kernel: userspace: fix dynamic kernel object alignment

Previous commit 55350a9 fixing
address-of-packed-mem warnings uncovered an issue with
the alignment of dynamic kernel objects. On 64-bit platforms,
the alignment is 16 bytes instead of 4/8 bytes (as in pointer,
void *). This changes the function of mapping between kernel
object types and alignments to use the dynamic object struct
as basis for alignment instead of simply using pointers.

This also uncomments the assertion added in the previous commit
55350a9 so that we can keep
an eye on the alignment in the future. Note that the assertion
is moved after checking if the incoming kernel object is
dynamically allocated. Static kernel objects are not subjected
to this alignment requirement.

Fixes #41062

Signed-off-by: Daniel Leung <[email protected]>

Author: dcpleung

kernel/userspace.c

@@ -190,11 +190,11 @@ static size_t obj_align_get(enum k_objects otype)
 #ifdef ARCH_DYMANIC_OBJ_K_THREAD_ALIGNMENT
 		ret = ARCH_DYMANIC_OBJ_K_THREAD_ALIGNMENT;
 #else
-		ret = sizeof(void *);
+		ret = __alignof(struct dyn_obj);
 #endif
 		break;
 	default:
-		ret = sizeof(void *);
+		ret = __alignof(struct dyn_obj);
 		break;
 	}
 
@@ -466,15 +466,16 @@ static void unref_check(struct z_object *ko, uintptr_t index)
 	sys_bitfield_clear_bit((mem_addr_t)&ko->perms, index);
 
 #ifdef CONFIG_DYNAMIC_OBJECTS
+	if ((ko->flags & K_OBJ_FLAG_ALLOC) == 0U) {
+		/* skip unref check for static kernel object */
+		goto out;
+	}
+
 	void *vko = ko;
 
 	struct dyn_obj *dyn = CONTAINER_OF(vko, struct dyn_obj, kobj);
-	/* TODO: check why this assert hits */
-	/*__ASSERT(IS_PTR_ALIGNED(dyn, struct dyn_obj), "unaligned z_object");*/
 
-	if ((ko->flags & K_OBJ_FLAG_ALLOC) == 0U) {
-		goto out;
-	}
+	__ASSERT(IS_PTR_ALIGNED(dyn, struct dyn_obj), "unaligned z_object");
 
 	for (int i = 0; i < CONFIG_MAX_THREAD_BYTES; i++) {
 		if (ko->perms[i] != 0U) {