OptimisticStateTransformerFactory.java

/*
 * OptimisticStateTransformerFactory.java - This file is part of the Jakstab project.
 * Copyright 2007-2015 Johannes Kinder <jk@jakstab.org>
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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 Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, see <http://www.gnu.org/licenses/>.
 */
package org.jakstab.cfa;

import java.util.Collections;
import java.util.Set;

import org.jakstab.Program;
import org.jakstab.analysis.AbstractState;
import org.jakstab.asm.AbsoluteAddress;
import org.jakstab.rtl.Context;
import org.jakstab.cfa.RTLLabel;
import org.jakstab.rtl.expressions.ExpressionFactory;
import org.jakstab.rtl.expressions.RTLExpression;
import org.jakstab.rtl.expressions.RTLNumber;
import org.jakstab.rtl.statements.*;
import org.jakstab.util.FastSet;
import org.jakstab.util.Logger;
import org.jakstab.util.Tuple;

/**
 * Assumes that all calls return. Treats calls as two way branches with one call 
 * and one UnknownProcedureCall-edge, returns are treated as halts. Useful for
 * disassembly of large compiler generated executables. 
 * 
 * @author Johannes Kinder
 */
public class OptimisticStateTransformerFactory extends ResolvingTransformerFactory {

	private static final Logger logger = Logger.getLogger(OptimisticStateTransformerFactory.class);

	@Override
	public Set<CFAEdge> resolveGoto(final AbstractState a, final RTLGoto stmt) {

		assert stmt.getCondition() != null;
		Set<CFAEdge> results = new FastSet<CFAEdge>();

		// Calls always get a fallthrough edge in optimistic mode
		if (stmt.getType() == RTLGoto.Type.CALL) {
			RTLLabel nextLabel = stmt.getNextLabel();

			if (Program.getProgram().getHarness().contains(stmt.getAddress())) {
				nextLabel = new RTLLabel(Program.getProgram().getHarness().getFallthroughAddress(stmt.getAddress()));
			}

			if (nextLabel != null) {
				RTLUnknownProcedureCall unknownCallEdge = new RTLUnknownProcedureCall(stmt);
				unknownCallEdge.setLabel(stmt.getLabel());
				unknownCallEdge.setNextLabel(nextLabel);
				results.add(new CFAEdge(stmt.getLabel(), nextLabel, unknownCallEdge));
				sound = false;
			}
		} 
		// Replace return with halt, since control flow passes over calls anyway
		else if (stmt.getType() == RTLGoto.Type.RETURN) {
			sound = false;
			return Collections.emptySet();
		}

		Set<Tuple<RTLNumber>> valuePairs = a.projectionFromConcretization(
				stmt.getCondition(), stmt.getTargetExpression());
		for (Tuple<RTLNumber> pair : valuePairs) {
			RTLNumber conditionValue = pair.get(0);
			RTLNumber targetValue = pair.get(1);
			RTLLabel nextLabel;
			// assume correct condition case 
			assert conditionValue != null;
			RTLExpression assumption = 
					ExpressionFactory.createEqual(stmt.getCondition(), conditionValue);
			if (conditionValue.equals(ExpressionFactory.FALSE)) {
				// assume (condition = false), and set next statement to fallthrough
				nextLabel = stmt.getNextLabel();
			} else {
				if (targetValue == null) {
					// if target could not be resolved, just leave the edge out for now
					// Can only happen here with indirect jumps
					logger.info(stmt.getLabel() + ": Cannot resolve target expression " + 
							stmt.getTargetExpression() + ".");
					logger.debug("State is: " + a);
					sound = false;
					unresolvedBranches.add(stmt.getLabel());
					continue;
				} else {
					// assume (condition = true AND targetExpression = targetValue)
					assumption = ExpressionFactory.createAnd(
							assumption,
							ExpressionFactory.createEqual(
									stmt.getTargetExpression(),
									targetValue)
							);
					// set next label to jump target
					nextLabel = new RTLLabel(new AbsoluteAddress(targetValue));
				}
			}
			assumption = assumption.evaluate(new Context());
			RTLAssume assume = new RTLAssume(assumption, stmt);
			assume.setLabel(stmt.getLabel());
			assume.setNextLabel(nextLabel);
			results.add(new CFAEdge(assume.getLabel(), assume.getNextLabel(), assume));
		}
		return results;
	}

}