Actual heap allocation!!!!!!!!!!!!

Cargo.lock

@@ -41,12 +41,15 @@ dependencies = [
 name = "kernel"
 version = "0.1.0"
 dependencies = [
+ "bitflags 2.5.0",
  "lazy_static",
  "log",
  "multiboot2",
+ "once",
  "pc-keyboard",
  "pic8259",
  "spin 0.9.8",
+ "talc",
  "uart_16550",
  "x86",
  "x86_64",
@@ -90,6 +93,12 @@ dependencies = [
  "uefi-raw",
 ]
 
+[[package]]
+name = "once"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60bfe75a40f755f162b794140436c57845cb106fd1467598631c76c6fff08e28"
+
 [[package]]
 name = "pc-keyboard"
 version = "0.7.0"
@@ -190,6 +199,15 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "talc"
+version = "4.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "04be12ec299aadd63a0bf781d893e4b6139d33cdca6dcd6f6be31f849cedcac8"
+dependencies = [
+ "lock_api",
+]
+
 [[package]]
 name = "uart_16550"
 version = "0.3.0"

boot/boot.s

@@ -94,6 +94,10 @@ check_long_mode:
     jmp error
 
 set_up_page_tables:
+    mov eax, p4_table
+    or eax, 0b11 ; present + writable
+    mov [p4_table + 511 * 8], eax
+
     ; map first P4 entry to P3 table
     mov eax, p3_table
     or eax, 0b11 ; present + writable

kernel/Cargo.toml

@@ -11,12 +11,15 @@ crate-type=["staticlib"]
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+bitflags = "2.5.0"
 lazy_static = { version = "1.4.0", features = ["spin_no_std"] }
 log = "0.4.21"
 multiboot2 = "0.20.2"
+once = "0.3.4"
 pc-keyboard = "0.7.0"
 pic8259 = "0.11.0"
 spin = "0.9.8"
+talc = "4.4.1"
 uart_16550 = "0.3.0"
 x86 = "0.52.0"
 x86_64 = "0.15.1"

kernel/src/gdt/mod.rs

@@ -38,7 +38,7 @@ struct Selectors {
 }
 
 pub fn init() {
-    log::debug!("GDT init");
+    log::info!("GDT init");
     use x86_64::instructions::tables::load_tss;
     use x86_64::instructions::segmentation::{CS, Segment};
     

kernel/src/interrupts/mod.rs

@@ -40,7 +40,7 @@ pub enum InterruptIndex {
 }
 
 pub fn init_idt() {
-    log::debug!("IDT init");
+    log::info!("IDT init");
     IDT.load();
     unsafe { PICS.lock().initialize() };
     x86_64::instructions::interrupts::enable();

kernel/src/lib.rs

@@ -2,10 +2,13 @@
 #![no_main]
 #![feature(abi_x86_interrupt)]
 #![feature(associated_type_defaults)]
+#![allow(internal_features)]
+#![feature(ptr_internals)]
+#![feature(allocator_api)]
 
-use events::EVENTMAN;
+use alloc::vec::Vec;
 
-use crate::events::Event;
+extern crate alloc;
 
 #[macro_use]
 mod logger;
@@ -21,23 +24,38 @@ mod mem;
 
 #[no_mangle]
 extern "C" fn kmain(mb2_info_addr: usize) -> ! {
+    // Init
     logger::init(log::LevelFilter::Trace).unwrap();
     gdt::init();
     interrupts::init_idt();
-    let mem_info = mem::MemInfo::load(mb2_info_addr);
-    let mut _alloc = mem::area_frame_alloc::AreaFrameAllocator::new(mem_info);
+    utils::enable_nxe_bit();
+    utils::enable_write_protect_bit();
     
-    EVENTMAN.lock().add_listener(events::Event::Ps2KeyPress(None), |k| {
-        let Event::Ps2KeyPress(v) = k else {panic!()};
+    mem::init(mb2_info_addr);
 
-        log::debug!("Keypress event received! ({:?})", v.unwrap());
-        Ok(())
-    });
+    let mut a = Vec::new();
     
 
+    a.push(6);
+    a.push(9);
+    a.push(4);
+    a.push(2);
+    a.push(0);
+    
+    log::error!("{:?}", a); 
+
+
+    
+    // EVENTMAN.lock().add_listener(events::Event::Ps2KeyPress(None), |k| {
+    //    let Event::Ps2KeyPress(v) = k else {panic!()};
+    //
+    //    log::debug!("Keypress event received! ({:?})", v.unwrap());
+    //   Ok(())
+    // });
+
     // let (level_4_page_table, _) = Cr3::read();
     // println!("Level 4 page table at: {:?}", level_4_page_table.start_address());
-
+    log::info!("end of work");
 
     utils::hcf();
 }

kernel/src/mem/area_frame_alloc.rs

@@ -68,11 +68,11 @@ impl<'a> AreaFrameAllocator<'a> {
             }
         }
     }
-    pub fn new(mi: MemInfo) -> AreaFrameAllocator<'a> {
+    pub fn new(mi: &MemInfo) -> AreaFrameAllocator<'a> {
         let mut allocator = AreaFrameAllocator {
             next_free_frame: Frame::containing_address(0),
             current_area: None,
-            areas: mi.mem_area_iter,
+            areas: mi.mem_area_iter.clone(),
             kernel_start: Frame::containing_address(mi.kernel_start),
             kernel_end: Frame::containing_address(mi.kernel_end),
             multiboot_start: Frame::containing_address(mi.mb_start),

kernel/src/mem/heap/mod.rs

@@ -0,0 +1,46 @@
+use core::{alloc::{AllocError, GlobalAlloc, Layout}, sync::atomic::{AtomicUsize, Ordering}};
+
+use x86_64::align_up;
+
+pub const HEAP_START: usize = 0o_000_001_000_000_0000;
+pub const HEAP_SIZE: usize = 100 * 1024; // 100 KiB
+
+/// A simple allocator that allocates memory linearly and ignores freed memory.
+#[derive(Debug)]
+pub struct BumpAllocator {
+    heap_start: usize,
+    heap_end: usize,
+    next: AtomicUsize,
+}
+
+impl BumpAllocator {
+    pub const fn new(heap_start: usize, heap_end: usize) -> Self {
+        Self { heap_start, heap_end, next: AtomicUsize::new(heap_start) }
+    }
+}
+
+unsafe impl GlobalAlloc for BumpAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        loop {
+            // load current state of the `next` field
+            let current_next = self.next.load(Ordering::Relaxed);
+            let alloc_start = align_up(current_next as u64, layout.align() as u64);
+            let alloc_end = alloc_start.saturating_add(layout.size() as u64);
+
+            if alloc_end <= self.heap_end as u64 {
+                // update the `next` pointer if it still has the value `current_next`
+                let next_now = self.next.compare_exchange(current_next, alloc_end as usize, Ordering::Relaxed, Ordering::Relaxed).unwrap();
+                if next_now == current_next {
+                    // next address was successfully updated, allocation succeeded
+                    return alloc_start as *mut u8;
+                }
+            } else {
+                panic!("OUT OF MEMORY");
+            }
+        }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        // do nothing, leak memory
+    }
+}

kernel/src/mem/mod.rs

@@ -1,11 +1,23 @@
 use core::alloc::{GlobalAlloc, Layout};
 
-use multiboot2::{BootInformationHeader, MemoryArea, MemoryAreaType, MemoryMapTag, TagTrait};
+use multiboot2::{BootInformation, BootInformationHeader, MemoryArea, MemoryAreaType, MemoryMapTag, TagTrait};
+use talc::{ErrOnOom, Span, Talc, Talck};
+use crate::mem::paging::entry::EntryFlags;
 
+use self::heap::{HEAP_SIZE, HEAP_START};
+pub use self::paging::remap_the_kernel;
+
+pub mod heap;
 pub mod area_frame_alloc;
+pub mod paging;
+
+//#[global_allocator]
+//static GLOBAL_ALLOCATOR: heap::BumpAllocator = heap::BumpAllocator::new(HEAP_START, HEAP_START + HEAP_SIZE);
 
 #[global_allocator]
-static GLOBAL_ALLOCATOR: DummyAlloc = DummyAlloc;
+static GLOBAL_ALLOCATOR: Talck<spin::Mutex<()>, ErrOnOom> = Talc::new(ErrOnOom).lock();
+
+
 pub struct DummyAlloc;
 unsafe impl GlobalAlloc for DummyAlloc {
     unsafe fn alloc(&self, _: Layout) -> *mut u8 { 0 as *mut u8 }
@@ -24,7 +36,39 @@ impl Frame {
     fn containing_address(address: usize) -> Frame {
         Frame{ number: address / PAGE_SIZE }
     }
+    fn start_address(&self) -> paging::PhysicalAddress {
+        self.number * PAGE_SIZE
     }
+    fn clone(&self) -> Frame {
+        Frame { number: self.number }
+    }
+    fn range_inclusive(start: Frame, end: Frame) -> FrameIter {
+        FrameIter {
+            start,
+            end,
+        }
+    }
+}
+
+struct FrameIter {
+    start: Frame,
+    end: Frame,
+}
+
+impl Iterator for FrameIter {
+    type Item = Frame;
+
+    fn next(&mut self) -> Option<Frame> {
+        if self.start <= self.end {
+            let frame = self.start.clone();
+            self.start.number += 1;
+            Some(frame)
+        } else {
+            None
+        }
+    }
+ }
+
 
 #[allow(dead_code)]
 pub trait FrameAllocator {
@@ -70,8 +114,9 @@ impl MemoryAreaIter {
 }
 
 
-#[derive(Debug, Clone)]
-pub struct MemInfo{
+#[derive(Debug)]
+pub struct MemInfo<'a>{
+    boot_info: BootInformation<'a>,
     mem_area_iter: MemoryAreaIter,
     pub kernel_start: usize,
     pub kernel_end: usize,
@@ -79,7 +124,7 @@ pub struct MemInfo{
     pub mb_end: usize,
 }
 
-impl MemInfo {
+impl MemInfo<'_> {
     pub fn load(mb_ptr: usize) -> Self {
         let boot_info = unsafe {
             multiboot2::BootInformation::load(mb_ptr as *const BootInformationHeader).unwrap()
@@ -96,8 +141,9 @@ impl MemInfo {
         //     log::debug!("{}: start: 0x{:x}, sz: 0x{:x}, flags: 0b{:b}", section.name().unwrap_or("NONE"),
         //         section.start_address(), section.size(), section.flags());
         // }
-        let kernel_start = boot_info.elf_sections().unwrap().clone().map(|s| s.start_address()).min().unwrap() as usize;
-        let kernel_end = boot_info.elf_sections().unwrap().clone().map(|s| s.end_address()).max().unwrap() as usize;
+        let elf_secs =  boot_info.elf_sections().unwrap(); 
+        let kernel_start = elf_secs.clone().filter(|s| s.is_allocated()).map(|s| s.start_address()).min().unwrap() as usize;
+        let kernel_end = elf_secs.clone().filter(|s| s.is_allocated()).map(|s| s.end_address()).min().unwrap() as usize;
         let mb_start = boot_info.start_address();
         let mb_end = boot_info.end_address();
 
@@ -105,6 +151,7 @@ impl MemInfo {
         //log::debug!("Multiboot: start: 0x{:x} sz: 0x{:x}", mi.mb_start, mi.mb_end - mi.mb_start);
         
         Self {
+            boot_info:unsafe { multiboot2::BootInformation::load(mb_ptr as *const BootInformationHeader).unwrap()},
             mem_area_iter: MemoryAreaIter::new(mmap_tag),
             kernel_start,
             kernel_end,
@@ -114,3 +161,22 @@ impl MemInfo {
     }
 }
 
+pub fn init(mb_ptr: usize) {
+    once::assert_has_not_been_called!("mem::init must be called only once");
+    let mem_info = MemInfo::load(mb_ptr);
+    let mut frame_alloc = area_frame_alloc::AreaFrameAllocator::new(&mem_info);
+    
+    let mut active_table = remap_the_kernel(&mut frame_alloc, &mem_info);
+
+    use self::paging::Page;
+
+    let heap_start_page = Page::containing_address(HEAP_START);
+    let heap_end_page = Page::containing_address(HEAP_START + HEAP_SIZE-1);
+
+    for page in Page::range_inclusive(heap_start_page, heap_end_page) {
+        active_table.map(page, EntryFlags::WRITABLE, &mut frame_alloc);
+    }
+    unsafe {
+        GLOBAL_ALLOCATOR.lock().claim(Span::from_base_size(HEAP_START as *mut u8, HEAP_SIZE)).unwrap();
+    }
+}

kernel/src/mem/paging/entry.rs

@@ -0,0 +1,76 @@
+use multiboot2::ElfSection;
+
+use crate::mem::Frame;
+
+pub struct Entry(u64);
+
+bitflags::bitflags! {
+    #[derive(Debug, Clone, Copy)]
+    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;
+    }
+}
+
+impl EntryFlags {
+    pub fn from_elf_section_flags(section: &ElfSection) -> EntryFlags {
+        use multiboot2::ElfSectionFlags;
+
+        let mut flags = EntryFlags::empty();
+
+        if section.flags().contains(ElfSectionFlags::ALLOCATED) {
+            // section is loaded to memory
+            flags = flags | EntryFlags::PRESENT;
+        }
+        if section.flags().contains(ElfSectionFlags::WRITABLE) {
+            flags = flags | EntryFlags::WRITABLE;
+        }
+        if !section.flags().contains(ElfSectionFlags::EXECUTABLE) {
+            flags = flags | EntryFlags::NO_EXECUTE;
+        }
+
+        flags
+    }
+}
+
+
+
+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(EntryFlags::PRESENT) {
+            Some(Frame::containing_address(
+                self.0 as usize & 0x000fffff_fffff000
+            ))
+        } else {
+            None
+        }
+    }
+
+    pub fn set(&mut self, frame: Frame, flags: EntryFlags) {
+        assert!(frame.start_address() & !0x000fffff_fffff000 == 0);
+        self.0 = (frame.start_address() as u64) | flags.bits();
+    }
+    
+    
+}
+

kernel/src/mem/paging/mapper.rs

@@ -0,0 +1,141 @@
+use x86_64::VirtAddr;
+
+use super::{
+    entry::*, tables::{
+        Level4, Table, P4
+    }, 
+    Frame, FrameAllocator,
+    PAGE_SIZE, PhysicalAddress,
+    VirtualAddress, Page,
+    ENTRY_COUNT, InactivePageTable
+};
+use core::ptr::Unique;
+
+pub struct Mapper {
+    p4: Unique<Table<Level4>>,
+}
+
+impl Mapper {
+    pub unsafe fn new() -> Mapper {
+        Mapper {
+            p4: Unique::new_unchecked(P4),
+        }
+    }
+    pub fn p4(&self) -> &Table<Level4> {
+        unsafe { self.p4.as_ref() }
+    }
+
+    pub fn p4_mut(&mut self) -> &mut Table<Level4> {
+        unsafe { self.p4.as_mut() }
+    }
+    
+    /// Translates a virtual to the corresponding physical address.
+    /// Returns `None` if the address is not mapped.
+    pub fn translate(&self, virtual_address: VirtualAddress)
+        -> Option<PhysicalAddress>
+    {
+        let offset = virtual_address % PAGE_SIZE;
+        self.translate_page(Page::containing_address(virtual_address))
+            .map(|frame| frame.number * PAGE_SIZE + offset)
+    }
+
+    pub fn translate_page(&self, page: Page) -> Option<Frame> {
+
+        let p3 = self.p4().next_table(page.p4_index());
+
+        let huge_page = || {
+            p3.and_then(|p3| {
+            let p3_entry = &p3[page.p3_index()];
+            // 1GiB page?
+            if let Some(start_frame) = p3_entry.pointed_frame() {
+                if p3_entry.flags().contains(EntryFlags::HUGE_PAGE) {
+                    // address must be 1GiB aligned
+                    assert!(start_frame.number % (ENTRY_COUNT * ENTRY_COUNT) == 0);
+                    return Some(Frame {
+                        number: start_frame.number + page.p2_index() *
+                                ENTRY_COUNT + page.p1_index(),
+                    });
+                }
+            }
+            if let Some(p2) = p3.next_table(page.p3_index()) {
+                let p2_entry = &p2[page.p2_index()];
+                // 2MiB page?
+                if let Some(start_frame) = p2_entry.pointed_frame() {
+                    if p2_entry.flags().contains(EntryFlags::HUGE_PAGE) {
+                        // address must be 2MiB aligned
+                        assert!(start_frame.number % ENTRY_COUNT == 0);
+                        return Some(Frame {
+                            number: start_frame.number + page.p1_index()
+                        });
+                    }
+                }
+            }
+            None
+          })
+        };
+
+        p3.and_then(|p3| p3.next_table(page.p3_index()))
+          .and_then(|p2| p2.next_table(page.p2_index()))
+          .and_then(|p1| p1[page.p1_index()].pointed_frame())
+          .or_else(huge_page)
+    }
+    
+    /// Maps the page to the frame with the provided flags.
+    /// The `EntryFlags::PRESENT` flag is added by default. Needs a
+    /// `FrameAllocator` as it might need to create new page tables.
+    pub fn map_to<A>(&mut self, page: Page, frame: Frame, flags: EntryFlags,
+                     allocator: &mut A)
+        where A: FrameAllocator
+    {
+        let p4 = self.p4_mut();
+        let p3 = p4.next_table_create(page.p4_index(), allocator);
+        let p2 = p3.next_table_create(page.p3_index(), allocator);
+        let p1 = p2.next_table_create(page.p2_index(), allocator);
+
+        assert!(p1[page.p1_index()].is_unused());
+        p1[page.p1_index()].set(frame, flags | EntryFlags::PRESENT);
+    }
+    
+    /// Maps the page to some free frame with the provided flags.
+    /// The free frame is allocated from the given `FrameAllocator`.
+    pub fn map<A>(&mut self, page: Page, flags: EntryFlags, allocator: &mut A)
+        where A: FrameAllocator
+    {
+        let frame = allocator.allocate_frame().expect("out of memory");
+        self.map_to(page, frame, flags, allocator)
+    }
+    
+    /// Identity map the the given frame with the provided flags.
+    /// The `FrameAllocator` is used to create new page tables if needed.
+    pub fn identity_map<A>(&mut self, frame: Frame, flags: EntryFlags, allocator: &mut A)
+        where A: FrameAllocator
+    {
+        let page = Page::containing_address(frame.start_address());
+        self.map_to(page, frame, flags, allocator)
+    }
+    
+    /// Unmaps the given page and adds all freed frames to the given
+    /// `FrameAllocator`.
+    pub fn unmap<A>(&mut self, page: Page, _allocator: &mut A)
+        where A: FrameAllocator
+    {
+        assert!(self.translate(page.start_address()).is_some());
+
+        let p1 = self.p4_mut()
+                     .next_table_mut(page.p4_index())
+                     .and_then(|p3| p3.next_table_mut(page.p3_index()))
+                     .and_then(|p2| p2.next_table_mut(page.p2_index()))
+                     .expect("mapping code does not support huge pages");
+        let _frame = p1[page.p1_index()].pointed_frame().unwrap();
+        p1[page.p1_index()].set_unused();
+
+        use x86_64::instructions::tlb;
+        tlb::flush(VirtAddr::new(page.start_address().try_into().unwrap()));
+        // TODO free p(1,2,3) table if empty
+        // _allocator.deallocate_frame(_frame);
+    }
+
+   
+
+}
+

kernel/src/mem/paging/mod.rs

@@ -0,0 +1,263 @@
+use core::ops::{Deref, DerefMut};
+use self::{entry::*, mapper::Mapper, temporary::TemporaryPage};
+use super::{Frame, FrameAllocator, MemInfo, PAGE_SIZE};
+use x86_64::{registers::control::{self, Cr3Flags}, structures::paging::PhysFrame, PhysAddr};
+
+pub mod tables;
+pub mod entry;
+pub mod temporary;
+pub mod mapper;
+
+const ENTRY_COUNT: usize = 512;
+
+pub type PhysicalAddress = usize;
+pub type VirtualAddress = usize;
+
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Page {
+   number: usize,
+}
+
+
+pub struct ActivePageTable {
+    mapper: Mapper
+}
+
+impl Deref for ActivePageTable {
+    type Target = Mapper;
+    fn deref(&self) -> &Mapper {
+        &self.mapper
+    }
+}
+
+impl DerefMut for ActivePageTable {
+    fn deref_mut(&mut self) -> &mut Mapper {
+        &mut self.mapper
+    }
+}
+
+
+
+impl ActivePageTable {
+    unsafe fn new() -> ActivePageTable {
+        ActivePageTable {
+            mapper: Mapper::new(),
+        }
+    }
+
+    pub fn with<F>(&mut self, table: &mut InactivePageTable, 
+        temporary_page: &mut temporary::TemporaryPage, f: F)
+        where F: FnOnce(&mut Mapper)
+    {
+        use x86_64::instructions::tlb;
+
+        {
+            let backup = Frame::containing_address(
+                control::Cr3::read().0.start_address().as_u64() as usize);
+
+            // map temporary_page to current p4 table
+            let p4_table = temporary_page.map_table_frame(backup.clone(), self);
+
+            // overwrite recursive mapping
+            self.p4_mut()[511].set(table.p4_frame.clone(), EntryFlags::PRESENT | EntryFlags::WRITABLE);
+            tlb::flush_all();
+
+            // execute f in the new context
+            f(self);
+
+            // restore recursive mapping to original p4 table
+            p4_table[511].set(backup, EntryFlags::PRESENT | EntryFlags::WRITABLE);
+            tlb::flush_all();
+        }
+
+        temporary_page.unmap(self);
+    }
+
+    pub fn switch(&mut self, new_table: InactivePageTable) -> InactivePageTable {
+
+        let old_table = InactivePageTable {
+            p4_frame: Frame::containing_address(
+                control::Cr3::read().0.start_address().as_u64() as usize
+            ),
+        };
+        unsafe {
+            let v = PhysFrame::containing_address(
+                PhysAddr::new(
+                    new_table.p4_frame.start_address() as u64
+                )
+            );
+            control::Cr3::write(v, Cr3Flags::PAGE_LEVEL_CACHE_DISABLE);
+        }
+        old_table
+    }
+
+}
+
+
+pub struct InactivePageTable {
+    p4_frame: Frame,
+}
+
+impl InactivePageTable {
+    pub fn new(frame: Frame, active_table: &mut ActivePageTable, 
+        temporary_page: &mut temporary::TemporaryPage) -> InactivePageTable {
+        {
+            let table = temporary_page.map_table_frame(frame.clone(),
+                active_table);
+            // now we are able to zero the table
+            table.zero();
+            // set up recursive mapping for the table
+            table[511].set(frame.clone(), EntryFlags::PRESENT | EntryFlags::WRITABLE);
+        }
+        temporary_page.unmap(active_table);
+
+        InactivePageTable { p4_frame: frame }
+    }
+}
+
+
+impl Page {
+    pub fn containing_address(address: VirtualAddress) -> Page {
+        assert!(address < 0x0000_8000_0000_0000 ||
+            address >= 0xffff_8000_0000_0000,
+            "invalid address: 0x{:x}", address);
+        Page { number: address / PAGE_SIZE }
+    }
+    fn start_address(&self) -> usize {
+        self.number * PAGE_SIZE
+    }
+    fn p4_index(&self) -> usize {
+        (self.number >> 27) & 0o777
+    }
+    fn p3_index(&self) -> usize {
+        (self.number >> 18) & 0o777
+    }
+    fn p2_index(&self) -> usize {
+        (self.number >> 9) & 0o777
+    }
+    fn p1_index(&self) -> usize {
+        (self.number >> 0) & 0o777
+    }
+    pub fn range_inclusive(start: Page, end: Page) -> PageIter {
+        PageIter {
+            start,
+            end,
+        }
+    }
+}
+
+pub struct PageIter {
+    start: Page,
+    end: Page,
+}
+
+impl Iterator for PageIter {
+    type Item = Page;
+
+    fn next(&mut self) -> Option<Page> {
+        if self.start <= self.end {
+            let page = self.start;
+            self.start.number += 1;
+            Some(page)
+        } else {
+            None
+        }
+    }
+}
+
+pub fn remap_the_kernel<A>(allocator: &mut A, mem_info: &MemInfo) -> ActivePageTable
+    where A: FrameAllocator
+{
+    let mut temporary_page = TemporaryPage::new(Page { number: 0xcafebabe },
+        allocator);
+
+    let mut active_table = unsafe { ActivePageTable::new() };
+    let mut new_table = {
+        let frame = allocator.allocate_frame().expect("no more frames");
+        InactivePageTable::new(frame, &mut active_table, &mut temporary_page)
+    };
+
+    log::info!("Remaping kernel");
+
+    active_table.with(&mut new_table, &mut temporary_page, |mapper| {
+
+        for section in mem_info.boot_info.elf_sections().unwrap() {
+
+            if !section.is_allocated() {
+                // section is not loaded to memory
+                continue;
+            }
+            
+            log::debug!("mapping section '{}' at addr: {:#x}, size: {:#x}", section.name().unwrap_or("NONE"), section.start_address(), section.size());
+            assert!(section.start_address() as usize % PAGE_SIZE == 0,
+                    "sections need to be page aligned");
+
+
+            let flags = EntryFlags::from_elf_section_flags(&section);
+
+            let start_frame = Frame::containing_address(section.start_address().try_into().unwrap());
+            let end_frame = Frame::containing_address(section.end_address() as usize - 1);
+            for frame in Frame::range_inclusive(start_frame, end_frame) {
+                mapper.identity_map(frame, flags, allocator);
+            }
+        }
+        let vga_buffer_frame = Frame::containing_address(0xb8000);
+        mapper.identity_map(vga_buffer_frame, EntryFlags::WRITABLE, allocator);
+        let multiboot_start = Frame::containing_address(mem_info.boot_info.start_address());
+        let multiboot_end = Frame::containing_address(mem_info.boot_info.end_address() - 1);
+        for frame in Frame::range_inclusive(multiboot_start, multiboot_end) {
+            mapper.identity_map(frame, EntryFlags::PRESENT, allocator);
+        }
+    });
+    
+    let old_table = active_table.switch(new_table);
+    log::debug!("Switched to new table");
+
+    let old_p4_page = Page::containing_address(
+      old_table.p4_frame.start_address()
+    );
+    active_table.unmap(old_p4_page, allocator);
+    log::debug!("Put guard page at {:#x}", old_p4_page.start_address());
+
+    active_table
+}
+
+
+
+pub fn test_paging<A>(allocator: &mut A)
+    where A: FrameAllocator
+{
+    let mut page_table = unsafe { ActivePageTable::new() };
+    
+    let addr = 42 * 512 * 512 * 4096; // 42th P3 entry
+    log::debug!("Virt addr: 0x{:x}", addr);
+    {   // ActivePageTable::map_to
+        log::debug!("TEST: ActivePageTable::map_to");
+        let page = Page::containing_address(addr);
+        let frame = allocator.allocate_frame().expect("no more frames");
+        log::debug!("Phys addr = {:?}, map to frame: {:?}",
+                 page_table.translate(addr),
+                 frame);
+        page_table.map_to(page, frame, EntryFlags::empty(), allocator);
+        log::debug!("Phys addr = {:?}", page_table.translate(addr));
+        log::debug!("next free frame: {:?}", allocator.allocate_frame());
+    }
+
+    {   // ActivePageTable::unmap
+        log::debug!("TEST: ActivePageTable::unmap");
+        log::debug!("Val: {:#x}", unsafe {
+            *(Page::containing_address(addr).start_address() as *const u64)
+        });
+        page_table.unmap(Page::containing_address(addr), allocator);
+        log::debug!("Phys addr: {:?} (unmapped addr)", page_table.translate(addr));
+
+        // Panic = good
+        // log::debug!("Val: {:#x}", unsafe {
+        //    *(Page::containing_address(addr).start_address() as *const u64)
+        // });
+
+    }
+
+    // test it
+}

kernel/src/mem/paging/tables.rs

@@ -0,0 +1,95 @@
+use crate::mem::FrameAllocator;
+
+use super::{Entry, ENTRY_COUNT, EntryFlags};
+use core::{marker::PhantomData, ops::{Index, IndexMut}};
+
+pub const P4: *mut Table<Level4> = 0xffffffff_fffff000 as *mut _;
+
+pub struct Table<L: TableLevel> {
+    entries: [Entry; ENTRY_COUNT],
+    level: PhantomData<L>
+}
+
+
+impl<L> Table<L> where L: TableLevel {
+    pub fn zero(&mut self) {
+        for entry in self.entries.iter_mut() {
+            entry.set_unused();
+        }
+    }
+}
+
+
+impl<L> Table<L> where L: HierarchicalLevel {
+    fn next_table_address(&self, index: usize) -> Option<usize> {
+        let entry_flags = self[index].flags();
+        if entry_flags.contains(EntryFlags::PRESENT) && 
+            !entry_flags.contains(EntryFlags::HUGE_PAGE) {
+            let table_address = self as *const _ as usize;
+            Some((table_address << 9) | (index << 12))
+        } else {
+            None
+        }
+    }
+    pub fn next_table_create<A>(&mut self, index: usize, allocator: &mut A) -> &mut Table<L::NextLevel> 
+        where A: FrameAllocator 
+    {
+        if self.next_table(index).is_none() {
+            assert!(!self.entries[index].flags().contains(EntryFlags::HUGE_PAGE),
+                    "mapping code does not support huge pages");
+            let frame = allocator.allocate_frame().expect("no frames available");
+            self.entries[index].set(frame, EntryFlags::PRESENT | EntryFlags::WRITABLE);
+            self.next_table_mut(index).unwrap().zero();
+        }
+        self.next_table_mut(index).unwrap()
+    }
+
+    pub fn next_table<'a>(&'a self, index: usize) -> Option<&'a Table<L::NextLevel>> {
+        self.next_table_address(index)
+            .map(|address| unsafe { &*(address as *const _) })
+    }
+
+    pub fn next_table_mut<'a>(&'a mut self, index: usize) -> Option<&'a mut Table<L::NextLevel>> {
+        self.next_table_address(index)
+            .map(|address| unsafe { &mut *(address as *mut _) })
+    }
+
+}
+
+impl<L> Index<usize> for Table<L> where L: TableLevel {
+    type Output = Entry;
+
+    fn index(&self, index: usize) -> &Entry {
+        &self.entries[index]
+    }
+}
+
+impl<L> IndexMut<usize> for Table<L> where L: TableLevel {
+    fn index_mut(&mut self, index: usize) -> &mut Entry {
+        &mut self.entries[index]
+    }
+}
+
+pub trait TableLevel {}
+pub trait HierarchicalLevel: TableLevel {
+    type NextLevel: 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 {}
+impl HierarchicalLevel for Level4 {
+    type NextLevel = Level3;
+}
+impl HierarchicalLevel for Level3 {
+    type NextLevel = Level2;
+}
+impl HierarchicalLevel for Level2 {
+    type NextLevel = Level1;
+}

kernel/src/mem/paging/temporary.rs

@@ -0,0 +1,81 @@
+
+use crate::mem::paging::EntryFlags;
+use crate::mem::FrameAllocator;
+use super::tables::{Level1, Table};
+use super::{ActivePageTable, VirtualAddress, Frame};
+use super::Page;
+
+pub struct TemporaryPage {
+    page: Page,
+    allocator: TinyAllocator
+}
+
+struct TinyAllocator([Option<Frame>; 3]);
+
+
+impl TemporaryPage {
+    pub fn new<A>(page: Page, allocator: &mut A) -> TemporaryPage
+        where A: FrameAllocator
+    {
+        TemporaryPage {
+            page: page,
+            allocator: TinyAllocator::new(allocator),
+        }
+    }
+    /// Maps the temporary page to the given frame in the active table.
+    /// Returns the start address of the temporary page.
+    pub fn map(&mut self, frame: Frame, active_table: &mut ActivePageTable)
+        -> VirtualAddress
+    {
+
+        assert!(active_table.translate_page(self.page).is_none(),
+                "temporary page is already mapped");
+        active_table.map_to(self.page, frame, EntryFlags::WRITABLE, &mut self.allocator);
+        self.page.start_address()
+    }
+
+    /// Unmaps the temporary page in the active table.
+    pub fn unmap(&mut self, active_table: &mut ActivePageTable) {
+        active_table.unmap(self.page, &mut self.allocator)
+    }
+
+    /// Maps the temporary page to the given page table frame in the active
+    /// table. Returns a reference to the now mapped table.
+    pub fn map_table_frame(&mut self,
+                           frame: Frame,
+                           active_table: &mut ActivePageTable)
+                           -> &mut Table<Level1> {
+        unsafe { &mut *(self.map(frame, active_table) as *mut Table<Level1>) }
+    }
+}
+
+impl FrameAllocator for TinyAllocator {
+    fn allocate_frame(&mut self) -> Option<Frame> {
+        for frame_option in &mut self.0 {
+            if frame_option.is_some() {
+                return frame_option.take();
+            }
+        }
+        None
+    }
+
+    fn deallocate_frame(&mut self, frame: Frame) {
+        for frame_option in &mut self.0 {
+            if frame_option.is_none() {
+                *frame_option = Some(frame);
+                return;
+            }
+        }
+        panic!("Tiny allocator can hold only 3 frames.");
+    }
+}
+
+impl TinyAllocator {
+    fn new<A>(allocator: &mut A) -> TinyAllocator
+        where A: FrameAllocator
+    {
+        let mut f = || allocator.allocate_frame();
+        let frames = [f(), f(), f()];
+        TinyAllocator(frames)
+    }
+}

kernel/src/utils.rs

@@ -1,4 +1,5 @@
-use x86_64::instructions;
+use x86::msr::{rdmsr, wrmsr, IA32_EFER};
+use x86_64::{instructions, registers::control::{Cr0, Cr0Flags}};
 
 
 
@@ -7,6 +8,17 @@ pub fn hcf() -> ! {
         instructions::hlt();
         core::hint::spin_loop();
     }
-
-
+}
+
+pub fn enable_nxe_bit() {
+
+    let nxe_bit = 1 << 11;
+    unsafe {
+        let efer = rdmsr(IA32_EFER);
+        wrmsr(IA32_EFER, efer | nxe_bit);
+    }
+}
+pub fn enable_write_protect_bit() {
+
+    unsafe { Cr0::write(Cr0::read() | Cr0Flags::WRITE_PROTECT) };
 }

linker.ld

@@ -3,25 +3,58 @@ ENTRY(_start)
 SECTIONS {
     . = 1M;
 
-    .boot :
+    .rodata :
     {
       /* ensure that the multiboot header is at the beginning */
       KEEP(*(.multiboot_header))
+      *(.rodata .rodata.*)
+      . = ALIGN(4K);
+    }
     
+    .eh_frame :
+    {
+    
+        *(.eh_frame)
+        . = ALIGN(4K);
     }
 
     .text :
     {
       *(.text .text.*)
+      . = ALIGN(4K);
     }
 
-    .rodata :
+    .data :
     {
-        *(.rodata .rodata.*)
+      *(.data .data.*)
+      . = ALIGN(4K);
     }
 
-    .data.rel.ro :
+    .bss :
     {
+      *(.bss .bss.*)
+      . = ALIGN(4K);
+    }
+
+    .got :
+    {
+      *(.got)
+      . = ALIGN(4K);
+    }
+
+    .got.plt :
+    {
+      *(.got.plt)
+      . = ALIGN(4K);
+    }
+
+    .data.rel.ro : ALIGN(4K) {
       *(.data.rel.ro.local*) *(.data.rel.ro .data.rel.ro.*)
+      . = ALIGN(4K);
     }
+
+    .gcc_except_table : ALIGN(4K) {
+      *(.gcc_except_table)
+      . = ALIGN(4K);
+    }`
 }