From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 13584 invoked by alias); 12 Apr 2011 20:26:54 -0000 Received: (qmail 13574 invoked by uid 22791); 12 Apr 2011 20:26:54 -0000 X-SWARE-Spam-Status: No, hits=-6.9 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,SPF_HELO_PASS,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Tue, 12 Apr 2011 20:26:42 +0000 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id p3CKQZGu015745 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Tue, 12 Apr 2011 16:26:35 -0400 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx02.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id p3CKQYVX008891; Tue, 12 Apr 2011 16:26:34 -0400 Received: from opsy.redhat.com (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id p3CKQXAc021125; Tue, 12 Apr 2011 16:26:34 -0400 Received: by opsy.redhat.com (Postfix, from userid 500) id 482F13791BA; Tue, 12 Apr 2011 14:26:32 -0600 (MDT) From: Tom Tromey To: Pedro Alves Cc: gdb-patches@sourceware.org, Sergio Durigan Junior Subject: Re: [PATCH 2/6] Introduce `pre_expanded sals' References: <201104121218.08910.pedro@codesourcery.com> Date: Tue, 12 Apr 2011 20:26:00 -0000 In-Reply-To: <201104121218.08910.pedro@codesourcery.com> (Pedro Alves's message of "Tue, 12 Apr 2011 12:18:08 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2011-04/txt/msg00172.txt.bz2 >>>>> "Pedro" == Pedro Alves writes: Tom> This is just a way for decode_line_1 to tell the breakpoint code that Tom> the returned sals has multiple locations but should still create just a Tom> single breakpoint. We needed this because a given SystemTap probe name Tom> may have multiple locations. Pedro> Hmm, doesn't sound right. Conceptually, breakpoint locations are Pedro> multiple expansions of the same source location. Different Pedro> source locations are different breakpoints. E.g, bp_location Pedro> doesn't have line number or source file fields. From the user's Pedro> perpective, there's only a single "point" in the source code for Pedro> all the multiple locations for a single breakpoint. Could you explain why this is important? I agree this is how it is, but I think it is actually somewhat confusing at times. The problem I see with respect to the SystemTap change is that a given probe location does not have a canonical name. E.g., suppose you have a probe `program:name' that is invoked at 2 different spots in the source. Suppose further that `break probe:program:name' sets 2 breakpoints. Now consider 2 scenarios: First, the developer deletes a probe point. Second, the developer adds a probe point. With the single-breakpoint approach, both of these do (what I consider to be) the right thing -- the user ends up with what he asked for. I don't see how they can work with the multiple-breakpoint approach. Furthermore, I think the `probe:' prefix should let us lift this restriction anyhow. It is a way of saying "this is not an ordinary source location, but something else". I think the deeper confusion in gdb is that an ambiguous name sets a single breakpoint, with a single location, but the meaning of this name is decided arbitrarily (say, by psymtab expansion order). That is, `break file.c:73' sets a breakpoint in the first `file.c' we happen to trip across. Or, `break function' sets a breakpoint in the first `function'. I'd rather change gdb to set a breakpoint at all matching locations, and let the user disambiguate if that is really what he wanted. I hit this while debugging gdb itself from time to time -- try `break parse_number' and guess where it gets set. Tom