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[81.40.121.39]) by smtp.gmail.com with ESMTPSA id v7sm4316558wrs.2.2021.04.15.09.45.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 15 Apr 2021 09:45:46 -0700 (PDT) Subject: Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system To: Greg Kurz , Paolo Bonzini , Thomas Huth References: <20210409160339.500167-1-groug@kaod.org> <20210409160339.500167-2-groug@kaod.org> <25ab34ad-0950-65f0-6cb2-d3f7a4a86744@redhat.com> <20210415153056.04f981a8@bahia.lan> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Thu, 15 Apr 2021 18:45:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210415153056.04f981a8@bahia.lan> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=philmd@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=unavailable 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?= , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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... > >> -- >8 -- >> --- a/hw/core/meson.build >> +++ b/hw/core/meson.build >> @@ -24,6 +24,8 @@ >> common_ss.add(when: 'CONFIG_SPLIT_IRQ', if_true: files('split-irq.c')) >> common_ss.add(when: 'CONFIG_XILINX_AXI', if_true: files('stream.c')) >> >> +user_ss.add(files('qdev-user.c')) >> + >> softmmu_ss.add(files( >> 'fw-path-provider.c', >> 'loader.c', >> --- >> >> Thanks, >> >> Phil. >> >