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use crate::structures::tss::TaskStateSegment;
use crate::PrivilegeLevel;
use bit_field::BitField;
use bitflags::bitflags;
use core::fmt;
#[derive(Clone, Copy, PartialEq, Eq)]
#[repr(transparent)]
pub struct SegmentSelector(pub u16);
impl SegmentSelector {
pub const fn new(index: u16, rpl: PrivilegeLevel) -> SegmentSelector {
SegmentSelector(index << 3 | (rpl as u16))
}
pub fn index(&self) -> u16 {
self.0 >> 3
}
pub fn rpl(&self) -> PrivilegeLevel {
PrivilegeLevel::from_u16(self.0.get_bits(0..2))
}
}
impl fmt::Debug for SegmentSelector {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let mut s = f.debug_struct("SegmentSelector");
s.field("index", &self.index());
s.field("rpl", &self.rpl());
s.finish()
}
}
#[derive(Debug, Clone)]
pub struct GlobalDescriptorTable {
table: [u64; 8],
next_free: usize,
}
impl GlobalDescriptorTable {
pub fn new() -> GlobalDescriptorTable {
GlobalDescriptorTable {
table: [0; 8],
next_free: 1,
}
}
pub fn add_entry(&mut self, entry: Descriptor) -> SegmentSelector {
let index = match entry {
Descriptor::UserSegment(value) => self.push(value),
Descriptor::SystemSegment(value_low, value_high) => {
let index = self.push(value_low);
self.push(value_high);
index
}
};
SegmentSelector::new(index as u16, PrivilegeLevel::Ring0)
}
#[cfg(target_arch = "x86_64")]
pub fn load(&'static self) {
use crate::instructions::tables::{lgdt, DescriptorTablePointer};
use core::mem::size_of;
let ptr = DescriptorTablePointer {
base: self.table.as_ptr() as u64,
limit: (self.table.len() * size_of::<u64>() - 1) as u16,
};
unsafe { lgdt(&ptr) };
}
fn push(&mut self, value: u64) -> usize {
if self.next_free < self.table.len() {
let index = self.next_free;
self.table[index] = value;
self.next_free += 1;
index
} else {
panic!("GDT full");
}
}
}
#[derive(Debug, Clone)]
pub enum Descriptor {
UserSegment(u64),
SystemSegment(u64, u64),
}
bitflags! {
pub struct DescriptorFlags: u64 {
const CONFORMING = 1 << 42;
const EXECUTABLE = 1 << 43;
const USER_SEGMENT = 1 << 44;
const PRESENT = 1 << 47;
const LONG_MODE = 1 << 53;
}
}
impl Descriptor {
pub fn kernel_code_segment() -> Descriptor {
use self::DescriptorFlags as Flags;
let flags = Flags::USER_SEGMENT | Flags::PRESENT | Flags::EXECUTABLE | Flags::LONG_MODE;
Descriptor::UserSegment(flags.bits())
}
pub fn tss_segment(tss: &'static TaskStateSegment) -> Descriptor {
use self::DescriptorFlags as Flags;
use bit_field::BitField;
use core::mem::size_of;
let ptr = tss as *const _ as u64;
let mut low = Flags::PRESENT.bits();
low.set_bits(16..40, ptr.get_bits(0..24));
low.set_bits(56..64, ptr.get_bits(24..32));
low.set_bits(0..16, (size_of::<TaskStateSegment>() - 1) as u64);
low.set_bits(40..44, 0b1001);
let mut high = 0;
high.set_bits(0..32, ptr.get_bits(32..64));
Descriptor::SystemSegment(low, high)
}
}