From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261973AbUBFL7P (ORCPT ); Fri, 6 Feb 2004 06:59:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263185AbUBFL7P (ORCPT ); Fri, 6 Feb 2004 06:59:15 -0500 Received: from svr44.ehostpros.com ([66.98.192.92]:37523 "EHLO svr44.ehostpros.com") by vger.kernel.org with ESMTP id S261973AbUBFL7N (ORCPT ); Fri, 6 Feb 2004 06:59:13 -0500 From: "Amit S. Kale" Organization: EmSysSoft To: Andi Kleen Subject: Re: kgdb support in vanilla 2.6.2 Date: Fri, 6 Feb 2004 17:28:36 +0530 User-Agent: KMail/1.5 Cc: akpm@osdl.org, pavel@ucw.cz, linux-kernel@vger.kernel.org, piggy@timesys.com, trini@kernel.crashing.org, george@mvista.com References: <20040204230133.GA8702@elf.ucw.cz.suse.lists.linux.kernel> <200402052320.04393.amitkale@emsyssoft.com> <20040206032054.3fd7db8d.ak@suse.de> In-Reply-To: <20040206032054.3fd7db8d.ak@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200402061728.36989.amitkale@emsyssoft.com> X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - svr44.ehostpros.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - emsyssoft.com Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Friday 06 Feb 2004 7:50 am, 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. OK. It don't deadlock when kgdb accesses kernel addresses. When a user space address is accessed through kgdb, won't the kernel attempt to fault in the user page? We don't want that to happen inside kgdb. -Amit > > > 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) > > -Andi