Re: [PATCH for-next 3/6] xen/sched: Fix build when NR_CPUS == 1

[Connor Davis <connojdavis@xxxxxxxxx>]

On Thu, Feb 25, 2021 at 04:50:02PM +0100, Jan Beulich wrote:
> On 25.02.2021 16:24, Connor Davis wrote:
> > Return from cpu_schedule_up when either cpu is 0 or
> > NR_CPUS == 1. This fixes the following:
> > 
> > core.c: In function 'cpu_schedule_up':
> > core.c:2769:19: error: array subscript 1 is above array bounds
> > of 'struct vcpu *[1]' [-Werror=array-bounds]
> >  2769 |     if ( idle_vcpu[cpu] == NULL )
> >       |
> > 
> > Signed-off-by: Connor Davis <connojdavis@xxxxxxxxx>
> > ---
> >  xen/common/sched/core.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
> > index 9745a77eee..f5ec65bf9b 100644
> > --- a/xen/common/sched/core.c
> > +++ b/xen/common/sched/core.c
> > @@ -2763,7 +2763,7 @@ static int cpu_schedule_up(unsigned int cpu)
> >      cpumask_set_cpu(cpu, &sched_res_mask);
> >  
> >      /* Boot CPU is dealt with later in scheduler_init(). */
> > -    if ( cpu == 0 )
> > +    if ( cpu == 0 || NR_CPUS == 1 )
> >          return 0;
> >  
> >      if ( idle_vcpu[cpu] == NULL )
> 
> I'm not convinced a compiler warning is due here, and in turn
> I'm not sure we want/need to work around this the way you do.

It seems like a reasonable warning to me, but of course I'm open
to dealing with it in a different way.

> First question is whether that's just a specific compiler
> version that's flawed. If it's not just a special case (e.g.

The docker container uses gcc 10.2.0 from
https://github.com/riscv/riscv-gnu-toolchain

> some unreleased version) we may want to think of possible
> alternatives - the addition looks really odd to me.
> 
> Jan

    Connor