Re: [RFC PATCH] checkpatch: check for function calls with struct or union on stack

From: Joe Perches <joe@perches.com>
To: David Laight <David.Laight@ACULAB.COM>,
	'Andrew Morton' <akpm@linux-foundation.org>,
	Andy Whitcroft <apw@canonical.com>,
	LKML <linux-kernel@vger.kernel.org>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Subject: Re: [RFC PATCH] checkpatch: check for function calls with struct or union on stack
Date: Fri, 27 Jul 2018 03:36:39 -0700	[thread overview]
Message-ID: <1a75fda0861a0b2bce208fbf9b53785bf0e76fa2.camel@perches.com> (raw)
In-Reply-To: <9f0377fa74bd4964912ba5a4fc76526d@AcuMS.aculab.com>

On Fri, 2018-07-27 at 10:21 +0000, David Laight wrote:
> From: Joe Perches Sent: 27 July 2018 11:09
> > On Fri, 2018-07-27 at 10:04 +0000, David Laight wrote:
> > > From: Andrew Morton Sent: 26 July 2018 20:28
> > > > On Thu, 26 Jul 2018 12:25:33 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > 
> > > > > I'll give it a spin, see how noisy it is.
> > > > 
> > > > Actually, I would prefer if the message, changelog and title
> > > > used the term "passed by value".  It's a more familiar term
> > > > and it is possible for a passed-by-value aggregate to in fact
> > > > be passed in registers.
> > > 
> > > You need to detect (and ignore) 'small' structures.
> > 
> > checkpatch is stupid and basically can't do that
> > as it has no context other than the current line.
> > 
> > It would need a list of specific struct types to
> > ignore.  Care to create and send that list to me?
> 
> Does it even have the type?

Yes, kinda.  But only on the line being matched.

i.e.: <const> [struct or union] [type] [name]

> If it has the prototype it could ignore aggregates that
> are marked 'const'.

checkpatch has no visibility of any prototype.

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/