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POWhy does this simple Java bytecode cause a StackOverflow error?
 

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  1. POWhy does this simple Java bytecode cause a StackOverflow error?
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    <p>I need to instrument native methods to make a simple static call before executing normally. Because the methods are native, I have to use the <a href="http://download.oracle.com/javase/6/docs/api/java/lang/instrument/Instrumentation.html#setNativeMethodPrefix%28java.lang.instrument.ClassFileTransformer,%20java.lang.String%29" rel="nofollow">"setNativePrefix" feature</a> and wrap the native methods with an intermediate call with the original method signature. </p> <p>After what I thought was a simple bytecode change to accomplish this, I'm getting a StackOverflowError right before the wrapper method gets executed even though the stack is basically empty. Here's my test class:</p> <pre><code>public class SimpleTest { public static void main(String[] args) throws IOException { Perf.getPerf().highResCounter(); } } </code></pre> <p>Normally, that program would produce nothing on the console. However, my instrumented bytecode executes a println() before executing the native method $wrapper$highResCounter(). This can be seen in the relevant Perf class bytecode after instrumentation:</p> <pre><code>public long highResCounter() { getstatic PrintStream System.out ldc String Constant "this is an instrumented println" invokevirtual void PrintStream.println(String) aload 0 invokevirtual long Perf.$wrapped$highResCounter() lreturn } public native long $wrapped$highResCounter(); </code></pre> <p>I'm sort of new to Java bytecode, so I probably made a mistake here. Here's the output of the program, which shows that the println() gets executed, but somewhere after the first <em>invokevirtual</em> call a StackOverflowError is thrown:</p> <pre><code>this is an instrumented println call Exception in thread "main" java.lang.StackOverflowError at com.foo.SimpleTest.main(SimpleTest.java:17) </code></pre> <p>What could be causing this StackOverflowError? And how do I fix it?</p>
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    1. CODo you have the complete SimpleTest.java for us? Have you stepped through with a debugger? Maybe you aren't running what you think you are running. (Reminds me of a bug years ago I searched for hours until I realized that my classpath was pointing to old class files :)
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      1. USJochen Bedersdorfer
    2. COThat is the entirety of the class, minus import statement and package identifier. No static initializers or anything.
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    3. COIt also happens on any native method: like StrictMath.sin(). I don't think it has anything to do with Perf.
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