From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: + gcov-gcc_4_7-replace-zero-length-array-with-flexible-array-member.patch added to -mm tree Date: Wed, 26 Feb 2020 20:11:03 -0800 Message-ID: <20200227041103.b3028mJYR%akpm@linux-foundation.org> References: <20200203173311.6269a8be06a05e5a4aa08a93@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:60752 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727735AbgB0ELF (ORCPT ); Wed, 26 Feb 2020 23:11:05 -0500 In-Reply-To: <20200203173311.6269a8be06a05e5a4aa08a93@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: gustavo@embeddedor.com, mm-commits@vger.kernel.org, oberpar@linux.ibm.com The patch titled Subject: gcov: gcc_4_7: replace zero-length array with flexible-array member has been added to the -mm tree. Its filename is gcov-gcc_4_7-replace-zero-length-array-with-flexible-array-member.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/gcov-gcc_4_7-replace-zero-length-array-with-flexible-array-member.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/gcov-gcc_4_7-replace-zero-length-array-with-flexible-array-member.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: "Gustavo A. R. Silva" Subject: gcov: gcc_4_7: replace zero-length array with flexible-array member The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Link: http://lkml.kernel.org/r/20200213152241.GA877@embeddedor Signed-off-by: Gustavo A. R. Silva Acked-by: Peter Oberparleiter Signed-off-by: Andrew Morton --- kernel/gcov/gcc_4_7.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/gcov/gcc_4_7.c~gcov-gcc_4_7-replace-zero-length-array-with-flexible-array-member +++ a/kernel/gcov/gcc_4_7.c @@ -68,7 +68,7 @@ struct gcov_fn_info { unsigned int ident; unsigned int lineno_checksum; unsigned int cfg_checksum; - struct gcov_ctr_info ctrs[0]; + struct gcov_ctr_info ctrs[]; }; /** _ Patches currently in -mm which might be from gustavo@embeddedor.com are lib-bch-replace-zero-length-array-with-flexible-array-member.patch lib-ts_bm-replace-zero-length-array-with-flexible-array-member.patch lib-ts_fsm-replace-zero-length-array-with-flexible-array-member.patch lib-ts_kmp-replace-zero-length-array-with-flexible-array-member.patch gcov-gcc_4_7-replace-zero-length-array-with-flexible-array-member.patch