linux-kernel - __bitwise versus __bitwise__ [Was: [PATCH] mac80211: check endianness/types in sparse runs]

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Message-ID: <20080221223239.GA31048@uranus.ravnborg.org>
Date:	Thu, 21 Feb 2008 23:32:39 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Harvey Harrison <harvey.harrison@...il.com>,
	Al Viro <viro@....linux.org.uk>
Cc:	Johannes Berg <johannes@...solutions.net>,
	John Linville <linville@...driver.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Stefano Brivio <stefano.brivio@...imi.it>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: __bitwise versus __bitwise__ [Was: [PATCH] mac80211: check endianness/types in sparse runs]

Al - can I ask you to explain the difference between __bitwise
and __bitwise__ as used by the kernel.

Se below for a bit of background info.

Thanks,
	Sam

On Thu, Feb 21, 2008 at 12:01:31PM -0800, Harvey Harrison wrote:
> On Thu, 2008-02-21 at 13:42 +0100, Johannes Berg wrote:
> > >> [patch doing CHECKFLAGS += -D__CHECK_ENDIAN__ in the
> > >> net/mac80211/Makefile]
> > 
> > > I would prefer it to be kernel wide enabled.
> > > Tried a defconfig build.
> > 
> > Hm. I tend to think there was a reason for this, since this is actually
> > explicitly disabled by include/linux/types.h:
> > 
> > #ifdef __CHECKER__
> > #define __bitwise__ __attribute__((bitwise))
> > #else 
> > #define __bitwise__
> > #endif
> > 
> > #ifdef __CHECK_ENDIAN__
> > #define __bitwise __bitwise__
> > #else
> > #define __bitwise
> > #endif
> > 
> 
> This seems somewhat suspect.
> 
> > I recently ran sparse on my config and was surprised by the number of
> > warnings. Then again, something in mmzone.h or so generated billions of
> > them...
> 
> Potentially expensive pointer subtraction 640:....
> 
> Patch in -mm.
> 
> > 
> > In any case, I would love to have __CHECK_ENDIAN__ enabled by default at
> > least on the wireless code (just caught another bug with it...)
> > 
> 
> I'd love to have it too, but there are so many trivial warnings that
> clutter up valid warnings that it is prohibitive.  I'm working on
> reducing the noise level a bit for 2.6.26, we'll see about turning
> it on then.
> 
> Harvey
> 
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