Re: [PATCH 3/8] gnttab: Remove unused-but-set variable

[Michal Orzel <michal.orzel@xxxxxxx>]

On 28.04.2022 09:27, Jan Beulich wrote:
>>> diff --git a/xen/arch/arm/include/asm/grant_table.h
>>> b/xen/arch/arm/include/asm/grant_table.h
>>> index d31a4d6805d6..9f68c2a37eb6 100644
>>> --- a/xen/arch/arm/include/asm/grant_table.h
>>> +++ b/xen/arch/arm/include/asm/grant_table.h
>>> @@ -31,10 +31,10 @@ static inline void gnttab_mark_dirty(struct domain
>>> *d, mfn_t mfn)
>>>  
>>>  int create_grant_host_mapping(unsigned long gpaddr, mfn_t mfn,
>>>                                unsigned int flags, unsigned int
>>> cache_flags);
>>> -#define gnttab_host_mapping_get_page_type(ro, ld, rd) (0)
>>> +#define gnttab_host_mapping_get_page_type(ro, ld, rd) (ro, ld, rd, 0)
>>>  int replace_grant_host_mapping(unsigned long gpaddr, mfn_t mfn,
>>>                                 unsigned long new_gpaddr, unsigned int
>>> flags);
>>> -#define gnttab_release_host_mappings(domain) 1
>>> +#define gnttab_release_host_mappings(domain) (domain, 1)
>>>  
>>>  /*
>>>   * The region used by Xen on the memory will never be mapped in DOM0
>>>
>>> It's about parameter evaluation, not about adding extra code when compiled.
>>>
>>
>> Unfortunately, solution presented by Andrew does not work.
>> We will get the following error due to -Werror=unused-value:
>> "left-hand operand of comma expression has no effect"
> 
> Perhaps
> 
> #define gnttab_host_mapping_get_page_type(ro, ld, rd) \
>     ((void)(ro), (void)(ld), (void)(rd), 0)
> 
> ?
I already tried that and it won't work producing the following:
"error: void value not ignored as it ought to be"

Michal