content: /*
   * Copyright (C) 2014 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 dexfuzz.program.mutators;
  
  import dexfuzz.Log;
  import dexfuzz.MutationStats;
  import dexfuzz.program.MInsn;
  import dexfuzz.program.MutatableCode;
  import dexfuzz.program.Mutation;
  import dexfuzz.rawdex.Instruction;
  import dexfuzz.rawdex.Opcode;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Random;
  
  public class CmpBiasChanger extends CodeMutator {
    /**
     * Every CodeMutator has an AssociatedMutation, representing the
     * mutation that this CodeMutator can perform, to allow separate
     * generateMutation() and applyMutation() phases, allowing serialization.
     */
    public static class AssociatedMutation extends Mutation {
      public int cmpBiasInsnIdx;
  
      @Override
      public String getString() {
        return Integer.toString(cmpBiasInsnIdx);
      }
  
      @Override
      public void parseString(String[] elements) {
        cmpBiasInsnIdx = Integer.parseInt(elements[2]);
      }
    }
  
    // The following two methods are here for the benefit of MutationSerializer,
    // so it can create a CodeMutator and get the correct associated Mutation, as it
    // reads in mutations from a dump of mutations.
    @Override
    public Mutation getNewMutation() {
      return new AssociatedMutation();
    }
  
    public CmpBiasChanger() { }
  
    public CmpBiasChanger(Random rng, MutationStats stats, List<Mutation> mutations) {
      super(rng, stats, mutations);
      likelihood = 30;
    }
  
    // A cache that should only exist between generateMutation() and applyMutation(),
    // or be created at the start of applyMutation(), if we're reading in mutations from
    // a file.
    private List<MInsn> cmpBiasInsns = null;
  
    private void generateCachedCmpBiasInsns(MutatableCode mutatableCode) {
      if (cmpBiasInsns != null) {
        return;
      }
  
      cmpBiasInsns = new ArrayList<MInsn>();
  
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (isCmpBiasOperation(mInsn)) {
          cmpBiasInsns.add(mInsn);
        }
      }
    }
  
    @Override
    protected boolean canMutate(MutatableCode mutatableCode) {
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (isCmpBiasOperation(mInsn)) {
          return true;
        }
      }
  
      Log.debug("No cmp-with-bias operations in method, skipping...");
      return false;
    }
  
    @Override
    protected Mutation generateMutation(MutatableCode mutatableCode) {
      generateCachedCmpBiasInsns(mutatableCode);
  
      int cmpBiasInsnIdx = rng.nextInt(cmpBiasInsns.size());
  
      AssociatedMutation mutation = new AssociatedMutation();
      mutation.setup(this.getClass(), mutatableCode);
      mutation.cmpBiasInsnIdx = cmpBiasInsnIdx;
      return mutation;
    }
  
    @Override
    protected void applyMutation(Mutation uncastMutation) {
      // Cast the Mutation to our AssociatedMutation, so we can access its fields.
      AssociatedMutation mutation = (AssociatedMutation) uncastMutation;
      MutatableCode mutatableCode = mutation.mutatableCode;
  
      generateCachedCmpBiasInsns(mutatableCode);
  
      MInsn cmpBiasInsn = cmpBiasInsns.get(mutation.cmpBiasInsnIdx);
  
      String oldInsnString = cmpBiasInsn.toString();
  
      Opcode newOpcode = getLegalDifferentOpcode(cmpBiasInsn);
  
      cmpBiasInsn.insn.info = Instruction.getOpcodeInfo(newOpcode);
  
      Log.info("Changed " + oldInsnString + " to " + cmpBiasInsn);
  
      stats.incrementStat("Changed comparison bias");
  
      // Clear cache.
      cmpBiasInsns = null;
    }
  
    private Opcode getLegalDifferentOpcode(MInsn mInsn) {
      Opcode opcode = mInsn.insn.info.opcode;
      if (opcode == Opcode.CMPG_DOUBLE) {
        return Opcode.CMPL_DOUBLE;
      }
      if (opcode == Opcode.CMPL_DOUBLE) {
        return Opcode.CMPG_DOUBLE;
      }
      if (opcode == Opcode.CMPG_FLOAT) {
        return Opcode.CMPL_FLOAT;
      }
      return Opcode.CMPG_FLOAT;
    }
  
    private boolean isCmpBiasOperation(MInsn mInsn) {
      Opcode opcode = mInsn.insn.info.opcode;
      if (Opcode.isBetween(opcode, Opcode.CMPL_FLOAT, Opcode.CMPG_DOUBLE)) {
        return true;
      }
      return false;
    }
  }
  