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WALA/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/MethodEditor.java

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/*******************************************************************************
* Copyright (c) 2002,2006 IBM Corporation.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package com.ibm.wala.shrikeBT;
import java.util.ArrayList;
import java.util.IdentityHashMap;
/**
* The MethodEditor is the core of the ShrikeBT code rewriting mechanism. To rewrite code, construct a MethodEditor initialized with
* the intial code for the method. Then perform a series of passes. In each pass you call beginPass(), insert a number of patches
* using the insert...() or replace...() methods, then optionally call applyPatches() to update the code with your changes, then
* call endPass(). The end of each pass updates the code in the MethodData that you passed in, so the new code can be extracted from
* that MethodData object. Note that if applyPatches() is not called, or it is called but no patches had been inserted, then the
* code will not be updated and that pass is essentially aborted.
*
* A patch is simply a subclass of MethodEditor.Patch, representing a code sequence to insert into the method. Each patch class
* implements one method, emitTo(), which writes the patch code into the code stream using the provided MethodEditor.Output
* instance. Anonymous inner classes are very useful for writing patches.
*
* Patches can be inserted at the following points:
* <ul>
* <li>Before the start of the method
* <li>Before or after a particular instruction
* <li>Replacing a particular instruction
* <li>Handling an exception on a particular instruction
* <li>Handling an exception anywhere in the method
* <li>After the end of the method, where code will not normally be executed, but can be branched to by another patch
* </ul>
* Patch application is deterministic; if two patches are applied at the same point, then the order of application determines the
* order of code generation, in a way specified by the particular application point. See the patch application methods below.
*
* MethodEditor relies on labels. A label is an integer representing a point in the code. Labels are valid only during a single
* pass; at the end of each pass, instructions are reordered and old labels become invalid. At the beginning of a pass every
* instruction in the instructions array is labelled with the index of that instruction in the array. During instrumentation new
* labels can be allocated by calling MethodEditor.allocateLabel(); control instructions can be created referring to these new
* labels or the existing labels. At the end of a pass, as patch code is spliced into the method body, all instructions are updated
* to refer to the new labels which are simply the indices of instructions in the instruction array.
*/
public final class MethodEditor {
private static final ExceptionHandler[] noHandlers = new ExceptionHandler[0];
/** Records which original bytecode instruction each Instruction belongs to. */
private int[] instructionsToBytecodes;
private IInstruction[] instructions;
private ExceptionHandler[][] handlers;
final private MethodData methodInfo;
// working
private static final int BEFORE_PASS = 0x01;
private static final int DURING_PASS = 0x02;
private static final int EMITTING_CODE = 0x04;
private static final int BEFORE_END_PASS = 0x08;
private int state = BEFORE_PASS;
private int patchCount;
private Patch[] beforePatches;
private Patch[] afterPatches;
private Patch[] lastAfterPatches;
private Patch[] replacementPatches;
private Patch methodStartPatches;
private Patch afterMethodPatches;
private HandlerPatch[] instructionHandlerPatches;
private HandlerPatch methodHandlerPatches;
private int nextLabel;
/**
* This patch lets us stuff an exception handler into the code.
*/
private static class HandlerPatch {
final HandlerPatch next;
final String catchClass;
final int label;
final Patch patch;
HandlerPatch(HandlerPatch next, String catchClass, int label, Patch patch) {
this.next = next;
this.catchClass = catchClass;
this.label = label;
this.patch = patch;
}
}
/**
* Build an editor for the given method. This editor will write back its changes to the method info.
*
* @throws IllegalArgumentException if info is null
*/
public MethodEditor(MethodData info) {
if (info == null) {
throw new IllegalArgumentException("info is null");
}
methodInfo = info;
instructionsToBytecodes = info.getInstructionsToBytecodes();
instructions = info.getInstructions();
handlers = info.getHandlers();
}
/**
* Build an editor for specific method data. After patching the code you can retrieve the new code, handlers and
* instructions-to-bytecode-offsets map.
*/
public MethodEditor(Instruction[] instructions, ExceptionHandler[][] handlers, int[] instructionsToBytecodes) {
if (instructions == null) {
throw new IllegalArgumentException("null instructions");
}
if (handlers == null) {
throw new IllegalArgumentException("null handlers");
}
methodInfo = null;
this.instructionsToBytecodes = instructionsToBytecodes;
this.instructions = instructions;
this.handlers = handlers;
}
private void verifyState(int state) {
if ((state & this.state) == 0) {
throw new IllegalArgumentException(getStateMessage(state));
}
}
private static String getStateMessage(int state) {
switch (state) {
case BEFORE_PASS:
return "This operation can only be performed before or after an editing pass";
case DURING_PASS:
return "This operation can only be performed during an editing pass";
case EMITTING_CODE:
return "This operation can only be performed while applying patches and emitting code";
case BEFORE_END_PASS:
return "This operation can only be performed after applying patches";
default:
return "This operation cannot be performed in this state";
}
}
/**
* @return the current handler array
*/
public ExceptionHandler[][] getHandlers() {
verifyState(BEFORE_PASS | DURING_PASS);
return handlers;
}
/**
* @return the current instruction array
*/
public IInstruction[] getInstructions() {
verifyState(BEFORE_PASS | DURING_PASS);
return instructions;
}
/**
* @return the current instructions-to-bytecode-offsets map
*/
public int[] getInstructionsToBytecodes() {
verifyState(BEFORE_PASS | DURING_PASS);
return instructionsToBytecodes;
}
static ExceptionHandler[] mergeHandlers(ExceptionHandler[] h1, ExceptionHandler[] h2) {
if (h1.length == 0) {
return h2;
} else if (h2.length == 0) {
return h1;
} else {
ExceptionHandler[] r = new ExceptionHandler[h1.length + h2.length];
System.arraycopy(h1, 0, r, 0, h1.length);
System.arraycopy(h2, 0, r, h1.length, h2.length);
return r;
}
}
/**
* Output is the interface that patches use to emit their code into a method body.
*/
public final static class Output {
final ArrayList<IInstruction> newInstructions = new ArrayList<>();
final ArrayList<ExceptionHandler[]> newInstructionHandlers = new ArrayList<>();
int[] instructionsToBytecodes = new int[10];
final int[] labelDefs;
ExceptionHandler[] additionalHandlers;
int originalBytecode;
boolean codeChanged = false;
Output(int numLabels) {
labelDefs = new int[numLabels];
}
/**
* Emit a label definition at the current point in the code. The label must have been previously allocated using
* MethodEditor.allocateLabel.
*/
public void emitLabel(int label) {
labelDefs[label] = newInstructions.size();
}
/**
* Emit an instruction at the current point in the code.
*/
public void emit(Instruction i) {
codeChanged = true;
internalEmitInstruction(i);
}
/**
* Emit an instruction with some exception handlers at the current point in the code.
*/
public void emit(Instruction i, ExceptionHandler[] handlers) {
codeChanged = true;
int s = newInstructions.size();
if (s + 1 > instructionsToBytecodes.length) {
int[] t = new int[instructionsToBytecodes.length * 2];
System.arraycopy(instructionsToBytecodes, 0, t, 0, instructionsToBytecodes.length);
instructionsToBytecodes = t;
}
instructionsToBytecodes[s] = originalBytecode;
newInstructions.add(i);
newInstructionHandlers.add(mergeHandlers(handlers, additionalHandlers));
}
void internalEmitInstruction(IInstruction i) {
int s = newInstructions.size();
if (s + 1 > instructionsToBytecodes.length) {
int[] t = new int[instructionsToBytecodes.length * 2];
System.arraycopy(instructionsToBytecodes, 0, t, 0, instructionsToBytecodes.length);
instructionsToBytecodes = t;
}
instructionsToBytecodes[s] = originalBytecode;
newInstructions.add(i);
newInstructionHandlers.add(additionalHandlers);
}
/**
* Emit a list of instructions at the current point in the code.
*/
public void emit(Instruction[] instrs) {
emit(instrs, noHandlers);
}
/**
* Emit a list of instructions with some exception handlers at the current point in the code. All the instructions are covered
* by all the handlers.
*/
public void emit(Instruction[] instrs, ExceptionHandler[] handlers) {
if (instrs.length == 0) {
return;
}
codeChanged = true;
int s = newInstructions.size();
if (s + instrs.length > instructionsToBytecodes.length) {
int[] t = new int[instructionsToBytecodes.length * 2 + instrs.length];
System.arraycopy(instructionsToBytecodes, 0, t, 0, instructionsToBytecodes.length);
instructionsToBytecodes = t;
}
ExceptionHandler[] hs = mergeHandlers(handlers, additionalHandlers);
for (int i = 0; i < instrs.length; i++) {
instructionsToBytecodes[s + i] = originalBytecode;
newInstructions.add(instrs[i]);
newInstructionHandlers.add(hs);
}
}
}
/**
* This class is subclassed for each kind of patch that you want to apply.
*/
public static abstract class Patch {
Patch next;
public Patch() {
}
final Patch insert(Patch next) {
this.next = next;
return this;
}
/**
* Override this method to emit the code for your patch.
*/
public abstract void emitTo(Output w);
}
/**
* This must be called before inserting any patches.
*/
public void beginPass() {
verifyState(BEFORE_PASS);
state = DURING_PASS;
nextLabel = instructions.length;
beforePatches = new Patch[instructions.length];
afterPatches = new Patch[instructions.length];
lastAfterPatches = new Patch[instructions.length];
replacementPatches = new Patch[instructions.length];
instructionHandlerPatches = new HandlerPatch[instructions.length];
methodStartPatches = null;
afterMethodPatches = null;
methodHandlerPatches = null;
patchCount = 0;
}
/**
* This must be called after inserting any patches.
*/
public void endPass() {
state = BEFORE_PASS;
// lose references to the stored patches so they can be garbage collected
beforePatches = null;
afterPatches = null;
lastAfterPatches = null;
replacementPatches = null;
instructionHandlerPatches = null;
methodStartPatches = null;
afterMethodPatches = null;
methodHandlerPatches = null;
}
/**
* Allocate a fresh label. This must be called during a pass and not during code emission.
*/
public int allocateLabel() throws IllegalArgumentException {
verifyState(DURING_PASS);
return nextLabel++;
}
/**
* Insert code to be executed whenever the method is entered. This code is not protected by any exception handlers (other than
* handlers declared in the patch).
*
* When multiple 'start' patches are given, the last one added is first in execution order.
*
* @throws IllegalArgumentException if p is null
*/
public void insertAtStart(Patch p) {
if (p == null) {
throw new IllegalArgumentException("p is null");
}
verifyState(DURING_PASS);
methodStartPatches = p.insert(methodStartPatches);
patchCount++;
}
/**
* Insert code to be executed before the instruction. Branches to the instruction will branch to this code. Exception handlers
* that cover the instruction will be extended to cover the patch.
*
* When multiple 'before' patches are given, the last one added is first in execution order.
*
* @throws IllegalArgumentException if p is null
*/
public void insertBefore(int i, Patch p) {
if (p == null) {
throw new IllegalArgumentException("p is null");
}
verifyState(DURING_PASS);
beforePatches[i] = p.insert(beforePatches[i]);
patchCount++;
}
/**
* Insert code to be executed after the instruction. This code will only execute if the instruction "falls through". For example,
* code inserted after a "goto" will never be executed. Likewise if the instruction throws an execution the 'after' code will not
* be executed. Exception handlers that cover the instruction will be extended to cover the patch.
*
* When multiple 'after' patches are given, the last one added is LAST in execution order.
*/
public void insertAfter(int i, Patch p) {
verifyState(DURING_PASS);
try {
if (afterPatches[i] == null) {
lastAfterPatches[i] = afterPatches[i] = p.insert(null);
} else {
lastAfterPatches[i].next = p;
lastAfterPatches[i] = p.insert(null);
}
patchCount++;
} catch (ArrayIndexOutOfBoundsException e) {
throw new IllegalArgumentException("invalid i", e);
}
}
/**
* Insert code to replace the instruction. Exception handlers that cover the instruction will cover the patch.
*
* Multiple replacements are not allowed.
*
* @throws NullPointerException if p is null
* @throws IllegalArgumentException if p is null
*/
public void replaceWith(int i, Patch p) throws NullPointerException {
if (p == null) {
throw new IllegalArgumentException("p is null");
}
verifyState(DURING_PASS);
if (replacementPatches[i] != null) {
throw new IllegalArgumentException("Instruction " + i + " cannot be replaced more than once");
}
replacementPatches[i] = p.insert(null);
patchCount++;
}
/**
* An "instruction exception handler" handles exceptions generated by a specific instruction (including patch code that may be
* inserted before, after, or instead of the instruction in this pass). If the patch code falls through, control resumes with the
* next instruction. This exception handler handles exceptions before any exception handler already attached to the instruction.
* Furthermore, the patch itself is covered by the exception handlers already attached to the instruction.
*
* If multiple instruction exception handlers are given, then the last one added handles the exception first; if an exception is
* rethrown, then the next-to-last one added handles that exception, etc.
*/
public void addInstructionExceptionHandler(int i, String catchClass, Patch p) {
verifyState(DURING_PASS);
try {
instructionHandlerPatches[i] = new HandlerPatch(instructionHandlerPatches[i], catchClass, allocateLabel(), p);
patchCount++;
} catch (ArrayIndexOutOfBoundsException e) {
throw new IllegalArgumentException("invalid i: " + i, e);
}
}
/**
* A "method exception handler" handles exceptions generated anywhere in the method. The patch code must not fall through; it must
* return or throw an exception.
*
* If multiple method exception handlers are given, then the last one added handles the exception first; if an exception is
* rethrown, then the next-to-last one added handles that exception, etc.
*/
public void addMethodExceptionHandler(String catchClass, Patch p) {
verifyState(DURING_PASS);
if (p == null) {
throw new IllegalArgumentException("null p");
}
methodHandlerPatches = new HandlerPatch(methodHandlerPatches, catchClass, allocateLabel(), p);
patchCount++;
}
/**
* This method inserts code that will be placed after the method body. This code will not be executed normally, but it can emit
* label definitions that other patches can branch to. No exception handlers cover this code (other than exception handlers
* emitted by patch p itself).
*
* @throws IllegalArgumentException if p is null
*/
public void insertAfterBody(Patch p) {
if (p == null) {
throw new IllegalArgumentException("p is null");
}
verifyState(DURING_PASS);
afterMethodPatches = p.insert(afterMethodPatches);
patchCount++;
}
/**
* @return the MethodData used to create this editor, or null if no MethodData is linked to this editor
*/
public MethodData getData() {
return methodInfo;
}
private static ExceptionHandler[] makeExceptionArray(HandlerPatch hp) {
if (hp == null) {
return noHandlers;
} else {
int count = 0;
for (HandlerPatch hpIterator = hp; hpIterator != null; hpIterator = hpIterator.next) {
count++;
}
ExceptionHandler[] patchedHandlers = new ExceptionHandler[count];
count = 0;
for (HandlerPatch hpIterator = hp; hpIterator != null; hpIterator = hpIterator.next) {
patchedHandlers[count] = new ExceptionHandler(hpIterator.label, hpIterator.catchClass);
count++;
}
return patchedHandlers;
}
}
/**
* This method finishes a pass. All code is updated; instructions are reordered and old labels may not be valid.
*
* If no patches were issued, we don't need to do anything at all; this case is detected quickly and no updates are made.
*
* @return true iff non-trivial patches were applied
*/
public boolean applyPatches() throws IllegalArgumentException {
verifyState(DURING_PASS);
state = EMITTING_CODE;
if (patchCount == 0) {
state = BEFORE_END_PASS;
// no patches issued; drop out
return false;
}
Output w = new Output(nextLabel);
int[] oldInstructionsToNew = new int[instructions.length];
w.additionalHandlers = noHandlers;
w.originalBytecode = 0;
for (Patch p = methodStartPatches; p != null; p = p.next) {
p.emitTo(w);
}
ExceptionHandler[] methodHandlers = makeExceptionArray(methodHandlerPatches);
if (methodHandlers.length > 0) {
// if a method handler is added, the code has changed even though
// the patch might not emit any actual code
w.codeChanged = true;
}
for (int i = 0; i < instructions.length; i++) {
ExceptionHandler[] basicHandlers = mergeHandlers(handlers[i], methodHandlers);
HandlerPatch hp = instructionHandlerPatches[i];
w.emitLabel(i);
w.originalBytecode = instructionsToBytecodes[i];
w.additionalHandlers = basicHandlers;
for (Patch p = beforePatches[i]; p != null; p = p.next) {
p.emitTo(w);
}
w.additionalHandlers = mergeHandlers(makeExceptionArray(hp), basicHandlers);
Patch replace = replacementPatches[i];
if (replace == null) {
oldInstructionsToNew[i] = w.newInstructions.size();
w.internalEmitInstruction(instructions[i]);
} else {
// a patch might delete an instruction, in which case the
// code is definitely modified
w.codeChanged = true;
oldInstructionsToNew[i] = -1;
replace.emitTo(w);
}
w.additionalHandlers = basicHandlers;
for (Patch p = afterPatches[i]; p != null; p = p.next) {
p.emitTo(w);
}
if (hp != null) {
// if an instruction handler is added, the code has changed even though
// the patch might not emit any actual code
w.codeChanged = true;
GotoInstruction branchOver = GotoInstruction.make(i + 1);
w.internalEmitInstruction(branchOver);
for (HandlerPatch hpIterator = hp; hpIterator != null; hpIterator = hpIterator.next) {
w.additionalHandlers = mergeHandlers(makeExceptionArray(hpIterator.next), basicHandlers);
w.emitLabel(hpIterator.label);
hpIterator.patch.emitTo(w);
w.internalEmitInstruction(branchOver);
}
}
}
w.originalBytecode = 0;
for (HandlerPatch hpIterator = methodHandlerPatches; hpIterator != null; hpIterator = hpIterator.next) {
w.additionalHandlers = makeExceptionArray(hpIterator.next);
w.emitLabel(hpIterator.label);
hpIterator.patch.emitTo(w);
}
w.additionalHandlers = noHandlers;
for (Patch p = afterMethodPatches; p != null; p = p.next) {
p.emitTo(w);
}
state = BEFORE_END_PASS;
if (!w.codeChanged) {
return false;
}
instructions = new Instruction[w.newInstructions.size()];
handlers = new ExceptionHandler[instructions.length][];
instructionsToBytecodes = new int[instructions.length];
w.newInstructions.toArray(instructions);
w.newInstructionHandlers.toArray(handlers);
System.arraycopy(w.instructionsToBytecodes, 0, instructionsToBytecodes, 0, instructionsToBytecodes.length);
int[] labelDefs = w.labelDefs;
int[] newInstructionsToOld = new int[instructions.length];
for (int i = 0; i < instructions.length; i++) {
instructions[i] = instructions[i].redirectTargets(labelDefs);
newInstructionsToOld[i] = -1;
}
// We want to update each exception handler array exactly once
IdentityHashMap<ExceptionHandler, Object> adjustedHandlers = null;
for (int i = 0; i < handlers.length; i++) {
ExceptionHandler[] hs = handlers[i];
if (hs.length > 0 && (i == 0 || hs != handlers[i - 1])) {
if (adjustedHandlers == null) {
adjustedHandlers = new IdentityHashMap<>();
}
for (ExceptionHandler element : hs) {
ExceptionHandler h = element;
if (!adjustedHandlers.containsKey(h)) {
adjustedHandlers.put(h, null);
h.handler = labelDefs[h.handler]; // breaks invariant of ExceptionHandler: immutable!
}
}
}
}
if (methodInfo != null) {
for (int i = 0; i < oldInstructionsToNew.length; i++) {
if (oldInstructionsToNew[i] != -1) {
newInstructionsToOld[oldInstructionsToNew[i]] = i;
}
}
methodInfo.update(instructions, handlers, newInstructionsToOld, instructionsToBytecodes);
}
return true;
}
/**
* Apply Visitor v to each instruction in the code, for the purpose of patching the code.
*/
public void visitInstructions(Visitor v) {
verifyState(DURING_PASS);
for (int i = 0; i < instructions.length; i++) {
v.setIndex(this, i);
instructions[i].visit(v);
}
}
/**
* A specialized Instruction.Visitor providing convenience methods for inserting patches. In particular it maintains a notion of
* the "current position" in the code array.
*/
public static class Visitor extends IInstruction.Visitor {
private int index;
private MethodEditor editor;
/**
* Set the current editor and instruction index for this visitor.
*/
final public void setIndex(MethodEditor e, int i) {
index = i;
editor = e;
}
/**
* @return the index of the current instruction in the code array
*/
final public int getIndex() {
return index;
}
/**
* Insert a patch after the current instruction in the code.
*/
final public void insertAfter(Patch p) {
editor.insertAfter(index, p);
}
/**
* Insert a patch before the current instruction in the code.
*/
final public void insertBefore(Patch p) {
editor.insertBefore(index, p);
}
/**
* Replace the current instruction in the code with a patch.
*/
final public void replaceWith(Patch p) {
editor.replaceWith(index, p);
}
/**
* Add an exception handler to the current instruction.
*
* @param catchClass the JVM type for the exception to be caught (e.g., Ljava.io.IOException;), or null to catch all exceptions
* @param p the code to handle the exception
*/
final public void addInstructionExceptionHandler(String catchClass, Patch p) {
editor.addInstructionExceptionHandler(index, catchClass, p);
}
}
}
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