struct bug: mismanagement of static slot store.

The bug_unless statement was found to go off, indicating an
internal problem. Indeed, the store of inherited static slots
were being set to non-nil by incorrect copying in two places.
This is harmless in and of itself; it's just a way of being
tidy. If a slot's value is located elsewhere, then the local
store must be nil.

* struct.c (static_slot_home_fixup): After fetching a fresh
copy of the home type's stslot entry, clear the store to nil.
(make_struct_type): Likewise.
(struct_type_mark): Use assert for this rather than
bug_unless, because it happens in the middle of garbage
collection. Throwing an exception out of the middle of gc is a
nonstarter.

1 files changed, 4 insertions, 1 deletions

diff --git a/struct.c b/struct.c
index cfa3c3b8..c3d7293e 100644
--- a/struct.c
+++ b/struct.c
@@ -33,6 +33,7 @@
 #include <stdlib.h>
 #include <limits.h>
 #include <signal.h>
+#include <assert.h>
 #include "config.h"
 #include ALLOCA_H
 #include "lib.h"
@@ -220,6 +221,7 @@ static void static_slot_home_fixup(struct struct_type *st)
       struct struct_type *shome = coerce(struct struct_type *,
                                          s->home_type->co.handle);
       *s = shome->stslot[s->home_offs];
+      s->store = nil;
     }
   }
 }
@@ -311,6 +313,7 @@ val make_struct_type(val name, val super,
           ss->store = if2(msl, stslot_place(&su->stslot[m]));
         } else {
           *ss = su->stslot[m];
+          ss->store = nil;
         }
         sethash(slot_hash, cons(slot, id), num(n + STATIC_SLOT_BASE));
       } else {
@@ -408,7 +411,7 @@ static void struct_type_mark(val obj)
     if (sl->home_type == st->self)
       gc_mark(sl->store);
     else
-      bug_unless (sl->store == nil);
+      assert (sl->store == nil);
   }
 }