From owner-freebsd-hackers@freebsd.org Wed Dec 23 00:02:56 2015 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id EDA38A50588 for ; Wed, 23 Dec 2015 00:02:56 +0000 (UTC) (envelope-from arlie@worldash.org) Received: from mailman.ysv.freebsd.org (mailman.ysv.freebsd.org [IPv6:2001:1900:2254:206a::50:5]) by mx1.freebsd.org (Postfix) with ESMTP id E174E1766 for ; Wed, 23 Dec 2015 00:02:56 +0000 (UTC) (envelope-from arlie@worldash.org) Received: by mailman.ysv.freebsd.org (Postfix) id DDC0DA50587; Wed, 23 Dec 2015 00:02:56 +0000 (UTC) Delivered-To: hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id DD503A50586 for ; Wed, 23 Dec 2015 00:02:56 +0000 (UTC) (envelope-from arlie@worldash.org) Received: from ansuz.worldash.org (ansuz.worldash.org [198.144.201.100]) by mx1.freebsd.org (Postfix) with ESMTP id C63511765 for ; Wed, 23 Dec 2015 00:02:53 +0000 (UTC) (envelope-from arlie@worldash.org) Received: by ansuz.worldash.org (Postfix, from userid 1000) id 00CA7E1923; Tue, 22 Dec 2015 15:59:20 -0800 (PST) Date: Tue, 22 Dec 2015 15:59:20 -0800 From: Arlie Stephens To: hackers@FreeBSD.ORG Subject: Examining Page Tables in Kernel Crash Dumps (amd64) Message-ID: <20151222235920.GA21736@worldash.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Dec 2015 00:02:57 -0000 I'm chasing a bug in an elderly, customized freebsd kernel that appears to result in corrupted page tables. kgdb is not cooperating when I attempt to look at addresses of kernel page tables. I've replicated that part on an elderly stock freebsd system, running freebsd 8.4. , and it looks to me like it's probably getting that limitation from libkvm. Obviously I don't expect community help with an ancient freebsd issue... particularly one probably caused by our own customizations. But given the tool chain changes upstream, I don't expect testing with whatever kgdb has turned into there to be very relevant ;-( So far, the only way I know to get a look at kernel page table contents in FreeBSD is on live systems with ddb. I would like to know whether there are any tools I haven't noticed for dealing with page tables in crash dumps - or, for that matter, whether kgdb is supposed to be able to display the kernel's recursive page tables. Failing that, I may just have to write one ;-) (Or figure out how to chase my problem on live systems.) -- Arlie (Arlie Stephens arlie@worldash.org)