From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Monjalon Subject: Re: [PATCH] ixgbe: fix build with gcc 4.4 Date: Tue, 14 Apr 2015 17:13:25 +0200 Message-ID: <1704204.vBeNmeNBCG@xps13> References: <1429003900-20074-1-git-send-email-thomas.monjalon@6wind.com> <54963304.brPH8sEe9A@xps13> <552D2B59.9000907@cloudius-systems.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: dev-VfR2kkLFssw@public.gmane.org To: Vlad Zolotarov Return-path: In-Reply-To: <552D2B59.9000907-RmZWMc9puTNJc61us3aD9laTQe2KTcn/@public.gmane.org> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces-VfR2kkLFssw@public.gmane.org Sender: "dev" 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-RmZWMc9puTNJc61us3aD9laTQe2KTcn/@public.gmane.org] > >>>> 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. I don't know how to deal differently with this constraint. > 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 :)