feat(cpu): add GDT and TSS for ring 0 and ring 3 segments

include/gdt.h

@@ -0,0 +1,15 @@
+#ifndef FROSTBYTE_GDT_H
+#define FROSTBYTE_GDT_H
+
+#include "types.h"
+
+#define kernelCodeSelector 0x08
+#define kernelDataSelector 0x10
+#define userCodeSelector   0x18
+#define userDataSelector   0x20
+#define tssSelector        0x28
+
+void gdtInit(void);
+void gdtInstallTss(uint64 base, uint32 limit);
+
+#endif

include/tss.h

@@ -0,0 +1,9 @@
+#ifndef FROSTBYTE_TSS_H
+#define FROSTBYTE_TSS_H
+
+#include "types.h"
+
+void tssInit(uint64 rsp0);
+void tssSetRsp0(uint64 rsp0);
+
+#endif