v4.19.13 snapshot.
diff --git a/include/linux/gcd.h b/include/linux/gcd.h
new file mode 100644
index 0000000..cb57267
--- /dev/null
+++ b/include/linux/gcd.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _GCD_H
+#define _GCD_H
+
+#include <linux/compiler.h>
+
+unsigned long gcd(unsigned long a, unsigned long b) __attribute_const__;
+
+#endif /* _GCD_H */