Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761086AbXHBXJ0 (ORCPT ); Thu, 2 Aug 2007 19:09:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757177AbXHBXJT (ORCPT ); Thu, 2 Aug 2007 19:09:19 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:59473 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757134AbXHBXJS (ORCPT ); Thu, 2 Aug 2007 19:09:18 -0400 Date: Fri, 3 Aug 2007 00:09:15 +0100 From: Al Viro To: Guennadi Liakhovetski Cc: Stefan Richter , Andi Kleen , linux-kernel@vger.kernel.org Subject: Re: gcc fixed size char array initialization bug - known? Message-ID: <20070802230914.GT21089@ftp.linux.org.uk> References: <46B25B5E.30406@s5r6.in-berlin.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1376 Lines: 33 On Fri, Aug 03, 2007 at 12:51:16AM +0200, Guennadi Liakhovetski wrote: > On Fri, 3 Aug 2007, Stefan Richter wrote: > > > Guennadi Liakhovetski wrote: > > > with > > > > > > char c[4] = "012345"; > > > > > > the compiler warns, but actually allocates a 6-byte long array... > > > > Off-topic here, but: sizeof c / sizeof *c == 4. > > Don't think it is OT here - kernel depends on gcc. And, what I meant, is, > that gcc places all 7 (sorry, not 6 as I said above) characters in the > .rodata section of the compiled object file. Of course, it doesn't mean, > that c is 7 characters long. So gcc does that kind of recovery, after having warned you. Makes sense, as long as it's for ordinary variables (and not, say it, struct fields) - you get less likely runtime breakage on the undefined behaviour (e.g. passing c to string functions). So gcc has generated some padding between the global variables, that's all. It doesn't change the fact that use of c[4] or strlen(c) or strcpy(..., c) means nasal demon country for you. Now, if gcc does that for similar situation with struct fields, you'd have a cause to complain. - 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/