linux-kernel - Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

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Message-ID: <20120803214806.GM15477@google.com>
Date:	Fri, 3 Aug 2012 14:48:06 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	paul.gortmaker@...driver.com, davem@...emloft.net,
	rostedt@...dmis.org, mingo@...e.hu, ebiederm@...ssion.com,
	aarcange@...hat.com, ericvh@...il.com, netdev@...r.kernel.org
Subject: Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

Hello,

On Fri, Aug 03, 2012 at 11:41:34PM +0200, Sasha Levin wrote:
> I forgot to comment on that one, sorry.
> 
> If we put hash entries after struct hash_table we don't take the
> bits field size into account, or did I miss something?

So, if you do the following,

	struct {
		struct {
			int i;
			long ar[];
		} B;
		long __ar_storage[32];
	} A;

It should always be safe to dereference A.B.ar[31].  I'm not sure
whether this is something guaranteed by C tho.  Maybe compilers are
allowed to put members in reverse order but I think we already depend
on the above.

Thanks.

-- 
tejun
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