linux-kernel - Re: [PATCH] staging: rtl8712: fix Prefer ether_addr

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Message-ID: <20150129195423.GA12196@localhost.localdomain>
Date:	Thu, 29 Jan 2015 21:54:23 +0200
From:	Aya Mahfouz <mahfouz.saif.elyazal@...il.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Larry Finger <Larry.Finger@...inger.net>,
	devel@...verdev.osuosl.org, florian.c.schilhabel@...glemail.com,
	thomas@...uk.net, rickard_strandqvist@...ctrumdigital.se,
	gregkh@...uxfoundation.org, tapaswenipathak@...il.com,
	linux-kernel@...r.kernel.org, Heba Aamer <heba93aamer@...il.com>,
	sudipm.mukherjee@...il.com
Subject: Re: [PATCH] staging: rtl8712: fix Prefer ether_addr_copy() over
 memcpy()

On Thu, Jan 29, 2015 at 02:51:57PM +0300, Dan Carpenter wrote:
> On Wed, Jan 28, 2015 at 11:30:11PM +0200, Aya Mahfouz wrote:
> > On Wed, Jan 28, 2015 at 10:48:40AM -0600, Larry Finger wrote:
> > > On 01/28/2015 09:53 AM, Heba Aamer wrote:
> > > >This patch fixes the following checkpatch.pl warning:
> > > >Prefer ether_addr_copy() over memcpy()
> > > >if the Ethernet addresses are __aligned(2)
> > > >
> > > >I used the following coccinelle script:
> > > >
> > > >@@
> > > >expression E1,E2;constant E3;
> > > >@@
> > > >
> > > >- memcpy(E1, E2, E3)
> > > >+ ether_addr_copy(E1, E2)
> > > >
> > > >
> > > >pahole showed that the used structs are aligned to u16.
> > > 
> > > I think you can stop here. The commit message is much too long for a 2-line patch.
> > > 
> > > BTW, have you tested this patch? In particular, it needs to be tested on an
> > > architecture where alignment is important. Using x86 is not sufficient. The
> > > reason I ask is that there have been a lot of patches lately that change
> > > locking and alignment issues that are only build tested, and have never been
> > > tested with real hardware on any platform.
> > > 
> > > One other thing, checkpatch only suggests that this change should be made.
> > > It is certainly not mandatory. As you have not indicated that it has been
> > > tested,
> > > 
> > > NACK
> > > 
> > > Larry
> > >
> > Hello Larry,
> > 
> > Thank you for your patience. Heba has submitted this patch as part
> > of a workshop she currently attends. She has checked the alignment
> > through pahole and it showed that the variables of complex structs
> > are aligned. She has attached the output of pahole, so that the
> > community can verify her results and hence the lengthy output.
> > 
> > She can also cross compile the kernel and verify the output for
> > other architectures using pahole. Kindly let us know if this suits
> > you. And please name any specific architecture that you would to see
> > tested. If this is still not enough from your point of view, let
> > us know what should be done further to verify the correctness of
> > the patch.
> > 
> 
> Really, I hate this checkpatch.pl warning, too.  The patches are
> difficult to review because you need a lot of context and there is a
> small chance that the patch will introduce a bug.
> 
> I was the person who introduced the rule that the patch submitter has to
> prove the alignment is correct after two people told me basically that,
> "The patch submitter's job is to sed the code and the maintainer's job
> is to review the code."
> 
> In this case we don't really need to use pahole.  "mac" is a 6 byte
> char array declared on the stack after a couple of integers.
> pnetdev->dev_addr is a pointer.  &pdata[0x12] is a pointer plus an even
> offset.  This patch is fine.  But the changelog is too long and has a
> lot of not at all relevant output from pahole.
> 
Thanks for your analysis.

> It's not really a practical thing to say that the patch writer has to
> cross compile on a different arch.
>
I was trying to make ends meet. Thanks for the advice and ruling out 
a very difficult option.

> regards,
> dan carpenter
>

Heba, kindly resend the patch with an adjusted description. Include
the relevant blocks of any struct and state more details in the
last sentence.

Kind Regards,
Aya Saif El-yazal Mahfouz

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