linux-kernel - Re: [PATCH] pwm: fix used-uninitialized warning in pwm

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Message-ID: <20120704055828.GC18779@avionic-0098.mockup.avionic-design.de>
Date:	Wed, 4 Jul 2012 07:58:28 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	linux-kernel@...r.kernel.org, Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCH] pwm: fix used-uninitialized warning in pwm_get()

On Tue, Jul 03, 2012 at 02:34:21PM -0600, Stephen Warren wrote:
> From: Stephen Warren <swarren@...dia.com>
> 
> This fixes:
> drivers/pwm/core.c: In function 'pwm_get':
> drivers/pwm/core.c:534:15: warning: 'index' may be used uninitialized in this function
> 
> The addition to the if condition at end of the function isn't strictly
> necessary to solve the warning, but does make it more obvious that the
> initialization of "index" to a dummy value isn't just hiding the
> problem.

Actually this seems to be a false positive, and one that I don't see (I
use GCC 4.6.3). index will be initialized when chip is set in the loop.
My guess is that GCC 4.6.3 actually notices while your version doesn't.

Thierry

> Signed-off-by: Stephen Warren <swarren@...dia.com>
> ---
>  drivers/pwm/core.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index dbab530..2b401c0 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -531,7 +531,7 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>  	struct pwm_chip *chip = NULL;
>  	unsigned int best = 0;
>  	struct pwm_lookup *p;
> -	unsigned int index;
> +	unsigned int index = -1;
>  	unsigned int match;
>  
>  	/* look up via DT first */
> @@ -588,7 +588,7 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>  		}
>  	}
>  
> -	if (chip)
> +	if (chip && index != -1)
>  		pwm = pwm_request_from_chip(chip, index, con_id ?: dev_id);
>  
>  	mutex_unlock(&pwm_lookup_lock);
> -- 
> 1.7.0.4
> 
> 
> 

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