structs: bugfix: crash in static slot inheritance.

* struct.c (make_struct_type): When a struct defines a static
slot that exists as an instancee slot in the supertype, there
is a crash. This is because the code assumes that the
supertype's slot is static. The index value m ends up negative
due to subtracting STATIC_SLOT_BASE from an instance slot
index, and so the code tries to copy the value of a negatively
indexed static slot from the supertype into the new static
slot. We can fix this by not doing the copy when a negative
index has been calculated. That way we treat the situation as
if the supertype didn't have that slot at all.

1 files changed, 1 insertions, 1 deletions

diff --git a/struct.c b/struct.c
index a8d1f373..c44dbc7a 100644
--- a/struct.c
+++ b/struct.c
@@ -370,7 +370,7 @@ val make_struct_type(val name, val super,
           ss->home_type = stype;
           ss->home_offs = n;
           ss->home = &ss->store;
-          ss->store = if2(msl, stslot_place(&su->stslot[m]));
+          ss->store = if2(m >= 0, stslot_place(&su->stslot[m]));
         } else {
           *ss = su->stslot[m];
           ss->store = nil;