init

.idea/.gitignore

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+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

.idea/misc.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="MakefileSettings">
+    <option name="linkedExternalProjectsSettings">
+      <MakefileProjectSettings>
+        <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="modules">
+          <set>
+            <option value="$PROJECT_DIR$" />
+          </set>
+        </option>
+        <option name="version" value="2" />
+      </MakefileProjectSettings>
+    </option>
+  </component>
+  <component name="MakefileWorkspace" PROJECT_DIR="$PROJECT_DIR$" />
+</project>

Makefile

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+# Compiler and flags
+ASM = i686-elf-as
+CPP = i686-elf-g++
+LD = i686-elf-gcc
+CFLAGS = -ffreestanding -O2 -Wall -Wextra -fno-exceptions -fno-rtti
+LDFLAGS = -T linker.ld -ffreestanding -O2 -nostdlib -lgcc
+
+# Directories
+SRC_DIR = src
+BUILD_DIR = build
+
+# Source files
+SRC_FILES := $(wildcard $(SRC_DIR)/*.cpp) $(wildcard $(SRC_DIR)/*/*.cpp)
+ASM_FILES := $(wildcard $(SRC_DIR)/*.s) $(wildcard $(SRC_DIR)/*/*.s)
+
+# Object files
+OBJ_FILES := $(patsubst $(SRC_DIR)/%.cpp,$(BUILD_DIR)/%.o,$(SRC_FILES))
+OBJ_FILES += $(patsubst $(SRC_DIR)/%.s,$(BUILD_DIR)/%.o,$(ASM_FILES))
+
+# Output binary
+OUTPUT = myos.bin
+
+# Build target
+all: $(BUILD_DIR) $(OUTPUT)
+
+# Create the build directory if it doesn't exist
+$(BUILD_DIR):
+	mkdir -p $(BUILD_DIR)
+
+# Compile C++ source files
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.cpp
+	$(CPP) -c $< -o $@ $(CFLAGS)
+
+# Assemble assembly source files
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.s
+	$(ASM) $< -o $@
+
+# Link the object files to create the final binary
+$(OUTPUT): $(OBJ_FILES)
+	$(LD) $(LDFLAGS) -o $@ $^
+
+# Run QEMU after a successful build
+run: all
+	qemu-system-i386 -kernel $(OUTPUT)
+
+# Clean build files
+clean:
+	rm -rf $(BUILD_DIR) $(OUTPUT)
+
+.PHONY: all run clean

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
+{
+	/* Begin putting sections at 1 MiB, a conventional place for kernels to be
+	   loaded at by the bootloader. */
+	. = 1M;
+ 
+	/* First put the multiboot header, as it is required to be put very early
+	   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. */
+}

src/IO/GDT.cpp

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+//
+// Created by Mika on 06.09.23.
+//
+
+#include "GDT.h"

src/IO/GDT.h

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+//
+// Created by Mika on 06.09.23.
+//
+
+#ifndef OS_GDT_H
+#define OS_GDT_H
+
+
+class GDT {
+};
+
+
+#endif //OS_GDT_H

src/IO/IO.h

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+//
+// Created by Mika on 06.09.23.
+//
+
+#ifndef OS_IO_H
+#define OS_IO_H
+#include <stdint.h>
+
+class IO {
+public:
+    static inline void outb(uint16_t port, uint8_t val)
+    {
+        asm volatile ( "outb %0, %1" : : "a"(val), "Nd"(port) :"memory");
+        /* There's an outb %al, $imm8  encoding, for compile-time constant port numbers that fit in 8b.  (N constraint).
+         * Wider immediate constants would be truncated at assemble-time (e.g. "i" constraint).
+         * The  outb  %al, %dx  encoding is the only option for all other cases.
+         * %1 expands to %dx because  port  is a uint16_t.  %w1 could be used if we had the port number a wider C type */
+    }
+
+    static inline uint8_t inb(uint16_t port)
+    {
+        uint8_t ret;
+        asm volatile ( "inb %1, %0"
+                : "=a"(ret)
+                : "Nd"(port)
+                : "memory");
+        return ret;
+    }
+};
+
+
+#endif //OS_IO_H

src/IO/Interrupts.cpp

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+//
+// Created by Mika on 06.09.23.
+//
+
+#include "Interrupts.h"
+
+void Interrupts::disable() {
+    asm("cli");
+}
+
+void Interrupts::enable() {
+    asm("sti");
+}

src/IO/Interrupts.h

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+//
+// Created by Mika on 06.09.23.
+//
+
+#ifndef OS_INTERRUPTS_H
+#define OS_INTERRUPTS_H
+
+
+class Interrupts {
+public:
+    void disable();
+    void enable();
+};
+
+
+#endif //OS_INTERRUPTS_H

src/Terminal.cpp

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+//
+// Created by Mika on 06.09.23.
+//
+
+#include "Terminal.h"
+
+void Terminal::init() {
+    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_HEIGHT; 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;
+}
+
+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);
+}
+
+void Terminal::putChar(char c) {
+    if(c == '\n') {
+        if(++terminal_row == VGA_HEIGHT)
+            terminal_row = 0;
+        terminal_column = 0;
+        return;
+    }
+
+    Terminal::putEntryAt(c, terminal_color, terminal_column, terminal_row);
+    if(++terminal_column == VGA_WIDTH) {
+        terminal_column = 0;
+
+        if(++terminal_row == VGA_HEIGHT)
+            terminal_row = 0;
+    }
+}
+
+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, utils.strlen(data));
+}

src/Terminal.h

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+//
+// Created by Mika on 06.09.23.
+//
+
+#ifndef OS_TERMINAL_H
+#define OS_TERMINAL_H
+#include "Utils.h"
+
+class Terminal {
+public:
+    void init();
+    void putEntryAt(char c, uint8_t color, size_t x, size_t y);
+    void putChar(char c);
+    void setColor(uint8_t color);
+    void write(const char *data, size_t size);
+    void writeString(const char *data);
+
+    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 void kerror(const char* str, Terminal* terminal) {
+        terminal->setColor(vga_entry_color(VGA_COLOR_RED, VGA_COLOR_BLACK));
+        terminal->writeString("[ERROR] ");
+        terminal->writeString(str);
+        terminal->writeString("\n\n");
+        terminal->setColor(vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK));
+    }
+
+private:
+    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;
+    static Utils utils;
+
+    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;
+    }
+};
+
+
+#endif //OS_TERMINAL_H

src/Utils.h

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+//
+// Created by Mika on 06.09.23.
+//
+
+#ifndef OS_UTILS_H
+#define OS_UTILS_H
+#include <stddef.h>
+#include <stdint.h>
+#include "Terminal.h"
+
+class Utils {
+public:
+    static size_t strlen(const char* str) {
+        size_t len = 0;
+        while(str[len])
+            len++;
+
+        return len;
+    }
+};
+
+
+#endif //OS_UTILS_H

src/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  /* 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 c_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

src/main.cpp

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+#include "Terminal.h"
+
+void kernel_main() {
+    Terminal terminal{};
+
+    terminal.init();
+    terminal.writeString("Hallo Jana\n");
+    Terminal::kerror("Testing kerror", &terminal);
+    terminal.writeString("Hallo Arad\n");
+}
+
+extern "C" [[noreturn]] void c_kernel_main() {
+    kernel_main();
+    while(true) {}
+}