From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21118 invoked by alias); 12 Dec 2017 00:52:01 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 21108 invoked by uid 89); 12 Dec 2017 00:52:00 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,SPF_HELO_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 spammy= X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 12 Dec 2017 00:51:58 +0000 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C9702820F4; Tue, 12 Dec 2017 00:51:57 +0000 (UTC) Received: from [127.0.0.1] (ovpn04.gateway.prod.ext.ams2.redhat.com [10.39.146.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id D27645FCA0; Tue, 12 Dec 2017 00:51:51 +0000 (UTC) Subject: Re: [PATCH v2] Implement pahole-like 'ptype /o' option To: Sergio Durigan Junior References: <20171121160709.23248-1-sergiodj@redhat.com> <20171128212137.15655-1-sergiodj@redhat.com> <87o9n5drbn.fsf@redhat.com> <99286acb-ce9f-42f0-41c3-ef10e03171ff@ericsson.com> <87tvwxc6t9.fsf@redhat.com> <964bae42-6e60-4e9d-048c-ef570c1d3a5b@redhat.com> <87fu8gdgl8.fsf@redhat.com> <0d314798-6e0d-f7a9-ace8-3cb43bda9947@redhat.com> <87shcg94hp.fsf@redhat.com> Cc: Simon Marchi , GDB Patches , Tom Tromey , Eli Zaretskii From: Pedro Alves Message-ID: Date: Tue, 12 Dec 2017 00:52:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <87shcg94hp.fsf@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-SW-Source: 2017-12/txt/msg00265.txt.bz2 On 12/12/2017 12:25 AM, Sergio Durigan Junior wrote: > On Monday, December 11 2017, Pedro Alves wrote: >> IMO, the right way to go about this is to decide on a format, >> document it in the wiki and then we can point everyone at it with a URL. >> (ISTR that GCC's coding conventions documents yet another >> way to break the line, and in that case, not even GCC follows it.) >> >> IMO, the format you've chosen isn't ideal because it requires >> manual right-alignment for every line, while breaking before the >> parens makes emacs's TAB automatically align the following lines. >> The latter also gives a lot more space for the params again; it's >> sort of a "well, I have to do something, so might as well start >> way back from the left again). > > No, it's not ideal at all. But at least on my Emacs, the other format > has the downside of being always realigned to the column zero when I > press TAB on it. But again, I'm not saying this is Emacs fault nor your > nor Simon's fault; this is just something I noticed. Seems easier to fix (just two spaces, and only on one line) than the other approach, which depends a varying number of space/delete strokes. Maybe there's a way to configure emacs not to do that, even? > >>>>>> But I don't mind it, it just stuck out as a little inconsistency. >>>>> >>>>> I don't see the inconsistency. >>>>> >>>>> If a field is inside a struct, it has its offset *and* size printed. No >>>>> matter if the field is an int, another struct, or an union. >>>>> >>>>> If a field is inside an union, it has only its size printed. >>>>> >>>>> In the case above, it makes sense to have the offsets printed for the >>>>> fields inside the two structs (inside the union), because there might be >>>>> holes to report (well, one can argue that it doesn't matter if there are >>>>> holes or not in this case, because if the other struct is bigger then >>>>> the union size will stay the same). However, it doesn't make sense to >>>>> print the offsets for the two structs themselves, because they are >>>>> members of the union. >>>>> >>>>> I hope it makes more sense now. >>>> >>>> But why do we need the special case? Does it help anything? >>>> So far, it seems it only added confusion. >>> >>> What do you mean by "special case"? >> >> Special case: >> >> "If a field is inside a union, it has only its size printed; otherwise >> print the offset and size." >> >> No special case: >> >> "Always print the offset and size." > > I don't like the expression "special case" because it diminishes the > difference that exist between structs and unions. I don't follow, but OK... > It is not like I went > out of my way to treat this difference and made the code complex; it is > also not like the output is extremely complex with it. The point isn't about the implementation complexity, it's about user expectations. Simon was seemingly surprised by "an inconsistency" (i.e., a case is not consistent with the others; i.e., there's special/different case), so I think it's valid to discuss a bit and maybe double check the rationale and see if we can save users from being confused too. If after chatting a bit we come to the conclusion skipping the offsets makes sense, than that's fine. No harm done. >>> I don't consider this a >>> special case; I consider it to be the natural thing to do, because >>> offsets don't make much sense in unions. >> >> Of course they do. You can do 'offsetof(foo_union, foo_field)' just >> fine, for example. Saying that the offsets happen to be the same >> is not the same as saying that the offsets don't exist. > > I don't remember saying offsets don't exist in unions. What I said is > that in this specific case they don't matter/make much sense to be > printed. Guess we're discussing semantics, which is kind of pointless... "Don't make sense" to me is like talking about what's the "weight of a mile", which is truly meaningless. Stating that all union members live at offset 0 is not meaningless, because that's exactly how you define a union! >> So from that angle, I see value in not printing the offsets >> of union members. > > Since it's still not clear whether the offsets should be printed or not > in this case, and I am not a global maintainer, I adjusted the code to > print them and will post the patch as a reply to the v4 e-mail. This > way you can decide which version is best. Fun, just when I agreed with not printing the offsets... :-P :-) Thanks, Pedro Alves