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Use type system tricks to make next_table methods safe

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Philipp Oppermann
2017-04-13 19:11:31 +02:00
parent 0874625269
commit a7170a4a44
1 changed files with 39 additions and 7 deletions
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46
src/memory/paging/table.rs
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@@ -1,20 +1,24 @@
use core::marker::PhantomData;
use core::ops::{Index, IndexMut}; use core::ops::{Index, IndexMut};
use memory::paging::entry::*; use memory::paging::entry::*;
use memory::paging::ENTRY_COUNT; use memory::paging::ENTRY_COUNT;
pub const P4: *mut Table = 0xffffffff_fffff000 as *mut _; pub const P4: *mut Table<Level4> = 0xffffffff_fffff000 as *mut _;
pub struct Table { pub struct Table<L: TableLevel> {
entries: [Entry; ENTRY_COUNT], entries: [Entry; ENTRY_COUNT],
level: PhantomData<L>,
} }
impl Table { impl<L> Table<L> where L: TableLevel {
pub fn zero(&mut self) { pub fn zero(&mut self) {
for entry in self.entries.iter_mut() { for entry in self.entries.iter_mut() {
entry.set_unused(); entry.set_unused();
} }
} }
}
impl<L> Table<L> where L: HierarchicalLevel {
fn next_table_address(&self, index: usize) -> Option<usize> { fn next_table_address(&self, index: usize) -> Option<usize> {
let entry_flags = self[index].flags(); let entry_flags = self[index].flags();
if entry_flags.contains(PRESENT) && !entry_flags.contains(HUGE_PAGE) { if entry_flags.contains(PRESENT) && !entry_flags.contains(HUGE_PAGE) {
@@ -25,18 +29,18 @@ impl Table {
} }
} }
pub fn next_table(&self, index: usize) -> Option<&Table> { pub fn next_table(&self, index: usize) -> Option<&Table<L::NextLevel>> {
self.next_table_address(index) self.next_table_address(index)
.map(|address| unsafe { &*(address as *const _) }) .map(|address| unsafe { &*(address as *const _) })
} }
pub fn next_table_mut(&mut self, index: usize) -> Option<&mut Table> { pub fn next_table_mut(&mut self, index: usize) -> Option<&mut Table<L::NextLevel>> {
self.next_table_address(index) self.next_table_address(index)
.map(|address| unsafe { &mut *(address as *mut _) }) .map(|address| unsafe { &mut *(address as *mut _) })
} }
} }
impl Index<usize> for Table { impl<L> Index<usize> for Table<L> where L: TableLevel {
type Output = Entry; type Output = Entry;
fn index(&self, index: usize) -> &Entry { fn index(&self, index: usize) -> &Entry {
@@ -44,8 +48,36 @@ impl Index<usize> for Table {
} }
} }
impl IndexMut<usize> for Table { impl<L> IndexMut<usize> for Table<L> where L: TableLevel {
fn index_mut(&mut self, index: usize) -> &mut Entry { fn index_mut(&mut self, index: usize) -> &mut Entry {
&mut self.entries[index] &mut self.entries[index]
} }
} }
pub trait TableLevel {}
pub enum Level4 {}
pub enum Level3 {}
pub enum Level2 {}
pub enum Level1 {}
impl TableLevel for Level4 {}
impl TableLevel for Level3 {}
impl TableLevel for Level2 {}
impl TableLevel for Level1 {}
pub trait HierarchicalLevel: TableLevel {
type NextLevel: TableLevel;
}
impl HierarchicalLevel for Level4 {
type NextLevel = Level3;
}
impl HierarchicalLevel for Level3 {
type NextLevel = Level2;
}
impl HierarchicalLevel for Level2 {
type NextLevel = Level1;
}