set_sys_gdt
set_sys_gdt(slot, tss, sizeof(struct x86_64_tss) - 1, SDT_SYS386TSS,
set_sys_gdt(slot, ldtp, len - 1, SDT_SYSLDT, SEL_KPL, 0);
static void set_sys_gdt(int, void *, size_t, int, int, int);