From 5c0dc6965ffb6e6bb86b56a363c0f9a38a38be61 Mon Sep 17 00:00:00 2001
From: Peter Jones <pjones@redhat.com>
Date: Mon, 15 Jun 2020 10:58:42 -0400
Subject: [PATCH 300/336] 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>
Upstream-commit-id: de1c315841a
---
 include/grub/compiler.h |  8 ++++++++
 include/grub/safemath.h | 37 +++++++++++++++++++++++++++++++++++++
 INSTALL                 | 21 +++------------------
 3 files changed, 48 insertions(+), 18 deletions(-)
 create mode 100644 include/grub/safemath.h

diff --git a/include/grub/compiler.h b/include/grub/compiler.h
index a9a684ccba6..60d9c7fae25 100644
--- a/include/grub/compiler.h
+++ b/include/grub/compiler.h
@@ -48,6 +48,14 @@
 #  define WARN_UNUSED_RESULT
 #endif
 
+#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
+
 #include "types.h"
 
 union component64
diff --git a/include/grub/safemath.h b/include/grub/safemath.h
new file mode 100644
index 00000000000..c17b89bba17
--- /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 */
diff --git a/INSTALL b/INSTALL
index b67cd7f3476..8f46a3e999c 100644
--- a/INSTALL
+++ b/INSTALL
@@ -11,24 +11,9 @@ GRUB depends on some software packages installed into your system. If
 you don't have any of them, please obtain and install them before
 configuring the GRUB.
 
-* GCC 4.1.3 or later
-  Note: older versions may work but support is limited
-  Note: clang 3.2 or later works for i386 and x86_64 targets but results in
-        much bigger binaries.
-	earlier versions not tested
-  Note: clang 3.2 or later works for arm
-	None of tested clang versions generated usable thumb code
-	earlier versions not tested
-  Note: clang 3.3 or later works for arm64
-	earlier versions have no arm64 support
-  Note: clang 3.3 or later works for mips(el)
-	earlier versions fail to generate .reginfo and hence gprel relocations
-	fail.
-  Note: clang 3.2 or later works for powerpc
-	earlier versions not tested
-  Note: clang doesn't support -mno-app-regs and so can't be used for sparc64
-  Note: clang has no support for ia64 and hence you can't compile GRUB
-	for ia64 with clang
+* GCC 5.1.0 or later
+  Experimental support for clang 3.8.0 or later (results in much bigger binaries)
+  for i386, x86_64, arm (including thumb), arm64, mips(el), powerpc, sparc64
 * GNU Make
 * GNU Bison 2.3 or later
 * GNU gettext 0.17 or later
-- 
2.26.2