GDT_UCODE
set_usegd(&gdt[GDT_UCODE], SDP_LONG, NULL, 0, SDT_MEMERA, SEL_UPL,
ucs_on = ucs_off = gdt[GDT_UCODE];
gdt_update_usegd(GDT_UCODE, &ucs_on);
gdt_update_usegd(GDT_UCODE, &ucs_off);
#define UCS_SEL SEL_GDT(GDT_UCODE, SEL_UPL)