linux-kernel - sound/soc/codecs/wm8962.c:2790:32: warning: 'fratio' may be used uninitialized in this function

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Date:	Mon, 25 Jan 2016 15:15:36 +0800
From:	kbuild test robot <fengguang.wu@...el.com>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:	kbuild-all@...org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: sound/soc/codecs/wm8962.c:2790:32: warning: 'fratio' may be used
 uninitialized in this function

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   92e963f50fc74041b5e9e744c330dca48e04f08d
commit: c6d308534aef6c99904bf5862066360ae067abc4 UBSAN: run-time undefined behavior sanity checker
date:   4 days ago
config: x86_64-randconfig-n0-01251456 (attached as .config)
reproduce:
        git checkout c6d308534aef6c99904bf5862066360ae067abc4
        # save the attached .config to linux build tree
        make ARCH=x86_64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   sound/soc/codecs/wm8962.c: In function 'wm8962_set_fll':
>> sound/soc/codecs/wm8962.c:2790:32: warning: 'fratio' may be used uninitialized in this function [-Wmaybe-uninitialized]
     fll_div->n = target / (fratio * Fref);
                                   ^
   sound/soc/codecs/wm8962.c:2740:15: note: 'fratio' was declared here
     unsigned int fratio, gcd_fll;
                  ^

vim +/fratio +2790 sound/soc/codecs/wm8962.c

9a76f1ff Mark Brown      2010-08-05  2774  
9a76f1ff Mark Brown      2010-08-05  2775  	pr_debug("FLL Fvco=%dHz\n", target);
9a76f1ff Mark Brown      2010-08-05  2776  
25985edc Lucas De Marchi 2011-03-30  2777  	/* Find an appropriate FLL_FRATIO and factor it out of the target */
9a76f1ff Mark Brown      2010-08-05  2778  	for (i = 0; i < ARRAY_SIZE(fll_fratios); i++) {
9a76f1ff Mark Brown      2010-08-05  2779  		if (fll_fratios[i].min <= Fref && Fref <= fll_fratios[i].max) {
9a76f1ff Mark Brown      2010-08-05  2780  			fll_div->fll_fratio = fll_fratios[i].fll_fratio;
9a76f1ff Mark Brown      2010-08-05  2781  			fratio = fll_fratios[i].ratio;
9a76f1ff Mark Brown      2010-08-05  2782  			break;
9a76f1ff Mark Brown      2010-08-05  2783  		}
9a76f1ff Mark Brown      2010-08-05  2784  	}
9a76f1ff Mark Brown      2010-08-05  2785  	if (i == ARRAY_SIZE(fll_fratios)) {
9a76f1ff Mark Brown      2010-08-05  2786  		pr_err("Unable to find FLL_FRATIO for Fref=%uHz\n", Fref);
9a76f1ff Mark Brown      2010-08-05  2787  		return -EINVAL;
9a76f1ff Mark Brown      2010-08-05  2788  	}
9a76f1ff Mark Brown      2010-08-05  2789  
9a76f1ff Mark Brown      2010-08-05 @2790  	fll_div->n = target / (fratio * Fref);
9a76f1ff Mark Brown      2010-08-05  2791  
9a76f1ff Mark Brown      2010-08-05  2792  	if (target % Fref == 0) {
9a76f1ff Mark Brown      2010-08-05  2793  		fll_div->theta = 0;
9a76f1ff Mark Brown      2010-08-05  2794  		fll_div->lambda = 0;
9a76f1ff Mark Brown      2010-08-05  2795  	} else {
9a76f1ff Mark Brown      2010-08-05  2796  		gcd_fll = gcd(target, fratio * Fref);
9a76f1ff Mark Brown      2010-08-05  2797  
9a76f1ff Mark Brown      2010-08-05  2798  		fll_div->theta = (target - (fll_div->n * fratio * Fref))

:::::: The code at line 2790 was first introduced by commit
:::::: 9a76f1ff6e299fbb04149fe15aff061351fd0dab ASoC: Add initial WM8962 CODEC driver

:::::: TO: Mark Brown <broonie@...nsource.wolfsonmicro.com>
:::::: CC: Mark Brown <broonie@...nsource.wolfsonmicro.com>

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