On 23.10.2023 18:07, Julien Grall wrote:
> Hi Jan,
>
> On 23/10/2023 16:15, Jan Beulich wrote:
>> On 23.10.2023 17:00, Julien Grall wrote:
>>>
>>>
>>> On 23/10/2023 15:51, Nicola Vetrini wrote:
>>>> Hi,
>>>
>>> Hi Nicola,
>>>
>>>> while taking care of some patches regarding MISRA C Rule 2.1 (code
>>>> shouldn't be unreachable), I
>>>> came across this function:
>>>>
>>>> long subarch_do_domctl(struct xen_domctl *domctl, struct domain *d,
>>>> XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
>>>> {
>>>> switch ( domctl->cmd )
>>>> {
>>>> case XEN_DOMCTL_set_address_size:
>>>> switch ( domctl->u.address_size.size )
>>>> {
>>>> case 32:
>>>> if ( !cpu_has_el1_32 )
>>>> return -EINVAL;
>>>> /* SVE is not supported for 32 bit domain */
>>>> if ( is_sve_domain(d) )
>>>> return -EINVAL;
>>>> return switch_mode(d, DOMAIN_32BIT);
>>>> case 64:
>>>> return switch_mode(d, DOMAIN_64BIT);
>>>> default:
>>>> return -EINVAL;
>>>> }
>>>> break;
>>>>
>>>> default:
>>>> return -ENOSYS;
>>>> }
>>>> }
>>>>
>>>> here the break after the innermost switch is clearly unreachable, but
>>>> it's also guarding a possible fallthrough.
>>>> I can see a couple of solutions to this:
>>>>
>>>> - mark the part after the switch unreachable;
>>>> - introduce a variable 'long rc' to store the return value, and
>>>> consequently rework the control flow of all the switches
>>>> (e.g. rc = -EINVAL and similar);
>>>> - remove the break, but I consider this a risky move, unless -ENOSYS
>>>> would be an ok value to be returned if some case
>>>> from the switch above does not have a return statement.
>>>
>>> - move the nested switch in a separate function, so the code in
>>> subarch_do_domctl() can be replaced with:
>>>
>>> return set_address_size(...);
>>
>> But that would help only if inside the new function you still re-
>> layout the switch() (or replace it by, say, if/else-if/else),
>> wouldn't it?
>
> I am not sure why I would need to re-layout the switch. This should work
> (untested):
>
> diff --git a/xen/arch/arm/arm64/domctl.c b/xen/arch/arm/arm64/domctl.c
> index 14fc622e9956..8720d126c97d 100644
> --- a/xen/arch/arm/arm64/domctl.c
> +++ b/xen/arch/arm/arm64/domctl.c
> @@ -33,27 +33,31 @@ static long switch_mode(struct domain *d, enum
> domain_type type)
> return 0;
> }
>
> +static long set_address_size(struct domain *d, uint32_t address_size)
> +{
> + switch ( address_size )
> + {
> + case 32:
> + if ( !cpu_has_el1_32 )
> + return -EINVAL;
> + /* SVE is not supported for 32 bit domain */
> + if ( is_sve_domain(d) )
> + return -EINVAL;
> + return switch_mode(d, DOMAIN_32BIT);
> + case 64:
> + return switch_mode(d, DOMAIN_64BIT);
> + default:
> + return -EINVAL;
> + }
> +}
Well, yes, if you're happy to have a function returning a value without
a return statement at its end.
Jan
