start implementing TSS

4 files changed, 89 insertions, 39 deletions

diff --git a/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp b/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
index 6474739..2b399f8 100644
--- a/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
@@ -1,61 +1,87 @@
 #include "arch/context_switching/descriptor_table/global_descriptor_table.hpp"
 
 #include "arch/context_switching/descriptor_table/segment_descriptor.hpp"
+#include "arch/context_switching/descriptor_table/task_state_segment.hpp"
 #include "arch/exception_handling/assert.hpp"
-#include "arch/kernel/cpu/lgdt.hpp"
+#include "arch/kernel/cpu/gdtr.hpp"
+#include "arch/kernel/cpu/tr.hpp"
 #include "arch/stl/vector.hpp"
 
 namespace teachos::arch::context_switching::descriptor_table
 {
+  auto create_segment_descriptor(segment_descriptor_type segment_descriptor_type, access_level access_level)
+      -> segment_descriptor
+  {
+    uint8_t access_level_bitset = access_byte::PRESENT | access_byte::CODE_OR_DATA_SEGMENT;
+    if (access_level == access_level::KERNEL)
+    {
+      access_level_bitset |= access_byte::ACCESS_LEVEL_KERNEL;
+    }
+    else if (access_level == access_level::USER)
+    {
+      access_level_bitset = access_byte::ACCESS_LEVEL_USER;
+    }
+
+    uint8_t gdt_flags_bitset = gdt_flags::GRANULARITY;
+    if (segment_descriptor_type == segment_descriptor_type::CODE_SEGMENT)
+    {
+      gdt_flags_bitset |= gdt_flags::LENGTH;
+      access_level_bitset |= access_byte::CODE_SEGMENT | access_byte::READABLE;
+    }
+    else if (segment_descriptor_type == segment_descriptor_type::DATA_SEGMENT)
+    {
+      gdt_flags_bitset |= gdt_flags::UPPER_BOUND;
+      access_level_bitset |= access_byte::WRITABLE;
+    }
+
+    std::bitset<20U> limit{0xFFFFF};
+    access_byte access_byte{access_level_bitset};
+    gdt_flags gdt_flags{gdt_flags_bitset, limit};
+    segment_descriptor code_segment{access_byte, gdt_flags, 0, limit};
+
+    return code_segment;
+  }
+
   auto create_global_descriptor_table() -> global_descriptor_table
   {
     segment_descriptor null_segment{0};
+    segment_descriptor kernel_code_segment =
+        create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_level::KERNEL);
+    segment_descriptor kernel_data_segment =
+        create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_level::KERNEL);
+    segment_descriptor user_code_segment =
+        create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_level::USER);
+    segment_descriptor user_data_segment =
+        create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_level::USER);
 
-    std::bitset<20U> limit{0xFFFFF};
+    stl::vector<segment_descriptor> global_descriptor_table{null_segment, kernel_code_segment, kernel_data_segment,
+                                                            user_code_segment, user_data_segment};
+    return global_descriptor_table;
+  }
 
-    // Kernel space code segment
-    access_byte kernel_code_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_KERNEL |
-                                        access_byte::CODE_OR_DATA_SEGMENT | access_byte::CODE_SEGMENT |
-                                        access_byte::READABLE};
-    gdt_flags kernel_code_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::LENGTH, limit};
-    segment_descriptor kernel_code_segment{kernel_code_access_byte, kernel_code_gdt_flags, 0, limit};
-
-    // Kernel space data segment
-    access_byte kernel_data_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_KERNEL |
-                                        access_byte::CODE_OR_DATA_SEGMENT | access_byte::WRITABLE};
-    gdt_flags kernel_data_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::UPPER_BOUND, limit};
-    segment_descriptor kernel_data_segment{kernel_data_access_byte, kernel_data_gdt_flags, 0, limit};
-
-    // User space code segment
-    access_byte user_code_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_USER |
-                                      access_byte::CODE_OR_DATA_SEGMENT | access_byte::CODE_SEGMENT |
-                                      access_byte::READABLE};
-    gdt_flags user_code_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::LENGTH, limit};
-    segment_descriptor user_code_segment{user_code_access_byte, user_code_gdt_flags, 0, limit};
-
-    // User space data segment
-    access_byte user_data_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_USER |
-                                      access_byte::CODE_OR_DATA_SEGMENT | access_byte::WRITABLE};
-    gdt_flags user_data_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::UPPER_BOUND, limit};
-    segment_descriptor user_data_segment{user_data_access_byte, user_data_gdt_flags, 0, limit};
-
-    // Task state segment
-    // TODO: Create TSS
+  auto create_task_state_segment_descriptor(task_state_segment * tss) -> segment_descriptor
+  {
+    std::bitset<20U> limit{0xFFFFF};
     access_byte tss_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_KERNEL |
                                 access_byte::TASK_STATE_SEGMENT_AVAILABLE};
     gdt_flags tss_gdt_flags{0U, limit};
-    uint64_t tss_address = 0;  // &TSS
-    uint64_t tss_limit = 0U;   // sizeof(TSS) - 1
-    segment_descriptor task_state_segment{tss_access_byte, tss_gdt_flags, tss_address, tss_limit};
+    uint64_t tss_address = reinterpret_cast<uint64_t>(tss);
+    constexpr uint64_t tss_limit = sizeof(task_state_segment) - 1;
+    segment_descriptor tss_descriptor{tss_access_byte, tss_gdt_flags, tss_address, tss_limit};
 
-    stl::vector<segment_descriptor> global_descriptor_table{null_segment, kernel_code_segment, kernel_data_segment,
-                                                            user_code_segment, user_data_segment};
-    return global_descriptor_table;
+    return tss_descriptor;
   }
 
   auto initialize_global_descriptor_table() -> global_descriptor_table
   {
-    decltype(auto) gdt = create_global_descriptor_table();
+    auto gdt = create_global_descriptor_table();
+
+    // Add TSS segment descriptor to GDT
+    auto tss = new task_state_segment();
+    auto tss_descriptor = create_task_state_segment_descriptor(tss);
+    gdt.push_back(tss_descriptor);
+
+    // Load GDT into GDTR
     global_descriptor_table_pointer gdt_pointer{static_cast<uint16_t>(gdt.size() - 1), &gdt};
     kernel::cpu::load_global_descriptor_table(gdt_pointer);
 
@@ -64,6 +90,14 @@ namespace teachos::arch::context_switching::descriptor_table
         gdt_pointer == stored_gdt_pointer,
         "[Global Descriptor Table] Loaded GDTR value is not the same as the stored value.");
 
+    // Load Task Register (LTR) using the index of TSS descriptor
+    uint16_t tss_selector = (gdt.size() - 1) * sizeof(segment_descriptor);
+    kernel::cpu::load_task_register(tss_selector);
+
+    auto 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.");
+
     return gdt;
   }
 }  // namespace teachos::arch::context_switching::descriptor_table
diff --git a/arch/x86_64/src/kernel/cpu/lgdt.cpp b/arch/x86_64/src/kernel/cpu/gdtr.cpp
index 386914f..2fe3a99 100644
--- a/arch/x86_64/src/kernel/cpu/lgdt.cpp
+++ b/arch/x86_64/src/kernel/cpu/gdtr.cpp
@@ -1,4 +1,4 @@
-#include "arch/kernel/cpu/lgdt.hpp"
+#include "arch/kernel/cpu/gdtr.hpp"
 
 #include "arch/context_switching/descriptor_table/global_descriptor_table_pointer.hpp"
 
diff --git a/arch/x86_64/src/kernel/cpu/tr.cpp b/arch/x86_64/src/kernel/cpu/tr.cpp
new file mode 100644
index 0000000..a28b9fc
--- /dev/null
+++ b/arch/x86_64/src/kernel/cpu/tr.cpp
@@ -0,0 +1,17 @@
+#include "arch/kernel/cpu/tr.hpp"
+
+namespace teachos::arch::kernel::cpu
+{
+  auto store_task_register() -> uint16_t
+  {
+    uint16_t current_value{};
+    asm("str %[output]" : [output] "=m"(current_value));
+    return current_value;
+  }
+
+  // TODO: Is this really correct?
+  auto load_task_register(uint16_t gdt_offset) -> void
+  {
+    asm volatile("ltr %[input]" : /* no output from call */ : [input] "m"(gdt_offset));
+  }
+}  // namespace teachos::arch::kernel::cpu
diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index 2c0b6c8..c1e134a 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -1,7 +1,6 @@
 #include "arch/kernel/main.hpp"
 
 #include "arch/context_switching/descriptor_table/global_descriptor_table.hpp"
-#include "arch/kernel/cpu/lgdt.hpp"
 #include "arch/memory/heap/bump_allocator.hpp"
 #include "arch/memory/heap/global_heap_allocator.hpp"
 #include "arch/memory/main.hpp"