linux-kernel - Re: [PATCH v2] kernel.h: handle pointers to arrays better in container

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Message-ID: <20170523112415.nmbazvqmlhy343f2@hirez.programming.kicks-ass.net>
Date:   Tue, 23 May 2017 13:24:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ian Abbott <abbotti@....co.uk>
Cc:     Michal Nazarewicz <mina86@...a86.com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
        Borislav Petkov <bp@...e.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Johannes Berg <johannes.berg@...el.com>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH v2] kernel.h: handle pointers to arrays better in
 container_of()

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.