From patchwork Thu May 7 18:56:01 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: 11534709 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 A632015AB for ; Thu, 7 May 2020 18:51:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E9FF2495D for ; Thu, 7 May 2020 18:51:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877496; bh=jS1JZUc/306T2uxJxfJMUJJif1/i/lbkHg/ck6XKeHg=; h=Date:From:To:Cc:Subject:List-ID:From; b=bW9wnsPfCHEll6pJaZr5a4fAJpF1nkhewMDDbaVITb2vZsbG+oZfzOHV+XuWDtbkx nPulPo/wxfKlYu3bnLWyR/DLz38KyMlXreujCMwBQ2x8cuyLhndIqsrI6fGUplcfXa ZaRLObCMjqMQznj7x79jjmbN+nv7LLKTTx8EPtwI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727799AbgEGSvg (ORCPT ); Thu, 7 May 2020 14:51:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:52306 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726950AbgEGSvg (ORCPT ); Thu, 7 May 2020 14:51:36 -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 E582824957; Thu, 7 May 2020 18:51:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877495; bh=jS1JZUc/306T2uxJxfJMUJJif1/i/lbkHg/ck6XKeHg=; h=Date:From:To:Cc:Subject:From; b=RNyFnZUIZ90jofZMnACoBPDAGi9K3ssrewWXIWSHXKu2NAbgmSsBTd/aLRrAbmvj6 LpKjnNlOb6hZRuzH9Y6ITmOQT5qP7rdwqalohVkgD2VVByrvQq4LvFG3v4V819+6sb xDs3H3kjn0ZehPI2UXNs4Ro+zePY/TaeUt8q9J0Y= Date: Thu, 7 May 2020 13:56:01 -0500 From: "Gustavo A. R. Silva" To: Masahiro Yamada , Michal Marek Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] modpost: Replace zero-length array with flexible-array Message-ID: <20200507185601.GA14759@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@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 --- scripts/basic/fixdep.c | 2 +- scripts/mod/modpost.c | 2 +- scripts/mod/modpost.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c index 877ca2c88246..d98540552941 100644 --- a/scripts/basic/fixdep.c +++ b/scripts/basic/fixdep.c @@ -160,7 +160,7 @@ struct item { struct item *next; unsigned int len; unsigned int hash; - char name[0]; + char name[]; }; #define HASHSZ 256 diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 5c3c50c5ec52..4d4b979d76be 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -166,7 +166,7 @@ struct symbol { * (only for external modules) **/ unsigned int is_static:1; /* 1 if symbol is not global */ enum export export; /* Type of export */ - char name[0]; + char name[]; }; static struct symbol *symbolhash[SYMBOL_HASH_SIZE]; diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h index 60dca9b7106b..39f6c29fb568 100644 --- a/scripts/mod/modpost.h +++ b/scripts/mod/modpost.h @@ -111,7 +111,7 @@ buf_write(struct buffer *buf, const char *s, int len); struct namespace_list { struct namespace_list *next; - char namespace[0]; + char namespace[]; }; struct module {