From owner-freebsd-hackers@FreeBSD.ORG Fri Jan 16 11:01:03 2009 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 4376910656EC for ; Fri, 16 Jan 2009 11:01:03 +0000 (UTC) (envelope-from christoph.mallon@gmx.de) Received: from mail.gmx.net (mail.gmx.net [213.165.64.20]) by mx1.freebsd.org (Postfix) with SMTP id 401F88FC2A for ; Fri, 16 Jan 2009 11:01:01 +0000 (UTC) (envelope-from christoph.mallon@gmx.de) Received: (qmail invoked by alias); 16 Jan 2009 11:00:54 -0000 Received: from p54A3E7DB.dip.t-dialin.net (EHLO tron.homeunix.org) [84.163.231.219] by mail.gmx.net (mp034) with SMTP; 16 Jan 2009 12:00:54 +0100 X-Authenticated: #1673122 X-Provags-ID: V01U2FsdGVkX1/VdG5LfTrVWG2NEBDL8kpovESwO4M9fj3Z0ysDTi iIfJe4W7I79gal Message-ID: <497068E5.1050903@gmx.de> Date: Fri, 16 Jan 2009 12:00:53 +0100 From: Christoph Mallon User-Agent: Thunderbird 2.0.0.19 (X11/20090103) MIME-Version: 1.0 To: Garrett Cooper References: <7d6fde3d0901160041n55466290l55f737d274a40895@mail.gmail.com> <49704AEC.3080709@gmx.de> <200901161039.00232.christian.kandeler@hob.de> <49705FA2.2020605@gmx.de> <7d6fde3d0901160235o6aa1f096q11c5096b70f3577@mail.gmail.com> In-Reply-To: <7d6fde3d0901160235o6aa1f096q11c5096b70f3577@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Y-GMX-Trusted: 0 X-FuHaFi: 0.48 Cc: Christian Kandeler , freebsd-hackers@freebsd.org Subject: Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 Jan 2009 11:01:04 -0000 Garrett Cooper schrieb: > On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon > wrote: >> Christian Kandeler schrieb: >>> On Friday 16 January 2009 09:53, Christoph Mallon wrote: >>> >>>>> int >>>>> main() { >>>>> >>>>> int mib[4]; >>>>> >>>>> size_t len; >>>>> >>>>> if (sysctlnametomib("kern.ipc.shmmax", mib, &len) != 0) { >>>>> printf("Errno: %d\n", errno); >>>>> errx(errno, "Error: %s", strerror(errno)); >>>> The use of errno is wrong. printf might change errno. >>> I don't think printf() can set errno. And even if it could, it >> Of course it can. See ISO/IEC 9899:1999 (E) §7.5:3. >> >>> wouldn't matter, because C has call-by-value semantics. >> This has nothing to do with call-by-value. errno is read (even twice!) >> *after* the call to printf(). > > Ok, I just installworld'ed, recompiled the program with the > following modifications, and I still get segfaults. And the question > of the night is: why amd64 on a VERY recent CURRENT? > I'm going to try the same app on an amd64 freebsd VMware instance > with RELENG_7. > Remember: just because a bunch of other people aren't reporting > issues with CURRENT/amd64 doesn't mean that it isn't environmental, > related to my hardware or compile options ;). > Cheers, > -Garrett > > #include > #include > #include > > int > main() > { > > struct stat sb; > > int o_errno; > > if (stat("/some/file/that/doesn't/exist", &sb) != 0) { > o_errno = errno; > printf("Errno: %d\n", errno); > printf("%s\n", strerror(o_errno)); > } > > return 0; > > } > > #include > #include > #include > > int > main() > { > > struct stat sb; > > int o_errno; > > if (stat("/some/file/that/doesn't/exist", &sb) != 0) { > o_errno = errno; > printf("Errno: %d\n", errno); > printf("%s\n", strerror(o_errno)); > } > > return 0; > > } > > [gcooper@optimus ~]$ gcc -o badfile badfile.c > [gcooper@optimus ~]$ ./badfile > Errno: 2 > Segmentation fault: 11 (core dumped) > [gcooper@optimus ~]$ Compile with -Wall (you ALWAYS should do that) and then you'll see what the problem is.