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package soot.dexpler;
/*-
* #%L
* Soot - a J*va Optimization Framework
* %%
* Copyright (C) 2012 Michael Markert, Frank Hartmann
*
* (c) 2012 University of Luxembourg - Interdisciplinary Centre for
* Security Reliability and Trust (SnT) - All rights reserved
* Alexandre Bartel
*
* %%
* 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
* <http://www.gnu.org/licenses/lgpl-2.1.html>.
* #L%
*/
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import soot.ArrayType;
import soot.Body;
import soot.Local;
import soot.SootMethodRef;
import soot.Type;
import soot.Unit;
import soot.UnknownType;
import soot.Value;
import soot.ValueBox;
import soot.dexpler.tags.ObjectOpTag;
import soot.jimple.AbstractStmtSwitch;
import soot.jimple.ArrayRef;
import soot.jimple.AssignStmt;
import soot.jimple.BinopExpr;
import soot.jimple.CastExpr;
import soot.jimple.ClassConstant;
import soot.jimple.ConditionExpr;
import soot.jimple.DefinitionStmt;
import soot.jimple.EnterMonitorStmt;
import soot.jimple.ExitMonitorStmt;
import soot.jimple.FieldRef;
import soot.jimple.IdentityStmt;
import soot.jimple.IfStmt;
import soot.jimple.InstanceFieldRef;
import soot.jimple.IntConstant;
import soot.jimple.InvokeExpr;
import soot.jimple.InvokeStmt;
import soot.jimple.LengthExpr;
import soot.jimple.LongConstant;
import soot.jimple.NewArrayExpr;
import soot.jimple.NewExpr;
import soot.jimple.NullConstant;
import soot.jimple.ReturnStmt;
import soot.jimple.StaticFieldRef;
import soot.jimple.Stmt;
import soot.jimple.StringConstant;
import soot.jimple.ThrowStmt;
import soot.jimple.internal.AbstractInstanceInvokeExpr;
import soot.jimple.internal.AbstractInvokeExpr;
/**
* BodyTransformer to find and change IntConstant(0) to NullConstant where locals are used as objects.
*
* @author Michael Markert
*/
public class DexNullTransformer extends AbstractNullTransformer {
// Note: we need an instance variable for inner class access, treat this as
// a local variable (including initialization before use)
private boolean usedAsObject;
private boolean doBreak = false;
public static DexNullTransformer v() {
return new DexNullTransformer();
}
private Local l = null;
@Override
protected void internalTransform(final Body body, String phaseName, Map<String, String> options) {
final DexDefUseAnalysis localDefs = new DexDefUseAnalysis(body);
AbstractStmtSwitch checkDef = new AbstractStmtSwitch() { // Alex: should also end as
// soon as detected as not
// used as an object
@Override
public void caseAssignStmt(AssignStmt stmt) {
Value r = stmt.getRightOp();
if (r instanceof FieldRef) {
usedAsObject = isObject(((FieldRef) r).getFieldRef().type());
doBreak = true;
return;
} else if (r instanceof ArrayRef) {
ArrayRef ar = (ArrayRef) r;
if (ar.getType() instanceof UnknownType) {
usedAsObject = stmt.hasTag(ObjectOpTag.NAME); // isObject
// (findArrayType
// (g,
// localDefs,
// localUses,
// stmt));
} else {
usedAsObject = isObject(ar.getType());
}
doBreak = true;
return;
} else if (r instanceof StringConstant || r instanceof NewExpr || r instanceof NewArrayExpr
|| r instanceof ClassConstant) {
usedAsObject = true;
doBreak = true;
return;
} else if (r instanceof CastExpr) {
usedAsObject = isObject(((CastExpr) r).getCastType());
doBreak = true;
return;
} else if (r instanceof InvokeExpr) {
usedAsObject = isObject(((InvokeExpr) r).getType());
doBreak = true;
return;
} else if (r instanceof LengthExpr) {
usedAsObject = false;
doBreak = true;
return;
// introduces alias
}
}
@Override
public void caseIdentityStmt(IdentityStmt stmt) {
if (stmt.getLeftOp() == l) {
usedAsObject = isObject(stmt.getRightOp().getType());
doBreak = true;
return;
}
}
};
AbstractStmtSwitch checkUse = new AbstractStmtSwitch() {
private boolean examineInvokeExpr(InvokeExpr e) {
List<Value> args = e.getArgs();
List<Type> argTypes = e.getMethodRef().parameterTypes();
assert args.size() == argTypes.size();
for (int i = 0; i < args.size(); i++) {
if (args.get(i) == l && isObject(argTypes.get(i))) {
return true;
}
}
// check for base
SootMethodRef sm = e.getMethodRef();
if (!sm.isStatic()) {
if (e instanceof AbstractInvokeExpr) {
AbstractInstanceInvokeExpr aiiexpr = (AbstractInstanceInvokeExpr) e;
Value b = aiiexpr.getBase();
if (b == l) {
return true;
}
}
}
return false;
}
@Override
public void caseInvokeStmt(InvokeStmt stmt) {
InvokeExpr e = stmt.getInvokeExpr();
usedAsObject = examineInvokeExpr(e);
doBreak = true;
return;
}
@Override
public void caseAssignStmt(AssignStmt stmt) {
Value left = stmt.getLeftOp();
Value r = stmt.getRightOp();
if (left instanceof ArrayRef) {
ArrayRef ar = (ArrayRef) left;
if (ar.getIndex() == l) {
doBreak = true;
return;
} else if (ar.getBase() == l) {
usedAsObject = true;
doBreak = true;
return;
}
}
if (left instanceof InstanceFieldRef) {
InstanceFieldRef ifr = (InstanceFieldRef) left;
if (ifr.getBase() == l) {
usedAsObject = true;
doBreak = true;
return;
}
}
// used to assign
if (stmt.getRightOp() == l) {
Value l = stmt.getLeftOp();
if (l instanceof StaticFieldRef && isObject(((StaticFieldRef) l).getFieldRef().type())) {
usedAsObject = true;
doBreak = true;
return;
} else if (l instanceof InstanceFieldRef && isObject(((InstanceFieldRef) l).getFieldRef().type())) {
usedAsObject = true;
doBreak = true;
return;
} else if (l instanceof ArrayRef) {
Type aType = ((ArrayRef) l).getType();
if (aType instanceof UnknownType) {
usedAsObject = stmt.hasTag(ObjectOpTag.NAME); // isObject(
// findArrayType(g,
// localDefs,
// localUses,
// stmt));
} else {
usedAsObject = isObject(aType);
}
doBreak = true;
return;
}
}
// is used as value (does not exclude assignment)
if (r instanceof FieldRef) {
usedAsObject = true; // isObject(((FieldRef)
// r).getFieldRef().type());
doBreak = true;
return;
} else if (r instanceof ArrayRef) {
ArrayRef ar = (ArrayRef) r;
if (ar.getBase() == l) {
usedAsObject = true;
} else { // used as index
usedAsObject = false;
}
doBreak = true;
return;
} else if (r instanceof StringConstant || r instanceof NewExpr) {
throw new RuntimeException("NOT POSSIBLE StringConstant or NewExpr at " + stmt);
} else if (r instanceof NewArrayExpr) {
usedAsObject = false;
doBreak = true;
return;
} else if (r instanceof CastExpr) {
usedAsObject = isObject(((CastExpr) r).getCastType());
doBreak = true;
return;
} else if (r instanceof InvokeExpr) {
usedAsObject = examineInvokeExpr((InvokeExpr) stmt.getRightOp());
doBreak = true;
return;
} else if (r instanceof LengthExpr) {
usedAsObject = true;
doBreak = true;
return;
} else if (r instanceof BinopExpr) {
usedAsObject = false;
doBreak = true;
return;
}
}
@Override
public void caseIdentityStmt(IdentityStmt stmt) {
if (stmt.getLeftOp() == l) {
throw new RuntimeException("IMPOSSIBLE 0");
}
}
@Override
public void caseEnterMonitorStmt(EnterMonitorStmt stmt) {
usedAsObject = stmt.getOp() == l;
doBreak = true;
return;
}
@Override
public void caseExitMonitorStmt(ExitMonitorStmt stmt) {
usedAsObject = stmt.getOp() == l;
doBreak = true;
return;
}
@Override
public void caseReturnStmt(ReturnStmt stmt) {
usedAsObject = stmt.getOp() == l && isObject(body.getMethod().getReturnType());
doBreak = true;
return;
}
@Override
public void caseThrowStmt(ThrowStmt stmt) {
usedAsObject = stmt.getOp() == l;
doBreak = true;
return;
}
};
for (Local loc : getNullCandidates(body)) {
usedAsObject = false;
Set<Unit> defs = localDefs.collectDefinitionsWithAliases(loc);
// process normally
doBreak = false;
for (Unit u : defs) {
// put correct local in l
if (u instanceof DefinitionStmt) {
l = (Local) ((DefinitionStmt) u).getLeftOp();
} else if (u instanceof IfStmt) {
throw new RuntimeException("ERROR: def can not be something else than Assign or Identity statement! (def: " + u
+ " class: " + u.getClass() + "");
}
// check defs
u.apply(checkDef);
if (doBreak) {
break;
}
// check uses
for (Unit use : localDefs.getUsesOf(l)) {
use.apply(checkUse);
if (doBreak) {
break;
}
} // for uses
if (doBreak) {
break;
}
} // for defs
// change values
if (usedAsObject) {
for (Unit u : defs) {
replaceWithNull(u);
Set<Value> defLocals = new HashSet<Value>();
for (ValueBox vb : u.getDefBoxes()) {
defLocals.add(vb.getValue());
}
Local l = (Local) ((DefinitionStmt) u).getLeftOp();
for (Unit uuse : localDefs.getUsesOf(l)) {
Stmt use = (Stmt) uuse;
// If we have a[x] = 0 and a is an object, we may not conclude 0 -> null
if (!use.containsArrayRef() || !defLocals.contains(use.getArrayRef().getBase())) {
replaceWithNull(use);
}
}
}
} // end if
}
// Check for inlined zero values
AbstractStmtSwitch inlinedZeroValues = new AbstractStmtSwitch() {
final NullConstant nullConstant = NullConstant.v();
Set<Value> objects = null;
@Override
public void caseAssignStmt(AssignStmt stmt) {
// Case a = 0 with a being an object
if (isObject(stmt.getLeftOp().getType()) && isConstZero(stmt.getRightOp())) {
stmt.setRightOp(nullConstant);
return;
}
// Case a = (Object) 0
if (stmt.getRightOp() instanceof CastExpr) {
CastExpr ce = (CastExpr) stmt.getRightOp();
if (isObject(ce.getCastType()) && isConstZero(ce.getOp())) {
stmt.setRightOp(nullConstant);
}
}
// Case a[0] = 0
if (stmt.getLeftOp() instanceof ArrayRef && isConstZero(stmt.getRightOp())) {
ArrayRef ar = (ArrayRef) stmt.getLeftOp();
if (objects == null) {
objects = getObjectArray(body);
}
if (objects.contains(ar.getBase()) || stmt.hasTag(ObjectOpTag.NAME)) {
stmt.setRightOp(nullConstant);
}
}
}
private boolean isConstZero(Value rightOp) {
if ((rightOp instanceof IntConstant && ((IntConstant) rightOp).value == 0)
|| (rightOp instanceof LongConstant && ((LongConstant) rightOp).value == 0)) {
return true;
}
return false;
}
@Override
public void caseReturnStmt(ReturnStmt stmt) {
if (stmt.getOp() instanceof IntConstant && isObject(body.getMethod().getReturnType())) {
IntConstant iconst = (IntConstant) stmt.getOp();
assert iconst.value == 0;
stmt.setOp(nullConstant);
}
}
@Override
public void caseEnterMonitorStmt(EnterMonitorStmt stmt) {
if (stmt.getOp() instanceof IntConstant && ((IntConstant) stmt.getOp()).value == 0) {
stmt.setOp(nullConstant);
}
}
@Override
public void caseExitMonitorStmt(ExitMonitorStmt stmt) {
if (stmt.getOp() instanceof IntConstant && ((IntConstant) stmt.getOp()).value == 0) {
stmt.setOp(nullConstant);
}
}
};
final NullConstant nullConstant = NullConstant.v();
for (Unit u : body.getUnits()) {
u.apply(inlinedZeroValues);
if (u instanceof Stmt) {
Stmt stmt = (Stmt) u;
if (stmt.containsInvokeExpr()) {
InvokeExpr invExpr = stmt.getInvokeExpr();
for (int i = 0; i < invExpr.getArgCount(); i++) {
if (isObject(invExpr.getMethodRef().parameterType(i))) {
if (invExpr.getArg(i) instanceof IntConstant) {
IntConstant iconst = (IntConstant) invExpr.getArg(i);
assert iconst.value == 0;
invExpr.setArg(i, nullConstant);
}
}
}
}
}
}
}
private static Set<Value> getObjectArray(Body body) {
Set<Value> objArrays = new HashSet<Value>();
for (Unit u : body.getUnits()) {
if (u instanceof AssignStmt) {
AssignStmt assign = (AssignStmt) u;
if (assign.getRightOp() instanceof NewArrayExpr) {
NewArrayExpr nea = (NewArrayExpr) assign.getRightOp();
if (isObject(nea.getBaseType())) {
objArrays.add(assign.getLeftOp());
}
} else if (assign.getRightOp() instanceof FieldRef) {
FieldRef fr = (FieldRef) assign.getRightOp();
if (fr.getType() instanceof ArrayType) {
if (isObject(((ArrayType) fr.getType()).getArrayElementType())) {
objArrays.add(assign.getLeftOp());
}
}
}
}
}
return objArrays;
}
/**
* Collect all the locals which are assigned a IntConstant(0) or are used within a zero comparison.
*
* @param body
* the body to analyze
*/
private Set<Local> getNullCandidates(Body body) {
Set<Local> candidates = null;
for (Unit u : body.getUnits()) {
if (u instanceof AssignStmt) {
AssignStmt a = (AssignStmt) u;
if (!(a.getLeftOp() instanceof Local)) {
continue;
}
Local l = (Local) a.getLeftOp();
Value r = a.getRightOp();
if ((r instanceof IntConstant && ((IntConstant) r).value == 0)
|| (r instanceof LongConstant && ((LongConstant) r).value == 0)) {
if (candidates == null) {
candidates = new HashSet<Local>();
}
candidates.add(l);
}
} else if (u instanceof IfStmt) {
ConditionExpr expr = (ConditionExpr) ((IfStmt) u).getCondition();
if (isZeroComparison(expr) && expr.getOp1() instanceof Local) {
if (candidates == null) {
candidates = new HashSet<Local>();
}
candidates.add((Local) expr.getOp1());
}
}
}
return candidates == null ? Collections.<Local>emptySet() : candidates;
}
}