feat: use offset page table

Author: criskell

src/main.rs

@@ -7,19 +7,20 @@
 use bootloader::{BootInfo, entry_point};
 use core::panic::PanicInfo;
 use osdev_rust::println;
+use x86_64::structures::paging::Translate;
 
 entry_point!(kernel_main);
 
 fn kernel_main(boot_info: &'static BootInfo) -> ! {
-    use osdev_rust::memory::translate_addr;
+    use osdev_rust::memory;
     use x86_64::VirtAddr;
 
     println!("Hello World!");
 
     osdev_rust::init();
 
     let phys_mem_offset = VirtAddr::new(boot_info.physical_memory_offset);
-
+    let mapper = unsafe { memory::init(phys_mem_offset) };
     let addresses = [
         0xb8000,
         0x201008,
@@ -29,7 +30,7 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
 
     for &address in &addresses {
         let virt = VirtAddr::new(address);
-        let phys = unsafe { translate_addr(virt, phys_mem_offset) };
+        let phys = mapper.translate_addr(virt);
         println!("{:?} -> {:?}", virt, phys);
     }
 

src/memory.rs

@@ -1,8 +1,20 @@
 use core::panic;
 
-use x86_64::{PhysAddr, VirtAddr, structures::paging::PageTable};
+use x86_64::{
+    PhysAddr, VirtAddr,
+    structures::paging::{
+        FrameAllocator, Mapper, OffsetPageTable, Page, PageTable, PhysFrame, Size4KiB,
+    },
+};
 
-pub unsafe fn active_level_4_table(physical_memory_offset: VirtAddr) -> &'static mut PageTable {
+pub unsafe fn init(physical_memory_offset: VirtAddr) -> OffsetPageTable<'static> {
+    unsafe {
+        let level_4_table = active_level_4_table(physical_memory_offset);
+        OffsetPageTable::new(level_4_table, physical_memory_offset)
+    }
+}
+
+unsafe fn active_level_4_table(physical_memory_offset: VirtAddr) -> &'static mut PageTable {
     use x86_64::registers::control::Cr3;
 
     let (level_4_table_frame, _) = Cr3::read();
@@ -14,6 +26,29 @@ pub unsafe fn active_level_4_table(physical_memory_offset: VirtAddr) -> &'static
     unsafe { &mut *page_table_ptr }
 }
 
+pub fn create_example_mapping(
+    page: Page,
+    mapper: &mut OffsetPageTable,
+    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
+) {
+    use x86_64::structures::paging::PageTableFlags as Flags;
+
+    let frame = PhysFrame::containing_address(PhysAddr::new(0xb8000));
+    let flags = Flags::PRESENT | Flags::WRITABLE;
+
+    let map_to_result = unsafe { mapper.map_to(page, frame, flags, frame_allocator) };
+
+    map_to_result.expect("map_to failed").flush();
+}
+
+pub struct EmptyFrameAllocator;
+
+unsafe impl FrameAllocator<Size4KiB> for EmptyFrameAllocator {
+    fn allocate_frame(&mut self) -> Option<PhysFrame> {
+        None
+    }
+}
+
 pub unsafe fn translate_addr(addr: VirtAddr, physical_memory_offset: VirtAddr) -> Option<PhysAddr> {
     translate_addr_inner(addr, physical_memory_offset)
 }