From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by dpdk.org (Postfix) with ESMTP id 5E1547E28 for ; Mon, 15 Dec 2014 14:48:18 +0100 (CET) Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga102.fm.intel.com with ESMTP; 15 Dec 2014 05:47:59 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,579,1413270000"; d="scan'208";a="647807480" Received: from irsmsx153.ger.corp.intel.com ([163.33.192.75]) by fmsmga002.fm.intel.com with ESMTP; 15 Dec 2014 05:47:58 -0800 Received: from irsmsx102.ger.corp.intel.com ([169.254.2.213]) by IRSMSX153.ger.corp.intel.com ([163.33.192.75]) with mapi id 14.03.0195.001; Mon, 15 Dec 2014 13:47:57 +0000 From: "Wodkowski, PawelX" To: Thomas Monjalon Thread-Topic: [dpdk-dev] error: value computed is not used Thread-Index: AdASxiisLi704rCnRgagZfyMuDIXlQANP/TQAVaWb4AAALwbsAAEld2AAABHqiA= Date: Mon, 15 Dec 2014 13:47:57 +0000 Message-ID: References: <533710CFB86FA344BFBF2D6802E60286C9D989@SHSMSX101.ccr.corp.intel.com> <19703944.gAxOdpYSXo@xps13> <3427289.cFFhb9tNHS@xps13> In-Reply-To: <3427289.cFFhb9tNHS@xps13> Accept-Language: pl-PL, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [163.33.239.180] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] error: value computed is not used X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 15 Dec 2014 13:48:19 -0000 > -----Original Message----- > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] > Sent: Monday, December 15, 2014 2:27 PM > To: Wodkowski, PawelX > Cc: Qiu, Michael; dev@dpdk.org > Subject: Re: [dpdk-dev] error: value computed is not used >=20 > 2014-12-15 11:27, Wodkowski, PawelX: > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] > > > 2014-12-08 15:26, Wodkowski, PawelX: > > > > From: Qiu, Michael > > > > > 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 i= s 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 wi= ll 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, si= ze_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 workaro= und 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 everyt= hing > > > > > > but my conclusion was that there was some bug in compiler. I th= ink, > > > > > > when 'n' I constant and/or small compiler is inlining memcpy an= d > 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 leas= t > > > > > > explicitly throw it away by casting to void. I like solution wi= th static > > > > > > > > > > Actually, I try to pass "n" as a Int value like 4, it still repor= t this > > > > > error :) > > > > > > > > My workaround was: > > > > (void) rte_memcpy(...); > > > > > > > > But this is only a workaround. > > > > > > It's not so bad. > > > > > > > > > inline but someone else should spoke about possible side effect= s. > > > > > > > > > > Yes, but as I know inline is better than macros. > > > > > > From the GCC manual: > > > " > > > You may use this built-in function in either a macro or an inline fun= ction. > > > However, if you use it in an inlined function and pass an argument of= the > > > function as the argument to the built-in, GCC never returns 1 when yo= u call > > > the inline function with a string constant or compound literal and do= es not > > > return 1 when you pass a constant numeric value to the inline functio= n unless > > > you specify the -O option. > > > " > > > > > > It seems the "inline fix" cannot be used. > > > > > > I'm going to send a patch with Pawel's workaround. > > > > And something like this? > > > > #define rte_memcpy(dst, src, n) \ > > - ((__builtin_constant_p(n)) ? \ > > + ({ (__builtin_constant_p(n)) ? \ > > memcpy((dst), (src), (n)) : \ > > - rte_memcpy_func((dst), (src), (n))) > > + rte_memcpy_func((dst), (src), (n)); }) >=20 > What happens to the returned value after this change? > ptr =3D rte_memcpy(dst, src, n) + offset: >=20 https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs Whole expression should be 'void *' type (like *memcpy()) and it should wor= k as usual (see maxint() example in above link). It is GCC extension.=20 > > Thomas, can you check build with EXTRA_CFLAG=3D'-Wunused-value'. >=20 > You mean EXTRA_CFLAGS (with a S). > It fails in many locations. > What's your point? I am just asking if this is an typo, error or intend to do statements with = no effects like bellow. ixgbe_common.c:4429:3: error: statement with no effect [-Werror=3Dunused-va= lue] 4426: /* first pull in the header so we know the buffer length */ 4427: for (bi =3D 0; bi < dword_len; bi++) { 4428: buffer[bi] =3D IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi); 4429: IXGBE_LE32_TO_CPUS(&buffer[bi]); // <------ here 4430 } > Do you to support -Wunused-value? No, I just turned this on to check above change and was surprised what happ= ened. --=20 Pawel