From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E5F5BC33CB1 for ; Thu, 16 Jan 2020 11:27:28 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B97252073A for ; Thu, 16 Jan 2020 11:27:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B97252073A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ispras.ru Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:40266 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is3J9-0001M7-VU for qemu-devel@archiver.kernel.org; Thu, 16 Jan 2020 06:27:27 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:55166) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is3IS-0000wQ-Ns for qemu-devel@nongnu.org; Thu, 16 Jan 2020 06:26:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1is3IO-00084K-GK for qemu-devel@nongnu.org; Thu, 16 Jan 2020 06:26:44 -0500 Received: from mail.ispras.ru ([83.149.199.45]:33316) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1is3IO-00081u-5J for qemu-devel@nongnu.org; Thu, 16 Jan 2020 06:26:40 -0500 Received: from PASHAISP (unknown [85.142.117.226]) by mail.ispras.ru (Postfix) with ESMTPSA id 62007725C1; Thu, 16 Jan 2020 14:26:34 +0300 (MSK) From: "Pavel Dovgalyuk" To: =?UTF-8?Q?'Alex_Benn=C3=A9e'?= References: <157709434917.12933.4351155074716553976.stgit@pasha-Precision-3630-Tower> <87o8v3lkq8.fsf@linaro.org> In-Reply-To: <87o8v3lkq8.fsf@linaro.org> Subject: RE: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB Date: Thu, 16 Jan 2020 14:26:28 +0300 Message-ID: <000f01d5cc5f$cccb90b0$6662b210$@ru> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: AdXMXauVF1t13q8sQOSrCcJacuzMtAAADgrg Content-Language: ru X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 83.149.199.45 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, peter.maydell@linaro.org, pavel.dovgaluk@ispras.ru, crosthwaite.peter@gmail.com, ciro.santilli@gmail.com, jasowang@redhat.com, quintela@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, maria.klimushenkova@ispras.ru, mst@redhat.com, kraxel@redhat.com, boost.lists@gmail.com, thomas.dullien@googlemail.com, pbonzini@redhat.com, mreitz@redhat.com, artem.k.pisarenko@gmail.com, dgilbert@redhat.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" > From: Alex Benn=C3=A9e [mailto:alex.bennee@linaro.org] > Pavel Dovgalyuk writes: >=20 > > GDB remote protocol supports reverse debugging of the targets. > > It includes 'reverse step' and 'reverse continue' operations. > > The first one finds the previous step of the execution, > > and the second one is intended to stop at the last breakpoint that > > would happen when the program is executed normally. > > > > Reverse debugging is possible in the replay mode, when at least > > one snapshot was created at the record or replay phase. > > QEMU can use these snapshots for travelling back in time with GDB. > > > > Running the execution in replay mode allows using GDB reverse = debugging > > commands: > > - reverse-stepi (or rsi): Steps one instruction to the past. > > QEMU loads on of the prior snapshots and proceeds to the desired > > instruction forward. When that step is reaches, execution stops. > > - reverse-continue (or rc): Runs execution "backwards". > > QEMU tries to find breakpoint or watchpoint by loaded prior = snapshot > > and replaying the execution. Then QEMU loads snapshots again and > > replays to the latest breakpoint. When there are no breakpoints = in > > the examined section of the execution, QEMU finds one more = snapshot > > and tries again. After the first snapshot is processed, execution > > stops at this snapshot. > > > > The set of patches include the following modifications: > > - gdbstub update for reverse debugging support > > - functions that automatically perform reverse step and reverse > > continue operations > > - hmp/qmp commands for manipulating the replay process > > - improvement of the snapshotting for saving the execution step > > in the snapshot parameters > > > > The patches are available in the repository: > > https://github.com/ispras/qemu/tree/rr-191223 >=20 > So I tried with your additional patch. Launching QEMU as: >=20 > ./aarch64-softmmu//qemu-system-aarch64 -monitor none \ > -display none -M virt -cpu max -display none \ > -semihosting-config enable=3Don \ > -kernel ./tests/tcg/aarch64-softmmu/memory \ > -icount shift=3D5,rr=3Dreplay,rrfile=3Drecord.bin \ > -s -S -d trace:gdbstub\* >=20 > And gdb: >=20 > gdb tests/tcg/aarch64-softmmu/memory \ > -ex "target remote localhost:1234" >=20 > I get the following log: >=20 > (gdb) x/3i $pc > =3D> 0x400037b0 <__start>: adr x0, 0x40003000 = > 0x400037b4 <__start+4>: msr vbar_el1, x0 > 0x400037b8 <__start+8>: adrp x0, 0x40200000 > (gdb) p/x $x0 > $1 =3D 0x0 > (gdb) si > 92 msr vbar_el1, x0 > (gdb) p/x $x0 > $2 =3D 0x40003000 > (gdb) rsi > warning: Remote failure reply: E14 >=20 > Program stopped. > __start () at = /home/alex.bennee/lsrc/qemu.git/tests/tcg/aarch64/system/boot.S:92 > 92 msr vbar_el1, x0 > (gdb) p/x $x0 > $3 =3D 0x40003000 >=20 > So it doesn't seem to be working. That's ok, you'll need at least one VM snapshot available to recover the = initial VM state. Try changing the command lines in the following way: First, create empty.qcow2 which will be used for saving the snapshots. Then record with initial snapshot and attached empty.qcow2: ./aarch64-softmmu//qemu-system-aarch64 -monitor none \ -display none -M virt -cpu max \ -kernel ./tests/tcg/aarch64-softmmu/memory \ -icount = shift=3D5,rr=3Drecord,rrfile=3Drecord.bin,rrsnapshot=3Dinit \ -drive file=3Dempty.qcow2 After that you can replay the execution with the support of reverse = debugging: ./aarch64-softmmu//qemu-system-aarch64 -monitor none \ -display none -M virt -cpu max \ -kernel ./tests/tcg/aarch64-softmmu/memory \ -icount = shift=3D5,rr=3Dreplay,rrfile=3Drecord.bin,rrsnapshot=3Dinit \ -drive file=3Dempty.qcow2 I removed "-semihosting-config enable=3Don", because I'm not sure what = is it for. It may break the replay, because there is no implementation of semihosting input record/replay. Pavel Dovgalyuk