From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 20831 invoked by alias); 16 Jul 2003 03:21:25 -0000 Mailing-List: contact gdb-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sources.redhat.com Received: (qmail 20808 invoked from network); 16 Jul 2003 03:21:25 -0000 Received: from unknown (HELO nevyn.them.org) (66.93.172.17) by sources.redhat.com with SMTP; 16 Jul 2003 03:21:25 -0000 Received: from drow by nevyn.them.org with local (Exim 3.36 #1 (Debian)) id 19ccr0-0003aF-00; Tue, 15 Jul 2003 23:21:18 -0400 Date: Wed, 16 Jul 2003 03:21:00 -0000 From: Daniel Jacobowitz To: Andrew Cagney Cc: gdb@sources.redhat.com Subject: Re: RFC: Unpredictable register set operations Message-ID: <20030716032118.GA13750@nevyn.them.org> Mail-Followup-To: Andrew Cagney , gdb@sources.redhat.com References: <20030715220923.GA30513@nevyn.them.org> <3F14BC94.4070405@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3F14BC94.4070405@redhat.com> User-Agent: Mutt/1.5.1i X-SW-Source: 2003-07/txt/msg00185.txt.bz2 On Tue, Jul 15, 2003 at 10:46:44PM -0400, Andrew Cagney wrote: > >I'm sure this has come up before, but I couldn't find a discussion anywhere > >so I'll just have to ask again... > > It come up before: > http://sources.redhat.com/ml/gdb/2003-06/msg00108.html > > >Consider PowerPC and the $ps register (MSR). When debugging a kernel or > >embedded application, GDB has pretty complete control (?) over this > >register. In GNU/Linux userspace, however, only two bits of it can be > >set. The rest are read-only. > > > >So what happens if you "set $ps = 0"? Well, the right thing happens, but > >until the next time the target stops "print $ps" will print 0. Which is > >not > >actually the value of the $ps register. > > > >Here's the options that I see: > > - Ignore and document this. > > - Refetch registers after storing them. > > - Invalidate registers for lazy re-fetch after storing them. > > - Add a target hook for might-be-volatile registers, and invalidate > > only those registers after storing them - or don't cache them at > > all. > > > >Thoughts? Is this a problem worth fixing? > > This is a straight bug. The register cache should be marked as invalid > after the store. What puzzles me is why store.exp doesn't tickle this, > or is this a hangover from lval_register vs lval_reg_frame_relative? Where's the invalidation supposed to happen presently? Perhaps I need to retest. -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer