Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762352AbXHCOEW (ORCPT ); Fri, 3 Aug 2007 10:04:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761737AbXHCOEN (ORCPT ); Fri, 3 Aug 2007 10:04:13 -0400 Received: from out2.smtp.messagingengine.com ([66.111.4.26]:48982 "EHLO out2.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761695AbXHCOEL (ORCPT ); Fri, 3 Aug 2007 10:04:11 -0400 Message-Id: <1186149850.31083.1203581997@webmail.messagingengine.com> X-Sasl-Enc: Hv8HTSoEsGuVA+B1GDPMEXc4DtRi73Vu9lsNXcSV8d0e 1186149850 From: "Alexander van Heukelum" To: "Al Viro" , "Guennadi Liakhovetski" Cc: "Stefan Richter" , "Andi Kleen" , linux-kernel@vger.kernel.org Content-Disposition: inline Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="ISO-8859-1" MIME-Version: 1.0 X-Mailer: MessagingEngine.com Webmail Interface References: <46B25B5E.30406@s5r6.in-berlin.de> <20070802230914.GT21089@ftp.linux.org.uk> Subject: Re: gcc fixed size char array initialization bug - known? In-Reply-To: <20070802230914.GT21089@ftp.linux.org.uk> Date: Fri, 03 Aug 2007 16:04:10 +0200 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2275 Lines: 65 On Fri, 3 Aug 2007 00:09:15 +0100, "Al Viro" said: > 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. Hi! (It took me a while before I understood that that last that referred to padding inside a struct generated by gcc due to overlong initializers.) But from the rest of the thread it seems that some people expect the compiler to warn about the following... struct {char c[4];} s1 = {"abcd"}; It doesn't. Of course if one wants to be warned in such cases (initialisation of a character array of specified length using a string constant) one could tell the compiler that the 0 at the end should really be there: struct {char c[4];} s2 = {"abcd" "\0"}; Writing it like this will give them the expected warning. Greetings, Alexander -- Alexander van Heukelum heukelum@fastmail.fm -- http://www.fastmail.fm - Choose from over 50 domains or use your own - 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/