[Soot-list] How can I avoid the java.lang.VerifyError?

[Sunny]

Hi,

I am trying to record the values of a local variable before and after an
assignment to it. Below
I listed my code snippet to achieve this and described two problems.

The source code to be instrumented (part of TestInvoke.java):

public void test()
{
   String x;
   x = "from test";
}


The method to report the value as well as the containing context:

public static void reportLocal(Object enclosingObj, Object value)
{
   System.out.println("enclosing = " + enclosingObj + ", value = " + value);
}

And finally, the code in internalTransform to insert statements:

 Vector args = new Vector();
 args.add(body.getThisLocal());
 args.add(loc);
 InvokeExpr reportExpr = Jimple.v().newStaticInvokeExpr(reportLocal.makeRef(),
args);
 Stmt reportStmtBefore = Jimple.v().newInvokeStmt(reportExpr);
 // Stmt reportStmtAfter = Jimple.v().newInvokeStmt(reportExpr);
 units.insertBefore(reportStmtBefore, stmt);
 // units.insertAfter(reportStmtAfter, stmt);


The above code only injects an invoke statement before the assignment.

Problem1:

After the TestInvoke.java is instrumented and executed, I always got the
exception:

java.lang.VerifyError: (class: src/TestInvoke, method: test signature: ()V)
Accessing value from uninitialized register 1
Exception in thread "main"

How should I avoid this error and obtain the variable's value before
assignment? It worked if I only injected
invoke statements AFTER the assignment, as the commented lines show.

Problem2:
There are two kinds of local variables in a jimple method, those implicitly
defined by
jimple representing stack positions, and those that are explicitly defined
by a user's program. Can I distinguish
these two simply by using Local#getName().startsWith("$"))?

Thank you very much for any help!

Sunny
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