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

["Wodkowski, PawelX" <pawelx.wodkowski@intel.com>]

> -----Original Message-----
> From: Qiu, Michael
> Sent: Monday, December 08, 2014 4:24 PM
> To: Wodkowski, PawelX; dev@dpdk.org
> Subject: Re: error: value computed is not used
> 
> 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 :)

My workaround was:
(void) rte_memcpy(...);

But this is only a workaround.

> 
> > inline but someone else should spoke about possible side effects.
> 
> Yes, but as I know inline is better than macros.
> 
> Thanks,
> Michael
> >
> > Pawel
> >
> >