include/hw/qdev-core: Detect most empty Property lists at compile time

Add a macro expansion of device_class_set_props which can check
on the type and size of PROPS before calling the function.

Avoid the macro in migration.c because migration_properties
is defined externally with indeterminate size.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Lei Yang <leiyang@redhat.com>
Link: https://lore.kernel.org/r/20241218134251.4724-13-richard.henderson@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/core/qdev-properties.c

@@ -1061,7 +1061,7 @@ static void qdev_class_add_legacy_property(DeviceClass *dc, const Property *prop
         NULL, NULL, (Property *)prop);
 }
 
-void device_class_set_props(DeviceClass *dc, const Property *props)
+void (device_class_set_props)(DeviceClass *dc, const Property *props)
 {
     const Property *prop;
 

include/hw/qdev-core.h

@@ -940,9 +940,26 @@ char *qdev_get_own_fw_dev_path_from_handler(BusState *bus, DeviceState *dev);
  * This will add a set of properties to the object. It will fault if
  * you attempt to add an existing property defined by a parent class.
  * To modify an inherited property you need to use????
+ *
+ * Validate that @props has at least one Property plus the terminator.
+ * Validate that the array is terminated at compile-time (with -O2),
+ * which requires the array to be const.
  */
 void device_class_set_props(DeviceClass *dc, const Property *props);
 
+#define device_class_set_props(dc, props) \
+    do {                                                                \
+        QEMU_BUILD_BUG_ON(sizeof(props) != sizeof(const Property *) &&  \
+                          sizeof(props) < 2 * sizeof(Property));        \
+        if (sizeof(props) != sizeof(const Property *)) {                \
+            size_t props_count_ = sizeof(props) / sizeof(Property) - 1; \
+            if ((props)[props_count_].name != NULL) {                   \
+                qemu_build_not_reached();                               \
+            }                                                           \
+        }                                                               \
+        (device_class_set_props)((dc), (props));                        \
+    } while (0)
+
 /**
  * device_class_set_parent_realize() - set up for chaining realize fns
  * @dc: The device class

migration/migration.c

@@ -3822,7 +3822,7 @@ static void migration_class_init(ObjectClass *klass, void *data)
     DeviceClass *dc = DEVICE_CLASS(klass);
 
     dc->user_creatable = false;
-    device_class_set_props(dc, migration_properties);
+    (device_class_set_props)(dc, migration_properties);
 }
 
 static void migration_instance_finalize(Object *obj)