nicely, although I'm happy to try and clarify. But at the end of the day, I presented the idea to help understand the focus of my question, which is the technical part about data flow analysis. That's where, dear StackOverflow, I could really use your help.
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