3 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86_64/include/x86_64/cpu/control_register.hpp b/arch/x86_64/include/x86_64/cpu/control_register.hpp
index 9c3bad5..67ae87e 100644
--- a/arch/x86_64/include/x86_64/cpu/control_register.hpp
+++ b/arch/x86_64/include/x86_64/cpu/control_register.hpp
@@ -85,6 +85,9 @@ namespace teachos::cpu::x86_64
   template<typename Derived, typename ValueType, typename = void>
   struct control_register_with_flags
   {
+  private:
+    constexpr control_register_with_flags() noexcept = default;
+    friend Derived;
   };
 
   //! @copydoc control_register_with_flags
diff --git a/arch/x86_64/include/x86_64/cpu/model_specific_register.hpp b/arch/x86_64/include/x86_64/cpu/model_specific_register.hpp
index 857b444..39765fe 100644
--- a/arch/x86_64/include/x86_64/cpu/model_specific_register.hpp
+++ b/arch/x86_64/include/x86_64/cpu/model_specific_register.hpp
@@ -52,6 +52,9 @@ namespace teachos::cpu::x86_64
   template<typename Derived, typename ValueType, typename = void>
   struct model_specific_register_with_flags
   {
+  private:
+    constexpr model_specific_register_with_flags() noexcept = default;
+    friend Derived;
   };
 
   //! @copydoc model_specific_register_with_flags
diff --git a/arch/x86_64/include/x86_64/device_io/port_io.hpp b/arch/x86_64/include/x86_64/device_io/port_io.hpp
index c3e5271..295a0cd 100644
--- a/arch/x86_64/include/x86_64/device_io/port_io.hpp
+++ b/arch/x86_64/include/x86_64/device_io/port_io.hpp
@@ -38,6 +38,9 @@ namespace teachos::io::x86_64
     }
 
   private:
+    constexpr port_read() noexcept = default;
+    friend Derived;
+
     //! The assembly templates used for reading from an I/O port.
     constexpr auto static code = std::array{
       std::string_view{"mov %[port], %%dx\nin %%dx, %%al\nmov %%al, %[data]"},
@@ -61,6 +64,9 @@ namespace teachos::io::x86_64
     }
 
   private:
+    constexpr port_write() noexcept = default;
+    friend Derived;
+
     //! The assembly templates used for writing to an I/O port.
     constexpr auto static code = std::array{
       std::string_view{"mov %[port], %%dx\nmov %%dx, %[data]\nout %%al, %%dx"},