Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759292AbXF0MUA (ORCPT ); Wed, 27 Jun 2007 08:20:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753822AbXF0MTv (ORCPT ); Wed, 27 Jun 2007 08:19:51 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:46183 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751811AbXF0MTu (ORCPT ); Wed, 27 Jun 2007 08:19:50 -0400 Date: Wed, 27 Jun 2007 13:19:48 +0100 From: Al Viro To: Neil Booth Cc: Josh Triplett , Segher Boessenkool , Linus Torvalds , linux-kernel@vger.kernel.org, linux-sparse@vger.kernel.org Subject: Re: [PATCH 16/16] fix handling of integer constant expressions Message-ID: <20070627121948.GN21478@ftp.linux.org.uk> References: <20070624183547.GA21478@ftp.linux.org.uk> <1a25667a20e43a072f733a3ec2b8e79d@kernel.crashing.org> <20070624203837.GE21478@ftp.linux.org.uk> <467F531A.3030702@freedesktop.org> <20070626221040.GI21478@ftp.linux.org.uk> <20070626221134.GA21350@ftp.linux.org.uk> <20070626233226.GO7590@daikokuya.co.uk> <20070627001803.GJ21478@ftp.linux.org.uk> <20070627115245.GP7590@daikokuya.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070627115245.GP7590@daikokuya.co.uk> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1398 Lines: 40 On Wed, Jun 27, 2007 at 08:52:45PM +0900, Neil Booth wrote: > Al Viro wrote:- > > > > > sparse simply doesn't check that. We don't have anything resembling > > support of VLA. Note that check for integer constant expression > > has nothing to do with that; > > > > int x[(int)(0.6 + 0.6)]; > > > > is valid (if stupid). > > It isn't valid; it fails the test twice. Both 0.6 are not "immediate > operands of casts". Their sum is, but that's irrelevant. > Therefore the dimension is not an ICE and a diagnostic is required. Egads... After rereading that... What a mess. int foo(void) { static int a[1][0,2]; } is, AFAICS, allowed. Reason: int a[0,2] is a VLA due to 6.7.5.2[4] (0,2 is not an ICE). However, due to the language in the same section, int a[1][0,2] is *not* a VLA, since (a) 2 is an ICE and (b) its element type "has a known constant size" (it does - the value of 0,2 is certainly guaranteed to be 2). I.e., it's VM type, but not a VLA. I.e. only the first part of 6.7.5.2[2] applies and we are actually fine. So we can have a static single-element array of int [0,2], but not a plain static int [0,2]. Lovely, that... - 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/