From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f171.google.com (mail-wi0-f171.google.com [209.85.212.171]) by dpdk.org (Postfix) with ESMTP id A71352E83 for ; Tue, 14 Apr 2015 17:32:22 +0200 (CEST) Received: by wizk4 with SMTP id k4so118653274wiz.1 for ; Tue, 14 Apr 2015 08:32:22 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=rcfwzVI1LAuX8f+75IOB9Veuy9EhnPFQSn4lpaIzOPQ=; b=YKnYFJyBTpn6pYQ5nrzLj1yW80wN5hIECP/ri3u62IoF7qStmvxJ9iS2bcSorbe/jo HQQTkuxfFt9DsMT7mDLC6uo98y0DI1/EzaqFuhoaQjaaFtvTHYHfjgVn2vJsBrF8T1ce p5Hl1Y2fL/oBQVC1qKl/K2HLRc5BRsvr5k0jh5HU/hNMomA87cb0jBZR7sJxpfGVQtib dcaJeL5xt5bloF2CoZE+9YRmp6HvBS7mucs/vyDJWfNsr+xDnm7sWeL583mTgNfJ89ff AvjsCGjwCQZ79G4wdUjtl+SPRDdSs9S+8M7h51+SNilJaiKc3FdFbfdKhYaCGVzhdUAF f0Mw== X-Gm-Message-State: ALoCoQkP9YVFSuqU+SG/andWAvi74m4+3Ge2nxnRFMIRPmUSF2S0KnE5IkWSltshIco6C6Vc0b4L X-Received: by 10.180.87.199 with SMTP id ba7mr12840028wib.81.1429025542519; Tue, 14 Apr 2015 08:32:22 -0700 (PDT) Received: from [10.0.0.166] ([212.143.139.214]) by mx.google.com with ESMTPSA id k6sm17710761wia.6.2015.04.14.08.32.21 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Apr 2015 08:32:22 -0700 (PDT) Message-ID: <552D3304.20901@cloudius-systems.com> Date: Tue, 14 Apr 2015 18:32:20 +0300 From: Vlad Zolotarov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Thomas Monjalon References: <1429003900-20074-1-git-send-email-thomas.monjalon@6wind.com> <1704204.vBeNmeNBCG@xps13> <552D308B.3010000@cloudius-systems.com> <1958525.YbKd0lDtje@xps13> In-Reply-To: <1958525.YbKd0lDtje@xps13> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: dev@dpdk.org Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix build with gcc 4.4 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: Tue, 14 Apr 2015 15:32:22 -0000 On 04/14/15 18:28, Thomas Monjalon wrote: > 2015-04-14 18:21, Vlad Zolotarov: >> On 04/14/15 18:13, Thomas Monjalon wrote: >>> 2015-04-14 17:59, Vlad Zolotarov: >>>> On 04/14/15 17:17, Thomas Monjalon wrote: >>>>> 2015-04-14 16:38, Vlad Zolotarov: >>>>>> On 04/14/15 16:06, Ananyev, Konstantin wrote: >>>>>>> From: Vlad Zolotarov [mailto:vladz@cloudius-systems.com] >>>>>>>> On 04/14/15 12:31, Thomas Monjalon wrote: >>>>>>>>> - struct rte_eth_dev_info dev_info = { 0 }; >>>>>>>>> + struct rte_eth_dev_info dev_info = { .max_rx_queues = 0 }; >>>>>>>> Hmmm... Unless I miss something this and one above would zero only a >>>>>>>> single field - "max_rx_queues"; and would leave the rest uninitialized. >>>>>>>> The original code intend to zero the whole struct. The alternative to >>>>>>>> the original lines could be usage of memset(). >>>>>>> As I understand, in that case compiler had to set all non-explicitly initialised members to 0. >>>>>>> So I think we are ok here. >>>>>> Yeah, I guess it does zero-initializes the rest >>>>>> (https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html) however I >>>>>> don't understand how the above change fixes the error if it complains >>>>>> about the dev_info.driver_name? >>>>> As only 1 field is required, I chose the one which should not be removed >>>>> from this structure in the future. >>>>> >>>>>> What I'm trying to say - the proposed fix is completely unclear and >>>>>> confusing. Think of somebody reading this line in a month from today - >>>>>> he wouldn't get a clue why is it there, why to explicitly set >>>>>> max_rx_queues to zero and leave the rest be zeroed automatically... Why >>>>>> to add such artifacts to the code instead of just zeroing the struct >>>>>> with a memset() and putting a good clear comment above it explaining why >>>>>> we use a memset() and not and initializer? >>>>> We can make it longer yes. >>>>> I think you agree we should avoid extra lines if not needed. >>>>> In this case, when reading "= { .field = 0 }", it seems clear our goal >>>>> is to zero the structure (it is to me). >>>> I'm sorry but it's not clear to me at all since the common C practice >>>> for zeroing the struct would be >>>> >>>> struct st a = {0}; >>>> >>>> Like in the lines u are changing. The lines as above are clearly should >>>> not be commented and are absolutely clear. >>>> The lines u are adding on the other hand are absolutely unclear and >>>> confusing outside the gcc bug context. Therefore it should be clearly >>>> stated so in a form of comment. Otherwise somebody (like myself) may see >>>> this and immediately fix it back (as it should be). >>>> >>>>> I thought it is a basic C practice. >>>> I doubt that. ;) Explained above. >>>> >>>>> You should try "git grep '\.[^ ]\+ *= *0 *}'" to be convinced that we are >>>>> not going to comment each occurence of this coding style. >>>>> But it must be explained in the coding style document. Agree? >>>> OMG! This is awful! I think everybody agrees that this is a workaround >>>> and has nothing to do with a codding style (it's an opposite to a style >>>> actually). I don't know where this should be explained, frankly. >>> Once we assert we want to support this buggy compiler, the workarounds >>> are automatically parts of the coding style. >> It'd rather not... ;) >> >>> I don't know how to deal differently with this constraint. >> Add -Wno-missing-braces compilation option for compiler versions below >> 4.7. U (and me and I guess most other developers) compile DPDK code with >> a newer compiler thus the code would be properly inspected with these >> compilers and we may afford to be less restrictive with compilation >> warnings with legacy compiler versions... > You're right. > I will test it and submit a v2. > Then I could use the above grep command to replace other occurences of this > workaround. U read my mind!.. ;) > >>>> Getting back to the issue - I'm a bit surprised since I use this kind of >>>> initializer ({0}) in a C code for quite a long time - long before 2012. >>>> I'd like to understand what is a problem with this specific gcc version. >>>> This seems to trivial. I'm surprised CentOS has a gcc version with this >>>> kind of bugs. >>> Each day brings its surprise :) >