agent/src/jmh/java/com/code_intelligence/jazzer/instrumentor/UnsafeBranchfreeCoverageMap.java


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// Copyright 2022 Code Intelligence GmbH
//
// 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 com.code_intelligence.jazzer.instrumentor;

import java.lang.reflect.Field;
import sun.misc.Unsafe;

public final class UnsafeBranchfreeCoverageMap {
  private static final Unsafe UNSAFE;

  static {
    Unsafe unsafe;
    try {
      Field f = Unsafe.class.getDeclaredField("theUnsafe");
      f.setAccessible(true);
      unsafe = (Unsafe) f.get(null);
    } catch (IllegalAccessException | NoSuchFieldException e) {
      e.printStackTrace();
      System.exit(1);
      // Not reached.
      unsafe = null;
    }
    UNSAFE = unsafe;
  }

  // The current target, JsonSanitizer, uses less than 2048 coverage counters.
  private static final long NUM_COUNTERS = 4096;
  private static final long countersAddress = UNSAFE.allocateMemory(NUM_COUNTERS);

  static {
    UNSAFE.setMemory(countersAddress, NUM_COUNTERS, (byte) 0);
  }

  public static void enlargeIfNeeded(int nextId) {
    // Statically sized counters buffer.
  }

  public static void recordCoverage(final int id) {
    final long address = countersAddress + id;
    final int incrementedCounter = UNSAFE.getByte(address) + 1;
    UNSAFE.putByte(address, (byte) (incrementedCounter ^ (incrementedCounter >>> 8)));
  }
}