On Thu, 15 Apr 2021 14:39:55 +0200 Philippe Mathieu-Daudé <phi...@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 <th...@redhat.com> > > Signed-off-by: Greg Kurz <gr...@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. >