Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752096Ab3CIWeW (ORCPT ); Sat, 9 Mar 2013 17:34:22 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:38302 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751843Ab3CIWeU (ORCPT ); Sat, 9 Mar 2013 17:34:20 -0500 Date: Sun, 10 Mar 2013 01:34:03 +0300 From: Dan Carpenter To: Christopher Li Cc: Andrew Morton , linux-kernel , Linux-Sparse , Linus Torvalds Subject: Re: Suggestion for fixing the variable length array used in the kernel. Message-ID: <20130309223403.GZ9138@mwanda> References: <20130308162922.88ad40997d01099949008452@linux-foundation.org> <20130309053859.GY9138@mwanda> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1850 Lines: 51 On Sat, Mar 09, 2013 at 10:10:08AM -0800, Christopher Li wrote: > On Fri, Mar 8, 2013 at 9:39 PM, Dan Carpenter wrote: > > On Fri, Mar 08, 2013 at 04:29:22PM -0800, Andrew Morton wrote: > >> Roughly how many instances of this are there kernel-wide? > >> > > > > Around 150 on x86 allmodconfig. They are pretty well audited. > > I saw 207 on x86-64 allmodconfig. See the list that I attached. > Ah. Sorry, I'm on my laptop and my sparse output was old. > Can you elaborate the well audited part? How it was audited? > The problems is if we go over the 8k stack. So big arrays are bad. Also if the dynamically sized array is inside a loop then normally GCC frees it after each iteration, but on some arches it didn't free it until after the last iteration. Btw, I've Smatch has cross function analysis, and I'd like to use it here to figure out if the max size for dynamically sized arrays. I ran into a problem: The code looks like this: char buf[a]; The size expression should be an EXPR_SYMBOL, but smatch gets: char buf[*a]; Where the size expression is an EXPR_PREOP. In smatch, how I use sparse is that I call sparse_keep_tokens() and then I parse the resulting symbol list myself. The problem is in examine_array_type() we call get_expression_value() which changes the symbols from normal symbols to dereferences. The call tree is: examine_array_type() -> get_expression_value() -> __get_expression_value() -> evaluate_expression() -> evaluate_symbol_expression() <- change happens here. I'm not sure what to do. regards, dan carpenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/