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

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Message-ID: <CAKwvOdmjTRJd+UB+0WU3umQZ3YYvOhh9tM3sN8HJLz6qpkaQQw@mail.gmail.com>
Date:   Wed, 2 Aug 2017 16:13:12 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     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>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Doug Anderson <dianders@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>
Subject: Re: [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL

don't forget to include linux/bitops.h now in memory.h

/usr/local/google/home/ndesaulniers/android/kernel-wahoo/private/msm-google/arch/arm64/kernel/head.S:47:8:
error:
      function-like macro 'GENMASK_ULL' is not defined
#elif (PAGE_OFFSET & 0x1fffff) != 0
       ^
/usr/local/google/home/ndesaulniers/android/kernel-wahoo/private/msm-google/arch/arm64/include/asm/memory.h:52:22:
note:

      expanded from macro 'PAGE_OFFSET'
#define PAGE_OFFSET             GENMASK_ULL(BITS_PER_LONG_LONG - 1, VA_BITS - 1)
                                ^
1 error generated.

On Wed, Aug 2, 2017 at 3:51 PM, Matthias Kaehlcke <mka@...omium.org> wrote:
> 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
>



-- 
Thanks,
~Nick Desaulniers