init_gdt_entry(0,0,0,0,0);                              // null segment
    init_gdt_entry(1,0xffffffff,0,0b10011010,0b11001111);   // code segment
    init_gdt_entry(2,0xffffffff,0,0b10010010,0b11001111);   // data segment
    init_gdt_entry(3,0xffffffff,0,0b11111010,0b11001111);   // user mode code segment
    init_gdt_entry(4,0xffffffff,0,0b11110010,0b11001111);   // user mode data segment