linux-kernel - Re: [PATCH] Coccicheck: Remove memcpy to struct assignment test

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Message-ID: <1395237927.12633.29.camel@thorin>
Date:	Wed, 19 Mar 2014 15:05:27 +0100
From:	Bernd Petrovitsch <bernd@...rovitsch.priv.at>
To:	Peter Senna Tschudin <peter.senna@...il.com>
Cc:	Julia Lawall <Julia.Lawall@...6.fr>,
	Gilles Muller <Gilles.Muller@...6.fr>,
	Nicolas Palix <nicolas.palix@...g.fr>, mmarek@...e.cz,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cocci@...teme.lip6.fr" <cocci@...teme.lip6.fr>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andreea Bernat <bernat.ada@...il.com>,
	Ezequiel Garcia <elezegarcia@...il.com>,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] Coccicheck: Remove memcpy to struct assignment test

Hi!

On Mit, 2014-03-19 at 14:39 +0100, Peter Senna Tschudin wrote:
> On Wed, Mar 19, 2014 at 1:02 PM, Bernd Petrovitsch
> <bernd@...rovitsch.priv.at> wrote:
> > On Die, 2014-03-18 at 22:11 +0100, Peter Senna Tschudin wrote:
> >> The Coccinelle script scripts/coccinelle/misc/memcpy-assign.cocci look
> >> for opportunities to replace a call to memcpy by a struct assignment.
> >> This patch removes memcpy-assign.cocci as it is not clear that this
> >> convention has an impact on the generated code.
> >
> > Using struct assignment keeps the type check and is just for this reason
> > always preferable over memcpy().
> What about the assignment hiding that a potentially large memcpy is
> happening instead of just a pointer assignment?

It makes no difference if you copy 2KB with a struct assignment or with
a memcpy(). IMHO most probably each and every C compiler produces the
same code for both cases.

And - more important - I assume that people which actually read the code
(to understand the code) also know if the variables there are
pointers/ints or a (somewhat large) struct (if only one see an field
access in the struct, it should be pretty clear).
I don't think it makes actually much sense trying to read source without
that ....

	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@...rovitsch.priv.at
                     LUGA : http://www.luga.at

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