4 files changed, 110 insertions, 3 deletions
diff --git a/arch/x86_64/include/arch/context_switching/descriptor_table/global_descriptor_table.hpp b/arch/x86_64/include/arch/context_switching/descriptor_table/global_descriptor_table.hpp
index c4d0e30..ab8f1ac 100644
--- a/arch/x86_64/include/arch/context_switching/descriptor_table/global_descriptor_table.hpp
+++ b/arch/x86_64/include/arch/context_switching/descriptor_table/global_descriptor_table.hpp
@@ -2,12 +2,54 @@
 #define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_DESCRIPTOR_TABLE_GLOBAL_DESCRIPTOR_TABLE_HPP
 
 #include "arch/context_switching/descriptor_table/global_descriptor_table_pointer.hpp"
+#include "arch/context_switching/descriptor_table/task_state_segment.hpp"
 
 namespace teachos::arch::context_switching::descriptor_table
 {
+  enum class access_level
+  {
+    KERNEL,
+    USER
+  };
+
+  /**
+   * @brief Creates a generic segment_descriptor from the passed arguments.
+   *
+   * @param segment_descriptor_type Defines the type of the segment descriptor.
+   * @param access_level Defines the segment descriptor access level (KERNEL or USER).
+   * @return Created segment_descriptor.
+   */
+  auto create_segment_descriptor(segment_descriptor_type segment_descriptor_type, access_level access_level)
+      -> segment_descriptor;
+
+  /**
+   * @brief Creates a global_descriptor_table on the heap and fills it with the following segment registers:
+   *
+   * - Kernel Code Segment
+   * - Kernel Data Segment
+   * - User Code Segment
+   * - User Data Segment
+   *
+   * @return Created global_descriptor_table.
+   */
   auto create_global_descriptor_table() -> global_descriptor_table;
 
+  /**
+   * @brief Creates a task_state_segment segment_descriptor on the heap.
+   *
+   * @param tss task_state_segment whose pointer is used in the segment_descriptor
+   * @return Created segment_descriptor.
+   */
+  auto create_task_state_segment_descriptor(task_state_segment * tss) -> segment_descriptor;
+
+  /**
+   * @brief Initializes the global_descriptor_table and task_state_segment by loading them
+   * in the GDTR and TR registers respectively.
+   *
+   * @return Created global_descriptor_table.
+   */
   auto initialize_global_descriptor_table() -> global_descriptor_table;
+
 }  // namespace teachos::arch::context_switching::descriptor_table
 
 #endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_DESCRIPTOR_TABLE_GLOBAL_DESCRIPTOR_TABLE_HPP
diff --git a/arch/x86_64/include/arch/context_switching/descriptor_table/task_state_segment.hpp b/arch/x86_64/include/arch/context_switching/descriptor_table/task_state_segment.hpp
new file mode 100644
index 0000000..af7ae7c
--- /dev/null
+++ b/arch/x86_64/include/arch/context_switching/descriptor_table/task_state_segment.hpp
@@ -0,0 +1,39 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_DESCRIPTOR_TABLE_TASK_STATE_SEGMENT_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_DESCRIPTOR_TABLE_TASK_STATE_SEGMENT_HPP
+
+#include <cstdint>
+
+namespace teachos::arch::context_switching::descriptor_table
+{
+  /**
+   * @brief 64-bit task state segment
+   */
+  struct [[gnu::packed]] task_state_segment
+  {
+  private:
+    uint16_t io_map_base_address = {};
+
+    uint16_t reserved_1 = {};
+    uint32_t reserved_2 = {};
+    uint32_t reserved_3 = {};
+
+    uint64_t ist7 = {};
+    uint64_t ist6 = {};
+    uint64_t ist5 = {};
+    uint64_t ist4 = {};
+    uint64_t ist3 = {};
+    uint64_t ist2 = {};
+    uint64_t ist1 = {};
+
+    uint32_t reserved_4 = {};
+    uint32_t reserved_5 = {};
+
+    uint64_t rsp2 = {};
+    uint64_t rsp1 = {};
+    uint64_t rsp0 = {};
+
+    uint32_t reserved_6 = {};
+  };
+}  // namespace teachos::arch::context_switching::descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_DESCRIPTOR_TABLE_TASK_STATE_SEGMENT_HPP
+\ No newline at end of file
diff --git a/arch/x86_64/include/arch/kernel/cpu/lgdt.hpp b/arch/x86_64/include/arch/kernel/cpu/gdtr.hpp
index 85e2949..f9220b9 100644
--- a/arch/x86_64/include/arch/kernel/cpu/lgdt.hpp
+++ b/arch/x86_64/include/arch/kernel/cpu/gdtr.hpp
@@ -1,5 +1,5 @@
-#ifndef TEACHOS_ARCH_X86_64_KERNEL_CPU_LGDT_HPP
-#define TEACHOS_ARCH_X86_64_KERNEL_CPU_LGDT_HPP
+#ifndef TEACHOS_ARCH_X86_64_KERNEL_CPU_GDTR_HPP
+#define TEACHOS_ARCH_X86_64_KERNEL_CPU_GDTR_HPP
 
 #include "arch/context_switching/descriptor_table/global_descriptor_table_pointer.hpp"
 
@@ -25,4 +25,4 @@ namespace teachos::arch::kernel::cpu
 
 }  // namespace teachos::arch::kernel::cpu
 
-#endif  // TEACHOS_ARCH_X86_64_KERNEL_CPU_LGDT_HPP
+#endif  // TEACHOS_ARCH_X86_64_KERNEL_CPU_GDTR_HPP
diff --git a/arch/x86_64/include/arch/kernel/cpu/tr.hpp b/arch/x86_64/include/arch/kernel/cpu/tr.hpp
new file mode 100644
index 0000000..5f99472
--- /dev/null
+++ b/arch/x86_64/include/arch/kernel/cpu/tr.hpp
@@ -0,0 +1,26 @@
+#ifndef TEACHOS_ARCH_X86_64_KERNEL_CPU_TR_HPP
+#define TEACHOS_ARCH_X86_64_KERNEL_CPU_TR_HPP
+
+#include "arch/context_switching/descriptor_table/task_state_segment.hpp"
+
+#include <bitset>
+#include <cstdint>
+
+namespace teachos::arch::kernel::cpu
+{
+
+  /**
+   * @brief Returns the value in the LTR register.
+   *
+   * @return Value of LTR register.
+   */
+  auto store_task_register() -> uint16_t;
+
+  /**
+   * @brief Loads the tss_pointer into the task register (TR).
+   */
+  auto load_task_register(uint16_t gdt_offset) -> void;
+
+}  // namespace teachos::arch::kernel::cpu
+
+#endif  // TEACHOS_ARCH_X86_64_KERNEL_CPU_TR_HPP