rustos 0.4.3

Writing an OS in Rust
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//! Global Descriptor Table handling
use lazy_static::lazy_static;
use x86_64::{
    instructions::{segmentation::set_cs, tables::load_tss},
    structures::{
        gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector},
        tss::TaskStateSegment,
    },
    VirtAddr,
};

pub(crate) fn init() {
    GDT.0.load();
    unsafe {
        set_cs(GDT.1.code_selector);
        load_tss(GDT.1.tss_selector);
    }
}

lazy_static! {
    static ref GDT: (GlobalDescriptorTable, Selectors) = {
        let mut gdt = GlobalDescriptorTable::new();
        let code_selector = gdt.add_entry(Descriptor::kernel_code_segment());
        let tss_selector = gdt.add_entry(Descriptor::tss_segment(&TSS));
        (
            gdt,
            Selectors {
                code_selector,
                tss_selector,
            },
        )
    };
}

struct Selectors {
    code_selector: SegmentSelector,
    tss_selector: SegmentSelector,
}

const DOUBLE_FAULT_IST_INDEX: u16 = 0;

lazy_static! {
    static ref TSS: TaskStateSegment = {
        let mut tss = TaskStateSegment::new();
        const STACK_SIZE: usize = 4096;
        static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];
        let stack_end = VirtAddr::from_ptr(unsafe { &STACK }) + STACK_SIZE;
        tss.interrupt_stack_table[DOUBLE_FAULT_IST_INDEX as usize] = stack_end;
        tss
    };
}