Bytecode and Objects

Posted by HH on Stack Overflow See other posts from Stack Overflow or by HH
Published on 2010-05-07T18:03:20Z Indexed on 2010/05/07 18:08 UTC
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java

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bytecode

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verification

Hey everyone,

I am working on a bytecode instrumentation project. Currently when handling objects, the verifier throws an error most of the time. So I would like to get things clear concerning rules with objects (I read the JVMS but couldn't find the answer I was looking for):

I am instrumenting the NEW instruction:

original bytecode

NEW <MyClass>
DUP
INVOKESPECIAL <MyClass.<init>>

after instrumentation

NEW <MyClass>
DUP
INVOKESTATIC <Profiler.handleNEW>
DUP
INVOKESPECIAL <MyClass.<init>>

Note that I added a call to Profiler.handleNEW() which takes as argument an object reference (the newly created object).

The piece of code above throws a VerificationError. While if I don't add the INVOKESTATIC (leaving only the DUP), it doesn't. So what is the rule that I'm violating? I can duplicate an uninitialized reference but I can't pass it as parameter? I would appreciate any help. Thank you

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