obj: add header-offset field to object_type

this allows the object header to be placed anywhere within the larger
object structure.

the object system now also ensures that the object is zero-initialised
during allocation.

include/socks/object.h

@@ -48,6 +48,7 @@ struct object_type {
 	enum object_type_flags ob_flags;
 	char ob_name[32];
 	unsigned int ob_size;
+	unsigned int ob_header_offset;
 	struct vm_cache ob_cache;
 	struct queue_entry ob_list;
 	struct queue ob_attrib;

kxld/kext.c

@@ -34,6 +34,7 @@ static kern_status_t kext_destroy(struct object *obj)
 static struct object_type kext_type = {
 	.ob_name = "kext",
 	.ob_size = sizeof(struct kext),
+	.ob_header_offset = offsetof(struct kext, k_base),
 	.ob_ops = {
 		.query_name = kext_query_name,
 	},

obj/namespace.c

@@ -33,6 +33,7 @@ static kern_status_t ns_get_child_named(struct object *obj, const char *name, st
 static struct object_type ns_type = {
 	.ob_name = "namespace",
 	.ob_size = sizeof(struct object_namespace),
+	.ob_header_offset = offsetof(struct object_namespace, ns_base),
 	.ob_ops = {
 		.query_name = ns_query_name,
 		.get_named = ns_get_child_named,

obj/object.c

@@ -48,11 +48,15 @@ struct object *object_create(struct object_type *type)
 	}
 
 	struct vm_cache *cache = &type->ob_cache;
-	struct object *obj = vm_cache_alloc(cache, 0);
+	void *obj_buf = vm_cache_alloc(cache, 0);
-	if (!obj) {
+	if (!obj_buf) {
 		return NULL;
 	}
 
+	memset(obj_buf, 0x00, type->ob_size);
+
+	struct object *obj = (struct object *)((unsigned char *)obj_buf + type->ob_header_offset);
+
 	obj->ob_type = type;
 	obj->ob_lock = SPIN_LOCK_INIT;
 	obj->ob_magic = OBJECT_MAGIC;

obj/set.c

@@ -58,6 +58,7 @@ static kern_status_t set_get_child_named(struct object *obj, const char *name, s
 static struct object_type set_type = {
 	.ob_name = "set",
 	.ob_size = sizeof(struct set),
+	.ob_header_offset = offsetof(struct set, s_base),
 	.ob_ops = {
 		.query_name = set_query_name,
 		.get_named = set_get_child_named,

sched/task.c

@@ -11,6 +11,7 @@
 static struct object_type task_type = {
 	.ob_name = "task",
 	.ob_size = sizeof(struct task),
+	.ob_header_offset = offsetof(struct task, t_base),
 };
 
 static struct task *__kernel_task;

sched/thread.c

@@ -8,6 +8,7 @@
 static struct object_type thread_type = {
 	.ob_name = "thread",
 	.ob_size = sizeof(struct thread),
+	.ob_header_offset = offsetof(struct thread, thr_base),
 };
 
 kern_status_t thread_object_type_init(void)