From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from msg-2.mailo.com (msg-2.mailo.com [213.182.54.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1E53420E2 for ; Mon, 28 Nov 2022 07:45:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=mailo.com; s=mailo; t=1669621549; bh=wYZlN96pJuQ8Qrp+PoOImcb4RGZJwH09T2Ok2nM5puc=; h=X-EA-Auth:Date:From:To:Cc:Subject:Message-ID:References: MIME-Version:Content-Type:In-Reply-To; b=OUNY7pg5SGi7uFe/7Nok53OSdDhJgUysatqxNvXXb9IfBI6PeRB4Z8B8V19SC2GdD /6/5N7g4Hd9XxJJV3GO8wfm52gxBcX1mQJOQOcT3mdbNkGucdVr55Ra866R+EobSLw CEMs8xS5OWel5m91NIjCbSRipwnbtD6kTsxnVrOU= Received: by b-5.in.mailobj.net [192.168.90.15] with ESMTP via ip-206.mailobj.net [213.182.55.206] Mon, 28 Nov 2022 08:45:48 +0100 (CET) X-EA-Auth: j8P34HFCLhZ7GZTTP7tVWbf4kJ0AtgmdBJOgHoKNeFxhwTeYFL+kIesUS7aPIzfcBoicB+Lc7fOxN+J1zvXsBm7I3VCnj8UU Date: Mon, 28 Nov 2022 13:15:43 +0530 From: Deepak R Varma To: Greg Kroah-Hartman Cc: linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, gustavoars@kernel.org Subject: Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper Message-ID: References: Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sat, Nov 19, 2022 at 08:08:15PM +0530, Deepak R Varma wrote: > On Thu, Nov 17, 2022 at 07:03:21PM +0100, Greg Kroah-Hartman wrote: > > On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote: > > > On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote: > > > > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote: > > > > > > > > > > struct hfa384x_pdr_refdac_measurements { > > > > > - u16 value[0]; > > > > > + DECLARE_FLEX_ARRAY(u16, value); > > > > > } __packed; > > > > > > > > Why? This structure is never used anywhere, right? So why is this > > > > needed to be changed and not just removed entirely? Same for the other > > > > structures in this patch. > > > > > > Hello Greg, > > > I am unable to confirm that these structures are truly not needed in the absence > > > if a real device based testing. I could only validate that using the compile > > > build and driver loading. > > > > Think this through, if no one is actually using this structure, and it > > is of 0 size, then do you think it is being used? > > Hello Greg, > I did not find any memory allocation for these zero length array structures. > Also, the union or its enclosing structure do not appear to access the members. > Hence I am leaning towards concluding that these zero length array structures do > not appear to be necessary. > > There are a few other structures that are part of the same union, however, they > too do not appear to be used for accessing the memory assigned to the union [or > its enclosing structure]. I think most of the members of these unions can be > replaced by one max size structure of this union [e.g. struct > hfa384x_pdr_mkk_measurements]. > > Could you please comment if I am reading the code right? > > For your quick reference, the zero length structure declaration are online 963 > whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h Hello Greg, can you please suggest how should I approach this clean-up/correction? Thank you, ./drv > > > Thank you, > ./drv > > > > > > > This change that I am proposing in the interim would enable the compiler to > > > protect the structure from addition of a new member below the zero length array. > > > > Why would you want to add a new member below this? That's not what is > > happening here at all. > > I came across this one old commit where such an accident happened. This is from > a recent LWN article: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e48f129c2f20 > > I understand the C99 now protects from such an attempt at the compile time > itself. > > Thank you, > ./drv > > > > > > Please think this through a bit more. > > > > good luck! > > > > greg k-h > >