From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932263AbWFRSfV (ORCPT ); Sun, 18 Jun 2006 14:35:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751217AbWFRSfV (ORCPT ); Sun, 18 Jun 2006 14:35:21 -0400 Received: from xenotime.net ([66.160.160.81]:59575 "HELO xenotime.net") by vger.kernel.org with SMTP id S1751213AbWFRSfU (ORCPT ); Sun, 18 Jun 2006 14:35:20 -0400 Date: Sun, 18 Jun 2006 11:38:04 -0700 From: "Randy.Dunlap" To: sturmflut@lieberbiber.de Cc: linux-kernel@vger.kernel.org Subject: Re: [patch 2/3] vdso: improve print_fatal_signals support by adding memory maps Message-Id: <20060618113804.ce5418dd.rdunlap@xenotime.net> In-Reply-To: <200606182029.30247.sturmflut@lieberbiber.de> References: <200606171614.58610.sturmflut@lieberbiber.de> <200606181525.42199.sturmflut@lieberbiber.de> <20060618104218.b07fb540.rdunlap@xenotime.net> <200606182029.30247.sturmflut@lieberbiber.de> Organization: YPO4 X-Mailer: Sylpheed version 2.2.5 (GTK+ 2.8.3; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 18 Jun 2006 20:29:21 +0200 Simon Raffeiner wrote: > Am Sonntag, 18. Juni 2006 19:42 schrieben Sie: > > On Sun, 18 Jun 2006 15:25:35 +0200 Simon Raffeiner wrote: > > > Am Sonntag, 18. Juni 2006 07:58 schrieben Sie: > > > > On Sat, 17 Jun 2006 21:58:18 -0700 > > > > > > > > "Randy.Dunlap" wrote: > > > > > On Sat, 17 Jun 2006 16:14:52 +0200 Simon Raffeiner wrote: > > > > > > When compiling 2.6.17-rc6-mm2 (which contains this patch) my gcc > > > > > > 4.0.3 (Ubuntu 4.0.3-1ubuntu5) complains about "int len;" being used > > > > > > uninitialized in print_vma(). AFAICS len is not initialized and > > > > > > then passed to > > > > > > pad_len_spaces(int len), which uses it for some calculations. > > > > > > > > > > > > I also noticed that similar code is used in fs/proc/task_mmu.c, > > > > > > where show_map_internal() passes an uninitialised int len; to > > > > > > pad_len_spaces(struct seq_file *m, int len). > > > > > > > > > > Ack both of those. And both of them pass &len as a parameter to > > > > > printk/seq_printf where it looks as though they want just > > > > > (after it has been initialized). > > > > > > > > printk("%n", &len) will initialise `len'. gcc is being wrong again. > > > > > > pad_len_spaces() is called in the following way: > > > > > > > > > static int print_vma(struct vm_area_struct *vma) > > > { > > > int len; > > > > > > (...) > > > > > > pad_len_spaces(len); > > > > > > (...) > > > > > > > > > and is defined as: > > > > > > > > > static void pad_len_spaces(int len) > > > { > > > len = 25 + sizeof(void*) * 6 - len; > > > > > > if (len < 1) > > > len = 1; > > > > > > printk("%*c", len, ' '); > > > } > > > > > > > > > len is passed to pad_len_spaces() without initialization and is used for > > > calculations BEFORE printk() is called. > > > > Nope, len is used after printk(..., &len) is called. > > But I don't see how printk() inits len... ? :( Magic? > > I finally got it: %n in the format string advises printk (have a look at > lib/vsprintf.c, where vsnprintf() does the real work) to store the number of > characters that have been written so far to a given memory location. So len > is actually initialised. Carp. I knew that. I was just misreading it. Sorry about my confuzion. --- ~Randy