Completed (only MVP) gdp.h and started implementing it.

Also corrected a typo in types.h .

src/gdt.cpp

@@ -0,0 +1,32 @@
+#include "gdt.h"
+
+#define _64_MEGABYTES 64*1024*1024
+#define CSS_FLAGS 0x9A
+#define DSS_FLAGS 0x92
+#define EXPECTED_BYTES_NUM 2
+#define GDT_ADDRESS 0
+#define SEGMENT_INTEGER_HIGH_BYTES 1
+#define HIGH_BYTES_LSHIFT 16
+
+GlobalDescriptorTable::GlobalDescriptorTable()
+: nullSegmentSelector(0, 0, 0), unusedSegmentSelector(0, 0, 0),
+codeSegmentSelector(0, _64_MEGABYTES, CSS_FLAGS),
+dataSegmentSelector(0, _64_MEGABYTES, DSS_FLAGS) {
+
+    uint32_t expectedBytes[EXPECTED_BYTES_NUM];
+    expectedBytes[GDT_ADDRESS] = (uint32_t)this;
+    expectedBytes[SEGMENT_INTEGER_HIGH_BYTES] = sizeof(GlobalDescriptorTable) << HIGH_BYTES_LSHIFT;
+
+    asm volatile("lgdt (%0)": :"p" (((uint8_t*) expectedBytes+2)));
+}
+
+// TODO: Unload the GDT.
+GlobalDescriptorTable::~GlobalDescriptorTable(){}
+
+uint16_t GlobalDescriptorTable::GetDataSegmentSelectorOffset(){
+    return (uint8_t*)&dataSegmentSelector - (uint8_t*)this;
+}
+
+uint16_t GlobalDescriptorTable::GetCodeSegmentSelectorOffset() {
+    return (uint8_t*)&codeSegmentSelector - (uint8_t*)this;
+}

src/gdt.h

@@ -22,7 +22,28 @@ class GlobalDescriptorTable {
                 uint8_t access;
                 uint8_t flags_and_limit_high_halfbyte;
                 uint8_t base_highbyte_high;
+
+            public:
+                SegmentDescriptor(uint32_t base, uint32_t limit, uint8_t access);
+                uint32_t GetBase();
+                uint32_t GetLimit();
+
         } __attribute__((packed));
+
+        SegmentDescriptor nullSegmentSelector;
+        SegmentDescriptor unusedSegmentSelector;
+        // TODO: This is only an MVP, there should NOT be only 1 code and data segment,
+        //       right now they spread through the whole memory, but this is a huge
+        //       security vulnerability.
+        SegmentDescriptor codeSegmentSelector;
+        SegmentDescriptor dataSegmentSelector;
+
+        GlobalDescriptorTable();
+        ~GlobalDescriptorTable();
+
+        uint16_t GetCodeSegmentSelectorOffset();
+        uint16_t GetDataSegmentSelectorOffset();
+
 };
 
 #endif

src/types.h

@@ -21,6 +21,6 @@ typedef int int32_t;
 typedef unsigned int uint32_t;
 
 typedef long long int int64_t;
-typedef unsigned long long int uin64_t;
+typedef unsigned long long int uint64_t;
 
 #endif