1 files changed, 109 insertions, 1 deletions

diff --git a/arch/x86_64/kapi/system.cpp b/arch/x86_64/kapi/system.cpp
index 5bcae4d..ca4418e 100644
--- a/arch/x86_64/kapi/system.cpp
+++ b/arch/x86_64/kapi/system.cpp
@@ -1,14 +1,122 @@
 #include "kapi/system.hpp"
 
+#include "arch/cpu/global_descriptor_table.hpp"
+#include "arch/cpu/segment_descriptor.hpp"
+#include "arch/cpu/task_state_segment.hpp"
+
 #include <kstd/print>
 
+#include <bit>
+#include <cstdint>
+
 namespace kapi::system
 {
 
+  namespace
+  {
+    constexpr auto gdt_null_descriptor = arch::cpu::segment_descriptor{};
+
+    constexpr auto gdt_kernel_code_descriptor = arch::cpu::segment_descriptor{
+      .limit_low = 0xffff,
+      .base_low = 0,
+      .accessed = false,
+      .read_write = false,
+      .direction_or_conforming = false,
+      .executable = true,
+      .type = arch::cpu::segment_type::code_or_data,
+      .privilege_level = 0,
+      .present = true,
+      .limit_high = 0xf,
+      .long_mode = true,
+      .protected_mode = false,
+      .granularity = arch::cpu::segment_granularity::page,
+      .base_high = 0,
+    };
+
+    constexpr auto gdt_kernel_data_descriptor = arch::cpu::segment_descriptor{
+      .limit_low = 0xffff,
+      .base_low = 0,
+      .accessed = false,
+      .read_write = true,
+      .direction_or_conforming = false,
+      .executable = false,
+      .type = arch::cpu::segment_type::code_or_data,
+      .privilege_level = 0,
+      .present = true,
+      .limit_high = 0xf,
+      .long_mode = false,
+      .protected_mode = true,
+      .granularity = arch::cpu::segment_granularity::page,
+      .base_high = 0,
+    };
+
+    constexpr auto gdt_user_code_descriptor = arch::cpu::segment_descriptor{
+      .limit_low = 0xffff,
+      .base_low = 0,
+      .accessed = false,
+      .read_write = false,
+      .direction_or_conforming = false,
+      .executable = true,
+      .type = arch::cpu::segment_type::code_or_data,
+      .privilege_level = 3,
+      .present = true,
+      .limit_high = 0xf,
+      .long_mode = true,
+      .protected_mode = false,
+      .granularity = arch::cpu::segment_granularity::page,
+      .base_high = 0,
+    };
+
+    constexpr auto gdt_user_data_descriptor = arch::cpu::segment_descriptor{
+      .limit_low = 0xffff,
+      .base_low = 0,
+      .accessed = false,
+      .read_write = true,
+      .direction_or_conforming = false,
+      .executable = false,
+      .type = arch::cpu::segment_type::code_or_data,
+      .privilege_level = 3,
+      .present = true,
+      .limit_high = 0xf,
+      .long_mode = false,
+      .protected_mode = false,
+      .granularity = arch::cpu::segment_granularity::page,
+      .base_high = 0,
+    };
+  }  // namespace
+
   auto memory_initialized() -> void
   {
+    auto static tss = arch::cpu::task_state_segment{};
+    auto static tss_descriptor = arch::cpu::system_segment_descriptor{
+      {
+       .limit_low = (sizeof(tss) - 1) & 0xffff,                     // NOLINT(readability-magic-numbers)
+        .base_low = std::bit_cast<std::uintptr_t>(&tss) & 0xffffff,  // NOLINT(readability-magic-numbers)
+        .accessed = false,
+       .read_write = false,
+       .direction_or_conforming = false,
+       .executable = false,
+       .type = arch::cpu::segment_type::system,
+       .privilege_level = 0,
+       .present = true,
+       .limit_high = ((sizeof(tss) - 1) >> 16) & 0xf,  // NOLINT(readability-magic-numbers)
+        .long_mode = false,
+       .protected_mode = false,
+       .granularity = arch::cpu::segment_granularity::byte,
+       .base_high = (std::bit_cast<std::uintptr_t>(&tss) >> 24) & 0xff,  // NOLINT(readability-magic-numbers)
+      },
+      (std::bit_cast<std::uintptr_t>(&tss) >> 32) & 0xffff'ffff, // NOLINT(readability-magic-numbers)
+    };
+
+    auto static gdt = arch::cpu::global_descriptor_table{
+      gdt_null_descriptor,      gdt_kernel_code_descriptor, gdt_kernel_data_descriptor,
+      gdt_user_code_descriptor, gdt_user_data_descriptor,   tss_descriptor,
+    };
+
+    kstd::println("[x86_64:SYS] Reloading Global Descriptor Table.");
+    gdt.load(1, 2);
+
     kstd::println("[x86_64:SYS] TODO: initialize Interrupt Descriptor Table.");
-    kstd::println("[x86_64:SYS] TODO: reload Global Descriptor Table.");
   }
 
 }  // namespace kapi::system
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