diff --git a/Documentation/perf_counter/util/string.h b/Documentation/perf_counter/util/string.h
new file mode 100644
index 0000000..72812c1
--- /dev/null
+++ b/Documentation/perf_counter/util/string.h
@@ -0,0 +1,8 @@
+#ifndef _PERF_STRING_H_
+#define _PERF_STRING_H_
+
+#include <linux/types.h>
+
+int hex2u64(const char *ptr, __u64 *val);
+
+#endif