linux-kernel - Re: [PATCH] trivial: disable sparse' warning for "potentially expensive pointer subtraction".

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Date:	Thu, 23 Sep 2010 14:41:43 +0200
From:	Bernd Petrovitsch <bernd@...prog.at>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	linux-kbuild@...r.kernel.org, Namhyung Kim <namhyung@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, dhowells@...hat.com,
	MXns RullgXrd <mans@...sr.com>, linux-sparse@...r.kernel.org
Subject: Re: [PATCH] trivial: disable sparse' warning for "potentially
 expensive pointer subtraction".

Also Cc:ed linux-sparse@...r.kernel.org

On Don, 2010-09-23 at 13:23 +0200, Jiri Kosina wrote:
> On Fri, 20 Aug 2010, Bernd Petrovitsch wrote:
> 
> > Rationale: With a somewhat current gcc (or a somewhat sane peephole
> > optimizer), the (expensive) "div" is converted to a "shift" or
> > "mul" with the inverse.
> > This warning is disabled per default in sparse but the "-Wall" in
> > the kernels CFLAGS enables it.
> > 
> > Signed-off-by: Bernd Petrovitsch <bernd@...prog.at>
> > ---
> > This patch is trivial and affects only calls to sparse (read: make C=1) and
> > removes false warnings. So it should be considered for inclusion immediately.
> > 
> > Sorry for the long Cc: - I included everyone in the thread and added
> > linux-kbuild@ (as it IMHO belongs there) and trivial@ (because of the
> > complexity of the patch).
> > 
> >  Makefile |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/Makefile b/Makefile
> > index f3bdff8..851c0fa 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -330,7 +330,7 @@ PERL		= perl
> >  CHECK		= sparse
> >  
> >  CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
> > -		  -Wbitwise -Wno-return-void $(CF)
> > +		  -Wbitwise -Wno-return-void -Wno-ptr-subtraction-blows $(CF)
> >  CFLAGS_MODULE   =
> >  AFLAGS_MODULE   =
> >  LDFLAGS_MODULE  =
> 
> What is the status of this patch? I don't see it Nacked, but it's not in 
> linux-next either.

More details:

The head (as in
git://git.kernel.org/pub/scm/devel/sparse/chrisl/sparse.git) has "-Wall"
renamed to "-Wsparse-all". So the above patch is pretty pointless.

But sparse-0.4.2 - the latest release according to
https://sparse.wiki.kernel.org/index.php/Main_Page - hasn't that
renamed.

	Bernd
-- 
mobile: +43 664 4416156              http://www.sysprog.at/
    Linux Software Development, Consulting and Services

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