Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S271362AbTHMDtK (ORCPT ); Tue, 12 Aug 2003 23:49:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S271369AbTHMDtK (ORCPT ); Tue, 12 Aug 2003 23:49:10 -0400 Received: from rwcrmhc12.comcast.net ([216.148.227.85]:11709 "EHLO rwcrmhc12.comcast.net") by vger.kernel.org with ESMTP id S271362AbTHMDtH (ORCPT ); Tue, 12 Aug 2003 23:49:07 -0400 Subject: Re: generic strncpy - off-by-one error From: Albert Cahalan To: andersen@codepoet.org Cc: Albert Cahalan , linux-kernel mailing list , bernd@firmix.at, Anthony.Truong@mascorp.com, alan@lxorguk.ukuu.org.uk, schwab@suse.de, ysato@users.sourceforge.jp, willy@w.ods.org, Valdis.Kletnieks@vt.edu, william.gallafent@virgin.net In-Reply-To: <20030813024752.GA20369@codepoet.org> References: <1060741101.948.245.camel@cube> <20030813024752.GA20369@codepoet.org> Content-Type: text/plain Organization: Message-Id: <1060745910.948.268.camel@cube> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.2.4 Date: 12 Aug 2003 23:38:31 -0400 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1566 Lines: 56 On Tue, 2003-08-12 at 22:47, Erik Andersen wrote: > On Tue Aug 12, 2003 at 10:18:21PM -0400, Albert Cahalan wrote: > > You're all wrong. This is some kind of programming > > test for sure! > > > > Let us imagine that glibc has a correct version. > > By exhaustive testing, I found a version that works. > > Here it is, along with the test code: > > > > ////////////////////////////////////////////////////// > > #define _GNU_SOURCE > > #include > > #include > > #include > > > > // first correct implementation! > > char * strncpy_good(char *dest, const char *src, size_t count){ > > char *tmp = dest; > > memset(dest,'\0',count); > > while (count-- && (*tmp++ = *src++)) > > ; > > return dest; > > } > > char *strncpy(char * s1, const char * s2, size_t n) > { > register char *s = s1; > while (n) { > if ((*s = *s2) != 0) s2++; > ++s; > --n; > } > return s1; > } That's excellent. On ppc I count 12 instructions, 4 of which would go away for typical usage if inlined. Annoyingly, gcc doesn't get the same assembly from my attempt at that general idea: char * strncpy_5(char *dest, const char *src, size_t count){ char *tmp = dest; while (count--){ if(( *tmp++ = *src )) src++; } return dest; } I suppose that gcc could use a bug report. - 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/