linux-kernel - Re: [PATCH v3 03/33] staging: rtl8192e: Mark unaligned memcpy()

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Date:	Thu, 14 May 2015 22:29:39 +0200
From:	Mateusz Kulikowski <mateusz.kulikowski@...il.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	devel@...verdev.osuosl.org, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 03/33] staging: rtl8192e: Mark unaligned memcpy()

On 13.05.2015 10:22, Dan Carpenter wrote:
> On Tue, May 12, 2015 at 10:00:13PM +0200, Mateusz Kulikowski wrote:
>> On 11.05.2015 10:26, Dan Carpenter wrote:
(...)
>>>
>>> Which part isn't aligned?  I think they both are.
>>>
>> struct rtllib_rxb *prxb = prxbIndicateArray[j];
>>
>> struct rtllib_rxb {
>> 	u8 nr_subframes;
>> 	struct sk_buff *subframes[MAX_SUBFRAME_COUNT == 64];
>> 	u8 dst[ETH_ALEN]; // here
>> 	u8 src[ETH_ALEN]; // here
>> } __packed;
>>
>> Either I forgot alignment / packing rules or this fields are never aligned "by design".
> 
> You must have forgotten something...  Everything after the pointer is
> going to be aligned sizeof(void *).

That would be true, if structure was not __packed:

$ pahole drivers/staging/rtl8192e/rtllib.ko -C rtllib_rxb
struct rtllib_rxb {
	u8                         nr_subframes;         /*     0     1 */
	struct sk_buff *           subframes[64];        /*     1   256 */
	/* --- cacheline 4 boundary (256 bytes) was 1 bytes ago --- */
	u8                         dst[6];               /*   257     6 */
	u8                         src[6];               /*   263     6 */

	/* size: 269, cachelines: 5, members: 4 */
	/* last cacheline: 13 bytes */
};

Am I right?

Regards,
Mateusz
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