From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 4151 invoked by alias); 4 May 2002 02:59:29 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 4143 invoked from network); 4 May 2002 02:59:28 -0000 Received: from unknown (HELO zwingli.cygnus.com) (208.245.165.35) by sources.redhat.com with SMTP; 4 May 2002 02:59:28 -0000 Received: by zwingli.cygnus.com (Postfix, from userid 442) id C66A45EA11; Fri, 3 May 2002 21:59:26 -0500 (EST) To: Daniel Jacobowitz Cc: gdb-patches@sources.redhat.com Subject: Re: PATCH: don't corrupt cv_type chain References: <20020504002026.6E6BA5EA11@zwingli.cygnus.com> <20020504003229.GB4915@nevyn.them.org> From: Jim Blandy Date: Fri, 03 May 2002 19:59:00 -0000 In-Reply-To: <20020504003229.GB4915@nevyn.them.org> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SW-Source: 2002-05/txt/msg00097.txt.bz2 Daniel Jacobowitz writes: > > *** gdb/gdbtypes.c 26 Apr 2002 20:08:18 -0000 1.44 > > --- gdb/gdbtypes.c 4 May 2002 00:18:05 -0000 > > *************** > > *** 521,530 **** > > > > /* Replace the contents of ntype with the type *type. > > > > ! This function should not be necessary, but is due to quirks in the stabs > > ! reader. This should go away. It does not handle the replacement type > > ! being cv-qualified; it could be easily fixed to, but it should go away, > > ! remember? */ > > void > > replace_type (struct type *ntype, struct type *type) > > { > > --- 521,530 ---- > > > > /* Replace the contents of ntype with the type *type. > > > > ! When building recursive types, it is necessary to update a type's > > ! definition after people already have references to it. The C > > ! language's concept of an `incomplete type' is an acknowledgement of > > ! this. */ > > void > > replace_type (struct type *ntype, struct type *type) > > { > > First, you removed the editorial; I think it is correct still. More on > that at the bottom. Second, you removed the fact that it will not > properly handle the replacement type being cv-qualified. That's > important! Yes, it is. I'll put it back. > > Index: gdb/stabsread.c > > =================================================================== > > RCS file: /cvs/src/src/gdb/stabsread.c,v > > retrieving revision 1.31 > > diff -c -r1.31 stabsread.c > > *** gdb/stabsread.c 4 May 2002 00:02:50 -0000 1.31 > > --- gdb/stabsread.c 4 May 2002 00:18:08 -0000 > > *************** > > *** 2537,2543 **** > > the related problems with unnecessarily stubbed types; > > someone motivated should attempt to clean up the issue > > here as well. Once a type pointed to has been created it > > ! should not be modified. */ > > replace_type (type, xtype); > > TYPE_NAME (type) = NULL; > > TYPE_TAG_NAME (type) = NULL; > > --- 2537,2560 ---- > > the related problems with unnecessarily stubbed types; > > someone motivated should attempt to clean up the issue > > here as well. Once a type pointed to has been created it > > ! should not be modified. > > ! > > ! Well, it's not *absolutely* wrong. Constructing recursive > > ! types (trees, linked lists) necessarily entails modifying > > ! types after creating them. Constructing any loop structure > > ! entails side effects. The Dwarf 2 reader does handle this > > ! more gracefully (it never constructs more than once > > ! instance of a type object, so it doesn't have to copy type > > ! objects wholesale), but it still mutates type objects after > > ! other folks have references to them. > > ! > > ! Keep in mind that this circularity/mutation issue shows up > > ! at the source language level, too: C's "incomplete types", > > ! for example. So the proper cleanup, I think, would be to > > ! limit GDB's type smashing to match exactly those required > > ! by the source language. So GDB could have a > > ! "complete_this_type" function, but never create unnecessary > > ! copies of a type otherwise. */ > > replace_type (type, xtype); > > TYPE_NAME (type) = NULL; > > TYPE_TAG_NAME (type) = NULL; > > DWARF-2 has to mutate types somewhat, certainly; but this sort of > smashing is avoidable and quite disgusting. There should be an > explicit list of things it is safe to modify, rather than the axe that > is replace_type. Adding a size or a a field list is legitimate, but > many of the other fields should not change. Isn't this, essentially, what my comment says?