From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 7863 invoked by alias); 16 Dec 2013 15:56:07 -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 7851 invoked by uid 89); 16 Dec 2013 15:56:07 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.4 required=5.0 tests=AWL,BAYES_00,RP_MATCHES_RCVD,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mga09.intel.com Received: from mga09.intel.com (HELO mga09.intel.com) (134.134.136.24) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 16 Dec 2013 15:56:06 +0000 Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga102.jf.intel.com with ESMTP; 16 Dec 2013 07:52:15 -0800 X-ExtLoop1: 1 Received: from irsmsx102.ger.corp.intel.com ([163.33.3.155]) by orsmga001.jf.intel.com with ESMTP; 16 Dec 2013 07:55:59 -0800 Received: from irsmsx106.ger.corp.intel.com (163.33.3.31) by IRSMSX102.ger.corp.intel.com (163.33.3.155) with Microsoft SMTP Server (TLS) id 14.3.123.3; Mon, 16 Dec 2013 15:54:31 +0000 Received: from irsmsx104.ger.corp.intel.com ([169.254.5.135]) by IRSMSX106.ger.corp.intel.com ([169.254.8.15]) with mapi id 14.03.0123.003; Mon, 16 Dec 2013 15:54:30 +0000 From: "Metzger, Markus T" To: Pedro Alves CC: "jan.kratochvil@redhat.com" , "gdb-patches@sourceware.org" , Eli Zaretskii Subject: RE: [patch v8 24/24] record-btrace: add (reverse-)stepping support Date: Mon, 16 Dec 2013 15:56:00 -0000 Message-ID: References: <1386839747-8860-1-git-send-email-markus.t.metzger@intel.com> <1386839747-8860-25-git-send-email-markus.t.metzger@intel.com> <52AB5E6A.1010105@redhat.com> In-Reply-To: <52AB5E6A.1010105@redhat.com> Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-IsSubscribed: yes X-SW-Source: 2013-12/txt/msg00576.txt.bz2 > -----Original Message----- > From: Pedro Alves [mailto:palves@redhat.com] > Sent: Friday, December 13, 2013 8:22 PM Thanks for your review. > > + /* Clear the executing flag to allow changes to the current frame. = */ > > + executing =3D is_executing (tp->ptid); > > + set_executing (tp->ptid, 0); >=20 > Why is this necessary? Is this so you can start replaying > even when the current thread is really executing? No. When we just start replaying with a reverse stepping command, we need to recompute stack frames so we can compare them to detect subroutine calls in infrun.c. See also https://sourceware.org/ml/gdb-patches/2013-11/msg00874.html and https://sourceware.org/ml/gdb-patches/2013-11/msg00891.html. This function is called from to_wait to enable replaying as part of reverse stepping. We need to temporarily set is_executing to false in order to be able to call get_current_frame below. I extended the existing comments here and below to explain this in more det= ail. > > + /* Restore the previous execution state. */ > > + set_executing (tp->ptid, executing); > > + > > + if (except.reason < 0) > > + throw_exception (except); >=20 > If something throws, things are being left > possibly in an inconsistent state, it seems to me. > Also, "replay" leaks. Replay is stored in BTINFO. We checked that we have trace before the try block, so btrace_insn_end () won't throw and we're not leaking REPLAY - we just transitioned from not replaying to replaying. It may still be better to revert the changes and not start replaying in case of errors. Changed that. I'm also calling registers_changed_ptid and get_current_frame again to avoid leaving things behind that are based on replaying. This might trigger another throw. > > + if (tp !=3D NULL && !btrace_is_replaying (tp) > > + && execution_direction !=3D EXEC_REVERSE) > > + ALL_THREADS (other) > > + record_btrace_stop_replaying (other); >=20 > Why's that? Imagine the user does: (gdb) thread 1 (gdb) reverse-steop (gdb) thread 2 (gdb) record goto 42 (gdb) thread 3 (gdb) continue We could either error out and make him go to thread 1 and thread 2 again to stop replaying those threads. Or we could more or less silently stop replaying those other threads before we continue. I chose to silently stop replaying; no warnings and no questions. I find both somewhat annoying after some time. > > + /* Find the thread to move. */ > > + if (ptid_equal (minus_one_ptid, ptid) || ptid_is_pid (ptid)) > > + { > > + ALL_THREADS (tp) > > + record_btrace_resume_thread (tp, flag); >=20 > Seems like this steps all threads, when gdb only wants to > step inferior_ptid and continue others? Only if gdb passes -1 or the ptid of the process. In the end, we will move exactly one thread and keep all others where they are. This one thread will hit a breakpoint or run out of execution history. Are you suggesting that I should only mark inferior_ptid in this case? If I marked the others as continue, I would later on need to prefer a thread that only wanted to step. I'm preferring inferior_ptid in to_wait later on when the threads are actually moved. The effect should be the same, but it might be more clear if I also did not mark the other threads. > > + if (breakpoint_here_p (aspace, insn->pc)) > > + return btrace_step_stopped (); >=20 > How is adjust_pc_after_break handled? I'm not doing anything special. The PC register is writable, so the PC can be adjusted. There is already code to omit the adjustment when reverse-executing. > > +# navigate in the trace history for both threads > > +gdb_test "thread 1" ".*" "mts, 1.1" > > +gdb_test "record goto begin" ".*" "mts, 1.2" > > +gdb_test "info record" ".*Replay in progress\. At instruction 1\." "m= ts, > 1.3" > > +gdb_test "thread 2" ".*" "mts, 1.4" > > +gdb_test "record goto begin" ".*" "mts, 1.5" > > +gdb_test "info record" ".*Replay in progress\. At instruction 1\." "m= ts, > 1.6" >=20 > What does this "mts" that appears everywhere mean? > (with_test_prefix could help here to create more meaningful test names.) It's a simple tag so I find the failing test quickly. With_test_prefix wouldn't really help. I could use "mts, " as test prefix,= but this would leave the raw numbers "1.1", "1.2", ... in the tests. I don't really need the prefix since the failing .exp file is already inclu= ded in the fail message. If it is confusing, I might as well omit it and use t= he numbers only. > > diff --git a/gdb/testsuite/gdb.btrace/rn-dl-bind.exp > b/gdb/testsuite/gdb.btrace/rn-dl-bind.exp > > new file mode 100644 > > index 0000000..4d803f9 > > --- /dev/null > > +++ b/gdb/testsuite/gdb.btrace/rn-dl-bind.exp >=20 > What's this testing? I can't infer it from the test name. > Please add a comment. It's testing a reverse-next over the dynamic linker's symbol lookup code. I added a comment to the top of the test. Regards, Markus. 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