diff --git a/include/verilated.cpp b/include/verilated.cpp
index 63affb724..dc23517cc 100644
--- a/include/verilated.cpp
+++ b/include/verilated.cpp
@@ -693,7 +693,7 @@ std::string VL_DECIMAL_NW(int width, const WDataInP lwp) VL_MT_SAFE {
 }
 
 template <typename T>
-std::string _vl_vsformat_time(char* tmp, T ld, int timeunit, bool left, size_t width) {
+std::string _vl_vsformat_time(char* tmp, T ld, int timeunit, bool left, size_t width) VL_MT_SAFE {
     const VerilatedContextImp* const ctxImpp = Verilated::threadContextp()->impp();
     const std::string suffix = ctxImpp->timeFormatSuffix();
     const int userUnits = ctxImpp->timeFormatUnits();  // 0..-15
diff --git a/include/verilated_imp.h b/include/verilated_imp.h
index e357ddcc8..dfc1cdf92 100644
--- a/include/verilated_imp.h
+++ b/include/verilated_imp.h
@@ -148,7 +148,7 @@ public:
 private:
     VL_UNCOPYABLE(VerilatedThreadMsgQueue);
     // METHODS
-    static VerilatedThreadMsgQueue& threadton() {
+    static VerilatedThreadMsgQueue& threadton() VL_MT_SAFE {
         static thread_local VerilatedThreadMsgQueue t_s;
         return t_s;
     }
diff --git a/include/verilatedos.h b/include/verilatedos.h
index da40b1edd..625552d4f 100644
--- a/include/verilatedos.h
+++ b/include/verilatedos.h
@@ -603,8 +603,12 @@ reverse_wrapper<T> reverse_view(const T& v) {
 }
 
 // C++17's std::as_const
+// `VL_MT_SAFE` annotation only applies to this function.
+// Object that is returned by this function is not considered
+// as MT_SAFE and any function call on this object still
+// needs to be `VL_MT_SAFE`.
 template <class T>
-T const& as_const(T& v) {
+T const& as_const(T& v) VL_MT_SAFE {
     return v;
 }
 
diff --git a/nodist/clang_check_attributes b/nodist/clang_check_attributes
index dba884b49..0cea38289 100755
--- a/nodist/clang_check_attributes
+++ b/nodist/clang_check_attributes
@@ -49,14 +49,16 @@ class VlAnnotations:
     release: bool = False
 
     def is_mt_safe_context(self):
-        return (not (self.mt_unsafe or self.mt_unsafe_one)
-                and (self.mt_safe or self.mt_start))
+        return (not (self.mt_unsafe or self.mt_unsafe_one) and self.mt_safe)
 
     def is_pure_context(self):
         return self.pure
 
     def is_stabe_tree_context(self):
-        return self.stable_tree
+        # stable tree context requires calls to be marked
+        # as MT_SAFE or MT_STABLE
+        # Functions in MT_START needs to be MT_SAFE or MT_STABLE
+        return self.stable_tree or self.mt_start
 
     def is_mt_unsafe_call(self):
         return self.mt_unsafe or self.mt_unsafe_one
@@ -389,7 +391,8 @@ class CallAnnotationsValidator:
 
         # stable tree context
         if ctx.is_stabe_tree_context():
-            if not (annotations.is_stabe_tree_call()
+            if annotations.is_mt_unsafe_call() or not (
+                    annotations.is_stabe_tree_call()
                     or annotations.is_pure_call()
                     or self.check_mt_safe_call(node, refd, annotations)):
                 self.emit_diagnostic(
@@ -417,7 +420,8 @@ class CallAnnotationsValidator:
 
         # stable tree context
         if ctx.is_stabe_tree_context():
-            if not (annotations.is_pure_call()
+            if annotations.is_mt_unsafe_call() or not (
+                    annotations.is_pure_call()
                     or annotations.is_mt_safe_call()
                     or annotations.is_stabe_tree_call()):
                 self.emit_diagnostic(
@@ -465,11 +469,19 @@ class CallAnnotationsValidator:
         if not supported:
             self.iterate_children(node.get_children(),
                                   self.dispatch_node_inside_definition)
-            return
+            return True
 
         assert refd is not None
         if self._is_ignored_call(refd):
-            return
+            return True
+
+        if "std::function" in refd.displayname:
+            # Workaroud for missing support for lambda annotations
+            # in c++11.
+            # If function takes std::function as argument,
+            # assume, that this std::function will be called inside it.
+            self.process_function_definition(node)
+            return False
 
         assert self._call_location is not None
         node_file = os.path.abspath(node.location.file.name)
@@ -481,47 +493,40 @@ class CallAnnotationsValidator:
                 or refd.kind == CursorKind.CXX_METHOD
                 and refd.is_static_method()):
             self.process_function_call(refd, annotations)
-            self.iterate_children(node.get_children(),
-                                  self.dispatch_node_inside_definition)
-            return
         # Function pointer
-        if refd.kind in [
+        elif refd.kind in [
                 CursorKind.VAR_DECL, CursorKind.FIELD_DECL,
                 CursorKind.PARM_DECL
         ]:
             self.process_function_call(refd, annotations)
-            self.iterate_children(node.get_children(),
-                                  self.dispatch_node_inside_definition)
-            return
         # Non-static class methods
-        if refd.kind == CursorKind.CXX_METHOD:
+        elif refd.kind == CursorKind.CXX_METHOD:
             self.process_method_call(node, refd, annotations)
-            self.iterate_children(node.get_children(),
-                                  self.dispatch_node_inside_definition)
-            return
         # Conversion method (e.g. `operator int()`)
-        if refd.kind == CursorKind.CONVERSION_FUNCTION:
+        elif refd.kind == CursorKind.CONVERSION_FUNCTION:
             self.process_method_call(node, refd, annotations)
-            self.iterate_children(node.get_children(),
-                                  self.dispatch_node_inside_definition)
-            return
         # Constructors
-        if refd.kind == CursorKind.CONSTRUCTOR:
+        elif refd.kind == CursorKind.CONSTRUCTOR:
             self.process_constructor_call(refd, annotations)
-            self.iterate_children(node.get_children(),
-                                  self.dispatch_node_inside_definition)
-            return
-
-        # Ignore other callables
-        print(f"{refd.location.file.name}:{refd.location.line}: "
-              f"{refd.displayname}    {refd.kind}\n"
-              f"    from: {node.location.file.name}:{node.location.line}")
+        else:
+            # Ignore other callables, but report them
+            print("Unknown callable: "
+                  f"{refd.location.file.name}:{refd.location.line}: "
+                  f"{refd.displayname}    {refd.kind}\n"
+                  f"    from: {node.location.file.name}:{node.location.line}")
+        return True
 
     # Definition handling
 
     def dispatch_node_inside_definition(self, node: clang.cindex.Cursor):
         if node.kind == CursorKind.CALL_EXPR:
-            self.dispatch_call_node(node)
+            if self.dispatch_call_node(node) is False:
+                return None
+        elif node.is_definition() and node.kind in [
+                CursorKind.CXX_METHOD, CursorKind.FUNCTION_DECL,
+                CursorKind.CONSTRUCTOR, CursorKind.CONVERSION_FUNCTION
+        ]:
+            self.process_function_definition(node)
             return None
 
         return self.iterate_children(node.get_children(),
@@ -556,12 +561,14 @@ class CallAnnotationsValidator:
         # for callees validation.
         self._caller = FunctionInfo.from_node(node, refd,
                                               def_annotations | annotations)
+        prev_call_location = self._call_location
         self._call_location = self._caller
 
         self.iterate_children(node_children,
                               self.dispatch_node_inside_definition)
 
-        self._call_location = None
+        self._call_location = prev_call_location
+        self._caller = prev_call_location
 
         return None
 
@@ -826,7 +833,7 @@ class TopDownSummaryPrinter():
             elif func.reason == DiagnosticKind.NON_PURE_CALL_IN_PURE_CTX:
                 name += "is pure but calls non-pure function(s)"
             elif func.reason == DiagnosticKind.NON_STABLE_TREE_CALL_IN_STABLE_TREE_CTX:
-                name += "calls stable_tree function(s) but isn't annotated as stable_tree"
+                name += "is stable_tree but calls non-stable_tree or non-mtsafe"
             else:
                 name += "for unknown reason (please add description)"
 
diff --git a/src/V3Active.cpp b/src/V3Active.cpp
index a333f65f7..87194907f 100644
--- a/src/V3Active.cpp
+++ b/src/V3Active.cpp
@@ -54,7 +54,7 @@ private:
     const string m_name;  // Only used for .dot file generation
     const VertexType m_type;  // Vertex type (BLOCK/BRANCH/OUTPUT)
 
-    string typestr() const {  //   "
+    string typestr() const VL_MT_SAFE {  //   "
         switch (m_type) {
         case VT_BLOCK: return "(||)";  // basic block node
         case VT_BRANCH: return "(&&)";  // if/else branch mode
diff --git a/src/V3Ast.cpp b/src/V3Ast.cpp
index e19729116..dcc43148c 100644
--- a/src/V3Ast.cpp
+++ b/src/V3Ast.cpp
@@ -285,7 +285,7 @@ string AstNode::vpiName(const string& namein) {
     return pretty;
 }
 
-string AstNode::prettyTypeName() const {
+string AstNode::prettyTypeName() const VL_MT_STABLE {
     if (name() == "") return typeName();
     return std::string{typeName()} + " '" + prettyName() + "'";
 }
diff --git a/src/V3Ast.h b/src/V3Ast.h
index ea3c1bb61..6a286bde8 100644
--- a/src/V3Ast.h
+++ b/src/V3Ast.h
@@ -470,7 +470,7 @@ public:
         _ENUM_MAX
     };
     enum en m_e;
-    const char* ascii() const {
+    const char* ascii() const VL_MT_SAFE {
         static const char* const names[] = {"%E-unk",
                                             "bit",
                                             "byte",
@@ -1693,13 +1693,14 @@ public:
     static string prettyNameQ(const string& namein) {  // Quoted pretty name (for errors)
         return std::string{"'"} + prettyName(namein) + "'";
     }
-    static string
-    encodeName(const string& namein);  // Encode user name into internal C representation
+    // Encode user name into internal C representation
+    static string encodeName(const string& namein);
     static string encodeNumber(int64_t num);  // Encode number into internal C representation
     static string vcdName(const string& namein);  // Name for printing out to vcd files
     string prettyName() const VL_MT_STABLE { return prettyName(name()); }
     string prettyNameQ() const { return prettyNameQ(name()); }
-    string prettyTypeName() const;  // "VARREF" for error messages (NOT dtype's pretty name)
+    // "VARREF" for error messages (NOT dtype's pretty name)
+    string prettyTypeName() const VL_MT_STABLE;
     virtual string prettyOperatorName() const { return "operator " + prettyTypeName(); }
     FileLine* fileline() const VL_MT_SAFE { return m_fileline; }
     void fileline(FileLine* fl) { m_fileline = fl; }
diff --git a/src/V3AstNodeOther.h b/src/V3AstNodeOther.h
index e923385d3..cff2cfdbe 100644
--- a/src/V3AstNodeOther.h
+++ b/src/V3AstNodeOther.h
@@ -1151,7 +1151,7 @@ public:
     void cloneRelink() override { V3ERROR_NA; }
     string name() const override VL_MT_STABLE { return "$root"; }
     void dump(std::ostream& str) const override;
-    AstNodeModule* topModulep() const {  // Top module in hierarchy
+    AstNodeModule* topModulep() const VL_MT_STABLE {  // Top module in hierarchy
         return modulesp();  // First one in the list, for now
     }
     AstTypeTable* typeTablep() { return m_typeTablep; }
@@ -1789,7 +1789,7 @@ public:
     string dpiTmpVarType(const string& varName) const;
     // Return Verilator internal type for argument: CData, SData, IData, WData
     string vlArgType(bool named, bool forReturn, bool forFunc, const string& namespc = "",
-                     bool asRef = false) const VL_MT_SAFE;
+                     bool asRef = false) const VL_MT_STABLE;
     string vlEnumType() const;  // Return VerilatorVarType: VLVT_UINT32, etc
     string vlEnumDir() const;  // Return VerilatorVarDir: VLVD_INOUT, etc
     string vlPropDecl(const string& propName) const;  // Return VerilatorVarProps declaration
@@ -2001,8 +2001,8 @@ public:
     string name() const override VL_MT_STABLE { return scopep()->name() + "->" + varp()->name(); }
     void dump(std::ostream& str) const override;
     bool hasDType() const override { return true; }
-    AstVar* varp() const { return m_varp; }  // [After Link] Pointer to variable
-    AstScope* scopep() const { return m_scopep; }  // Pointer to scope it's under
+    AstVar* varp() const VL_MT_STABLE { return m_varp; }  // [After Link] Pointer to variable
+    AstScope* scopep() const VL_MT_STABLE { return m_scopep; }  // Pointer to scope it's under
     void scopep(AstScope* nodep) { m_scopep = nodep; }
     bool isTrace() const { return m_trace; }
     void trace(bool flag) { m_trace = flag; }
diff --git a/src/V3AstNodes.cpp b/src/V3AstNodes.cpp
index a88ef0a06..3ebd67499 100644
--- a/src/V3AstNodes.cpp
+++ b/src/V3AstNodes.cpp
@@ -397,7 +397,7 @@ string AstVar::verilogKwd() const {
 }
 
 string AstVar::vlArgType(bool named, bool forReturn, bool forFunc, const string& namespc,
-                         bool asRef) const VL_MT_SAFE {
+                         bool asRef) const VL_MT_STABLE {
     UASSERT_OBJ(!forReturn, this,
                 "Internal data is never passed as return, but as first argument");
     string ostatic;
diff --git a/src/V3EmitCBase.h b/src/V3EmitCBase.h
index e3c001be9..5ae0074c4 100644
--- a/src/V3EmitCBase.h
+++ b/src/V3EmitCBase.h
@@ -55,14 +55,14 @@ public:
         return className + "* const __restrict vlSelf VL_ATTR_UNUSED = static_cast<" + className
                + "*>(voidSelf);\n";
     }
-    static string symClassName() {
+    static string symClassName() VL_MT_STABLE {
         return v3Global.opt.prefix() + "_" + VIdProtect::protect("_Syms");
     }
     static string symClassVar() { return symClassName() + "* __restrict vlSymsp"; }
     static string symClassAssign() {
         return symClassName() + "* const __restrict vlSymsp VL_ATTR_UNUSED = vlSelf->vlSymsp;\n";
     }
-    static string prefixNameProtect(const AstNode* nodep) VL_MT_SAFE {  // C++ name with prefix
+    static string prefixNameProtect(const AstNode* nodep) VL_MT_STABLE {  // C++ name with prefix
         return v3Global.opt.modPrefix() + "_" + VIdProtect::protect(nodep->name());
     }
     static bool isAnonOk(const AstVar* varp) {
diff --git a/src/V3FileLine.h b/src/V3FileLine.h
index 0bf14ae3f..8f1cf140b 100644
--- a/src/V3FileLine.h
+++ b/src/V3FileLine.h
@@ -165,7 +165,7 @@ private:
         static FileLineSingleton s;
         return s;
     }
-    static FileLine& defaultFileLine() {
+    static FileLine& defaultFileLine() VL_MT_SAFE {
         static FileLine s;
         return s;
     }
@@ -364,7 +364,7 @@ public:
 private:
     string warnContext() const;
     string warnContextParent() const VL_REQUIRES(V3Error::s().m_mutex);
-    const MsgEnBitSet& msgEn() const { return singleton().msgEn(m_msgEnIdx); }
+    const MsgEnBitSet& msgEn() const VL_MT_SAFE { return singleton().msgEn(m_msgEnIdx); }
 };
 std::ostream& operator<<(std::ostream& os, FileLine* fileline);
 
diff --git a/src/V3Gate.cpp b/src/V3Gate.cpp
index 2929916bc..640cade21 100644
--- a/src/V3Gate.cpp
+++ b/src/V3Gate.cpp
@@ -76,7 +76,7 @@ public:
     ~GateEitherVertex() override = default;
     // ACCESSORS
     string dotStyle() const override { return m_consumed ? "" : "dotted"; }
-    AstScope* scopep() const { return m_scopep; }
+    AstScope* scopep() const VL_MT_STABLE { return m_scopep; }
     bool reducible() const { return m_reducible; }
     bool dedupable() const { return m_dedupable; }
     void setConsumed(const char* /*consumedReason*/) {
@@ -133,7 +133,7 @@ public:
         , m_varScp{varScp} {}
     ~GateVarVertex() override = default;
     // ACCESSORS
-    AstVarScope* varScp() const { return m_varScp; }
+    AstVarScope* varScp() const VL_MT_STABLE { return m_varScp; }
     string name() const override VL_MT_STABLE {
         return (cvtToHex(m_varScp) + " " + varScp()->name());
     }
diff --git a/src/V3Number.cpp b/src/V3Number.cpp
index 3a80da8c2..9e5e295c5 100644
--- a/src/V3Number.cpp
+++ b/src/V3Number.cpp
@@ -385,7 +385,7 @@ void V3Number::create(const char* sourcep) {
     // m_value[0]);
 }
 
-void V3Number::nodep(AstNode* nodep) {
+void V3Number::nodep(AstNode* nodep) VL_MT_STABLE {
     m_nodep = nodep;
     if (!nodep) return;
     m_fileline = nodep->fileline();
@@ -498,7 +498,7 @@ V3Number& V3Number::setMask(int nbits) {
 //======================================================================
 // ACCESSORS - as strings
 
-string V3Number::ascii(bool prefixed, bool cleanVerilog) const VL_MT_SAFE {
+string V3Number::ascii(bool prefixed, bool cleanVerilog) const VL_MT_STABLE {
     std::ostringstream out;
 
     if (is1Step()) {
@@ -604,11 +604,11 @@ string V3Number::displayPad(size_t fmtsize, char pad, bool left, const string& i
     return left ? (in + padding) : (padding + in);
 }
 
-string V3Number::displayed(AstNode* nodep, const string& vformat) const VL_MT_SAFE {
+string V3Number::displayed(AstNode* nodep, const string& vformat) const VL_MT_STABLE {
     return displayed(nodep->fileline(), vformat);
 }
 
-string V3Number::displayed(FileLine* fl, const string& vformat) const VL_MT_SAFE {
+string V3Number::displayed(FileLine* fl, const string& vformat) const VL_MT_STABLE {
     auto pos = vformat.cbegin();
     UASSERT(pos != vformat.cend() && pos[0] == '%',
             "$display-like function with non format argument " << *this);
@@ -847,7 +847,7 @@ string V3Number::displayed(FileLine* fl, const string& vformat) const VL_MT_SAFE
     }
 }
 
-string V3Number::toDecimalS() const {
+string V3Number::toDecimalS() const VL_MT_STABLE {
     if (isNegative()) {
         V3Number lhsNoSign = *this;
         lhsNoSign.opNegate(*this);
@@ -857,7 +857,7 @@ string V3Number::toDecimalS() const {
     }
 }
 
-string V3Number::toDecimalU() const {
+string V3Number::toDecimalU() const VL_MT_STABLE {
     const int maxdecwidth = (width() + 3) * 4 / 3;
 
     // Or (maxdecwidth+7)/8], but can't have more than 4 BCD bits per word
@@ -1013,7 +1013,7 @@ bool V3Number::isAllX() const VL_MT_SAFE {
     }
     return true;
 }
-bool V3Number::isEqZero() const {
+bool V3Number::isEqZero() const VL_MT_SAFE {
     if (isString()) return m_data.str().empty();
     for (int i = 0; i < words(); i++) {
         const ValueAndX v = m_data.num()[i];
diff --git a/src/V3Number.h b/src/V3Number.h
index b94a212fb..46ba16094 100644
--- a/src/V3Number.h
+++ b/src/V3Number.h
@@ -52,7 +52,7 @@ public:
         uint32_t m_value;
         // Each bit is true if it's X or Z, 10=z, 11=x
         uint32_t m_valueX;
-        bool operator==(const ValueAndX& other) const {
+        bool operator==(const ValueAndX& other) const VL_MT_SAFE {
             return m_value == other.m_value && m_valueX == other.m_valueX;
         }
     };
@@ -210,7 +210,7 @@ public:
         UASSERT(isString(), "`str` member accessed when data type is " << m_type);
         return m_string;
     }
-    const std::string& str() const {
+    const std::string& str() const VL_MT_SAFE {
         UASSERT(isString(), "`str` member accessed when data type is " << m_type);
         return m_string;
     }
@@ -356,7 +356,7 @@ class V3Number final {
     void opCleanThis(bool warnOnTruncation = false);
 
 public:
-    void nodep(AstNode* nodep);
+    void nodep(AstNode* nodep) VL_MT_STABLE;
     FileLine* fileline() const VL_MT_SAFE { return m_fileline; }
     V3Number& setZero();
     V3Number& setQuad(uint64_t value);
@@ -560,8 +560,8 @@ private:
         }
     }
     static string displayPad(size_t fmtsize, char pad, bool left, const string& in) VL_PURE;
-    string displayed(FileLine* fl, const string& vformat) const VL_MT_SAFE;
-    string displayed(const string& vformat) const VL_MT_SAFE {
+    string displayed(FileLine* fl, const string& vformat) const VL_MT_STABLE;
+    string displayed(const string& vformat) const VL_MT_STABLE {
         return displayed(m_fileline, vformat);
     }
 
@@ -583,8 +583,8 @@ public:
     V3Number& setMask(int nbits);  // IE if nbits=1, then 0b1, if 2->0b11, if 3->0b111 etc
 
     // ACCESSORS
-    string ascii(bool prefixed = true, bool cleanVerilog = false) const VL_MT_SAFE;
-    string displayed(AstNode* nodep, const string& vformat) const VL_MT_SAFE;
+    string ascii(bool prefixed = true, bool cleanVerilog = false) const VL_MT_STABLE;
+    string displayed(AstNode* nodep, const string& vformat) const VL_MT_STABLE;
     static bool displayedFmtLegal(char format, bool isScan);  // Is this a valid format letter?
     int width() const VL_MT_SAFE { return m_data.width(); }
     int widthMin() const;  // Minimum width that can represent this number (~== log2(num)+1)
@@ -612,7 +612,7 @@ public:
         return m_data.type() == V3NumberDataType::LOGIC
                || m_data.type() == V3NumberDataType::DOUBLE;
     }
-    bool isNegative() const { return !isString() && bitIs1(width() - 1); }
+    bool isNegative() const VL_MT_SAFE { return !isString() && bitIs1(width() - 1); }
     bool is1Step() const VL_MT_SAFE { return m_data.m_is1Step; }
     bool isNull() const VL_MT_SAFE { return m_data.m_isNull; }
     bool isFourState() const VL_MT_SAFE;
@@ -626,7 +626,7 @@ public:
     }
     bool isAllZ() const VL_MT_SAFE;
     bool isAllX() const VL_MT_SAFE;
-    bool isEqZero() const;
+    bool isEqZero() const VL_MT_SAFE;
     bool isNeqZero() const;
     bool isBitsZero(int msb, int lsb) const;
     bool isEqOne() const;
@@ -642,8 +642,8 @@ public:
     uint64_t toUQuad() const VL_MT_SAFE;
     int64_t toSQuad() const VL_MT_SAFE;
     string toString() const VL_MT_SAFE;
-    string toDecimalS() const;  // return ASCII signed decimal number
-    string toDecimalU() const;  // return ASCII unsigned decimal number
+    string toDecimalS() const VL_MT_STABLE;  // return ASCII signed decimal number
+    string toDecimalU() const VL_MT_STABLE;  // return ASCII unsigned decimal number
     double toDouble() const VL_MT_SAFE;
     V3Hash toHash() const;
     uint32_t edataWord(int eword) const;
diff --git a/src/V3OrderGraph.h b/src/V3OrderGraph.h
index c1e3f2a91..d51a540a0 100644
--- a/src/V3OrderGraph.h
+++ b/src/V3OrderGraph.h
@@ -123,7 +123,7 @@ public:
     virtual bool domainMatters() = 0;
 
     // ACCESSORS
-    AstSenTree* domainp() const { return m_domainp; }
+    AstSenTree* domainp() const VL_MT_STABLE { return m_domainp; }
     void domainp(AstSenTree* domainp) {
 #if VL_DEBUG
         UASSERT(!m_domainp, "Domain should only be set once");
@@ -154,8 +154,8 @@ public:
     bool domainMatters() override { return true; }
 
     // ACCESSORS
-    AstNode* nodep() const { return m_nodep; }
-    AstScope* scopep() const { return m_scopep; }
+    AstNode* nodep() const VL_MT_STABLE { return m_nodep; }
+    AstScope* scopep() const VL_MT_STABLE { return m_scopep; }
     AstSenTree* hybridp() const { return m_hybridp; }
 
     // LCOV_EXCL_START // Debug code
@@ -181,7 +181,7 @@ public:
 
     // LCOV_EXCL_START // Debug code
     string dotShape() const override final { return "ellipse"; }
-    virtual string nameSuffix() const = 0;
+    virtual string nameSuffix() const VL_MT_SAFE = 0;
     string name() const override final VL_MT_STABLE {
         return cvtToHex(m_vscp) + " " + nameSuffix() + "\\n " + m_vscp->name();
     }
@@ -199,7 +199,7 @@ public:
     bool domainMatters() override { return true; }
 
     // LCOV_EXCL_START // Debug code
-    string nameSuffix() const override { return ""; }
+    string nameSuffix() const override VL_MT_SAFE { return ""; }
     string dotColor() const override { return "grey"; }
     // LCOV_EXCL_STOP
 };
@@ -215,7 +215,7 @@ public:
     bool domainMatters() override { return false; }
 
     // LCOV_EXCL_START // Debug code
-    string nameSuffix() const override { return "PRE"; }
+    string nameSuffix() const override VL_MT_SAFE { return "PRE"; }
     string dotColor() const override { return "green"; }
     // LCOV_EXCL_STOP
 };
@@ -231,7 +231,7 @@ public:
     bool domainMatters() override { return false; }
 
     // LCOV_EXCL_START // Debug code
-    string nameSuffix() const override { return "POST"; }
+    string nameSuffix() const override VL_MT_SAFE { return "POST"; }
     string dotColor() const override { return "red"; }
     // LCOV_EXCL_STOP
 };
@@ -247,7 +247,7 @@ public:
     bool domainMatters() override { return false; }
 
     // LCOV_EXCL_START // Debug code
-    string nameSuffix() const override { return "PORD"; }
+    string nameSuffix() const override VL_MT_SAFE { return "PORD"; }
     string dotColor() const override { return "blue"; }
     // LCOV_EXCL_STOP
 };
diff --git a/src/V3OrderMoveGraph.h b/src/V3OrderMoveGraph.h
index 426b410ff..fb54ac7a0 100644
--- a/src/V3OrderMoveGraph.h
+++ b/src/V3OrderMoveGraph.h
@@ -75,7 +75,7 @@ public:
         }
         return nm;
     }
-    OrderLogicVertex* logicp() const { return m_logicp; }
+    OrderLogicVertex* logicp() const VL_MT_STABLE { return m_logicp; }
     bool isWait() const { return m_state == POM_WAIT; }
     void setReady() {
         UASSERT(m_state == POM_WAIT, "Wait->Ready on node not in proper state");
diff --git a/src/V3Partition.cpp b/src/V3Partition.cpp
index 04d34e842..a10ffec1c 100644
--- a/src/V3Partition.cpp
+++ b/src/V3Partition.cpp
@@ -268,7 +268,7 @@ public:
     uint32_t id() const override { return m_serialId; }
     void id(uint32_t id) { m_serialId = id; }
     // Abstract cost of every logic mtask
-    uint32_t cost() const override { return m_cost; }
+    uint32_t cost() const override VL_MT_SAFE { return m_cost; }
     void setCost(uint32_t cost) { m_cost = cost; }  // For tests only
     uint32_t stepCost() const { return stepCost(m_cost); }
     static uint32_t stepCost(uint32_t cost) {
diff --git a/src/V3PartitionGraph.h b/src/V3PartitionGraph.h
index b83679a06..0827ca381 100644
--- a/src/V3PartitionGraph.h
+++ b/src/V3PartitionGraph.h
@@ -72,7 +72,7 @@ public:
         , m_bodyp{bodyp}
         , m_id{id} {}
     AstMTaskBody* bodyp() const { return m_bodyp; }
-    uint32_t id() const override { return m_id; }
+    uint32_t id() const override VL_MT_SAFE { return m_id; }
     uint32_t priority() const { return m_priority; }
     void priority(uint32_t pri) { m_priority = pri; }
     uint32_t cost() const override { return m_cost; }
diff --git a/src/V3ThreadPool.h b/src/V3ThreadPool.h
index c7f92195a..69e093fcc 100644
--- a/src/V3ThreadPool.h
+++ b/src/V3ThreadPool.h
@@ -85,8 +85,14 @@ public:
     void resize(unsigned n) VL_MT_UNSAFE;
 
     // Enqueue a job for asynchronous execution
+    // Due to missing support for lambda annotations in c++11,
+    // `clang_check_attributes` script assumes that if
+    // function takes `std::function` as argument, it
+    // will call it. `VL_MT_START` here indicates that
+    // every function call inside this `std::function` requires
+    // annotations.
     template <typename T>
-    std::future<T> enqueue(std::function<T()>&& f) VL_MT_SAFE;
+    std::future<T> enqueue(std::function<T()>&& f) VL_MT_START;
 
     // Request exclusive access to processing.
     // It sends request to stop all other threads and waits for them to stop.
@@ -190,7 +196,7 @@ T V3ThreadPool::waitForFuture(std::future<T>& future) VL_MT_SAFE_EXCLUDES(m_mute
 }
 
 template <typename T>
-std::future<T> V3ThreadPool::enqueue(std::function<T()>&& f) VL_MT_SAFE {
+std::future<T> V3ThreadPool::enqueue(std::function<T()>&& f) VL_MT_START {
     std::shared_ptr<std::promise<T>> prom = std::make_shared<std::promise<T>>();
     std::future<T> result = prom->get_future();
     pushJob(prom, std::move(f));
diff --git a/src/V3Timing.cpp b/src/V3Timing.cpp
index afbba68f5..a71ad592e 100644
--- a/src/V3Timing.cpp
+++ b/src/V3Timing.cpp
@@ -81,7 +81,7 @@ private:
         ~DependencyVertex() override = default;
 
         // ACCESSORS
-        virtual AstNode* nodep() const { return m_nodep; }
+        virtual AstNode* nodep() const VL_MT_STABLE { return m_nodep; }
     };
 
     // NODE STATE
diff --git a/src/V3Tristate.cpp b/src/V3Tristate.cpp
index 0028d2bc8..61720c2a4 100644
--- a/src/V3Tristate.cpp
+++ b/src/V3Tristate.cpp
@@ -152,7 +152,7 @@ public:
         , m_nodep{nodep} {}
     ~TristateVertex() override = default;
     // ACCESSORS
-    AstNode* nodep() const { return m_nodep; }
+    AstNode* nodep() const VL_MT_STABLE { return m_nodep; }
     const AstVar* varp() const { return VN_CAST(nodep(), Var); }
     string name() const override VL_MT_STABLE {
         return ((isTristate() ? "tri\\n"
@@ -170,9 +170,9 @@ public:
     }
     FileLine* fileline() const override { return nodep()->fileline(); }
     void isTristate(bool flag) { m_isTristate = flag; }
-    bool isTristate() const { return m_isTristate; }
+    bool isTristate() const VL_MT_SAFE { return m_isTristate; }
     void feedsTri(bool flag) { m_feedsTri = flag; }
-    bool feedsTri() const { return m_feedsTri; }
+    bool feedsTri() const VL_MT_SAFE { return m_feedsTri; }
     void processed(bool flag) { m_processed = flag; }
     bool processed() const { return m_processed; }
 };
diff --git a/test_regress/t/t_dist_attributes_bad.out b/test_regress/t/t_dist_attributes_bad.out
index e7649a02f..fea14b7b0 100644
--- a/test_regress/t/t_dist_attributes_bad.out
+++ b/test_regress/t/t_dist_attributes_bad.out
@@ -65,7 +65,7 @@ t/t_dist_attributes_bad.h:204:    [mt_unsafe_one]                        TestCla
 t/t_dist_attributes_bad.h:209:    [mt_safe, mt_unsafe, pure]             TestClass::cm_ea_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:209:    [mt_safe, mt_unsafe_one, pure]         TestClass::cm_ea_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::cm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::cm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.cpp:155:  [mt_start]                           TestClass::cm_test_caller_smethod_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:191:    [mt_unsafe]                            TestClass::cm_au_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:191:    [mt_unsafe_one]                        TestClass::cm_au_VL_MT_UNSAFE_ONE(VerilatedMutex &)
@@ -143,7 +143,7 @@ t/t_dist_attributes_bad.h:204:    [mt_unsafe_one]                        TestCla
 t/t_dist_attributes_bad.h:209:    [mt_safe, mt_unsafe, pure]             TestClass::cm_ea_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:209:    [mt_safe, mt_unsafe_one, pure]         TestClass::cm_ea_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::cm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::cm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.h:212:    [mt_start]                           TestClass::cm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:191:    [mt_unsafe]                            TestClass::cm_au_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:191:    [mt_unsafe_one]                        TestClass::cm_au_VL_MT_UNSAFE_ONE(VerilatedMutex &)
@@ -273,7 +273,7 @@ t/t_dist_attributes_bad.cpp:175:  [mt_safe]                            TestClass
 t/t_dist_attributes_bad.h:235:    [mt_unsafe]                            TestClass::icm_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:235:    [mt_unsafe_one]                        TestClass::icm_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::icm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::icm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.cpp:175:  [mt_start]                           TestClass::icm_test_caller_smethod_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:235:    [mt_unsafe]                            TestClass::icm_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:235:    [mt_unsafe_one]                        TestClass::icm_VL_MT_UNSAFE_ONE(VerilatedMutex &)
@@ -299,7 +299,7 @@ t/t_dist_attributes_bad.h:238:    [mt_safe]                            TestClass
 t/t_dist_attributes_bad.h:235:    [mt_unsafe]                            TestClass::icm_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:235:    [mt_unsafe_one]                        TestClass::icm_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::icm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::icm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.h:238:    [mt_start]                           TestClass::icm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:235:    [mt_unsafe]                            TestClass::icm_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:235:    [mt_unsafe_one]                        TestClass::icm_VL_MT_UNSAFE_ONE(VerilatedMutex &)
@@ -327,7 +327,7 @@ t/t_dist_attributes_bad.h:170:    [mt_start]                             TestCla
 t/t_dist_attributes_bad.h:170:    [mt_unsafe]                            TestClass::iscm_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:170:    [mt_unsafe_one]                        TestClass::iscm_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::iscm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::iscm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.cpp:119:  [mt_start]                           TestClass::iscm_test_caller_smethod_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:170:    []                                     TestClass::iscm_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:170:    [mt_start]                             TestClass::iscm_VL_MT_START(VerilatedMutex &)
@@ -357,7 +357,7 @@ t/t_dist_attributes_bad.h:170:    [mt_start]                             TestCla
 t/t_dist_attributes_bad.h:170:    [mt_unsafe]                            TestClass::iscm_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:170:    [mt_unsafe_one]                        TestClass::iscm_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::iscm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::iscm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.h:173:    [mt_start]                           TestClass::iscm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:170:    []                                     TestClass::iscm_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:170:    [mt_start]                             TestClass::iscm_VL_MT_START(VerilatedMutex &)
@@ -467,7 +467,7 @@ t/t_dist_attributes_bad.h:133:    [mt_unsafe_one]                        TestCla
 t/t_dist_attributes_bad.h:138:    [mt_safe, mt_unsafe, pure]             TestClass::scm_ea_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:138:    [mt_safe, mt_unsafe_one, pure]         TestClass::scm_ea_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::scm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::scm_test_caller_smethod_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.cpp:93:   [mt_start]                           TestClass::scm_test_caller_smethod_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:120:    []                                     TestClass::scm_au_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:120:    [mt_start]                             TestClass::scm_au_VL_MT_START(VerilatedMutex &)
@@ -585,7 +585,7 @@ t/t_dist_attributes_bad.h:133:    [mt_unsafe_one]                        TestCla
 t/t_dist_attributes_bad.h:138:    [mt_safe, mt_unsafe, pure]             TestClass::scm_ea_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:138:    [mt_safe, mt_unsafe_one, pure]         TestClass::scm_ea_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "TestClass::scm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "TestClass::scm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.h:141:    [mt_start]                           TestClass::scm_test_caller_smethod_hdr_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:120:    []                                     TestClass::scm_au_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:120:    [mt_start]                             TestClass::scm_au_VL_MT_START(VerilatedMutex &)
@@ -759,7 +759,7 @@ t/t_dist_attributes_bad.h:94:     [mt_start]                             ifh_VL_
 t/t_dist_attributes_bad.h:94:     [mt_unsafe]                            ifh_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:94:     [mt_unsafe_one]                        ifh_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "ifh_test_caller_func_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "ifh_test_caller_func_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.cpp:53:   [mt_start]                           ifh_test_caller_func_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:94:     []                                     ifh_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:94:     [mt_start]                             ifh_VL_MT_START(VerilatedMutex &)
@@ -789,7 +789,7 @@ t/t_dist_attributes_bad.h:94:     [mt_start]                             ifh_VL_
 t/t_dist_attributes_bad.h:94:     [mt_unsafe]                            ifh_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:94:     [mt_unsafe_one]                        ifh_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "ifh_test_caller_func_hdr_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "ifh_test_caller_func_hdr_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.h:97:     [mt_start]                           ifh_test_caller_func_hdr_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:94:     []                                     ifh_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:94:     [mt_start]                             ifh_VL_MT_START(VerilatedMutex &)
@@ -899,7 +899,7 @@ t/t_dist_attributes_bad.h:75:     [mt_unsafe_one]                        nsf_ae_
 t/t_dist_attributes_bad.h:80:     [mt_safe, mt_unsafe, pure]             nsf_ea_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:80:     [mt_safe, mt_unsafe_one, pure]         nsf_ea_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "nsf_test_caller_func_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "nsf_test_caller_func_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.cpp:42:   [mt_start]                           nsf_test_caller_func_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:62:     []                                     nsf_au_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:62:     [mt_start]                             nsf_au_VL_MT_START(VerilatedMutex &)
@@ -1017,7 +1017,7 @@ t/t_dist_attributes_bad.h:75:     [mt_unsafe_one]                        nsf_ae_
 t/t_dist_attributes_bad.h:80:     [mt_safe, mt_unsafe, pure]             nsf_ea_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.h:80:     [mt_safe, mt_unsafe_one, pure]         nsf_ea_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "nsf_test_caller_func_hdr_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "nsf_test_caller_func_hdr_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.h:83:     [mt_start]                           nsf_test_caller_func_hdr_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.h:62:     []                                     nsf_au_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.h:62:     [mt_start]                             nsf_au_VL_MT_START(VerilatedMutex &)
@@ -1163,7 +1163,7 @@ t/t_dist_attributes_bad.cpp:60:   [mt_start]                             sfc_VL_
 t/t_dist_attributes_bad.cpp:60:   [mt_unsafe]                            sfc_VL_MT_UNSAFE(VerilatedMutex &)
 t/t_dist_attributes_bad.cpp:60:   [mt_unsafe_one]                        sfc_VL_MT_UNSAFE_ONE(VerilatedMutex &)
 
-%Error: "sfc_test_caller_func_VL_MT_START(VerilatedMutex &)" is mtsafe but calls non-mtsafe function(s)
+%Error: "sfc_test_caller_func_VL_MT_START(VerilatedMutex &)" is stable_tree but calls non-stable_tree or non-mtsafe
 t/t_dist_attributes_bad.cpp:63:   [mt_start]                           sfc_test_caller_func_VL_MT_START(VerilatedMutex &)
 t/t_dist_attributes_bad.cpp:60:   []                                     sfc_NO_ANNOTATION(VerilatedMutex &)
 t/t_dist_attributes_bad.cpp:60:   [mt_start]                             sfc_VL_MT_START(VerilatedMutex &)