linux-kernel - Re: [PATCH v2 05/15] hwmon: mark const init data with __initconst instead of _

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Message-ID: <20120331140924.GW15647@pengutronix.de>
Date:	Sat, 31 Mar 2012 16:09:24 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Guenter Roeck <guenter.roeck@...csson.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	Jean Delvare <khali@...ux-fr.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>
Subject: Re: [PATCH v2 05/15] hwmon: mark const init data with __initconst
 instead of __initdata

Hello Guenter,

On Fri, Mar 30, 2012 at 08:54:42PM -0700, Guenter Roeck wrote:
> On Fri, Mar 30, 2012 at 04:04:55PM -0400, Uwe Kleine-König wrote:
> > As long as there is no other non-const variable marked __initdata in the
> > same compilation unit it doesn't hurt. If there were one however
> > compilation would fail with
> > 
> > 	error: $variablename causes a section type conflict
> > 
> > because a section containing const variables is marked read only and so
> > cannot contain non-const variables.
> > 
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > Cc: Jean Delvare <khali@...ux-fr.org>
> > Cc: Guenter Roeck <guenter.roeck@...csson.com>
> > Cc: lm-sensors@...sensors.org
> > ---
> > changes since (implicit) v1:
> >  - drop wrong changes to drivers/hwmon/w83627hf.c
> > 
> >  drivers/hwmon/w83627ehf.c |   18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/hwmon/w83627ehf.c b/drivers/hwmon/w83627ehf.c
> > index a25350c..54922ed 100644
> > --- a/drivers/hwmon/w83627ehf.c
> > +++ b/drivers/hwmon/w83627ehf.c
> > @@ -2619,15 +2619,15 @@ static struct platform_driver w83627ehf_driver = {
> >  static int __init w83627ehf_find(int sioaddr, unsigned short *addr,
> >  				 struct w83627ehf_sio_data *sio_data)
> >  {
> > -	static const char __initdata sio_name_W83627EHF[] = "W83627EHF";
> > -	static const char __initdata sio_name_W83627EHG[] = "W83627EHG";
> > -	static const char __initdata sio_name_W83627DHG[] = "W83627DHG";
> > -	static const char __initdata sio_name_W83627DHG_P[] = "W83627DHG-P";
> > -	static const char __initdata sio_name_W83627UHG[] = "W83627UHG";
> > -	static const char __initdata sio_name_W83667HG[] = "W83667HG";
> > -	static const char __initdata sio_name_W83667HG_B[] = "W83667HG-B";
> > -	static const char __initdata sio_name_NCT6775[] = "NCT6775F";
> > -	static const char __initdata sio_name_NCT6776[] = "NCT6776F";
> > +	static const char sio_name_W83627EHF[] __initconst = "W83627EHF";
> > +	static const char sio_name_W83627EHG[] __initconst = "W83627EHG";
> > +	static const char sio_name_W83627DHG[] __initconst = "W83627DHG";
> > +	static const char sio_name_W83627DHG_P[] __initconst = "W83627DHG-P";
> > +	static const char sio_name_W83627UHG[] __initconst = "W83627UHG";
> > +	static const char sio_name_W83667HG[] __initconst = "W83667HG";
> > +	static const char sio_name_W83667HG_B[] __initconst = "W83667HG-B";
> > +	static const char sio_name_NCT6775[] __initconst = "NCT6775F";
> > +	static const char sio_name_NCT6776[] __initconst = "NCT6776F";
> >  
> Applied.
> 
> Just wondering: Why not the following ?
> 
> > +	static const char __initconst sio_name_NCT6776[] = "NCT6776F";
> 
> It does not make a difference in the generated code, and appears to be
> less confusing, at least to me.
hmm, I thought it does, maybe it's compiler dependant?! At least
gcc-4.4.info tells:

	An attribute specifier list may appear immediately before the
	comma, `=' or semicolon terminating the declaration of an
	identifier other than a function definition.

and include/linux/init.h has:

	You should insert __initdata between the variable name and equal
	sign followed by value [...].

I seem to remember that placing the attribute at the wrong place for a
function made gcc ignore it (or apply it so something unintended).

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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