src.main.java.com.mebigfatguy.fbcontrib.detect.SuspiciousNullGuard Maven / Gradle / Ivy
/*
* fb-contrib - Auxiliary detectors for Java programs
* Copyright (C) 2005-2019 Dave Brosius
*
* This library 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 library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package com.mebigfatguy.fbcontrib.detect;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import javax.annotation.Nullable;
import org.apache.bcel.Const;
import org.apache.bcel.classfile.Code;
import org.apache.bcel.classfile.LocalVariable;
import org.apache.bcel.classfile.LocalVariableTable;
import com.mebigfatguy.fbcontrib.utils.BugType;
import com.mebigfatguy.fbcontrib.utils.RegisterUtils;
import com.mebigfatguy.fbcontrib.utils.ToString;
import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.OpcodeStack;
import edu.umd.cs.findbugs.OpcodeStack.CustomUserValue;
import edu.umd.cs.findbugs.ba.ClassContext;
import edu.umd.cs.findbugs.ba.XField;
/**
* looks for code that checks to see if a field or local variable is not null,
* before entering a code block either an if, or while statement, and reassigns
* that field or variable. It seems that perhaps the guard should check if the
* field or variable is null.
*/
@CustomUserValue
public class SuspiciousNullGuard extends BytecodeScanningDetector {
private final BugReporter bugReporter;
private OpcodeStack stack;
private Map nullGuards;
/**
* constructs a SNG detector given the reporter to report bugs on
*
* @param bugReporter the sync of bug reports
*/
public SuspiciousNullGuard(BugReporter bugReporter) {
this.bugReporter = bugReporter;
}
/**
* overrides the visitor to initialize and tear down the opcode stack
*
* @param classContext the context object of the currently parsed class
*/
@Override
public void visitClassContext(ClassContext classContext) {
try {
stack = new OpcodeStack();
nullGuards = new HashMap<>();
super.visitClassContext(classContext);
} finally {
stack = null;
}
}
/**
* overrides the visitor to reset the stack
*
* @param obj the context object of the currently parsed code block
*/
@Override
public void visitCode(Code obj) {
stack.resetForMethodEntry(this);
nullGuards.clear();
super.visitCode(obj);
}
/**
* overrides the visitor to look for bad null guards
*
* @param seen the opcode of the currently visited instruction
*/
@Override
public void sawOpcode(int seen) {
Integer sawALOADReg = null;
try {
stack.precomputation(this);
int pc = getPC();
nullGuards.remove(Integer.valueOf(pc));
clearEndOfLifeRegisters();
switch (seen) {
case Const.IFNULL: {
if (stack.getStackDepth() > 0) {
OpcodeStack.Item itm = stack.getStackItem(0);
int reg = itm.getRegisterNumber();
Integer target = Integer.valueOf(getBranchTarget());
if (reg >= 0) {
int eol = Integer.MAX_VALUE;
LocalVariableTable lvt = getMethod().getLocalVariableTable();
if (lvt != null) {
LocalVariable lv = lvt.getLocalVariable(reg, pc);
if (lv != null) {
eol = pc + lv.getLength();
}
}
nullGuards.put(target, new NullGuard(reg, pc, eol, itm.getSignature()));
} else {
XField xf = itm.getXField();
Integer sourceFieldReg = (Integer) itm.getUserValue();
if ((xf != null) && (sourceFieldReg != null)) {
nullGuards.put(target,
new NullGuard(xf, sourceFieldReg.intValue(), pc, itm.getSignature()));
}
}
}
}
break;
case Const.ASTORE:
case Const.ASTORE_0:
case Const.ASTORE_1:
case Const.ASTORE_2:
case Const.ASTORE_3: {
if (stack.getStackDepth() > 0) {
OpcodeStack.Item itm = stack.getStackItem(0);
if (!itm.isNull()) {
NullGuard guard = findNullGuardWithRegister(RegisterUtils.getAStoreReg(this, seen));
if (guard != null) {
bugReporter.reportBug(new BugInstance(this, BugType.SNG_SUSPICIOUS_NULL_LOCAL_GUARD.name(),
NORMAL_PRIORITY).addClass(this).addMethod(this).addSourceLine(this));
removeNullGuard(guard);
}
}
}
}
break;
case Const.ALOAD:
case Const.ALOAD_0:
case Const.ALOAD_1:
case Const.ALOAD_2:
case Const.ALOAD_3: {
NullGuard guard = findNullGuardWithRegister(RegisterUtils.getALoadReg(this, seen));
if (guard != null) {
removeNullGuard(guard);
}
sawALOADReg = Integer.valueOf(RegisterUtils.getALoadReg(this, seen));
}
break;
case Const.PUTFIELD: {
if (stack.getStackDepth() <= 1) {
break;
}
OpcodeStack.Item itm = stack.getStackItem(0);
if (itm.isNull()) {
break;
}
XField xf = getXFieldOperand();
itm = stack.getStackItem(1);
Integer fieldSourceReg = (Integer) itm.getUserValue();
if ((xf != null) && (fieldSourceReg != null)) {
NullGuard guard = findNullGuardWithField(xf, fieldSourceReg.intValue());
if (guard != null) {
bugReporter.reportBug(
new BugInstance(this, BugType.SNG_SUSPICIOUS_NULL_FIELD_GUARD.name(), NORMAL_PRIORITY)
.addClass(this).addMethod(this).addSourceLine(this));
removeNullGuard(guard);
}
}
}
break;
case Const.GETFIELD: {
if (stack.getStackDepth() > 0) {
XField xf = getXFieldOperand();
OpcodeStack.Item itm = stack.getStackItem(0);
Integer fieldSourceReg = (Integer) itm.getUserValue();
if ((xf != null) && (fieldSourceReg != null)) {
NullGuard guard = findNullGuardWithField(xf, fieldSourceReg.intValue());
if (guard != null) {
removeNullGuard(guard);
} else {
sawALOADReg = (Integer) itm.getUserValue();
}
}
}
}
break;
case Const.IFEQ:
case Const.IFNE:
case Const.IFLT:
case Const.IFGE:
case Const.IFGT:
case Const.IFLE:
case Const.IF_ICMPEQ:
case Const.IF_ICMPNE:
case Const.IF_ICMPLT:
case Const.IF_ICMPGE:
case Const.IF_ICMPGT:
case Const.IF_ICMPLE:
case Const.IF_ACMPEQ:
case Const.IF_ACMPNE:
case Const.GOTO:
case Const.GOTO_W:
case Const.IFNONNULL:
nullGuards.clear();
break;
default:
break;
}
} finally {
stack.sawOpcode(this, seen);
if ((sawALOADReg != null) && (stack.getStackDepth() > 0)) {
OpcodeStack.Item itm = stack.getStackItem(0);
itm.setUserValue(sawALOADReg);
}
}
}
@Nullable
private NullGuard findNullGuardWithRegister(int reg) {
for (NullGuard guard : nullGuards.values()) {
if (guard.getRegister() == reg) {
return guard;
}
}
return null;
}
@Nullable
private NullGuard findNullGuardWithField(XField field, int fieldSourceReg) {
for (NullGuard guard : nullGuards.values()) {
if (field.equals(guard.getField()) && (fieldSourceReg == guard.getFieldSourceReg())) {
return guard;
}
}
return null;
}
private void removeNullGuard(NullGuard guard) {
Iterator it = nullGuards.values().iterator();
while (it.hasNext()) {
NullGuard potentialNG = it.next();
if (potentialNG.equals(guard)) {
it.remove();
break;
}
}
}
private void clearEndOfLifeRegisters() {
int pc = getPC();
Iterator it = nullGuards.values().iterator();
while (it.hasNext()) {
NullGuard potentialEOL = it.next();
if (potentialEOL.isEOL(pc)) {
it.remove();
}
}
}
static class NullGuard {
int register;
XField field;
int fieldSourceReg;
int location;
int scopeEnd;
String signature;
NullGuard(int reg, int start, int end, String guardSignature) {
register = reg;
field = null;
location = start;
scopeEnd = end;
signature = guardSignature;
}
NullGuard(XField xf, int fieldSource, int start, String guardSignature) {
register = -1;
field = xf;
fieldSourceReg = fieldSource;
location = start;
scopeEnd = Integer.MAX_VALUE;
signature = guardSignature;
}
int getRegister() {
return register;
}
XField getField() {
return field;
}
int getFieldSourceReg() {
return fieldSourceReg;
}
int getLocation() {
return location;
}
boolean isEOL(int pc) {
return pc >= scopeEnd;
}
String getSignature() {
return signature;
}
@Override
public String toString() {
return ToString.build(this);
}
}
}
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