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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 DDAE8C433ED for ; Thu, 15 Apr 2021 19:09:20 +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 0FC48610A1 for ; Thu, 15 Apr 2021 19:09:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0FC48610A1 Authentication-Results: mail.kernel.org; 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]:48222 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lX7Mc-0007c0-Vw for qemu-devel@archiver.kernel.org; Thu, 15 Apr 2021 15:09:19 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33906) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lX7L9-00076B-1A for qemu-devel@nongnu.org; Thu, 15 Apr 2021 15:07:48 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55013) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lX7L3-0008Nz-QL for qemu-devel@nongnu.org; Thu, 15 Apr 2021 15:07:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618513660; 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=w2ZC9N4LOsUb+p3Rd7GQLJYGOsE+Kg7MiMKU3M7XGgo=; b=Y/gIMWm0mblNkYJZSIPgNM6uOm0gtuWjkpyXqtojbHYwXrrxmU2C0Cs4fkJdR7sEdy6uiz vC3dM1Dq09xD/c83LCWgcuS1PWWFppX8lqoG49E4FsIBs26XWmDPIZFYWsOP6xxGNdOFbf MtztFJ37fNm3DPvi83wB519AtXcJ7XQ= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-493-tKMErO1-NTyBhkeiGHEz7g-1; Thu, 15 Apr 2021 15:07:36 -0400 X-MC-Unique: tKMErO1-NTyBhkeiGHEz7g-1 Received: by mail-wr1-f71.google.com with SMTP id t14-20020a5d6a4e0000b029010277dcae0fso3171551wrw.22 for ; Thu, 15 Apr 2021 12:07:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=w2ZC9N4LOsUb+p3Rd7GQLJYGOsE+Kg7MiMKU3M7XGgo=; b=XC8sJfMLaT3TDScKyYOuD69x6kZ9DVZTluNNHRDgneGnXyWVSghqSIZUIwYu/IYazD hp3g3OM+NWNkFCofrIGbacLz2el4ggmGEY1iDS8H2vBWJCdDWVDzcd7N+DtUmHtxzOfw bFuhTmsa7oxZqdS71VZvyybFJLenWqPMugpaRbgzSgeMuV7CX91K8GkhrxNgUfNls1em HhlTdGVAJE5DqX6v+qgNcEdAsRBTLh+Iv7l/X36YJ9i1F9XEhDAwyXF1kjzSgTRLXLWx rBzMCHvA3C66lrelAfVTeOQclR65N4q9SWq/6bC7TAW5Z7AmPEqQgAE41nuNBynp/bU3 clog== X-Gm-Message-State: AOAM533r734k+nxiB4prJZHbuwf9MKsXD3vzjbKPBxN2rYlJzNf05ir9 IeWyFJTwa+m2iqv5fqu4hsWd5CyJqLRqWJgIcU5kTUBLjrBEmrDqOf9v2IpqbC5ZGWl+kwRuXo/ n4YtGFhiXE97A1vc= X-Received: by 2002:a1c:1f92:: with SMTP id f140mr4475805wmf.108.1618513655068; Thu, 15 Apr 2021 12:07:35 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw2/0XuopO1NJaaAit7EQBHMzPRQoer6R1eGo3/OL3zpFiznCYkvqFSncpYwjQE0Y3kVB2D7Q== X-Received: by 2002:a1c:1f92:: with SMTP id f140mr4475783wmf.108.1618513654829; Thu, 15 Apr 2021 12:07:34 -0700 (PDT) Received: from [192.168.1.36] (39.red-81-40-121.staticip.rima-tde.net. [81.40.121.39]) by smtp.gmail.com with ESMTPSA id t19sm4303394wmq.14.2021.04.15.12.07.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 15 Apr 2021 12:07:34 -0700 (PDT) Subject: Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system To: Greg Kurz 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> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <1a68b426-47da-9fba-a34a-d024ac9ed148@redhat.com> Date: Thu, 15 Apr 2021 21:07:33 +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: <20210415185639.12300368@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=216.205.24.124; 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=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: Thomas Huth , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Eduardo Habkost , qemu-devel@nongnu.org, Markus Armbruster , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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... > except maybe an improvement on the > file location. Thanks for tip !