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diff --git a/libipt/internal/include/pt_retstack.h b/libipt/internal/include/pt_retstack.h
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+++ b/libipt/internal/include/pt_retstack.h
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+/*
+ * Copyright (c) 2013-2019, Intel Corporation
+ *
+ * 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.
+ *  * Neither the name of Intel Corporation nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * 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 PT_RETSTACK_H
+#define PT_RETSTACK_H
+
+#include <stdint.h>
+
+
+/* The size of the call/return stack in number of entries. */
+enum {
+	pt_retstack_size	= 64
+};
+
+/* A stack of return addresses used for return compression. */
+struct pt_retstack {
+	/* The stack of return addresses.
+	 *
+	 * We use one additional entry in order to distinguish a full from
+	 * an empty stack.
+	 */
+	uint64_t stack[pt_retstack_size + 1];
+
+	/* The top of the stack. */
+	uint8_t top;
+
+	/* The bottom of the stack. */
+	uint8_t bottom;
+};
+
+/* Initialize (or reset) a call/return stack. */
+extern void pt_retstack_init(struct pt_retstack *);
+
+/* Test a call/return stack for emptiness.
+ *
+ * Returns zero if @retstack contains at least one element.
+ * Returns a positive integer if @retstack is empty.
+ * Returns -pte_invalid if @retstack is NULL.
+ */
+extern int pt_retstack_is_empty(const struct pt_retstack *retstack);
+
+/* Pop and return the topmost IP.
+ *
+ * If @ip is not NULL, provides the topmost return address on success.
+ * If @retstack is not empty, pops the topmost return address on success.
+ *
+ * Returns zero on success.
+ * Returns -pte_invalid if @retstack is NULL.
+ * Returns -pte_noip if @retstack is empty.
+ */
+extern int pt_retstack_pop(struct pt_retstack *retstack, uint64_t *ip);
+
+/* Push a return address onto the stack.
+ *
+ * Pushes @ip onto @retstack.
+ * If @retstack is full, drops the oldest return address.
+ *
+ * Returns zero on success.
+ */
+extern int pt_retstack_push(struct pt_retstack *retstack, uint64_t ip);
+
+#endif /* PT_RETSTACK_H */