Kernel: Implement somewhat functioning multithread support

This still uses only a single cpu, but we can now have 'parallelization'

This seems to work fine in qemu and bochs, but my own computer did not
like this when I last tried.

I have absolutely no idea how multithreading should actually be
implmemented and I just thought and implemented the most simple one I
could think of. This might not be in any way correct :D

kernel/Makefile

@@ -43,10 +43,12 @@ kernel/kmalloc.o				\
 kernel/PIC.o					\
 kernel/PIT.o					\
 kernel/RTC.o					\
+kernel/Scheduler.o				\
 kernel/Serial.o					\
 kernel/Shell.o					\
 kernel/SpinLock.o				\
 kernel/SSP.o					\
+kernel/Thread.o					\
 kernel/TTY.o					\
 kernel/VesaTerminalDriver.o		\
 icxxabi.o						\

kernel/include/kernel/PIT.h

@@ -2,6 +2,8 @@
 
 #include <stdint.h>
 
+#define PIT_IRQ 0
+
 namespace PIT
 {
 

kernel/include/kernel/Scheduler.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <BAN/LinkedList.h>
+#include <kernel/Thread.h>
+
+namespace Kernel
+{
+
+	class Scheduler
+	{
+		BAN_NON_COPYABLE(Scheduler);
+		BAN_NON_MOVABLE(Scheduler);
+		
+	public:
+		static void Initialize();
+		static Scheduler& Get();
+
+		const Thread& CurrentThread() const;
+
+		void AddThread(void(*)());
+		void Switch();
+		void Start();
+
+		static constexpr size_t ms_between_switch = 4;
+
+	private:
+		Scheduler() {}
+
+	private:
+		BAN::LinkedList<Thread>				m_threads;
+		BAN::LinkedList<Thread>::iterator	m_current_iterator;
+	};
+
+}

kernel/include/kernel/TTY.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <kernel/TerminalDriver.h>
+#include <kernel/SpinLock.h>
 
 class TTY
 {
@@ -51,4 +52,5 @@ private:
 	Cell*					m_buffer		{ nullptr };
 	AnsiState				m_ansi_state;
 	TerminalDriver*			m_terminal_driver { nullptr };
+	Kernel::SpinLock		m_lock;
 };

kernel/include/kernel/Thread.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <BAN/Memory.h>
+
+namespace Kernel
+{
+
+	class Thread
+	{
+		BAN_NON_COPYABLE(Thread);
+		BAN_NON_MOVABLE(Thread);
+
+	public:
+		enum class State
+		{
+			NotStarted,
+			Running,
+			Paused,
+			Done,
+		};
+
+	public:
+		Thread(void(*)());
+		~Thread();
+
+		uint32_t id() const { return m_id; }
+
+		void set_rip(uintptr_t rip) { m_rip = rip; }
+		void set_rsp(uintptr_t rsp) { m_rsp = rsp; }
+		void set_state(State state) { m_state = state; }
+		uintptr_t rip() const { return m_rip; }
+		uintptr_t rsp() const { return m_rsp; }
+		State state() const { return m_state; }
+
+	private:
+		static void on_exit();
+		
+	private:
+		void*			m_stack_base	= nullptr;
+		State			m_state			= State::NotStarted;
+		uintptr_t		m_rip			= 0;
+		uintptr_t		m_rsp			= 0;
+		const uint32_t	m_id			= 0;
+	};
+
+
+}

kernel/kernel/PIT.cpp

@@ -2,8 +2,7 @@
 #include <kernel/InterruptController.h>
 #include <kernel/IO.h>
 #include <kernel/kprint.h>
-
-#define IRQ_TIMER			0
+#include <kernel/Scheduler.h>
 
 #define TIMER0_CTL			0x40
 #define TIMER1_CTL			0x41
@@ -26,9 +25,10 @@ namespace PIT
 {
 	static uint64_t s_system_time = 0;
 
-	void clock_handle()
+	void irq_handler()
 	{
 		s_system_time++;
+		Kernel::Scheduler::Get().Switch();
 	}
 
 	uint64_t ms_since_boot()
@@ -45,9 +45,9 @@ namespace PIT
 		IO::outb(TIMER0_CTL, (timer_reload >> 0) & 0xff);
 		IO::outb(TIMER0_CTL, (timer_reload >> 8) & 0xff);
 
-		IDT::register_irq_handler(IRQ_TIMER, clock_handle);
+		IDT::register_irq_handler(PIT_IRQ, irq_handler);
 
-		InterruptController::Get().EnableIrq(IRQ_TIMER);
+		InterruptController::Get().EnableIrq(PIT_IRQ);
 	}
 
 }

kernel/kernel/Scheduler.cpp

@@ -0,0 +1,150 @@
+#include <kernel/Arch.h>
+#include <kernel/InterruptController.h>
+#include <kernel/Scheduler.h>
+
+namespace Kernel
+{
+
+	static Scheduler* s_instance = nullptr;
+
+	extern "C" uintptr_t read_rip();
+	asm(
+	".global read_rip;"
+	"read_rip:"
+#if ARCH(x86_64)
+		"popq %rax;"
+		"jmp *%rax"
+#else
+		"popl %eax;"
+		"jmp *%eax"
+#endif
+	);
+
+	void Scheduler::Initialize()
+	{
+		ASSERT(!s_instance);
+		s_instance = new Scheduler();
+	}
+
+	Scheduler& Scheduler::Get()
+	{
+		ASSERT(s_instance);
+		return *s_instance;
+	}
+
+	const Thread& Scheduler::CurrentThread() const
+	{
+		return *m_current_iterator;
+	}
+
+	void Scheduler::AddThread(void(*thread)())
+	{
+		MUST(m_threads.EmplaceBack(thread));
+		if (!m_current_iterator)
+			m_current_iterator = m_threads.begin();
+	}
+
+	void Scheduler::Switch()
+	{
+		static uint8_t cnt = 0;
+		if (cnt++ % ms_between_switch)
+			return;
+
+		ASSERT(InterruptController::Get().IsInService(PIT_IRQ));
+
+		ASSERT(m_threads.Size() > 0);
+		if (m_threads.Size() == 1)
+			return;
+
+		ASSERT(m_current_iterator);
+
+		auto next_iterator = m_current_iterator;
+		if (++next_iterator == m_threads.end())
+			next_iterator = m_threads.begin();
+
+		Thread& current = *m_current_iterator;
+		Thread& next 	= *next_iterator;
+
+		if (current.state() == Thread::State::Done)
+		{
+			// NOTE: this does not invalidate the next/next_iterator
+			//       since we are working with linked list
+			m_threads.Remove(m_current_iterator);
+			m_current_iterator = decltype(m_threads)::iterator();
+		}
+
+		uintptr_t rip = read_rip();
+		if (rip == 0)
+			return;
+
+		uintptr_t rsp;
+#if ARCH(x86_64)
+		asm volatile("movq %%rsp, %0" : "=r"(rsp));
+#else
+		asm volatile("movl %%esp, %0" : "=r"(rsp));
+#endif
+
+		if (m_current_iterator)
+		{
+			current.set_rip(rip);
+			current.set_rsp(rsp);
+			current.set_state(Thread::State::Paused);
+		}
+
+		m_current_iterator = next_iterator;
+
+		if (next.state() == Thread::State::NotStarted)
+		{
+			InterruptController::Get().EOI(PIT_IRQ);
+			next.set_state(Thread::State::Running);
+			asm volatile(
+#if ARCH(x86_64)
+				"movq %0, %%rsp;"
+#else
+				"movl %0, %%esp;"
+#endif
+				"sti;"
+				"jmp *%1;"
+				:: "r"(next.rsp()), "r"(next.rip())
+			);
+		}
+		else if (next.state() == Thread::State::Paused)
+		{
+			next.set_state(Thread::State::Running);
+			asm volatile(
+#if ARCH(x86_64)
+				"movq %0, %%rsp;"
+				"movq $0, %%rax;"
+#else
+				"movl %0, %%esp;"
+				"movl $0, %%eax;"
+#endif
+				"jmp *%1;"
+				:: "r"(next.rsp()), "r"(next.rip())
+			);
+		}
+		
+		ASSERT(false);
+	}
+
+	void Scheduler::Start()
+	{
+		ASSERT(m_threads.Size() > 0);
+		ASSERT(m_current_iterator);
+
+		Thread& current = *m_current_iterator;
+		ASSERT(current.state() == Thread::State::NotStarted);
+		current.set_state(Thread::State::Running);
+		asm volatile(
+#if ARCH(x86_64)
+			"movq %0, %%rsp;"
+#else
+			"movl %0, %%esp;"
+#endif
+			"sti;"
+			"jmp *%1;"
+			:: "r"(current.rsp()), "r"(current.rip())
+		);
+	}
+
+}

kernel/kernel/TTY.cpp

@@ -1,5 +1,7 @@
 #include <BAN/Errors.h>
+#include <BAN/ScopeGuard.h>
 #include <kernel/Debug.h>
+#include <kernel/LockGuard.h>
 #include <kernel/TTY.h>
 
 #include <string.h>
@@ -261,6 +263,8 @@ void TTY::PutCharAt(uint16_t ch, uint32_t x, uint32_t y)
 
 void TTY::PutChar(char ch)
 {
+	Kernel::LockGuard guard(m_lock);
+	
 	uint16_t cp = handle_unicode(ch);
 	if (cp == 0xFFFF)
 		return;

kernel/kernel/Thread.cpp

@@ -0,0 +1,53 @@
+#include <BAN/Errors.h>
+#include <kernel/Arch.h>
+#include <kernel/InterruptController.h>
+#include <kernel/kmalloc.h>
+#include <kernel/Scheduler.h>
+#include <kernel/Thread.h>
+
+#define PAGE_SIZE 4096
+
+namespace Kernel
+{
+
+	static uint32_t s_next_id = 1;
+
+	static constexpr size_t thread_stack_size = PAGE_SIZE;
+
+	template<typename T>
+	static void write_to_stack(uintptr_t& rsp, const T& value)
+	{
+		rsp -= sizeof(T);
+		*(T*)rsp = value;
+	}
+
+	Thread::Thread(void(*function)())
+		: m_id(s_next_id++)
+	{
+		m_stack_base = kmalloc(thread_stack_size, PAGE_SIZE);
+		ASSERT(m_stack_base);
+
+		m_rip = (uintptr_t)function;
+		m_rsp = (uintptr_t)m_stack_base + thread_stack_size;
+		write_to_stack(m_rsp, this);
+		write_to_stack(m_rsp, &Thread::on_exit);
+	}
+
+	Thread::~Thread()
+	{
+		kfree(m_stack_base);
+	}
+
+	void Thread::on_exit()
+	{
+		Thread* thread = nullptr;
+#if ARCH(x86_64)
+		asm volatile("movq (%%rsp), %0" : "=r"(thread));
+#else
+		asm volatile("movl (%%esp), %0" : "=r"(thread));
+#endif
+		thread->m_state = State::Done;
+		for (;;) asm volatile("hlt");
+	}
+
+}

kernel/kernel/kernel.cpp

@@ -10,6 +10,7 @@
 #include <kernel/PIT.h>
 #include <kernel/Serial.h>
 #include <kernel/Shell.h>
+#include <kernel/Scheduler.h>
 #include <kernel/TTY.h>
 #include <kernel/VesaTerminalDriver.h>
 
@@ -55,8 +56,12 @@ ParsedCommandLine ParseCommandLine()
 	return result;
 }
 
+static TTY* tty1 = nullptr;
+
 extern "C" void kernel_main()
 {
+	using namespace Kernel;
+
 	DISABLE_INTERRUPTS();
 
 	auto cmdline = ParseCommandLine();
@@ -82,7 +87,7 @@ extern "C" void kernel_main()
 	TerminalDriver* terminal_driver = VesaTerminalDriver::Create();
 	ASSERT(terminal_driver);
 	dprintln("VESA initialized");
-	TTY* tty1 = new TTY(terminal_driver);
+	tty1 = new TTY(terminal_driver);
 	
 	InterruptController::Initialize(cmdline.force_pic);
 	dprintln("Interrupt controller initialized");
@@ -93,15 +98,18 @@ extern "C" void kernel_main()
 		return;
 	dprintln("8042 initialized");
 
-	ENABLE_INTERRUPTS();
-
-	kprintln("Hello from the kernel!");
-
-	Kernel::Shell shell(tty1);
-	shell.Run();
-
-	for (;;)
+	Scheduler::Initialize();
+	Scheduler& scheduler = Scheduler::Get();
+	scheduler.AddThread([](){ Shell(tty1).Run(); });
+	scheduler.AddThread(
+		[]()
 		{
-		asm("hlt");
+			uint64_t start = PIT::ms_since_boot();
+			while (PIT::ms_since_boot() < start + 3000)
+				continue;
+			kprintln("\nHello!");
 		}
+	);
+	scheduler.Start();
+	ASSERT(false);
 }