linux-kernel - Re: [PATCH v5 06/17] sched/debug: Output SD flag names rather than their values

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Message-ID: <20200813120249.vdadn3nutkx3mq7y@ltop.local>
Date:   Thu, 13 Aug 2020 14:02:49 +0200
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     kernel test robot <lkp@...el.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kbuild-all@...ts.01.org,
        mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, morten.rasmussen@....com,
        Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH v5 06/17] sched/debug: Output SD flag names rather than
 their values

On Wed, Aug 12, 2020 at 07:51:08PM +0100, Valentin Schneider wrote:
> On 12/08/20 17:35, kernel test robot wrote:
> 
> > config: i386-randconfig-s001-20200811 (attached as .config)
> > reproduce:
> >         # sparse version: v0.6.2-168-g9554805c-dirty
> >         make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=i386
> >
> >>> kernel/sched/debug.c:279:17: sparse: sparse: non size-preserving pointer to integer cast
> >>> kernel/sched/debug.c:279:17: sparse: sparse: non size-preserving integer to pointer cast
> >
> >  > 279		tmp += *ppos;
> 
> I pretty much copied kernel/sysctl.c::_proc_do_string() and I think that's
> exactly the same types here: char* buffer incremented by loff_t offset. It
> does look fine to me, but I can't really parse that warning.

The warnings mean that there is a cast from a pointer to an integer with
a size other than the size of a pointer and the other way around.

I's indeed the case here, on i386, where pointers are 32-bit and loff_t
is 64-bit. But yes, I agree:
1) these messages are far from clear
2) these casts are internal and are probably not appropriate here.

I'll look later what can be done at sparse level.

Regards,
-- Luc