soot.dava.toolkits.base.AST.transformations.RemoveEmptyBodyDefaultConstructor Maven / Gradle / Ivy

package soot.dava.toolkits.base.AST.transformations;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 1997 - 2018 Raja Vallée-Rai and others
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import soot.Body;
import soot.SootClass;
import soot.SootMethod;
import soot.dava.DavaBody;
import soot.dava.internal.AST.ASTMethodNode;
import soot.dava.internal.AST.ASTNode;
import soot.util.Chain;

/*
 * It has been seen that Dava's output contains the default constructor with just the invocation
 * to super()
 * 
 * According to the java specs the default constructor is not needed unless the constructor has been
 * overloaded.
 * 
 * The analysis checks whether there is only one constructor in the class being decompiled.
 * If this is true and the constructor IS THE DEFAULT CONSTRUCTOR i.e. no arguments
 * and has an empty body (there will always be a call to super
 * but that is invoked automatically....) we can remove the constructor from the code
 * also check tht the call to super has no arguments i.e. default super
 */
public class RemoveEmptyBodyDefaultConstructor {
  public static boolean DEBUG = false;

  public static void checkAndRemoveDefault(SootClass s) {
    debug("\n\nRemoveEmptyBodyDefaultConstructor----" + s.getName());
    List methods = s.getMethods();
    Iterator it = methods.iterator();
    List constructors = new ArrayList();

    while (it.hasNext()) {
      SootMethod method = (SootMethod) it.next();
      debug("method name is" + method.getName());
      if (method.getName().indexOf("") > -1) {
        // constructor add to constructor list
        constructors.add(method);
      }
    }

    if (constructors.size() != 1) {
      // cant do anything since there are more than one constructors
      debug("class has more than one constructors cant do anything");
      return;
    }

    // only one constructor check its default (no arguments)
    SootMethod constructor = constructors.get(0);
    if (constructor.getParameterCount() != 0) {
      // can only deal with default constructors
      debug("constructor is not the default constructor");
      return;
    }

    debug("Check that the body is empty....and call to super contains no arguments and delete");

    if (!constructor.hasActiveBody()) {
      debug("No active body found for the default constructor");
      return;
    }
    
    if (!constructor.isPublic()) {
      debug("Default constructor is not public.");
      return;
    }

    Body body = constructor.getActiveBody();
    Chain units = ((DavaBody) body).getUnits();

    if (units.size() != 1) {
      debug(" DavaBody AST does not have single root");
      return;
    }

    ASTNode AST = (ASTNode) units.getFirst();
    if (!(AST instanceof ASTMethodNode)) {
      throw new RuntimeException("Starting node of DavaBody AST is not an ASTMethodNode");
    }

    ASTMethodNode methodNode = (ASTMethodNode) AST;
    debug("got methodnode check body is empty and super has nothing in it");

    List