Init

.gitignore

@@ -0,0 +1 @@
+/build

Makefile

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+ARCHDIR=../arch/i686
+
+
+CFLAGS=-O2 \
+-std=gnu99 \
+-ffreestanding \
+-Wall -Wextra \
+-I $(INCLUDEDIR)
+
+
+KERNEL_OBJS=kernel.o
+LIB_OBJS=bootstrap.o \
+tty.o\
+strlib.o\
+interrupt.o
+OBJS=$(KERNEL_OBJS) $(LIB_OBJS)
+LDFLAGS=$(OBJS) \
+-ffreestanding \
+-O2 \
+-nostdlib \
+-lgcc
+
+
+INCLUDEDIR=../include
+
+
+all:
+	mkdir build || true
+	cp Makefile build
+	$(MAKE) -C build test-kernel-qemu
+
+architecture:
+	i686-elf-as $(ARCHDIR)/bootstrap.s -o bootstrap.o
+
+	i686-elf-gcc -c $(ARCHDIR)/tty.c -o tty.o $(CFLAGS)
+	i686-elf-gcc -c $(ARCHDIR)/interrupt.c -o interrupt.o $(CFLAGS)
+	i686-elf-gcc -c $(ARCHDIR)/strlib.c -o strlib.o $(CFLAGS)
+
+kernel:
+	i686-elf-gcc -c ../kernel/kernel.c -o kernel.o $(CFLAGS)
+
+
+myos-bin: architecture kernel
+	i686-elf-gcc -T $(ARCHDIR)/linker.ld -o myos.bin $(LDFLAGS)
+	
+	grub-file --is-x86-multiboot myos.bin
+
+test-kernel-qemu: myos-bin
+	qemu-system-i386 -kernel myos.bin
+

arch/i686/bootstrap.s

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+/* 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
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
+
+/*
+The multiboot standard does not define the value of the stack pointer register
+(esp) and it is up to the kernel to provide a stack. This allocates room for a
+small stack by creating a symbol at the bottom of it, then allocating 16384
+bytes for it, and finally creating a symbol at the top. The stack grows
+downwards on x86. The stack is in its own section so it can be marked nobits,
+which means the kernel file is smaller because it does not contain an
+uninitialized stack. The stack on x86 must be 16-byte aligned according to the
+System V ABI standard and de-facto extensions. The compiler will assume the
+stack is properly aligned and failure to align the stack will result in
+undefined behavior.
+*/
+.section .bss
+.align 16
+stack_bottom:
+.skip 16384 # 16 KiB
+stack_top:
+
+/*
+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
+.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.
+	*/
+
+	/*
+	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.
+	*/
+	mov $stack_top, %esp
+
+	/*
+	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.
+	*/
+	call kernel_main
+
+	/*
+	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.
+	*/
+	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/interrupt.c

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+#include <kernel/tty.h>
+#include <kernel/interrupt.h>
+#include <stdint.h>
+
+const uint16_t NUM_ID = 0;
+
+void load_idt(struct InterruptDescriptorTable *idt) 
+{
+    asm("lidt %0" : : "m"(idt));
+}
+
+void interrupt_initialize(struct InterruptDescriptorTable IDT) 
+{
+    terminal_writestring("Loading IDT\n");
+    load_idt(&IDT);
+}

arch/i686/linker.ld

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+/* The bootloader will look at this image and start execution at the symbol
+   designated as the entry point. */
+ENTRY(_start)
+
+/* Tell where the various sections of the object files will be put in the final
+   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;
+
+	/* 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)
+	}
+
+	/* Read-only data. */
+	.rodata BLOCK(4K) : ALIGN(4K)
+	{
+		*(.rodata)
+	}
+
+	/* Read-write data (initialized) */
+	.data BLOCK(4K) : ALIGN(4K)
+	{
+		*(.data)
+	}
+
+	/* Read-write data (uninitialized) and stack */
+	.bss BLOCK(4K) : ALIGN(4K)
+	{
+		*(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. */
+}

arch/i686/strlib.c

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+#include <stddef.h>
+
+size_t strlen(const char* str) 
+{
+	size_t len = 0;
+	while (str[len])
+		len++;
+	return len;
+}
+
+char to_upper_char(char c) 
+{
+    if ('a' <= c && c <= 'z') {
+        return c - 0x20;
+    } else {
+        return c;
+    }
+}
+
+char to_lower_char(char c) 
+{
+    if ('A' <= c && c <= 'Z') {
+        return c + 0x20;
+    } else {
+        return c;
+    }
+}
+
+char* to_lower_str(char* str)
+{
+    for (size_t i = 0; i < strlen(str); i++) {
+        str[i] = to_lower_char(str[i]);
+    }
+    return str;
+}
+
+char* to_upper_str(char* str)
+{
+    for (size_t i = 0; i < strlen(str); i++) {
+        str[i] = to_upper_char(str[i]);
+    }
+    return str;
+}
+

arch/i686/tty.c

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+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <strlib.h>
+
+/* Check if the compiler thinks you are targeting the wrong operating system. */
+#if defined(__linux__)
+#error "You are not using a cross-compiler, you will most certainly run into trouble"
+#endif
+
+/* This tutorial will only work for the 32-bit ix86 targets. */
+#if !defined(__i386__)
+#error "This tutorial needs to be compiled with a ix86-elf compiler"
+#endif
+
+/* Hardware text mode color constants. */
+enum vga_color {
+	VGA_COLOR_BLACK = 0,
+	VGA_COLOR_BLUE = 1,
+	VGA_COLOR_GREEN = 2,
+	VGA_COLOR_CYAN = 3,
+	VGA_COLOR_RED = 4,
+	VGA_COLOR_MAGENTA = 5,
+	VGA_COLOR_BROWN = 6,
+	VGA_COLOR_LIGHT_GREY = 7,
+	VGA_COLOR_DARK_GREY = 8,
+	VGA_COLOR_LIGHT_BLUE = 9,
+	VGA_COLOR_LIGHT_GREEN = 10,
+	VGA_COLOR_LIGHT_CYAN = 11,
+	VGA_COLOR_LIGHT_RED = 12,
+	VGA_COLOR_LIGHT_MAGENTA = 13,
+	VGA_COLOR_LIGHT_BROWN = 14,
+	VGA_COLOR_WHITE = 15,
+};
+
+static inline uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg) 
+{
+	return fg | bg << 4;
+}
+
+static inline uint16_t vga_entry(unsigned char uc, uint8_t color) 
+{
+	return (uint16_t) uc | (uint16_t) color << 8;
+}
+
+static inline unsigned char vga_char(uint16_t entry) 
+{
+    return entry & 0xFF;
+}
+
+static inline uint8_t vga_color(uint16_t entry) 
+{
+    return (entry >> 8) & 0xFF;
+}
+
+static const size_t VGA_WIDTH = 80;
+static const size_t VGA_HEIGHT = 25;
+
+size_t terminal_row;
+size_t terminal_column;
+uint8_t terminal_color;
+uint16_t* terminal_buffer;
+
+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;
+	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;
+			terminal_buffer[index] = vga_entry(' ', terminal_color);
+		}
+	}
+}
+
+void terminal_setcolor(uint8_t color) 
+{
+	terminal_color = color;
+}
+
+static void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) 
+{
+	const size_t index = y * VGA_WIDTH + x;
+	terminal_buffer[index] = vga_entry(c, color);
+}
+
+static uint16_t terminal_getentryat(size_t x, size_t y) 
+{
+	const size_t index = y * VGA_WIDTH + x;
+    return terminal_buffer[index];
+}
+
+static void terminal_scroll() 
+{
+    for (size_t y = 0; y < VGA_HEIGHT; y++) {
+        for (size_t x = 0; x < VGA_WIDTH; x++) {
+            if (y == VGA_HEIGHT - 1) {
+                terminal_putentryat(' ', terminal_color, x, y);
+            }
+            uint16_t entry = terminal_getentryat(x, y + 1);
+            char scrolled = vga_char(entry);
+            uint8_t color = vga_color(entry);
+            terminal_putentryat(scrolled, color, x, y);
+        }
+    }
+    terminal_row = VGA_HEIGHT - 1;
+    terminal_column = 0;
+}
+
+static void terminal_newline() {
+    if (++terminal_row == VGA_HEIGHT) {
+        terminal_scroll();
+    }
+    terminal_column = 0;
+}
+
+void terminal_putchar(char c) 
+{
+    if (c == '\n') {
+        terminal_newline();
+        return;
+    }
+	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
+	if (++terminal_column == VGA_WIDTH) {
+		terminal_column = 0;
+		if (++terminal_row == VGA_HEIGHT)
+			terminal_scroll();
+	}
+}
+
+static void terminal_write(const char* data, size_t size) 
+{
+	for (size_t i = 0; i < size; i++)
+		terminal_putchar(data[i]);
+}
+
+void terminal_writestring(const char* data) 
+{
+	terminal_write(data, strlen(data));
+}

include/debugging.c

@@ -0,0 +1,146 @@
+#include <kernel/tty.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <strlib.h>
+
+static inline uint8_t inb(uint16_t port)
+{
+    uint8_t ret;
+    __asm__ volatile ( "inb %w1, %b0"
+                   : "=a"(ret)
+                   : "Nd"(port)
+                   : "memory");
+    return ret;
+}
+
+bool is_in_shift;
+
+static unsigned char keyboard_char(unsigned char scancode) {
+    if (0x01 < scancode && scancode < 0x0B) {
+        return scancode - 2 + '1';
+    }
+
+    if (scancode == 0x0B) {
+        return '0';
+    }
+
+    switch (scancode) {
+        case 0x10:
+            return 'Q';
+        case 0x11:
+            return 'W';
+        case 0x12:
+            return 'E';
+        case 0x13:
+            return 'R';
+        case 0x14:
+            return 'T';
+        case 0x15:
+            return 'Y';
+        case 0x16:
+            return 'U';
+        case 0x17:
+            return 'I';
+        case 0x18:
+            return 'O';
+        case 0x19:
+            return 'P';
+        case 0x1a:
+            return '[';
+        case 0x1b:
+            return ']';
+        case 0x1c:
+            return '\n';
+        case 0x1d:
+            return '\b';
+        case 0x1e:
+            return 'A';
+        case 0x1f:
+            return 'S';
+        case 0x20:
+            return 'D';
+        case 0x21:
+            return 'F';
+        case 0x22:
+            return 'G';
+        case 0x23:
+            return 'H';
+        case 0x24:
+            return 'J';
+        case 0x25:
+            return 'K';
+        case 0x26:
+            return 'L';
+        case 0x27:
+            return ';';
+        case 0x28:
+            return '\'';
+        case 0x29:
+            return '`';
+        case 0x2a:
+            is_in_shift = true;
+            break;
+        case 0x2b:
+            return '\\';
+        case 0x2c:
+            return 'Z';
+        case 0x2d:
+            return 'X';
+        case 0x2e:
+            return 'C';
+        case 0x2f:
+            return 'V';
+        case 0x30:
+            return 'B';
+        case 0x31:
+            return 'N';
+        case 0x32:
+            return 'M';
+        case 0x33:
+            return ',';
+        case 0x34:
+            return '.';
+        case 0x35:
+            return '/';
+        case 0x36:
+            is_in_shift = true;
+            break;
+        case 0x39:
+            return ' ';
+        case 0xaa:
+            is_in_shift = false;
+            break;
+        case 0xb6:
+            is_in_shift = false;
+            break;
+    }
+
+    return -1;
+}
+
+char get_last_key_pressed() {
+    char scancode = inb(0x60);
+
+    if (is_in_shift) {
+        return keyboard_char(scancode);
+    }
+
+    return to_lower_char(keyboard_char(scancode));
+}
+
+void print_hex_digit(uint8_t digit) {
+    digit = digit & 0xf;
+    if (digit < 0xA) {
+        terminal_putchar(digit + 0x30);
+    } else {
+        terminal_putchar(digit + 0x41 - 0xA);
+    }
+}
+
+void print_hex_byte(uint8_t byte) {
+    int upper = byte >> 4;
+    int lower = byte & 0x0F;
+
+    print_hex_digit(upper);
+    print_hex_digit(lower);
+}

include/kernel/interrupt.h

@@ -0,0 +1,14 @@
+#include <stdint.h>
+
+struct InterruptDescriptor 
+{
+
+};
+
+struct InterruptDescriptorTable
+{
+    uint16_t  limit;                   /* Size of IDT array - 1 */
+    struct InterruptDescriptor* base;  /* Pointer to IDT array  */
+} __attribute__((packed));
+
+void interrupt_initialize(struct InterruptDescriptorTable IDT);

include/kernel/tty.h

@@ -0,0 +1,6 @@
+#include <stdint.h>
+
+void terminal_writestring(const char* data);
+void terminal_initialize(void);
+void terminal_putchar(char c);
+void terminal_setcolor(uint8_t color);

include/strlib.h

@@ -0,0 +1,8 @@
+#include <stddef.h>
+
+size_t strlen(const char* str);
+
+char to_upper_char(char c);
+char to_lower_char(char c);
+char* to_lower_str(char* str);
+char* to_upper_str(char* str);

kernel/kernel.c

@@ -0,0 +1,27 @@
+#include <kernel/tty.h>
+#include <kernel/interrupt.h>
+#include <debugging.c>
+
+void kernel_main(void) 
+{
+	/* Initialize terminal interface */
+	terminal_initialize();
+
+    terminal_putchar(get_last_key_pressed());
+
+    char current_character = get_last_key_pressed();
+    while (current_character != ',') {
+        char tmp = get_last_key_pressed();
+        if (current_character != -1 && tmp != current_character) {
+            terminal_putchar(current_character);
+        }
+        current_character = tmp;
+    }
+
+    struct InterruptDescriptorTable IDTR = {
+
+    };
+    interrupt_initialize(IDTR);
+
+    terminal_writestring("Hello World!");
+}