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dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57080 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lYW70-0005RP-Hx for qemu-devel@archiver.kernel.org; Mon, 19 Apr 2021 11:46:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58288) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYW5o-0004qD-0c for qemu-devel@nongnu.org; Mon, 19 Apr 2021 11:45:44 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:31260) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYW5k-0007yl-2f for qemu-devel@nongnu.org; Mon, 19 Apr 2021 11:45:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618847139; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JYhFrufnGcxntRt6JOjNrex1wURkHbnRF21AC3VnYik=; b=M38N/kRhDVFt0NwnY+nYgl289XTeE1j3e4omGb89OdX0MBme+m6KmJpaHmBL6InkatzzB7 2RhlH7b9l+eBnLEO4AQY0En9ZRFVRRfagnQq+aHluN4XJnsAEJtvAp4D0RqpoMksy0Mcsd FEXn01RavRGiPJnDrWNlSyXUhPh0o08= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-326--tHuSRFvO8GaHVOTJlCQZA-1; Mon, 19 Apr 2021 11:45:37 -0400 X-MC-Unique: -tHuSRFvO8GaHVOTJlCQZA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A3D868030BB; Mon, 19 Apr 2021 15:45:33 +0000 (UTC) Received: from thuth.remote.csb (ovpn-112-129.ams2.redhat.com [10.36.112.129]) by smtp.corp.redhat.com (Postfix) with ESMTP id ABE8160843; Mon, 19 Apr 2021 15:45:31 +0000 (UTC) Subject: Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Greg Kurz , Paolo Bonzini References: <20210409160339.500167-1-groug@kaod.org> <20210409160339.500167-2-groug@kaod.org> <25ab34ad-0950-65f0-6cb2-d3f7a4a86744@redhat.com> <20210415153056.04f981a8@bahia.lan> <20210415185639.12300368@bahia.lan> <1a68b426-47da-9fba-a34a-d024ac9ed148@redhat.com> From: Thomas Huth Message-ID: Date: Mon, 19 Apr 2021 17:45:30 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <1a68b426-47da-9fba-a34a-d024ac9ed148@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Markus Armbruster , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Eduardo Habkost , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 15/04/2021 21.07, Philippe Mathieu-Daudé wrote: > On 4/15/21 6:56 PM, Greg Kurz wrote: >> On Thu, 15 Apr 2021 18:45:45 +0200 >> Philippe Mathieu-Daudé wrote: >> >>> On 4/15/21 3:30 PM, Greg Kurz wrote: >>>> On Thu, 15 Apr 2021 14:39:55 +0200 >>>> Philippe Mathieu-Daudé wrote: >>>> >>>>> On 4/9/21 6:03 PM, Greg Kurz wrote: >>>>>> Despite its simple name and common usage of "getting a pointer to >>>>>> the machine" in system-mode emulation, qdev_get_machine() has some >>>>>> subtilities. >>>>>> >>>>>> First, it can be called when running user-mode emulation : this is >>>>>> because user-mode partly relies on qdev to instantiate its CPU >>>>>> model. >>>>>> >>>>>> Second, but not least, it has a side-effect : if it cannot find an >>>>>> object at "/machine" in the QOM tree, it creates a dummy "container" >>>>>> object and put it there. A simple check on the type returned by >>>>>> qdev_get_machine() allows user-mode to run the common qdev code, >>>>>> skipping the parts that only make sense for system-mode. >>>>>> >>>>>> This side-effect turns out to complicate the use of qdev_get_machine() >>>>>> for the system-mode case though. Most notably, qdev_get_machine() must >>>>>> not be called before the machine object is added to the QOM tree by >>>>>> qemu_create_machine(), otherwise the existing dummy "container" object >>>>>> would cause qemu_create_machine() to fail with something like : >>>>>> >>>>>> Unexpected error in object_property_try_add() at ../../qom/object.c:1223: >>>>>> qemu-system-ppc64: attempt to add duplicate property 'machine' to >>>>>> object (type 'container') >>>>>> Aborted (core dumped) >>>>>> >>>>>> This situation doesn't exist in the current code base, mostly because >>>>>> of preventive fixing of some "latent bugs" in QEMU 4.0 (see 1a3ec8c1564 >>>>>> and e2fb3fbbf9c for details). >>>>>> >>>>>> A new kind of breakage was spotted very recently though : >>>>>> >>>>>> $ ./qemu-system-ppc64 -device power8_v2.0-spapr-cpu-core,help >>>>>> /home/thuth/devel/qemu/include/hw/boards.h:24: >>>>>> MACHINE: Object 0x5635bd53af10 is not an instance of type machine >>>>>> Aborted (core dumped) >>>>>> >>>>>> This comes from the change 3df261b6676b in QEMU 5.0. It unwillingly >>>>>> added a new condition for qdev_get_machine() to be called too early, >>>>>> breaking MACHINE(qdev_get_machine()) in generic cpu-core code this >>>>>> time. >>>>>> >>>>>> In order to avoid further subtle breakages like this, change the >>>>>> implentation of qdev_get_machine() to: >>>>>> - keep the existing behaviour of creating the dummy "container" >>>>>> object for the user-mode case only ; >>>>>> - abort() if the machine doesn't exist yet in the QOM tree for >>>>>> the system-mode case. This gives a precise hint to developpers >>>>>> that calling qdev_get_machine() too early is a programming bug. >>>>>> >>>>>> This is achieved with a new do_qdev_get_machine() function called >>>>>> from qdev_get_machine(), with different implementations for system >>>>>> and user mode. >>>>>> >>>>>> $ ./qemu-system-ppc64 -device power8_v2.0-spapr-cpu-core,help >>>>>> qemu-system-ppc64: ../../hw/core/machine.c:1290: >>>>>> qdev_get_machine: Assertion `machine != NULL' failed. >>>>>> Aborted (core dumped) >>>>>> >>>>>> Reported-by: Thomas Huth >>>>>> Signed-off-by: Greg Kurz >>>>>> --- >>>>>> hw/core/machine.c | 14 ++++++++++++++ >>>>>> hw/core/qdev.c | 2 +- >>>>>> include/hw/qdev-core.h | 1 + >>>>>> stubs/meson.build | 1 + >>>>>> stubs/qdev-get-machine.c | 11 +++++++++++ >>>>>> 5 files changed, 28 insertions(+), 1 deletion(-) >>>>>> create mode 100644 stubs/qdev-get-machine.c >>>>> ... >>>>> >>>>>> diff --git a/stubs/meson.build b/stubs/meson.build >>>>>> index be6f6d609e58..b99ee2b33e94 100644 >>>>>> --- a/stubs/meson.build >>>>>> +++ b/stubs/meson.build >>>>>> @@ -54,3 +54,4 @@ if have_system >>>>>> else >>>>>> stub_ss.add(files('qdev.c')) >>>>>> endif >>>>>> +stub_ss.add(files('qdev-get-machine.c')) >>>>> >>>>> Adding this as a stub looks suspicious... >>>>> Why not add it in to user_ss in hw/core/meson.build? >>>>> Maybe name the new file hw/core/qdev-user.c? >>>>> >>>> >>>> It turns out that this isn't specific to user-mode but rather >>>> to any non-qemu-system-FOO binary built with qdev, e.g. >>>> test-qdev-global-props : >>>> >>>> #0 do_qdev_get_machine () at ../../stubs/qdev-get-machine.c:10 >>>> #1 0x0000000100017938 in qdev_get_machine () at ../../hw/core/qdev.c:1134 >>>> #2 0x000000010001855c in device_set_realized (obj=0x100128b60, value=, errp=0x7fffffffd4e0) at ../../hw/core/qdev.c:745 >>>> #3 0x000000010001cc5c in property_set_bool (obj=0x100128b60, v=, name=, opaque=0x1000f33f0, errp=0x7fffffffd4e0) at ../../qom/object.c:2257 >>>> #4 0x0000000100020a9c in object_property_set (obj=0x100128b60, name=0x100093f78 "realized", v=0x100136d30, errp=0x1000e3af8 ) at ../../qom/object.c:1402 >>>> #5 0x000000010001c38c in object_property_set_qobject (obj=0x100128b60, name=0x100093f78 "realized", value=, errp=0x1000e3af8 ) at ../../qom/qom-qobject.c:28 >>>> #6 0x0000000100020e20 in object_property_set_bool (obj=0x100128b60, name=0x100093f78 "realized", value=, errp=0x1000e3af8 ) at ../../qom/object.c:1472 >>>> #7 0x000000010001612c in qdev_realize (dev=0x100128b60, bus=, errp=0x1000e3af8 ) at ../../hw/core/qdev.c:389 >>>> #8 0x000000010000fb10 in test_static_prop_subprocess () at /home/greg/Work/qemu/qemu-master/include/hw/qdev-core.h:17 >>>> #9 0x00007ffff7e95654 in g_test_run_suite_internal () from /lib64/libglib-2.0.so.0 >>>> #10 0x00007ffff7e954b8 in g_test_run_suite_internal () from /lib64/libglib-2.0.so.0 >>>> #11 0x00007ffff7e954b8 in g_test_run_suite_internal () from /lib64/libglib-2.0.so.0 >>>> #12 0x00007ffff7e954b8 in g_test_run_suite_internal () from /lib64/libglib-2.0.so.0 >>>> #13 0x00007ffff7e954b8 in g_test_run_suite_internal () from /lib64/libglib-2.0.so.0 >>>> #14 0x00007ffff7e959cc in g_test_run_suite () from /lib64/libglib-2.0.so.0 >>>> #15 0x00007ffff7e95a80 in g_test_run () from /lib64/libglib-2.0.so.0 >>>> #16 0x000000010000ecec in main (argc=, argv=) at ../../tests/unit/test-qdev-global-props.c:316 >>>> >>>> Is there a meson thingy to handle this dependency ? >>> >>> if not have_system >>> common_ss.add(files('qdev-machine-stubs.c')) >>> endif >>> >>> This is not pretty, but better than a generic stubs/qdev-get-machine.c >>> IMO... >>> >> >> Yeah it isn't that much different, > > I'd expect symbols in stubs/ to be declared weak, while not with this > approach, so we'd catch clash for incorrect configs. Maybe I'm wrong... See https://gitlab.com/qemu-project/qemu/-/commit/3bc2f570ec9fc93 for the reason why symbols in stubs are *not* declared as weak anymore. Thomas