From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from rhirst.linuxcare.com (sleepie.demon.co.uk [194.222.23.208]) by puffin.external.hp.com (8.9.3/8.9.3) with ESMTP id FAA25032 for ; Thu, 16 Nov 2000 05:10:26 -0700 Received: by rhirst.linuxcare.com (Postfix, from userid 501) id 73B30B008; Thu, 16 Nov 2000 12:09:57 +0000 (GMT) Date: Thu, 16 Nov 2000 12:09:57 +0000 From: Richard Hirst To: John David Anglin Cc: parisc-linux@puffin.external.hp.com Subject: Re: [parisc-linux] Single-stepping Message-ID: <20001116120957.V32715@linuxcare.com> References: <20001115184808.P32715@linuxcare.com> <200011151949.OAA22929@hiauly1.hia.nrc.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <200011151949.OAA22929@hiauly1.hia.nrc.ca>; from dave@hiauly1.hia.nrc.ca on Wed, Nov 15, 2000 at 02:49:02PM -0500 List-ID: On Wed, Nov 15, 2000 at 02:49:02PM -0500, John David Anglin wrote: > > I've been helping Alan Modra out with kernel changes to support > > single stepping for gdb. Paul Bame suggested I bounced our ideas > > off you in case you (or anyone else) had any comments. I havn't > > actually committed my changes yet. > > > > The basic approach is to use the recovery counter to generate > > a trap every instruction. The scheme is complicated because a > > suspended process may or may not return to user space via an RFI. > > I really don't know enough to comment on the implementation choice. Why > did you decide on this approach as opposed to inserting breaks and > enabling the taken branch branch trap (T)? It would appear that the recovery > counter was intended to provide software recovery from hardware faults > in fault tolerant systems. Possibly, Grant could comment on whether > it is actually useful for this purpose. Alan Modra made those early decisions, but I gather that he went for the recovery counter because it at least appears to be rather more straightforward. Richard