From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Alexander Burmashev <alexander.burmashev@oracle.com>
Date: Wed, 22 Jul 2020 06:04:38 -0700
Subject: [PATCH] update safemath with fallback code for gcc older than 5.1

The code used in the header was taken from linux kernel commit
f0907827a8a9152aedac2833ed1b674a7b2a44f2.  Rasmus Villemoes
<linux@rasmusvillemoes.dk>, the original author of the patch, was
contacted directly, confirmed his authorship of the code, and gave his
permission on treating that dual license as MIT and including into GRUB2
sources

Signed-off-by: Alex Burmashev <alexander.burmashev@oracle.com>
---
 include/grub/safemath.h | 119 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 118 insertions(+), 1 deletion(-)

diff --git a/include/grub/safemath.h b/include/grub/safemath.h
index c17b89bba17..1ccac276b59 100644
--- a/include/grub/safemath.h
+++ b/include/grub/safemath.h
@@ -31,7 +31,124 @@
 #define grub_mul(a, b, res)	__builtin_mul_overflow(a, b, res)
 
 #else
-#error gcc 5.1 or newer or clang 3.8 or newer is required
+/*
+ * Copyright 2020 Rasmus Villemoes
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+/*
+ * The code used in this header was taken from linux kernel commit
+ * f0907827a8a9152aedac2833ed1b674a7b2a44f2
+ * Rasmus Villemoes <linux@rasmusvillemoes.dk>, the original author of the
+ * patch, was contacted directly, confirmed his authorship of the code, and
+ * gave his permission on treating that dual license as MIT and including into
+ * GRUB2 sources
+ */
+
+#include <grub/types.h>
+#define is_signed_type(type)	(((type)(-1)) < (type)1)
+#define __type_half_max(type)	((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
+#define type_max(T)		((T)((__type_half_max(T) - 1) + __type_half_max(T)))
+#define type_min(T)		((T)((T)-type_max(T)-(T)1))
+
+#define __unsigned_add_overflow(a, b, d) ({	\
+	typeof(+(a)) __a = (a);			\
+	typeof(+(b)) __b = (b);			\
+	typeof(d) __d = (d);			\
+	(void) (&__a == &__b);			\
+	(void) (&__a == __d);			\
+	*__d = __a + __b;			\
+	*__d < __a;				\
+})
+#define __unsigned_sub_overflow(a, b, d) ({     \
+	typeof(+(a)) __a = (a);			\
+	typeof(+(b)) __b = (b);			\
+	typeof(d) __d = (d);			\
+	(void) (&__a == &__b);			\
+	(void) (&__a == __d);			\
+	*__d = __a - __b;			\
+	__a < __b;				\
+})
+#define __unsigned_mul_overflow(a, b, d) ({		\
+	typeof(+(a)) __a = (a);				\
+	typeof(+(b)) __b = (b);				\
+	typeof(d) __d = (d);				\
+	(void) (&__a == &__b);				\
+	(void) (&__a == __d);				\
+	*__d = __a * __b;				\
+	__builtin_constant_p(__b) ?			\
+	  __b > 0 && __a > type_max(typeof(__a)) / __b :\
+	  __a > 0 && __b > type_max(typeof(__b)) / __a; \
+})
+
+#define __signed_add_overflow(a, b, d) ({		\
+	typeof(+(a)) __a = (a);				\
+	typeof(+(b)) __b = (b);				\
+	typeof(d) __d = (d);				\
+	(void) (&__a == &__b);				\
+	(void) (&__a == __d);				\
+	*__d = (grub_uint64_t)__a + (grub_uint64_t)__b;	\
+	(((~(__a ^ __b)) & (*__d ^ __a))		\
+		& type_min(typeof(__a))) != 0;		\
+})
+
+#define __signed_sub_overflow(a, b, d) ({		\
+	typeof(+(a)) __a = (a);				\
+	typeof(+(b)) __b = (b);				\
+	typeof(d) __d = (d);				\
+	(void) (&__a == &__b);				\
+	(void) (&__a == __d);				\
+	*__d = (grub_uint64_t)__a - (grub_uint64_t)__b;	\
+	((((__a ^ __b)) & (*__d ^ __a))			\
+		& type_min(typeof(__a))) != 0;		\
+})
+
+#define __signed_mul_overflow(a, b, d) ({			\
+	typeof(+(a)) __a = (a);					\
+	typeof(+(b)) __b = (b);					\
+	typeof(d) __d = (d);					\
+	typeof(+(a)) __tmax = type_max(typeof(+(a)));		\
+	typeof(+(a)) __tmin = type_min(typeof(+(a)));		\
+	(void) (&__a == &__b);					\
+	(void) (&__a == __d);					\
+	*__d = (grub_uint64_t)__a * (grub_uint64_t)__b;		\
+	(__b > 0   && (__a > __tmax/__b || __a < __tmin/__b)) ||\
+	(__b < (typeof(__b))-1  &&				\
+	 (__a > __tmin/__b || __a < __tmax/__b)) ||		\
+	(__b == (typeof(__b))-1 && __a == __tmin);		\
+})
+
+#define grub_add(a, b, d)					\
+	__builtin_choose_expr(is_signed_type(typeof(+(a))),	\
+			__signed_add_overflow(a, b, d),		\
+			__unsigned_add_overflow(a, b, d))
+
+#define grub_sub(a, b, d)					\
+	__builtin_choose_expr(is_signed_type(typeof(+(a))),	\
+			__signed_sub_overflow(a, b, d),		\
+			__unsigned_sub_overflow(a, b, d))
+
+#define grub_mul(a, b, d)					\
+	__builtin_choose_expr(is_signed_type(typeof(+(a))),	\
+			__signed_mul_overflow(a, b, d),		\
+			__unsigned_mul_overflow(a, b, d))
+
 #endif
 
 #endif /* GRUB_SAFEMATH_H */