feat: add bump and linked list allocator

criskell · criskell · commit 4876cbe29cbd · 2025-11-23T09:16:02.000-03:00
diff --git a/kernel/src/allocator.rs b/kernel/src/allocator.rs
@@ -8,6 +8,11 @@ use x86_64::{
     },
 };
 
+use crate::allocator::{bump::BumpAllocator, linked_list::LinkedListAllocator};
+
+pub mod bump;
+pub mod linked_list;
+
 pub const HEAP_START: usize = 0x_4444_4444_0000;
 pub const HEAP_SIZE: usize = 100 * 1024; // 100 KiB
 
@@ -44,7 +49,7 @@ pub fn init_heap(
 }
 
 #[global_allocator]
-static ALLOCATOR: LockedHeap = LockedHeap::empty();
+static ALLOCATOR: LockedHeap = Locked::new(LinkedListAllocator::new());
 
 pub struct Dummy;
 
@@ -57,3 +62,42 @@ unsafe impl GlobalAlloc for Dummy {
         panic!("dealloc should be never called")
     }
 }
+
+pub struct Locked<A> {
+    inner: spin::Mutex<A>,
+}
+
+impl<A> Locked<A> {
+    pub const fn new(inner: A) -> Self {
+        Locked {
+            inner: spin::Mutex::new(inner),
+        }
+    }
+
+    pub fn lock(&self) -> spin::MutexGuard<A> {
+        self.inner.lock()
+    }
+}
+
+fn align_up_slow(addr: usize, align: usize) -> usize {
+    let remainder = addr % align;
+
+    if remainder == 0 {
+        addr
+    } else {
+        addr - remainder + align
+    }
+}
+
+/// Require that `align` is power of two.
+fn align_up(addr: usize, align: usize) -> usize {
+    // align é uma potência de dois, portanto tem apenas um único bit setado
+    // align - 1 deixa todos os bits menores desligados
+    // ! deixa todos os bits setados com exceção daqueles que são menores que align
+
+    // fazer um AND com um endereço e essa máscara, alinhamos o endereço para baixo, devido que
+    // desligamos todos os bits abaixo
+
+    // para fazer um alinhamento pra cima, somamos com align - 1 antes de aplicar a máscara.
+    (addr + align - 1) & !(align - 1)
+}
diff --git a/kernel/src/allocator/bump.rs b/kernel/src/allocator/bump.rs
@@ -0,0 +1,56 @@
+use super::{Layout, align_up};
+use core::alloc::{GlobalAlloc, Layout};
+
+pub struct BumpAllocator {
+    heap_start: usize,
+    heap_end: usize,
+    next: usize,
+    allocations: usize,
+}
+
+impl BumpAllocator {
+    pub const fn new() -> Self {
+        BumpAllocator {
+            heap_start: 0,
+            heap_end: 0,
+            next: 0,
+            allocations: 0,
+        }
+    }
+
+    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
+        self.heap_start = heap_start;
+        self.heap_end = heap_start + heap_size;
+        self.next = heap_start;
+    }
+}
+
+unsafe impl GlobalAlloc for Locked<BumpAllocator> {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        let mut bump = self.lock();
+
+        let alloc_start = align_up(bump.next, layout.align());
+        let alloc_end = match alloc_start.checked_add(layout.size()) {
+            Some(end) => end,
+            None => return ptr::null_mut(),
+        };
+
+        if alloc_end > bump.heap_end {
+            ptr::null_mut()
+        } else {
+            bump.next = alloc_end;
+            bump.allocations += 1;
+            alloc_start as *mut u8
+        }
+    }
+
+    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {
+        let bump = self.lock();
+
+        bump.allocations -= 1;
+
+        if bump.allocations == 0 {
+            bump.next = bump.heap_start;
+        }
+    }
+}
diff --git a/kernel/src/allocator/linked_list.rs b/kernel/src/allocator/linked_list.rs
@@ -0,0 +1,138 @@
+use super::align_up;
+use core::mem;
+
+struct ListNode {
+    size: usize,
+    next: Option<&'static mut ListNode>,
+}
+
+impl ListNode {
+    const fn new(size: usize) -> Self {
+        ListNode { size, next: None }
+    }
+
+    fn start_addr(&self) -> usize {
+        self as *const Self as usize
+    }
+
+    fn end_addr(&self) -> usize {
+        self.start_addr() + self.size
+    }
+}
+
+pub struct LinkedListAllocator {
+    head: ListNode,
+}
+
+impl LinkedListAllocator {
+    pub const fn new() -> Self {
+        Self {
+            head: ListNode::new(0),
+        }
+    }
+
+    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
+        unsafe {
+            self.add_free_region(heap_start, heap_size);
+        }
+    }
+
+    unsafe fn add_free_region(&mut self, addr: usize, size: usize) {
+        // verifica que a região liberada é capaz de armazenar um ListNode
+        assert_eq!(align_up(addr, mem::align_of::<ListNode>()), addr);
+        assert!(size >= mem::size_of::<ListNode>());
+
+        let mut node = ListNode::new(size);
+        node.next = self.head.next.take();
+        let node_ptr = addr as *mut ListNode;
+
+        unsafe {
+            node_ptr.write(node);
+            self.head.next = Some(&mut *node_ptr);
+        }
+    }
+
+    fn find_region(&mut self, size: usize, align: usize) -> Option<(&'static mut ListNode, usize)> {
+        let mut current = &mut self.head;
+
+        while let Some(ref mut region) = current.next {
+            if let Ok(alloc_start) = Self::alloc_from_region(&region, size, align) {
+                let next = region.next.take();
+                let ret = Some((current.next.take().unwrap(), alloc_start));
+                current.next = next;
+                return ret;
+            } else {
+                current = current.next.as_mut().unwrap();
+            }
+        }
+
+        None
+    }
+
+    fn alloc_from_region(region: &ListNode, size: usize, align: usize) -> Result<(usize, ())> {
+        let alloc_start = align_up(region.start_addr(), align);
+        let alloc_end = alloc_start.checked_add(size).ok_or(())?;
+
+        if alloc_end > region.end_addr() {
+            // região pequena
+            return Err(());
+        }
+
+        let excess_size = region.end_addr() - alloc_end;
+
+        // a alocação divide a região em uma parte usada e livre
+        // portanto a parte excedente deve conseguir armazenar um ListNode
+        if excess_size > 0 && excess_size < mem::size_of::<ListNode>() {
+            return Err(());
+        }
+
+        Ok(alloc_start)
+    }
+
+    /// ajusta o layout de forma que a região alocada de memória
+    /// possa armazenar um ListNode.
+    /// alguma hora, as regiões serão desalocadas portanto devem serem capazes de armazenarem
+    /// ListNode sem causar UB.
+    fn size_align(layout: Layout) -> (usize, usize) {
+        let layout = layout
+            .align_to(mem::align_of::<ListNode>()) // aumenta o alinhamento para o alinhamento de um ListNode
+            .expect("adjusting alignment failed")
+            // arredonda o tamanho para um múltiplo do alinhamento para garantir que o próximo bloco de memória vai ter
+            // o alinhamento correto para armazenar um ListNode
+            .pad_to_align();
+
+        // garante um tamanho mínimo de mem::size_of::<ListNode>
+        // dessa maneira, o dealloc pode escrever de forma segura um ListNode para o bloco de memória liberado
+        let size = layout.size().max(mem::size_of::<ListNode>());
+
+        (size, layout.align())
+    }
+}
+
+unsafe impl GlobalAlloc for Locked<LinkedListAllocator> {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        let (size, align) = LinkedListAllocator::size_align(layout);
+        let mut allocator = self.lock();
+
+        if let Some((region, alloc_start)) = allocator.find_region(size, align) {
+            let alloc_end = alloc_start.checked_add(size).expect("overflow");
+            let excess_size = region.end_addr() - alloc_end;
+
+            if excess_size > 0 {
+                unsafe {
+                    allocator.add_free_region(alloc_end, excess_size);
+                }
+            }
+
+            alloc_start as *mut u8
+        } else {
+            ptr::null_mut()
+        }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        let (size, _) = LinkedListAllocator::size_align(layout);
+
+        unsafe { self.lock().add_free_region(ptr as usize, size) }
+    }
+}
diff --git a/kernel/src/gdt.rs b/kernel/src/gdt.rs
@@ -78,13 +78,13 @@ pub fn init() {
     GDT.0.load();
 
     unsafe {
-        CS::set_reg(GDT.1.kernel_code_selector);
-        DS::set_reg(GDT.1.kernel_data_selector);
-        ES::set_reg(GDT.1.kernel_data_selector);
-        FS::set_reg(GDT.1.kernel_data_selector);
-        SS::set_reg(GDT.1.kernel_data_selector);
-        GS::set_reg(GDT.1.kernel_data_selector);
-
-        load_tss(GDT.1.tss_selector);
+        // CS::set_reg(GDT.1.kernel_code_selector);
+        // DS::set_reg(GDT.1.kernel_data_selector);
+        // ES::set_reg(GDT.1.kernel_data_selector);
+        // FS::set_reg(GDT.1.kernel_data_selector);
+        // SS::set_reg(GDT.1.kernel_data_selector);
+        // GS::set_reg(GDT.1.kernel_data_selector);
+
+        // load_tss(GDT.1.tss_selector);
     }
 }
diff --git a/kernel/src/userspace.rs b/kernel/src/userspace.rs
@@ -77,7 +77,7 @@ pub unsafe fn jump_to_userspace(physical_memory_offset: VirtAddr) {
             "mov {tmp:r}, rsp",
             "push rdx", // SS (DS)
             "push {tmp:r}", // Current ESP
-            "pushfq", // EFLAGS
+            "pushf", // EFLAGS
             "push {code_selector:r}", // CS
             "push {user_code:r}", // EIP
             "iretq",
diff --git a/kernel/tests/heap_allocation.rs b/kernel/tests/heap_allocation.rs
@@ -72,3 +72,15 @@ fn many_boxes() {
         assert_eq!(*x, i);
     }
 }
+
+#[test_case]
+fn many_boxes_long_lived() {
+    let long_lived = Box::new(1);
+
+    for i in 0..HEAP_SIZE {
+        let x = Box::new(i);
+        assert_eq!(*x, i);
+    }
+
+    assert_eq!(*long_lived, 1);
+}
