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

[Bob Eshleman <bobbyeshleman@xxxxxxxxx>]

On 2/25/21 7:24 AM, 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 )
> 

Interesting.  I wonder when this changed in GCC.

I haven't yet seen this issue compiling with:
  NR_CPUS=1
  ARCH=riscv64
  riscv64-unknown-linux-gnu-gcc (GCC) 10.1.0

Which version of GCC are you seeing emit this?

- Bob