From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id 3B871A052E; Mon, 9 Mar 2020 12:30:05 +0100 (CET) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id E6AEE1C010; Mon, 9 Mar 2020 12:30:03 +0100 (CET) Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by dpdk.org (Postfix) with ESMTP id 74EF81BFF4; Mon, 9 Mar 2020 12:30:01 +0100 (CET) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Mar 2020 04:30:00 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,533,1574150400"; d="scan'208";a="230893291" Received: from fyigit-mobl.ger.corp.intel.com (HELO [10.237.221.20]) ([10.237.221.20]) by orsmga007.jf.intel.com with ESMTP; 09 Mar 2020 04:29:56 -0700 To: Gavin Hu , "dev@dpdk.org" Cc: nd , "david.marchand@redhat.com" , "thomas@monjalon.net" , "ktraynor@redhat.com" , "jerinj@marvell.com" , Honnappa Nagarahalli , Ruifeng Wang , Phil Yang , Joyce Kong , "stable@dpdk.org" , Olivier MATZ , Konstantin Ananyev , Andrew Rybchenko References: <20200303162728.93744-1-gavin.hu@arm.com> <20200307155629.45021-1-gavin.hu@arm.com> <4135ab73-75d3-421a-264d-2951fc096133@intel.com> From: Ferruh Yigit Autocrypt: addr=ferruh.yigit@intel.com; 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charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [dpdk-dev] [PATCH v2] mbuf: replace zero-length marker with unnamed union X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 3/9/2020 9:45 AM, Gavin Hu wrote: > Hi Ferruh, > >> -----Original Message----- >> From: Ferruh Yigit >> Sent: Monday, March 9, 2020 4:55 PM >> To: Gavin Hu ; dev@dpdk.org >> Cc: nd ; david.marchand@redhat.com; thomas@monjalon.net; >> ktraynor@redhat.com; jerinj@marvell.com; Honnappa Nagarahalli >> ; Ruifeng Wang >> ; Phil Yang ; Joyce Kong >> ; stable@dpdk.org; Olivier MATZ >> ; Konstantin Ananyev >> ; Andrew Rybchenko >> >> Subject: Re: [dpdk-dev] [PATCH v2] mbuf: replace zero-length marker with >> unnamed union >> >> On 3/7/2020 3:56 PM, Gavin Hu wrote: >>> Declaring zero-length arrays in other contexts, including as interior >>> members of structure objects or as non-member objects, is discouraged. >>> Accessing elements of zero-length arrays declared in such contexts is >>> undefined and may be diagnosed.[1] >>> >>> Fix by using unnamed union and struct. >>> >>> https://bugs.dpdk.org/show_bug.cgi?id=396 >>> >>> Bugzilla ID: 396 >>> >>> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html >>> >>> Fixes: 3e6181b07038 ("mbuf: use structure marker from EAL") >>> Cc: stable@dpdk.org >>> >>> Signed-off-by: Gavin Hu >>> --- >>> v2: >>> * change 'uint64_t rearm_data' to 'uint_64_t rearm_data[1]' to fix >>> the SFC PMD compiling error on x86. >>> --- >>> lib/librte_mbuf/rte_mbuf_core.h | 54 +++++++++++++++++++-------------- >>> 1 file changed, 32 insertions(+), 22 deletions(-) >>> >>> diff --git a/lib/librte_mbuf/rte_mbuf_core.h >> b/lib/librte_mbuf/rte_mbuf_core.h >>> index b9a59c879..34cb152e2 100644 >>> --- a/lib/librte_mbuf/rte_mbuf_core.h >>> +++ b/lib/librte_mbuf/rte_mbuf_core.h >>> @@ -480,31 +480,41 @@ struct rte_mbuf { >>> rte_iova_t buf_physaddr; /**< deprecated */ >>> } __rte_aligned(sizeof(rte_iova_t)); >>> >>> - /* next 8 bytes are initialised on RX descriptor rearm */ >>> - RTE_MARKER64 rearm_data; >>> - uint16_t data_off; >>> - >>> - /** >>> - * Reference counter. Its size should at least equal to the size >>> - * of port field (16 bits), to support zero-copy broadcast. >>> - * It should only be accessed using the following functions: >>> - * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and >>> - * rte_mbuf_refcnt_set(). The functionality of these functions (atomic, >>> - * or non-atomic) is controlled by the >> CONFIG_RTE_MBUF_REFCNT_ATOMIC >>> - * config option. >>> - */ >>> RTE_STD_C11 >>> union { >>> - rte_atomic16_t refcnt_atomic; /**< Atomically accessed >> refcnt */ >>> - /** Non-atomically accessed refcnt */ >>> - uint16_t refcnt; >>> - }; >>> - uint16_t nb_segs; /**< Number of segments. */ >>> + /* next 8 bytes are initialised on RX descriptor rearm */ >>> + uint64_t rearm_data[1]; >> We are using zero length array as markers only and know what we are doing >> with them, >> what would you think disabling the warning instead of increasing the >> complexity >> in mbuf struct? > Okay, I will add -Wno-zero-length-bounds to the compiler toolchain flags. This would be my preference but I would like to get more input, can you please for more comments before changing the implementation in case there are some strong opinion on it?