Finish implementing 8-byte GDT entries and syscall arg loads.

16 files changed, 225 insertions, 232 deletions

diff --git a/arch/x86_64/CMakeLists.txt b/arch/x86_64/CMakeLists.txt
index 58afdb5..21dbddd 100644
--- a/arch/x86_64/CMakeLists.txt
+++ b/arch/x86_64/CMakeLists.txt
@@ -97,7 +97,6 @@ target_sources("_context" PRIVATE
   "src/context_switching/segment_descriptor_table/gdt_flags.cpp"
   "src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp"
   "src/context_switching/segment_descriptor_table/global_descriptor_table.cpp"
-  "src/context_switching/segment_descriptor_table/segment_descriptor.cpp"
   "src/context_switching/segment_descriptor_table/segment_descriptor_base.cpp"
   "src/context_switching/segment_descriptor_table/segment_descriptor_extension.cpp"
   "src/context_switching/main.cpp"
diff --git a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
index 8748448..5be449f 100644
--- a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
+++ b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
@@ -79,11 +79,11 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
     auto operator|=(std::bitset<3U> other) -> void;
 
     /**
-     * @brief Combines all bits in the underlying data in the correct order to return a raw value containing all bits.
+     * @brief Cast the underlying data into a combined 16-bit form, that contains all data.
      *
      * @return Underlying value combined into it's full size.
      */
-    operator uint16_t() const { return static_cast<uint64_t>(_flags) | (static_cast<uint64_t>(_index) << 3U); }
+    operator uint16_t() const;
 
   private:
     uint8_t _flags : 3 = {};  ///< Underlying bits used to read the flags from.
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table.hpp
index 84a24a2..44f2692 100644
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table.hpp
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table.hpp
@@ -30,7 +30,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
    * @note This method should only be called after update_gdtr() and a far jump has been
    * executed. Because before that trying to access the segment will cause an exception.
    */
-  auto update_task_state_segment_register() -> void;
+  auto update_tss_register() -> void;
 
 }  // namespace teachos::arch::context_switching::segment_descriptor_table
 
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp
index c54647d..292ff70 100644
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp
@@ -1,24 +1,13 @@
 #ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_GLOBAL_DESCRIPTOR_TABLE_POINTER_HPP
 #define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_GLOBAL_DESCRIPTOR_TABLE_POINTER_HPP
 
-#include "arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp"
-#include "arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp"
 #include "arch/stl/vector.hpp"
 
 #include <cstdint>
 
 namespace teachos::arch::context_switching::segment_descriptor_table
 {
-  struct __attribute__((packed, aligned(8))) global_descriptor_table
-  {
-    segment_descriptor_base null;
-    segment_descriptor_base kernel_code;
-    segment_descriptor_base kernel_data;
-    segment_descriptor_base user_code;
-    segment_descriptor_base user_data;
-    segment_descriptor_base tss_low;
-    segment_descriptor_extension tss_high;
-  };
+  using global_descriptor_table = stl::vector<uint64_t>;
 
   /**
    * @brief Represents a pointer to the Global Descriptor Table (GDT).
@@ -36,7 +25,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
     /**
      * @brief Constructor.
      */
-    global_descriptor_table_pointer(uint16_t table_length, seg_desc * address);
+    global_descriptor_table_pointer(uint16_t table_length, uint64_t * address);
 
     /**
      * @brief Defaulted three-way comparsion operator.
@@ -45,7 +34,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
 
   private:
     uint16_t table_length = {};  ///< The amount of segment descriptor entries in the global descriptor table - 1.
-    seg_desc * address = {};     ///< Non-owning pointer to the GDT base address.
+    uint64_t * address = {};     ///< Non-owning pointer to the GDT base address.
   };
 }  // namespace teachos::arch::context_switching::segment_descriptor_table
 
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor.hpp
deleted file mode 100644
index ccd604d..0000000
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor.hpp
+++ /dev/null
@@ -1,83 +0,0 @@
-#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_HPP
-#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_HPP
-
-#include "arch/context_switching/segment_descriptor_table/access_byte.hpp"
-#include "arch/context_switching/segment_descriptor_table/gdt_flags.hpp"
-#include "arch/context_switching/segment_descriptor_table/segment_descriptor_type.hpp"
-
-namespace teachos::arch::context_switching::segment_descriptor_table
-{
-  __extension__ typedef __int128 int128_t;
-  __extension__ typedef unsigned __int128 uint128_t;
-
-  struct seg_desc
-  {
-  private:
-    uint64_t : 64;  ///< Makes sure the struct is 8-Bytes big
-  };
-
-  /**
-   * @brief Defines helper function for all states and the actual data the segment descriptor can have.
-   */
-  struct [[gnu::packed]] segment_descriptor
-  {
-    /**
-     * @brief Default Constructor.
-     */
-    segment_descriptor() = default;
-
-    /**
-     * @brief Constructor.
-     *
-     * @note Created segment descriptor copies the given bytes into theese components ending with a 32 bit reserved
-     * field that has to be used, because the 64-bit segment descriptor needs to be big enough for two 32-bit segment
-     * descriptor.
-     * - 8 bit Access Type
-     * - 4 bit Flags
-     * - 64 bit Base Address
-     * - 20 bit Limit
-     *
-     * @param flags Copies the bits set from the given data into the individual components of a segment
-     * descriptor.
-     */
-    explicit segment_descriptor(uint128_t flags);
-
-    /**
-     * @brief Constructor.
-     *
-     * @param access_byte, flags, base, limit Copies the bits set from the given data into the individual components of
-     * a segment descriptor.
-     */
-    segment_descriptor(access_byte access_byte, gdt_flags flags, uint64_t base, std::bitset<20U> limit);
-
-    auto get_limit_1() -> uint16_t;
-    auto get_base_1() -> uint32_t;
-    auto get_access() -> access_byte;
-    auto get_flag() -> gdt_flags;
-    auto get_base_2() -> uint64_t;
-
-    /**
-     * @brief Calculates the underlying segment type that this segement descriptor is describing.
-     */
-    auto get_segment_type() const -> segment_descriptor_type;
-
-    /**
-     * @brief Allows to compare the underlying bits of two instances.
-     *
-     * @param other Other instance that we want to compare with.
-     * @return Whether the underlying set bits of both types are the same.
-     */
-    auto operator==(segment_descriptor const & other) const -> bool = default;
-
-  private:
-    // The order in private variables starts for the first variable being the rightmost bit.
-    uint16_t _limit_1 = {};      ///< First part of the limit field (0 - 15)
-    uint32_t _base_1 : 24 = {};  ///< First part of the base field (16 - 39)
-    access_byte _access = {};    ///< Access byte field (40 - 47)
-    gdt_flags _flag = {};        ///< Second part of the limit field + Flags field (48 - 55)
-    uint64_t _base_2 : 40 = {};  ///< Second part of the base field (56 - 95)
-    uint32_t : 32;               ///< Reserved field used to ensure this struct is 128 bits big (96 - 127)
-  };
-}  // namespace teachos::arch::context_switching::segment_descriptor_table
-
-#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_HPP
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp
index 18c9da1..933fb4d 100644
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp
@@ -3,7 +3,6 @@
 
 #include "arch/context_switching/segment_descriptor_table/access_byte.hpp"
 #include "arch/context_switching/segment_descriptor_table/gdt_flags.hpp"
-#include "arch/context_switching/segment_descriptor_table/segment_descriptor.hpp"
 #include "arch/context_switching/segment_descriptor_table/segment_descriptor_type.hpp"
 
 namespace teachos::arch::context_switching::segment_descriptor_table
@@ -11,7 +10,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
   /**
    * @brief Defines helper function for all states and the actual data the segment descriptor can have.
    */
-  struct [[gnu::packed]] segment_descriptor_base : seg_desc
+  struct [[gnu::packed]] segment_descriptor_base
   {
     /**
      * @brief Default Constructor.
@@ -20,14 +19,54 @@ namespace teachos::arch::context_switching::segment_descriptor_table
 
     /**
      * @brief Constructor.
+     *
+     * @note Created segment descriptor copies the given bytes into these components requiring the space of one
+     * segment descriptor entry in the global descriptor table being 64-bit.
+     * - 8 bit Access Type
+     * - 4 bit Flags
+     * - 32 bit Base Address
+     * - 20 bit Limit
+     *
+     * @param flags Copies the bits set from the given data into the individual components of a segment
+     * descriptor.
      */
-    segment_descriptor_base(segment_descriptor segment_descriptor);
+    explicit segment_descriptor_base(uint64_t flags);
+
+    /**
+     * @brief Constructor.
+     *
+     * @param access_byte, flags, base, limit Copies the bits set from the given data into the individual components of
+     * a segment descriptor.
+     */
+    segment_descriptor_base(access_byte access_byte, gdt_flags flags, uint32_t base, std::bitset<20U> limit);
+
+    /**
+     * @brief Calculates the underlying segment type that this segement descriptor is describing.
+     */
+    auto get_segment_type() const -> segment_descriptor_type;
+
+    /**
+     * @brief Cast the underlying data into a combined 64-bit form, that contains all data.
+     *
+     * @return Underlying value combined into it's full size.
+     */
+    operator uint64_t() const;
+
+    /**
+     * @brief Allows to compare the underlying bits of two instances.
+     *
+     * @param other Other instance that we want to compare with.
+     * @return Whether the underlying set bits of both types are the same.
+     */
+    auto operator==(segment_descriptor_base const & other) const -> bool = default;
 
   private:
+    // The order in private variables starts for the first variable being the rightmost bit.
     uint16_t _limit_1 = {};      ///< First part of the limit field (0 - 15)
     uint32_t _base_1 : 24 = {};  ///< First part of the base field (16 - 39)
     access_byte _access = {};    ///< Access byte field (40 - 47)
     gdt_flags _flag = {};        ///< Second part of the limit field + Flags field (48 - 55)
+    uint8_t _base_2 = {};        ///< Second part of the base field (56 - 63)
   };
 }  // namespace teachos::arch::context_switching::segment_descriptor_table
 
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp
index 0b724f2..40bcc8a 100644
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp
@@ -1,16 +1,17 @@
 #ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_EXTENSION_HPP
 #define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_EXTENSION_HPP
 
-#include "arch/context_switching/segment_descriptor_table/segment_descriptor.hpp"
-
-#include <cstdint>
+#include "arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp"
 
 namespace teachos::arch::context_switching::segment_descriptor_table
 {
+  __extension__ typedef __int128 int128_t;
+  __extension__ typedef unsigned __int128 uint128_t;
+
   /**
    * @brief Defines helper function for all states and the actual data the segment descriptor can have.
    */
-  struct [[gnu::packed]] segment_descriptor_extension : seg_desc
+  struct [[gnu::packed]] segment_descriptor_extension
   {
     /**
      * @brief Default Constructor.
@@ -19,12 +20,54 @@ namespace teachos::arch::context_switching::segment_descriptor_table
 
     /**
      * @brief Constructor.
+     *
+     * @note Created segment descriptor copies the given bytes into these components requiring the space of two
+     * segment descriptor entry in the global descriptor table being 128-bit. Ending with a 32 bit reserved
+     * field that has to be used, because the segment descriptor needs to be big enough for two segment
+     * descriptor entries.
+     * - 8 bit Access Type
+     * - 4 bit Flags
+     * - 64 bit Base Address
+     * - 20 bit Limit
+     *
+     * @param flags Copies the bits set from the given data into the individual components of a segment
+     * descriptor.
+     */
+    explicit segment_descriptor_extension(uint128_t flags);
+
+    /**
+     * @brief Constructor.
+     *
+     * @param access_byte, flags, base, limit Copies the bits set from the given data into the individual components of
+     * a segment descriptor.
+     */
+    segment_descriptor_extension(access_byte access_byte, gdt_flags flags, uint64_t base, std::bitset<20U> limit);
+
+    /**
+     * @brief Returns the underlying base segment descriptor, being the first part of the segment descriptor consisting
+     * of two entries in the global descriptor table.
+     */
+    auto get_first_gdt_entry() const -> segment_descriptor_base;
+
+    /**
+     * @brief Returns the underlying extension to the segment descriptor, being the second part of the segment
+     * descriptor consiting of two entries in the global descriptor table.
+     */
+    auto get_second_gdt_entry() const -> uint64_t;
+
+    /**
+     * @brief Allows to compare the underlying bits of two instances.
+     *
+     * @param other Other instance that we want to compare with.
+     * @return Whether the underlying set bits of both types are the same.
      */
-    segment_descriptor_extension(segment_descriptor segment_descriptor);
+    auto operator==(segment_descriptor_extension const & other) const -> bool = default;
 
   private:
-    uint64_t _base_2 : 40 = {};  ///< Second part of the base field (56 - 95)
-    uint32_t : 32;               ///< Reserved field used to ensure this struct is 128 bits big (96 - 127)
+    // The order in private variables starts for the first variable being the rightmost bit.
+    segment_descriptor_base _base = {};  ///< Base Segment Descriptor representing single entry in GDT (0 - 63)
+    uint32_t _base_3 = {};               ///< Third part of the base field (63 - 95)
+    uint32_t : 32;                       ///< Reserved field used to ensure this struct is 128 bits big (96 - 127)
   };
 }  // namespace teachos::arch::context_switching::segment_descriptor_table
 
diff --git a/arch/x86_64/src/context_switching/interrupt_descriptor_table/segment_selector.cpp b/arch/x86_64/src/context_switching/interrupt_descriptor_table/segment_selector.cpp
index 0e29356..8568447 100644
--- a/arch/x86_64/src/context_switching/interrupt_descriptor_table/segment_selector.cpp
+++ b/arch/x86_64/src/context_switching/interrupt_descriptor_table/segment_selector.cpp
@@ -8,4 +8,6 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
   }
 
   auto segment_selector::operator|=(std::bitset<3U> other) -> void { _flags |= other.to_ulong(); }
+
+  segment_selector::operator uint16_t() const { return *reinterpret_cast<uint16_t const *>(this); }
 }  // namespace teachos::arch::context_switching::interrupt_descriptor_table
diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 5901998..7449d84 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -31,14 +31,14 @@ namespace teachos::arch::context_switching
 
     auto reload_gdtr() -> void
     {
-      // asm volatile("pushq $0x8\n\t"            // Push new CS
-      //              "lea 1f(%%rip), %%rax\n\t"  // Get address of label 1 into RAX
-      //              "pushq %%rax\n\t"           // Push return address
-      //              "lretq\n"                   // Far return (loads CS:RIP)
-      //              "1:\n\t"                    // Label to return to
-      //              :
-      //              :
-      //              : "rax", "memory");
+      /*asm volatile("pushq $0x8\n\t"            // Push new CS
+                   "lea 1f(%%rip), %%rax\n\t"  // Get address of label 1 into RAX
+                   "pushq %%rax\n\t"           // Push return address
+                   "lretq\n"                   // Far return (loads CS:RIP)
+                   "1:\n\t"                    // Label to return to
+                   :
+                   :
+                   : "rax", "memory");*/
 
       kernel::cpu::call(KERNEL_CODE_POINTER);
     }
@@ -57,21 +57,33 @@ namespace teachos::arch::context_switching
 
       // Actual Source: https://man7.org/linux/man-pages/man2/syscall.2.html More cleare documentation:
       // https://sys.readthedocs.io/en/latest/doc/05_calling_system_calls.html
-      uint64_t new_value = 60U;
+      uint64_t syscall_number = 60U;
       asm volatile("mov %[input], %%rax"
                    : /* no output from call */
-                   : [input] "r"(new_value)
+                   : [input] "r"(syscall_number)
                    : "memory");
       asm volatile("syscall");
 
-      video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!",
-                              video::vga::text::common_attributes::green_on_black);
+      // TODO: Reading RAX value does not work because the read itself changes the RAX value?!
+      // asm volatile("mov %%rax, %[output]" : [output] "=r"(syscall_value));
+
+      // TODO: Causes a general protection fault after the sysreturn?
+      // If removed instead it will cause a general protection fault after leaving this main method to return to kernel
+      // mode. But CS and SS are still configured for User mode.
+      /*video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!",
+                              video::vga::text::common_attributes::green_on_black);*/
     }
 
     auto syscall_handler() -> void
     {
-      uint64_t syscall_number{};
+      uint64_t syscall_number, arg_0, arg_1, arg_2, arg_3, arg_4, arg_5 = {};
       asm volatile("mov %%rax, %[output]" : [output] "=r"(syscall_number));
+      asm volatile("mov %%rdi, %[output]" : [output] "=r"(arg_0));
+      asm volatile("mov %%rsi, %[output]" : [output] "=r"(arg_1));
+      asm volatile("mov %%rdx, %[output]" : [output] "=r"(arg_2));
+      asm volatile("mov %%r10, %[output]" : [output] "=r"(arg_3));
+      asm volatile("mov %%r8, %[output]" : [output] "=r"(arg_4));
+      asm volatile("mov %%r9, %[output]" : [output] "=r"(arg_5));
 
       switch (syscall_number)
       {
@@ -85,7 +97,17 @@ namespace teachos::arch::context_switching
           break;
       }
 
-      asm volatile("sysretq");
+      uint64_t result = 0U;
+      asm volatile("mov %[input], %%rax"
+                   : /* no output from call */
+                   : [input] "r"(result)
+                   : "memory");
+
+      // Use SYSRET instead of SYSRETQ, because the latter would add 0x10 to bits [48:63] of IA32_STAR_ADDRESS for the
+      // Code Segment. But only add 0x8 to bits [48:63] of IA32_STAR_ADDRESS for the Stack Segment, which means either
+      // the Stack Segment or Code Segment is wrong. Whereas the former does not add 0x10 for the Code Segment and
+      // therefore fixes the aformentioned issue.
+      asm volatile("sysret");
     }
 
     auto enable_systemcall() -> void
@@ -94,9 +116,9 @@ namespace teachos::arch::context_switching
       kernel::cpu::write_msr(IA32_LSTAR_ADDRESS, syscall_function);
       kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 0U);
 
-      uint64_t kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;
-      uint64_t user_cs = KERNEL_CODE_SEGMENT_SELECTOR;
-      uint64_t star_value = (kernel_cs << 32) | (user_cs << 48);
+      uint64_t const kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;
+      uint64_t const user_cs = USER_CODE_SEGMENT_SELECTOR;
+      uint64_t const star_value = (kernel_cs << 32) | (user_cs << 48);
       kernel::cpu::write_msr(IA32_STAR_ADDRESS, star_value);
 
       kernel::cpu::set_efer_bit(kernel::cpu::efer_flags::SCE);
@@ -116,7 +138,7 @@ namespace teachos::arch::context_switching
       interrupt_descriptor_table::update_interrupt_descriptor_table_register();
 
       reload_gdtr();
-      segment_descriptor_table::update_task_state_segment_register();
+      segment_descriptor_table::update_tss_register();
 
       kernel::cpu::set_interrupt_flag();
       initalized = true;
diff --git a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp
index dd22603..d692e51 100644
--- a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp
@@ -1,8 +1,6 @@
 #include "arch/context_switching/segment_descriptor_table/global_descriptor_table.hpp"
 
-#include "arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp"
 #include "arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp"
-#include "arch/context_switching/segment_descriptor_table/task_state_segment.hpp"
 #include "arch/exception_handling/assert.hpp"
 #include "arch/kernel/cpu/gdtr.hpp"
 #include "arch/kernel/cpu/tr.hpp"
@@ -12,7 +10,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
   namespace
   {
     auto create_segment_descriptor(segment_descriptor_type segment_descriptor_type, access_byte access_level)
-        -> segment_descriptor
+        -> segment_descriptor_base
     {
       uint64_t const base = 0x0;
       std::bitset<20U> const limit{0xFFFFF};
@@ -29,57 +27,53 @@ namespace teachos::arch::context_switching::segment_descriptor_table
         access_level |= access_byte::WRITABLE;
       }
 
-      segment_descriptor const segment_descriptor{access_level, flags, base, limit};
-      return segment_descriptor;
+      segment_descriptor_base const segment_descriptor_base{access_level, flags, base, limit};
+      return segment_descriptor_base;
     }
 
-    auto create_tss_descriptor(task_state_segment * tss) -> segment_descriptor
+    auto create_tss_descriptor(task_state_segment * tss) -> segment_descriptor_extension
     {
       constexpr uint64_t TSS_LIMIT = sizeof(task_state_segment) - 1;
       access_byte const tss_access_byte{access_byte::PRESENT | access_byte::DESCRIPTOR_LEVEL_KERNEL |
                                         access_byte::TASK_STATE_SEGMENT_AVAILABLE};
       gdt_flags const tss_gdt_flags{0U, TSS_LIMIT};
-      segment_descriptor const tss_descriptor{tss_access_byte, tss_gdt_flags, reinterpret_cast<uint64_t>(tss),
-                                              TSS_LIMIT};
+      segment_descriptor_extension const tss_descriptor{tss_access_byte, tss_gdt_flags, reinterpret_cast<uint64_t>(tss),
+                                                        TSS_LIMIT};
       return tss_descriptor;
     }
 
-    auto create_gdt() -> global_descriptor_table *
+    auto create_gdt() -> global_descriptor_table
     {
-      segment_descriptor_base const null_segment{segment_descriptor{0}};
-      segment_descriptor_base const kernel_code_segment{
-          create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL)};
-      segment_descriptor_base const kernel_data_segment{
-          create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL)};
-      segment_descriptor_base const user_code_segment{
-          create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER)};
-      segment_descriptor_base const user_data_segment{
-          create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER)};
+      segment_descriptor_base const null_segment{0};
+      segment_descriptor_base const kernel_code_segment =
+          create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL);
+      segment_descriptor_base const kernel_data_segment =
+          create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL);
+      segment_descriptor_base const user_code_segment =
+          create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER);
+      segment_descriptor_base const user_data_segment =
+          create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER);
 
       // Task State Segment needs to be kept alive
       static auto tss = new task_state_segment();
-      segment_descriptor const tss_descriptor = create_tss_descriptor(tss);
-      segment_descriptor_base const tss_descriptor_base{tss_descriptor};
-      segment_descriptor_extension const tss_descriptor_extension{tss_descriptor};
-
-      decltype(auto) gdt = new global_descriptor_table{};
-      gdt->null = null_segment;
-      gdt->kernel_code = kernel_code_segment;
-      gdt->kernel_data = kernel_data_segment;
-      gdt->user_code = user_code_segment;
-      gdt->user_data = user_data_segment;
-      gdt->tss_low = tss_descriptor_base;
-      gdt->tss_high = tss_descriptor_extension;
-
-      return gdt;
-    };
+      segment_descriptor_extension const tss_descriptor = create_tss_descriptor(tss);
+
+      global_descriptor_table global_descriptor_table{null_segment,
+                                                      kernel_code_segment,
+                                                      kernel_data_segment,
+                                                      user_code_segment,
+                                                      user_data_segment,
+                                                      tss_descriptor.get_first_gdt_entry(),
+                                                      tss_descriptor.get_second_gdt_entry()};
+      return global_descriptor_table;
+    }
   }  // namespace
 
   auto get_or_create_gdt() -> global_descriptor_table &
   {
     // Global Descriptor Table needs to be kept alive
-    static global_descriptor_table * gdt = create_gdt();
-    return *gdt;
+    static global_descriptor_table gdt = create_gdt();
+    return gdt;
   }
 
   auto update_gdtr() -> void
@@ -88,7 +82,8 @@ namespace teachos::arch::context_switching::segment_descriptor_table
 
     // Calculate the size of the gdt in bytes - 1. This subtraction occurs because the maximum value of Size is 65535,
     // while the GDT can be up to 65536 bytes in length (8192 entries). Further, no GDT can have a size of 0 bytes.
-    global_descriptor_table_pointer gdt_pointer{static_cast<uint16_t>((7 * sizeof(seg_desc)) - 1), &gdt.null};
+    uint16_t gdt_size = static_cast<uint16_t>((gdt.size() * sizeof(segment_descriptor_base)) - 1);
+    global_descriptor_table_pointer gdt_pointer{gdt_size, gdt.data()};
     kernel::cpu::load_global_descriptor_table(gdt_pointer);
 
     auto const stored_gdt_pointer = kernel::cpu::store_global_descriptor_table();
@@ -97,13 +92,13 @@ namespace teachos::arch::context_switching::segment_descriptor_table
         "[Global Descriptor Table] Loaded GDTR value is not the same as the stored value.");
   }
 
-  auto update_task_state_segment_register() -> void
+  auto update_tss_register() -> void
   {
-    get_or_create_gdt();
+    decltype(auto) gdt = get_or_create_gdt();
 
     // Load task state segment descriptor from the last element in the global descriptor table, done by calculating
-    // offset in bytes to the start of the segment descriptor (5 * 16) = 80
-    uint16_t const tss_selector = (7 - 1) * sizeof(segment_descriptor_table::segment_descriptor);
+    // offset in bytes to the start of the segment descriptor (5 * 8) = 40
+    uint16_t tss_selector = (gdt.size() * sizeof(segment_descriptor_base)) - sizeof(segment_descriptor_extension);
     kernel::cpu::load_task_register(tss_selector);
 
     auto const stored_task_register = kernel::cpu::store_task_register();
diff --git a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp
index b7d2da4..79088b8 100644
--- a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp
+++ b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp
@@ -2,7 +2,7 @@
 
 namespace teachos::arch::context_switching::segment_descriptor_table
 {
-  global_descriptor_table_pointer::global_descriptor_table_pointer(uint16_t table_length, seg_desc * address)
+  global_descriptor_table_pointer::global_descriptor_table_pointer(uint16_t table_length, uint64_t * address)
       : table_length(table_length)
       , address(address)
   {
diff --git a/arch/x86_64/src/context_switching/segment_descriptor_table/segment_descriptor.cpp b/arch/x86_64/src/context_switching/segment_descriptor_table/segment_descriptor.cpp
deleted file mode 100644
index e74156b..0000000
--- a/arch/x86_64/src/context_switching/segment_descriptor_table/segment_descriptor.cpp
+++ /dev/null
@@ -1,46 +0,0 @@
-#include "arch/context_switching/segment_descriptor_table/segment_descriptor.hpp"
-
-namespace teachos::arch::context_switching::segment_descriptor_table
-{
-  segment_descriptor::segment_descriptor(uint128_t flags)
-      : _limit_1(flags)
-      , _base_1(flags >> 16U)
-      , _access(flags >> 40U)
-      , _flag(flags >> 52U, flags >> 48U)
-      , _base_2(flags >> 56U)
-  {
-    // Nothing to do.
-  }
-
-  segment_descriptor::segment_descriptor(access_byte access_byte, gdt_flags flags, uint64_t base,
-                                         std::bitset<20U> limit)
-      : _limit_1(limit.to_ulong())
-      , _base_1(base)
-      , _access(access_byte)
-      , _flag(flags)
-      , _base_2(base >> 24U)
-  {
-    // Nothing to do
-  }
-
-  aut