From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 30390 invoked by alias); 3 Jan 2003 15:17:48 -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 30383 invoked from network); 3 Jan 2003 15:17:45 -0000 Received: from unknown (HELO crack.them.org) (65.125.64.184) by 209.249.29.67 with SMTP; 3 Jan 2003 15:17:45 -0000 Received: from nevyn.them.org ([66.93.61.169] ident=mail) by crack.them.org with asmtp (Exim 3.12 #1 (Debian)) id 18UVRc-0002UB-00; Fri, 03 Jan 2003 11:17:16 -0600 Received: from drow by nevyn.them.org with local (Exim 3.36 #1 (Debian)) id 18UTZ4-0008Kh-00; Fri, 03 Jan 2003 10:16:50 -0500 Date: Fri, 03 Jan 2003 15:17:00 -0000 From: Daniel Jacobowitz To: Michael Elizabeth Chastain Cc: gdb-patches@sources.redhat.com Subject: Re: [RFA/PATCH] breakpoint.c: fix until command Message-ID: <20030103151649.GA31921@nevyn.them.org> Mail-Followup-To: Michael Elizabeth Chastain , gdb-patches@sources.redhat.com References: <200301030649.h036nSq08310@duracef.shout.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200301030649.h036nSq08310@duracef.shout.net> User-Agent: Mutt/1.5.1i X-SW-Source: 2003-01/txt/msg00063.txt.bz2 On Fri, Jan 03, 2003 at 12:49:28AM -0600, Michael Elizabeth Chastain wrote: > Daniel J says: > > > With a modern compiler, "after $PC" is pretty much meaningless. Not > > going to fly. It could be re-ordered; there can be out-of-line code in > > separate sections. > > I'm thinking of a famous promise in the gcc manual: > > Without `-O', the compiler's goal is to reduce the cost of > compilation and to make debugging produce the expected results. > Statements are independent: if you stop the program with a > breakpoint between statements, you can then assign a new value to > any variable or change the program counter to any other statement > in the function and get exactly the results you would expect from > the source code. > > Statements which are independent can could be re-ordered, like moving > error-handling blocks far away to a different section of the address > space to improve cache locality. So we might need additional promises. > I think it would be reasonable for us to ask for them if we decide > we need them. I don't. Promises don't mean anything; we have existing code. > With optimized code, I agree, gdb is just going to degrade, the way > it does now with stepping through for loops. Which isn't OK. We need to do something about this; it requires some substantial planning but with DWARF-2 we really should have all the information we need to do better. > > And what it means when LOCATION is not in function is not clear. > > The problem is, do we know well enough when LOCATION is or is not in > > FUNCTION to make any statements? > > If we can get more promises from gcc, then we can know this is true > in un-optimized code. > > We can also know whether LOCATION is in the function if we operate > on LOCATION while it is in source form before we translate to object > code location. If we are in foo:67, and the user asks to 'until 70', > then I bet we can figure out that '70' is in the current function no > matter where its object code addresses are. No, we can't. It's a pretty fundamental rule that we can never do anything except display source lines. Consider code re-organization, templates, macros, #line directives... > > I'm still undecided about what to do if LOCATION is not in the > > function. Maybe you're right and we should make this an error. What > > if LOCATION is in the frame that called this one? > > I still say, make it an error. I like the idea that 'until' is all > about the current frame. > > And it seems weird. The user should know it's not in the current > frame when they type in in LOCATION. And they know that 'until' rolls > right over function calls. So the user knows that LOCATION is in a > calling frame. This collides head on with the idea that 'until' has > a momentary breakpoint on the return location in the caller. Try it. > It will always take the return-breakpoint. It will never reach LOCATION. Oh, you're right of course. -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer