restore the stack pointer on finalizer

When error on finalizer, the exception will be ignored.
To restart the code, we need to restore the stack pointer.

fix [Bug #20042]

gc.c

@@ -4426,16 +4426,20 @@ run_finalizer(rb_objspace_t *objspace, VALUE obj, VALUE table)
         VALUE objid;
         VALUE final;
         rb_control_frame_t *cfp;
+        VALUE *sp;
         long finished;
     } saved;
+
     rb_execution_context_t * volatile ec = GET_EC();
 #define RESTORE_FINALIZER() (\
         ec->cfp = saved.cfp, \
+        ec->cfp->sp = saved.sp, \
         ec->errinfo = saved.errinfo)
 
     saved.errinfo = ec->errinfo;
     saved.objid = rb_obj_id(obj);
     saved.cfp = ec->cfp;
+    saved.sp = ec->cfp->sp;
     saved.finished = 0;
     saved.final = Qundef;
 

test/ruby/test_gc.rb

@@ -810,6 +810,15 @@ class TestGc < Test::Unit::TestCase
         obj = nil
       end
     end;
+
+    assert_normal_exit "#{<<~"begin;"}\n#{<<~'end;'}", '[Bug #20042]'
+    begin;
+      def (f = Object.new).call = nil # missing ID
+      o = Object.new
+      ObjectSpace.define_finalizer(o, f)
+      o = nil
+      GC.start
+    end;
   end
 
   def test_object_ids_never_repeat