From owner-freebsd-hackers Sat Nov 17 20:14:18 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from tomts12-srv.bellnexxia.net (tomts12.bellnexxia.net [209.226.175.56]) by hub.freebsd.org (Postfix) with ESMTP id A24DF37B417 for ; Sat, 17 Nov 2001 20:14:16 -0800 (PST) Received: from xena.gsicomp.on.ca ([199.243.144.157]) by tomts12-srv.bellnexxia.net (InterMail vM.4.01.03.16 201-229-121-116-20010115) with ESMTP id <20011118041415.EZZA3045.tomts12-srv.bellnexxia.net@xena.gsicomp.on.ca> for ; Sat, 17 Nov 2001 23:14:15 -0500 Received: from hermes (hermes.gsicomp.on.ca [192.168.0.18]) by xena.gsicomp.on.ca (8.11.1/8.11.1) with SMTP id fAI463W26198 for ; Sat, 17 Nov 2001 23:06:03 -0500 (EST) (envelope-from matt@gsicomp.on.ca) Message-ID: <048401c16fe7$7bf13b60$1200a8c0@gsicomp.on.ca> From: "Matthew Emmerton" To: Subject: Does DDB's watch feature actually work? Date: Sat, 17 Nov 2001 23:14:10 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4807.1700 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4807.1700 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG I've been using DDB the last few days attempting to track down a supposed bug in our TCP/IP stack. (See PR/31746). From what I've been able to tell so far (using the ugly insert-printf-here mechanism of debugging), a structure is getting zeroed which is causing the problem reported in the PR. So, I decided to learn how to use DDB, and set a watch on the data element that's getting blown away. The problem is, once I've got a watch in place, the system traps (page fault) at the strangest locations in the networking code -- %eip is nowhere near any code that modifies the data that I'm watching. There is a note in the ddb(4) man page, that states that "attempts to watch wired kernel memory may cause unrecoverable errors in some systems such as i386". Is this the cause of what I'm seeing? -- Matt Emmerton To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message