heap allocator

Cargo.lock

@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "autocfg"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ace50bade8e6234aa140d9a2f552bbee1db4d353f69b8217bc503490fc1a9f26"
+
 [[package]]
 name = "bit_field"
 version = "0.10.2"
@@ -14,10 +20,21 @@ version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f68f53c83ab957f72c32642f3868eec03eb974d1fb82e453128456482613d36"
 
+[[package]]
+name = "lock_api"
+version = "0.4.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "07af8b9cdd281b7915f413fa73f29ebd5d55d0d3f0155584dade1ff18cea1b17"
+dependencies = [
+ "autocfg",
+ "scopeguard",
+]
+
 [[package]]
 name = "mxrox_kernel"
 version = "0.1.0"
 dependencies = [
+ "spin",
  "stable-vec",
  "volatile 0.6.1",
  "x86_64",
@@ -35,6 +52,21 @@ version = "1.0.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f7c45b9784283f1b2e7fb61b42047c2fd678ef0960d4f6f1eba131594cc369d4"
 
+[[package]]
+name = "scopeguard"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
+
+[[package]]
+name = "spin"
+version = "0.9.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
+dependencies = [
+ "lock_api",
+]
+
 [[package]]
 name = "stable-vec"
 version = "0.4.1"

Cargo.toml

@@ -6,4 +6,5 @@ edition = "2021"
 [dependencies]
 x86_64 = "0.15.2"
 volatile = "0.6.1"
-stable-vec = "0.4.1"
+stable-vec = "0.4.1"
+spin = "0.9"

Makefile

@@ -9,7 +9,7 @@ build/boot.o: boot.s build_dir
 	nasm -f elf32 '$<' -o '$@'
 
 build/kernel.elf: linker.ld build/boot.o build/kernel.o
-	i686-elf-ld -m elf_i386 -nostdlib -o '$@' -T $^
+	i686-elf-ld -m elf_i386 -o '$@' -T $^
 
 build/kernel.o: build_dir
 	rustup override set nightly
@@ -26,8 +26,8 @@ build: build/mxrox.iso
 
 clean:
 	rm -rf build
-#	rm -rf target
+	rm -rf target
-#	rm -rf Cargo.lock
+#   rm -rf Cargo.lock
 	mkdir build
 
 run-kernel: build/kernel.elf

README.md

@@ -5,7 +5,7 @@ Mixray's small x86_64 OS
 ## How to build
 
 ```bash
-make clean      # removes target/
+make clean      # removes target/, build/
 make build      # builds iso image (build/mxrox.iso)
 make run        # runs iso image in QEMU emulator
 make run-kernel # runs only kernel in QEMU emulator

boot.s

@@ -1,40 +1,90 @@
-global loader
+; Declare constants for the multiboot header.
-global stack_ptr
+MBALIGN  equ  1 << 0            ; align loaded modules on page boundaries
+MEMINFO  equ  1 << 1            ; provide memory map
+MBFLAGS  equ  MBALIGN | MEMINFO ; this is the Multiboot 'flag' field
+MAGIC    equ  0x1BADB002        ; 'magic number' lets bootloader find the header
+CHECKSUM equ -(MAGIC + MBFLAGS)   ; checksum of above, to prove we are multiboot
 
-extern main
+; Declare a multiboot header that marks the program as a kernel. These are magic
-
+; values that are documented in the multiboot standard. The bootloader will
-MODULEALIGN equ 1<<0
+; search for this signature in the first 8 KiB of the kernel file, aligned at a
-MEMINFO equ 1<<1
+; 32-bit boundary. The signature is in its own section so the header can be
-FLAGS equ MODULEALIGN | MEMINFO
+; forced to be within the first 8 KiB of the kernel file.
-MAGIC equ 0x1BADB002
+section .multiboot
-CHECKSUM equ -(MAGIC + FLAGS)
-
-section .mbheader
 align 4
-MultiBootHeader:
+    dd MAGIC
-  dd MAGIC
+    dd MBFLAGS
-  dd FLAGS
+    dd CHECKSUM
-  dd CHECKSUM
-
-section .text
-
-STACKSIZE equ 0x4000
-
-loader:
-  mov esp, stack+STACKSIZE
-  push eax
-  push ebx
-
-  call main
-
-  cli
-
-hang:
-  hlt
-  jmp hang
 
+; The multiboot standard does not define the value of the stack pointer register
+; (esp) and it is up to the kernel to provide a stack. This allocates room for a
+; small stack by creating a symbol at the bottom of it, then allocating 16384
+; bytes for it, and finally creating a symbol at the top. The stack grows
+; downwards on x86. The stack is in its own section so it can be marked nobits,
+; which means the kernel file is smaller because it does not contain an
+; uninitialized stack. The stack on x86 must be 16-byte aligned according to the
+; System V ABI standard and de-facto extensions. The compiler will assume the
+; stack is properly aligned and failure to align the stack will result in
+; undefined behavior.
 section .bss
-align 4
+align 16
-stack:
+stack_bottom:
-  resb STACKSIZE
+resb 16384 ; 16 KiB
-stack_ptr:
+stack_top:
+
+; The linker script specifies _start as the entry point to the kernel and the
+; bootloader will jump to this position once the kernel has been loaded. It
+; doesn't make sense to return from this function as the bootloader is gone.
+; Declare _start as a function symbol with the given symbol size.
+section .text
+global _start:function (_start.end - _start)
+_start:
+    ; The bootloader has loaded us into 32-bit protected mode on a x86
+    ; machine. Interrupts are disabled. Paging is disabled. The processor
+    ; state is as defined in the multiboot standard. The kernel has full
+    ; control of the CPU. The kernel can only make use of hardware features
+    ; and any code it provides as part of itself. There's no printf
+    ; function, unless the kernel provides its own <stdio.h> header and a
+    ; printf implementation. There are no security restrictions, no
+    ; safeguards, no debugging mechanisms, only what the kernel provides
+    ; itself. It has absolute and complete power over the
+    ; machine.
+
+    ; To set up a stack, we set the esp register to point to the top of our
+    ; stack (as it grows downwards on x86 systems). This is necessarily done
+    ; in assembly as languages such as C cannot function without a stack.
+    mov esp, stack_top
+
+    ; This is a good place to initialize crucial processor state before the
+    ; high-level kernel is entered. It's best to minimize the early
+    ; environment where crucial features are offline. Note that the
+    ; processor is not fully initialized yet: Features such as floating
+    ; point instructions and instruction set extensions are not initialized
+    ; yet. The GDT should be loaded here. Paging should be enabled here.
+    ; C++ features such as global constructors and exceptions will require
+    ; runtime support to work as well.
+
+    ; Enter the high-level kernel. The ABI requires the stack is 16-byte
+    ; aligned at the time of the call instruction (which afterwards pushes
+    ; the return pointer of size 4 bytes). The stack was originally 16-byte
+    ; aligned above and we've since pushed a multiple of 16 bytes to the
+    ; stack since (pushed 0 bytes so far) and the alignment is thus
+    ; preserved and the call is well defined.
+        ; note, that if you are building on Windows, C functions may have "_" prefix in assembly: _kernel_main
+    extern main
+    call main
+
+    ; If the system has nothing more to do, put the computer into an
+    ; infinite loop. To do that:
+    ; 1) Disable interrupts with cli (clear interrupt enable in eflags).
+    ;    They are already disabled by the bootloader, so this is not needed.
+    ;    Mind that you might later enable interrupts and return from
+    ;    kernel_main (which is sort of nonsensical to do).
+    ; 2) Wait for the next interrupt to arrive with hlt (halt instruction).
+    ;    Since they are disabled, this will lock up the computer.
+    ; 3) Jump to the hlt instruction if it ever wakes up due to a
+    ;    non-maskable interrupt occurring or due to system management mode.
+    cli
+.hang:  hlt
+    jmp .hang
+.end:

src/kernel/heap.rs

@@ -0,0 +1,133 @@
+use core::alloc::{GlobalAlloc, Layout};
+use core::ptr::null_mut;
+use core::mem;
+use core::cell::UnsafeCell;
+use core::sync::atomic::{AtomicUsize, Ordering};
+
+struct FreeListNode {
+    size: usize,
+    next: *mut FreeListNode,
+}
+
+pub struct FreeListAllocator {
+    head: UnsafeCell<*mut FreeListNode>, 
+    heap_start: AtomicUsize,
+    heap_end: AtomicUsize,
+}
+
+unsafe impl Send for FreeListAllocator {}
+unsafe impl Sync for FreeListAllocator {}
+
+impl FreeListAllocator {
+    pub const fn new() -> Self {
+        FreeListAllocator {
+            head: UnsafeCell::new(null_mut()),
+            heap_start: AtomicUsize::new(0),
+            heap_end: AtomicUsize::new(0),
+        }
+    }
+
+    pub unsafe fn init(&self, heap_start: usize, heap_size: usize) {
+        self.heap_start.store(heap_start, Ordering::Relaxed) ;
+        self.heap_end.store(heap_start + heap_size, Ordering::Relaxed) ;
+
+        let first_node = heap_start as *mut FreeListNode;
+        first_node.write(FreeListNode { size: heap_size, next: null_mut() });
+
+        *self.head.get() = first_node;
+    }
+
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        let mut prev: *mut FreeListNode = null_mut();
+        let mut current = *self.head.get();
+
+        while !current.is_null() {
+            let node = &mut *current;
+
+            let alloc_start = (current as usize + mem::size_of::<FreeListNode>() + layout.align() - 1)
+                & !(layout.align() - 1);
+            let alloc_end = alloc_start + layout.size();
+
+            if alloc_end > self.heap_end.load(Ordering::Relaxed) || alloc_end > (current as usize + node.size) {
+                prev = current;
+                current = node.next;
+                continue;
+            }
+
+            let remaining_size = (current as usize + node.size) - alloc_end;
+            if remaining_size > mem::size_of::<FreeListNode>() {
+                let new_node = alloc_end as *mut FreeListNode;
+                new_node.write(FreeListNode {
+                    size: remaining_size,
+                    next: node.next,
+                });
+
+                if prev.is_null() {
+                    *self.head.get() = new_node;
+                } else {
+                    (*prev).next = new_node;
+                }
+            } else {
+                if prev.is_null() {
+                    *self.head.get() = node.next;
+                } else {
+                    (*prev).next = node.next;
+                }
+            }
+
+            return alloc_start as *mut u8;
+        }
+
+        null_mut()
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        let free_node = ptr as *mut FreeListNode;
+        free_node.write(FreeListNode {
+            size: layout.size(),
+            next: *self.head.get(),
+        });
+
+        *self.head.get() = free_node;
+    }
+}
+
+#[global_allocator]
+static ALLOCATOR: FreeListAllocator = FreeListAllocator::new();
+
+unsafe impl GlobalAlloc for FreeListAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        self.alloc(layout)
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        self.dealloc(ptr, layout)
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn memcpy(dest: *mut u8, src: *const u8, n: usize) -> *mut u8 {
+    for i in 0..n {
+        unsafe {
+            *dest.add(i) = *src.add(i);
+        }
+    }
+    dest
+}
+
+#[no_mangle]
+pub extern "C" fn memset(dest: *mut u8, value: i32, n: usize) -> *mut u8 {
+    let byte = value as u8;
+    for i in 0..n {
+        unsafe {
+            *dest.add(i) = byte;
+        }
+    }
+    dest
+}
+
+pub fn init_heap(heap_start: usize, heap_size: usize) {
+    unsafe { 
+        ALLOCATOR.init(heap_start, heap_size); 
+    }
+}

src/kernel/mod.rs

@@ -1,3 +1,4 @@
+use heap::init_heap;
 use stable_vec::StableVec;
 use vga::{
     fill_with_color, 
@@ -10,6 +11,7 @@ mod vga;
 mod ps2;
 mod acpi;
 mod thread;
+mod heap;
 
 type Vec<T> = StableVec<T>;
 
@@ -18,6 +20,8 @@ pub fn show_error(message: &str) {
     put_string_by_index(0, message, VGA_COLOR_BLACK, VGA_COLOR_RED);
 }
 
-pub fn start_kernel() {
+pub fn init_kernel() {
+    init_heap(16400, 16384);
+
     show_error("error test");
 }

src/main.rs

@@ -8,7 +8,7 @@ extern "C" fn eh_personality() {}
 
 use core::panic::PanicInfo;
 
-use kernel::{start_kernel, show_error};
+use kernel::{init_kernel, show_error};
 
 mod kernel;
 
@@ -19,9 +19,8 @@ fn panic(info: &PanicInfo) -> ! {
     loop {}
 }
 
-
 #[no_mangle]
-extern "C" fn main() -> ! {
+pub extern "C" fn main() -> ! {
-    start_kernel();
+    init_kernel();
     loop {}
 }