diff --git a/libc/malloc_debug/GuardData.h b/libc/malloc_debug/GuardData.h
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+++ b/libc/malloc_debug/GuardData.h
@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef DEBUG_MALLOC_GUARDDATA_H
+#define DEBUG_MALLOC_GUARDDATA_H
+
+#include <stdint.h>
+#include <string.h>
+
+#include <vector>
+
+#include <private/bionic_macros.h>
+
+// Forward declarations.
+class DebugData;
+struct Header;
+struct Config;
+
+class GuardData {
+ public:
+  GuardData(int init_value, size_t num_bytes);
+  virtual ~GuardData() = default;
+
+  bool Valid(void* data) { return memcmp(data, cmp_mem_.data(), cmp_mem_.size()) == 0; }
+
+  void LogFailure(const Header* header, const void* pointer, const void* data);
+
+ protected:
+  std::vector<uint8_t> cmp_mem_;
+
+  virtual const char* GetTypeName() = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(GuardData);
+};
+
+class FrontGuardData : public GuardData {
+ public:
+  FrontGuardData(const Config& config, size_t* offset);
+  virtual ~FrontGuardData() = default;
+
+  bool Valid(DebugData& debug, const Header* header);
+
+  void LogFailure(DebugData& debug, const Header* header);
+
+  size_t offset() { return offset_; }
+
+ private:
+  const char* GetTypeName() override { return "FRONT"; }
+
+  size_t offset_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(FrontGuardData);
+};
+
+class RearGuardData : public GuardData {
+ public:
+  RearGuardData(const Config& config);
+  virtual ~RearGuardData() = default;
+
+  bool Valid(DebugData& debug, const Header* header);
+
+  void LogFailure(DebugData& debug, const Header* header);
+
+ private:
+  const char* GetTypeName() override { return "REAR"; }
+
+  DISALLOW_COPY_AND_ASSIGN(RearGuardData);
+};
+
+#endif // DEBUG_MALLOC_GUARDDATA_H