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.MInsnWithData;
  import dexfuzz.program.MutatableCode;
  import dexfuzz.program.Mutation;
  
  import java.util.List;
  import java.util.Random;
  
  public class InstructionDeleter 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 insnToDeleteIdx;
  
      @Override
      public String getString() {
        return Integer.toString(insnToDeleteIdx);
      }
  
      @Override
      public void parseString(String[] elements) {
        insnToDeleteIdx = 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 InstructionDeleter() { }
  
    public InstructionDeleter(Random rng, MutationStats stats, List<Mutation> mutations) {
      super(rng, stats, mutations);
      likelihood = 40;
    }
  
    @Override
    protected boolean canMutate(MutatableCode mutatableCode) {
      if (mutatableCode.getInstructionCount() < 4) {
        // TODO: Make this more sophisticated - right now this is to avoid problems with
        // a method that has 3 instructions: fill-array-data; return-void; <data for fill-array-data>
        Log.debug("Cannot delete insns in a method with only a few.");
        return false;
      }
      return true;
    }
  
    @Override
    protected Mutation generateMutation(MutatableCode mutatableCode) {
      // Pick an instruction at random...
      int insnIdx = rng.nextInt(mutatableCode.getInstructionCount());
  
      AssociatedMutation mutation = new AssociatedMutation();
      mutation.setup(this.getClass(), mutatableCode);
      mutation.insnToDeleteIdx = insnIdx;
      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;
  
      MInsn toBeDeleted =
          mutatableCode.getInstructionAt(mutation.insnToDeleteIdx);
  
      Log.info("Deleting " + toBeDeleted);
  
      stats.incrementStat("Deleted instruction");
  
      // Delete the instruction.
      mutatableCode.deleteInstruction(mutation.insnToDeleteIdx);
  
      // If we delete a with-data insn, we should delete the associated data insn as well.
      if (toBeDeleted instanceof MInsnWithData) {
        Log.info(toBeDeleted + " had associated data, so the data insn was deleted.");
        // Get the data instruction.
        MInsn dataInsn =
            ((MInsnWithData)toBeDeleted).dataTarget;
        mutatableCode.deleteInstruction(dataInsn);
        stats.incrementStat("Deleted a with-data insn's data");
      }
      // If we delete a data insn, we should delete the associated with-data insn as well.
      if (toBeDeleted.insn.justRaw) {
        // .justRaw implies that this is a data insn.
        Log.info(toBeDeleted
            + " was data, so the associated with-data insn was deleted.");
  
        // First, find the with-data insn that is pointing to this insn.
        MInsn withDataInsn = null;
        for (MInsn mInsn : mutatableCode.getInstructions()) {
          if (mInsn instanceof MInsnWithData) {
            if (((MInsnWithData)mInsn).dataTarget == toBeDeleted) {
              withDataInsn = mInsn;
              break;
            }
          }
        }
  
        // Now delete the with-data insn.
        if (withDataInsn != null) {
          mutatableCode.deleteInstruction(withDataInsn);
          stats.incrementStat("Deleted a data insn's with-data insn");
        } else {
          Log.errorAndQuit("Tried to delete a data insn, "
              + "but it didn't have any with-data insn pointing at it?");
        }
      }
    }
  }
  