linux-kernel - Re: {PATCH] fix __packed in exported kernel headers

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Date:	Fri, 24 Jun 2011 19:01:26 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Michal Marek <mmarek@...e.cz>, Joe Perches <joe@...ches.com>,
	Nick Bowler <nbowler@...iptictech.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Frysinger <vapier@...too.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Subject: Re: {PATCH] fix __packed in exported kernel headers

On 2011.06.24 at 18:33 +0200, Arnd Bergmann wrote:
> On Friday 24 June 2011, Markus Trippelsdorf wrote:
> > checkpatch.pl warns about using __attribute__((packed)) in kernel
> > headers: "__packed is preferred over __attribute__((packed))". If one
> > follows that advice it could cause problems in the exported header
> > files, because the outside world doesn't know about this shortcut.
> > 
> > For example busybox will fail to compile:
> >  CC      miscutils/ubi_attach_detach.o
> >  In file included from miscutils/ubi_attach_detach.c:27:0:
> >  /usr/include/mtd/ubi-user.h:330:3: error: conflicting types for ‘__packed’
> >  /usr/include/mtd/ubi-user.h:314:3: note: previous declaration of ‘__packed’ was here
> > ...
> > 
> > Fix the problem by substituting __packed with __attribute__((packed)) in
> > the header_install.pl script.
> 
> No objections to the patch, but it should probably be noted that user
> visible data structures should ideally not have any attributes, because
> that requires building all applictions using that interface with gcc.
> 
> We generally try to add no such requirements on user applications.

Both icc and clang support __attribute__((packed)).

And a rough count shows:
% grep -R "packed" /usr/src/linux/usr/include | wc -l
262

-- 
Markus
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