have to actually learn paging so pushing progress for now

kernel/.cargo/config.toml

@@ -8,3 +8,5 @@ rustflags = [
     "-C", "link-arg=--omagic",
 ]
 
+[unstable]
+build-std = ["core", "compiler_builtins", "alloc"]

kernel/Cargo.lock

@@ -83,6 +83,7 @@ dependencies = [
  "bootloader_api",
  "embedded-graphics",
  "lazy_static",
+ "linked_list_allocator",
  "pc-keyboard",
  "pic8259",
  "spin 0.9.8",
@@ -99,6 +100,15 @@ dependencies = [
  "spin 0.5.2",
 ]
 
+[[package]]
+name = "linked_list_allocator"
+version = "0.10.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9afa463f5405ee81cdb9cc2baf37e08ec7e4c8209442b5d72c04cfb2cd6e6286"
+dependencies = [
+ "spinning_top",
+]
+
 [[package]]
 name = "lock_api"
 version = "0.4.11"
@@ -175,6 +185,15 @@ dependencies = [
  "lock_api",
 ]
 
+[[package]]
+name = "spinning_top"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b9eb1a2f4c41445a3a0ff9abc5221c5fcd28e1f13cd7c0397706f9ac938ddb0"
+dependencies = [
+ "lock_api",
+]
+
 [[package]]
 name = "uart_16550"
 version = "0.3.0"

kernel/Cargo.toml

@@ -12,6 +12,7 @@ bench = false
 embedded-graphics = "0.8.1"
 spin = "0.9.8"
 pc-keyboard = "0.5.0"
+linked_list_allocator = "0.10.5"
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 pic8259 = "0.10.1"

kernel/src/allocator.rs

@@ -0,0 +1,13 @@
+use linked_list_allocator::LockedHeap;
+
+#[global_allocator]
+static ALLOCATOR: LockedHeap = LockedHeap::empty();
+
+pub const HEAP_START: *mut u8 = 0x9000_0000 as *mut u8;
+pub const HEAP_SIZE: usize = 100 * 1024;
+
+pub fn init_heap() {
+    unsafe {
+        ALLOCATOR.lock().init(HEAP_START, HEAP_SIZE);
+    }
+}

kernel/src/arch/riscv64/csr.rs

@@ -0,0 +1,64 @@
+macro_rules! csrr {
+    ($name:expr) => {{
+        let mut out: u64;
+        unsafe {
+            core::arch::asm!(
+                concat!("csrr {out}, ", $name),
+                out = out(reg) out,
+            );
+        }
+        out
+    }};
+}
+
+macro_rules! csrw {
+    ($name:expr, $func:path) => {
+        unsafe {
+            core::arch::asm!(
+                "la t0, {func}",
+                concat!("csrw ", $name, ", t0"),
+                func = sym $func,
+            );
+        }
+    };
+    ($name:expr, $val:expr) => {
+        unsafe {
+            core::arch::asm!(
+                concat!("csrw ", $name, ", {val}"),
+                val = in(reg) $val
+            );
+        }
+    };
+}
+pub(crate) use csrw;
+
+pub mod hartid {
+    pub fn read() -> u64 {
+        csrr!("mhartid")
+    }
+}
+
+pub mod mtvec {
+    macro_rules! init {
+        ($func:path) => {
+            let _: fn() -> ! = $func;
+            crate::arch::csr::csrw!("mtvec", $func);
+        };
+    }
+    pub(crate) use init;
+    pub fn read() -> u64 {
+        csrr!("mtvec")
+    }
+}
+
+pub mod mcause {
+    pub fn read() -> u64 {
+        csrr!("mcause")
+    }
+}
+
+pub mod satp {
+    pub fn read() -> u64 {
+        csrr!("satp")
+    }
+}

kernel/src/arch/riscv64/init.rs

@@ -0,0 +1,45 @@
+use crate::{
+    arch::{csr, instructions, interrupts, wait}, main, println
+};
+
+#[no_mangle]
+#[link_section = ".text.init"]
+#[naked]
+unsafe extern "C" fn _start() -> ! {
+    core::arch::asm!(
+        // set up gp & sp
+        ".option push",
+        ".option norelax",
+        "la gp, global_pointer",
+        "la sp, stack_top",
+        ".option pop",
+        // set up stack for each hart
+        "csrr t0, mhartid",
+        "slli t0, t0, 12",
+        "sub sp, sp, t0",
+        // continue to rest of program
+        "tail {entry}",
+
+        entry = sym entry,
+        options(noreturn)
+    );
+}
+
+pub fn entry() -> ! {
+    let dt_addr = instructions::reg!("a1");
+    let hart = csr::hartid::read();
+    println!("yo from hart {hart}");
+    if hart != 0 {
+        wait();
+    }
+    interrupts::init();
+    println!(
+        "machine trap vector base address: 0x{:x}",
+        csr::mtvec::read()
+    );
+    println!(
+        "physical address bits: {}",
+        csr::satp::read()
+    );
+    main(dt_addr)
+}

kernel/src/arch/riscv64/instructions.rs

@@ -0,0 +1,16 @@
+use core::arch::asm;
+
+pub fn wfi() {
+    unsafe { asm!("wfi") }
+}
+
+macro_rules! reg {
+    ($name:expr) => {{
+        let out: u64;
+        unsafe {
+            core::arch::asm!(concat!("mv {out}, ", $name), out = out(reg) out);
+        }
+        out
+    }};
+}
+pub(crate) use reg;

kernel/src/arch/riscv64/interrupts.rs

@@ -0,0 +1,12 @@
+use super::csr;
+
+pub fn init() {
+    csr::mtvec::init!(stuff);
+}
+
+#[repr(align(4))]
+pub fn stuff() -> ! {
+    let mcause = csr::mcause::read();
+    crate::println!("interrupt triggered: {mcause}");
+    super::qemu::exit();
+}

kernel/src/arch/riscv64/mod.rs

@@ -1,48 +1,12 @@
-use crate::{main, println};
+pub mod csr;
-
+pub mod init;
+pub mod instructions;
+pub mod interrupts;
+pub mod page;
 pub mod qemu;
 
-#[no_mangle]
+pub fn wait() -> ! {
-#[link_section = ".text.init"]
+    loop {
-#[naked]
+        instructions::wfi();
-unsafe extern "C" fn _start() -> ! {
-    core::arch::asm!(
-        ".option push",
-        ".option norelax",
-        "la gp, global_pointer",
-        "la sp, stack_top",
-        ".option pop",
-
-        "csrr a0, mhartid",
-        "slli t0, a0, 12",
-        "sub sp, sp, t0",
-        "tail {entry}",
-
-        entry = sym entry,
-        options(noreturn)
-    );
     }
-
-fn get_hartid() -> u64 {
-    let mut hart: u64;
-    unsafe {
-        core::arch::asm!(
-            "csrr {hart}, mhartid",
-            hart = out(reg) hart
-        );
-    }
-    return hart
-}
-
-fn entry() -> ! {
-    let hart = get_hartid();
-    println!("yo from hart {hart}");
-    if hart != 0 {
-        loop {}
-    }
-    main()
-}
-
-pub fn hlt_loop() -> ! {
-    loop {}
 }

kernel/src/arch/riscv64/page.rs

@@ -0,0 +1,547 @@
+// stolen from https://osblog.stephenmarz.com/index.html chapter 3 which I'm prolly gonna start
+// following for now bc don't wanna learn x86_64 :)
+
+use core::{mem::size_of, ptr::null_mut};
+
+use crate::{print, println};
+
+// ////////////////////////////////
+// // Allocation routines
+// ////////////////////////////////
+extern "C" {
+	static HEAP_START: usize;
+	static HEAP_SIZE: usize;
+}
+
+// We will use ALLOC_START to mark the start of the actual
+// memory we can dish out.
+static mut ALLOC_START: usize = 0;
+const PAGE_ORDER: usize = 12;
+pub const PAGE_SIZE: usize = 1 << 12;
+
+/// Align (set to a multiple of some power of two)
+/// This takes an order which is the exponent to 2^order
+/// Therefore, all alignments must be made as a power of two.
+/// This function always rounds up.
+pub const fn align_val(val: usize, order: usize) -> usize {
+	let o = (1usize << order) - 1;
+	(val + o) & !o
+}
+
+#[repr(u8)]
+pub enum PageBits {
+	Empty = 0,
+	Taken = 1 << 0,
+	Last = 1 << 1,
+}
+
+impl PageBits {
+	// We convert PageBits to a u8 a lot, so this is
+	// for convenience.
+	pub fn val(self) -> u8 {
+		self as u8
+	}
+}
+
+// Each page is described by the Page structure. Linux does this
+// as well, where each 4096-byte chunk of memory has a structure
+// associated with it. However, there structure is much larger.
+pub struct Page {
+	flags: u8,
+}
+
+impl Page {
+	// If this page has been marked as the final allocation,
+	// this function returns true. Otherwise, it returns false.
+	pub fn is_last(&self) -> bool {
+		if self.flags & PageBits::Last.val() != 0 {
+			true
+		}
+		else {
+			false
+		}
+	}
+
+	// If the page is marked as being taken (allocated), then
+	// this function returns true. Otherwise, it returns false.
+	pub fn is_taken(&self) -> bool {
+		if self.flags & PageBits::Taken.val() != 0 {
+			true
+		}
+		else {
+			false
+		}
+	}
+
+	// This is the opposite of is_taken().
+	pub fn is_free(&self) -> bool {
+		!self.is_taken()
+	}
+
+	// Clear the Page structure and all associated allocations.
+	pub fn clear(&mut self) {
+		self.flags = PageBits::Empty.val();
+	}
+
+	// Set a certain flag. We ran into trouble here since PageBits
+	// is an enumeration and we haven't implemented the BitOr Trait
+	// on it.
+	pub fn set_flag(&mut self, flag: PageBits) {
+		self.flags |= flag.val();
+	}
+
+	pub fn clear_flag(&mut self, flag: PageBits) {
+		self.flags &= !(flag.val());
+	}
+}
+
+/// Initialize the allocation system. There are several ways that we can
+/// implement the page allocator:
+/// 1. Free list (singly linked list where it starts at the first free
+/// allocation) 2. Bookkeeping list (structure contains a taken and length)
+/// 3. Allocate one Page structure per 4096 bytes (this is what I chose)
+/// 4. Others
+pub fn init() {
+	unsafe {
+		let num_pages = HEAP_SIZE / PAGE_SIZE;
+		let ptr = HEAP_START as *mut Page;
+		// Clear all pages to make sure that they aren't accidentally
+		// taken
+		for i in 0..num_pages {
+			(*ptr.add(i)).clear();
+		}
+		// Determine where the actual useful memory starts. This will be
+		// after all Page structures. We also must align the ALLOC_START
+		// to a page-boundary (PAGE_SIZE = 4096). ALLOC_START =
+		// (HEAP_START + num_pages * size_of::<Page>() + PAGE_SIZE - 1)
+		// & !(PAGE_SIZE - 1);
+		ALLOC_START = align_val(
+		                        HEAP_START
+		                        + num_pages * size_of::<Page,>(),
+		                        PAGE_ORDER,
+		);
+	}
+}
+
+/// Allocate a page or multiple pages
+/// pages: the number of PAGE_SIZE pages to allocate
+pub fn alloc(pages: usize) -> *mut u8 {
+	// We have to find a contiguous allocation of pages
+	assert!(pages > 0);
+	unsafe {
+		// We create a Page structure for each page on the heap. We
+		// actually might have more since HEAP_SIZE moves and so does
+		// the size of our structure, but we'll only waste a few bytes.
+		let num_pages = HEAP_SIZE / PAGE_SIZE;
+		let ptr = HEAP_START as *mut Page;
+		for i in 0..num_pages - pages {
+			let mut found = false;
+			// Check to see if this Page is free. If so, we have our
+			// first candidate memory address.
+			if (*ptr.add(i)).is_free() {
+				// It was FREE! Yay!
+				found = true;
+				for j in i..i + pages {
+					// Now check to see if we have a
+					// contiguous allocation for all of the
+					// request pages. If not, we should
+					// check somewhere else.
+					if (*ptr.add(j)).is_taken() {
+						found = false;
+						break;
+					}
+				}
+			}
+			// We've checked to see if there are enough contiguous
+			// pages to form what we need. If we couldn't, found
+			// will be false, otherwise it will be true, which means
+			// we've found valid memory we can allocate.
+			if found {
+				for k in i..i + pages - 1 {
+					(*ptr.add(k)).set_flag(PageBits::Taken);
+				}
+				// The marker for the last page is
+				// PageBits::Last This lets us know when we've
+				// hit the end of this particular allocation.
+				(*ptr.add(i+pages-1)).set_flag(PageBits::Taken);
+				(*ptr.add(i+pages-1)).set_flag(PageBits::Last);
+				// The Page structures themselves aren't the
+				// useful memory. Instead, there is 1 Page
+				// structure per 4096 bytes starting at
+				// ALLOC_START.
+				return (ALLOC_START + PAGE_SIZE * i)
+				       as *mut u8;
+			}
+		}
+	}
+
+	// If we get here, that means that no contiguous allocation was
+	// found.
+	null_mut()
+}
+
+/// Allocate and zero a page or multiple pages
+/// pages: the number of pages to allocate
+/// Each page is PAGE_SIZE which is calculated as 1 << PAGE_ORDER
+/// On RISC-V, this typically will be 4,096 bytes.
+pub fn zalloc(pages: usize) -> *mut u8 {
+	// Allocate and zero a page.
+	// First, let's get the allocation
+	let ret = alloc(pages);
+	if !ret.is_null() {
+		let size = (PAGE_SIZE * pages) / 8;
+		let big_ptr = ret as *mut u64;
+		for i in 0..size {
+			// We use big_ptr so that we can force an
+			// sd (store doubleword) instruction rather than
+			// the sb. This means 8x fewer stores than before.
+			// Typically we have to be concerned about remaining
+			// bytes, but fortunately 4096 % 8 = 0, so we
+			// won't have any remaining bytes.
+			unsafe {
+				(*big_ptr.add(i)) = 0;
+			}
+		}
+	}
+	ret
+}
+
+/// Deallocate a page by its pointer
+/// The way we've structured this, it will automatically coalesce
+/// contiguous pages.
+pub fn dealloc(ptr: *mut u8) {
+	// Make sure we don't try to free a null pointer.
+	assert!(!ptr.is_null());
+	unsafe {
+		let addr =
+			HEAP_START + (ptr as usize - ALLOC_START) / PAGE_SIZE;
+		// Make sure that the address makes sense. The address we
+		// calculate here is the page structure, not the HEAP address!
+		assert!(addr >= HEAP_START && addr < HEAP_START + HEAP_SIZE);
+		let mut p = addr as *mut Page;
+		// Keep clearing pages until we hit the last page.
+		while (*p).is_taken() && !(*p).is_last() {
+			(*p).clear();
+			p = p.add(1);
+		}
+		// If the following assertion fails, it is most likely
+		// caused by a double-free.
+		assert!(
+		        (*p).is_last() == true,
+		        "Possible double-free detected! (Not taken found \
+		         before last)"
+		);
+		// If we get here, we've taken care of all previous pages and
+		// we are on the last page.
+		(*p).clear();
+	}
+}
+
+/// Print all page allocations
+/// This is mainly used for debugging.
+pub fn print_page_allocations() {
+	unsafe {
+		let num_pages = HEAP_SIZE / PAGE_SIZE;
+		let mut beg = HEAP_START as *const Page;
+		let end = beg.add(num_pages);
+		let alloc_beg = ALLOC_START;
+		let alloc_end = ALLOC_START + num_pages * PAGE_SIZE;
+		println!();
+		println!(
+		         "PAGE ALLOCATION TABLE\nMETA: {:p} -> {:p}\nPHYS: \
+		          0x{:x} -> 0x{:x}",
+		         beg, end, alloc_beg, alloc_end
+		);
+		println!("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");
+		let mut num = 0;
+		while beg < end {
+			if (*beg).is_taken() {
+				let start = beg as usize;
+				let memaddr = ALLOC_START
+				              + (start - HEAP_START)
+				                * PAGE_SIZE;
+				print!("0x{:x} => ", memaddr);
+				loop {
+					num += 1;
+					if (*beg).is_last() {
+						let end = beg as usize;
+						let memaddr = ALLOC_START
+						              + (end
+						                 - HEAP_START)
+						                * PAGE_SIZE
+						              + PAGE_SIZE - 1;
+						print!(
+						       "0x{:x}: {:>3} page(s)",
+						       memaddr,
+						       (end - start + 1)
+						);
+						println!(".");
+						break;
+					}
+					beg = beg.add(1);
+				}
+			}
+			beg = beg.add(1);
+		}
+		println!("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");
+		println!(
+		         "Allocated: {:>5} pages ({:>9} bytes).",
+		         num,
+		         num * PAGE_SIZE
+		);
+		println!(
+		         "Free     : {:>5} pages ({:>9} bytes).",
+		         num_pages - num,
+		         (num_pages - num) * PAGE_SIZE
+		);
+		println!();
+	}
+}
+
+// ////////////////////////////////
+// // MMU Routines
+// ////////////////////////////////
+
+// Represent (repr) our entry bits as
+// unsigned 64-bit integers.
+#[repr(i64)]
+#[derive(Copy, Clone)]
+pub enum EntryBits {
+	None = 0,
+	Valid = 1 << 0,
+	Read = 1 << 1,
+	Write = 1 << 2,
+	Execute = 1 << 3,
+	User = 1 << 4,
+	Global = 1 << 5,
+	Access = 1 << 6,
+	Dirty = 1 << 7,
+
+	// Convenience combinations
+	ReadWrite = 1 << 1 | 1 << 2,
+	ReadExecute = 1 << 1 | 1 << 3,
+	ReadWriteExecute = 1 << 1 | 1 << 2 | 1 << 3,
+
+	// User Convenience Combinations
+	UserReadWrite = 1 << 1 | 1 << 2 | 1 << 4,
+	UserReadExecute = 1 << 1 | 1 << 3 | 1 << 4,
+	UserReadWriteExecute = 1 << 1 | 1 << 2 | 1 << 3 | 1 << 4,
+}
+
+// Helper functions to convert the enumeration
+// into an i64, which is what our page table
+// entries will be.
+impl EntryBits {
+	pub fn val(self) -> i64 {
+		self as i64
+	}
+}
+
+// A single entry. We're using an i64 so that
+// this will sign-extend rather than zero-extend
+// since RISC-V requires that the reserved sections
+// take on the most significant bit.
+pub struct Entry {
+	pub entry: i64,
+}
+
+// The Entry structure describes one of the 512 entries per table, which is
+// described in the RISC-V privileged spec Figure 4.18.
+impl Entry {
+	pub fn is_valid(&self) -> bool {
+		self.get_entry() & EntryBits::Valid.val() != 0
+	}
+
+	// The first bit (bit index #0) is the V bit for
+	// valid.
+	pub fn is_invalid(&self) -> bool {
+		!self.is_valid()
+	}
+
+	// A leaf has one or more RWX bits set
+	pub fn is_leaf(&self) -> bool {
+		self.get_entry() & 0xe != 0
+	}
+
+	pub fn is_branch(&self) -> bool {
+		!self.is_leaf()
+	}
+
+	pub fn set_entry(&mut self, entry: i64) {
+		self.entry = entry;
+	}
+
+	pub fn get_entry(&self) -> i64 {
+		self.entry
+	}
+}
+
+// Table represents a single table, which contains 512 (2^9), 64-bit entries.
+pub struct Table {
+	pub entries: [Entry; 512],
+}
+
+impl Table {
+	pub fn len() -> usize {
+		512
+	}
+}
+
+/// Map a virtual address to a physical address using 4096-byte page
+/// size.
+/// root: a mutable reference to the root Table
+/// vaddr: The virtual address to map
+/// paddr: The physical address to map
+/// bits: An OR'd bitset containing the bits the leaf should have.
+///       The bits should contain only the following:
+///          Read, Write, Execute, User, and/or Global
+///       The bits MUST include one or more of the following:
+///          Read, Write, Execute
+///       The valid bit automatically gets added.
+pub fn map(root: &mut Table, vaddr: usize, paddr: usize, bits: i64, level: usize) {
+	// Make sure that Read, Write, or Execute have been provided
+	// otherwise, we'll leak memory and always create a page fault.
+	assert!(bits & 0xe != 0);
+	// Extract out each VPN from the virtual address
+	// On the virtual address, each VPN is exactly 9 bits,
+	// which is why we use the mask 0x1ff = 0b1_1111_1111 (9 bits)
+	let vpn = [
+	           // VPN[0] = vaddr[20:12]
+	           (vaddr >> 12) & 0x1ff,
+	           // VPN[1] = vaddr[29:21]
+	           (vaddr >> 21) & 0x1ff,
+	           // VPN[2] = vaddr[38:30]
+	           (vaddr >> 30) & 0x1ff,
+	];
+
+	// Just like the virtual address, extract the physical address
+	// numbers (PPN). However, PPN[2] is different in that it stores
+	// 26 bits instead of 9. Therefore, we use,
+	// 0x3ff_ffff = 0b11_1111_1111_1111_1111_1111_1111 (26 bits).
+	let ppn = [
+	           // PPN[0] = paddr[20:12]
+	           (paddr >> 12) & 0x1ff,
+	           // PPN[1] = paddr[29:21]
+	           (paddr >> 21) & 0x1ff,
+	           // PPN[2] = paddr[55:30]
+	           (paddr >> 30) & 0x3ff_ffff,
+	];
+	// We will use this as a floating reference so that we can set
+	// individual entries as we walk the table.
+	let mut v = &mut root.entries[vpn[2]];
+	// Now, we're going to traverse the page table and set the bits
+	// properly. We expect the root to be valid, however we're required to
+	// create anything beyond the root.
+	// In Rust, we create a range iterator using the .. operator.
+	// The .rev() will reverse the iteration since we need to start with
+	// VPN[2] The .. operator is inclusive on start but exclusive on end.
+	// So, (0..2) will iterate 0 and 1.
+	for i in (level..2).rev() {
+		if !v.is_valid() {
+			// Allocate a page
+			let page = zalloc(1);
+			// The page is already aligned by 4,096, so store it
+			// directly The page is stored in the entry shifted
+			// right by 2 places.
+			v.set_entry(
+			            (page as i64 >> 2)
+			            | EntryBits::Valid.val(),
+			);
+		}
+		let entry = ((v.get_entry() & !0x3ff) << 2) as *mut Entry;
+		v = unsafe { entry.add(vpn[i]).as_mut().unwrap() };
+	}
+	// When we get here, we should be at VPN[0] and v should be pointing to
+	// our entry.
+	// The entry structure is Figure 4.18 in the RISC-V Privileged
+	// Specification
+	let entry = (ppn[2] << 28) as i64 |   // PPN[2] = [53:28]
+	            (ppn[1] << 19) as i64 |   // PPN[1] = [27:19]
+				(ppn[0] << 10) as i64 |   // PPN[0] = [18:10]
+				bits |                    // Specified bits, such as User, Read, Write, etc
+				EntryBits::Valid.val();   // Valid bit
+			 // Set the entry. V should be set to the correct pointer by the loop
+			 // above.
+	v.set_entry(entry);
+}
+
+/// Unmaps and frees all memory associated with a table.
+/// root: The root table to start freeing.
+/// NOTE: This does NOT free root directly. This must be
+/// freed manually.
+/// The reason we don't free the root is because it is
+/// usually embedded into the Process structure.
+pub fn unmap(root: &mut Table) {
+	// Start with level 2
+	for lv2 in 0..Table::len() {
+		let ref entry_lv2 = root.entries[lv2];
+		if entry_lv2.is_valid() && entry_lv2.is_branch() {
+			// This is a valid entry, so drill down and free.
+			let memaddr_lv1 = (entry_lv2.get_entry() & !0x3ff) << 2;
+			let table_lv1 = unsafe {
+				// Make table_lv1 a mutable reference instead of a pointer.
+				(memaddr_lv1 as *mut Table).as_mut().unwrap()
+			};
+			for lv1 in 0..Table::len() {
+				let ref entry_lv1 = table_lv1.entries[lv1];
+				if entry_lv1.is_valid() && entry_lv1.is_branch()
+				{
+					let memaddr_lv0 = (entry_lv1.get_entry()
+					                   & !0x3ff) << 2;
+					// The next level is level 0, which
+					// cannot have branches, therefore,
+					// we free here.
+					dealloc(memaddr_lv0 as *mut u8);
+				}
+			}
+			dealloc(memaddr_lv1 as *mut u8);
+		}
+	}
+}
+
+/// Walk the page table to convert a virtual address to a
+/// physical address.
+/// If a page fault would occur, this returns None
+/// Otherwise, it returns Some with the physical address.
+pub fn virt_to_phys(root: &Table, vaddr: usize) -> Option<usize> {
+	// Walk the page table pointed to by root
+	let vpn = [
+	           // VPN[0] = vaddr[20:12]
+	           (vaddr >> 12) & 0x1ff,
+	           // VPN[1] = vaddr[29:21]
+	           (vaddr >> 21) & 0x1ff,
+	           // VPN[2] = vaddr[38:30]
+	           (vaddr >> 30) & 0x1ff,
+	];
+
+	let mut v = &root.entries[vpn[2]];
+	for i in (0..=2).rev() {
+		if v.is_invalid() {
+			// This is an invalid entry, page fault.
+			break;
+		}
+		else if v.is_leaf() {
+			// According to RISC-V, a leaf can be at any level.
+
+			// The offset mask masks off the PPN. Each PPN is 9
+			// bits and they start at bit #12. So, our formula
+			// 12 + i * 9
+			let off_mask = (1 << (12 + i * 9)) - 1;
+			let vaddr_pgoff = vaddr & off_mask;
+			let addr = ((v.get_entry() << 2) as usize) & !off_mask;
+			return Some(addr | vaddr_pgoff);
+		}
+		// Set v to the next entry which is pointed to by this
+		// entry. However, the address was shifted right by 2 places
+		// when stored in the page table entry, so we shift it left
+		// to get it back into place.
+		let entry = ((v.get_entry() & !0x3ff) << 2) as *const Entry;
+		// We do i - 1 here, however we should get None or Some() above
+		// before we do 0 - 1 = -1.
+		v = unsafe { entry.add(vpn[i - 1]).as_ref().unwrap() };
+	}
+
+	// If we get here, we've exhausted all valid tables and haven't
+	// found a leaf.
+	None
+}

kernel/src/arch/x86_64/mod.rs

@@ -13,7 +13,7 @@ fn _start(boot_info: &'static mut bootloader_api::BootInfo) -> ! {
     if let Some(framebuffer) = boot_info.framebuffer.as_mut() {
         framebuffer::draw_test(framebuffer);
     }
-    main();
+    main(0);
 }
 
 pub fn hlt_loop() -> ! {

kernel/src/fdt.rs

@@ -0,0 +1,64 @@
+use core::mem::transmute;
+
+use alloc::vec;
+
+use crate::println;
+
+pub struct FDT {
+    pub header: FDTHeader,
+}
+
+const MAGIC: u32 = 0xd00dfeed;
+
+#[repr(u32)]
+#[derive(Clone, Copy, Debug)]
+enum Token {
+    BeginNode = 0x00000001,
+    EndNode = 0x00000002,
+    Prop = 0x00000003,
+    Nop = 0x00000004,
+    End = 0x00000009,
+}
+
+#[derive(Clone, Copy)]
+#[repr(C)]
+pub struct FDTHeader {
+    pub magic: u32,
+    pub totalsize: u32,
+    pub off_dt_struct: u32,
+    pub off_dt_strings: u32,
+    pub off_mem_rsvmap: u32,
+    pub version: u32,
+    pub last_comp_version: u32,
+    pub boot_cpuid_phys: u32,
+    pub size_dt_strings: u32,
+    pub size_dt_struct: u32,
+}
+
+const HEADER_SIZE: usize = core::mem::size_of::<FDTHeader>();
+
+impl FDT {
+    pub fn new(addr: u64) -> Self {
+        let header: FDTHeader = unsafe { transmute(from_be_32::<HEADER_SIZE>(addr)) };
+        if header.magic != MAGIC {
+            panic!("FDT magic incorrect");
+        }
+        if header.version != 17 {
+            panic!("FDT version not implemented {}", header.version);
+        }
+        let dt_structs = addr + header.off_dt_struct as u64;
+        let first_node: Token = unsafe { transmute(from_be_32::<4>(dt_structs)) };
+        println!("{first_node:?}");
+        let a = vec![1, 2];
+        println!("arst{a:?}");
+        Self { header }
+    }
+}
+
+pub unsafe fn from_be_32<const S: usize>(addr: u64) -> [u8; S] {
+    let mut data = *(addr as *mut [u8; S]);
+    for slice in data.chunks_mut(4) {
+        slice.reverse();
+    }
+    data
+}

kernel/src/main.rs

@@ -2,15 +2,23 @@
 #![no_main]
 #![feature(abi_x86_interrupt)]
 #![feature(naked_functions)]
+#![feature(fn_align)]
 
+extern crate alloc;
+
+pub mod allocator;
 pub mod arch;
+pub mod fdt;
 pub mod log;
 pub mod qemu;
-pub mod sync;
 
-pub fn main() -> ! {
+pub fn main(dt_addr: u64) -> ! {
     println!("we out here vibin");
-    for _ in 0..20000000 {}
+    allocator::init_heap();
+    let fdt = fdt::FDT::new(dt_addr);
+    // for _ in 0..40000000 {}
+    let x = unsafe { *(0xdeadbeef as *mut u8) };
+    println!("we got {x}");
     qemu::exit();
 }
 

kernel/src/sync/mod.rs

@@ -1,26 +0,0 @@
-// use core::sync::atomic::AtomicBool;
-//
-// struct SpinLock(AtomicBool);
-//
-// impl SpinLock {
-//     pub fn new() -> Self {
-//         Self(AtomicBool::new(false))
-//     }
-//     pub fn lock(&mut self) {
-//         while self.0.swap(true, core::sync::atomic::Ordering::Acquire) {}
-//     }
-//     pub fn release(&mut self) {
-//         self.0.store(false, core::sync::atomic::Ordering::Release);
-//     }
-// }
-//
-// struct Mutex<T> {
-//     lock: SpinLock,
-//     data: T
-// }
-//
-// struct MutexGuard<T>(T);
-//
-// impl <T> MutexGuard<T> {
-// }
-//