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

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Date:	Fri, 24 Jun 2011 13:00:44 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	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>,
	Sam Ravnborg <sam@...nborg.org>,
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Subject: Re: {PATCH] fix __packed in exported kernel headers

On Fri, Jun 24, 2011 at 12:33, 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.

the only real solution there is to export the compiler.h headers too

plus, many compilers nowadays (like icc/llvm) tend to include support
for common gcc attributes ...
-mike
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