Adds GDT SegmentDescriptors.

prototypes/base/Makefile

@@ -45,7 +45,7 @@ kernel-base.ker: $(OBJS)
 
 
 run:
-	qemu-system-i386 -kernel kernel-base.ker
+	qemu-system-i386 -kernel kernel-base.ker -m 64
 
 bnr: kernel-base.ker run
 

prototypes/base/include/gdt.hpp

@@ -0,0 +1,83 @@
+#pragma once
+
+#include <inttypes.h>
+
+enum class SegmentAccess : uint8_t
+{
+  None = 0,
+  Accessed = (1 << 0),
+  
+  Readable = (1<<1),
+  Writable = (1<<1),
+  
+  Direction = (1<<2),
+  Conforming = (1<<2),
+  
+  Executable = (1 << 3),
+  Segment = (1 << 4),
+  
+  Ring0 = 0,
+  Ring1 = (1<<5),
+  Ring2 = (1<<6),
+  Ring3 = (1<<5) | (1<<6),
+  
+  Present = (1 << 7),
+};
+
+static inline SegmentAccess operator | (SegmentAccess lhs, SegmentAccess rhs)
+{
+  return static_cast<SegmentAccess>(static_cast<uint8_t>(lhs) | static_cast<uint8_t>(rhs));
+}
+
+static inline SegmentAccess operator & (SegmentAccess lhs, SegmentAccess rhs)
+{
+  return static_cast<SegmentAccess>(static_cast<uint8_t>(lhs) & static_cast<uint8_t>(rhs));
+}
+
+struct SegmentDescriptor
+{
+  uint16_t limit0;
+  uint16_t base0;
+  uint8_t base1;
+  SegmentAccess access;
+  uint8_t limit1 : 4;
+  uint8_t flags : 4;
+  uint8_t base2;
+  
+  uint32_t limit()
+  {
+    return this->limit0 | (this->limit1 << 16);
+  }
+  
+  void setLimit(uint32_t value)
+  {
+      this->limit0 = (value & 0x0FFFF) >> 0;
+      this->limit1 = (value & 0xFFFFF) >> 16;
+  }
+  
+  uint32_t base()
+  {
+    return this->base0 | (this->base1 << 16) | (this->base2 << 24);
+  }
+  
+  void setBase(uint32_t value)
+  {
+    this->base0 = (value & 0x0000FFFF) >> 0;
+    this->base1 = (value & 0x00FF0000) >> 16;
+    this->base2 = (value & 0xFF000000) >> 24;
+  }
+} __attribute__((packed));
+
+static_assert(sizeof(SegmentDescriptor) == 8, "SegmentDescriptor must be 8 bytes large.");
+
+class GDT
+{
+public:
+  static const uint32_t length = 8;
+private:
+  static SegmentDescriptor descriptors[length];
+  GDT() = delete;
+public:
+  
+  static SegmentDescriptor & descriptor(uint32_t index);
+};

prototypes/base/src/gdt.cpp

@@ -0,0 +1,12 @@
+#include "gdt.hpp"
+
+SegmentDescriptor GDT::descriptors[GDT::length];
+
+SegmentDescriptor & GDT::descriptor(uint32_t index)
+{
+  static SegmentDescriptor invalid;
+  if(index >= GDT::length) {
+    return invalid;
+  }
+  return GDT::descriptors[index];
+}