From 68708c4503018d61dbcce7ac11cbb511d6425f4d Mon Sep 17 00:00:00 2001
From: Peter Jones <pjones@redhat.com>
Date: Mon, 15 Jun 2020 10:58:42 -0400
Subject: [PATCH 02/27] safemath: Add some arithmetic primitives that check for
 overflow

This adds a new header, include/grub/safemath.h, that includes easy to
use wrappers for __builtin_{add,sub,mul}_overflow() declared like:

  bool OP(a, b, res)

where OP is grub_add, grub_sub or grub_mul. OP() returns true in the
case where the operation would overflow and res is not modified.
Otherwise, false is returned and the operation is executed.

These arithmetic primitives require newer compiler versions. So, bump
these requirements in the INSTALL file too.

Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 include/grub/compiler.h |  8 ++++++++
 include/grub/safemath.h | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 include/grub/safemath.h

diff --git a/include/grub/compiler.h b/include/grub/compiler.h
index 9859ff4..61c0cb3 100644
--- a/include/grub/compiler.h
+++ b/include/grub/compiler.h
@@ -50,4 +50,12 @@
 
 #define UNUSED __attribute__((__unused__))
 
+#if defined(__clang__) && defined(__clang_major__) && defined(__clang_minor__)
+#  define CLANG_PREREQ(maj,min) \
+          ((__clang_major__ > (maj)) || \
+	   (__clang_major__ == (maj) && __clang_minor__ >= (min)))
+#else
+#  define CLANG_PREREQ(maj,min) 0
+#endif
+
 #endif /* ! GRUB_COMPILER_HEADER */
diff --git a/include/grub/safemath.h b/include/grub/safemath.h
new file mode 100644
index 0000000..c17b89b
--- /dev/null
+++ b/include/grub/safemath.h
@@ -0,0 +1,37 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2020  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *  Arithmetic operations that protect against overflow.
+ */
+
+#ifndef GRUB_SAFEMATH_H
+#define GRUB_SAFEMATH_H 1
+
+#include <grub/compiler.h>
+
+/* These appear in gcc 5.1 and clang 3.8. */
+#if GNUC_PREREQ(5, 1) || CLANG_PREREQ(3, 8)
+
+#define grub_add(a, b, res)	__builtin_add_overflow(a, b, res)
+#define grub_sub(a, b, res)	__builtin_sub_overflow(a, b, res)
+#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
+#endif
+
+#endif /* GRUB_SAFEMATH_H */
-- 
2.23.0

