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diff --git a/src/main/java/com/code_intelligence/jazzer/runtime/CoverageMap.java b/src/main/java/com/code_intelligence/jazzer/runtime/CoverageMap.java
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+++ b/src/main/java/com/code_intelligence/jazzer/runtime/CoverageMap.java
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+// Copyright 2021 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.runtime;
+
+import static com.code_intelligence.jazzer.runtime.Constants.IS_ANDROID;
+
+import com.code_intelligence.jazzer.utils.UnsafeProvider;
+import com.github.fmeum.rules_jni.RulesJni;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import sun.misc.Unsafe;
+
+/**
+ * Represents the Java view on a libFuzzer 8 bit counter coverage map. By using a direct ByteBuffer,
+ * the counters are shared directly with native code.
+ */
+final public class CoverageMap {
+  static {
+    RulesJni.loadLibrary("jazzer_driver", "/com/code_intelligence/jazzer/driver");
+  }
+
+  private static final String ENV_MAX_NUM_COUNTERS = "JAZZER_MAX_NUM_COUNTERS";
+
+  private static final int MAX_NUM_COUNTERS = System.getenv(ENV_MAX_NUM_COUNTERS) != null
+      ? Integer.parseInt(System.getenv(ENV_MAX_NUM_COUNTERS))
+      : 1 << 20;
+
+  private static final Unsafe UNSAFE = UnsafeProvider.getUnsafe();
+  private static final Class<?> LOG;
+  private static final MethodHandle LOG_INFO;
+  private static final MethodHandle LOG_ERROR;
+
+  static {
+    try {
+      LOG = Class.forName(
+          "com.code_intelligence.jazzer.utils.Log", false, ClassLoader.getSystemClassLoader());
+      LOG_INFO = MethodHandles.lookup().findStatic(
+          LOG, "info", MethodType.methodType(void.class, String.class));
+      LOG_ERROR = MethodHandles.lookup().findStatic(
+          LOG, "error", MethodType.methodType(void.class, String.class, Throwable.class));
+    } catch (ClassNotFoundException | NoSuchMethodException | IllegalAccessException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /**
+   * The collection of coverage counters directly interacted with by classes that are instrumented
+   * for coverage. The instrumentation assumes that this is always one contiguous block of memory,
+   * so it is allocated once at maximum size. Using a larger number here increases the memory usage
+   * of all fuzz targets, but has otherwise no impact on performance.
+   */
+  public static final long countersAddress = UNSAFE.allocateMemory(MAX_NUM_COUNTERS);
+
+  static {
+    UNSAFE.setMemory(countersAddress, MAX_NUM_COUNTERS, (byte) 0);
+    initialize(countersAddress);
+  }
+
+  private static final int INITIAL_NUM_COUNTERS = 1 << 9;
+
+  static {
+    registerNewCounters(0, INITIAL_NUM_COUNTERS);
+  }
+
+  /**
+   * The number of coverage counters that are currently registered with libFuzzer. This number grows
+   * dynamically as classes are instrumented and should be kept as low as possible as libFuzzer has
+   * to iterate over the whole map for every execution.
+   */
+  private static int currentNumCounters = INITIAL_NUM_COUNTERS;
+
+  // Called via reflection.
+  @SuppressWarnings("unused")
+  public static void enlargeIfNeeded(int nextId) {
+    int newNumCounters = currentNumCounters;
+    while (nextId >= newNumCounters) {
+      newNumCounters = 2 * newNumCounters;
+      if (newNumCounters > MAX_NUM_COUNTERS) {
+        logError(
+            String.format(
+                "Maximum number (%s) of coverage counters exceeded. Try to limit the scope of a single fuzz target as "
+                    + "much as possible to keep the fuzzer fast. If that is not possible, the maximum number of "
+                    + "counters can be increased via the %s environment variable.",
+                MAX_NUM_COUNTERS, ENV_MAX_NUM_COUNTERS),
+            null);
+        System.exit(1);
+      }
+    }
+    if (newNumCounters > currentNumCounters) {
+      registerNewCounters(currentNumCounters, newNumCounters);
+      currentNumCounters = newNumCounters;
+      logInfo("New number of coverage counters: " + currentNumCounters);
+    }
+  }
+
+  // Called by the coverage instrumentation.
+  @SuppressWarnings("unused")
+  public static void recordCoverage(final int id) {
+    if (IS_ANDROID) {
+      enlargeIfNeeded(id);
+    }
+
+    final long address = countersAddress + id;
+    final byte counter = UNSAFE.getByte(address);
+    UNSAFE.putByte(address, (byte) (counter == -1 ? 1 : counter + 1));
+  }
+
+  public static Set<Integer> getCoveredIds() {
+    Set<Integer> coveredIds = new HashSet<>();
+    for (int id = 0; id < currentNumCounters; id++) {
+      if (UNSAFE.getByte(countersAddress + id) > 0) {
+        coveredIds.add(id);
+      }
+    }
+    return Collections.unmodifiableSet(coveredIds);
+  }
+
+  public static void replayCoveredIds(Set<Integer> coveredIds) {
+    for (int id : coveredIds) {
+      UNSAFE.putByte(countersAddress + id, (byte) 1);
+    }
+  }
+
+  private static void logInfo(String message) {
+    try {
+      LOG_INFO.invokeExact(message);
+    } catch (Throwable error) {
+      // Should not be reached, Log.error does not throw.
+      error.printStackTrace();
+      System.err.println("Failed to call Log.info:");
+      System.err.println(message);
+    }
+  }
+
+  private static void logError(String message, Throwable t) {
+    try {
+      LOG_ERROR.invokeExact(message, t);
+    } catch (Throwable error) {
+      // Should not be reached, Log.error does not throw.
+      error.printStackTrace();
+      System.err.println("Failed to call Log.error:");
+      System.err.println(message);
+    }
+  }
+
+  // Returns the IDs of all blocks that have been covered in at least one run (not just the current
+  // one).
+  public static native int[] getEverCoveredIds();
+
+  private static native void initialize(long countersAddress);
+
+  private static native void registerNewCounters(int oldNumCounters, int newNumCounters);
+}