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Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for
From: |
Greg Kurz |
Subject: |
Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system |
Date: |
Thu, 15 Apr 2021 15:30:56 +0200 |
On Thu, 15 Apr 2021 14:39:55 +0200
Philippe Mathieu-Daudé <philmd@redhat.com> 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 <thuth@redhat.com>
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> > 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=<optimized out>, errp=0x7fffffffd4e0) at ../../hw/core/qdev.c:745
#3 0x000000010001cc5c in property_set_bool (obj=0x100128b60, v=<optimized
out>, name=<optimized out>, opaque=0x1000f33f0, errp=0x7fffffffd4e0) at
../../qom/object.c:2257
#4 0x0000000100020a9c in object_property_set (obj=0x100128b60,
name=0x100093f78 "realized", v=0x100136d30, errp=0x1000e3af8 <error_fatal>) at
../../qom/object.c:1402
#5 0x000000010001c38c in object_property_set_qobject (obj=0x100128b60,
name=0x100093f78 "realized", value=<optimized out>, errp=0x1000e3af8
<error_fatal>) at ../../qom/qom-qobject.c:28
#6 0x0000000100020e20 in object_property_set_bool (obj=0x100128b60,
name=0x100093f78 "realized", value=<optimized out>, errp=0x1000e3af8
<error_fatal>) at ../../qom/object.c:1472
#7 0x000000010001612c in qdev_realize (dev=0x100128b60, bus=<optimized out>,
errp=0x1000e3af8 <error_fatal>) 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=<optimized out>, argv=<optimized out>) at
../../tests/unit/test-qdev-global-props.c:316
Is there a meson thingy to handle this dependency ?
> -- >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.
>
- [PATCH 0/2] cpu/core: Fix "help" of CPU core device types, Greg Kurz, 2021/04/09
- [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Greg Kurz, 2021/04/09
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Eduardo Habkost, 2021/04/09
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Thomas Huth, 2021/04/10
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Markus Armbruster, 2021/04/10
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Eduardo Habkost, 2021/04/14
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Philippe Mathieu-Daudé, 2021/04/15
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system,
Greg Kurz <=
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Philippe Mathieu-Daudé, 2021/04/15
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Greg Kurz, 2021/04/15
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Philippe Mathieu-Daudé, 2021/04/15
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Greg Kurz, 2021/04/16
- Re: [PATCH 1/2] qdev: Separate implementations of qdev_get_machine() for user and system, Thomas Huth, 2021/04/19
[PATCH 2/2] cpu/core: Fix "help" of CPU core device types, Greg Kurz, 2021/04/09