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From: "Qiu, Michael" <michael.qiu@intel.com>
To: "Wodkowski, PawelX" <pawelx.wodkowski@intel.com>, "dev@dpdk.org"
 <dev@dpdk.org>
Thread-Topic: error: value computed is not used
Thread-Index: AdASxiisLi704rCnRgagZfyMuDIXlQ==
Date: Mon, 8 Dec 2014 15:23:34 +0000
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Subject: Re: [dpdk-dev] error: value computed is not used
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On 2014/12/8 19:00, Wodkowski, PawelX wrote:=0A=
>> lib/librte_pmd_enic/enic_main.c: In function =91enic_set_rsskey=92:=0A=
>> lib/librte_pmd_enic/enic_main.c:862:2: error: value computed is not used=
=0A=
>>=0A=
>> I dig out that, it was ome issue of  the macros rte_memcpy()=0A=
>> #define rte_memcpy(dst, src, n)              \=0A=
>>         ((__builtin_constant_p(n)) ?          \=0A=
>>         memcpy((dst), (src), (n)) :          \=0A=
>>         rte_memcpy_func((dst), (src), (n)))=0A=
>>=0A=
>> When I use only (n) instead of (__builtin_constant_p(n), it will pass( I=
=0A=
>> know that it was incorrect, just a experiment).=0A=
>>=0A=
>> But I try to use inline function instead of macros:=0A=
>> static inline void * rte_memcpy(void *dst, const void *src, size_t n)=0A=
>> {=0A=
>>         return __builtin_constant_p(n) ? memcpy(dst, src, n) :=0A=
>>                                          rte_memcpy_func(dst, src, n);=
=0A=
>> }=0A=
>>=0A=
>> It will pass:), and works, this could be one potential workaround fix.=
=0A=
>>=0A=
>> Who knows why? The root cause is what?=0A=
>>=0A=
>> I've no idea about this.=0A=
>>=0A=
> I got the same issue while ago. I don't remember exactly everything=0A=
> but my conclusion was that there was some bug in compiler. I think,=0A=
> when 'n' I constant and/or small compiler is inlining memcpy and throwing=
=0A=
> everything else (including returned value). In that case error is not=0A=
> produced (I think this is a bug in compiler). In other case it is computi=
ng=0A=
> some value calling memcpy or rte_ memcpy and you should at least=0A=
> explicitly throw it away by casting to void. I like solution with static=
=0A=
=0A=
Actually, I try to pass "n" as a Int value like 4, it still report this=0A=
error :)=0A=
=0A=
> inline but someone else should spoke about possible side effects.=0A=
=0A=
Yes, but as I know inline is better than macros.=0A=
=0A=
Thanks,=0A=
Michael=0A=
>=0A=
> Pawel=0A=
>=0A=
>=0A=
=0A=