[jboss-jira] [JBoss JIRA] Created: (JASSIST-61) clone on a member array causes an NPE in MemberResolver when instrumenting

[Yanic Inghelbrecht (JIRA)]

clone on a member array causes an NPE in MemberResolver when instrumenting
--------------------------------------------------------------------------

                 Key: JASSIST-61
                 URL: http://jira.jboss.com/jira/browse/JASSIST-61
             Project: Javassist
          Issue Type: Bug
         Environment:  Javassist 3.7.1 (latest from cvs HEAD)
Eclipse Version: 3.3.1.1, Build id: M20071023-1652 running in the JRE included with JDK1.6.0_03 on winXP and compiler compliance set to 5.0.
Show »
Javassist 3.7.1 (latest from cvs HEAD) Eclipse Version: 3.3.1.1, Build id: M20071023-1652 running in the JRE included with JDK1.6.0_03 on winXP and compiler compliance set to 5.0.

            Reporter: Yanic Inghelbrecht
         Assigned To: Shigeru Chiba


In the instrumentation of JHotDraw, I encountered an NPE in javassist.compiler.MemberResolver#lookupMethod(...).

When replacing a method call with a trivial block, a null pointer exception occurs in MemberResolver if that method calls clone() on a member array. The method that is being looked up is the clone method.

The simplest testcase to reproduce this bug consists of two classes : Client (to be instrumented) and Main (does the instrumentation). 

It produces the following stack trace :

Exception in thread "main" java.lang.ClassNotFoundException: caught an exception while obtaining a class file for test_clone_member_array.Client
	at javassist.Loader.findClass(Loader.java:359)
	at javassist.Loader.loadClass(Loader.java:311)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at test_clone_member_array.Main.main(Main.java:25)
Caused by: java.lang.NullPointerException
	at javassist.compiler.MemberResolver.lookupMethod(MemberResolver.java:110)
	at javassist.compiler.MemberResolver.lookupMethod(MemberResolver.java:96)
	at javassist.compiler.TypeChecker.atMethodCallCore(TypeChecker.java:704)
	at javassist.compiler.TypeChecker.atCallExpr(TypeChecker.java:681)
	at javassist.compiler.JvstTypeChecker.atCallExpr(JvstTypeChecker.java:156)
	at javassist.compiler.ast.CallExpr.accept(CallExpr.java:45)
	at javassist.compiler.Javac$1.setReturnType(Javac.java:459)
	at javassist.compiler.JvstTypeChecker.atCallExpr(JvstTypeChecker.java:146)
	at javassist.compiler.ast.CallExpr.accept(CallExpr.java:45)
	at javassist.compiler.TypeChecker.atVariableAssign(TypeChecker.java:248)
	at javassist.compiler.TypeChecker.atAssignExpr(TypeChecker.java:217)
	at javassist.compiler.ast.AssignExpr.accept(AssignExpr.java:38)
	at javassist.compiler.CodeGen.doTypeCheck(CodeGen.java:241)
	at javassist.compiler.CodeGen.atStmnt(CodeGen.java:329)
	at javassist.compiler.ast.Stmnt.accept(Stmnt.java:49)
	at javassist.compiler.CodeGen.atStmnt(CodeGen.java:350)
	at javassist.compiler.ast.Stmnt.accept(Stmnt.java:49)
	at javassist.compiler.Javac.compileStmnt(Javac.java:568)
	at javassist.expr.MethodCall.replace(MethodCall.java:234)
	at test_clone_member_array.Main$MyTranslator.edit(Main.java:48)
	at javassist.expr.ExprEditor.loopBody(ExprEditor.java:191)
	at javassist.expr.ExprEditor.doit(ExprEditor.java:90)
	at javassist.CtBehavior.instrument(CtBehavior.java:548)
	at test_clone_member_array.Main$MyTranslator.modify(Main.java:40)
	at test_clone_member_array.Main$MyTranslator.onLoad(Main.java:35)
	at javassist.Loader.findClass(Loader.java:340)
	... 3 more


The source code for this testcase :

// ----- file Client.java

package test_clone_member_array;
public class Client {
	private Object[] oa;

	public void test() throws Exception {
		this.oa.clone();
	}
}

// ----- file Main.java

package test_clone_member_array;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.Loader;
import javassist.NotFoundException;
import javassist.Translator;
import javassist.expr.ExprEditor;
import javassist.expr.MethodCall;


public class Main {
	public static void main(String[] args) throws Exception {
		ClassPool pool = new ClassPool(true);
		Loader cl = new Loader();
		try {
			cl.addTranslator(pool, new MyTranslator());
		} catch (Exception e) {
			e.printStackTrace();
			return;
		}
		
		// load the Client class
		Class clientClass=cl.loadClass("test_clone_member_array.Client");
		
		// create an instance
		Object client=clientClass.newInstance();
	}
	
	static public class MyTranslator extends ExprEditor implements Translator {

		public void onLoad(ClassPool pool, String classname) throws NotFoundException, CannotCompileException {
			CtClass cc = pool.get(classname);
			modify(cc);
		}

		public void modify(CtClass c) throws CannotCompileException {
			for (CtMethod m : c.getMethods()) {
				m.instrument(this);
			}
		}

		@Override
		public void edit(MethodCall mc) throws CannotCompileException {
			// no changes, for simplicity's sake
			String block = "{$_=$proceed($$);}";
			mc.replace(block);
		}

		public void start(ClassPool pool) throws NotFoundException, CannotCompileException {
			// do nothing
		}
	}
}

I hope it's an easy fix for you, I did not find a usable workaround.

Thanks in advance.

Best regards,
Yanic

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators: http://jira.jboss.com/jira/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira