Re: [kvm:queue 27/38] arch/x86/kvm/hyperv.c:186:41: sparse: incorrect type in argument 2 (different modifiers)

[Roman Kagan <rkagan@virtuozzo.com>]

On Fri, Sep 18, 2015 at 03:55:00PM +0200, Paolo Bonzini wrote:
> 
> 
> On 18/09/2015 15:51, Denis V. Lunev wrote:
> >>     185   
> >>   > 186        task_cputime_adjusted(current, &utime, &stime);
> >>     187        return div_u64(cputime_to_nsecs(utime + stime), 100);
> >>     188    }
> >>     189   
> >>     190    static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr,
> >> u64 data, bool host)
> >>     191    {
> >>     192        struct kvm_vcpu_hv *hv = &vcpu->arch.hyperv;
> >>     193   
> >>     194        switch (msr) {
> >>
> >> ---
> >> 0-DAY kernel test infrastructure                Open Source Technology
> >> Center
> >> https://lists.01.org/pipermail/kbuild-all                   Intel
> >> Corporation
> > can not get an idea what is this warning about...
> > For me it looks pretty lame.
> 
> I think it wants you to do
> 
> -	return div_u64(cputime_to_nsecs(utime + stime), 100);
> +	return div_u64(cputime_to_nsecs(utime) +
> +		       cputime_to_nsecs(stime), 100);

The warning is pretty specific about the point where it triggered.

I have reduced it to the following standalone reproducer:

%%% cat x.c
#ifdef __CHECKER__
# define __nocast       __attribute__((nocast))
#else
# define __nocast
#endif

typedef unsigned long __nocast cputime_t;

extern void task_cputime_adjusted(cputime_t *);
extern void current_task_runtime_100ns(void);

void current_task_runtime_100ns(void)
{
        cputime_t utime;

        task_cputime_adjusted(&utime);
}
%%% gcc -c x.c -Wall -Werror -O2; echo $?
0
%%% sparse x.c
x.c:16:32: warning: incorrect type in argument 1 (different modifiers)
x.c:16:32:    expected unsigned long [nocast] [usertype] *<noident>
x.c:16:32:    got unsigned long *<noident>
x.c:16:32: warning: implicit cast to nocast type

Looks like a sparse bug to me.

Roman.