linux-kernel - Re: [PATCH v3 07/11] power: supply: core: tabularize HWMON temperature labels

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Date:   Fri, 1 May 2020 14:47:32 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        kbuild test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 07/11] power: supply: core: tabularize HWMON
 temperature labels

Hi,

On Mon, Apr 20, 2020 at 11:22:09AM +0200, Michał Mirosław wrote:
> On Tue, Apr 07, 2020 at 11:13:50AM -0700, Nick Desaulniers wrote:
> > On Sat, Apr 4, 2020 at 6:53 PM kbuild test robot <lkp@...el.com> wrote:
> > >
> > > Hi "Michał,
> > >
> > > I love your patch! Perhaps something to improve:
> > >
> > > [auto build test WARNING on power-supply/for-next]
> > > [also build test WARNING on hwmon/hwmon-next linus/master v5.6 next-20200404]
> > > [if your patch is applied to the wrong git tree, please drop us a note to help
> > > improve the system. BTW, we also suggest to use '--base' option to specify the
> > > base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
> > >
> > > url:    https://github.com/0day-ci/linux/commits/Micha-Miros-aw/extensions-and-fixes/20200405-044024
> > > base:   https://git.kernel.org/pub/scm/linux/kernel/git/sre/linux-power-supply.git for-next
> > > config: x86_64-randconfig-b002-20200405 (attached as .config)
> > > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 62f3a9650a9f289a07a5f480764fb655178c2334)
> > > reproduce:
> > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > >         chmod +x ~/bin/make.cross
> > >         # save the attached .config to linux build tree
> > >         COMPILER=clang make.cross ARCH=x86_64
> > >
> > > If you fix the issue, kindly add following tag as appropriate
> > > Reported-by: kbuild test robot <lkp@...el.com>
> > >
> > > All warnings (new ones prefixed by >>):
> > >
> > > >> drivers/power/supply/power_supply_hwmon.o: warning: objtool: power_supply_hwmon_read_string() falls through to next function power_supply_hwmon_write()
> > 
> > I'm guessing this is from the unreachable:
> > https://github.com/0day-ci/linux/commit/b8b2d14ca46ca54257f55c9af58ea25695b9ee36
> > I'll need to play with this some more as I couldn't reproduce with a
> > simplified test case, but looks like a compiler bug.  Filed
> > https://github.com/ClangBuiltLinux/linux/issues/978 for me to track.
> 
> Hi,
> 
> For gcc this is bug 51513 [1]. This does not affect correctness of the
> code, so I wonder if we should/need be trying to work around it.
> 
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51513

Yes, we need to work around it for now. If I understand the situation
correctly, a simple workaround would be:

default:
    /*
     * unreachable, but not explicitly marked because this triggers
     * a compiler bug in gcc and llvm:
     *
     *  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51513
     *  https://github.com/ClangBuiltLinux/linux/issues/978
     */
    break;

-- Sebastian

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