From ce1fdcf7683fce359f38eedcccecf238f32340e6 Mon Sep 17 00:00:00 2001
From: Philipp Oppermann <dev@phil-opp.com>
Date: Wed, 22 Jan 2020 16:15:23 +0100
Subject: [PATCH] Wip

---
 src/interrupts.rs |  1 +
 src/lib.rs        |  3 +++
 src/main.rs       | 38 +++++++++++++++++++++++++++++++++++++-
 src/memory.rs     | 30 ++++++++++++++++++++++++++++++
 4 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/src/interrupts.rs b/src/interrupts.rs
index c833af7f..35ab3d66 100644
--- a/src/interrupts.rs
+++ b/src/interrupts.rs
@@ -77,6 +77,7 @@ extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: &mut InterruptSt
         PICS.lock()
             .notify_end_of_interrupt(InterruptIndex::Timer.as_u8());
     }
+    crate::multitasking::scheduler();
 }
 
 extern "x86-interrupt" fn keyboard_interrupt_handler(_stack_frame: &mut InterruptStackFrame) {
diff --git a/src/lib.rs b/src/lib.rs
index e79038ae..170bd639 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -6,6 +6,8 @@
 #![feature(const_fn)]
 #![feature(alloc_layout_extra)]
 #![feature(const_in_array_repeat_expressions)]
+#![feature(global_asm)]
+#![feature(asm)]
 #![test_runner(crate::test_runner)]
 #![reexport_test_harness_main = "test_main"]
 
@@ -17,6 +19,7 @@ pub mod allocator;
 pub mod gdt;
 pub mod interrupts;
 pub mod memory;
+pub mod multitasking;
 pub mod serial;
 pub mod vga_buffer;
 
diff --git a/src/main.rs b/src/main.rs
index 84d42343..2813b4c9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -7,9 +7,10 @@
 extern crate alloc;
 
 use alloc::{boxed::Box, rc::Rc, vec, vec::Vec};
-use blog_os::println;
+use blog_os::{print, println};
 use bootloader::{entry_point, BootInfo};
 use core::panic::PanicInfo;
+use x86_64::structures::paging::{FrameAllocator, Mapper, Size4KiB};
 
 entry_point!(kernel_main);
 
@@ -54,10 +55,45 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
     #[cfg(test)]
     test_main();
 
+    create_thread(thread_1, &mut mapper, &mut frame_allocator);
+    create_thread(thread_2, &mut mapper, &mut frame_allocator);
+
     println!("It did not crash!");
     blog_os::hlt_loop();
 }
 
+fn create_thread(
+    f: fn() -> !,
+    mapper: &mut impl Mapper<Size4KiB>,
+    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
+) {
+    let mut stack = blog_os::memory::alloc_stack(1, 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 {
+        blog_os::multitasking::add_thread(stack);
+    }
+}
+
+fn thread_1() -> ! {
+    loop {
+        print!("1");
+        x86_64::instructions::hlt();
+    }
+}
+
+fn thread_2() -> ! {
+    loop {
+        print!("2");
+        x86_64::instructions::hlt();
+    }
+}
+
 /// This function is called on panic.
 #[cfg(not(test))]
 #[panic_handler]
diff --git a/src/memory.rs b/src/memory.rs
index e9380203..c2ebfab0 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -36,6 +36,36 @@ unsafe fn active_level_4_table(physical_memory_offset: VirtAddr) -> &'static mut
     &mut *page_table_ptr // unsafe
 }
 
+pub fn alloc_stack(
+    size_in_pages: u64,
+    mapper: &mut impl Mapper<Size4KiB>,
+    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
+) -> Result<VirtAddr, ()> {
+    use core::sync::atomic::{AtomicU64, Ordering};
+    use x86_64::structures::paging::PageTableFlags as Flags;
+
+    const PAGE_SIZE: u64 = 4096;
+    static STACK_ALLOC_NEXT: AtomicU64 = AtomicU64::new(0x_5555_5555_0000);
+
+    let guard_page_start =
+        STACK_ALLOC_NEXT.fetch_add((size_in_pages + 1) * PAGE_SIZE, Ordering::SeqCst);
+    // skip one page as guard page
+    let stack_start_addr = VirtAddr::new(guard_page_start + PAGE_SIZE);
+    let stack_end_addr = stack_start_addr + size_in_pages * PAGE_SIZE;
+
+    let flags = Flags::PRESENT | Flags::WRITABLE;
+    let stack_start_page = Page::from_start_address(stack_start_addr).unwrap();
+    let stack_end_page = Page::from_start_address(stack_end_addr).unwrap();
+    for page in Page::range(stack_start_page, stack_end_page) {
+        let frame = frame_allocator.allocate_frame().ok_or(())?;
+        mapper
+            .map_to(page, frame, flags, frame_allocator)
+            .map_err(|_| ())?
+            .flush();
+    }
+    Ok(stack_end_addr)
+}
+
 /// Creates an example mapping for the given page to frame `0xb8000`.
 pub fn create_example_mapping(
     page: Page,