From owner-freebsd-current@FreeBSD.ORG Fri May 14 04:55:39 2010 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 907DE1065675 for ; Fri, 14 May 2010 04:55:39 +0000 (UTC) (envelope-from kaduk@mit.edu) Received: from dmz-mailsec-scanner-5.mit.edu (DMZ-MAILSEC-SCANNER-5.MIT.EDU [18.7.68.34]) by mx1.freebsd.org (Postfix) with ESMTP id 4DD458FC1A for ; Fri, 14 May 2010 04:55:38 +0000 (UTC) X-AuditID: 12074422-b7c13ae000003829-dc-4becd7ca8f4f Received: from mailhub-auth-2.mit.edu (MAILHUB-AUTH-2.MIT.EDU [18.7.62.36]) by dmz-mailsec-scanner-5.mit.edu (Symantec Brightmail Gateway) with SMTP id 87.6C.14377.AC7DCEB4; Fri, 14 May 2010 00:55:38 -0400 (EDT) Received: from outgoing.mit.edu (OUTGOING-AUTH.MIT.EDU [18.7.22.103]) by mailhub-auth-2.mit.edu (8.13.8/8.9.2) with ESMTP id o4E4tbdo025121; Fri, 14 May 2010 00:55:37 -0400 Received: from multics.mit.edu (MULTICS.MIT.EDU [18.187.1.73]) (authenticated bits=56) (User authenticated as kaduk@ATHENA.MIT.EDU) by outgoing.mit.edu (8.13.6/8.12.4) with ESMTP id o4E4tZr6003377 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Fri, 14 May 2010 00:55:37 -0400 (EDT) Received: (from kaduk@localhost) by multics.mit.edu (8.12.9.20060308) id o4E4tZUd003072; Fri, 14 May 2010 00:55:35 -0400 (EDT) Date: Fri, 14 May 2010 00:55:35 -0400 (EDT) From: Benjamin Kaduk To: alc@freebsd.org, attilio@freebsd.org, freebsd-current@freebsd.org Message-ID: User-Agent: Alpine 1.10 (GSO 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII X-Brightmail-Tracker: AAAAAA== Cc: Subject: kgdb unuseable with cores on current (for some people) X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 14 May 2010 04:55:39 -0000 Hi all, As was revealed in a recent thread here [1], several people have been unable to use kgdb on coredumps for the past few months (but possibly not everyone). I am one of those affected, and have narrowed the breakage with a binary search to between SVN revisions 202883 and 202954 (that is, Jan 23 1200h and Jan 25 0000h). Looking at the changes, alc's revision 202897 and attilio's revision 202933 look to be the most plausible culprits in terms of what they touched. I will continue with my bisection, but with only 36 revisions in play, it is probably worth looking for the bug in parallel with the bisection. To recall, this manifests itself as kgdb printing the following on startup: Cannot access memory at address 0xffffff0127ffffe0 'bt' seems to think that it is on a NULL stack pointer (and fails), and attempting to set a different current process/thread using the 'proc' or 'thread' commands errors with "invalid [p|t]id". However, I can walk the process list starting from allproc .... Looking at kgdb/kthr.c , the kgdb troubles would seem to stem from static struct kthr *first failing to get properly initialized, as the 'proc' command searches starting from that pointer. It's not immediately clear to me where in kgdb_thr_init() it is failing, though --- I see none of the warning messages from its error cases. If no one has thoughts on a possible cause, I guess I can start instrumenting kgdb to locate its failure, but help would be appreciated. Since this may be machine- and/or configuration-dependent, I have posted a dmesg and pciconf output here [2]; it's an amd64 machine with a Core2 Duo (T9400). Thanks, Ben Kaduk [1] http://lists.freebsd.org/pipermail/freebsd-current/2010-May/017195.html [2] http://stuff.mit.edu/afs/sipb.mit.edu/user/kaduk/freebsd/glossolalia/