From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 26037 invoked by alias); 30 Sep 2013 10:25:41 -0000 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 Received: (qmail 26022 invoked by uid 89); 30 Sep 2013 10:25:41 -0000 Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 30 Sep 2013 10:25:41 +0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.7 required=5.0 tests=AWL,BAYES_00,RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r8UAPb4h008781 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Mon, 30 Sep 2013 06:25:38 -0400 Received: from host2.jankratochvil.net (ovpn-116-66.ams2.redhat.com [10.36.116.66]) by int-mx01.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id r8UAPXE0029405 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NO); Mon, 30 Sep 2013 06:25:36 -0400 Date: Mon, 30 Sep 2013 10:25:00 -0000 From: Jan Kratochvil To: "Metzger, Markus T" Cc: "gdb-patches@sourceware.org" Subject: Re: [patch v4 23/24] record-btrace: add (reverse-)stepping support Message-ID: <20130930102533.GA29665@host2.jankratochvil.net> References: <1372842874-28951-1-git-send-email-markus.t.metzger@intel.com> <1372842874-28951-24-git-send-email-markus.t.metzger@intel.com> <20130818190935.GR24153@host2.jankratochvil.net> <20130929172416.GA15087@host2.jankratochvil.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-IsSubscribed: yes X-SW-Source: 2013-09/txt/msg01004.txt.bz2 On Mon, 30 Sep 2013 11:30:14 +0200, Metzger, Markus T wrote: > > -----Original Message----- > > From: gdb-patches-owner@sourceware.org [mailto:gdb-patches- > > owner@sourceware.org] On Behalf Of Jan Kratochvil > > > > > But this code compares a NORMAL_FRAME from before the step with a > > > BTRACE_FRAME from after the wait. They will always be unequal hence > > > we will never recognize that we just reverse-stepped into a function. > > > > > > When I reset the frame cache, GDB re-computes the stored frame and > > now > > > compares two BTRACE_FRAMEs, which works OK. > > [...] > > > See above. Alternatively, I might add a special case to frame comparison, > > > but this would be quite ugly, as well. Do you have a better idea? > > > > +record_btrace_start_replaying (struct thread_info *tp) > > [...] > > + /* Make sure we're not using any stale registers. */ > > + registers_changed_ptid (tp->ptid); > > + > > + /* We just started replaying. The frame id cached for stepping is based > > + on unwinding, not on branch tracing. Recompute it. */ > > + frame = get_current_frame_nocheck (); > > + insn = btrace_insn_get (replay); > > + sal = find_pc_line (insn->pc, 0); > > + set_step_info (frame, sal); > > > > The problem comes from the new commands like "record goto" which > > change > > inferior content without resuming+stopping it. > > > > Former "record full" could only change history position by "step/reverse- > > step" > > (or similar commands) which did resume+stop the inferior. > > > > To make the "record goto" command friendly to the GDB infrastructure > > expectations I think you should put a temporary breakpoint to the target > > instruction, resume the inferior and simulate stop at the temporary > > breakpoint. > > > > I think all the registers_changed_ptid() calls could be removed afterwards. > > That would cause quite some overhead if we're moving by a big number > of instructions. > > First, we'd single-step instead of just setting the PC. Second, I'd need to > examine all instruction addresses on the way in order to compute the ignore > count of that temporary breakpoint. I did not mean single-stepping. Just do the single to_resume + to_wait where to_wait will return the new PC. Unfortunately one has to create a temporary breakpoint otherwise GDB will print unexpected SIGTRAP but many commands (like "next" over a function call) create temporary breakpoints. This way all the actions in current proceed(), handle_inferior_event() etc. get executed. Jan