[kernel] Let objects inherit caps from superclasses

The main point of this change is to allow "global" capabilities defined
on the base object type. The example here is the clone capability on all
objects, which governs the ability to clone a handle.

Related changes in this commit:
- Renamed `kobject` to `object` as far as the syscall interface is
  concerned. `kobject` is the cname, but j6_cap_kobject_clone feels
  clunky.
- The above change made me realize that the "object <type>" syntax for
  specifying object references was also clunky, so now it's "ref <type>"
- Having to add `.object` on everywhere to access objects in
  interface.exposes or object.super was cumbersome, so those properties
  now return object types directly, instead of ObjectRef.
- syscall_verify.cpp.cog now generates code to check capabilities on
  handles if they're specified in the definition, even when not passing
  an object to the implementation function.

src/kernel/syscall_verify.cpp.cog

@@ -17,7 +17,7 @@ ctx.parse("syscalls.def")
 syscalls = ctx.interfaces["syscalls"]
 
 for obj in syscalls.exposes:
-    cog.outl(f'#include "objects/{obj.object.cname}.h"')
+    cog.outl(f'#include "objects/{obj.cname}.h"')
 ]]]*/
 //[[[end]]]
 
@@ -51,7 +51,9 @@ for id, scope, method in syscalls.methods:
     argdefs = []
     cxxargdefs = []
     refparams = []
+
     handles = []
+    objparams = []
 
     if method.constructor:
         argdefs.append("j6_handle_t *self")
@@ -63,11 +65,10 @@ for id, scope, method in syscalls.methods:
         argdefs.append("j6_handle_t self")
         cxxargdefs.append(f"obj::{scope.cname} *self")
         args.append("self_obj")
-        handles.append((
-            f"obj::{scope.cname} *",
-            "self",
-            "self_obj",
-            get_caps(method.options, scope)))
+
+        type = f"obj::{scope.cname} *"
+        handles.append((type, "self", get_caps(method.options, scope)))
+        objparams.append((type, "self"))
 
     for param in method.params:
         needs_obj = param.type.needs_object(param.options)
@@ -81,12 +82,17 @@ for id, scope, method in syscalls.methods:
             cxxargdefs.append(f"{type} {arg}")
 
             if needs_obj:
-                oarg = f"{arg}_obj"
-                handles.append((type, arg, oarg, get_caps(param.options, param.type.object)))
-                args.append(oarg)
+                handles.append((type, arg, get_caps(param.options, param.type.object)))
+                objparams.append((type, arg))
+                args.append(f"{arg}_obj")
+                break
             else:
                 args.append(arg)
 
+        if not needs_obj and param.caps:
+            handles.append((
+                f"obj::{param.type.object.cname}",
+                arg, get_caps(param.options, param.type.object)))
 
         if param.refparam:
             subs = param.type.c_names(param.options)
@@ -103,20 +109,24 @@ for id, scope, method in syscalls.methods:
         cog.outl( "        return j6_err_invalid_arg;")
         cog.outl()
 
-    for type, inarg, outarg, caps in handles:
+    for type, arg, caps in handles:
         if type.endswith('*'):
             type = type[:-1].strip()
 
-        cog.outl(f"    obj::handle *{inarg}_handle = get_handle<typename {type}>({inarg});")
-        cog.outl(f"    if (!{inarg}_handle) return j6_err_invalid_arg;")
+        cog.outl(f"    obj::handle *{arg}_handle = get_handle<typename {type}>({arg});")
+        cog.outl(f"    if (!{arg}_handle) return j6_err_invalid_arg;")
 
         if caps:
             allcaps = " | ".join(caps)
-            cog.outl(f"    j6_cap_t {inarg}_caps_req = {allcaps};")
-            cog.outl(f"    if (!{inarg}_handle->has_cap({inarg}_caps_req)) return j6_err_denied;")
+            cog.outl(f"    j6_cap_t {arg}_caps_req = {allcaps};")
+            cog.outl(f"    if (!{arg}_handle->has_cap({arg}_caps_req)) return j6_err_denied;")
 
-        cog.outl(f"    {type} *{outarg} = {inarg}_handle->as<typename {type}>();")
-        cog.outl(f"    if (!{outarg}) return j6_err_invalid_arg;")
+    for type, arg in objparams:
+        if type.endswith('*'):
+            type = type[:-1].strip()
+
+        cog.outl(f"    {type} *{arg}_obj = {arg}_handle->as<typename {type}>();")
+        cog.outl(f"    if (!{arg}_obj) return j6_err_invalid_arg;")
         cog.outl()
 
     cog.outl(f"""    return {name}({", ".join(args)});""")