feat: make kernel architecture-agnostic; primitive work on arm port

kernel/src/Arch/x86_64/GDT.hpp

@@ -0,0 +1,61 @@
+/*
+    * gdt.hpp
+    * Intel Global Descriptor Table
+    * Copyright (c) 2025 Daniel Hammer
+*/
+
+#pragma once
+#include <cstdint>
+
+using namespace std;
+
+namespace Hal {
+    class GDTEntry {
+        public:
+            uint16_t LimitLow;
+            uint16_t BaseLow;
+            uint8_t BaseMiddle;
+            uint8_t AccessByte;
+            uint8_t GranularityByte;
+            uint8_t BaseHigh;
+        }__attribute__((packed));
+
+        struct BasicGDT {
+            GDTEntry Null;          // 0x00
+            GDTEntry KernelCode;    // 0x08
+            GDTEntry KernelData;    // 0x10
+            GDTEntry UserData;      // 0x18  (before UserCode for SYSRET)
+            GDTEntry UserCode;      // 0x20
+            GDTEntry TSS;           // 0x28  (low 8 bytes of 16-byte TSS descriptor)
+            GDTEntry TSSHigh;       // 0x30  (high 8 bytes of 16-byte TSS descriptor)
+        }__attribute__((packed));
+
+        struct GDTPointer {
+            uint16_t Size;
+            uint64_t GDTAddress;
+        }__attribute__((packed));
+
+        struct TSS64 {
+            uint32_t reserved0;
+            uint64_t rsp0;
+            uint64_t rsp1;
+            uint64_t rsp2;
+            uint64_t reserved1;
+            uint64_t ist1;
+            uint64_t ist2;
+            uint64_t ist3;
+            uint64_t ist4;
+            uint64_t ist5;
+            uint64_t ist6;
+            uint64_t ist7;
+            uint64_t reserved2;
+            uint16_t reserved3;
+            uint16_t iopbOffset;
+        }__attribute__((packed));
+
+        extern TSS64 g_tss;
+
+        void BridgeLoadGDT();
+        void PrepareGDT();
+        void LoadTSS();
+};