linux-kernel - Re: [PATCH v4.4-rc8] iio: magnetometer: ak8975: Silence 'may be used uninitialized' warning

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Date:	Sat, 9 Jan 2016 16:25:17 +0000
From:	Jonathan Cameron <jic23@...nel.org>
To:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	tim.gardner@...onical.com, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>
Subject: Re: [PATCH v4.4-rc8] iio: magnetometer: ak8975: Silence 'may be used
 uninitialized' warning

On 09/01/16 16:17, Srinivas Pandruvada wrote:
> On Sat, 2016-01-09 at 16:00 +0000, Jonathan Cameron wrote:
>> On 09/01/16 00:17, tim.gardner@...onical.com wrote:
>>> From: Tim Gardner <tim.gardner@...onical.com>
>>>
>>> drivers/iio/magnetometer/ak8975.c: In function 'ak8975_probe':
>>> drivers/iio/magnetometer/ak8975.c:788:14: warning: 'chipset' may be
>>> used uninitialized in this function [-Wmaybe-uninitialized]
>>>   data->def = &ak_def_array[chipset];
>>>
>>> gcc version 5.3.1 20151219 (Ubuntu 5.3.1-4ubuntu1)
>>>
>>> Cc: Jonathan Cameron <jic23@...nel.org>
>>> Cc: Hartmut Knaack <knaack.h@....de>
>>> Cc: Lars-Peter Clausen <lars@...afoo.de>
>>> Cc: Peter Meerwald <pmeerw@...erw.net>
>>> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
>>> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
>> Doesn't look to be an actual bug as we either end up with chipset
>> being filled
>> based on the traditional match table in which case it'll be assigned
>> or based on the acpi match, which should succeed seeing as we've
>> already
>> had to have matched one or the other for the probe to match in the
>> first place.
>>
>> So probably worth the change to make it easier to tell that it should
>> be fine
>> and suppress the warning.  However, whilst we are here, I note that
>> *match_acpi_table has a path which returns NULL as the name and
>> doesn't assign
>> the chipset.  We should be therefore checking if (!name) return 
>> -ENOSYS;
>> Though maybe another error code would be more appropriate.
>>
> 
> Since in this case we are enumerated by ACPI using our match table, so
> name can't be null. The "name" we provided in 
> static const struct acpi_device_id ak_acpi_match[] = {..}
> Same with the *chipset. Other than suppress warnings, I don't think it
> will cause any real issue.
True enough, in which case why are we checking the name?
I'd be included to drop that check and add a comment.
I haven't chased every path, but I think that might deal with the above
warning at it's root.
> 
> Thanks,
> Srinivas 
> 
>> Not sure that error path can actually happen either, but if we are
>> going to
>> bother having the error path out of match_acpi_table then we ought to
>> actually
>> handle it!
>>
>> Don't suppose you'd mind fixing that one as well whilst here?
>>
>> Jonathan 
>>> ---
>>>
>>> This seems like a legitimate warning, though gcc should have
>>> complained
>>> about an earlier use of chipset on line 782.
>>>
>>>  drivers/iio/magnetometer/ak8975.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/iio/magnetometer/ak8975.c
>>> b/drivers/iio/magnetometer/ak8975.c
>>> index b13936d..80ec0ce 100644
>>> --- a/drivers/iio/magnetometer/ak8975.c
>>> +++ b/drivers/iio/magnetometer/ak8975.c
>>> @@ -732,7 +732,7 @@ static int ak8975_probe(struct i2c_client
>>> *client,
>>>  	int eoc_gpio;
>>>  	int err;
>>>  	const char *name = NULL;
>>> -	enum asahi_compass_chipset chipset;
>>> +	enum asahi_compass_chipset chipset = AK_MAX_TYPE;
>>>  
>>>  	/* Grab and set up the supplied GPIO. */
>>>  	if (client->dev.platform_data)
>>>
>>
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