Brendan's Tutorial Step 1: done

.gdbinit

@@ -0,0 +1,5 @@
+file build/kernel
+target remote localhost:4242
+set arch i386
+set step-mode on
+directory src

build.zig

@@ -11,7 +11,7 @@ pub fn build(b: *Builder) void {
     kernel.addAssemblyFile("src/arch/x86/gdt.s");
     kernel.addAssemblyFile("src/arch/x86/isr.s");
     kernel.addAssemblyFile("src/arch/x86/paging.s");
-    // kernel.addAssemblyFile("src/arch/x86/switch_tasks.s");
+    kernel.addAssemblyFile("src/arch/x86/switch_tasks.s");
 
     kernel.setBuildMode(b.standardReleaseOptions());
     kernel.setTarget(builtin.Arch.i386, builtin.Os.freestanding, builtin.Abi.none);

qemu.sh

@@ -1,5 +1,5 @@
 QEMU_SOCKET=/tmp/qemu.sock
-QEMU_MONITOR="socat - UNIX-CONNECT:${QEMU_SOCKET}"
+QEMU_MONITOR="sudo socat - UNIX-CONNECT:${QEMU_SOCKET}"
 QEMU_GDB_PORT=4242
 KERNEL=build/kernel
 
@@ -11,11 +11,11 @@ start() {
 		-enable-kvm \
 		-m 1337M \
 		-curses \
-        -append "Hello" \
-        -drive file=disk.img,if=virtio\
 		-kernel ${KERNEL}
+		# -drive file=disk.img,if=virtio\
 		# -no-reboot \
 		# -device virtio-net,netdev=network0 -netdev tap,id=network0,ifname=tap0,script=no,downscript=no \
+		# -S \
 		# build/kernel.iso
 
 		# this allows to monitor with ^a-c, but doesn't
@@ -23,26 +23,16 @@ start() {
 		# -serial mon:stdio \
 }
 
-monitor() {
-    if [ "$1" == "" ]; then
-        sudo ${QEMU_MONITOR}
-    else
-        echo "$1" | sudo ${QEMU_MONITOR} >/dev/null
-    fi
-}
+monitor() { sudo ${QEMU_MONITOR}; }
+monitor-exec() { echo "$1" | sudo ${QEMU_MONITOR} >/dev/null; }
+
+quit() { monitor-exec quit; }
 
 reload() {
-    monitor stop
+	monitor-exec stop
 	# monitor "change ide1-cd0 ${KERNEL}"
-    monitor system_reset
-    monitor cont
-}
-
-gdb() {
-    gdb -q \
-        -symbols "${KERNEL}" \
-        -ex "target remote :${QEMU_GDB_PORT}" \
-        -ex "set arch i386"
+	monitor-exec system_reset
+	monitor-exec cont
 }
 
 "$@"

src/arch/x86/idt.zig

@@ -59,7 +59,12 @@ pub fn initialize() void {
     isr.install_syscalls();
     interrupt.registerIRQ(0, interrupt.pit_handler);
     interrupt.registerIRQ(1, kernel.ps2.keyboard_handler);
+    interrupt.register(3, test_b);
 
     // load IDT
     lidt(@ptrToInt(&idtr));
 }
+
+pub fn test_b() void {
+    kernel.println("int3!");
+}

src/arch/x86/lib/instructions.zig

@@ -1,9 +1,3 @@
-////
-// Load a new Task Register.
-//
-// Arguments:
-//     desc: Segment selector of the TSS.
-//
 pub inline fn ltr(desc: u16) void {
     asm volatile ("ltr %[desc]"
         :
@@ -11,27 +5,25 @@ pub inline fn ltr(desc: u16) void {
     );
 }
 
-////
-// Completely stop the computer.
-//
 pub inline fn hang() noreturn {
-    asm volatile ("cli");
+    cli();
     while (true) asm volatile ("hlt");
 }
 
-pub inline fn sti() void {
+//TODO: inline this
+pub fn cli() void {
+    asm volatile ("cli");
+}
+
+//TODO: inline this
+pub fn sti() void {
     asm volatile ("sti");
 }
+
 pub inline fn int3() void {
     asm volatile ("int3");
 }
 
-////
-// Load a new Interrupt Descriptor Table.
-//
-// Arguments:
-//     idtr: Address of the IDTR register.
-//
 pub inline fn lidt(idtr: usize) void {
     asm volatile ("lidt (%[idtr])"
         :

src/arch/x86/main.zig

@@ -7,7 +7,6 @@ pub fn x86_main(info: *const kernel.multiboot.MultibootInfo) void {
     idt.initialize();
     pmem.initialize(info);
     paging.initialize();
-
     // enable interrupts
     sti();
 }

src/arch/x86/pmem.zig

@@ -16,7 +16,7 @@ pub inline fn pageAlign(address: u32) u32 {
 
 // Return the amount of variable elements (in bytes).
 //
-pub inline fn available() usize {
+pub fn available() usize {
     return stack_index * PAGE_SIZE;
 }
 

src/arch/x86/switch_tasks.s

@@ -1,47 +1,55 @@
-;https://wiki.osdev.org/Multitasking_Systems
+//https://wiki.osdev.org/Multitasking_Systems
 
-;C declaration:
-;   void switch_tasks(thread_control_block *next_thread);
-;
-;WARNING: Caller is expected to disable IRQs before calling, and enable IRQs again after function returns
+//C declaration:
+//   void switch_tasks(thread_control_block *next_thread)//
+//
+//WARNING: Caller is expected to disable IRQs before calling, and enable IRQs again after function returns
+
+.type switch_tasks, @function
+.global switch_tasks
 
 switch_tasks:
+    push %ebp
+    mov %esp, %ebp
+    mov +12(%esp), %eax
+    mov %esp, (%eax) //save old esp
+    mov +8(%esp), %eax
+    mov %eax, %esp // move the forged stack to esp
+    pop %ebp // the top of the forged stack contains ebp
+    ret //the top of the forged stack contains eip to go to
 
-    ;Save previous task's state
+    //Save previous task's state
+    //Notes:
+    //  For cdecl// EAX, ECX, and EDX are already saved by the caller and don't need to be saved again
+    //  EIP is already saved on the stack by the caller's "CALL" instruction
+    //  The task isn't able to change CR3 so it doesn't need to be saved
+    //  Segment registers are constants (while running kernel code) so they don't need to be saved
 
-    ;Notes:
-    ;  For cdecl; EAX, ECX, and EDX are already saved by the caller and don't need to be saved again
-    ;  EIP is already saved on the stack by the caller's "CALL" instruction
-    ;  The task isn't able to change CR3 so it doesn't need to be saved
-    ;  Segment registers are constants (while running kernel code) so they don't need to be saved
+    // push %ebx
+    // push %esi
+    // push %edi
+    // push %ebp
 
-    push ebx
-    push esi
-    push edi
-    push ebp
+    // mov %edi,[current_task]    //edi = address of the previous task's "thread control block"
+    // mov [edi+TCB.ESP], %esp         //Save ESP for previous task's kernel stack in the thread's TCB
 
-    mov edi,[current_task_TCB]    ;edi = address of the previous task's "thread control block"
-    mov [edi+TCB.ESP],esp         ;Save ESP for previous task's kernel stack in the thread's TCB
+    // Load next task's state
 
-    ;Load next task's state
+    // mov %esi,[esp+(4+1)*4]         //esi = address of the next task's "thread control block" (parameter passed on stack)
+    // mov [current_task], %esi    //Current task's TCB is the next task TCB
 
-    mov esi,[esp+(4+1)*4]         ;esi = address of the next task's "thread control block" (parameter passed on stack)
-    mov [current_task_TCB],esi    ;Current task's TCB is the next task TCB
+    // mov %esp,[esi+TCB.ESP]         //Load ESP for next task's kernel stack from the thread's TCB
+    // mov eax,[esi+TCB.CR3]         //eax = address of page directory for next task
+    // mov %ebx,[esi+TCB.ESP0]        //ebx = address for the top of the next task's kernel stack
+    // mov [TSS.ESP0],ebx            //Adjust the ESP0 field in the TSS (used by CPU for for CPL=3 -> CPL=0 privilege level changes)
+    // mov ecx,cr3                   //ecx = previous task's virtual address space
 
-    mov esp,[esi+TCB.ESP]         ;Load ESP for next task's kernel stack from the thread's TCB
-    mov eax,[esi+TCB.CR3]         ;eax = address of page directory for next task
-    mov ebx,[esi+TCB.ESP0]        ;ebx = address for the top of the next task's kernel stack
-    mov [TSS.ESP0],ebx            ;Adjust the ESP0 field in the TSS (used by CPU for for CPL=3 -> CPL=0 privilege level changes)
-    mov ecx,cr3                   ;ecx = previous task's virtual address space
+    // cmp eax,ecx                   //Does the virtual address space need to being changed?
+    // je .doneVAS                   // no, virtual address space is the same, so don't reload it and cause TLB flushes
+    // mov cr3,eax                   // yes, load the next task's virtual address space
+// .doneVAS:
 
-    cmp eax,ecx                   ;Does the virtual address space need to being changed?
-    je .doneVAS                   ; no, virtual address space is the same, so don't reload it and cause TLB flushes
-    mov cr3,eax                   ; yes, load the next task's virtual address space
-.doneVAS:
-
-    pop ebp
-    pop edi
-    pop esi
-    pop ebx
-
-    ret                           ;Load next task's EIP from its kernel stack)
+    // pop %ebp
+    // pop %edi
+    // pop %esi
+    // pop %ebx

src/base.zig

@@ -1,4 +0,0 @@
-pub const assert = @import("std").debug.assert;
-pub const std = @import("std");
-
-pub usingnamespace @import("vga.zig");

src/console.zig

@@ -3,6 +3,13 @@ usingnamespace @import("index.zig");
 var command: [10]u8 = undefined;
 var command_len: usize = 0;
 
+fn test_a() void {
+    var a: u32 = 2;
+    a += 1;
+    a = 4;
+    a -= 1;
+}
+
 fn execute(input: []u8) void {
     const eql = std.mem.eql;
     if (eql(u8, input, "x86paging")) return x86.paging.introspect();
@@ -11,6 +18,10 @@ fn execute(input: []u8) void {
     if (eql(u8, input, "lspci")) return pci.lspci();
     if (eql(u8, input, "uptime")) return time.uptime();
     if (eql(u8, input, "topbar")) return topbar();
+    if (eql(u8, input, "test")) {
+        const tbar = task.Task.new(@ptrToInt(topbar)) catch unreachable;
+        while (true) tbar.switch_to();
+    }
     println("{}: command not found", input);
 }
 

src/main.zig

@@ -15,8 +15,6 @@ export const multiboot_header align(4) linksection(".multiboot") = multiboot: {
     };
 };
 
-extern fn switch_tasks(stack: u32) void;
-
 // arch independant initialization
 export fn kmain(magic: u32, info: *const multiboot.MultibootInfo) noreturn {
     assert(magic == multiboot.MULTIBOOT_BOOTLOADER_MAGIC);
@@ -24,10 +22,11 @@ export fn kmain(magic: u32, info: *const multiboot.MultibootInfo) noreturn {
     println("--- x86 initialization ---");
     x86.x86_main(info);
     println("--- core initialization ---");
-    // pci.scan();
     vmem.initialize();
-    task.initialize() catch unreachable;
-    console.initialize();
+    pci.scan();
 
-    while (true) asm volatile ("hlt");
+    console.initialize();
+    // while (true) asm volatile ("hlt");
+    const tbar = task.Task.new(@ptrToInt(topbar)) catch unreachable;
+    while (true) tbar.switch_to();
 }

src/task.zig

@@ -1,14 +1,18 @@
 pub usingnamespace @import("index.zig");
 const TASK_MAX = 1024;
-var tasks = [1]?*Task{null} ** TASK_MAX;
+var boot_task = Task{ .tid = 0, .esp = 0x47 };
+var current_task: *Task = &boot_task;
+pub var tasks = [1]?*Task{&boot_task} ++ ([1]?*Task{null} ** TASK_MAX);
 
 const STACK_SIZE = x86.PAGE_SIZE; // Size of thread stacks.
 var tid_counter: u16 = 1;
 
-pub const Task = struct {
+///ASM
+extern fn switch_tasks(new_esp: u32, old_esp_addr: u32) void;
+
+pub const Task = packed struct {
+    esp: usize,
     tid: u16,
-    stack_top: usize,
-    entrypoint: usize,
     //context: isr.Context,
     //cr3: usize,
 
@@ -16,13 +20,20 @@ pub const Task = struct {
         // Allocate and initialize the thread structure.
         var t = try vmem.allocate(Task);
 
-        t.entrypoint = entrypoint;
         t.tid = tid_counter;
         tid_counter +%= 1;
         assert(tid_counter != 0); //overflow
 
-        t.stack_top = try vmem.malloc(STACK_SIZE);
-        assert(t.stack_top < layout.USER_STACKS_END);
+        // allocate a new stack
+        t.esp = (try vmem.malloc(STACK_SIZE)) + STACK_SIZE;
+        // top of stack is the address that ret will pop
+        t.esp -= 4;
+        @intToPtr(*usize, t.esp).* = entrypoint;
+        // top of stack is ebp that we will pop
+        t.esp -= 4;
+        @intToPtr(*usize, t.esp).* = t.esp + 8;
+
+        println("new task esp=0x{x}, eip=0x{x}", t.esp, entrypoint);
 
         tasks[t.tid] = t;
         return t;
@@ -30,20 +41,38 @@ pub const Task = struct {
 
     pub fn destroy(self: *Task) void {
         tasks[self.tid] = null;
-        vmem.free(self.stack_top);
+        vmem.free(self.esp);
         vmem.free(@ptrToInt(self));
     }
-};
 
-pub fn initialize() !void {
-    const t = try Task.new(0x0);
-    println("task=0x{x}", t.stack_top);
+    pub fn switch_to(self: *Task) void {
+        assert(self != current_task);
+        // save old stack
+        const old_task_esp_addr = &current_task.esp;
+        current_task = self;
+        // x86.cli();
+        // don't inline the asm function, it needs to ret
+        @noInlineCall(switch_tasks, self.esp, @ptrToInt(old_task_esp_addr));
+        // comptime {
+        //     asm (
+        //         \\mov +8(%esp), %eax
+        //         \\mov %esp, (%eax)
+        //         \\mov +4(%esp), %eax
+        //         \\mov %eax, %esp
+        //         \\pop %ebp
+        //         \\ret
+        //     );
+        // }
+        // x86.sti();
+        println("after switch");
     }
+};
 
 pub fn introspect() void {
     for (tasks) |t| {
         if (t == null) continue;
-        println("{}", t);
+        if (t != current_task) println("{}", t);
+        if (t == current_task) println("*{}", t);
     }
 }
 

src/vga.zig

@@ -1,7 +1,7 @@
-// usingnamespace @import("index.zig");
-const time = @import("time.zig");
-const x86 = @import("arch/x86/index.zig");
-const std = @import("std");
+usingnamespace @import("index.zig");
+// const time = @import("time.zig");
+// const x86 = @import("arch/x86/index.zig");
+// const std = @import("std");
 // Screen size.
 pub const VGA_WIDTH = 80;
 pub const VGA_HEIGHT = 25;
@@ -56,9 +56,8 @@ const Errors = error{};
 pub fn print(comptime format: []const u8, args: ...) void {
     var a = std.fmt.format({}, Errors, printCallback, format, args);
 }
-
 pub fn println(comptime format: []const u8, args: ...) void {
-    var a = std.fmt.format({}, Errors, printCallback, format ++ "\n", args);
+    var a = print(format ++ "\n", args);
 }
 pub fn clear() void {
     vga.clear();
@@ -66,6 +65,7 @@ pub fn clear() void {
 pub fn topbar() void {
     const cursor = vga.cursor;
     const bg = vga.background;
+    while (true) {
         vga.cursor = 0;
         vga.background = Color.Red;
 
@@ -73,6 +73,8 @@ pub fn topbar() void {
 
         vga.cursor = cursor;
         vga.background = bg;
+        task.tasks[0].?.switch_to();
+    }
 }
 
 fn printCallback(context: void, string: []const u8) Errors!void {