linux-kernel - RE: [PATCH] ahci: qoriq: fixed using uninitialized variable warnings

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Message-ID: <DM2PR03MB574733935AECD0167EEF580FA510@DM2PR03MB574.namprd03.prod.outlook.com>
Date:	Thu, 10 Sep 2015 06:17:08 +0000
From:	Yuantian Tang <Yuantian.Tang@...escale.com>
To:	Tejun Heo <tj@...nel.org>
CC:	"hdegoede@...hat.com" <hdegoede@...hat.com>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH] ahci: qoriq: fixed using uninitialized variable warnings



> -----Original Message-----
> From: Tejun Heo [mailto:htejun@...il.com] On Behalf Of Tejun Heo
> Sent: Wednesday, September 09, 2015 10:02 PM
> To: Tang Yuantian-B29983 <Yuantian.Tang@...escale.com>
> Cc: hdegoede@...hat.com; linux-ide@...r.kernel.org; linux-
> kernel@...r.kernel.org; devicetree@...r.kernel.org
> Subject: Re: [PATCH] ahci: qoriq: fixed using uninitialized variable warnings
> 
> On Wed, Sep 09, 2015 at 05:16:22PM +0800, Yuantian.Tang@...escale.com
> wrote:
> > From: Tang Yuantian <Yuantian.Tang@...escale.com>
> >
> > kbuild test robot reports the warnings:
> > drivers/ata/ahci_qoriq.c: In function 'ahci_qoriq_hardreset':
> > >> include/asm-generic/io.h:163:2: warning: 'px_is' may be used
> > >> uninitialized in this function [-Wuninitialized]
> > drivers/ata/ahci_qoriq.c:70:14: note: 'px_is' was declared here
> > >> include/asm-generic/io.h:163:2: warning: 'px_cmd' may be used
> > >> uninitialized in this function [-Wuninitialized]
> > drivers/ata/ahci_qoriq.c:70:6: note: 'px_cmd' was declared here
> >
> > This patch fixed it by assigning 0 to px_is and px_cmd variables.
> > This patch also remove line 'struct ccsr_ahci *reg_base' which is not
> > referred by any other codes and thus a dead one.
> 
> Hmm... I think the problem here is that the complier can't know whether
> qoriq_priv->type would change across intervening function calls.  Maybe a
> better solution is caching the type in a local variable so that the compiler can
> tell that those two tests will always move together?  It generally isn't a good
> idea to clear variables unnecessarily as that can hide actual bugs that compiler
> can detect.
> 
I am not sure if the warning can be removed this way.
But I will send the patch as your suggestion. 
Unfortunately, I can't produce this warning no matter if I add -Wuninitialized.
So please let me know if the new patch is working.

Regards,
Yuantian

> Thanks.
> 
> --
> tejun
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