On Thu, Apr 20, 2017 at 10:44 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Thu, Apr 20, 2017 at 8:48 AM, Daniel Baluta <daniel.baluta@xxxxxxxxx> wrote: >> Hi Arnd, >> >> On Wed, Apr 19, 2017 at 8:04 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >>> The new PLL configuration code triggers a harmless warning: >>> >>> sound/soc/codecs/wm8960.c: In function 'wm8960_configure_clocking': >>> sound/soc/codecs/wm8960.c:735:3: error: 'best_freq_out' may be used uninitialized in this function [-Werror=maybe-uninitialized] >>> wm8960_set_pll(codec, freq_in, best_freq_out); >>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> sound/soc/codecs/wm8960.c:699:12: note: 'best_freq_out' was declared here >>> >>> I think the warning was introduced by Daniel's bugfix. I've come up >>> with a way to simplify the code in a way that is more readable to >>> both humans and to gcc, which gets us rid of the warning. >> >> I've struggled with this kind of warning when reworking wm8960 >> bitclock computation. >> >> Anyhow, for this exact patch the warning didn't showed up. >> >> I used: >> >> gcc version 6.2.1 20161016 (Linaro GCC 6.2-2016.11) > > I'm using gcc-7.0.1 here, which overall has better warnings for > -Wmaybe-uninitialized > than older versions, but sometimes also finds new false positives. > >> My next patch: >> >> https://patchwork.kernel.org/patch/9666921/ [1] >> >> which is under review, had the issue you mention (in v1) >> >> https://lkml.org/lkml/2017/4/5/246 >> >> but I initialized best_freq_out with 0 to get rid of the problem. > > I try hard not to do that, because it can hide real problems in case the > code gets modified further to actually have an uninitialized use that we > would otherwise get a warning for. > >>> @@ -720,22 +718,14 @@ int wm8960_configure_pll(struct snd_soc_codec *codec, int freq_in, >>> *sysclk_idx = i; >>> *dac_idx = j; >>> *bclk_idx = k; >>> - best_freq_out = freq_out; >>> - break; >>> + return freq_out; >>> } >>> } >>> - if (k != ARRAY_SIZE(bclk_divs)) >>> - break; >>> } >>> - if (j != ARRAY_SIZE(dac_divs)) >>> - break; >>> } >>> - >>> - if (*bclk_idx != -1) >>> - wm8960_set_pll(codec, freq_in, best_freq_out); >> >> I think the compiler is tricked into thinking that best_freq_out might >> be uninitialized. Notice >> that each time *bclk_idx is assigned a value (which is always >=0) we >> also initialize best_freq_out. > > Right. This is probably the result of one of two things that > prevent the compiler from figuring it out: > > a) bclk_idx being an indirect pointer might cause the compiler to > decide that another operation might overwrite it, e.g. if it points > to the same location as one of the other pointers. > > b) The flow analysis might just get too tricky, so when gcc gives > up trying to work out whether the assignment has happened > at least once for the two variables, it concludes that it doesn't > know, without seeing that the answer is always the same for > both of them. > >>> @@ -783,11 +773,12 @@ static int wm8960_configure_clocking(struct snd_soc_codec *codec) >>> } >>> } >>> >>> - ret = wm8960_configure_pll(codec, freq_in, &i, &j, &k); >>> - if (ret < 0) { >>> + freq_out = wm8960_configure_pll(codec, freq_in, &i, &j, &k); >>> + if (freq_out < 0) { >>> dev_err(codec->dev, "failed to configure clock via PLL\n"); >>> - return -EINVAL; >>> + return freq_out; >>> } >>> + wm8960_set_pll(codec, freq_in, freq_out); >>> >>> configure_clock: >>> /* configure sysclk clock */ >> >> Your idea looks good, will need to rework my follow up patch on it: >> >> https://patchwork.kernel.org/patch/9666921/ > > Ok. Or feel free to fold my patch into yours if that makes it easier for you. Great! I will fold your patch into my changes. thanks Arnd! Daniel. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
