com.android.tools.lint.checks.ControlFlowGraph Maven / Gradle / Ivy
/*
* Copyright (C) 2012 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.tools.lint.checks;
import com.android.annotations.NonNull;
import com.android.annotations.Nullable;
import com.google.common.collect.Maps;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.FrameNode;
import org.objectweb.asm.tree.InsnList;
import org.objectweb.asm.tree.LabelNode;
import org.objectweb.asm.tree.LineNumberNode;
import org.objectweb.asm.tree.MethodInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.TryCatchBlockNode;
import org.objectweb.asm.tree.analysis.Analyzer;
import org.objectweb.asm.tree.analysis.AnalyzerException;
import org.objectweb.asm.tree.analysis.BasicInterpreter;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
/**
* A {@linkplain ControlFlowGraph} is a graph containing a node for each
* instruction in a method, and an edge for each possible control flow; usually
* just "next" for the instruction following the current instruction, but in the
* case of a branch such as an "if", multiple edges to each successive location,
* or with a "goto", a single edge to the jumped-to instruction.
*
* It also adds edges for abnormal control flow, such as the possibility of a
* method call throwing a runtime exception.
*/
public class ControlFlowGraph {
/** Map from instructions to nodes */
private Map mNodeMap;
/**
* Creates a new {@link ControlFlowGraph} and populates it with the flow
* control for the given method. If the optional {@code initial} parameter is
* provided with an existing graph, then the graph is simply populated, not
* created. This allows subclassing of the graph instance, if necessary.
*
* @param initial usually null, but can point to an existing instance of a
* {@link ControlFlowGraph} in which that graph is reused (but
* populated with new edges)
* @param classNode the class containing the method to be analyzed
* @param method the method to be analyzed
* @return a {@link ControlFlowGraph} with nodes for the control flow in the
* given method
* @throws AnalyzerException if the underlying bytecode library is unable to
* analyze the method bytecode
*/
@NonNull
public static ControlFlowGraph create(
@Nullable ControlFlowGraph initial,
@NonNull ClassNode classNode,
@NonNull MethodNode method) throws AnalyzerException {
final ControlFlowGraph graph = initial != null ? initial : new ControlFlowGraph();
final InsnList instructions = method.instructions;
graph.mNodeMap = Maps.newHashMapWithExpectedSize(instructions.size());
// Create a flow control graph using ASM4's analyzer. According to the ASM 4 guide
// (download.forge.objectweb.org/asm/asm4-guide.pdf) there are faster ways to construct
// it, but those require a lot more code.
Analyzer analyzer = new Analyzer(new BasicInterpreter()) {
@Override
protected void newControlFlowEdge(int insn, int successor) {
// Update the information as of whether the this object has been
// initialized at the given instruction.
AbstractInsnNode from = instructions.get(insn);
AbstractInsnNode to = instructions.get(successor);
graph.add(from, to);
}
@Override
protected boolean newControlFlowExceptionEdge(int insn, TryCatchBlockNode tcb) {
AbstractInsnNode from = instructions.get(insn);
graph.exception(from, tcb);
return super.newControlFlowExceptionEdge(insn, tcb);
}
@Override
protected boolean newControlFlowExceptionEdge(int insn, int successor) {
AbstractInsnNode from = instructions.get(insn);
AbstractInsnNode to = instructions.get(successor);
graph.exception(from, to);
return super.newControlFlowExceptionEdge(insn, successor);
}
};
analyzer.analyze(classNode.name, method);
return graph;
}
/** A {@link Node} is a node in the control flow graph for a method, pointing to
* the instruction and its possible successors */
public static class Node {
/** The instruction */
public final AbstractInsnNode instruction;
/** Any normal successors (e.g. following instruction, or goto or conditional flow) */
public final List successors = new ArrayList(2);
/** Any abnormal successors (e.g. the handler to go to following an exception) */
public final List exceptions = new ArrayList(1);
/** A tag for use during depth-first-search iteration of the graph etc */
public int visit;
/**
* Constructs a new control graph node
*
* @param instruction the instruction to associate with this node
*/
public Node(@NonNull AbstractInsnNode instruction) {
this.instruction = instruction;
}
void addSuccessor(@NonNull Node node) {
if (!successors.contains(node)) {
successors.add(node);
}
}
void addExceptionPath(@NonNull Node node) {
if (!exceptions.contains(node)) {
exceptions.add(node);
}
}
/**
* Represents this instruction as a string, for debugging purposes
*
* @param includeAdjacent whether it should include a display of
* adjacent nodes as well
* @return a string representation
*/
@NonNull
public String toString(boolean includeAdjacent) {
StringBuilder sb = new StringBuilder(100);
sb.append(getId(instruction));
sb.append(':');
if (instruction instanceof LabelNode) {
//LabelNode l = (LabelNode) instruction;
//sb.append('L' + l.getLabel().getOffset() + ":");
//sb.append('L' + l.getLabel().info + ":");
sb.append("LABEL");
} else if (instruction instanceof LineNumberNode) {
sb.append("LINENUMBER ").append(((LineNumberNode)instruction).line);
} else if (instruction instanceof FrameNode) {
sb.append("FRAME");
} else {
int opcode = instruction.getOpcode();
// AbstractVisitor isn't available unless debug/util is included,
boolean printed = false;
try {
Class cls = Class.forName("org.objectweb.asm.util"); //$NON-NLS-1$
Field field = cls.getField("OPCODES");
String[] OPCODES = (String[]) field.get(null);
printed = true;
if (opcode > 0 && opcode <= OPCODES.length) {
sb.append(OPCODES[opcode]);
if (instruction.getType() == AbstractInsnNode.METHOD_INSN) {
sb.append('(').append(((MethodInsnNode)instruction).name).append(')');
}
}
} catch (Throwable t) {
// debug not installed: just do toString() on the instructions
}
if (!printed) {
if (instruction.getType() == AbstractInsnNode.METHOD_INSN) {
sb.append('(').append(((MethodInsnNode)instruction).name).append(')');
} else {
sb.append(instruction.toString());
}
}
}
if (includeAdjacent) {
if (successors != null && !successors.isEmpty()) {
sb.append(" Next:");
for (Node successor : successors) {
sb.append(' ');
sb.append(successor.toString(false));
}
}
if (exceptions != null && !exceptions.isEmpty()) {
sb.append(" Exceptions:");
for (Node exception : exceptions) {
sb.append(' ');
sb.append(exception.toString(false));
}
}
sb.append('\n');
}
return sb.toString();
}
}
/** Adds an exception flow to this graph */
protected void add(@NonNull AbstractInsnNode from, @NonNull AbstractInsnNode to) {
getNode(from).addSuccessor(getNode(to));
}
/** Adds an exception flow to this graph */
protected void exception(@NonNull AbstractInsnNode from, @NonNull AbstractInsnNode to) {
// For now, these edges appear useless; we also get more specific
// information via the TryCatchBlockNode which we use instead.
//getNode(from).addExceptionPath(getNode(to));
}
/** Adds an exception try block node to this graph */
protected void exception(@NonNull AbstractInsnNode from, @NonNull TryCatchBlockNode tcb) {
// Add tcb's to all instructions in the range
LabelNode start = tcb.start;
LabelNode end = tcb.end; // exclusive
// Add exception edges for all method calls in the range
AbstractInsnNode curr = start;
Node handlerNode = getNode(tcb.handler);
while (curr != end && curr != null) {
if (curr.getType() == AbstractInsnNode.METHOD_INSN) {
// Method call; add exception edge to handler
if (tcb.type == null) {
// finally block: not an exception path
getNode(curr).addSuccessor(handlerNode);
}
getNode(curr).addExceptionPath(handlerNode);
}
curr = curr.getNext();
}
}
/**
* Looks up (and if necessary) creates a graph node for the given instruction
*
* @param instruction the instruction
* @return the control flow graph node corresponding to the given
* instruction
*/
@NonNull
public Node getNode(@NonNull AbstractInsnNode instruction) {
Node node = mNodeMap.get(instruction);
if (node == null) {
node = new Node(instruction);
mNodeMap.put(instruction, node);
}
return node;
}
/**
* Creates a human readable version of the graph
*
* @param start the starting instruction, or null if not known or to use the
* first instruction
* @return a string version of the graph
*/
@NonNull
public String toString(@Nullable Node start) {
StringBuilder sb = new StringBuilder(400);
AbstractInsnNode curr;
if (start != null) {
curr = start.instruction;
} else {
if (mNodeMap.isEmpty()) {
return "";
} else {
curr = mNodeMap.keySet().iterator().next();
while (curr.getPrevious() != null) {
curr = curr.getPrevious();
}
}
}
while (curr != null) {
Node node = mNodeMap.get(curr);
if (node != null) {
sb.append(node.toString(true));
}
curr = curr.getNext();
}
return sb.toString();
}
@Override
public String toString() {
return toString(null);
}
// ---- For debugging only ----
private static Map sIds = null;
private static int sNextId = 1;
private static String getId(Object object) {
if (sIds == null) {
sIds = Maps.newHashMap();
}
String id = sIds.get(object);
if (id == null) {
id = Integer.toString(sNextId++);
sIds.put(object, id);
}
return id;
}
}