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From: "Wodkowski, PawelX" <pawelx.wodkowski@intel.com>
To: "Qiu, Michael" <michael.qiu@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] error: value computed is not used
Date: Mon, 8 Dec 2014 11:00:41 +0000
Message-ID: <F6F2A6264E145F47A18AB6DF8E87425D12B675CD@IRSMSX102.ger.corp.intel.com> (raw)
In-Reply-To: <533710CFB86FA344BFBF2D6802E60286C9D989@SHSMSX101.ccr.corp.intel.com>

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

Pawel

  reply	other threads:[~2014-12-08 11:01 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-08  9:05 Qiu, Michael
2014-12-08 11:00 ` Wodkowski, PawelX [this message]
2014-12-08 15:23   ` Qiu, Michael
2014-12-08 15:26     ` Wodkowski, PawelX
2014-12-15 10:54       ` Thomas Monjalon
2014-12-15 11:07         ` [dpdk-dev] [PATCH] enic: fix build on SUSE 11 Thomas Monjalon
2014-12-15 11:27         ` [dpdk-dev] error: value computed is not used Wodkowski, PawelX
2014-12-15 13:26           ` Thomas Monjalon
2014-12-15 13:47             ` Wodkowski, PawelX
2014-12-15 14:16               ` Thomas Monjalon
2014-12-15 15:44                 ` Wodkowski, PawelX
2014-12-15 16:35                   ` Ananyev, Konstantin
2014-12-15 16:00                 ` Ananyev, Konstantin
2014-12-15 16:40                   ` Thomas Monjalon
2014-12-15 17:03                 ` Jastrzebski, MichalX K
2014-12-16  0:49         ` Qiu, Michael
2014-12-09  9:19 ` Qiu, Michael
2014-12-10  9:26 ` Qiu, Michael

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