public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "qinzhao at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/108896] provide "element_count" attribute to give more context to __builtin_dynamic_object_size() and -fsanitize=bounds Date: Thu, 02 Mar 2023 19:47:56 +0000 [thread overview] Message-ID: <bug-108896-4-dyUQ2enABi@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-108896-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896 --- Comment #11 from qinzhao at gcc dot gnu.org --- (In reply to Martin Uecker from comment #9) > > https://www.open-std.org/jtc1/sc22/wg14/www/wg14_document_log thanks for the info. > > But we made variably modified types mandatory in C23 to > help with bounds checking and this already works quite > nicely with GCC / Clang: > > https://godbolt.org/z/ddfsdWPMj nice! can you provide a pointer to the section in C23 that made this change? > > > when this variable length concept is extended to global scope, not sure how to > > implement the size expression? need some study here. > > Here, we want to use a member of the struct as a size > expression. This could work equally at function and file scope. > But the semantics need to be worked out. I have started to work > on a patch for GCC a couple of weeks ago using PLACEHOLDER_EXPR, > but did not get very far. > > The idea is to evaluate the size expression whenever the member > with the size is accesses. If the size is not set before, this > would be undefined behavior. > > Other languages such as Ada support this, so in principle this > should be a piece of cake. Oh, Ada can support this already? how does Ada implement this? then we can just borrow Ada's implementation idea to implement this in C if this is approved as an GCC extension for C. > > this proposal basically is to extend the VLA concept from function scope to > > global scope. is my understanding correct? > > I would say the idea is to allow size expressions to refer > to member of a struct instead of only automatic variables. > Okay. > > a question here is: > > > > for the following nested structure: > > > > struct object { > > ... > > char items; > > ... > > struct inner { > > ... > > int flex[]; > > }; > > } *ptr; > > > > what kind of syntax is good to represent the upper bound of "flex" in the inner > > struct with "items" in the outer structure? any suggestion? > > I would disallow it. At least at first. It also raises some > questions: For example, one could form a pointer to the inner > struct, and then it is not clear how 'items' could be accessed > anymore. > Okay.
next prev parent reply other threads:[~2023-03-02 19:47 UTC|newest] Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-02-22 21:26 [Bug c/108896] New: " kees at outflux dot net 2023-02-22 21:31 ` [Bug c/108896] " kees at outflux dot net 2023-02-22 21:32 ` pinskia at gcc dot gnu.org 2023-02-23 8:44 ` rguenth at gcc dot gnu.org 2023-02-23 9:10 ` jakub at gcc dot gnu.org 2023-02-24 15:44 ` muecker at gwdg dot de 2023-03-01 22:54 ` qinzhao at gcc dot gnu.org 2023-03-01 23:27 ` kees at outflux dot net 2023-03-02 15:50 ` muecker at gwdg dot de 2023-03-02 17:34 ` qinzhao at gcc dot gnu.org 2023-03-02 18:17 ` muecker at gwdg dot de 2023-03-02 18:34 ` muecker at gwdg dot de 2023-03-02 19:47 ` qinzhao at gcc dot gnu.org [this message] 2023-03-02 19:56 ` qinzhao at gcc dot gnu.org 2023-03-02 20:07 ` muecker at gwdg dot de 2023-03-03 20:27 ` isanbard at gmail dot com 2023-03-03 21:32 ` muecker at gwdg dot de 2023-03-03 23:18 ` isanbard at gmail dot com 2023-03-04 7:52 ` muecker at gwdg dot de 2023-03-06 19:15 ` isanbard at gmail dot com 2023-03-06 19:18 ` jakub at gcc dot gnu.org 2023-03-06 19:38 ` muecker at gwdg dot de 2023-03-06 19:57 ` muecker at gwdg dot de 2023-03-06 20:05 ` siddhesh at gcc dot gnu.org 2023-03-08 16:56 ` qinzhao at gcc dot gnu.org 2023-03-08 17:13 ` qinzhao at gcc dot gnu.org 2023-03-08 17:36 ` qinzhao at gcc dot gnu.org 2023-03-08 17:38 ` qinzhao at gcc dot gnu.org 2023-03-08 17:43 ` qinzhao at gcc dot gnu.org 2023-03-08 17:48 ` muecker at gwdg dot de 2023-03-08 18:37 ` muecker at gwdg dot de 2023-03-08 19:20 ` qinzhao at gcc dot gnu.org 2023-03-08 19:47 ` qinzhao at gcc dot gnu.org 2023-03-08 20:20 ` muecker at gwdg dot de 2023-03-08 20:47 ` qinzhao at gcc dot gnu.org 2023-03-29 16:12 ` muecker at gwdg dot de 2023-04-03 20:29 ` qinzhao at gcc dot gnu.org 2023-04-03 21:53 ` muecker at gwdg dot de 2023-04-04 15:07 ` qinzhao at gcc dot gnu.org 2023-04-04 16:33 ` muecker at gwdg dot de 2023-04-04 20:08 ` qinzhao at gcc dot gnu.org 2023-04-19 16:32 ` qinzhao at gcc dot gnu.org 2023-05-03 13:57 ` qinzhao at gcc dot gnu.org 2023-05-03 15:32 ` kees at outflux dot net 2023-05-04 15:16 ` muecker at gwdg dot de 2023-05-04 15:30 ` qinzhao at gcc dot gnu.org 2023-05-25 18:14 ` qinzhao at gcc dot gnu.org 2023-05-25 18:47 ` ndesaulniers at google dot com 2023-10-05 19:54 ` tg at mirbsd dot org 2023-10-05 20:21 ` muecker at gwdg dot de 2023-12-27 6:31 ` sean@rogue-research.com 2024-03-06 14:40 ` qinzhao at gcc dot gnu.org 2024-05-31 17:50 ` qinzhao at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-108896-4-dyUQ2enABi@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).