linux-kernel - Re: coccinelle: generalized removal of unnecessary pointer casts?

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Message-ID: <1457994238.11972.138.camel@perches.com>
Date:	Mon, 14 Mar 2016 15:23:58 -0700
From:	Joe Perches <joe@...ches.com>
To:	Julia Lawall <julia.lawall@...6.fr>
Cc:	cocci <cocci@...teme.lip6.fr>, LKML <linux-kernel@...r.kernel.org>,
	Dan Carpenter <error27@...il.com>,
	kernel-janitors <kernel-janitors@...r.kernel.org>
Subject: Re: coccinelle: generalized removal of unnecessary pointer casts?

On Mon, 2016-03-14 at 21:43 +0100, Julia Lawall wrote:
> On Mon, 14 Mar 2016, Joe Perches wrote:
> > I wrote a little cocci script to remove unnecessary
> > casts for memset and memcpy (below) and tested it on
> > linux kernel's drivers/staging/ directory.
> > 
> > For instance, when dst and src are already pointers:
> > 
> > -     memcpy((u8 *)dst, (u8 *)src, r8712_get_wlan_bssid_ex_sz(src));
> > +     memcpy(dst, src, r8712_get_wlan_bssid_ex_sz(src));
> > 
> > It works ok, (it doesn't remove unnecessary parentheses
> > around the pointers) but it makes me wonder if there's a
> > generalized spatch mechanism to remove casts when an
> > arbitrary function takes a void * in any argument
> > position and a call to that function uses a cast of a
> > pointer to any pointer type for that argument.
> > 
> > $ cat remove_mem_casts.cocci 
> > @@
> > type t;
> > t *p;
> > type v;
> > expression e1;
> > expression e2;
> > @@
> > 
> > -     memset((v*)p, e1, e2)
> > +     memset(p, e1, e2)
> > 
> > @@
> > type t;
> > t *p;
> > type v;
> > expression e1;
> > expression e2;
> > @@
> > 
> > -     memcpy((v*)p, e1, e2)
> > +     memcpy(p, e1, e2)
> > 
> > @@
> > type t;
> > t *p;
> > type v;
> > expression e1;
> > expression e2;
> > @@
> > 
> > -     memcpy(e1, (v*)p, e2)
> > +     memcpy(e1, p, e2)
> > 
> > @@
> > type t1;
> > type t2;
> > t1 *p1;
> > t2 *p2;
> > type v1;
> > type v2;
> > expression e1;
> > @@
> > 
> > -     memcpy((v1*)p1, (v2*)p2, e1)
> > +     memcpy(p1, p2, e1)
> 
> This should do everything:
> 
> @@
> identifier f;
> expression *e;
> type T;
> @@
> 
> f(...,
> - (T *)(
>   e
> - )
>   ,...)
> 
> @@
> identifier f;
> expression *e;
> type T;
> @@
> 
> f(...,
> - (T *)
>   e
>   ,...)
> 
> julia

Hi Julia,

I think your proposed script is not correct.
The function must take a void * argument.
There's no validation of that here.

cheers, Joe