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.MSwitchInsn;
  import dexfuzz.program.MutatableCode;
  import dexfuzz.program.Mutation;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Random;
  
  public class SwitchBranchShifter 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 switchInsnIdx;
      public int switchTargetIdx;
      public int newTargetIdx;
  
      @Override
      public String getString() {
        StringBuilder builder = new StringBuilder();
        builder.append(switchInsnIdx).append(" ");
        builder.append(switchTargetIdx).append(" ");
        builder.append(newTargetIdx);
        return builder.toString();
      }
  
      @Override
      public void parseString(String[] elements) {
        switchInsnIdx = Integer.parseInt(elements[2]);
        switchTargetIdx = Integer.parseInt(elements[3]);
        newTargetIdx = Integer.parseInt(elements[4]);
      }
    }
  
    // 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 SwitchBranchShifter() { }
  
    public SwitchBranchShifter(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<MSwitchInsn> switchInsns;
  
    private void generateCachedSwitchInsns(MutatableCode mutatableCode) {
      if (switchInsns != null) {
        return;
      }
  
      switchInsns = new ArrayList<MSwitchInsn>();
  
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (mInsn instanceof MSwitchInsn) {
          switchInsns.add((MSwitchInsn) mInsn);
        }
      }
    }
  
    @Override
    protected boolean canMutate(MutatableCode mutatableCode) {
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (mInsn instanceof MSwitchInsn) {
          return true;
        }
      }
  
      Log.debug("Method contains no switch instructions.");
      return false;
    }
  
    @Override
    protected Mutation generateMutation(MutatableCode mutatableCode) {
      generateCachedSwitchInsns(mutatableCode);
  
      // Pick a random switch instruction.
      int switchInsnIdx = rng.nextInt(switchInsns.size());
      MSwitchInsn switchInsn = switchInsns.get(switchInsnIdx);
  
      // Pick a random one of its targets.
      int switchTargetIdx = rng.nextInt(switchInsn.targets.size());
  
      // Get the original target, find its index.
      MInsn oldTargetInsn = switchInsn.targets.get(switchTargetIdx);
      int oldTargetInsnIdx = mutatableCode.getInstructionIndex(oldTargetInsn);
  
      int newTargetIdx = oldTargetInsnIdx;
  
      int delta = 0;
  
      // Keep searching for a new index.
      while (newTargetIdx == oldTargetInsnIdx) {
        // Vary by +/- 2 instructions.
        delta = 0;
        while (delta == 0) {
          delta = (rng.nextInt(5) - 2);
        }
  
        newTargetIdx = oldTargetInsnIdx + delta;
  
        // Check the new index is legal
        if (newTargetIdx < 0) {
          newTargetIdx = 0;
        } else if (newTargetIdx >= mutatableCode.getInstructionCount()) {
          newTargetIdx = mutatableCode.getInstructionCount() - 1;
        }
      }
  
      AssociatedMutation mutation = new AssociatedMutation();
      mutation.setup(this.getClass(), mutatableCode);
      mutation.switchInsnIdx = switchInsnIdx;
      mutation.switchTargetIdx = switchTargetIdx;
      mutation.newTargetIdx = newTargetIdx;
      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;
  
      generateCachedSwitchInsns(mutatableCode);
  
      MSwitchInsn switchInsn = switchInsns.get(mutation.switchInsnIdx);
  
      // Get the new target.
      MInsn newTargetInsn =
          mutatableCode.getInstructionAt(mutation.newTargetIdx);
  
      // Set the new target.
      switchInsn.targets.remove(mutation.switchTargetIdx);
      switchInsn.targets.add(mutation.switchTargetIdx, newTargetInsn);
  
      Log.info("Shifted target #" + mutation.switchTargetIdx + " of " + switchInsn
          + " to point to " + newTargetInsn);
  
      stats.incrementStat("Shifted switch target");
  
      // Clear cache.
      switchInsns = null;
    }
  }
  