Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <b8d9aa953d1e760b35bd4ef6c689dfb777c8a6a0.camel@perches.com>
Subject: Re: [RFC PATCH] checkpatch: check for function calls with struct or
 union on stack
From:   Joe Perches <joe@perches.com>
To:     Julia Lawall <julia.lawall@lip6.fr>
Cc:     David Laight <David.Laight@ACULAB.COM>,
        'Andrew Morton' <akpm@linux-foundation.org>,
        Andy Whitcroft <apw@canonical.com>,
        LKML <linux-kernel@vger.kernel.org>
Date:   Sat, 28 Jul 2018 10:20:44 -0700
In-Reply-To: <alpine.DEB.2.20.1807280823200.2466@hadrien>
References: <1236369d28b2f1f5389ff652c4eb89e699e6481e.camel@perches.com>
         <20180726122533.104f6eea950853ef50ebc680@linux-foundation.org>
         <20180726122807.fad0566951e36d930edb6874@linux-foundation.org>
         <9d7441a14897426f8ed5befe8da0cad3@AcuMS.aculab.com>
         <0a6d2ecfacf3786228de664c8e01f6de10314c1b.camel@perches.com>
         <9f0377fa74bd4964912ba5a4fc76526d@AcuMS.aculab.com>
         <1a75fda0861a0b2bce208fbf9b53785bf0e76fa2.camel@perches.com>
         <alpine.DEB.2.20.1807280823200.2466@hadrien>
Content-Type: text/plain; charset="ISO-8859-1"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

(unintentionally sent partial reply, better now)

On Sat, 2018-07-28 at 08:25 +0200, Julia Lawall wrote:
> On Fri, 27 Jul 2018, Joe Perches wrote:
[]
> > It might make sense for this sort of check to be
> > added to coccinelle or maybe as a compiler warning
> > when the struct is larger than some size.
> > 
> > Original thread for Julia:
> > https://lore.kernel.org/patchwork/patch/967890/
> 
> Coccinelle doesn't directly know the size of the structure, but it can
> count the number of fields.  Maybe a case with an update in the function
> body

Perhaps this might be the most useful to check.

>  or at least 3 fields is worth reporting on?

Maybe, maybe not.  For instance:

lib/vsprintf.c uses struct printf_spec which is
5 fields totaling 8 bytes and that fits nicely in
a single register on x86-64 so there are good
reasons why structs could be passed by value.

Maybe structs with arrays or other structs would
make more sense.