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

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Message-ID: <CAM3j68rH8qyN8zX7TLZNvQz-1Vr6qMjS0cR7QKGAs6w54L7dag@mail.gmail.com>
Date:	Fri, 30 Nov 2012 12:12:46 +0100
From:	Tux9 <tuxding@...il.com>
To:	"Hans J. Koch" <hjk@...sjkoch.de>
Cc:	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

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.

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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