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Migrate to a struct based heap implementation

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This commit is contained in:
Alexander Neuhäuser
2025-09-14 17:59:50 +02:00
parent 4dbbfa1fcf
commit f0f71ea490
2 changed files with 165 additions and 109 deletions
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154
src/heap.rs
View File

@@ -1,6 +1,8 @@
#![allow(static_mut_refs)]
use core::{
alloc::GlobalAlloc,
ptr::{self, null, null_mut, read_volatile, write_volatile},
ptr::{self, null_mut, read_volatile},
};
use crate::NovaError;
@@ -11,7 +13,7 @@ extern "C" {
static mut __heap_end: u8;
}
#[repr(C)]
#[repr(C, align(16))]
pub struct HeapHeader {
pub next: *mut HeapHeader,
before: *mut HeapHeader,
@@ -22,42 +24,80 @@ pub struct HeapHeader {
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 {
malloc(layout.size()).unwrap()
HEAP.malloc(layout.size()).unwrap()
}
unsafe fn dealloc(&self, ptr: *mut u8, layout: core::alloc::Layout) {
free(ptr).unwrap();
unsafe fn dealloc(&self, ptr: *mut u8, _: core::alloc::Layout) {
HEAP.free(ptr).unwrap();
}
}
#[global_allocator]
static GLOBAL_ALLOCATOR: Novalloc = Novalloc;
pub fn init_heap() {
unsafe {
let heap_end = &raw const __heap_end as usize;
let heap_start = &raw const __heap_start as usize;
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(
&raw const __heap_start as *mut HeapHeader,
self.start_address,
HeapHeader {
next: null_mut(),
before: null_mut(),
size: heap_end - heap_start - HEAP_HEADER_SIZE,
size: self.raw_size - HEAP_HEADER_SIZE,
free: true,
},
);
}
}
pub fn malloc(mut size: usize) -> Result<*mut u8, NovaError> {
let mut head = &raw const __heap_start as *mut HeapHeader;
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::EmptyHeapNotAllowed);
}
@@ -71,26 +111,21 @@ pub fn malloc(mut size: usize) -> Result<*mut u8, NovaError> {
unsafe {
// Find First-Fit memory segment
while !(*head).free || size > (*head).size {
if (*head).next.is_null() {
return Err(NovaError::HeapFull);
}
head = (*head).next;
}
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 (*head).size < size + HEAP_HEADER_SIZE + MIN_BLOCK_SIZE {
(*head).free = false;
return Ok(head.byte_add(HEAP_HEADER_SIZE) as *mut u8);
if (*current).size < size + HEAP_HEADER_SIZE + MIN_BLOCK_SIZE {
(*current).free = false;
return Ok(current.byte_add(HEAP_HEADER_SIZE) as *mut u8);
}
let byte_offset = HEAP_HEADER_SIZE + size;
let new_address = head.byte_add(byte_offset);
let new_address = current.byte_add(byte_offset);
// Handle case where fragmenting center free space
let next = (*head).next;
if !(*head).next.is_null() {
let next = (*current).next;
if !(*current).next.is_null() {
(*next).before = new_address;
}
@@ -98,62 +133,49 @@ pub fn malloc(mut size: usize) -> Result<*mut u8, NovaError> {
new_address as *mut HeapHeader,
HeapHeader {
next,
before: head,
size: (*head).size - size - HEAP_HEADER_SIZE,
before: current,
size: (*current).size - size - HEAP_HEADER_SIZE,
free: true,
},
);
(*head).next = new_address;
(*head).free = false;
(*head).size = size;
(*current).next = new_address;
(*current).free = false;
(*current).size = size;
let data_start_address = head.byte_add(HEAP_HEADER_SIZE);
let data_start_address = current.byte_add(HEAP_HEADER_SIZE);
Ok(data_start_address as *mut u8)
}
}
pub fn free(pointer: *mut u8) -> Result<(), NovaError> {
let mut head = unsafe { pointer.sub(HEAP_HEADER_SIZE) as *mut HeapHeader };
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 !(*head).before.is_null() && (*(*head).before).free {
let before_head = (*head).before;
(*before_head).size += (*head).size + HEAP_HEADER_SIZE;
delete_header(head);
head = before_head;
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 !(*head).next.is_null() && (*(*head).next).free {
let next_head = (*head).next;
(*head).size += (*next_head).size + HEAP_HEADER_SIZE;
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
(*head).free = true;
(*segment).free = true;
}
Ok(())
}
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;
}
}
pub fn traverse_heap_tree() {
let mut pointer_address = &raw const __heap_start as *const HeapHeader;
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);
@@ -169,3 +191,21 @@ pub fn traverse_heap_tree() {
}
}
}
}
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;
}
}

26
src/main.rs
View File

@@ -1,7 +1,7 @@
#![no_main]
#![no_std]
#![feature(asm_experimental_arch)]
#![allow(static_mut_refs)]
use core::{
arch::{asm, global_asm},
panic::PanicInfo,
@@ -12,7 +12,7 @@ extern crate alloc;
use nova::{
framebuffer::{FrameBuffer, BLUE, GREEN, RED},
heap::init_heap,
heap::{init_global_heap, HEAP},
irq_interrupt::enable_irq_source,
mailbox::mb_read_soc_temp,
peripherals::{
@@ -88,8 +88,7 @@ unsafe fn zero_bss() {
pub extern "C" fn kernel_main() -> ! {
println!("EL: {}", get_current_el());
// Initialize the first heap header
init_heap();
heap_test();
sleep_us(500_000);
@@ -117,11 +116,28 @@ pub extern "C" fn kernel_main() -> ! {
}
}
fn heap_test() {
unsafe {
init_global_heap();
let a = HEAP.malloc(32).unwrap();
let b = HEAP.malloc(64).unwrap();
let c = HEAP.malloc(128).unwrap();
let _ = HEAP.malloc(256).unwrap();
HEAP.traverse_heap();
HEAP.free(b).unwrap();
HEAP.traverse_heap();
HEAP.free(a).unwrap();
HEAP.traverse_heap();
HEAP.free(c).unwrap();
HEAP.traverse_heap();
}
}
fn cos(x: u32) -> f64 {
libm::cos(x as f64 * 0.1) * 20.0
}
pub fn get_current_el() -> u64 {
fn get_current_el() -> u64 {
let el: u64;
unsafe {
asm!(