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

[Yanic Inghelbrecht (JIRA)]

    [ http://jira.jboss.com/jira/browse/JASSIST-61?page=comments#action_12409378 ] 
            
Yanic Inghelbrecht commented on JASSIST-61:
-------------------------------------------

Oh, the 'throws Exception' can be dropped from the signature of Client#test().

> 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

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