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

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Message-ID: <6439210644b66a1847e6fad9205fcc7056319de1.camel@perches.com>
Date:   Sat, 28 Jul 2018 10:14:34 -0700
From:   Joe Perches <joe@...ches.com>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     David Laight <David.Laight@...LAB.COM>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        Andy Whitcroft <apw@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] checkpatch: check for function calls with struct or
 union on stack

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?

a struct with 3 chars or bools might be faster
by value, but maybe for structs with arrays or
other structs.

For instance:

lib/vsprintf.c uses struct printf_spec which
is 16 bytes and that fits nicely in a