Implemented GDT initialisation

arch/x86_64/include/socks/machine/_gdt.h

@@ -0,0 +1,42 @@
+#ifndef SOCKS_X86_64__GDT_H_
+#define SOCKS_X86_64__GDT_H_
+
+#include <socks/compiler.h>
+#include <stdint.h>
+
+#define NR_GDT_ENTRIES 5
+
+#define GDT_A_PRESENT		(1 << 7)
+#define GDT_A_USER		(3 << 5)
+#define GDT_A_CODE		(3 << 3)
+#define GDT_A_DATA		(8 << 1)
+#define GDT_A_RPLK		(1 << 5)
+#define GDT_A_CODEREAD		(1 << 1)
+#define GDT_A_DATAWRITE		(1 << 1)
+#define GDT_A_GROWUP		(1 << 5)
+#define GDT_F_64BIT		(0x2F)
+#define GDT_F_32BIT		(0x4F)
+#define GDT_F_16BIT		(0xF)
+
+struct gdt_entry {
+	uint16_t ge_limit_low;
+	uint16_t ge_base_low;
+	uint8_t ge_base_mid;
+	uint8_t ge_access;
+	uint8_t ge_gran;
+	uint8_t ge_base_hi;
+} __packed;
+
+struct gdt {
+	struct gdt_entry g_entries[NR_GDT_ENTRIES];
+} __packed;
+
+struct gdt_ptr {
+	uint16_t g_limit;
+	uint64_t g_ptr;
+} __packed;
+
+extern int gdt_init(struct gdt *gdt, struct gdt_ptr *gdtp);
+extern int gdt_load(struct gdt_ptr *gdtp);
+
+#endif