Re: [dpdk-dev] error: value computed is not used

["Qiu, Michael" <michael.qiu@intel.com>]

On 2014/12/8 19:00, Wodkowski, PawelX wrote:
>> lib/librte_pmd_enic/enic_main.c: In function ‘enic_set_rsskey’:
>> lib/librte_pmd_enic/enic_main.c:862:2: error: value computed is not used
>>
>> I dig out that, it was ome issue of  the macros rte_memcpy()
>> #define rte_memcpy(dst, src, n)              \
>>         ((__builtin_constant_p(n)) ?          \
>>         memcpy((dst), (src), (n)) :          \
>>         rte_memcpy_func((dst), (src), (n)))
>>
>> When I use only (n) instead of (__builtin_constant_p(n), it will pass( I
>> know that it was incorrect, just a experiment).
>>
>> But I try to use inline function instead of macros:
>> static inline void * rte_memcpy(void *dst, const void *src, size_t n)
>> {
>>         return __builtin_constant_p(n) ? memcpy(dst, src, n) :
>>                                          rte_memcpy_func(dst, src, n);
>> }
>>
>> It will pass:), and works, this could be one potential workaround fix.
>>
>> Who knows why? The root cause is what?
>>
>> I've no idea about this.
>>
> I got the same issue while ago. I don't remember exactly everything
> but my conclusion was that there was some bug in compiler. I think,
> when 'n' I constant and/or small compiler is inlining memcpy and throwing
> everything else (including returned value). In that case error is not
> produced (I think this is a bug in compiler). In other case it is computing
> some value calling memcpy or rte_ memcpy and you should at least
> explicitly throw it away by casting to void. I like solution with static

Actually, I try to pass "n" as a Int value like 4, it still report this
error :)

> inline but someone else should spoke about possible side effects.

Yes, but as I know inline is better than macros.

Thanks,
Michael
>
> Pawel
>
>