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.formats.ContainsPoolIndex;
  import dexfuzz.rawdex.formats.ContainsPoolIndex.PoolIndexKind;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Random;
  
  public class PoolIndexChanger 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 poolIndexInsnIdx;
      public int newPoolIndex;
  
      @Override
      public String getString() {
        StringBuilder builder = new StringBuilder();
        builder.append(poolIndexInsnIdx).append(" ");
        builder.append(newPoolIndex);
        return builder.toString();
      }
  
      @Override
      public void parseString(String[] elements) {
        poolIndexInsnIdx = Integer.parseInt(elements[2]);
        newPoolIndex = Integer.parseInt(elements[3]);
      }
    }
  
    // 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 PoolIndexChanger() { }
  
    public PoolIndexChanger(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> poolIndexInsns = null;
  
    private void generateCachedPoolIndexInsns(MutatableCode mutatableCode) {
      if (poolIndexInsns != null) {
        return;
      }
  
      poolIndexInsns = new ArrayList<MInsn>();
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (mInsn.insn.info.format instanceof ContainsPoolIndex) {
          poolIndexInsns.add(mInsn);
        }
      }
    }
  
    @Override
    protected boolean canMutate(MutatableCode mutatableCode) {
      // Remember what kinds of pool indices we see.
      List<PoolIndexKind> seenKinds = new ArrayList<PoolIndexKind>();
  
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (mInsn.insn.info.format instanceof ContainsPoolIndex) {
  
          ContainsPoolIndex containsPoolIndex =
              (ContainsPoolIndex)mInsn.insn.info.format;
  
          PoolIndexKind newPoolIndexKind =
              containsPoolIndex.getPoolIndexKind(mInsn.insn.info);
  
          seenKinds.add(newPoolIndexKind);
        }
      }
  
      // Now check that there exists a kind such that the max pool index for
      // the kind is greater than 1 (i.e., something can be changed)
      if (!seenKinds.isEmpty()) {
  
        for (PoolIndexKind kind : seenKinds) {
          int numPoolIndices = mutatableCode.program.getTotalPoolIndicesByKind(kind);
          if (numPoolIndices > 1) {
            return true;
          }
        }
  
        Log.debug("Method does not contain any insns that index into a const pool size > 1");
        return false;
      }
  
      Log.debug("Method contains no instructions that index into the constant pool.");
      return false;
    }
  
    @Override
    protected Mutation generateMutation(MutatableCode mutatableCode) {
      generateCachedPoolIndexInsns(mutatableCode);
  
      int poolIndexInsnIdx = 0;
      boolean found = false;
  
      int oldPoolIndex = 0;
      int newPoolIndex = 0;
      int maxPoolIndex = 0;
  
      // Pick a random instruction.
      while (!found) {
        poolIndexInsnIdx = rng.nextInt(poolIndexInsns.size());
        MInsn poolIndexInsn = poolIndexInsns.get(poolIndexInsnIdx);
  
        found = true;
  
        ContainsPoolIndex containsPoolIndex =
            (ContainsPoolIndex)poolIndexInsn.insn.info.format;
  
        // Get the pool index.
        oldPoolIndex = containsPoolIndex.getPoolIndex(poolIndexInsn.insn);
        newPoolIndex = oldPoolIndex;
  
        // Get the largest pool index available for the provided kind of pool index.
        PoolIndexKind poolIndexKind =
            containsPoolIndex.getPoolIndexKind(poolIndexInsn.insn.info);
        maxPoolIndex = mutatableCode.program.getTotalPoolIndicesByKind(poolIndexKind);
  
        if (maxPoolIndex <= 1) {
          found = false;
        }
      }
  
      // Get a new pool index.
      while (newPoolIndex == oldPoolIndex) {
        newPoolIndex = rng.nextInt(maxPoolIndex);
      }
  
      AssociatedMutation mutation = new AssociatedMutation();
      mutation.setup(this.getClass(), mutatableCode);
      mutation.poolIndexInsnIdx = poolIndexInsnIdx;
      mutation.newPoolIndex = newPoolIndex;
      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;
  
      generateCachedPoolIndexInsns(mutatableCode);
  
      MInsn poolIndexInsn = poolIndexInsns.get(mutation.poolIndexInsnIdx);
  
      ContainsPoolIndex containsPoolIndex =
          (ContainsPoolIndex) poolIndexInsn.insn.info.format;
  
      int oldPoolIndex = containsPoolIndex.getPoolIndex(poolIndexInsn.insn);
  
      Log.info("Changed pool index " + oldPoolIndex + " to " + mutation.newPoolIndex
          + " in " + poolIndexInsn);
  
      stats.incrementStat("Changed constant pool index");
  
      // Set the new pool index.
      containsPoolIndex.setPoolIndex(poolIndexInsn.insn, mutation.newPoolIndex);
  
      // Clear cache.
      poolIndexInsns = null;
    }
  }
  