GDT, page frame allocator

kernel/src/Hal/GDT.hpp

@@ -0,0 +1,62 @@
+/*
+    * gdt.hpp
+    * Copyright (c) 2025 Daniel Hammer
+*/
+
+#pragma once
+#include <cstdint>
+
+using namespace std;
+
+// __attribute__((packed)) is the GCC extensions way of telling the compiler to ensure that it doesn't mess with these structures or add packing bytes
+// for optimization because that would easily result in a triple fault.
+
+namespace Hal {
+    class GDTEntry {
+        public:
+            // Base/Limit are obsolete in Long mode because segmentation is no longer used
+            // Sadly we must still build and load the GDT during kernel init
+        
+            uint16_t LimitLow;
+            uint16_t BaseLow;
+            uint8_t BaseMiddle;
+        
+            // Determine which processor rings this segment can be used in
+            uint8_t AccessByte;
+            // Lower 4 bits are the higher 4 bits of limit
+            uint8_t GranularityByte;
+        
+            uint8_t BaseHigh;
+        
+            // 16 + 16 + 8 + 8 = 48 bits
+        }__attribute__((packed));
+        
+        struct BasicGDT {
+            // Conventionally the first entry of the GDT has all values zeroed out.
+            GDTEntry Null;
+        
+            // Kernel code segment descriptor
+            GDTEntry KernelCode;
+        
+            // Kernel data segment descriptor
+            GDTEntry KernelData;
+        
+            // UM code segment descriptor
+            GDTEntry UserCode;
+        
+            // UM data segment descriptor
+            GDTEntry UserData;
+        
+            // Task State Segment
+            GDTEntry TSS;
+        }__attribute__((packed));
+        
+        // Simple structure that tells the CPU the size of the GDT, and it's address
+        struct GDTPointer {
+            uint16_t Size;
+            uint64_t GDTAddress;
+        }__attribute__((packed));
+        
+        void BridgeLoadGDT();
+        void PrepareGDT();
+};