WIP experiment with converting GDT to 8-Byte entries

6 files changed, 96 insertions, 13 deletions

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 7bfb563..8748448 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
@@ -44,17 +44,13 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
      * @brief Constructor.
      *
      * @param index Index into the local or global descriptor table. Processor multiplies the index value by 8 (number
-     * of bytes in 32-bit segment descriptor) and adds the result to the base GDT or LDT address. Because it only
-     * multiplies by 8, but we are using long mode the constructor additionally multiplies the given value by two. This
-     * is done because 64-bit segment descriptor are twice as big in size. If we wouldn't multiply by two, index 1 would
-     * result in the middle between the second part of the null entry and the first part of the code kernel segment and
-     * therefore be invalid.
+     * of bytes in 32-bit segment descriptor) and adds the result to the base GDT or LDT address.
      * @param flags Allows to set flags for the flags field using the unscoped enum contained in this class, used to
      * allow for direct integer conversion.
      */
     constexpr segment_selector(uint16_t index, uint8_t flags)
         : _flags(flags)
-        , _index(index * 2U)
+        , _index(index)
     {
       // Nothing to do.
     }
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 bd69a46..84a24a2 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
@@ -12,7 +12,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
    *
    * @return Reference to the created global_descriptor_table.
    */
-  auto get_or_create_global_descriptor_table() -> global_descriptor_table &;
+  auto get_or_create_gdt() -> global_descriptor_table &;
 
   /**
    * @brief Updates the GDTR with the created global descriptor table. If it has not been created yet this
@@ -21,13 +21,13 @@ namespace teachos::arch::context_switching::segment_descriptor_table
    * @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;
+  auto update_gdtr() -> 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
+   * @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;
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 6fac2a0..c54647d 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
@@ -1,14 +1,24 @@
 #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.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
 {
-  using global_descriptor_table = stl::vector<segment_descriptor>;
+  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;
+  };
 
   /**
    * @brief Represents a pointer to the Global Descriptor Table (GDT).
@@ -26,7 +36,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
     /**
      * @brief Constructor.
      */
-    global_descriptor_table_pointer(uint16_t table_length, segment_descriptor * address);
+    global_descriptor_table_pointer(uint16_t table_length, seg_desc * address);
 
     /**
      * @brief Defaulted three-way comparsion operator.
@@ -35,7 +45,7 @@ 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.
-    segment_descriptor * address = {};  ///< Non-owning pointer to the GDT base address.
+    seg_desc * 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
index 7fe4ecb..ccd604d 100644
--- 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
@@ -10,6 +10,12 @@ 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.
    */
@@ -44,6 +50,12 @@ namespace teachos::arch::context_switching::segment_descriptor_table
      */
     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.
      */
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
new file mode 100644
index 0000000..18c9da1
--- /dev/null
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp
@@ -0,0 +1,34 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_BASE_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_BASE_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.hpp"
+#include "arch/context_switching/segment_descriptor_table/segment_descriptor_type.hpp"
+
+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
+  {
+    /**
+     * @brief Default Constructor.
+     */
+    segment_descriptor_base() = default;
+
+    /**
+     * @brief Constructor.
+     */
+    segment_descriptor_base(segment_descriptor segment_descriptor);
+
+  private:
+    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)
+  };
+}  // namespace teachos::arch::context_switching::segment_descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_BASE_HPP
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
new file mode 100644
index 0000000..0b724f2
--- /dev/null
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp
@@ -0,0 +1,31 @@
+#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>
+
+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_extension : seg_desc
+  {
+    /**
+     * @brief Default Constructor.
+     */
+    segment_descriptor_extension() = default;
+
+    /**
+     * @brief Constructor.
+     */
+    segment_descriptor_extension(segment_descriptor segment_descriptor);
+
+  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)
+  };
+}  // namespace teachos::arch::context_switching::segment_descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SEGMENT_DESCRIPTOR_TABLE_SEGMENT_DESCRIPTOR_EXTENSION_HPP