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

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Date:	Fri, 15 May 2015 02:14:27 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Mateusz Kulikowski <mateusz.kulikowski@...il.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 Thu, May 14, 2015 at 10:29:39PM +0200, Mateusz Kulikowski wrote:
> 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:
> 

Oh.  Duh...  You are correct.

I'm not positive it's "by design" though, this is staging code so maybe
they just added __packed to every struct.  In fact, I'm pretty sure
unaligned pointers don't work on some arches so the __packed is probably
a bug.

regards,
dan carpenter

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