Clean up global descriptor table initalization

5 files changed, 40 insertions, 17 deletions

diff --git a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp
index e677cbb..22cd0f0 100644
--- a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp
+++ b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp
@@ -61,8 +61,7 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
     segment_selector _selector = {};  ///< Segment selector (16 - 31)
     ist_offset _ist = {};             ///< Interrupt Stack Table offset (32 - 39)
     idt_flags _flags = {};            ///< Gate Type and Flags (40 - 47)
-    uint16_t _offset_2 = {};          ///< Middle 16 bits of handler function address (48 - 63)
-    uint32_t _offset_3 = {};          ///< Upper 32 bits of handler function address (for x86_64) (64 - 95)
+    uint64_t _offset_2 : 48 = {};     ///< Upper 48 bits of handler function address (48 - 95)
     uint32_t : 32;                    ///< Reserved field used to ensure this struct is 128 bits big (96 - 127)
   };
 }  // namespace teachos::arch::context_switching::interrupt_descriptor_table
diff --git a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp
index e2ec4c5..b388e0e 100644
--- a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp
+++ b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp
@@ -6,12 +6,18 @@
 namespace teachos::arch::context_switching::interrupt_descriptor_table
 {
   /**
-   * @brief Initializes the interrupt_descriptor_table by loading it
-   * in the IDTR register.
+   * @brief Updates the IDTR with the created interrupt descriptor table. If it has not been created yet this
+   * method will create it.
+   */
+  auto update_interrupt_descriptor_table_register() -> void;
+
+  /**
+   * @brief Creates the interrupt descriptor table, with the minimum required configuration. If this method is called
+   * more than once, the previously created instance is returned instead.
    *
    * @return Reference to the created interrupt_descriptor_table.
    */
-  auto initialize_interrupt_descriptor_table() -> interrupt_descriptor_table &;
+  auto get_or_create_interrupt_descriptor_table() -> interrupt_descriptor_table &;
 
 }  // namespace teachos::arch::context_switching::interrupt_descriptor_table
 
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp
index 8217bcb..d8c3cd1 100644
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp
@@ -18,17 +18,16 @@ namespace teachos::arch::context_switching::segment_descriptor_table
      */
     enum bitset : uint8_t
     {
-      AVAILABLE = 1U << 0U,  ///< Available for use by System software. For our purposes this is basically reserved.
       LONG_MODE = 1U << 1U,  ///< Defines in IA-32e mode (64-bit code and 32-bit compatability mode) if the segment
                              ///< contains 64-bit code. Otherwise this bit should always be 0. Enable if instructions
                              ///< are executed in 64-bit code, otherwise they are executed in compatability 32-bit mode.
-                             ///< If this is set the DEFAULT_OPERAND_SIZE/BIG bit needs to be clear (0).
-
-      DEFAULT_OPERATION_SIZE =
-          1U << 2U,    ///< If clear, this is a 16-bit code segment; if set, this is a 32-bit segment.
-      BIG = 1U << 2U,  ///< If set, the maximum offset size for a data segment is increased to 32-bit
-                       ///< 0xffffffff. Otherwise it's the 16-bit max 0x0000ffff. Essentially the same meaning as "D".
-
+                             ///< If this bit is set the 3rd bit needs to be clear (0).
+      UPPER_BOUND = 1U << 2U,  ///< Specifies the upper bound of the segment for expand down data segment. Enable for 4
+                               ///< GiB, 4 KiB otherwise.
+      STACK_POINTER_SIZE = 1U << 2U,  ///< Specifies the size of the Stack Pointer (SP) for stack segments used for
+                                      ///< implicit stack operations. Enable for 32 bit, 16 bit otherwise.
+      DEFAULT_LENGTH = 1U << 2U,      ///< Indicates the default length for code segments with effective addresses and
+                                      ///< operands. Enable for 32 bit, 16 bit otherwise.
       GRANULARITY = 1U << 3U,  ///< Indicates the size the Limit value in the segment descriptor is scaled by 1 Byte
                                ///< blocks if the bit is not set or by 4 KiB blocks if the bit is set.
     };
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 f3067ba..bd69a46 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
@@ -7,12 +7,30 @@
 namespace teachos::arch::context_switching::segment_descriptor_table
 {
   /**
-   * @brief Initializes the global_descriptor_table and task_state_segment by loading them
-   * in the GDTR and TR registers respectively.
+   * @brief Creates the global descriptor table, with the minimum required configuration. If this method is called more
+   * than once, the previously created instance is returned instead.
    *
    * @return Reference to the created global_descriptor_table.
    */
-  auto initialize_global_descriptor_table() -> global_descriptor_table &;
+  auto get_or_create_global_descriptor_table() -> global_descriptor_table &;
+
+  /**
+   * @brief Updates the GDTR with the created global descriptor table. If it has not been created yet this
+   * method will create it.
+   *
+   * @note This method will only set the GDTR, but for the processor to actually register the change a far jump
+   * has to be executed. This also has to be done before updating the TR.
+   */
+  auto update_global_descriptor_table_register() -> void;
+
+  /**
+   * @brief Updates the TR with the created task state segment. If it has not been created yet this
+   * method will create it.
+   *
+   * @note This method should only be called after update_global_descriptor_table_register() 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;
 
 }  // namespace teachos::arch::context_switching::segment_descriptor_table
 
diff --git a/arch/x86_64/include/arch/kernel/cpu/jmp.hpp b/arch/x86_64/include/arch/kernel/cpu/jmp.hpp
index 0ed38e9..1657c18 100644
--- a/arch/x86_64/include/arch/kernel/cpu/jmp.hpp
+++ b/arch/x86_64/include/arch/kernel/cpu/jmp.hpp
@@ -13,7 +13,8 @@ namespace teachos::arch::kernel::cpu
   struct far_pointer
   {
     void (*function)();  ///< Address of the function we want to jump too. (0-63)
-    std::uint16_t index; ///< Index of the GDT entry we want to load into register CS. (64-79)
+    context_switching::interrupt_descriptor_table::segment_selector
+        selector;  ///< Segment selector pointing to the GDT entry we want to load into register CS. (64-79)
   };
 
   /**