Merge branch 'master' into heap_allocation

README.md

@@ -2,7 +2,7 @@
 
 NovaOS is a expository project where I build a kernel from scratch for a Raspberry PI 3 B+.
 
-[Technical write-up](https://blog.leafnova.net/projects/pi3_kernel/)
+[Technical write-up](https://leafnova.net/projects/pi3_kernel/)
 
 ## Features
 

src/heap.rs

@@ -0,0 +1,216 @@
+#![allow(static_mut_refs)]
+
+use core::{
+    alloc::GlobalAlloc,
+    ptr::{self, null_mut, read_volatile},
+};
+
+use crate::NovaError;
+extern crate alloc;
+
+extern "C" {
+    static mut __heap_start: u8;
+    static mut __heap_end: u8;
+}
+
+#[repr(C, align(16))]
+pub struct HeapHeader {
+    pub next: *mut HeapHeader,
+    before: *mut HeapHeader,
+    pub size: usize,
+    free: bool,
+}
+
+const HEAP_HEADER_SIZE: usize = size_of::<HeapHeader>();
+const MIN_BLOCK_SIZE: usize = 16;
+
+// TODO: This implementation has to be reevaluated when implementing multiprocessing
+// Spinlock could be a solution but has its issues:
+// https://matklad.github.io/2020/01/02/spinlocks-considered-harmful.html
+pub static mut HEAP: Heap = Heap {
+    start_address: &raw mut __heap_start as *mut HeapHeader,
+    end_address: &raw mut __heap_end as *mut HeapHeader,
+    raw_size: 0,
+};
+
+// TODO: investigate if there is a better alternative to this
+pub unsafe fn init_global_heap() {
+    HEAP.init();
+}
+
+#[derive(Default)]
+pub struct Novalloc;
+
+unsafe impl GlobalAlloc for Novalloc {
+    unsafe fn alloc(&self, layout: core::alloc::Layout) -> *mut u8 {
+        HEAP.malloc(layout.size()).unwrap()
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, _: core::alloc::Layout) {
+        HEAP.free(ptr).unwrap();
+    }
+}
+
+#[global_allocator]
+static GLOBAL_ALLOCATOR: Novalloc = Novalloc;
+
+pub struct Heap {
+    start_address: *mut HeapHeader,
+    end_address: *mut HeapHeader,
+    raw_size: usize,
+}
+impl Heap {
+    pub fn new(heap_start: usize, heap_end: usize) -> Self {
+        let mut instance = Self {
+            start_address: &raw const heap_start as *mut HeapHeader,
+            end_address: &raw const heap_end as *mut HeapHeader,
+            raw_size: heap_end - heap_start,
+        };
+        instance.init();
+        instance
+    }
+
+    fn init(&mut self) {
+        self.raw_size = self.end_address as usize - self.start_address as usize;
+
+        unsafe {
+            ptr::write(
+                self.start_address,
+                HeapHeader {
+                    next: null_mut(),
+                    before: null_mut(),
+                    size: self.raw_size - HEAP_HEADER_SIZE,
+                    free: true,
+                },
+            );
+        }
+    }
+
+    unsafe fn find_first_fit(&self, size: usize) -> Result<*mut HeapHeader, NovaError> {
+        let mut current = self.start_address;
+        while !fits(size, current) {
+            if (*self.start_address).next.is_null() {
+                return Err(NovaError::HeapFull);
+            }
+            current = (*current).next;
+        }
+        Ok(current)
+    }
+
+    pub fn malloc(&self, mut size: usize) -> Result<*mut u8, NovaError> {
+        if size == 0 {
+            return Err(NovaError::EmptyHeapSegmentNotAllowed);
+        }
+
+        if size < MIN_BLOCK_SIZE {
+            size = MIN_BLOCK_SIZE;
+        }
+
+        // Align size to the next 16 bytes
+        size += (16 - (size % 16)) % 16;
+
+        unsafe {
+            // Find First-Fit memory segment
+            let current = self.find_first_fit(size)?;
+
+            // Return entire block WITHOUT generating a new header
+            // if the current block doesn't have enough space to hold: requested size + HEAP_HEADER_SIZE + MIN_BLOCK_SIZE
+            if (*current).size < size + HEAP_HEADER_SIZE + MIN_BLOCK_SIZE {
+                (*current).free = false;
+                return Ok(current.byte_add(HEAP_HEADER_SIZE) as *mut u8);
+            }
+
+            Self::fragment_segment(current, size);
+
+            let data_start_address = current.byte_add(HEAP_HEADER_SIZE);
+
+            Ok(data_start_address as *mut u8)
+        }
+    }
+
+    unsafe fn fragment_segment(current: *mut HeapHeader, size: usize) {
+        let byte_offset = HEAP_HEADER_SIZE + size;
+        let new_address = current.byte_add(byte_offset);
+
+        // Handle case where fragmenting center free space
+        let next = (*current).next;
+        if !(*current).next.is_null() {
+            (*next).before = new_address;
+        }
+
+        ptr::write(
+            new_address as *mut HeapHeader,
+            HeapHeader {
+                next,
+                before: current,
+                size: (*current).size - size - HEAP_HEADER_SIZE,
+                free: true,
+            },
+        );
+        (*current).next = new_address;
+        (*current).free = false;
+        (*current).size = size;
+    }
+
+    pub fn free(&self, pointer: *mut u8) -> Result<(), NovaError> {
+        let mut segment = unsafe { pointer.sub(HEAP_HEADER_SIZE) as *mut HeapHeader };
+        unsafe {
+            // IF prev is free:
+            // Delete header, add size to previous and fix pointers.
+            // Move Head left
+            if !(*segment).before.is_null() && (*(*segment).before).free {
+                let before_head = (*segment).before;
+                (*before_head).size += (*segment).size + HEAP_HEADER_SIZE;
+                delete_header(segment);
+                segment = before_head;
+            }
+            // IF next is free:
+            // Delete next header and merge size, fix pointers
+            if !(*segment).next.is_null() && (*(*segment).next).free {
+                let next_head = (*segment).next;
+                (*segment).size += (*next_head).size + HEAP_HEADER_SIZE;
+                delete_header(next_head);
+            }
+
+            // Neither: Set free
+            (*segment).free = true;
+        }
+
+        Ok(())
+    }
+
+    pub fn traverse_heap(&self) {
+        let mut pointer_address = self.start_address;
+        loop {
+            let head = unsafe { read_volatile(pointer_address) };
+            println!("Header {:#x}", pointer_address as u32);
+            println!("free: {}", head.free);
+            println!("size: {}", head.size);
+            println!("hasNext: {}", !head.next.is_null());
+            println!("");
+            if !head.next.is_null() {
+                pointer_address = head.next;
+            } else {
+                println!("---------------");
+                return;
+            }
+        }
+    }
+}
+
+unsafe fn fits(size: usize, header: *mut HeapHeader) -> bool {
+    (*header).free && size <= (*header).size
+}
+
+unsafe fn delete_header(header: *mut HeapHeader) {
+    let before = (*header).before;
+    let next = (*header).next;
+
+    if !before.is_null() {
+        (*before).next = next;
+    }
+
+    if !next.is_null() {
+        (*next).before = before;
+    }
+}

src/lib.rs

@@ -51,6 +51,7 @@ pub mod peripherals;
 
 pub mod configuration;
 pub mod framebuffer;
+pub mod heap;
 pub mod irq_interrupt;
 pub mod mailbox;
 pub mod timer;