initial commit

kernel/src/gdt.rs

@@ -0,0 +1,49 @@
+use lazy_static::lazy_static;
+use x86_64::{
+    structures::{
+        gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector},
+        tss::TaskStateSegment,
+    },
+    VirtAddr, registers::segmentation::{CS, Segment}, instructions::tables::load_tss,
+};
+
+pub const DOUBLE_FAULT_IST_INDEX: u16 = 0;
+
+pub fn init() {
+    GDT.0.load();
+    unsafe {
+        CS::set_reg(GDT.1.code);
+        load_tss(GDT.1.tss);
+        // TODO: properly handle this
+        x86_64::registers::segmentation::SS::set_reg(SegmentSelector::NULL);
+    }
+}
+
+struct Selectors {
+    code: SegmentSelector,
+    tss: SegmentSelector,
+}
+
+lazy_static! {
+    static ref GDT: (GlobalDescriptorTable, Selectors) = {
+        let mut gdt = GlobalDescriptorTable::new();
+        let code = gdt.add_entry(Descriptor::kernel_code_segment());
+        let tss = gdt.add_entry(Descriptor::tss_segment(&TSS));
+        (gdt, Selectors { code, tss })
+    };
+}
+
+lazy_static! {
+    static ref TSS: TaskStateSegment = {
+        let mut tss = TaskStateSegment::new();
+        tss.interrupt_stack_table[DOUBLE_FAULT_IST_INDEX as usize] = {
+            const STACK_SIZE: usize = 4096 * 5;
+            static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];
+
+            let stack_start = VirtAddr::from_ptr(unsafe { &STACK });
+            let stack_end = stack_start + STACK_SIZE;
+            stack_end
+        };
+        tss
+    };
+}