From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261784AbUBJV5q (ORCPT ); Tue, 10 Feb 2004 16:57:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261799AbUBJV5q (ORCPT ); Tue, 10 Feb 2004 16:57:46 -0500 Received: from gateway-1237.mvista.com ([12.44.186.158]:9971 "EHLO av.mvista.com") by vger.kernel.org with ESMTP id S261784AbUBJV5n (ORCPT ); Tue, 10 Feb 2004 16:57:43 -0500 Message-ID: <40295388.5080901@mvista.com> Date: Tue, 10 Feb 2004 13:56:24 -0800 From: George Anzinger Organization: MontaVista Software User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2) Gecko/20021202 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andi Kleen CC: "Amit S. Kale" , akpm@osdl.org, pavel@ucw.cz, linux-kernel@vger.kernel.org, piggy@timesys.com, trini@kernel.crashing.org Subject: Re: kgdb support in vanilla 2.6.2 References: <20040204230133.GA8702@elf.ucw.cz.suse.lists.linux.kernel> <20040204155452.49c1eba8.akpm@osdl.org.suse.lists.linux.kernel> <200402052320.04393.amitkale@emsyssoft.com> <20040206032054.3fd7db8d.ak@suse.de> In-Reply-To: <20040206032054.3fd7db8d.ak@suse.de> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andi Kleen wrote: > On Thu, 5 Feb 2004 23:20:04 +0530 > "Amit S. Kale" wrote: > > >>On Thursday 05 Feb 2004 8:41 am, Andi Kleen wrote: >> >>>Andrew Morton writes: >>> >>>>need to take a look at such things and really convice ourselves that >>>>they're worthwhile. Personally, I'd only be interested in the basic >>>>stub. >>> >>>What I found always extremly ugly in the i386 stub was that it uses >>>magic globals to talk to the page fault handler. For the x86-64 >>>version I replaced that by just using __get/__put_user in the memory >>>accesses, which is much cleaner. I would suggest doing that for i386 >>>too. >> >>May be I am missing something obvious. When debugging a page fault handler if >>kgdb accesses an swapped-out user page doesn't it deadlock when trying to >>hold mm semaphore? > > > Modern i386 kernels don't grab the mm semaphore when the access is >= TASK_SIZE > and the access came from kernel space (actually I see x86-64 still does, but that's > a bug, will fix). You could only see a deadlock when using user addresses > and you already hold the mm semaphore for writing (normal read lock is ok). > Just don't do that. > > > >>George has coded cfi directives i386 too. He can use them to backtrace past >>irqs stack. > > > Problem is that he did it without binutils support. I don't think that's a good > idea because it makes the code basically unmaintainable for normal souls > (it's like writing assembly code directly in hex) Well, bin utils, at this time, makes it even worse in that it does not support the expression syntax. Also, it is not asm but dwarf2 and it is written in, IMHO, useful macros (not hex :) -- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml