linux-kernel - Re: fs/block_dev.c:953: warning: 'found' might be used uninitialized in this function

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Date:	Fri, 30 Mar 2007 21:47:01 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Kyle Moffett <mrmacman_g4@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jikos@...os.cz>,
	Lee Revell <rlrevell@...-job.com>,
	Toralf Förster <toralf.foerster@....de>,
	andrea@...e.de, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: fs/block_dev.c:953: warning: 'found' might be used uninitialized in this function

On Thu, Mar 29, 2007 at 11:16:39PM -0400, Kyle Moffett wrote:
> On Mar 28, 2007, at 16:14:54, Andrew Morton wrote:
> >On Wed, 28 Mar 2007 19:23:32 +0200 (CEST)
> >Jiri Kosina <jikos@...os.cz> wrote:
> >
> >>blockdev: bd_claim_by_kobject() could check value of unititalized  
> >>pointer
> >>
> >>Fixes this warning:
> >>
> >>fs/block_dev.c: In function `bd_claim_by_kobject':
> >>fs/block_dev.c:953: warning: 'found' might be used uninitialized  
> >>in this function
> >>
> >>struct bd_holder *found is initialized only when bd_claim()  
> >>returns zero. If it returns nonzero, ptr stays uninitialized.  
> >>Later the value of the pointer is checked.
> >
> >that generates extra code and people get upset.
> >
> >One approach which we could ue in here is
> >
> >	struct bd_holder *found = found;  /* Suppress bogus gcc warning */
> 
> Well, that would be correct except the warning is an actual kernel  
> bug.  Read Jiri's message (which you also quoted):
> >struct bd_holder *found is initialized only when bd_claim() returns  
> >zero. If it returns nonzero, ptr stays uninitialized. Later the  
> >value of the pointer is checked.
> 
> So in this case it has to be initialized to NULL or there's a  
> potential BUG() lurking.


No, the code is correct and it's impossible that the variable ever gets 
read uninitialized.

And BTW, i386 gcc 4.1 doesn't give me a warning for this.
Toralf, which gcc version and architecture did you see this with?


> Cheers,
> Kyle Moffett

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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