Re: [PATCH 1/2] bitops: Avoid integer overflow warning in GENMASK_ULL

From	Matthias Kaehlcke <mka@chromium.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] bitops: Avoid integer overflow warning in GENMASK_ULL
Date	2017-08-03 19:10 +0200
Message-ID	<uarNg-32O-21@gated-at.bofh.it> (permalink)
References	<uaaMq-7QI-5@gated-at.bofh.it> <uarNg-32O-23@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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El Thu, Aug 03, 2017 at 04:24:56PM +0300 Yury Norov ha dit:

> 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.

Will do, thanks.

Even though GENMASK_ULL can't be used (as is) to define the arm64
PAGE_OFFSET as initially intended it seems the change is still
worthwhile since there are a few other preprocessor expressions using
GENMASK_ULL.

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[PATCH 1/2] bitops: Avoid integer overflow warning in GENMASK_ULL Matthias Kaehlcke <mka@chromium.org> - 2017-08-03 01:00 +0200
  [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL Matthias Kaehlcke <mka@chromium.org> - 2017-08-03 01:00 +0200
    Re: [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL Nick Desaulniers <ndesaulniers@google.com> - 2017-08-03 01:20 +0200
      Re: [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL Matthias Kaehlcke <mka@chromium.org> - 2017-08-03 01:50 +0200
    Re: [PATCH 2/2] arm64: Define PAGE_OFFSET using GENMASK_ULL Nick Desaulniers <ndesaulniers@google.com> - 2017-08-03 01:20 +0200
  Re: [PATCH 1/2] bitops: Avoid integer overflow warning in GENMASK_ULL Matthias Kaehlcke <mka@chromium.org> - 2017-08-03 19:10 +0200

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