qdev: fix -device scsi-hd,help regression

Since commit ea9ce89, device_post_init() applies globals directly
from machines and accelerator classes.

There are cases, such as -device scsi-hd,help, where the machine is
setup but there in no accelerator.

Let's skip accelerator globals in this case.

Fixes SEGV:
 #0  0x0000555558ea04ff in object_get_class (obj=0x0) at /home/elmarco/src/qemu/build/../qom/object.c:857
 #1  0x000055555854c797 in object_apply_compat_props (obj=0x616000078980) at /home/elmarco/src/qemu/build/../hw/core/qdev.c:978
 #2  0x000055555854c797 in object_apply_compat_props (obj=0x616000078980) at /home/elmarco/src/qemu/build/../hw/core/qdev.c:973
 #3  0x000055555854c959 in device_post_init (obj=0x616000078980) at /home/elmarco/src/qemu/build/../hw/core/qdev.c:989
 #4  0x0000555558e9e250 in object_post_init_with_type (ti=<optimized out>, obj=0x616000078980) at /home/elmarco/src/qemu/build/../qom/object.c:365
 #5  0x0000555558e9e250 in object_initialize_with_type (data=0x616000078980, size=616, type=<optimized out>) at /home/elmarco/src/qemu/build/../qom/object.c:425
 #6  0x0000555558e9e571 in object_new_with_type (type=0x613000031900) at /home/elmarco/src/qemu/build/../qom/object.c:588
 #7  0x000055555830c048 in qmp_device_list_properties (typename=typename@entry=0x60200000c2d0 "scsi-hd", errp=errp@entry=0x7fffffffc540) at /home/elmarco/src/qemu/qmp.c:519
 #8  0x00005555582c4027 in qdev_device_help (opts=<optimized out>) at /home/elmarco/src/qemu/qdev-monitor.c:283
 #9  0x0000555559378fa2 in qemu_opts_foreach (list=<optimized out>, func=func@entry=0x5555582cfca0 <device_help_func>, opaque=opaque@entry=0x0, errp=errp@entry=0x0) at /home/elmarco/src/qemu/util/qemu-option.c:1171

https://bugzilla.redhat.com/show_bug.cgi?id=1664364

Signed-off-by: Marc-André Lureau <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Reviewed-by: Lukáš Doktor <[email protected]>
Reviewed-by: Igor Mammedov <[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>

Author: elmarco

hw/core/qdev.c

@@ -975,10 +975,13 @@ void object_apply_compat_props(Object *obj)
     if (object_dynamic_cast(qdev_get_machine(), TYPE_MACHINE)) {
         MachineState *m = MACHINE(qdev_get_machine());
         MachineClass *mc = MACHINE_GET_CLASS(m);
-        AccelClass *ac = ACCEL_GET_CLASS(m->accelerator);
 
-        if (ac->compat_props) {
-            object_apply_global_props(obj, ac->compat_props, &error_abort);
+        if (m->accelerator) {
+            AccelClass *ac = ACCEL_GET_CLASS(m->accelerator);
+
+            if (ac->compat_props) {
+                object_apply_global_props(obj, ac->compat_props, &error_abort);
+            }
         }
         object_apply_global_props(obj, mc->compat_props, &error_abort);
     }