Clean up global descriptor table initalization

11 files changed, 100 insertions, 77 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)
   };
 
   /**
diff --git a/arch/x86_64/src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp b/arch/x86_64/src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp
index d86c459..28f289c 100644
--- a/arch/x86_64/src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp
+++ b/arch/x86_64/src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp
@@ -8,7 +8,6 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
       , _ist(flags >> 32U)
       , _flags(flags >> 40U)
       , _offset_2(flags >> 48U)
-      , _offset_3(flags >> 64U)
   {
     // Nothing to do.
   }
@@ -19,7 +18,6 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
       , _ist(ist)
       , _flags(flags)
       , _offset_2(offset >> 16U)
-      , _offset_3(offset >> 48U)
   {
     // Nothing to do.
   }
diff --git a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
index 1c1de68..62b116b 100644
--- a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
@@ -6,26 +6,23 @@
 
 namespace teachos::arch::context_switching::interrupt_descriptor_table
 {
-  namespace
+  auto get_or_create_interrupt_descriptor_table() -> interrupt_descriptor_table &
   {
+    // @MTO: This address resolution is most certainly wrong -> numbers in dbg seem off (offset_3 = 0)
+    uint64_t offset = reinterpret_cast<uint64_t>(&interrupt_handling::generic_interrupt_handler);
+    segment_selector selector{0U, segment_selector::REQUEST_LEVEL_KERNEL};
+    ist_offset ist{0U};
+    idt_flags flags{idt_flags::DESCRIPTOR_LEVEL_KERNEL | idt_flags::PRESENT};
+    gate_descriptor descriptor{selector, ist, flags, offset};
 
-    auto create_interrupt_descriptor_table() -> interrupt_descriptor_table
-    {
-      // @MTO: This address resolution is most certainly wrong -> numbers in dbg seem off (offset_3 = 0)
-      uint64_t offset = reinterpret_cast<uint64_t>(&interrupt_handling::generic_interrupt_handler);
-      segment_selector selector{0U, segment_selector::REQUEST_LEVEL_KERNEL};
-      ist_offset ist{0U};
-      idt_flags flags{idt_flags::DESCRIPTOR_LEVEL_KERNEL | idt_flags::PRESENT};
-      gate_descriptor descriptor{selector, ist, flags, offset};
-
-      return interrupt_descriptor_table{descriptor};
-    }
-  }  // namespace
+    // Interrupt Descriptor Table needs to be kept alive
+    static interrupt_descriptor_table interrupt_descriptor_table{descriptor};
+    return interrupt_descriptor_table;
+  }
 
-  auto initialize_interrupt_descriptor_table() -> interrupt_descriptor_table &
+  auto update_interrupt_descriptor_table_register() -> void
   {
-    // Interrupt Descriptor Table needs to be kept alive
-    static auto idt = create_interrupt_descriptor_table();
+    static auto idt = get_or_create_interrupt_descriptor_table();
 
     interrupt_descriptor_table_pointer idt_pointer{static_cast<uint16_t>((idt.size() * sizeof(gate_descriptor)) - 1),
                                                    idt.data()};
@@ -35,7 +32,5 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
     arch::exception_handling::assert(
         idt_pointer == stored_gdt_pointer,
         "[Interrupt Descriptor Table] Loaded IDTR value is not the same as the stored value.");
-
-    return idt;
   }
 }  // 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 008da2f..db04b52 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -11,22 +11,16 @@ namespace teachos::arch::context_switching
   auto initialize_descriptor_tables() -> descriptor_tables
   {
     kernel::cpu::clear_interrupt_flag();
-    decltype(auto) global_descriptor_table = segment_descriptor_table::initialize_global_descriptor_table();
-    decltype(auto) interrupt_descriptor_table = interrupt_descriptor_table::initialize_interrupt_descriptor_table();
 
-    kernel::cpu::far_pointer pointer{&boot::reload_segment_register,
-                                     1 * sizeof(segment_descriptor_table::segment_descriptor)};
-    asm volatile("rex64 lcall *%[far_function_pointer]" : : [far_function_pointer] "m"(pointer));
+    segment_descriptor_table::update_global_descriptor_table_register();
+    interrupt_descriptor_table::update_interrupt_descriptor_table_register();
 
-    // 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 =
-        (global_descriptor_table.size() - 1) * sizeof(segment_descriptor_table::segment_descriptor);
-    kernel::cpu::load_task_register(tss_selector);
+    interrupt_descriptor_table::segment_selector segment_selector{
+        2U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
+    kernel::cpu::far_pointer pointer{&boot::reload_segment_register, segment_selector};
+    kernel::cpu::jmp(pointer);
 
-    auto const stored_task_register = kernel::cpu::store_task_register();
-    arch::exception_handling::assert(tss_selector == stored_task_register,
-                                     "[Global Descriptor Table] Loaded TR value is not the same as the stored value.");
+    segment_descriptor_table::update_task_state_segment_register();
 
     // FIXME: We currently cannot enable interrupts, since for some reason, we will later run into what looks like a GP
     // and triple fault.
@@ -34,7 +28,8 @@ namespace teachos::arch::context_switching
     // idt). NEVER happened when stepping through quickly. Can you reproduce this?
     kernel::cpu::set_interrupt_flag();
 
-    descriptor_tables tables = {global_descriptor_table, interrupt_descriptor_table};
+    descriptor_tables tables = {segment_descriptor_table::get_or_create_global_descriptor_table(),
+                                interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()};
     return tables;
   }
 }  // namespace teachos::arch::context_switching
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 d9ad91c..346db9e 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
@@ -24,7 +24,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
       }
       else if (segment_descriptor_type == segment_descriptor_type::DATA_SEGMENT)
       {
-        gdt_flags_bits |= 1 << 2;
+        gdt_flags_bits |= gdt_flags::UPPER_BOUND;
         access_level_bits |= access_byte::WRITABLE;
       }
 
@@ -46,33 +46,33 @@ namespace teachos::arch::context_switching::segment_descriptor_table
                                               TSS_LIMIT};
       return tss_descriptor;
     }
+  }  // namespace
 
-    auto create_global_descriptor_table() -> global_descriptor_table
-    {
-      segment_descriptor const null_segment{0};
-      segment_descriptor const kernel_code_segment =
-          create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL);
-      segment_descriptor const kernel_data_segment =
-          create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL);
-      segment_descriptor const user_code_segment =
-          create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER);
-      segment_descriptor const user_data_segment =
-          create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER);
+  auto get_or_create_global_descriptor_table() -> global_descriptor_table &
+  {
+    segment_descriptor const null_segment{0};
+    segment_descriptor const kernel_code_segment =
+        create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL);
+    segment_descriptor const kernel_data_segment =
+        create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL);
+    segment_descriptor const user_code_segment =
+        create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER);
+    segment_descriptor 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_task_state_segment_descriptor(tss);
+    // Task State Segment needs to be kept alive
+    static auto tss = new task_state_segment();
+    segment_descriptor const tss_descriptor = create_task_state_segment_descriptor(tss);
 
-      global_descriptor_table const global_descriptor_table{null_segment,      kernel_code_segment, kernel_data_segment,
-                                                            user_code_segment, user_data_segment,   tss_descriptor};
-      return global_descriptor_table;
-    }
-  }  // namespace
+    // Global Descriptor Table needs to be kept alive
+    static global_descriptor_table global_descriptor_table{null_segment,      kernel_code_segment, kernel_data_segment,
+                                                           user_code_segment, user_data_segment,   tss_descriptor};
+    return global_descriptor_table;
+  }
 
-  auto initialize_global_descriptor_table() -> global_descriptor_table &
+  auto update_global_descriptor_table_register() -> void
   {
-    // Global Descriptor Table needs to be kept alive
-    static auto gdt = create_global_descriptor_table();
+    decltype(auto) gdt = get_or_create_global_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.
@@ -84,8 +84,20 @@ namespace teachos::arch::context_switching::segment_descriptor_table
     arch::exception_handling::assert(
         gdt_pointer == stored_gdt_pointer,
         "[Global Descriptor Table] Loaded GDTR value is not the same as the stored value.");
+  }
+
+  auto update_task_state_segment_register() -> void
+  {
+    decltype(auto) gdt = get_or_create_global_descriptor_table();
+
+    // 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 = (gdt.size() - 1) * sizeof(segment_descriptor_table::segment_descriptor);
+    kernel::cpu::load_task_register(tss_selector);
 
-    return gdt;
+    auto const stored_task_register = kernel::cpu::store_task_register();
+    arch::exception_handling::assert(tss_selector == stored_task_register,
+                                     "[Global Descriptor Table] Loaded TR value is not the same as the stored value.");
   }
 
 }  // namespace teachos::arch::context_switching::segment_descriptor_table
diff --git a/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp b/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
index 68b4568..2f599e5 100644
--- a/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
+++ b/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
@@ -11,4 +11,4 @@ namespace teachos::arch::interrupt_handling
     (void)frame;
     video::vga::text::write("An Interrupt occurred.", video::vga::text::common_attributes::green_on_black);
   }
-}  // namespace teachos::arch::interrupt_handling
\ No newline at end of file
+}  // namespace teachos::arch::interrupt_handling
diff --git a/arch/x86_64/src/kernel/cpu/jmp.cpp b/arch/x86_64/src/kernel/cpu/jmp.cpp
index 0c94693..2833219 100644
--- a/arch/x86_64/src/kernel/cpu/jmp.cpp
+++ b/arch/x86_64/src/kernel/cpu/jmp.cpp
@@ -9,6 +9,6 @@ namespace teachos::arch::kernel::cpu
 
   auto jmp(far_pointer pointer) -> void
   {
-    asm volatile("rex64 ljmp *%[input]" : /* no output from call */ : [input] "m"(pointer));
+    asm volatile("rex64 lcall *%[input]" : /* no output from call */ : [input] "m"(pointer));
   }
 }  // namespace teachos::arch::kernel::cpu