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From: "kees at outflux dot net" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/108896] New: provide "element_count" attribute to give more context to __builtin_dynamic_object_size() and -fsanitize=bounds Date: Wed, 22 Feb 2023 21:26:58 +0000 [thread overview] Message-ID: <bug-108896-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896 Bug ID: 108896 Summary: provide "element_count" attribute to give more context to __builtin_dynamic_object_size() and -fsanitize=bounds Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: kees at outflux dot net Target Milestone: --- Frequently a structure containing a flexible array member will also contain a member where the count of array elements is stored. For example: struct foo { ... unsigned int count; ... int data[]; }; struct foo *allocate_foo(unsigned int how_many) { struct foo *p; p = malloc(sizeof(*p) + how_many * sizeof(*byte_array)); p->count = how_many; return p; } While __builtin_dynamic_object_size(p->data, 1) will know the size within "allocate_foo" due to malloc's __alloc_size hinting, this information is immediately lost on return. However, the information _is_ still available in p->count, but the compiler has no way to know about it. Please provide a struct member attribute "element_count" that can be used to associate the size of a flexible array to another struct member. For example: struct foo { ... unsigned int count; ... int data[] __attribute__((__element_count__(count))); }; Now any later examination of the size of "data" can be calculated. For example, this equality will hold true: __builtin_dynamic_object_size(p->data) == p->count * sizeof(*p->data) and -fsanitize-bounds can examine this as well, to trap: p->data[index] = ...; /* traps when index < 0, or index >= p->count */
next reply other threads:[~2023-02-22 21:26 UTC|newest] Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-02-22 21:26 kees at outflux dot net [this message] 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 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
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