From: Yury Norov <ynorov@caviumnetworks.com>
To: Matthias Kaehlcke <mka@chromium.org>
Cc: zijun_hu <zijun_hu@htc.com>,
Andrew Morton <akpm@linux-foundation.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Laura Abbott <labbott@redhat.com>,
Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org,
Greg Hackmann <ghackmann@google.com>,
Doug Anderson <dianders@chromium.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2] bitops: Avoid integer overflow warning in GENMASK_ULL
Date: Thu, 3 Aug 2017 16:24:56 +0300 [thread overview]
Message-ID: <20170803132456.mwrt6yspkbqxcffw@yury-thinkpad> (raw)
In-Reply-To: <20170802225159.159536-1-mka@chromium.org>
On Wed, Aug 02, 2017 at 03:51:58PM -0700, Matthias Kaehlcke wrote:
> GENMASK_ULL performs a left-shift of (~0ULL), which technically
> results in an integer overflow. clang raises a warning about
> this if the overflow occurs in a preprocessor expression. To
> avoid the overflow first perform a right-shift to clear the
> bits that are shifted out.
>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> include/linux/bitops.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index a83c822c35c2..21dfe63001e3 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -22,7 +22,7 @@
> (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
Once you touche GENMASK_ULL, why not to fix also GENMASK.
>
> #define GENMASK_ULL(h, l) \
> - (((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
> + ((((~0ULL) >> (l)) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
>
> extern unsigned int __sw_hweight8(unsigned int w);
> extern unsigned int __sw_hweight16(unsigned int w);
> --
> 2.14.0.rc1.383.gd1ce394fe2-goog
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2017-08-03 13:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-02 22:51 Matthias Kaehlcke
2017-08-02 22:51 ` [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL Matthias Kaehlcke
2017-08-02 23:13 ` Nick Desaulniers
2017-08-02 23:19 ` Nick Desaulniers
2017-08-02 23:44 ` Matthias Kaehlcke
2017-08-03 13:20 ` Yury Norov
2017-08-03 17:11 ` [PATCH] arm64: avoid overflow in VA_START and PAGE_OFFSET Nick Desaulniers
2017-08-03 17:20 ` Ard Biesheuvel
2017-08-03 17:53 ` Nick Desaulniers
2017-08-03 18:03 ` [PATCH v2] " Nick Desaulniers
2017-08-04 2:26 ` [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL kbuild test robot
2017-08-03 13:24 ` Yury Norov [this message]
2017-08-03 17:03 ` [PATCH 1/2] bitops: Avoid integer overflow warning in GENMASK_ULL Matthias Kaehlcke
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