linux-kernel - [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK

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Message-Id: <20170802225159.159536-2-mka@chromium.org>
Date:   Wed,  2 Aug 2017 15:51:59 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     zijun_hu <zijun_hu@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Laura Abbott <labbott@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Doug Anderson <dianders@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL

As is the definition causes an integer overflow, which is expected,
however clang raises the following warning:

arch/arm64/kernel/head.S:47:8: warning:
      integer overflow in preprocessor expression
  #elif (PAGE_OFFSET & 0x1fffff) != 0
         ^~~~~~~~~~~
arch/arm64/include/asm/memory.h:52:46: note:
      expanded from macro 'PAGE_OFFSET'
  #define PAGE_OFFSET             (UL(0xffffffffffffffff) << (VA_BITS - 1))
                                      ~~~~~~~~~~~~~~~~~~  ^  ~~~~~~~~~~~~~

Use GENMASK_ULL() instead of shifting explicitly, the macro takes care
of avoiding the overflow.

Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
---
 arch/arm64/include/asm/memory.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 32f82723338a..732d4eed8edd 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -65,7 +65,7 @@
  */
 #define VA_BITS			(CONFIG_ARM64_VA_BITS)
 #define VA_START		(UL(0xffffffffffffffff) << VA_BITS)
-#define PAGE_OFFSET		(UL(0xffffffffffffffff) << (VA_BITS - 1))
+#define PAGE_OFFSET		GENMASK_ULL(BITS_PER_LONG_LONG - 1, VA_BITS - 1)
 #define KIMAGE_VADDR		(MODULES_END)
 #define MODULES_END		(MODULES_VADDR + MODULES_VSIZE)
 #define MODULES_VADDR		(VA_START + KASAN_SHADOW_SIZE)
-- 
2.14.0.rc1.383.gd1ce394fe2-goog