From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 148/166] gcov: gcc_3_4: replace zero-length array with flexible-array member Date: Mon, 06 Apr 2020 20:11:55 -0700 Message-ID: <20200407031155.sjtwHB7DK%akpm@linux-foundation.org> References: <20200406200254.a69ebd9e08c4074e41ddebaf@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:57748 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726591AbgDGDL5 (ORCPT ); Mon, 6 Apr 2020 23:11:57 -0400 In-Reply-To: <20200406200254.a69ebd9e08c4074e41ddebaf@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, gustavo@embeddedor.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, oberpar@linux.ibm.com, torvalds@linux-foundation.org From: "Gustavo A. R. Silva" Subject: gcov: gcc_3_4: 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/20200302224501.GA14175@embeddedor Signed-off-by: Gustavo A. R. Silva Cc: Peter Oberparleiter Signed-off-by: Andrew Morton --- kernel/gcov/gcc_3_4.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/gcov/gcc_3_4.c~gcov-gcc_3_4-replace-zero-length-array-with-flexible-array-member +++ a/kernel/gcov/gcc_3_4.c @@ -38,7 +38,7 @@ static struct gcov_info *gcov_info_head; struct gcov_fn_info { unsigned int ident; unsigned int checksum; - unsigned int n_ctrs[0]; + unsigned int n_ctrs[]; }; /** @@ -78,7 +78,7 @@ struct gcov_info { unsigned int n_functions; const struct gcov_fn_info *functions; unsigned int ctr_mask; - struct gcov_ctr_info counts[0]; + struct gcov_ctr_info counts[]; }; /** @@ -352,7 +352,7 @@ struct gcov_iterator { unsigned int count; int num_types; - struct type_info type_info[0]; + struct type_info type_info[]; }; static struct gcov_fn_info *get_func(struct gcov_iterator *iter) _