From: Peter Zijlstra <peterz@infradead.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: kernel test robot <lkp@intel.com>,
Yafang Shao <laoar.shao@gmail.com>,
kbuild-all@lists.01.org, linux-kernel@vger.kernel.org,
linux-toolchains@vger.kernel.org
Subject: Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used
Date: Sun, 12 Sep 2021 00:33:13 +0200 [thread overview]
Message-ID: <20210911223313.GC4323@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20210911213041.GD1583@gate.crashing.org>
On Sat, Sep 11, 2021 at 04:30:41PM -0500, Segher Boessenkool wrote:
> Hi!
>
> On Sat, Sep 11, 2021 at 02:20:49PM +0200, Peter Zijlstra wrote:
> > On Sat, Sep 11, 2021 at 02:21:26AM +0800, kernel test robot wrote:
> > > compiler: m68k-linux-gcc (GCC) 11.2.0
> >
> > > kernel/sched/fair.c: In function 'update_curr':
> > > kernel/sched/fair.c:860:42: warning: unused variable 'stats' [-Wunused-variable]
> > > 860 | struct sched_statistics *stats = __schedstats_from_se(curr);
> > > | ^~~~~
> >
> > OK, compiler guys, this code reads like:
> >
> > #define schedstats_enabled() (0)
> > #define __schedstat_set(x, y) do { } while (0)
> >
> >
> > if (schedstats_enabled()) {
> > struct sched_statistics *stats = __schedstats_from_se(curr);
> >
> > __schedstat_set(stats->exec_max,
> > max(delta_exec, stats->exec_max));
> > }
> >
> > So yes, we initialize a variable that then isn't used, but the whole
> > bloody thing is inside if (0) which will not ever get ran *anyway*.
> >
> > This is a crap warning if ever I saw one...
>
> Yes, we really should warn "do not use a preprocessor macro if what you
> want is a function"? The variable really *is* unused, with this macro.
Why would I want to write a bunch of one-off functions and preprocessor
guard them? That's going to be a mess.
> If we would remove dead code before warning about unused variables
> there would be many *more* false positives, fwiw.
Not if you also remove any variables declared in dead code and all
variables only used in the dead code.
prev parent reply other threads:[~2021-09-11 22:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-10 18:21 [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used kernel test robot
2021-09-11 1:46 ` Yafang Shao
2021-09-11 12:20 ` Peter Zijlstra
2021-09-11 21:30 ` Segher Boessenkool
2021-09-11 22:33 ` Peter Zijlstra [this message]
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