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

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Date:	Wed, 9 Sep 2015 10:01:30 -0400
From:	Tejun Heo <tj@...nel.org>
To:	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.

Thanks.

-- 
tejun
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