From c961fdc32bb1edd69ddfb3ed964d1d4990701f37 Mon Sep 17 00:00:00 2001
From: Philipp Oppermann <dev@phil-opp.com>
Date: Wed, 25 May 2016 14:03:43 +0200
Subject: [PATCH] wip

---
 src/interrupts/gdt.rs | 115 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 src/interrupts/gdt.rs

diff --git a/src/interrupts/gdt.rs b/src/interrupts/gdt.rs
new file mode 100644
index 00000000..930b1caf
--- /dev/null
+++ b/src/interrupts/gdt.rs
@@ -0,0 +1,115 @@
+use bit_field::BitField;
+use collections::vec::Vec;
+use core::ops::Range;
+use x86::task::TaskStateSegment;
+
+pub struct Gdt(Vec<BitField<u64>>);
+
+impl Gdt {
+    pub fn new() -> Gdt {
+        let zero_entry = BitField::new(0);
+        Gdt(vec![zero_entry])
+    }
+
+    pub fn add_entry(&mut self, entry: Entry) -> Selector {
+        use core::mem::size_of;
+        let index = self.0.len() * size_of::<BitField<u64>>();
+
+        match entry {
+            Entry::UserSegment(entry) => self.0.push(entry),
+            Entry::SystemSegment(entry_low, entry_high) => {
+                self.0.push(entry_low);
+                self.0.push(entry_high);
+            }
+        }
+
+        Selector(index as u16)
+    }
+
+    pub unsafe fn load(&'static self) {
+        use x86::dtables::{DescriptorTablePointer, lgdt};
+        use core::mem::{self, size_of};
+
+        let ptr = DescriptorTablePointer {
+            base: self.0.as_ptr() as u64,
+            limit: (self.0.len() * size_of::<u64>() - 1) as u16,
+        };
+
+        lgdt(&ptr);
+    }
+}
+
+pub enum Entry {
+    UserSegment(BitField<u64>),
+    SystemSegment(BitField<u64>, BitField<u64>),
+}
+
+impl Entry {
+    pub fn code_segment() -> Entry {
+        let flags = DESCRIPTOR_TYPE | PRESENT | READ_WRITE | EXECUTABLE | LONG_MODE;
+        Entry::UserSegment(BitField::new(flags.bits()))
+    }
+
+    pub fn data_segment() -> Entry {
+        let flags = DESCRIPTOR_TYPE | PRESENT | READ_WRITE;
+        Entry::UserSegment(BitField::new(flags.bits()))
+    }
+
+    pub fn tss_segment(tss: &'static TaskStateSegment) -> Entry {
+        use core::mem::size_of;
+
+        let ptr = BitField::new(tss as *const _ as u64);
+
+        let mut low = BitField::new(PRESENT.bits());
+        low.set_range(0..16, (size_of::<TaskStateSegment>() - 1) as u64);
+        low.set_range(16..40, ptr.get_range(0..24));
+        low.set_range(40..44, 0b1001); // type: available 64-bit tss
+
+        let mut high = BitField::new(0);
+        high.set_range(0..32, ptr.get_range(32..64));
+
+        Entry::SystemSegment(low, high)
+    }
+}
+
+bitflags! {
+    flags EntryFlags: u64 {
+        const READ_WRITE        = 1 << 41,
+        const CONFORMING        = 1 << 42,
+        const EXECUTABLE        = 1 << 43,
+        const DESCRIPTOR_TYPE   = 1 << 44,
+        const PRESENT           = 1 << 47,
+        const LONG_MODE         = 1 << 53,
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Selector(u16);
+
+pub fn reload_segment_registers(code_selector: Selector, data_selector: Selector) {
+
+    let current_code_selector: u16;
+    let current_data_selector: u16;
+
+    unsafe {
+        asm!("mov $0, cs" : "=r" (current_code_selector) ::: "intel");
+        asm!("mov $0, ds" : "=r" (current_data_selector) ::: "intel");
+    }
+    assert_eq!(code_selector.0, current_code_selector);
+    assert_eq!(data_selector.0, current_data_selector);
+
+    // jmp ax:.new_code_segment // TODO
+    // .new_code_segment:
+    // unsafe { asm!("
+    // mov ax, $1
+    // mov ss, ax
+    // mov ds, ax
+    // mov es, ax
+    // ":: "r" (code_selector.0), "r" (data_selector.0) :: "intel")};
+    //
+}
+
+/// Load the task state register.
+pub unsafe fn load_ltr(selector: Selector) {
+    asm!("ltr $0" :: "r" (selector));
+}