src/class-layout-impl.lisp: Fix class pointers in secondary chains.

Consider:

	[link = SodClass] class MyClass: SodClass { }
	[metaclass = MyClass] class Foo: SodObject { }

GCC reports:

	/tmp/mdw/t.c:258:33: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
	   /*                _class = */ &Foo__classobj.obj.myclass,
	                                 ^
	/tmp/mdw/t.c:258:33: note: (near initialization for ‘Foo__vtable_obj.obj._class’)

What's going on here is that it's writing the wrong metaclass pointer
into the `_class' pointer on `Foo''s secondary `obj' chain.

Fix this by choosing, for each class pointer, the most specific
superclass of the overall metaclass that is (a) on the correct chain of
the metaclass, and (b) is a superclass of the metaclass of the most
specific class in the chain whose vtable we're writing.  Whew!

diff --git a/src/class-layout-impl.lisp b/src/class-layout-impl.lisp
index e93f401..1794e5a 100644 (file)
--- a/src/class-layout-impl.lisp
+++ b/src/class-layout-impl.lisp
@@ -267,17 +267,19 @@
     ((class sod-class) (chain-head sod-class)
      (metaclass sod-class) (meta-chain-head sod-class))
 
-  ;; Slightly tricky.  We don't necessarily want a pointer to the metaclass,
-  ;; but to its most specific subclass on the given chain.  Fortunately, CL
-  ;; is good at this game.
-  (let* ((meta-chains (sod-class-chains metaclass))
-        (meta-chain-tails (mapcar #'car meta-chains))
-        (meta-chain-tail (find meta-chain-head meta-chain-tails
-                               :key #'sod-class-chain-head)))
+  ;; Rather tricky.  This is a class pointer on a vtable for the CHAIN-HEAD
+  ;; chain, pointing into the META-CHAIN-HEAD chain of the metaclass.  We
+  ;; need to produce a pointer to the most specific superclass of the
+  ;; metaclass on the right chain that is a superclass of the metaclass of
+  ;; the most specific class in the superclass chain headed by CHAIN-HEAD.
+  (flet ((chain-tail (class head)
+          (find head (mapcar #'car (sod-class-chains class))
+                :key #'sod-class-chain-head)))
     (make-instance 'class-pointer
-                  :class class
-                  :chain-head chain-head
-                  :metaclass meta-chain-tail
+                  :class class :chain-head chain-head
+                  :metaclass (chain-tail (sod-class-metaclass
+                                          (chain-tail class chain-head))
+                                         meta-chain-head)
                   :meta-chain-head meta-chain-head)))
 
 ;;; base-offset
@@ -328,7 +330,8 @@
 
   ;; If this class introduces new metaclass chains, then emit pointers to
   ;; them.
-  (let* ((metasuper (sod-class-metaclass super))
+  (let* ((metaclass (sod-class-metaclass class))
+        (metasuper (sod-class-metaclass super))
         (metasuper-chains (sod-class-chains metasuper))
         (metasuper-chain-heads (mapcar (lambda (chain)
                                          (sod-class-chain-head (car chain)))
@@ -337,7 +340,7 @@
       (unless (member metasuper-chain-head *done-metaclass-chains*)
        (funcall emit (make-class-pointer class
                                          chain-head
-                                         metasuper
+                                         metaclass
                                          metasuper-chain-head))
        (push metasuper-chain-head *done-metaclass-chains*))))