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Subject: Re: [PATCH v2] kernel.h: handle pointers to arrays better in
 container_of()
To: Peter Zijlstra <peterz@infradead.org>
References: <20170522150340.15461-1-abbotti@mev.co.uk>
 <xa1tfufwhiyb.fsf@mina86.com>
 <139f0546-9b0a-d119-6b96-a9b35559be4b@mev.co.uk>
 <20170523112415.nmbazvqmlhy343f2@hirez.programming.kicks-ass.net>
Cc: Michal Nazarewicz <mina86@mina86.com>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>,
        Borislav Petkov <bp@suse.de>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Johannes Berg <johannes.berg@intel.com>,
        Alexander Potapenko <glider@google.com>
From: Ian Abbott <abbotti@mev.co.uk>
Message-ID: <ec5747cf-0222-42eb-91fa-e67c4c0f3f61@mev.co.uk>
Date: Tue, 23 May 2017 13:02:59 +0100
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On 23/05/17 12:24, Peter Zijlstra wrote:
> On Tue, May 23, 2017 at 11:32:02AM +0100, Ian Abbott wrote:
>
>>> #define container_of(ptr, type, member) (				\
>>> 	_Static_assert(__builtin_types_compatible_p(			\
>>>             typeof(*ptr), typeof( ((type *)0)->member )), "WUT"),	\
>>> 	((type *)((char *)(ptr) - offsetof(type, member)));		\
>>> )
>>
>> It's a fine suggestion (if more parentheses are added), but _Static_assert
>> is a C11 feature, and I thought the kernel was using gnu89 (unless it's been
>> updated since).
>
> We have BUILD_BUG_ON() that should be similar in functionality.

Yes, I think BUILD_BUG_ON_ZERO() will be better in this case to avoid 
some baggage.  Also, __same_type() can be used for type checking.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-