AddTranslator.java

/*
Copyright 2011-2016 Google Inc. All Rights Reserved.

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.google.security.zynamics.reil.translators.x86;

import com.google.security.zynamics.reil.OperandSize;
import com.google.security.zynamics.reil.ReilHelpers;
import com.google.security.zynamics.reil.ReilInstruction;
import com.google.security.zynamics.reil.translators.IInstructionTranslator;
import com.google.security.zynamics.reil.translators.ITranslationEnvironment;
import com.google.security.zynamics.reil.translators.InternalTranslationException;
import com.google.security.zynamics.reil.translators.TranslationHelpers;
import com.google.security.zynamics.reil.translators.TranslationResult;
import com.google.security.zynamics.zylib.disassembly.IInstruction;
import com.google.security.zynamics.zylib.disassembly.IOperandTree;

import java.util.List;


/**
 * Translates ADD instructions to REIL code.
 */
public class AddTranslator implements IInstructionTranslator {

  /**
   * Translates an ADD instruction to REIL code.
   *
   * @param environment A valid translation environment.
   * @param instruction The ADD instruction to translate.
   * @param instructions The generated REIL code will be added to this list
   *
   * @throws InternalTranslationException if any of the arguments are null the passed instruction is
   *         not an ADD instruction
   */
  @Override
  public void translate(final ITranslationEnvironment environment, final IInstruction instruction,
      final List<ReilInstruction> instructions) throws InternalTranslationException {

    TranslationHelpers.checkTranslationArguments(environment, instruction, instructions, "add");

    if (instruction.getOperands().size() != 2) {
      throw new InternalTranslationException(
          "Error: Argument instruction is not a add instruction (invalid number of operands)");
    }

    final long baseOffset = instruction.getAddress().toLong() * 0x100;
    long offset = baseOffset;

    final List<? extends IOperandTree> operands = instruction.getOperands();

    final IOperandTree targetOperand = operands.get(0);
    final IOperandTree sourceOperand = operands.get(1);

    // Load source operand.
    final TranslationResult sourceResult =
        Helpers.translateOperand(environment, offset, sourceOperand, true);
    instructions.addAll(sourceResult.getInstructions());

    // Adjust the offset of the next REIL instruction.
    offset = baseOffset + instructions.size();

    // Load destination operand.
    final TranslationResult targetResult =
        Helpers.translateOperand(environment, offset, targetOperand, true);
    instructions.addAll(targetResult.getInstructions());

    // Adjust the offset of the next REIL instruction.
    offset = baseOffset + instructions.size();

    final OperandSize size = targetResult.getSize();

    final String sourceRegister = sourceResult.getRegister();
    final String targetRegister = targetResult.getRegister();

    final String msbMask = String.valueOf(TranslationHelpers.getMsbMask(size));
    final String carryMask = String.valueOf(Helpers.getCarryMask(size));
    final String truncateMask = String.valueOf(TranslationHelpers.getAllBitsMask(size));
    final String shiftValue = String.valueOf(TranslationHelpers.getShiftMsbLsbMask(size));
    final String shiftCarry = String.valueOf(-size.getBitSize());

    final OperandSize resultSize = TranslationHelpers.getNextSize(size);

    final String msb1 = environment.getNextVariableString();
    final String msb2 = environment.getNextVariableString();
    final String addResult = environment.getNextVariableString();
    final String msbResult = environment.getNextVariableString();
    final String msbSameBefore = environment.getNextVariableString();
    final String msbSameBeforeNeg = environment.getNextVariableString();
    final String msbChanged = environment.getNextVariableString();
    final String tempOf = environment.getNextVariableString();
    final String tempCf = environment.getNextVariableString();
    final String truncatedResult = environment.getNextVariableString();

    // Isolate the MSBs of the two operands
    instructions
        .add(ReilHelpers.createAnd(offset, size, sourceRegister, size, msbMask, size, msb1));
    instructions.add(ReilHelpers.createAnd(offset + 1, size, targetRegister, size, msbMask, size,
        msb2));

    // Perform the addition
    instructions.add(ReilHelpers.createAdd(offset + 2, size, sourceRegister, size, targetRegister,
        resultSize, addResult));

    // Isolate the MSB of the result and put it into the Sign Flag
    instructions.add(ReilHelpers.createAnd(offset + 3, resultSize, addResult, resultSize, msbMask,
        size, msbResult));
    instructions.add(ReilHelpers.createBsh(offset + 4, size, msbResult, size, shiftValue,
        OperandSize.BYTE, Helpers.SIGN_FLAG));

    // Find out if the MSB of the two operands were different and whether the MSB of the first
    // operand changed
    instructions
        .add(ReilHelpers.createXor(offset + 5, size, msb1, size, msb2, size, msbSameBefore));
    instructions.add(ReilHelpers.createXor(offset + 6, size, msbSameBefore, size, msbMask, size,
        msbSameBeforeNeg));
    instructions.add(ReilHelpers.createXor(offset + 7, size, msb1, size, msbResult, size,
        msbChanged));
    instructions.add(ReilHelpers.createAnd(offset + 8, size, msbSameBeforeNeg, size, msbChanged,
        size, tempOf));

    // Write the result into the Overflow Flag
    instructions.add(ReilHelpers.createBsh(offset + 9, size, tempOf, size, shiftValue,
        OperandSize.BYTE, Helpers.OVERFLOW_FLAG));

    // Update the Carry Flag
    instructions.add(ReilHelpers.createAnd(offset + 10, resultSize, addResult, resultSize,
        carryMask, resultSize, tempCf));
    instructions.add(ReilHelpers.createBsh(offset + 11, resultSize, tempCf, resultSize, shiftCarry,
        OperandSize.BYTE, Helpers.CARRY_FLAG));

    // Truncate the result to fit into the target
    instructions.add(ReilHelpers.createAnd(offset + 12, resultSize, addResult, resultSize,
        truncateMask, size, truncatedResult));

    // Update the Zero Flag
    instructions.add(ReilHelpers.createBisz(offset + 13, size, truncatedResult, OperandSize.BYTE,
        Helpers.ZERO_FLAG));

    // Write the result of the ADD operation back into the target register
    Helpers.writeBack(environment, offset + 14, targetOperand, truncatedResult, size,
        targetResult.getAddress(), targetResult.getType(), instructions);
  }

}