From patchwork Thu May 7 18:56:08 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 11534711 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 3683A15AB for ; Thu, 7 May 2020 18:51:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 206F62495D for ; Thu, 7 May 2020 18:51:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877503; bh=g2B3WHP3TtTh6XPDE/6X/pw7R5qG55xrJfAjLiXMLog=; h=Date:From:To:Cc:Subject:List-ID:From; b=holScbqlPIDl+98nmF5gu6rXbWKvlcqCAO7GYyphTlVgvrEcRJXviqdrOB8xe87h6 WUj+0S9V0ocumVa48dn1CM6FZ6n2zx2MLq6LSyKlP7DGFt3cCEpSB25cOrfTwz9trI 6PQZVGgI2jW0K6V0JH8zF2SsRX27GEP6atW7y4ew= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728578AbgEGSvm (ORCPT ); Thu, 7 May 2020 14:51:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:52394 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728237AbgEGSvm (ORCPT ); Thu, 7 May 2020 14:51:42 -0400 Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 94C9D2495B; Thu, 7 May 2020 18:51:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877502; bh=g2B3WHP3TtTh6XPDE/6X/pw7R5qG55xrJfAjLiXMLog=; h=Date:From:To:Cc:Subject:From; b=M2kYlSroDA8yK19NxCXt3sWB0sdiIQlQWo1ZBS4p//O7WzVbRRE9snCfeymw212ic iUO0vWvAt63WMmD2T9garVTMdfNfB7aHFdZ1oc0pyyk01RriSyVRPRkRDcQbkQlh1d mAcicuXulY9ntyoUmsA+BwcUncRd4H6CjtRZWGMM= Date: Thu, 7 May 2020 13:56:08 -0500 From: "Gustavo A. R. Silva" To: Shuah Khan , Shuah Khan Cc: linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] tools/testing: Replace zero-length array with flexible-array Message-ID: <20200507185608.GA14779@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. 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") Signed-off-by: Gustavo A. R. Silva --- tools/testing/selftests/nsfs/pidns.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/testing/selftests/nsfs/pidns.c b/tools/testing/selftests/nsfs/pidns.c index e0d86e1668c0..e3c772c6a7c7 100644 --- a/tools/testing/selftests/nsfs/pidns.c +++ b/tools/testing/selftests/nsfs/pidns.c @@ -27,7 +27,7 @@ #define __stack_aligned__ __attribute__((aligned(16))) struct cr_clone_arg { char stack[128] __stack_aligned__; - char stack_ptr[0]; + char stack_ptr[]; }; static int child(void *args)