linux-kernel - Re: [PATCH] uio.c: Fix warning: 'ret' might be used uninitialized

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Message-ID: <20121130213333.GA2603@local>
Date:	Fri, 30 Nov 2012 22:33:33 +0100
From:	"Hans J. Koch" <hjk@...sjkoch.de>
To:	Tux9 <tuxding@...il.com>
Cc:	"Hans J. Koch" <hjk@...sjkoch.de>,
	Vitalii Demianets <vitas@...factor.kiev.ua>,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] uio.c: Fix warning: 'ret' might be used uninitialized

On Fri, Nov 30, 2012 at 12:12:46PM +0100, Tux9 wrote:
> I like Vitalii's solution more. Hans's solution assign the value
> -ENOMEM to ret in every round of the loop, which is a kind of wasting
> CPU cycles.

The difference between
1 files changed, 12 insertions(+), 4 deletions(-) and
1 files changed, 2 insertions(+), 0 deletions(-)

is more important. Note that this code is not in a fast path but only
called once at device creation.

Thanks,
Hans

> 
> On Fri, Nov 30, 2012 at 12:58 AM, Hans J. Koch <hjk@...sjkoch.de> wrote:
> > On Thu, Nov 29, 2012 at 06:36:59PM +0200, Vitalii Demianets wrote:
> >> > On Thursday 29 November 2012 18:05:27 Tux9 wrote:
> >> > > Hans, I think there are something wrong in your patch, while Vitalii's
> >> > > is right. The variable "ret" is reused in line 292 and line 295, so
> >> > > the value of "ret" would be overridden (if it goto err_map in line 284
> >> > > when mi>=1).
> >> >
> >> > Actually, both patches do exactly the same thing. Hans's patch establishes
> >> > default value for the ret for all those "other" cases when ret is not
> >> > explicitly overridden. My patch explicitly enumerates all those "other"
> >> > cases in more wordily manner.
> >> >
> >>
> >> Oops, disregard this. After looking at it more thoroughly I got your point.
> >> You are right, ret is overridden at first iteration (mi == 0), so Hans's
> >> approach does not work.
> >> I must do more thinking before replying in a hurry.
> >
> > You're right. Initialization of "ret" has to take place at the beginning of
> > the loop.
> >
> > I think this version is right:
> >
> >
> > From 00c3c734c0dde67873a628bcb18cee403c95c301 Mon Sep 17 00:00:00 2001
> > From: "Hans J. Koch" <hjk@...sjkoch.de>
> > Date: Fri, 30 Nov 2012 00:51:50 +0100
> > Subject: [PATCH] uio: Fix warning: 'ret' might be used uninitialized
> >
> > In two cases, the return value variable "ret" can be undefined.
> >
> > Signed-off-by: Hans J. Koch <hjk@...sjkoch.de>
> > ---
> >  drivers/uio/uio.c |    2 ++
> >  1 files changed, 2 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> > index 5110f36..0c80df2 100644
> > --- a/drivers/uio/uio.c
> > +++ b/drivers/uio/uio.c
> > @@ -273,6 +273,7 @@ static int uio_dev_add_attributes(struct uio_device *idev)
> >         struct uio_portio *portio;
> >
> >         for (mi = 0; mi < MAX_UIO_MAPS; mi++) {
> > +               ret = -ENOMEM;
> >                 mem = &idev->info->mem[mi];
> >                 if (mem->size == 0)
> >                         break;
> > @@ -298,6 +299,7 @@ static int uio_dev_add_attributes(struct uio_device *idev)
> >         }
> >
> >         for (pi = 0; pi < MAX_UIO_PORT_REGIONS; pi++) {
> > +               ret = -ENOMEM;
> >                 port = &idev->info->port[pi];
> >                 if (port->size == 0)
> >                         break;
> > --
> > 1.7.9
> >
> > --
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> 
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