/*
* ProGuard -- shrinking, optimization, obfuscation, and preverification
* of Java bytecode.
*
* Copyright (c) 2002-2011 Eric Lafortune (eric@graphics.cornell.edu)
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 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 Public License for
* more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package proguard.classfile.attribute.visitor;
import proguard.classfile.*;
import proguard.classfile.visitor.ClassPrinter;
import proguard.classfile.attribute.*;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.SimplifiedVisitor;
/**
* This AttributeVisitor computes the stack sizes at all instruction offsets
* of the code attributes that it visits.
*
* @author Eric Lafortune
*/
public class StackSizeComputer
extends SimplifiedVisitor
implements AttributeVisitor,
InstructionVisitor,
ExceptionInfoVisitor
{
//*
private static final boolean DEBUG = false;
/*/
private static boolean DEBUG = true;
//*/
private boolean[] evaluated = new boolean[ClassConstants.TYPICAL_CODE_LENGTH];
private int[] stackSizes = new int[ClassConstants.TYPICAL_CODE_LENGTH];
private boolean exitInstructionBlock;
private int stackSize;
private int maxStackSize;
/**
* Returns whether the instruction at the given offset is reachable in the
* most recently visited code attribute.
*/
public boolean isReachable(int instructionOffset)
{
return evaluated[instructionOffset];
}
/**
* Returns the stack size at the given instruction offset of the most
* recently visited code attribute.
*/
public int getStackSize(int instructionOffset)
{
if (!evaluated[instructionOffset])
{
throw new IllegalArgumentException("Unknown stack size at unreachable instruction offset ["+instructionOffset+"]");
}
return stackSizes[instructionOffset];
}
/**
* Returns the maximum stack size of the most recently visited code attribute.
*/
public int getMaxStackSize()
{
return maxStackSize;
}
// Implementations for AttributeVisitor.
public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
// DEBUG =
// clazz.getName().equals("abc/Def") &&
// method.getName(clazz).equals("abc");
// TODO: Remove this when the code has stabilized.
// Catch any unexpected exceptions from the actual visiting method.
try
{
// Process the code.
visitCodeAttribute0(clazz, method, codeAttribute);
}
catch (RuntimeException ex)
{
System.err.println("Unexpected error while computing stack sizes:");
System.err.println(" Class = ["+clazz.getName()+"]");
System.err.println(" Method = ["+method.getName(clazz)+method.getDescriptor(clazz)+"]");
System.err.println(" Exception = ["+ex.getClass().getName()+"] ("+ex.getMessage()+")");
if (DEBUG)
{
method.accept(clazz, new ClassPrinter());
}
throw ex;
}
}
public void visitCodeAttribute0(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
if (DEBUG)
{
System.out.println("StackSizeComputer: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
}
// Try to reuse the previous array.
int codeLength = codeAttribute.u4codeLength;
if (evaluated.length < codeLength)
{
evaluated = new boolean[codeLength];
stackSizes = new int[codeLength];
}
else
{
for (int index = 0; index < codeLength; index++)
{
evaluated[index] = false;
}
}
// The initial stack is always empty.
stackSize = 0;
maxStackSize = 0;
// Evaluate the instruction block starting at the entry point of the method.
evaluateInstructionBlock(clazz, method, codeAttribute, 0);
// Evaluate the exception handlers.
codeAttribute.exceptionsAccept(clazz, method, this);
}
// Implementations for InstructionVisitor.
public void visitSimpleInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, SimpleInstruction simpleInstruction)
{
byte opcode = simpleInstruction.opcode;
// Some simple instructions exit from the current instruction block.
exitInstructionBlock =
opcode == InstructionConstants.OP_IRETURN ||
opcode == InstructionConstants.OP_LRETURN ||
opcode == InstructionConstants.OP_FRETURN ||
opcode == InstructionConstants.OP_DRETURN ||
opcode == InstructionConstants.OP_ARETURN ||
opcode == InstructionConstants.OP_RETURN ||
opcode == InstructionConstants.OP_ATHROW;
}
public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
{
// Constant pool instructions never end the current instruction block.
exitInstructionBlock = false;
}
public void visitVariableInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, VariableInstruction variableInstruction)
{
byte opcode = variableInstruction.opcode;
// The ret instruction end the current instruction block.
exitInstructionBlock =
opcode == InstructionConstants.OP_RET;
}
public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)
{
byte opcode = branchInstruction.opcode;
// Evaluate the target instruction blocks.
evaluateInstructionBlock(clazz,
method,
codeAttribute,
offset +
branchInstruction.branchOffset);
// Evaluate the instructions after a subroutine branch.
if (opcode == InstructionConstants.OP_JSR ||
opcode == InstructionConstants.OP_JSR_W)
{
// We assume subroutine calls (jsr and jsr_w instructions) don't
// change the stack, other than popping the return value.
stackSize -= 1;
evaluateInstructionBlock(clazz,
method,
codeAttribute,
offset + branchInstruction.length(offset));
}
// Some branch instructions always end the current instruction block.
exitInstructionBlock =
opcode == InstructionConstants.OP_GOTO ||
opcode == InstructionConstants.OP_GOTO_W ||
opcode == InstructionConstants.OP_JSR ||
opcode == InstructionConstants.OP_JSR_W;
}
public void visitAnySwitchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, SwitchInstruction switchInstruction)
{
// Evaluate the target instruction blocks.
// Loop over all jump offsets.
int[] jumpOffsets = switchInstruction.jumpOffsets;
for (int index = 0; index < jumpOffsets.length; index++)
{
// Evaluate the jump instruction block.
evaluateInstructionBlock(clazz,
method,
codeAttribute,
offset + jumpOffsets[index]);
}
// Also evaluate the default instruction block.
evaluateInstructionBlock(clazz,
method,
codeAttribute,
offset + switchInstruction.defaultOffset);
// The switch instruction always ends the current instruction block.
exitInstructionBlock = true;
}
// Implementations for ExceptionInfoVisitor.
public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, ExceptionInfo exceptionInfo)
{
if (DEBUG)
{
System.out.println("Exception:");
}
// The stack size when entering the exception handler is always 1.
stackSize = 1;
// Evaluate the instruction block starting at the entry point of the
// exception handler.
evaluateInstructionBlock(clazz,
method,
codeAttribute,
exceptionInfo.u2handlerPC);
}
// Small utility methods.
/**
* Evaluates a block of instructions that hasn't been handled before,
* starting at the given offset and ending at a branch instruction, a return
* instruction, or a throw instruction. Branch instructions are handled
* recursively.
*/
private void evaluateInstructionBlock(Clazz clazz,
Method method,
CodeAttribute codeAttribute,
int instructionOffset)
{
if (DEBUG)
{
if (evaluated[instructionOffset])
{
System.out.println("-- (instruction block at "+instructionOffset+" already evaluated)");
}
else
{
System.out.println("-- instruction block:");
}
}
// Remember the initial stack size.
int initialStackSize = stackSize;
// Remember the maximum stack size.
if (maxStackSize < stackSize)
{
maxStackSize = stackSize;
}
// Evaluate any instructions that haven't been evaluated before.
while (!evaluated[instructionOffset])
{
// Mark the instruction as evaluated.
evaluated[instructionOffset] = true;
Instruction instruction = InstructionFactory.create(codeAttribute.code,
instructionOffset);
if (DEBUG)
{
int stackPushCount = instruction.stackPushCount(clazz);
int stackPopCount = instruction.stackPopCount(clazz);
System.out.println("["+instructionOffset+"]: "+
stackSize+" - "+
stackPopCount+" + "+
stackPushCount+" = "+
(stackSize+stackPushCount-stackPopCount)+": "+
instruction.toString(instructionOffset));
}
// Compute the instruction's effect on the stack size.
stackSize -= instruction.stackPopCount(clazz);
if (stackSize < 0)
{
throw new IllegalArgumentException("Stack size becomes negative after instruction "+
instruction.toString(instructionOffset)+" in ["+
clazz.getName()+"."+
method.getName(clazz)+
method.getDescriptor(clazz)+"]");
}
stackSizes[instructionOffset] =
stackSize += instruction.stackPushCount(clazz);
// Remember the maximum stack size.
if (maxStackSize < stackSize)
{
maxStackSize = stackSize;
}
// Remember the next instruction offset.
int nextInstructionOffset = instructionOffset +
instruction.length(instructionOffset);
// Visit the instruction, in order to handle branches.
instruction.accept(clazz, method, codeAttribute, instructionOffset, this);
// Stop evaluating after a branch.
if (exitInstructionBlock)
{
break;
}
// Continue with the next instruction.
instructionOffset = nextInstructionOffset;
if (DEBUG)
{
if (evaluated[instructionOffset])
{
System.out.println("-- (instruction at "+instructionOffset+" already evaluated)");
}
}
}
// Restore the stack size for possible subsequent instruction blocks.
this.stackSize = initialStackSize;
}
}