From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31868 invoked by alias); 11 Mar 2004 23:47:43 -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 31860 invoked from network); 11 Mar 2004 23:47:42 -0000 Received: from unknown (HELO localhost.redhat.com) (216.129.200.20) by sources.redhat.com with SMTP; 11 Mar 2004 23:47:42 -0000 Received: from gnu.org (localhost [127.0.0.1]) by localhost.redhat.com (Postfix) with ESMTP id C88C82B92; Thu, 11 Mar 2004 18:47:04 -0500 (EST) Message-ID: <4050FA78.7020904@gnu.org> Date: Fri, 19 Mar 2004 00:09:00 -0000 From: Andrew Cagney User-Agent: Mozilla/5.0 (X11; U; NetBSD macppc; en-GB; rv:1.4.1) Gecko/20040217 MIME-Version: 1.0 To: Daniel Jacobowitz Cc: gdb-patches@sources.redhat.com Subject: Re: [rfa/mips] Stop backtraces when we've lost the PC References: <20040306231743.GA9379@nevyn.them.org> <404BC4B2.7000100@gnu.org> <20040308032324.GA1325@nevyn.them.org> <20040308154814.GA17012@nevyn.them.org> <4050D13F.1040306@gnu.org> <20040311205751.GA28627@nevyn.them.org> In-Reply-To: <20040311205751.GA28627@nevyn.them.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-SW-Source: 2004-03/txt/msg00276.txt.bz2 > On Thu, Mar 11, 2004 at 03:51:11PM -0500, Andrew Cagney wrote: > >>>> >I hypothesize that if two consecutive frames, regardless of their type, >>>> >claim to save the PC register at the same location, then unwinding is >>>> >hosed. >> >>> >>> It would need to do a deep analysis of the location (think about a >>> register window architecture), hence I don't know that there's that much >>> cost benefit. >>> Something simpler such as a list of functions known to >>> terminate the stack might be more useful. > > > Er, no. frame_unwind_register tells us where, relative to the current > machine state, the register is saved. If it returns lval_register and > real_regnum == O7_REGNUM, then that means it leaves in > read_register(O7_REGNUM) at this moment, not that it did at some point > in the past. Isn't that the point of the recursive unwinder? "Er, no". to which part? I'll assume the first half of the first half. I suspect you're violently agreeing with me here - you're describing what I ment by a deep analysis of the location - tracking things all the way back to where in the inferior the value is. The architecture vector will need to be changed, the existing function deprecated, and new methods implemented. The introduction of "struct location" (or whatever) would then see it changed again. Given it is all for a marginal edge case (and to cover up breakage in glibc), I don't see any cost benefit in doing this. I think a more useful mechanism is for there to be a table of "start" functions that the user could manipulate (but would default to values specified by the OSABI). Andrew From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31868 invoked by alias); 11 Mar 2004 23:47:43 -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 31860 invoked from network); 11 Mar 2004 23:47:42 -0000 Received: from unknown (HELO localhost.redhat.com) (216.129.200.20) by sources.redhat.com with SMTP; 11 Mar 2004 23:47:42 -0000 Received: from gnu.org (localhost [127.0.0.1]) by localhost.redhat.com (Postfix) with ESMTP id C88C82B92; Thu, 11 Mar 2004 18:47:04 -0500 (EST) Message-ID: <4050FA78.7020904@gnu.org> Date: Thu, 11 Mar 2004 23:47:00 -0000 From: Andrew Cagney User-Agent: Mozilla/5.0 (X11; U; NetBSD macppc; en-GB; rv:1.4.1) Gecko/20040217 MIME-Version: 1.0 To: Daniel Jacobowitz Cc: gdb-patches@sources.redhat.com Subject: Re: [rfa/mips] Stop backtraces when we've lost the PC References: <20040306231743.GA9379@nevyn.them.org> <404BC4B2.7000100@gnu.org> <20040308032324.GA1325@nevyn.them.org> <20040308154814.GA17012@nevyn.them.org> <4050D13F.1040306@gnu.org> <20040311205751.GA28627@nevyn.them.org> In-Reply-To: <20040311205751.GA28627@nevyn.them.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-SW-Source: 2004-03.o/txt/msg00276.txt Message-ID: <20040311234700.dhTuRt9VrivmnauJNNdqrcHuulnZYoZcKy2Jt7cVrw4@z> > On Thu, Mar 11, 2004 at 03:51:11PM -0500, Andrew Cagney wrote: > >>>> >I hypothesize that if two consecutive frames, regardless of their type, >>>> >claim to save the PC register at the same location, then unwinding is >>>> >hosed. >> >>> >>> It would need to do a deep analysis of the location (think about a >>> register window architecture), hence I don't know that there's that much >>> cost benefit. >>> Something simpler such as a list of functions known to >>> terminate the stack might be more useful. > > > Er, no. frame_unwind_register tells us where, relative to the current > machine state, the register is saved. If it returns lval_register and > real_regnum == O7_REGNUM, then that means it leaves in > read_register(O7_REGNUM) at this moment, not that it did at some point > in the past. Isn't that the point of the recursive unwinder? "Er, no". to which part? I'll assume the first half of the first half. I suspect you're violently agreeing with me here - you're describing what I ment by a deep analysis of the location - tracking things all the way back to where in the inferior the value is. The architecture vector will need to be changed, the existing function deprecated, and new methods implemented. The introduction of "struct location" (or whatever) would then see it changed again. Given it is all for a marginal edge case (and to cover up breakage in glibc), I don't see any cost benefit in doing this. I think a more useful mechanism is for there to be a table of "start" functions that the user could manipulate (but would default to values specified by the OSABI). Andrew