started proper memory page handling with mapped page style

Cargo.toml

@@ -21,7 +21,7 @@ name = "stack_overflow"
 harness = false
 
 [dependencies]
-bootloader = "0.9"
+bootloader = {version = "0.9", features = ["map_physical_memory"]}
 volatile = "0.2.6"
 spin = "0.5.2"
 x86_64 = "0.14.2"

src/lib.rs

@@ -7,11 +7,18 @@
 
 use core::panic::PanicInfo;
 
+#[cfg(test)]
+use bootloader::{BootInfo, entry_point};
+
 pub mod gdt;
 pub mod interrupts;
+pub mod memory;
 pub mod serial;
 pub mod vga_buffer;
 
+#[cfg(test)]
+entry_point!(test_kernel_main);
+
 pub fn init() {
     interrupts::init_idt();
     gdt::init();
@@ -64,8 +71,7 @@ pub fn test_panic_handler(info: &PanicInfo) -> ! {
 // this this is here cuz lib.rs built separately, so need test for lib functions as well
 /// Entry point for `cargo test`
 #[cfg(test)]
-#[unsafe(no_mangle)]
-pub extern "C" fn _start() -> ! {
+fn test_kernel_main(_boot_info: &'static BootInfo) -> ! {
     init();
     test_main();
     hlt_loop();

src/main.rs

@@ -5,21 +5,39 @@
 #![reexport_test_harness_main = "test_main"]
 
 use core::panic::PanicInfo;
-use rusty_os::println;
+use rusty_os::{memory, println};
 
-#[unsafe(no_mangle)] // dont mangle name of this function, keep as-is
-pub extern "C" fn _start() -> ! {
+use bootloader::{BootInfo, entry_point};
+
+entry_point!(kernel_main);
+
+fn kernel_main(boot_info: &'static BootInfo) -> ! {
     println!("Hello there {}!", "Sameed");
 
     rusty_os::init();
 
-    use x86_64::registers::control::Cr3;
+    use x86_64::{VirtAddr, structures::paging::Translate};
 
-    let (level_4_page_table, _) = Cr3::read();
-    println!(
-        "Level 4 page table at: {:?}",
-        level_4_page_table.start_address()
-    );
+    let phys_mem_offset = VirtAddr::new(boot_info.physical_memory_offset);
+    // initialize a memory mapper
+    let mapper = unsafe { memory::init(phys_mem_offset) };
+
+    let addresses = [
+        // the identity-mapped vga buffer page
+        0xb8000,
+        // some code page
+        0x201008,
+        // some stack page
+        0x0100_0020_1a10,
+        // virtual address mapped to physical address 0
+        boot_info.physical_memory_offset,
+    ];
+
+    for &address in &addresses {
+        let virt = VirtAddr::new(address);
+        let phys = mapper.translate_addr(virt);
+        println!("{:?} -> {:?}", virt, phys);
+    }
 
     // if im runnign tests, jump to the test_main entrypoint
     #[cfg(test)]

src/memory.rs

@@ -0,0 +1,27 @@
+use x86_64::structures::paging::OffsetPageTable;
+use x86_64::{VirtAddr, structures::paging::PageTable};
+
+/// Initialize a new OffsetPageTable.
+///
+/// This function is unsafe because the caller must guarantee that the
+/// complete physical memory is mapped to virtual memory at the passed
+/// `physical_memory_offset`. Also, this function must be only called once
+/// to avoid aliasing `&mut` references (which is undefined behavior).
+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();
+
+    let phys = level_4_table_frame.start_address();
+    let virt = physical_memory_offset + phys.as_u64();
+    let page_table_ptr: *mut PageTable = virt.as_mut_ptr();
+
+    unsafe { &mut *page_table_ptr }
+}