1 files changed, 110 insertions, 0 deletions
diff --git a/java15/src/main/java/io/perfmark/java15/SecretHiddenClassMarkHolderProvider.java b/java15/src/main/java/io/perfmark/java15/SecretHiddenClassMarkHolderProvider.java
new file mode 100644
index 0000000..a296f40
--- /dev/null
+++ b/java15/src/main/java/io/perfmark/java15/SecretHiddenClassMarkHolderProvider.java
@@ -0,0 +1,110 @@
+/*
+ * Copyright 2021 Carl Mastrangelo
+ *
+ * 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 io.perfmark.java15;
+
+import io.perfmark.impl.MarkHolder;
+import io.perfmark.impl.MarkHolderProvider;
+import java.io.IOException;
+import java.io.InputStream;
+import java.lang.invoke.MethodHandles;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.util.Arrays;
+
+public final class SecretHiddenClassMarkHolderProvider {
+  public static final class HiddenClassMarkHolderProvider extends MarkHolderProvider {
+    private static final int DEFAULT_SIZE = 32768;
+
+    private final int[] maxEventsOffsets;
+    private final int[] maxEventsMaskOffsets;
+
+    private final byte[] markHolderClassData;
+
+    public HiddenClassMarkHolderProvider() {
+      try (InputStream classData = getClass().getResourceAsStream("HiddenClassVarHandleMarkHolder.class")) {
+        markHolderClassData = classData.readAllBytes();
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+
+      ByteBuffer expectedMaxEvents = ByteBuffer.allocate(4).order(ByteOrder.BIG_ENDIAN);
+      expectedMaxEvents.putInt(HiddenClassVarHandleMarkHolder.MAX_EVENTS);
+      byte[] maxEvents = expectedMaxEvents.array();
+      maxEventsOffsets = findOffsets(markHolderClassData, maxEvents);
+      if (maxEventsOffsets.length != 2) {
+        throw new RuntimeException("hop");
+      }
+
+      ByteBuffer expectedMaxEventsMask = ByteBuffer.allocate(8).order(ByteOrder.BIG_ENDIAN);
+      expectedMaxEventsMask.putLong(HiddenClassVarHandleMarkHolder.MAX_EVENTS_MASK);
+      byte[] maxEventsMax = expectedMaxEventsMask.array();
+      maxEventsMaskOffsets = findOffsets(markHolderClassData, maxEventsMax);
+      if (maxEventsMaskOffsets.length != 1) {
+        throw new RuntimeException("skip");
+      }
+
+      replaceSize(markHolderClassData, DEFAULT_SIZE);
+    }
+
+    @Override
+    public MarkHolder create(long markHolderId) {
+      return create(markHolderId, DEFAULT_SIZE);
+    }
+
+    MarkHolder create(long markHolderId, int size) {
+      final byte[] classData;
+      if (size != DEFAULT_SIZE) {
+        classData = Arrays.copyOf(markHolderClassData, markHolderClassData.length);
+        replaceSize(classData, size);
+      } else {
+        classData = markHolderClassData;
+      }
+      try {
+        Class<?> clz = MethodHandles.lookup().defineHiddenClass(classData, true).lookupClass();
+        return clz.asSubclass(MarkHolder.class).getDeclaredConstructor().newInstance();
+      } catch (ReflectiveOperationException e) {
+        throw new RuntimeException(e);
+      }
+    }
+
+    private void replaceSize(byte[] haystack, int size) {
+      ByteBuffer buf = ByteBuffer.wrap(haystack).order(ByteOrder.BIG_ENDIAN);
+      for (int off : maxEventsOffsets) {
+        buf.putInt(off, size);
+      }
+      for (int off : maxEventsMaskOffsets) {
+        buf.putLong(off, size - 1);
+      }
+    }
+
+    private static int[] findOffsets(byte[] haystack, byte[] needle) {
+      int[] matches = new int[0];
+      outer: for (int i = 0; i < haystack.length - needle.length; i++) {
+        for (int k = 0; k < needle.length; k++) {
+          if (haystack[i + k] != needle[k]) {
+            continue outer;
+          }
+        }
+        matches = Arrays.copyOf(matches, matches.length + 1);
+        matches[matches.length - 1] = i;
+      }
+      return matches;
+    }
+  }
+
+  private SecretHiddenClassMarkHolderProvider() {}
+}