diff --git a/byterun/include/runtime_externs.h b/byterun/include/runtime_externs.h
index 7585f14ba..c9ef96b75 100644
--- a/byterun/include/runtime_externs.h
+++ b/byterun/include/runtime_externs.h
@@ -84,7 +84,7 @@ struct re_pattern_buffer *Lregexp(char *regexp);
 
 int LregexpMatch(struct re_pattern_buffer *b, char *s, int pos);
 
-void *Bstring(void *);
+void *Bstring(void *p);
 
 void *Lclone(void *p);
 
diff --git a/byterun/include/stack.h b/byterun/include/stack.h
index 1679345e1..a3fde5a27 100644
--- a/byterun/include/stack.h
+++ b/byterun/include/stack.h
@@ -31,3 +31,7 @@ void s_enter_f(struct State *s, char *func_ip, size_t params_sz,
 void s_exit_f(struct State *s);
 
 void **var_by_category(struct State *s, enum VarCategory category, int id);
+
+// --- changed runtime operations ---
+
+void *s_Bsexp(struct State *state, int bn, int tag);
diff --git a/byterun/src/interpreter.c b/byterun/src/interpreter.c
index 03b93f39c..4caa5cd90 100644
--- a/byterun/src/interpreter.c
+++ b/byterun/src/interpreter.c
@@ -67,17 +67,19 @@ void run(bytefile *bf) {
       if (l < 1) {
         failure("BINOP: l < 1");
       }
-      f_binop(&s, ops[l-1]);
+      void* left = s_pop(&s);
+      void* right = s_pop(&s);
+      s_push(&s, (void*)ops_func[l-1](left, right));
       break;
       
     case 1:
       switch (l) {
       case  0: // CONST %d
-        s_put_i(&s, ip_read_int(&s.ip));
+        s_push(&s, (void*)BOX(ip_read_int(&s.ip)));
         break;
         
       case  1: // STRING %s
-        s_put_const_str(&s, ip_read_string(&s.ip, bf));
+        s_push(&s, Bstring((void*)ip_read_string(&s.ip, bf)));
         break;
           
       case  2: // SEXP %s %d // create sexpr with tag=%s and %d elements from stack
diff --git a/byterun/src/stack.c b/byterun/src/stack.c
index 07033b38b..834cb454a 100644
--- a/byterun/src/stack.c
+++ b/byterun/src/stack.c
@@ -4,6 +4,19 @@
 
 extern size_t STACK_SIZE;
 
+extern size_t __gc_stack_top, __gc_stack_bottom;
+
+#define PRE_GC()                                                                                   \
+  bool flag = false;                                                                               \
+  flag      = __gc_stack_top == 0;                                                                 \
+  if (flag) { __gc_stack_top = (size_t)__builtin_frame_address(0); }                               \
+  assert(__gc_stack_top != 0);                                                                     \
+  assert(__builtin_frame_address(0) <= (void *)__gc_stack_top);
+
+#define POST_GC()                                                                                  \
+  assert(__builtin_frame_address(0) <= (void *)__gc_stack_top);                                    \
+  if (flag) { __gc_stack_top = 0; }
+
 // ------ basic stack oprs ------
 
 void s_push(struct State *s, void *val) {
@@ -134,3 +147,5 @@ void **var_by_category(struct State *s, enum VarCategory category,
 
   return var;
 }
+
+// --- changed runtime operations ---
diff --git a/byterun/src/types.c b/byterun/src/types.c
index 8307b7724..5d2f3d06a 100644
--- a/byterun/src/types.c
+++ b/byterun/src/types.c
@@ -20,7 +20,7 @@ void **f_prev_fp(struct Frame *fp) {
 uint64_t f_locals_sz(struct Frame *fp) { return UNBOX(fp->locals_sz_box); }
 uint64_t f_args_sz(struct Frame *fp) { return UNBOX(fp->args_sz_box); }
 void **f_locals(struct Frame *fp) { return (void **)fp - f_locals_sz(fp) - frame_sz(); }
-void **f_args(struct Frame *fp) { return (void **)fp + f_args_sz(fp); }
+void **f_args(struct Frame *fp) { return (void **)fp + 1; }
 
 
 // --- State ---