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From: Behan Webster <behanw@converseincode.com>
To: David Laight <David.Laight@ACULAB.COM>,
	"davem@davemloft.net" <davem@davemloft.net>
Cc: "pablo@netfilter.org" <pablo@netfilter.org>,
	"kaber@trash.net" <kaber@trash.net>,
	"kadlec@blackhole.kfki.hu" <kadlec@blackhole.kfki.hu>,
	"netfilter-devel@vger.kernel.org"
	<netfilter-devel@vger.kernel.org>,
	"netfilter@vger.kernel.org" <netfilter@vger.kernel.org>,
	"coreteam@netfilter.org" <coreteam@netfilter.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"dwmw2@infradead.org" <dwmw2@infradead.org>,
	"pageexec@freemail.hu" <pageexec@freemail.hu>,
	"Mark Charlebois" <charlebm@gmail.com>,
	"Vinícius Tinti" <viniciustinti@gmail.com>
Subject: Re: [PATCH v2] net: netfilter: LLVMLinux: vlais-netfilter
Date: Tue, 18 Mar 2014 10:37:58 -0700	[thread overview]
Message-ID: <53288476.10801@converseincode.com> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D0F6E0286@AcuExch.aculab.com>

On 03/18/14 08:24, David Laight wrote:
> From: Behan Webster
>> On 03/18/14 02:41, David Laight wrote:
>>> From:  behanw@converseincode.com
>>>> From: Mark Charlebois <charlebm@gmail.com>
>>>>
>>>> Replaced non-standard C use of Variable Length Arrays In Structs (VLAIS) in
>>>> xt_repldata.h with a C99 compliant flexible array member and then calculated
>>>> offsets to the other struct members. These other members aren't referenced by
>>>> name in this code, however this patch maintains the same memory layout and
>>>> padding as was previously accomplished using VLAIS.
>>>>
>>>> Had the original structure been ordered differently, with the entries VLA at
>>>> the end, then it could have been a flexible member, and this patch would have
>>>> been a lot simpler. However since the data stored in this structure is
>>>> ultimately exported to userspace, the order of this structure can't be changed.
>>> Why not just remove the last element and allocate space for it after the
>>> structure?
>> Because that would still be employing VLAIS to solve the problem. The
>> last element may be a zero-length array (a flexible member), not a VLA.
>> Sadly both the last 2 elements in the struct need to be manually
>> calculated, which is what we've done.
> So make the last element a 'flexible member' and then work out where
> the final field goes.
> Something like:
> 	struct p {
> 		struct a a;
> 		struct b b[];
> 	} p = malloc(sizeof *p + n * sizeof (struct b) + alignof (struct c)
> 		+ sizeof (struct c);
> 	struct c *c = (void *)&p->b[n] + (-offsetof(struct p, b[n]) & (alignof(struct c) - 1);
Oh, I see. Will fix.

Thanks!

Behan

-- 
Behan Webster
behanw@converseincode.com

  reply	other threads:[~2014-03-18 17:37 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <022D9517-4804-47BB-B789-CCF25F25C1ED@me.com>
2014-03-18  6:12 ` [PATCH v2] net: netfilter: LLVMLinux: vlais-netfilter behanw
2014-03-18  9:41   ` David Laight
2014-03-18 14:47     ` Behan Webster
2014-03-18 15:24       ` David Laight
2014-03-18 17:37         ` Behan Webster [this message]
2014-03-19  1:50         ` [PATCH v3] " behanw
2014-03-19  9:52           ` David Laight
2014-03-19 17:25             ` Mark Charlebois
2014-03-23  6:55             ` [PATCH v4] " behanw
2014-04-18  0:40               ` Behan Webster

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