Changess

Makefile

@@ -25,16 +25,18 @@ kernel/elf.o \
 kernel/syscall.o \
 kernel/io/keyboard.o \
 kernel/heap.o \
+kernel/task.o \
 
 LIB_OBJS=\
 $(ARCHDIR)/bootstrap.o \
 $(ARCHDIR)/tty.o \
 $(ARCHDIR)/strlib.o \
+$(ARCHDIR)/paging.o \
+$(ARCHDIR)/gdt.o \
 $(ARCHDIR)/interrupts/idt.o \
 $(ARCHDIR)/interrupts/interrupt.o \
+$(ARCHDIR)/interrupts/irq0.o \
 $(ARCHDIR)/interrupts/syscall.o \
-$(ARCHDIR)/gdt.o \
-$(ARCHDIR)/userland.o \
 $(ARCHDIR)/interrupts/pic.o \
 
 OBJS=$(KERNEL_OBJS) $(LIB_OBJS)

arch/i686/bootstrap.s

@@ -1,18 +1,12 @@
-/* Declare constants for the multiboot header. */
-.set ALIGN,    1<<0             /* align loaded modules on page boundaries */
-.set MEMINFO,  1<<1             /* provide memory map */
-.set FLAGS,    ALIGN | MEMINFO  /* this is the Multiboot 'flag' field */
-.set MAGIC,    0x1BADB002       /* 'magic number' lets bootloader find the header */
-.set CHECKSUM, -(MAGIC + FLAGS) /* checksum of above, to prove we are multiboot */
+# Declare constants for the multiboot header.
+.set ALIGN,    1<<0             # align loaded modules on page boundaries
+.set MEMINFO,  1<<1             # provide memory map
+.set FLAGS,    ALIGN | MEMINFO  # this is the Multiboot 'flag' field
+.set MAGIC,    0x1BADB002       # 'magic number' lets bootloader find the header
+.set CHECKSUM, -(MAGIC + FLAGS) # checksum of above, to prove we are multiboot
 
-/* 
-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
-search for this signature in the first 8 KiB of the kernel file, aligned at a
-32-bit boundary. The signature is in its own section so the header can be
-forced to be within the first 8 KiB of the kernel file.
-*/
-.section .multiboot
+# Declare a multiboot header that marks the program as a kernel.
+.section .multiboot.data, "aw"
 .align 4
 .long MAGIC
 .long FLAGS
@@ -31,100 +25,109 @@ stack is properly aligned and failure to align the stack will result in
 undefined behavior.
 */
 
-.section .bss
+.section .bss, "aw", @nobits
 .align 16
 stack_bottom:
 .skip 16384 # 16 KiB
 stack_top:
 
+.global boot_page_directory
+ 	.align 4096
+boot_page_directory:
+	.skip 4096
+boot_page_table1:
+    .skip 4096
+
 /*
 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.
 */
-.section .text
+.section .multiboot.text, "a"
 .global _start
 .type _start, @function
 _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.
-	*/
+	# Physical address of boot_page_table1.
+	# TODO: I recall seeing some assembly that used a macro to do the
+	#       conversions to and from physical. Maybe this should be done in this
+	#       code as well?
+	movl $(boot_page_table1 - 0xC0000000), %edi
+	# First address to map is address 0.
+	# TODO: Start at the first kernel page instead. Alternatively map the first
+	#       1 MiB as it can be generally useful, and there's no need to
+	#       specially map the VGA buffer.
+	movl $0, %esi
+	# Map 1023 pages. The 1024th will be the VGA text buffer.
+	movl $1023, %ecx
 
-	/*
-	To set up a stack, we set the esp register to point to the top of the
-	stack (as it grows downwards on x86 systems). This is necessarily done
-	in assembly as languages such as C cannot function without a stack.
-	*/
+1:
+	# Only map the kernel.
+	cmpl $_kernel_start, %esi
+	jl 2f
+	cmpl $(_kernel_end - 0xC0000000), %esi
+	jge 3f
+
+	# Map physical address as "present, writable". Note that this maps
+	# .text and .rodata as writable. Mind security and map them as non-writable.
+	movl %esi, %edx
+	orl $0x003, %edx
+	movl %edx, (%edi)
+
+2:
+	# Size of page is 4096 bytes.
+	addl $4096, %esi
+	# Size of entries in boot_page_table1 is 4 bytes.
+	addl $4, %edi
+	# Loop to the next entry if we haven't finished.
+	loop 1b
+
+3:
+	# Map VGA video memory to 0xC03FF000 as "present, writable".
+	movl $(0x000B8000 | 0x003), boot_page_table1 - 0xC0000000 + 1023 * 4
+
+	# The page table is used at both page directory entry 0 (virtually from 0x0
+	# to 0x3FFFFF) (thus identity mapping the kernel) and page directory entry
+	# 768 (virtually from 0xC0000000 to 0xC03FFFFF) (thus mapping it in the
+	# higher half). The kernel is identity mapped because enabling paging does
+	# not change the next instruction, which continues to be physical. The CPU
+	# would instead page fault if there was no identity mapping.
+
+	# Map the page table to both virtual addresses 0x00000000 and 0xC0000000.
+	movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 0
+	movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 768 * 4
+
+	# Set cr3 to the address of the boot_page_directory.
+	movl $(boot_page_directory - 0xC0000000), %ecx
+	movl %ecx, %cr3
+
+	# Enable paging and the write-protect bit.
+	movl %cr0, %ecx
+	orl $0x80010000, %ecx
+	movl %ecx, %cr0
+
+	# Jump to higher half with an absolute jump. 
+	lea 4f, %ecx
+	jmp *%ecx
+
+.section .text
+
+4:
+	# At this point, paging is fully set up and enabled.
+
+	# Unmap the identity mapping as it is now unnecessary. 
+	movl $0, boot_page_directory + 0
+
+	# Reload crc3 to force a TLB flush so the changes to take effect.
+	movl %cr3, %ecx
+	movl %ecx, %cr3
+
+	# Set up the stack.
 	mov $stack_top, %esp
 
-    cli
-
-    call gdt_init
-
-    movw $0x10, %ax
-    movw %ax, %ds
-    movw %ax, %es
-    movw %ax, %fs
-    movw %ax, %gs
-    movw %ax, %ss
-    # jmp kernel
-    ljmp $0x08, $kernel
-    
-kernel:
-	/*
-	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 pushed a multiple of 16 bytes to the
-	stack since (pushed 0 bytes so far), so the alignment has thus been
-	preserved and the call is well defined.
-	*/
-    
+	# Enter the high-level kernel.
 	call kernel_main
 
-.global keyboard_test
-keyboard_test:
-    hlt
-
-	/*
-	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.
-	*/
+	# Infinite loop if the system has nothing more to do.
 	cli
 1:	hlt
 	jmp 1b
-
-/*
-Set the size of the _start symbol to the current location '.' minus its start.
-This is useful when debugging or when you implement call tracing.
-*/
-
-.size _start, . - _start

arch/i686/interrupts/idt.c

@@ -15,6 +15,15 @@
 #define IRQ6 (IRQ0 + 6)
 #define IRQ7 (IRQ0 + 7)
 
+#define IRQ8 0x28
+#define IRQ9  (IRQ8 + 1)
+#define IRQ10 (IRQ8 + 2)
+#define IRQ11 (IRQ8 + 3)
+#define IRQ12 (IRQ8 + 4)
+#define IRQ13 (IRQ8 + 5)
+#define IRQ14 (IRQ8 + 6)
+#define IRQ15 (IRQ8 + 7)
+
 #define NUM_ENTRIES 0x100
 
 struct InterruptDescriptor {
@@ -97,21 +106,20 @@ static void load_idt()
     idt.base = entries;
 
     asm ( "lidt %0" : : "m"(idt) );
-    asm ( "sti" );
 }
 
-struct InterruptDescriptor generate_entry(bool present, void isr(struct interrupt_frame*), uint8_t gate_type, uint8_t ring, uint8_t selector)
+static struct InterruptDescriptor generate_entry(bool present, void isr(struct interrupt_frame*), uint8_t gate_type, uint8_t ring, uint8_t selector)
 {
     struct InterruptDescriptor entry;
     entry.present = present;
-    entry.offset = (uint32_t)isr;
+    entry.offset = (size_t)isr;
     entry.gate_type = gate_type;
     entry.ring = ring;
     entry.selector = selector;
     return entry;
 }
 
-void idt_init()
+static void add_exceptions() 
 {
     struct InterruptDescriptor entry;
 
@@ -130,23 +138,47 @@ void idt_init()
     entry = generate_entry(true, double_fault, 0xF, 0, 0x8);
     add_entry(entry, DoubleFault);
 
-    entry = generate_entry(true, irq, 0xE, 0, 0x8);
+}
+
+static void add_irqs()
+{
+    struct InterruptDescriptor entry;
+    entry = generate_entry(true, irq_1, 0xE, 0, 0x8);
     for (int i = IRQ0; i <= IRQ7; i++)
     {
         add_entry(entry, i);
     }
 
+    entry = generate_entry(true, irq_2, 0xE, 0, 0x8);
+    for (int i = IRQ8; i <= IRQ15; i++)
+    {
+        add_entry(entry, i);
+    }
+
+    entry = generate_entry(true, irq0, 0xE, 0, 0x8);
+    add_entry(entry, IRQ0);
+
     entry = generate_entry(true, keyboard_interrupt, 0xE, 0, 0x8);
     add_entry(entry, IRQ1);
+}
 
+static void add_syscall()
+{
     struct InterruptDescriptor syscall_entry;
     syscall_entry.present = true;
-    syscall_entry.offset = (uint32_t)syscall;
+    syscall_entry.offset = (size_t)syscall;
     syscall_entry.gate_type = 0xE;
     syscall_entry.ring = 3;
     syscall_entry.selector = 0x8;
 
     add_entry(syscall_entry, 0x80);
+}
+
+void idt_init()
+{
+    add_exceptions();
+    add_irqs();
+    add_syscall();
 
     load_idt();
 }

arch/i686/interrupts/interrupt.c

@@ -1,15 +1,11 @@
 #include <kernel/tty.h>
+#include <kernel/task.h>
+#include "interrupt.h" 
 #include <stddef.h>
 #include <debugging.h>
 #include <kernel/io/keyboard.h>
 #include "../io.h"
 
-struct interrupt_frame {
-    uint32_t eflags;
-    uint32_t cs;
-    uint32_t eip;
-};
-
 uint8_t test = 'a';
 
 static void stack_trace() 
@@ -25,40 +21,54 @@ static void stack_trace()
     }
 }
 
-__attribute__((interrupt)) void divide_by_zero(void*) 
+__attribute__((interrupt)) void divide_by_zero(struct interrupt_frame*) 
 {
     terminal_writestring("Yo dude u cant divide by zero yao\n");
     while (1) { }
 }
 
-__attribute__((interrupt)) void general_protection_fault(void*)
+__attribute__((interrupt)) void general_protection_fault(struct interrupt_frame*)
 {
     terminal_writestring("GPF handler called\n");
-    while (1) { }
+    while (1) {
+        asm("cli");
+        asm("hlt");
+    }
 }
 
-__attribute__((interrupt)) void double_fault(void*) 
+__attribute__((interrupt)) void double_fault(struct interrupt_frame*) 
 {
     stack_trace();
     terminal_writestring("2 Errors in a row, u better behave naughty naughty\n");
-    while (1) { }
+    while (1) { 
+        asm("cli");
+        asm("hlt");
+    }
 }
 
-__attribute__((interrupt)) void exception(void*)
+__attribute__((interrupt)) void exception(struct interrupt_frame*)
 {
     terminal_writestring("Some weird error code stuff\n");
     while (1) { }
 }
 
-__attribute__((interrupt)) void keyboard_interrupt(void*)
+__attribute__((interrupt)) void keyboard_interrupt(struct interrupt_frame*)
 {
+    terminal_writestring("Keyboard Interrupt\n");
     uint8_t scancode = inb(0x60);
     handle_keyboard(scancode);
     outb(0x20, 0x20);
 }
 
-__attribute__((interrupt)) void irq(void*) 
+__attribute__((interrupt)) void irq_1(struct interrupt_frame*) 
 {
+    terminal_writestring("PIC 1\n");
     outb(0x20, 0x20);
 }
 
+__attribute__((interrupt)) void irq_2(struct interrupt_frame*) 
+{
+    terminal_writestring("PIC 2\n");
+    outb(0xA0, 0x20);
+    outb(0x20, 0x20);
+}

arch/i686/interrupts/interrupt.h

@@ -1,4 +1,12 @@
-struct interrupt_frame;
+#include <stddef.h>
+
+struct interrupt_frame {
+    size_t eip;
+    size_t cs;
+    size_t eflags;
+    size_t ss;
+    size_t esp;
+};
 
 __attribute__((interrupt)) void divide_by_zero(struct interrupt_frame* frame);
 __attribute__((interrupt)) void general_protection_fault(struct interrupt_frame* frame);
@@ -6,7 +14,10 @@ __attribute__((interrupt)) void double_fault(struct interrupt_frame* frame);
 
 __attribute__((interrupt)) void exception(struct interrupt_frame* frame);
 
-__attribute__((interrupt)) void syscall(void*);
+__attribute__((interrupt)) void syscall(struct interrupt_frame* frame);
 
 __attribute__((interrupt)) void keyboard_interrupt(struct interrupt_frame* frame);
-__attribute__((interrupt)) void irq(struct interrupt_frame* frame);
+__attribute__((interrupt)) void irq_1(struct interrupt_frame* frame);
+__attribute__((interrupt)) void irq_2(struct interrupt_frame* frame); 
+
+__attribute__((interrupt)) void irq0(struct interrupt_frame* frame);

arch/i686/interrupts/irq0.s

@@ -0,0 +1,68 @@
+.global irq0
+.extern _switch_task
+
+.global jump_kernel
+.global jump_user
+
+.extern ss
+.extern esp
+.extern eflags
+.extern cs
+.extern eip 
+
+irq0:
+pusha
+
+mov $0x10, %eax
+mov %ax, %ds
+mov %ax, %es
+mov %ax, %fs
+mov %ax, %gs
+
+call _switch_task
+
+iret
+
+jump_kernel:
+mov $0x20, %eax
+outb %al, $0x20
+
+mov (ss), %eax
+mov %ax, %ds
+mov %ax, %es
+mov %ax, %fs
+mov %ax, %gs
+
+popa
+
+mov (esp), %esp
+
+push (ss)
+push (esp)
+push (eflags)
+push (cs)
+push (eip)
+
+iret
+
+jump_user:
+mov $0x20, %eax
+outb %al, $0x20
+
+mov (ss), %eax
+mov %ax, %ds
+mov %ax, %es
+mov %ax, %fs
+mov %ax, %gs
+
+popa
+
+push (ss)
+push (esp)
+push (eflags)
+push (cs)
+push (eip)
+
+iret
+
+

arch/i686/interrupts/pic.c

@@ -21,17 +21,18 @@
 
 void init_pic() {
     uint8_t a1;
+    uint8_t a2;
     
     a1 = inb(PIC1_DATA);                        // save masks
-    inb(PIC2_DATA);
-    
+    a2 = inb(PIC2_DATA);
+
     outb(PIC1_COMMAND, ICW1_INIT | ICW1_ICW4);  // starts the initialization sequence (in cascade mode)
     io_wait();
     outb(PIC2_COMMAND, ICW1_INIT | ICW1_ICW4);
     io_wait();
     outb(PIC1_DATA, 0x20);                 // ICW2: Master PIC vector offset
     io_wait();
-    outb(PIC2_DATA, 0xFF);                 // ICW2: Slave PIC vector offset
+    outb(PIC2_DATA, 0x28);                 // ICW2: Slave PIC vector offset
     io_wait();
     outb(PIC1_DATA, 4);                       // ICW3: tell Master PIC that there is a slave PIC at IRQ2 (0000 0100)
     io_wait();
@@ -45,5 +46,5 @@ void init_pic() {
     
     outb(PIC1_DATA, a1);   // restore saved masks.
     // outb(PIC2_DATA, a2);
-    outb(PIC2_DATA, 0xFF);
+    outb(PIC2_DATA, a2);
 }

arch/i686/interrupts/syscall.s

@@ -1,9 +1,20 @@
 .extern _syscall
 .global syscall
 syscall:
-sti
+mov $0x10, %edx
+mov %ax, %ds
+mov %ax, %es
+mov %ax, %fs
+mov %ax, %gs
+
+mov %esp, %edx
+mov $0x00f00000, %esp
+push 0x10(%edx)
+push 0x0C(%edx)
+push 0x08(%edx)
+push 0x04(%edx)
+push 0x00(%edx)
 
-push %edx
 push %ecx
 push %ebx
 push %eax
@@ -13,6 +24,5 @@ call _syscall
 pop %eax
 pop %ebx
 pop %ecx
-pop %edx
 iret
 

arch/i686/linker.ld

@@ -6,47 +6,43 @@ ENTRY(_start)
    kernel image. */
 SECTIONS
 {
-	/* It used to be universally recommended to use 1M as a start offset,
-	   as it was effectively guaranteed to be available under BIOS systems.
-	   However, UEFI has made things more complicated, and experimental data
-	   strongly suggests that 2M is a safer place to load. In 2016, a new
-	   feature was introduced to the multiboot2 spec to inform bootloaders
-	   that a kernel can be loaded anywhere within a range of addresses and
-	   will be able to relocate itself to run from such a loader-selected
-	   address, in order to give the loader freedom in selecting a span of
-	   memory which is verified to be available by the firmware, in order to
-	   work around this issue. This does not use that feature, so 2M was
-	   chosen as a safer option than the traditional 1M. */
-	. = 2M;
+	. = 1M;
+    
+	_kernel_start = .;
+    .multiboot.data :
+    {
+		*(.multiboot.data)
+    }
 
-	/* First put the multiboot header, as it is required to be put very early
-	   in the image or the bootloader won't recognize the file format.
-	   Next we'll put the .text section. */
-	.text BLOCK (4K) : ALIGN(4K)
+    .multiboot.text :
+    {
+        *(.multiboot.text)
+    }
+
+    . += 0xC0000000;
+
+	.text BLOCK (4K) : AT (ADDR (.text) - 0xC0000000)
 	{
-		*(.multiboot)
 		*(.text)
 	}
 
 	/* Read-only data. */
-	.rodata BLOCK(4K) : ALIGN(4M)
+	.rodata BLOCK(4K) : AT (ADDR (.rodata) - 0xC0000000)
 	{
 		*(.rodata)
 	}
 
 	/* Read-write data (initialized) */
-	.data BLOCK(4K) : ALIGN(4K)
+	.data BLOCK(4K) : AT (ADDR (.data) - 0xC0000000)
 	{
 		*(.data)
 	}
 
 	/* Read-write data (uninitialized) and stack */
-	.bss BLOCK(4K) : ALIGN(4K)
+	.bss BLOCK(4K) : AT (ADDR (.bss) - 0xC0000000)
 	{
 		*(COMMON)
 		*(.bss)
 	}
-
-	/* The compiler may produce other sections, by default it will put them in
-	   a segment with the same name. Simply add stuff here as needed. */
+	_kernel_end = .;
 }

arch/i686/paging.c

@@ -0,0 +1,26 @@
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+#include <kernel/paging.h>
+#include <kernel/tty.h>
+
+struct x86_Page_Directory {
+    uint32_t address : 20;
+    uint8_t available_1 : 4;
+    bool page_Size: 1;
+    bool available_2: 1;
+    bool accesed: 1;
+    bool cache_disable: 1;
+    bool write_through: 1;
+    bool user_supervisor: 1;
+    bool read_write: 1;
+    bool present: 1;
+
+} __attribute__((packed));
+
+struct x86_Page_Directory page_directory[1024] __attribute__((aligned(4096)));
+
+void setup_paging() {
+    size_t size = sizeof(page_directory[0]);
+}

arch/i686/tty.c

@@ -60,7 +60,7 @@ void terminal_initialize(void)
     terminal_row = 0;
     terminal_column = 0;
     terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
-    terminal_buffer = (uint16_t*) 0xB8000;
+    terminal_buffer = (uint16_t*) 0xC03FF000;
     for (size_t y = 0; y < VGA_HEIGHT; y++) {
         for (size_t x = 0; x < VGA_WIDTH; x++) {
             const size_t index = y * VGA_WIDTH + x;
@@ -117,11 +117,13 @@ void terminal_putchar(char c)
         return;
     }
     terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
-    if (++terminal_column == VGA_WIDTH) {
+    if (++terminal_column >= VGA_WIDTH) {
         terminal_column = 0;
-        if (++terminal_row == VGA_HEIGHT)
-            terminal_scroll();
+        terminal_row++;
     }
+
+    if (terminal_row >= VGA_HEIGHT)
+        terminal_scroll();
 }
 
 static void terminal_write(const char* data, size_t size) 

arch/i686/userland.s

@@ -1,16 +0,0 @@
-.global jump_to_userspace
-jump_to_userspace:
-mov $0x20 | 0x3, %ax
-movw %ax, %ds
-movw %ax, %es
-movw %ax, %fs
-movw %ax, %gs
-pushl $0x20 | 0x3  /* SS*/ 
-pushl $0x00c00100  /* ESP */ 
-pushf              /* EFLAGS */    
-popl %eax
-orl $0x200, %eax
-pushl %eax         /* Set interrupts */
-pushl $0x18 | 0x3  /* CS */
-pushl $0x00800000  /* EIP */ 
-iret

include/kernel/elf.h

@@ -1,5 +1,5 @@
 #include <stdint.h>
 #include <stddef.h>
 
-void run_program(uint8_t* program, size_t length);
+void run_program(uint8_t* code, size_t code_length, uint8_t* data, size_t data_length);
 

include/kernel/paging.h

@@ -0,0 +1,11 @@
+#include <stddef.h>
+
+struct PageDirectory {
+    size_t page_table;
+};
+
+struct PageTable {
+    
+};
+
+void setup_paging();

include/kernel/task.h

@@ -0,0 +1,40 @@
+#include <stdint.h>
+#include <stddef.h>
+
+struct CPUState {
+    size_t eax;
+    size_t ebx;
+    size_t ecx;
+    size_t edx;
+    size_t eip;
+    size_t esp;
+    size_t ebp;
+    size_t edi;
+    size_t esi;
+    size_t cs;
+    size_t ds;
+    size_t eflags;
+};
+
+struct Task {
+    struct CPUState state;
+};
+
+void switch_task(
+    size_t eax, 
+    size_t ebx,
+    size_t ecx,
+    size_t edx,
+
+    size_t ebp,
+
+    size_t esp_real,
+
+    size_t eip,
+    size_t cs,
+    size_t eflags,
+    size_t esp_fake,
+    size_t ds
+);
+void setup_tasks();
+void add_task(struct Task task);

kernel/elf.c

@@ -3,6 +3,7 @@
 #include <debugging.h>
 #include <kernel/tty.h>
 #include <kernel/gdt.h>
+#include <kernel/task.h>
 #include <debugging.h>
 
 static void* memcpy(void* restrict dstptr, const void* restrict srcptr, size_t size) {
@@ -15,10 +16,30 @@ static void* memcpy(void* restrict dstptr, const void* restrict srcptr, size_t s
 
 extern void jump_to_userspace();
 
-void run_program(uint8_t* program, size_t length)
+void run_program(uint8_t* code, size_t code_length, uint8_t* data, size_t data_length)
 {
-    uint8_t* userland_code = (uint8_t*) 0x00800000;
-    memcpy(userland_code, program, length);
+    uint8_t* userland_code = (uint8_t*) 0x00000000;
+    uint8_t* userland_data = (uint8_t*) 0x00800000;
 
-    jump_to_userspace();
+    memcpy(userland_code, code, code_length);
+    memcpy(userland_data, data, data_length);
+
+    struct CPUState target = {
+        .eip = (size_t) userland_code,
+        .esp = 0x00000000,
+        .eax = 0,
+        .ebx = 0,
+        .ecx = 0,
+        .edx = 0,
+        .cs = 0x18 | 0x3,
+        .ds = 0x20 | 0x3,
+        .eflags = 0x0200,
+        .ebp = 0x00c00f00,
+    };
+
+    struct Task task = {
+        .state = target,
+    };
+
+    add_task(task);
 }

kernel/kernel.c

@@ -3,6 +3,8 @@
 #include <kernel/elf.h>
 #include <kernel/pic.h>
 #include <kernel/heap.h>
+#include <kernel/task.h>
+#include <kernel/paging.h>
 
 #include <debugging.h>
 
@@ -12,23 +14,36 @@
 #endif
 
 uint8_t program[] = {
-    0xba, 0x01, 0x00, 0x00, 0x00, // mov 1, %edx
-    0xb8, 0xff, 0x00, 0x80, 0x00, // mov $buffer, %eax
-    0xcd, 0x80, // int 0x80
-    0xba, 0x00, 0x00, 0x00, 0x00, // mov 0, %edx
+    // 0xba, 0x01, 0x00, 0x00, 0x00, // mov 1, %edx
+    0xb8, 0x00, 0x00, 0xC0, 0x00, // mov $buffer, %eax
+    // 0xcd, 0x80, // int 0x80
+    0xb9, 0x00, 0x00, 0x00, 0x00, // mov 0, %ecx
     0xcd, 0x80, // int 0x80
     0xb9, 0x00, 0x00, 0x80, 0x00, // mov $start, %ecx
     0xff, 0xe1, // jmp *%ecx
 };
 
+uint8_t data[] = "Hello From Userspace\n";
+
+
 void kernel_main(void) 
 {
     /* Initialize terminal interface */
     terminal_initialize();
+    terminal_writestring("Hello from Kernelspace\n");
 
-    init_pic();
     idt_init();
+    init_pic();
     heap_init();
 
-    run_program(program, sizeof(program));
+    setup_tasks();
+    setup_paging();
+
+    asm("sti");
+
+    run_program(program, sizeof(program), data, sizeof(data));
+
+    while (true) {
+        terminal_writestring("Hello from Kernelspace\n");
+    }
 }

kernel/syscall.c

@@ -9,6 +9,7 @@ static void print(char* buffer)
 
 static void input(char* buffer)
 {
+    terminal_writestring("Input: ");
     while (true) {
         for (size_t i = 0; i < keyboard_buffer_top; i++) {
             buffer[i] = keyboard_buffer[i];
@@ -22,9 +23,9 @@ static void input(char* buffer)
     }
 }
 
-void _syscall(uint32_t a, uint32_t b, uint32_t c, uint32_t d)
+void _syscall(uint32_t a, uint32_t b, uint32_t c)
 {
-    switch (d) {
+    switch (c) {
         case 0x00:
             print((char*) a);
             break;

kernel/task.c

@@ -0,0 +1,181 @@
+#include <kernel/task.h>
+#include <kernel/heap.h>
+#include <kernel/tty.h>
+
+struct Task* tasks;
+size_t tasks_capacity;
+size_t num_tasks;
+
+size_t current_task = 0;
+
+void setup_tasks()
+{
+    tasks = malloc(sizeof(*tasks));
+    tasks_capacity = 1;
+    num_tasks = 1;
+}
+
+void add_task(struct Task task)
+{
+    asm("cli");
+    if (num_tasks == tasks_capacity) {
+        struct Task* temp = malloc(sizeof(*tasks) * tasks_capacity * 2);
+
+        for (size_t i = 0; i < num_tasks; i++) {
+            temp[i] = tasks[i];
+        }
+        
+        tasks_capacity *= 2;
+
+        free(tasks);
+        tasks = temp;
+    }
+
+    tasks[num_tasks] = task;
+    num_tasks++;
+    asm("sti");
+}
+
+size_t ss;
+size_t esp;
+size_t eflags;
+size_t cs;
+size_t eip;
+
+void jump_kernel(
+    size_t edi,
+    size_t esi,
+    size_t ebp,
+    size_t esp,
+    size_t ebx,
+    size_t edx,
+    size_t ecx,
+    size_t eax
+);
+void jump_user(
+    size_t edi,
+    size_t esi,
+    size_t ebp,
+    size_t esp,
+    size_t ebx,
+    size_t edx,
+    size_t ecx,
+    size_t eax
+);
+
+static void save_state(
+    size_t eax,
+    size_t ebx,
+    size_t ecx,
+    size_t edx,
+
+    size_t esp,
+    size_t ebp,
+
+    size_t esi,
+    size_t edi,
+
+    size_t eip,
+
+    size_t cs,
+    size_t ds,
+
+    size_t eflags
+) {
+    struct CPUState state = {
+        .eax = eax,
+        .ebx = ebx,
+        .ecx = ecx,
+        .edx = edx,
+
+        .esp = esp,
+        .ebp = ebp,
+
+        .eip = eip,
+
+        .esi = esi,
+        .edi = edi,
+
+        .cs = cs,
+        .ds = ds,
+
+        .eflags = eflags,
+    };
+    
+    tasks[current_task].state = state;
+    
+    current_task++;
+    current_task %= num_tasks;
+}
+
+void next_task() {
+    struct CPUState s = tasks[current_task].state;
+
+    ss = s.ds;
+    esp = s.esp;
+    eflags = s.eflags;
+    cs = s.cs;
+    eip = s.eip;
+
+    if ((cs & 3) == 0) {
+        jump_kernel(
+            s.edi, 
+            s.esi, 
+            s.ebp, 
+            s.esp, 
+            s.ebx, 
+            s.edx, 
+            s.ecx, 
+            s.eax
+        );
+    } else {
+        jump_user(
+            s.edi, 
+            s.esi, 
+            s.ebp, 
+            s.esp, 
+            s.ebx, 
+            s.edx, 
+            s.ecx, 
+            s.eax
+        );
+    }
+}
+
+void _switch_task(
+    size_t edi,
+    size_t esi,
+    size_t ebp,
+    size_t esp_current,
+    size_t ebx,
+    size_t edx,
+    size_t ecx,
+    size_t eax,
+
+    size_t eip_passed,
+    size_t cs_passed,
+    size_t eflags_passed,
+    size_t esp_passed,
+    size_t ds_passed
+) 
+{
+    terminal_writestring("Switching task\n");
+    if (num_tasks == 0) {
+        return;
+    };
+    
+    size_t ds;
+    if ((cs & 3) == 0) {
+        ds = 0x10;
+        esp_current = esp_current + sizeof(size_t) * 3;
+    } else {
+        ds = ds_passed;
+        esp_current = esp_passed;
+    }
+
+    save_state(eax, ebx, ecx, edx, esp_current, ebp, esi, edi, eip_passed, cs_passed, ds, eflags_passed);
+
+    next_task();
+}
+
+