Add new modules

Cargo.toml

@@ -33,3 +33,6 @@ test-args = [
     "-display", "none"
 ]
 test-success-exit-code = 33         # (0x10 << 1) | 1
+
+[profile.release]
+lto = true

src/multitasking.rs

@@ -0,0 +1,54 @@
+use alloc::collections::VecDeque;
+use lazy_static::lazy_static;
+use x86_64::structures::paging::{FrameAllocator, Mapper, Size4KiB};
+use x86_64::VirtAddr;
+
+global_asm!(include_str!("multitasking/context_switch.s"));
+
+pub unsafe fn context_switch(stack_pointer: VirtAddr) {
+    asm!(
+        "call asm_context_switch"
+        :
+        : "{rdi}"(stack_pointer.as_u64())
+        : "rax", "rbx", "rcx", "rdx", "rsi", "rdi", "rpb", "r8", "r9", "r10",
+          "r11", "r12", "r13", "r14", "r15", "rflags", "memory"
+        : "intel", "volatile"
+    );
+}
+
+pub fn scheduler() {
+    let next = PAUSED_THREADS.try_lock().and_then(|mut t| t.pop_front());
+    if let Some(next) = next {
+        unsafe { context_switch(next) };
+    }
+}
+
+lazy_static! {
+    static ref PAUSED_THREADS: spin::Mutex<VecDeque<VirtAddr>> = spin::Mutex::new(VecDeque::new());
+}
+
+#[no_mangle]
+fn add_paused_thread(stack_pointer: VirtAddr) {
+    add_thread(stack_pointer)
+}
+
+fn add_thread(stack_pointer: VirtAddr) {
+    PAUSED_THREADS.lock().push_back(stack_pointer);
+}
+
+pub fn create_thread(
+    f: fn() -> !,
+    stack_size: u64,
+    mapper: &mut impl Mapper<Size4KiB>,
+    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
+) {
+    let mut stack = crate::memory::alloc_stack(stack_size, mapper, frame_allocator).unwrap();
+    stack -= core::mem::size_of::<u64>();
+    let ptr: *mut u64 = stack.as_mut_ptr();
+    unsafe { ptr.write(f as u64) };
+    stack -= core::mem::size_of::<u64>();
+    let ptr: *mut u64 = stack.as_mut_ptr();
+    let rflags = 0x200;
+    unsafe { ptr.write(rflags) };
+    unsafe { add_thread(stack) };
+}

src/multitasking/context_switch.s

@@ -0,0 +1,13 @@
+.intel_syntax noprefix
+
+asm_context_switch:
+    pushfq
+
+    mov rax, rsp
+    mov rsp, rdi
+    
+    mov rdi, rax
+    call add_paused_thread
+
+    popfq
+    ret