RolTranslator.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 ROL instructions to REIL code.
 */
public class RolTranslator implements IInstructionTranslator {

  // TODO(timkornau): Check this code again

  /**
   * Translates a ROL instruction to REIL code.
   *
   * @param environment A valid translation environment.
   * @param instruction The ROL 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 ROL instruction
   */
  @Override
  public void translate(final ITranslationEnvironment environment, final IInstruction instruction,
      final List<ReilInstruction> instructions) throws InternalTranslationException {

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

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

    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 target 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 sourceSize = sourceResult.getSize();
    final OperandSize targetSize = targetResult.getSize();

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

    final String rotateMask = environment.getNextVariableString();
    final String rotateMaskZero = environment.getNextVariableString();
    final String rotateMaskLessOne = environment.getNextVariableString();
    final String rotateMaskOne = environment.getNextVariableString();
    final String shrValue = environment.getNextVariableString();
    final String shredResult = environment.getNextVariableString();
    final String shledResult = environment.getNextVariableString();
    final String result = environment.getNextVariableString();
    final String tempOf = environment.getNextVariableString();
    final String tempOfLsb = environment.getNextVariableString();

    final String msbMask = String.valueOf(TranslationHelpers.getMsbMask(targetSize));
    final String modVal = String.valueOf(targetSize.getBitSize());
    final String shiftMsbLsb = String.valueOf(TranslationHelpers.getShiftMsbLsbMask(targetSize));

    final int linesBefore = instructions.size();

    // Make sure to rotate less than the size of the register
    instructions.add(ReilHelpers.createMod(offset, sourceSize, sourceRegister, targetSize, modVal,
        targetSize, rotateMask));

    // Find out if the rotate mask is 0 and negate the result
    instructions.add(ReilHelpers.createBisz(offset + 1, targetSize, rotateMask, OperandSize.BYTE,
        rotateMaskZero));

    // Find out if the rotate mask is 1
    instructions.add(ReilHelpers.createSub(offset + 2, targetSize, rotateMask, targetSize, "1",
        targetSize, rotateMaskLessOne));
    instructions.add(ReilHelpers.createBisz(offset + 3, targetSize, rotateMaskLessOne,
        OperandSize.BYTE, rotateMaskOne));

    // Perform the rotate
    instructions.add(ReilHelpers.createBsh(offset + 4, targetSize, targetRegister,
        OperandSize.BYTE, rotateMask, targetSize, shledResult));
    instructions.add(ReilHelpers.createAdd(offset + 5, OperandSize.BYTE, "-" + modVal,
        OperandSize.BYTE, rotateMask, OperandSize.BYTE, shrValue));
    instructions.add(ReilHelpers.createBsh(offset + 6, targetSize, targetRegister,
        OperandSize.BYTE, shrValue, targetSize, shredResult));
    instructions.add(ReilHelpers.createOr(offset + 7, targetSize, shledResult, targetSize,
        shredResult, targetSize, result));

    // Don't change the flags if the rotate value was zero
    final String jmpGoal =
        String.format("%d.%d", instruction.getAddress().toLong(), linesBefore + 16);
    instructions.add(ReilHelpers.createJcc(offset + 8, OperandSize.BYTE, rotateMaskZero,
        OperandSize.ADDRESS, jmpGoal));

    // Set the CF to the new LSB
    instructions.add(ReilHelpers.createAnd(offset + 9, targetSize, result, sourceSize, "1",
        OperandSize.BYTE, Helpers.CARRY_FLAG));

    // The OF needs to be set to a different value if the rotate-mask was 1
    final String jmpGoal2 =
        String.format("%d.%d", instruction.getAddress().toLong(), linesBefore + 13);
    instructions.add(ReilHelpers.createJcc(offset + 10, OperandSize.BYTE, rotateMaskOne,
        OperandSize.ADDRESS, jmpGoal2));

    // Set the OF to undefined if the rotate-mask was positive but not 1
    instructions.add(ReilHelpers.createUndef(offset + 11, OperandSize.BYTE, Helpers.OVERFLOW_FLAG));

    // Jump to the end
    final String jmpGoal3 =
        String.format("%d.%d", instruction.getAddress().toLong(), linesBefore + 16);
    instructions.add(ReilHelpers.createJcc(offset + 12, OperandSize.BYTE, "1",
        OperandSize.ADDRESS, jmpGoal3));

    // OF = MSB(DEST) XOR CF
    instructions.add(ReilHelpers.createAnd(offset + 13, targetSize, result, targetSize, msbMask,
        sourceSize, tempOf));
    instructions.add(ReilHelpers.createBsh(offset + 14, targetSize, tempOf, targetSize,
        shiftMsbLsb, OperandSize.BYTE, tempOfLsb));
    instructions.add(ReilHelpers.createBsh(offset + 15, OperandSize.BYTE, tempOfLsb,
        OperandSize.BYTE, Helpers.CARRY_FLAG, OperandSize.BYTE, Helpers.OVERFLOW_FLAG));

    Helpers.writeBack(environment, offset + 16, targetOperand, result, targetResult.getSize(),
        targetResult.getAddress(), targetResult.getType(), instructions);
  }
}