Initial commit.

.gitignore

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+# ignore binary files
+*.bin
+*.o
+*.iso
+
+# ignore build files
+isodir

Makefile

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+# General options
+TARGET=i686
+ARCH=$(shell echo $(TARGET) | sed s/i.86/x86/)
+# Assembly options
+AS=i686-elf-as
+AFLAGS=
+# C options
+CC=i686-elf-gcc
+CFLAGS?=-O0 -g
+CFLAGS:=$(CFLAGS) -std=gnu99 -ffreestanding -Wall -Wextra -Isrc/
+# Linker options
+LDFLAGS?=-O0
+LDFLAGS:=$(LDFLAGS) -ffreestanding -nostdlib
+LIBS=-lgcc
+
+# Binary variables
+OBJS=src/kernel/arch/$(ARCH)/boot.o src/kernel/kernel.o src/kernel/arch/$(ARCH)/tty.o
+
+untrue.bin: $(OBJS)
+	$(CC) -T src/kernel/arch/$(ARCH)/linker.ld -o $@ $(LDFLAGS) $^ $(LIBS)
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+%.o: %.s
+	$(AS) $(AFLAGS) $< -o $@
+
+.PHONY: all build-iso clean clean-all
+all: untrue.bin
+
+build-iso: untrue.iso
+
+clean:
+	rm -f $(OBJS)
+	rm -rf isodir
+
+clean-all: clean
+	rm -f *.iso *.bin
+
+untrue.iso: untrue.bin
+	mkdir -p isodir/boot/grub/
+	cp configs/grub.cfg isodir/boot/grub/
+	cp $< isodir/boot/
+	grub-mkrescue -o $@ isodir

configs/grub.cfg

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+menuentry "UntrueOS" {
+	multiboot /boot/untrue.bin
+}

src/kernel/arch/x86/boot.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   # the multiboot `FLAG' field
+.set MAGIC,      0x1BADB002        # 'magic number' letting the boot loader know we're here
+.set CHECKSUM ,  -(MAGIC + FLAGS)  # checksum of the above to prove we're multiboot
+
+/*
+ * Declare the multiboot header marking this program as a kernel. The bootloader
+ * will search for these values in the first 8 KiB of the kernel file aligned at
+ * 32-bit boundaries (4 bytes). We put the signature in its own section to force
+ * it within the first 8 KiB of the kernel file.
+ */
+.section .multiboot
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
+
+/*
+ * Create a 16 byte aligned stack with 16 KiB of size. We create labels at the
+ * bottom and top of the stack.
+ */
+.section .bss
+.align 16
+stack_bottom:
+.skip 16384  # 16 KiB
+stack_top:
+
+/*
+ * Create the GDT
+ */
+.section .data
+gdt_start:
+gdt_null:
+.long 0x0
+.long 0x0
+
+gdt_kcode:
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b10011010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+gdt_kdata:
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b10010010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+gdt_ucode:
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b11111010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+gdt_udata:
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b11110010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+gdt_end:
+
+gdtr:
+.word (gdt_end - gdt_start - 1)
+.long gdt_start
+
+/*
+ * The linker script specifies the `_start' label as the entry point to the kernel
+ * and the bootloader will jump to this position. That is, this is where the kernel
+ * starts.
+ */
+.section .text
+.global _start
+.type _start, @function
+_start:
+	# set the position of `%esp' to the top of the stack
+	mov $stack_top, %esp
+
+	# GDT, paging, and other features
+flush_gdt:
+	cli
+	lgdt (gdtr)
+	movw $0x10, %ax
+	movw %ax, %ds
+	movw %ax, %es
+	movw %ax, %fs
+	movw %ax, %gs
+	movw %ax, %ss
+	ljmp $0x08, $flush_end
+flush_end:
+
+boot_kernel:
+	# enter high-level kernel (C)
+	call kernel_main
+
+	# put computer into infinite loop
+	cli                    # disable interrupts by clearing the interrupt flag in `eflags'
+end_loop:
+	hlt                    # wait for next interrupt
+	jmp end_loop           # jump to the `hlt' instruction if it ever leaves it
+
+.size _start, . - _start

src/kernel/arch/x86/linker.ld

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+ENTRY(_start)
+
+SECTIONS
+{
+	/* put sections at 1 MiB as is conventional for kernels */
+	. = 1M;
+
+	/* place multiboot header early for boot loader and then `.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)
+	}
+}

src/kernel/arch/x86/tty.c

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+#include <stddef.h>
+#include <stdint.h>
+
+#include <kernel/tty.h>
+
+#include "vga.h"
+
+#define VGA_WIDTH 80
+#define VGA_HEIGHT 25
+#define VGA_MEMORY 0xb8000
+
+
+static size_t tty_row;
+static size_t tty_col;
+static uint8_t tty_color;
+static uint16_t *tty_buffer;
+
+void tty_init() {
+	tty_row = 0;
+	tty_col = 0;
+	tty_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
+	tty_buffer = (uint16_t*) VGA_MEMORY;
+	for(size_t y = 0; y < VGA_HEIGHT; ++y)
+	{
+		for(size_t x = 0; x < VGA_WIDTH; ++x)
+		{
+			const size_t index = GET_INDEX(x, y);
+			tty_buffer[index] = vga_entry(' ', tty_color);
+		}
+	}
+}
+
+void tty_setcolor(uint8_t color) {
+	tty_color = color;
+}
+
+void tty_putentryat(unsigned char c, uint8_t color, size_t x, size_t y) {
+	const size_t index = GET_INDEX(x, y);
+	tty_buffer[index] = vga_entry(c, color);
+}
+
+void tty_scroll_down() {
+	// clear first line
+	for(size_t x = 0; x < VGA_WIDTH; ++x)
+	{
+		const size_t i = GET_INDEX(x, 0);
+		tty_buffer[i] = vga_entry(' ', tty_color);
+	}
+
+	// scroll text
+	for(size_t y = 1; y < VGA_HEIGHT; ++y)
+	{
+		for(size_t x = 0; x < VGA_WIDTH; ++x)
+		{
+			const size_t srci = GET_INDEX(x, y);
+			const size_t dsti = GET_INDEX(x, y - 1);
+			tty_buffer[dsti] = tty_buffer[srci];
+		}
+	}
+}
+
+void tty_putchar(unsigned char c) {
+	tty_putentryat(c, tty_color, tty_col, tty_row);
+	if(++tty_col == VGA_WIDTH)
+	{
+		tty_col = 0;
+		if(tty_row + 1 == VGA_HEIGHT)
+			tty_scroll_down();
+		else
+			tty_row++;
+	}
+}
+
+void tty_write(const char *data, size_t size) {
+	for(size_t i = 0; i < size; ++i)
+		tty_putchar(data[i]);
+}
+
+void tty_write_s(const char *str) {
+	size_t len = 0;
+	while(str[len])
+		len++;
+	tty_write(str, len);
+}

src/kernel/arch/x86/vga.h

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+#pragma once
+
+#include <stdint.h>
+#define GET_INDEX(x, y)  y * VGA_WIDTH + x
+
+enum vga_color {
+	VGA_COLOR_BLACK             = 0x0,
+	VGA_COLOR_BLUE              = 0x1,
+	VGA_COLOR_GREEN             = 0x2,
+	VGA_COLOR_CYAN              = 0x3,
+	VGA_COLOR_RED               = 0x4,
+	VGA_COLOR_MAGENTA           = 0x5,
+	VGA_COLOR_BROWN             = 0x6,
+	VGA_COLOR_LIGHT_GREY        = 0x7,
+	VGA_COLOR_DARK_GREY         = 0x8,
+	VGA_COLOR_LIGHT_BLUE        = 0x9,
+	VGA_COLOR_LIGHT_GREEN       = 0xA,
+	VGA_COLOR_LIGHT_CYAN        = 0xB,
+	VGA_COLOR_LIGHT_RED         = 0xC,
+	VGA_COLOR_LIGHT_MAGENTA     = 0xD,
+	VGA_COLOR_LIGHT_BROWN       = 0xE,
+	VGA_COLOR_WHITE             = 0xF,
+};
+
+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 c, uint8_t color) {
+	return (uint16_t) c | (uint16_t) color << 8;
+}

src/kernel/kernel.c

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+#include <kernel/tty.h>
+
+void kernel_main() {
+	tty_init();
+	tty_write_s("Hello from the kernel!");
+}

src/kernel/ports.h

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+#pragma once
+
+static inline void outb(uint16_t port, uint8_t data) {
+	__asm__("outb %%al, %%dx" : : "a" (data), "d" (port));
+}
+
+static inline void outw(uint16_t port, uint16_t data) {
+	__asm__("outw %%ax, %%dx" : : "a" (data), "d" (port));
+}
+
+static inline uint8_t inb(uint16_t port) {
+	uint8_t res;
+	__asm__("inb %%dx, %%al" : "=a" (res) : "d" (port));
+	return res;
+}
+
+static inline uint16_t inw(uint16_t port) {
+	uint16_t res;
+	__asm__("inw %%dx, %%ax" : "=a" (res) : "d" (port));
+	return res;
+}

src/kernel/system.h

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+static inline void abort() {
+	while(1);
+}

src/kernel/tty.h

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+#pragma once
+
+#include <stddef.h>
+
+void tty_init();
+void tty_putchar(unsigned char c);
+void tty_write(const char *data, size_t size);
+void tty_write_s(const char *str);