Re: [PATCH 2/2] xen/arm: gnttab: modify macros to evaluate all arguments and only once

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.05.2022 12:36, Michal Orzel wrote:
> Modify macros to evaluate all the arguments and make sure the arguments
> are evaluated only once. While doing so, use typeof for basic types
> and use const qualifier when applicable.

Why only for basic types? To take an example, passing void * into
gnttab_need_iommu_mapping() would imo also better not work.

> @@ -98,13 +104,36 @@ int replace_grant_host_mapping(unsigned long gpaddr, 
> mfn_t mfn,
>  })
>  
>  #define gnttab_shared_gfn(d, t, i)                                       \
> -    (((i) >= nr_grant_frames(t)) ? INVALID_GFN : (t)->arch.shared_gfn[i])
> +    ({                                                                   \
> +        const struct domain *d_ = (d);                                   \
> +        const struct grant_table *t_ = (t);                              \
> +        const typeof(i) i_ = (i);                                        \
> +                                                                         \
> +        if ( d_ != NULL )                                                \
> +            ASSERT(d_->grant_table == t_);                               \

I'm puzzled by this NULL check (and the similar instance further down):
Are you suggesting NULL can legitimately come into here? If not, maybe
better ASSERT(d_ && d_->grant_table == t_)?

Jan