From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21369 invoked by alias); 14 Jun 2007 17:34:11 -0000 Received: (qmail 21360 invoked by uid 22791); 14 Jun 2007 17:34:10 -0000 X-Spam-Status: No, hits=-2.5 required=5.0 tests=AWL,BAYES_00,DK_POLICY_SIGNSOME,SPF_HELO_PASS,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (66.187.233.31) by sourceware.org (qpsmtpd/0.31) with ESMTP; Thu, 14 Jun 2007 17:34:07 +0000 Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.52.254]) by mx1.redhat.com (8.13.1/8.13.1) with ESMTP id l5EHY5qf012810 for ; Thu, 14 Jun 2007 13:34:05 -0400 Received: from pobox.corp.redhat.com (pobox.corp.redhat.com [10.11.255.20]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id l5EHY4IU019300; Thu, 14 Jun 2007 13:34:04 -0400 Received: from [127.0.0.1] (sebastian-int.corp.redhat.com [172.16.52.221]) by pobox.corp.redhat.com (8.13.1/8.13.1) with ESMTP id l5EHY2XH029110; Thu, 14 Jun 2007 13:34:02 -0400 Message-ID: <46717C1A.80000@redhat.com> Date: Thu, 14 Jun 2007 17:51:00 -0000 From: Andrew Cagney User-Agent: Thunderbird 1.5.0.12 (X11/20070530) MIME-Version: 1.0 To: Adam Jocksch CC: Stan Cox , Frysk List Subject: Re: hpd command for DisplayValues References: <4671652B.7080206@redhat.com> <1181839209.20944.28.camel@multics.rdu.redhat.com> <46717528.2040700@redhat.com> <467177C3.3090405@redhat.com> <46717870.4080805@redhat.com> In-Reply-To: <46717870.4080805@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-IsSubscribed: yes Mailing-List: contact frysk-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: frysk-owner@sourceware.org X-SW-Source: 2007-q2/txt/msg00282.txt.bz2 BTW, a gdb interaction looks like the below. The background to know is that "display" and "examine" are closely related vis: (gdb) x/i $pc 0x807b6c0
: lea 0x4(%esp),%ecx (gdb) stepi 0x0807b6c4 28 { (gdb) x/i $pc 0x807b6c4 : and $0xfffffff0,%esp (gdb) stepi 0x0807b6c7 28 { (gdb) display/i $pc 1: x/i $pc 0x807b6c7 : pushl 0xfffffffc(%ecx) (gdb) stepi 0x0807b6ca in main (argc=0x1, argv=0xbff4d0d4) at ../../gdb/gdb.c:28 28 { 1: x/i $pc 0x807b6ca : push %ebp (gdb) 0x0807b6cb 28 { 1: x/i $pc 0x807b6cb : mov %esp,%ebp The output reflects how "display" is implemented using the lower-level "examine" command - it doesn't detect change. Andrew Adam Jocksch wrote: > Andrew Cagney wrote: >> Adam Jocksch wrote: >>> Hrm, maybe. Although reading in the hpd spec: "By defining >>> actionpoints, the user may request in advance that target program >>> execution stop >> >> Nice quote, the display object doesn't fit that model since it is >> passive - it doesn't directly trigger a stop since it doesn't >> implement a mechanism for detecting changes in the data (that would >> be watch). Instead it detects when the variable has changed after a >> stop. >> >> For the command line, consider this: >> >>> [] break main >>> [] run .... >>> main hit >>> [] print argc >>> ... >>> [] step >>> [] print argc >>> [] step >> >> vs: >> >>> [] break main >>> [] run .... >>> main hit >>> [] display argc >>> ... >>> [] step >>> ... value of argc changed from 4 to -1 >>> [] step >>> [] step >>> Value of argc changed from -1 to 4 >> >> For a graphical interface the object facilitates the efficient >> implementation of a variable display window - it will only trigger a >> redraw of the display elements of the X display when there's >> something new to draw. >> >> Andrew >> >>> under certain conditions". Do we want the display to be similar to a >>> watchpoint, except it applies to an expression rather than a single >>> variable? Or do we want it to be an expression that is displayed >>> when the program stops (I remember Andrew saying something about how >>> gdb does this, and it's bad, so we probably want to avoid that). >>> >>> While what the DisplayValue object is capable is well defined, I >>> guess I'm not 100% sure of how it will be used. >> > That sounds similar to what I had envisioned.