From 8e2ee50f66c171c2aa592193b051d4987139585c Mon Sep 17 00:00:00 2001
From: Erin <erin@hashbang.sh>
Date: Sun, 4 Jun 2017 11:45:26 -0500
Subject: [PATCH] Preliminary data structures required for a page table manager

---
 src/arch/x86_64/memory/paging/entry.rs | 49 ++++++++++++++++++++++++++++++++++
 src/arch/x86_64/memory/paging/mod.rs   | 21 +++++++++++++++
 src/arch/x86_64/memory/paging/table.rs | 29 ++++++++++++++++++++
 3 files changed, 99 insertions(+)
 create mode 100644 src/arch/x86_64/memory/paging/entry.rs
 create mode 100644 src/arch/x86_64/memory/paging/mod.rs
 create mode 100644 src/arch/x86_64/memory/paging/table.rs

diff --git a/src/arch/x86_64/memory/paging/entry.rs b/src/arch/x86_64/memory/paging/entry.rs
new file mode 100644
index 0000000..e2c8f9b
--- /dev/null
+++ b/src/arch/x86_64/memory/paging/entry.rs
@@ -0,0 +1,49 @@
+use arch::x86_64::memory::Frame;
+
+pub struct Entry(u64);
+
+impl Entry {
+    pub fn is_unused(&self) -> bool {
+        self.0 == 0
+    }
+
+    pub fn set_unused(&mut self) {
+        self.0 = 0;
+    }
+
+    pub fn flags(&self) -> EntryFlags {
+        EntryFlags::from_bits_truncate(self.0)
+    }
+
+    pub fn pointed_frame(&self) -> Option<Frame> {
+        if self.flags().contains(PRESENT) {
+            Some(Frame::containing_address(
+                self.0 as usize & 0x000fffff_fffff000
+            ))
+        } else {
+            None
+        }
+    }
+
+    pub fn set(&mut self, frame: Frame, flags: EntryFlags) {
+        // Frame physical address must be page-aligned and smaller than 2^52
+        assert!(frame.start_address() & !0x000fffff_fffff000 == 0);
+
+        self.0 = (frame.start_address() as u64) | flags.bits();
+    }
+}
+
+bitflags! {
+    pub struct EntryFlags: u64 {
+        const PRESENT =         1 << 0;
+        const WRITABLE =        1 << 1;
+        const USER_ACCESSIBLE = 1 << 2;
+        const WRITE_THROUGH =   1 << 3;
+        const NO_CACHE =        1 << 4;
+        const ACCESSED =        1 << 5;
+        const DIRTY =           1 << 6;
+        const HUGE_PAGE =       1 << 7;
+        const GLOBAL =          1 << 8;
+        const NO_EXECUTE =      1 << 63;
+    }
+}
diff --git a/src/arch/x86_64/memory/paging/mod.rs b/src/arch/x86_64/memory/paging/mod.rs
new file mode 100644
index 0000000..cd4078e
--- /dev/null
+++ b/src/arch/x86_64/memory/paging/mod.rs
@@ -0,0 +1,21 @@
+//! Paging subsystem.
+//!
+//! Extremely ripped off from Phil Oppermann's tutorials, because I don't feel like writing
+//! a paging system off the top of my head today.
+
+use super::PAGE_SIZE;
+
+mod entry;
+mod table;
+
+/// Upper bound on entries per page table
+const ENTRY_COUNT: usize = 512;
+
+/// Helper type aliases used to make function signatures more expressive
+pub type PhysicalAddress = usize;
+pub type VirtualAddress = usize;
+
+/// A representation of a virtual page
+pub struct Page {
+    index: usize,
+}
diff --git a/src/arch/x86_64/memory/paging/table.rs b/src/arch/x86_64/memory/paging/table.rs
new file mode 100644
index 0000000..b5ec2d5
--- /dev/null
+++ b/src/arch/x86_64/memory/paging/table.rs
@@ -0,0 +1,29 @@
+use core::ops::{Index, IndexMut};
+use super::entry::*;
+use super::ENTRY_COUNT;
+
+pub struct Table {
+    entries: [Entry; ENTRY_COUNT],
+}
+
+impl Table {
+    pub fn zero(&mut self) {
+        for entry in self.entries.iter_mut() {
+            entry.set_unused();
+        }
+    }
+}
+
+impl Index<usize> for Table {
+    type Output = Entry;
+
+    fn index(&self, index: usize) -> &Entry {
+         &self.entries[index]
+    }
+}
+
+impl IndexMut<usize> for Table {
+    fn index_mut(&mut self, index: usize) -> &mut Entry {
+         &mut self.entries[index]
+    }
+}