From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D89BC38A2A for ; Fri, 8 May 2020 07:57:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64755207DD for ; Fri, 8 May 2020 07:57:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588924644; bh=+CkCpSuKwhhUOdlSl/nBxTRsMI4V6pgCGiLirtJvjnE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=01e/KpeI788GZnTf02jE5jko1yjU6zI1PT8abgUDxOll5HwvDNJxFMW45efmF7iVs 9+GNN9pmr5zkg1DwEVUpLTerXr7crbUkl9HrK6YxcOXlmvmp+NZ2l9k1sTTNQpSvIp D9a2Ljs5vYE7v+p6EZy2ZaHJgQKkwiN3X9+4lvOE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726767AbgEHH5X (ORCPT ); Fri, 8 May 2020 03:57:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:60428 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726036AbgEHH5X (ORCPT ); Fri, 8 May 2020 03:57:23 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 5DA39207DD; Fri, 8 May 2020 07:57:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588924641; bh=+CkCpSuKwhhUOdlSl/nBxTRsMI4V6pgCGiLirtJvjnE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=VHvg9PE1DV1GfVfbqhTNKfowsqct70VFs2BhegsCfzjdpPh275fCjWhmd0eC3360J nwlMzYwRSic09DyqMaxR5/g/mtF+8U0tI4681LrbzN0dFT8JbDyNHOT8Ovh8qg/DYl Mth0opGayuqRZCLUInzUJN681NKy2gou2k+1DWTA= Date: Fri, 8 May 2020 16:57:17 +0900 From: Masami Hiramatsu To: "Gustavo A. R. Silva" , Ingo Molnar Cc: "Naveen N. Rao" , Anil S Keshavamurthy , "David S. Miller" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] kprobes: Replace zero-length array with flexible-array Message-Id: <20200508165717.ed47c8fd3a2863f8ef3ce329@kernel.org> In-Reply-To: <20200507185733.GA14931@embeddedor> References: <20200507185733.GA14931@embeddedor> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 7 May 2020 13:57:33 -0500 "Gustavo A. R. Silva" wrote: > 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 Thanks for the complete explanation :-D This looks good to me. Acked-by: Masami Hiramatsu > --- > include/linux/kprobes.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h > index 04bdaf01112c..4477205e3e92 100644 > --- a/include/linux/kprobes.h > +++ b/include/linux/kprobes.h > @@ -161,7 +161,7 @@ struct kretprobe_instance { > kprobe_opcode_t *ret_addr; > struct task_struct *task; > void *fp; > - char data[0]; > + char data[]; > }; > > struct kretprobe_blackpoint { > -- Masami Hiramatsu