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,URIBL_BLOCKED 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 23E32C4724C for ; Thu, 7 May 2020 20:15:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F12062192A for ; Thu, 7 May 2020 20:15:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588882548; bh=Nn0Un6aRpakEtuYOCqVgYcTF+qUJFwkYBRemF7H3LDc=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=yMpTe1CBxyLuCecLpW12UkgIvwy1tb6M07cfaTux9UxAi/G6aTljHoZn5HxeKh/rp +PQhCDjTT+dAQpQads7EoUUTBR2W18jy1eq0Bh9aCTiHsrMXYoXXtpUZh3/cpqKeKu YEpPCcjmqKEobsY/lCwtj4P2aatUfZNfoAJK3ye0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726531AbgEGUPr (ORCPT ); Thu, 7 May 2020 16:15:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:54716 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726320AbgEGUPr (ORCPT ); Thu, 7 May 2020 16:15:47 -0400 Received: from localhost (mobile-166-175-190-200.mycingular.net [166.175.190.200]) (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 2F613216FD; Thu, 7 May 2020 20:15:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588882546; bh=Nn0Un6aRpakEtuYOCqVgYcTF+qUJFwkYBRemF7H3LDc=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=HsihGvs9E1JHhScXJwwRqnIX05f4Gdr8v3nBGOynUPJrvFOAzHEhc1KMZokZz1hY/ 4VrhsP5Yu/fkBU7y44yj8nwf5D+4WsA8KLiL4yP9EprqkrlAQZzsh2GQCU9lYe5Lkb 5hvvOlgjmqu9I9o4lT3nTIMjrjaZQoGGyAKguDqQ= Date: Thu, 7 May 2020 15:15:44 -0500 From: Bjorn Helgaas To: "Gustavo A. R. Silva" Cc: Bjorn Helgaas , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] PCI: Replace zero-length array with flexible-array Message-ID: <20200507201544.GA23633@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200507190544.GA15633@embeddedor> Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, May 07, 2020 at 02:05:44PM -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 Applied to pci/misc for v5.8, thanks! I assume this takes care of everything in drivers/pci/, right? I'd like to do them all at once, so if there are others, send another patch and I'll squash them. I took a quick look but didn't see any. > --- > drivers/pci/pci.c | 2 +- > include/linux/pci.h | 4 ++-- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index 595fcf59843f..bb78f580814e 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -1578,7 +1578,7 @@ EXPORT_SYMBOL(pci_restore_state); > > struct pci_saved_state { > u32 config_space[16]; > - struct pci_cap_saved_data cap[0]; > + struct pci_cap_saved_data cap[]; > }; > > /** > diff --git a/include/linux/pci.h b/include/linux/pci.h > index 83ce1cdf5676..0453ee458ab1 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -279,7 +279,7 @@ struct pci_cap_saved_data { > u16 cap_nr; > bool cap_extended; > unsigned int size; > - u32 data[0]; > + u32 data[]; > }; > > struct pci_cap_saved_state { > @@ -532,7 +532,7 @@ struct pci_host_bridge { > resource_size_t start, > resource_size_t size, > resource_size_t align); > - unsigned long private[0] ____cacheline_aligned; > + unsigned long private[] ____cacheline_aligned; > }; > > #define to_pci_host_bridge(n) container_of(n, struct pci_host_bridge, dev) >