Re: [PATCH] pwm: fix used-uninitialized warning in pwm_get()

From: Thierry Reding
Date: Wed Jul 04 2012 - 01:58:39 EST


On Tue, Jul 03, 2012 at 02:34:21PM -0600, Stephen Warren wrote:
> From: Stephen Warren <swarren@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> ---
> 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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