diff --git a/include/pocketpy/objects/codeobject.h b/include/pocketpy/objects/codeobject.h
index 607d1f0c..88af8a55 100644
--- a/include/pocketpy/objects/codeobject.h
+++ b/include/pocketpy/objects/codeobject.h
@@ -12,6 +12,7 @@
 
 #define BC_NOARG 0
 #define BC_KEEPLINE -1
+#define BC_RETURN_VIRTUAL 5
 
 typedef enum FuncType {
     FuncType_UNSET,
@@ -62,7 +63,6 @@ typedef struct CodeBlock {
 
 typedef struct BytecodeEx {
     int lineno;       // line number for each bytecode
-    bool is_virtual;  // whether this bytecode is virtual (not in source code)
     int iblock;       // block index
 } BytecodeEx;
 
diff --git a/scripts/98_profiler.py b/scripts/98_profiler.py
index af7c1d4a..d0554db0 100644
--- a/scripts/98_profiler.py
+++ b/scripts/98_profiler.py
@@ -9,3 +9,13 @@ y = 2
 costly_func(2)      # 3s
 
 time.sleep(1)       # 1s
+
+def new_func(a, b, c):
+    x = a + b
+    x = x + c
+    return a
+
+def new_func2(a, b, c):
+    x = a + b
+    x = x + c
+    return a
diff --git a/src/compiler/compiler.c b/src/compiler/compiler.c
index c9fc95ea..d1c3b9d0 100644
--- a/src/compiler/compiler.c
+++ b/src/compiler/compiler.c
@@ -76,7 +76,6 @@ static int Ctx__prepare_loop_divert(Ctx* self, int line, bool is_break);
 static int Ctx__enter_block(Ctx* self, CodeBlockType type);
 static void Ctx__exit_block(Ctx* self);
 static int Ctx__emit_(Ctx* self, Opcode opcode, uint16_t arg, int line);
-static int Ctx__emit_virtual(Ctx* self, Opcode opcode, uint16_t arg, int line, bool virtual);
 // static void Ctx__revert_last_emit_(Ctx* self);
 static int Ctx__emit_int(Ctx* self, int64_t value, int line);
 static void Ctx__patch_jump(Ctx* self, int index);
@@ -1177,9 +1176,9 @@ static void Ctx__s_emit_decorators(Ctx* self, int count) {
     }
 }
 
-static int Ctx__emit_virtual(Ctx* self, Opcode opcode, uint16_t arg, int line, bool is_virtual) {
+static int Ctx__emit_(Ctx* self, Opcode opcode, uint16_t arg, int line) {
     Bytecode bc = {(uint8_t)opcode, arg};
-    BytecodeEx bcx = {line, is_virtual, self->curr_iblock};
+    BytecodeEx bcx = {line, self->curr_iblock};
     c11_vector__push(Bytecode, &self->co->codes, bc);
     c11_vector__push(BytecodeEx, &self->co->codes_ex, bcx);
     int i = self->co->codes.length - 1;
@@ -1188,10 +1187,6 @@ static int Ctx__emit_virtual(Ctx* self, Opcode opcode, uint16_t arg, int line, b
     return i;
 }
 
-static int Ctx__emit_(Ctx* self, Opcode opcode, uint16_t arg, int line) {
-    return Ctx__emit_virtual(self, opcode, arg, line, false);
-}
-
 // static void Ctx__revert_last_emit_(Ctx* self) {
 //     c11_vector__pop(&self->co->codes);
 //     c11_vector__pop(&self->co->codes_ex);
@@ -1512,7 +1507,7 @@ static Error* pop_context(Compiler* self) {
     // previously, we only do this if the last opcode is not a return
     // however, this is buggy...since there may be a jump to the end (out of bound) even if the last
     // opcode is a return
-    Ctx__emit_virtual(ctx(), OP_RETURN_VALUE, 1, BC_KEEPLINE, true);
+    Ctx__emit_(ctx(), OP_RETURN_VALUE, BC_RETURN_VIRTUAL, BC_KEEPLINE);
 
     CodeObject* co = ctx()->co;
     // find the last valid token
@@ -2421,6 +2416,7 @@ static Error* consume_pep695_py312(Compiler* self) {
 
 static Error* compile_function(Compiler* self, int decorators) {
     Error* err;
+    int def_line = prev()->line;
     consume(TK_ID);
     c11_sv decl_name_sv = Token__sv(prev());
     int decl_index;
@@ -2450,7 +2446,7 @@ static Error* compile_function(Compiler* self, int decorators) {
         }
     }
 
-    Ctx__emit_(ctx(), OP_LOAD_FUNCTION, decl_index, prev()->line);
+    Ctx__emit_(ctx(), OP_LOAD_FUNCTION, decl_index, def_line);
     Ctx__s_emit_decorators(ctx(), decorators);
 
     py_Name decl_name = py_namev(decl_name_sv);
@@ -2463,9 +2459,9 @@ static Error* compile_function(Compiler* self, int decorators) {
             }
         }
 
-        Ctx__emit_(ctx(), OP_STORE_CLASS_ATTR, Ctx__add_name(ctx(), decl_name), prev()->line);
+        Ctx__emit_(ctx(), OP_STORE_CLASS_ATTR, Ctx__add_name(ctx(), decl_name), def_line);
     } else {
-        NameExpr* e = NameExpr__new(prev()->line, decl_name, name_scope(self));
+        NameExpr* e = NameExpr__new(def_line, decl_name, name_scope(self));
         vtemit_store((Expr*)e, ctx());
         vtdelete((Expr*)e);
     }
diff --git a/src/interpreter/ceval.c b/src/interpreter/ceval.c
index 23ce786a..4bcac41d 100644
--- a/src/interpreter/ceval.c
+++ b/src/interpreter/ceval.c
@@ -4,6 +4,7 @@
 #include "pocketpy/interpreter/vm.h"
 #include "pocketpy/common/sstream.h"
 #include "pocketpy/objects/codeobject.h"
+#include "pocketpy/objects/exception.h"
 #include "pocketpy/pocketpy.h"
 #include "pocketpy/objects/error.h"
 #include <stdbool.h>
@@ -105,13 +106,16 @@ __NEXT_STEP:
     byte = co_codes[frame->ip];
 
     if(self->trace_info.func) {
-        SourceLocation loc = Frame__source_location(frame);
-        SourceLocation prev_loc = self->trace_info.prev_loc;
-        if(loc.lineno != prev_loc.lineno || loc.src != prev_loc.src) {
-            if(prev_loc.src) PK_DECREF(prev_loc.src);
-            PK_INCREF(loc.src);
-            self->trace_info.prev_loc = loc;
-            self->trace_info.func(frame, TRACE_EVENT_LINE);
+        bool is_virtual = byte.op == OP_RETURN_VALUE && byte.arg == BC_RETURN_VIRTUAL;
+        if(!is_virtual) {
+            SourceLocation loc = Frame__source_location(frame);
+            SourceLocation prev_loc = self->trace_info.prev_loc;
+            if(loc.lineno != prev_loc.lineno || loc.src != prev_loc.src) {
+                if(prev_loc.src) PK_DECREF(prev_loc.src);
+                PK_INCREF(loc.src);
+                self->trace_info.prev_loc = loc;
+                self->trace_info.func(frame, TRACE_EVENT_LINE);
+            }
         }
     }
 
@@ -817,7 +821,8 @@ __NEXT_STEP:
                 return RES_YIELD;
             } else {
                 assert(self->last_retval.type == tp_StopIteration);
-                py_ObjectRef value = py_getslot(&self->last_retval, 0);
+                BaseException* ud = py_touserdata(py_retval());
+                py_ObjectRef value = &ud->args;
                 if(py_isnil(value)) value = py_None();
                 *TOP() = *value;  // [iter] -> [retval]
                 DISPATCH_JUMP((int16_t)byte.arg);
@@ -1219,14 +1224,15 @@ __NEXT_STEP:
     c11__unreachable();
 
 __ERROR:
-    py_BaseException__stpush(frame, &self->curr_exception,
+    py_BaseException__stpush(frame,
+                             &self->curr_exception,
                              frame->co->src,
                              Frame__lineno(frame),
                              !frame->is_locals_special ? frame->co->name->data : NULL);
 __ERROR_RE_RAISE:
     do {
     } while(0);
-    
+
     int target = Frame__prepare_jump_exception_handler(frame, &self->stack);
     if(target >= 0) {
         // 1. Exception can be handled inside the current frame
@@ -1306,7 +1312,10 @@ bool pk_stack_binaryop(VM* self, py_Name op, py_Name rop) {
 
     py_Type lhs_t = rop ? TOP()->type : SECOND()->type;
     py_Type rhs_t = rop ? SECOND()->type : TOP()->type;
-    return TypeError("unsupported operand type(s) for '%s': '%t' and '%t'", pk_op2str(op), lhs_t, rhs_t);
+    return TypeError("unsupported operand type(s) for '%s': '%t' and '%t'",
+                     pk_op2str(op),
+                     lhs_t,
+                     rhs_t);
 }
 
 bool py_binaryop(py_Ref lhs, py_Ref rhs, py_Name op, py_Name rop) {
diff --git a/src/interpreter/vm.c b/src/interpreter/vm.c
index 192896df..eb5109a6 100644
--- a/src/interpreter/vm.c
+++ b/src/interpreter/vm.c
@@ -635,7 +635,8 @@ void ManagedHeap__mark(ManagedHeap* self) {
     assert(p_stack->length == 0);
 
     // mark value stack
-    for(py_TValue* p = vm->stack.begin; p != vm->stack.end; p++) {
+    for(py_TValue* p = vm->stack.begin; p < vm->stack.sp; p++) {
+        // assert(p->type != tp_nil);
         pk__mark_value(p);
     }
     // mark modules
diff --git a/src/interpreter/vmx.c b/src/interpreter/vmx.c
index abb00a2b..5162165d 100644
--- a/src/interpreter/vmx.c
+++ b/src/interpreter/vmx.c
@@ -3,7 +3,7 @@
 
 void pk_print_stack(VM* self, py_Frame* frame, Bytecode byte) {
     return;
-    if(frame == NULL || py_isnil(self->main)) return;
+    if(frame == NULL || !self->main || py_isnil(self->main)) return;
 
     py_TValue* sp = self->stack.sp;
     c11_sbuf buf;
diff --git a/src/modules/dis.c b/src/modules/dis.c
index fbcffc92..213c4805 100644
--- a/src/modules/dis.c
+++ b/src/modules/dis.c
@@ -44,7 +44,7 @@ static bool disassemble(CodeObject* co) {
         c11_sbuf__write_cstr(&ss, buf);
 
         c11_sbuf__write_cstr(&ss, pk_opname(byte.op));
-        c11_sbuf__write_char(&ss, ex.is_virtual ? '*' : ' ');
+        c11_sbuf__write_char(&ss, ' ');
         int padding = 24 - strlen(pk_opname(byte.op));
         for(int j = 0; j < padding; j++)
             c11_sbuf__write_char(&ss, ' ');
diff --git a/src/modules/random.c b/src/modules/random.c
index bb9da9b8..cc6f2010 100644
--- a/src/modules/random.c
+++ b/src/modules/random.c
@@ -270,9 +270,9 @@ static bool Random_choices(int argc, py_Ref argv) {
     }
 
     py_f64 total = cum_weights[length - 1];
-    if(total <= 0) {
+    if(total <= 1e-6) {
         PK_FREE(cum_weights);
-        return ValueError("total of weights must be greater than zero");
+        return ValueError("total of weights must be greater than 1e-6");
     }
 
     py_newlistn(py_retval(), k);
diff --git a/src/objects/namedict.c b/src/objects/namedict.c
index 86f006f6..7e89c6df 100644
--- a/src/objects/namedict.c
+++ b/src/objects/namedict.c
@@ -5,27 +5,29 @@
 #include <string.h>
 #include <assert.h>
 
+#define HASH_KEY(__k) ((uintptr_t)(__k) >> 3U)
+
 #define HASH_PROBE_0(__k, ok, i)                                                                   \
     ok = false;                                                                                    \
-    i = (uintptr_t)(__k)&self->mask;                                                               \
+    i = HASH_KEY(__k) & self->mask;                                                                \
     do {                                                                                           \
         if(self->items[i].key == (__k)) {                                                          \
             ok = true;                                                                             \
             break;                                                                                 \
         }                                                                                          \
         if(self->items[i].key == NULL) break;                                                      \
-        i = (5 * i + 1) & self->mask;                                                              \
+        i = (i + 1) & self->mask;                                                                  \
     } while(true);
 
 #define HASH_PROBE_1(__k, ok, i)                                                                   \
     ok = false;                                                                                    \
-    i = (uintptr_t)(__k)&self->mask;                                                               \
+    i = HASH_KEY(__k) & self->mask;                                                                \
     while(self->items[i].key != NULL) {                                                            \
         if(self->items[i].key == (__k)) {                                                          \
             ok = true;                                                                             \
             break;                                                                                 \
         }                                                                                          \
-        i = (5 * i + 1) & self->mask;                                                              \
+        i = (i + 1) & self->mask;                                                                  \
     }
 
 static void NameDict__set_capacity_and_alloc_items(NameDict* self, int val) {
@@ -111,12 +113,12 @@ bool NameDict__del(NameDict* self, py_Name key) {
     self->items[i].value = *py_NIL();
     self->length--;
     /* tidy */
-    uint32_t posToRemove = i;
-    uint32_t posToShift = posToRemove;
+    uintptr_t posToRemove = i;
+    uintptr_t posToShift = posToRemove;
     while(true) {
-        posToShift = (5 * posToShift + 1) & self->mask;
+        posToShift = (posToShift + 1) & self->mask;
         if(self->items[posToShift].key == NULL) break;
-        uintptr_t hash_z = (uintptr_t)self->items[posToShift].key;
+        uintptr_t hash_z = HASH_KEY(self->items[posToShift].key);
         uintptr_t insertPos = hash_z & self->mask;
         bool cond1 = insertPos <= posToRemove;
         bool cond2 = posToRemove <= posToShift;
@@ -124,6 +126,7 @@ bool NameDict__del(NameDict* self, py_Name key) {
            // chain wrapped around capacity
            (posToShift < insertPos && (cond1 || cond2))) {
             NameDict_KV tmp = self->items[posToRemove];
+            assert(tmp.key == NULL);
             self->items[posToRemove] = self->items[posToShift];
             self->items[posToShift] = tmp;
             posToRemove = posToShift;
@@ -141,4 +144,5 @@ void NameDict__clear(NameDict* self) {
 }
 
 #undef HASH_PROBE_0
-#undef HASH_PROBE_1
\ No newline at end of file
+#undef HASH_PROBE_1
+#undef HASH_KEY
\ No newline at end of file
diff --git a/src/public/py_exception.c b/src/public/py_exception.c
index 93238296..4fb0d117 100644
--- a/src/public/py_exception.c
+++ b/src/public/py_exception.c
@@ -20,9 +20,14 @@ void py_BaseException__stpush(py_Frame* frame,
     frame_dump->lineno = lineno;
     frame_dump->name = func_name ? c11_string__new(func_name) : NULL;
 
-    if(py_debugger_isattached() && frame != NULL) {
-        py_Frame_newlocals(frame, &frame_dump->locals);
-        py_Frame_newglobals(frame, &frame_dump->globals);
+    if(py_debugger_isattached()) {
+        if(frame != NULL) {
+            py_Frame_newlocals(frame, &frame_dump->locals);
+            py_Frame_newglobals(frame, &frame_dump->globals);
+        } else {
+            py_newdict(&frame_dump->locals);
+            py_newdict(&frame_dump->globals);
+        }
     }
 }
 
diff --git a/src/public/values.c b/src/public/values.c
index f696f85d..0c35edb0 100644
--- a/src/public/values.c
+++ b/src/public/values.c
@@ -47,7 +47,10 @@ void py_newellipsis(py_OutRef out) {
     out->is_ptr = false;
 }
 
-void py_newnil(py_OutRef out) { out->type = 0; }
+void py_newnil(py_OutRef out) {
+    out->type = tp_nil;
+    out->is_ptr = false;
+}
 
 void py_newnativefunc(py_OutRef out, py_CFunction f) {
     out->type = tp_nativefunc;
diff --git a/tests/08_dict.py b/tests/08_dict.py
index 992603f7..48833e7b 100644
--- a/tests/08_dict.py
+++ b/tests/08_dict.py
@@ -165,4 +165,17 @@ for i in range(len(data)):
     b.append(z)
     if i % 3 == 0:
         y = b.pop()
-        delattr(a, y)
\ No newline at end of file
+        delattr(a, y)
+
+# bug test
+d = {
+    '__name__': '__main__',
+    '__package__': '',
+    '__path__': '__main__',
+    'a': [],
+    'gc': 1,
+}
+
+del d['a']
+assert 'a' not in d
+assert d['gc'] == 1
\ No newline at end of file
diff --git a/tests/71_gc_bug.py b/tests/71_gc_bug.py
new file mode 100644
index 00000000..24cd9002
--- /dev/null
+++ b/tests/71_gc_bug.py
@@ -0,0 +1,46 @@
+# a=[]
+# import gc
+# gc.collect()
+
+# # a.append(a)
+# print(globals().items())
+# del a
+# print(list(globals().items()))
+# print(globals()['gc'])
+# gc.collect()
+
+d = object()
+d.__name__ = '__main__'
+d.__package__ = ''
+d.__path__ = '__main__'
+d.a = []
+d.gc = 1
+
+assert d.gc == 1
+del d.a
+
+assert not hasattr(d, 'a')
+assert d.gc == 1
+
+# [0, 1, 6, 7, 4, 5, 2, 3]
+
+# 0 __name__      [0]
+# 1 __package__   [1]
+# 2 nil
+# 3 nil
+# 4 gc            [4]
+# 5 nil
+# 6 __path__      [2]
+# 7 a             [3]
+
+import gc
+gc.collect()
+
+a = []
+del a
+assert gc.collect() == 1
+
+a = []
+a.append(a)
+del a
+assert gc.collect() == 1