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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package dexfuzz.program.mutators;
     18 
     19 import dexfuzz.Log;
     20 import dexfuzz.MutationStats;
     21 import dexfuzz.program.MInsn;
     22 import dexfuzz.program.MutatableCode;
     23 import dexfuzz.program.Mutation;
     24 
     25 import java.util.List;
     26 import java.util.Random;
     27 
     28 public class InstructionSwapper extends CodeMutator {
     29   /**
     30    * Every CodeMutator has an AssociatedMutation, representing the
     31    * mutation that this CodeMutator can perform, to allow separate
     32    * generateMutation() and applyMutation() phases, allowing serialization.
     33    */
     34   public static class AssociatedMutation extends Mutation {
     35     public int swapInsnIdx;
     36     public int swapWithInsnIdx;
     37 
     38     @Override
     39     public String getString() {
     40       StringBuilder builder = new StringBuilder();
     41       builder.append(swapInsnIdx).append(" ");
     42       builder.append(swapWithInsnIdx);
     43       return builder.toString();
     44     }
     45 
     46     @Override
     47     public void parseString(String[] elements) {
     48       swapInsnIdx = Integer.parseInt(elements[2]);
     49       swapWithInsnIdx = Integer.parseInt(elements[3]);
     50     }
     51   }
     52 
     53   // The following two methods are here for the benefit of MutationSerializer,
     54   // so it can create a CodeMutator and get the correct associated Mutation, as it
     55   // reads in mutations from a dump of mutations.
     56   @Override
     57   public Mutation getNewMutation() {
     58     return new AssociatedMutation();
     59   }
     60 
     61   public InstructionSwapper() { }
     62 
     63   public InstructionSwapper(Random rng, MutationStats stats, List<Mutation> mutations) {
     64     super(rng, stats, mutations);
     65     likelihood = 80;
     66   }
     67 
     68   @Override
     69   protected boolean canMutate(MutatableCode mutatableCode) {
     70     if (mutatableCode.getInstructionCount() == 1) {
     71       // Cannot swap one instruction.
     72       Log.debug("Cannot swap insns in a method with only one.");
     73       return false;
     74     }
     75     return true;
     76   }
     77 
     78   @Override
     79   protected Mutation generateMutation(MutatableCode mutatableCode) {
     80     int swapInsnIdx = 0;
     81     int swapWithInsnIdx = 0;
     82 
     83     boolean foundFirstInsn = false;
     84     boolean foundSecondInsn = false;
     85 
     86     while (!foundFirstInsn || !foundSecondInsn) {
     87       // Look for the first insn.
     88       while (!foundFirstInsn) {
     89         swapInsnIdx = rng.nextInt(mutatableCode.getInstructionCount());
     90         MInsn toBeSwapped = mutatableCode.getInstructionAt(swapInsnIdx);
     91         foundFirstInsn = true;
     92         if (toBeSwapped.insn.justRaw) {
     93           foundFirstInsn = false;
     94         }
     95       }
     96 
     97       // Look for the second insn.
     98       int secondInsnAttempts = 0;
     99       while (!foundSecondInsn) {
    100         int delta = rng.nextInt(5) - 1;
    101 
    102         if (delta == 0) {
    103           continue;
    104         }
    105 
    106         swapWithInsnIdx = swapInsnIdx + delta;
    107         foundSecondInsn = true;
    108 
    109         // Check insn is in valid range.
    110         if (swapWithInsnIdx < 0) {
    111           foundSecondInsn = false;
    112         } else if (swapWithInsnIdx >= mutatableCode.getInstructionCount()) {
    113           foundSecondInsn = false;
    114         }
    115 
    116         // Finally, check if we're swapping with a raw insn.
    117         if (foundSecondInsn) {
    118           if (mutatableCode.getInstructionAt(swapWithInsnIdx).insn.justRaw) {
    119             foundSecondInsn = false;
    120           }
    121         }
    122 
    123         // If we've checked 10 times for an insn to swap with,
    124         // and still found nothing, then try a new first insn.
    125         if (!foundSecondInsn) {
    126           secondInsnAttempts++;
    127           if (secondInsnAttempts == 10) {
    128             foundFirstInsn = false;
    129             break;
    130           }
    131         }
    132       }
    133     }
    134 
    135     AssociatedMutation mutation = new AssociatedMutation();
    136     mutation.setup(this.getClass(), mutatableCode);
    137     mutation.swapInsnIdx = swapInsnIdx;
    138     mutation.swapWithInsnIdx = swapWithInsnIdx;
    139     return mutation;
    140   }
    141 
    142   @Override
    143   protected void applyMutation(Mutation uncastMutation) {
    144     // Cast the Mutation to our AssociatedMutation, so we can access its fields.
    145     AssociatedMutation mutation = (AssociatedMutation) uncastMutation;
    146     MutatableCode mutatableCode = mutation.mutatableCode;
    147 
    148     MInsn toBeSwapped = mutatableCode.getInstructionAt(mutation.swapInsnIdx);
    149     MInsn swappedWith = mutatableCode.getInstructionAt(mutation.swapWithInsnIdx);
    150 
    151     Log.info("Swapping " + toBeSwapped + " with " + swappedWith);
    152 
    153     stats.incrementStat("Swapped two instructions");
    154 
    155     mutatableCode.swapInstructionsByIndex(mutation.swapInsnIdx, mutation.swapWithInsnIdx);
    156 
    157     Log.info("Now " + swappedWith + " is swapped with " + toBeSwapped);
    158   }
    159 }
    160