code

.gitignore

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+CometOS.bin
+CometOS.iso
+build/
+iso/

Makefile

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+# ==============================================================================
+# 1. PROJECT CONFIGURATION
+# ==============================================================================
+BIN_TARGET := CometOS.bin
+TARGET     := CometOS.iso
+BUILD_DIR  := build
+LDSCRIPT   := linker.ld
+
+# Toolchain definitions
+CXX        := g++
+ASM        := as
+LD         := ld
+
+# Compiler and Linker Flags
+ASMFLAGS   := --32
+CXXFLAGS   := -Wall -Wextra -O3 -m32 -fno-use-cxa-atexit -nostdlib -fno-builtin -fno-rtti -fno-exceptions -fno-leading-underscore
+LDFLAGS    := -T $(LDSCRIPT) -melf_i386
+
+# ==============================================================================
+# 2. FILE SEARCH AND COMPONENT SETUP
+# ==============================================================================
+# Find all source files recursively in the current folder and subfolders
+SRCS      := $(wildcard src/**/*.cpp src/**/*.S)
+
+# Strip paths and convert extensions to .o (e.g., "src/main.cpp" -> "main.o")
+RAW_OBJS  := $(patsubst %.cpp,%.o,$(patsubst %.S,%.o,$(notdir $(SRCS))))
+
+# Place all object files into the build directory
+OBJS      := $(addprefix $(BUILD_DIR)/, $(RAW_OBJS))
+
+# Automagically tell Make where to find the original source files
+VPATH     := $(sort $(dir $(SRCS)))
+
+# ==============================================================================
+# 3. BUILD RULES
+# ==============================================================================
+.PHONY: all clean run
+
+# Default rule
+all: $(TARGET)
+
+run: $(TARGET)
+	qemu-system-i386 -cdrom $(TARGET) -m 1024
+
+# Link rule: Combines all objects using the linker script
+$(BIN_TARGET): $(OBJS) $(LDSCRIPT)
+	$(LD) $(OBJS) $(LDFLAGS) -o $@
+	@echo "Build successful: $(BIN_TARGET)"
+
+$(TARGET): $(BIN_TARGET)
+	@mkdir iso/boot/grub -p
+	@cp $< iso/boot/
+	@echo 'set default=0' > iso/boot/grub/grub.cfg
+	@echo 'set timeout=0' >> iso/boot/grub/grub.cfg
+	@echo '' >> iso/boot/grub/grub.cfg
+	@echo 'menuentry "CometOS" {' >> iso/boot/grub/grub.cfg
+	@echo '    multiboot /boot/CometOS.bin' >> iso/boot/grub/grub.cfg
+	@echo '    boot' >> iso/boot/grub/grub.cfg
+	@echo '}' >> iso/boot/grub/grub.cfg
+	grub-mkrescue --output=$@ iso
+
+# Compilation rule for C++ files
+$(BUILD_DIR)/%.o: %.cpp | $(BUILD_DIR)
+	$(CXX) $(CXXFLAGS) -c $< -o $@
+
+# Compilation rule for Assembly files
+$(BUILD_DIR)/%.o: %.S | $(BUILD_DIR)
+	$(ASM) $(ASMFLAGS) -c $< -o $@
+
+# Safely create the build directory if it doesn't exist
+$(BUILD_DIR):
+	mkdir -p $(BUILD_DIR)
+
+# Cleanup rule
+clean:
+	rm -rf $(BUILD_DIR) $(BIN_TARGET) $(TARGET)
+	@echo "Cleaned up build files."

linker.ld

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+ENTRY(loader)
+OUTPUT_FORMAT(elf32-i386)
+OUTPUT_ARCH(i386:i386)
+
+SECTIONS
+{
+    . = 0x0100000;
+
+    .text :
+    {
+        *(.multiboot)
+        *(.text*)
+        *(.rodata)
+    }
+
+    .data :
+    {
+        start_ctors = .;
+        KEEP(*( .init_array ));
+        KEEP(*(SORT_BY_INIT_PRIORITY( .init_array.* )))
+        end_ctors = .;
+
+        *(.data)
+    }
+
+    .bss :
+    {
+        *(.bss)
+    }
+
+    /DISCARD/ : 
+    {
+        *(.fini_array*)
+        *(.comment)
+    }
+}

src/boot/loader.S

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+.set MAGIC, 0x1badb002
+.set FLAGS, (1<<0 | 1<<1)
+.set CHECKSUM, -(MAGIC + FLAGS)
+
+.section .multiboot
+    .long MAGIC
+    .long FLAGS
+    .long CHECKSUM
+
+.section .text
+.extern kernelMain
+.extern callConstructors
+.global loader
+
+loader:
+    mov $kernel_stack, %esp
+
+    call callConstructors
+
+    push %eax
+    push %ebx
+    call kernelMain
+
+_stop: # should never actually reach this but just in case...
+    cli
+    hlt
+    jmp _stop
+
+.section .bss
+.space 2*1024*1024 # Give the kernel 2MB of stack space
+kernel_stack:

src/include/multiboot.h

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+#ifndef MULTIBOOT_H
+#define MULTIBOOT_H
+// The following was copied from https://www.gnu.org/software/grub/manual/multiboot/html_node/multiboot.h.html
+
+/* multiboot.h - the header for Multiboot */
+/* Copyright (C) 1999, 2001  Free Software Foundation, Inc.
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
+
+/* Macros. */
+
+/* The magic number for the Multiboot header. */
+#define MULTIBOOT_HEADER_MAGIC          0x1BADB002
+
+/* The flags for the Multiboot header. */
+#ifdef __ELF__
+# define MULTIBOOT_HEADER_FLAGS         0x00000003
+#else
+# define MULTIBOOT_HEADER_FLAGS         0x00010003
+#endif
+
+/* The magic number passed by a Multiboot-compliant boot loader. */
+#define MULTIBOOT_BOOTLOADER_MAGIC      0x2BADB002
+
+/* The size of our stack (16KB). */
+#define STACK_SIZE                      0x4000
+
+/* C symbol format. HAVE_ASM_USCORE is defined by configure. */
+#ifdef HAVE_ASM_USCORE
+# define EXT_C(sym)                     _ ## sym
+#else
+# define EXT_C(sym)                     sym
+#endif
+
+#ifndef ASM
+/* Do not include here in boot.S. */
+
+/* Types. */
+
+/* The Multiboot header. */
+typedef struct multiboot_header
+{
+ unsigned long magic;
+ unsigned long flags;
+ unsigned long checksum;
+ unsigned long header_addr;
+ unsigned long load_addr;
+ unsigned long load_end_addr;
+ unsigned long bss_end_addr;
+ unsigned long entry_addr;
+} multiboot_header_t;
+
+/* The symbol table for a.out. */
+typedef struct aout_symbol_table
+{
+ unsigned long tabsize;
+ unsigned long strsize;
+ unsigned long addr;
+ unsigned long reserved;
+} aout_symbol_table_t;
+
+/* The section header table for ELF. */
+typedef struct elf_section_header_table
+{
+ unsigned long num;
+ unsigned long size;
+ unsigned long addr;
+ unsigned long shndx;
+} elf_section_header_table_t;
+
+/* The Multiboot information. */
+typedef struct multiboot_info
+{
+ unsigned long flags;
+ unsigned long mem_lower;
+ unsigned long mem_upper;
+ unsigned long boot_device;
+ unsigned long cmdline;
+ unsigned long mods_count;
+ unsigned long mods_addr;
+ union
+ {
+   aout_symbol_table_t aout_sym;
+   elf_section_header_table_t elf_sec;
+ } u;
+ unsigned long mmap_length;
+ unsigned long mmap_addr;
+} multiboot_info_t;
+
+/* The module structure. */
+typedef struct module
+{
+ unsigned long mod_start;
+ unsigned long mod_end;
+ unsigned long string;
+ unsigned long reserved;
+} module_t;
+
+/* The memory map. Be careful that the offset 0 is base_addr_low
+  but no size. */
+typedef struct memory_map
+{
+ unsigned long size;
+ unsigned long base_addr_low;
+ unsigned long base_addr_high;
+ unsigned long length_low;
+ unsigned long length_high;
+ unsigned long type;
+} memory_map_t;
+
+#endif /* ! ASM */
+
+#endif /* MULTIBOOT_H */

src/kernel/kernel.cpp

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+#include "../include/multiboot.h"
+#include "vga_console.h"
+
+typedef void(*constructor)();
+extern "C" constructor start_ctors;
+extern "C" constructor end_ctors;
+extern "C" void callConstructors()
+{
+    for (constructor* i = &start_ctors; i != &end_ctors; i++) {
+        (*i)();
+    }
+}
+
+extern "C" void kernelMain(multiboot_info* multibootInfo, unsigned int magicNumber) {
+    vgaPrint("Hello, world!");
+
+    while (true);
+}

src/kernel/vga_console.cpp

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+#include "vga_console.h"
+
+void vgaPrint(char* string) {
+    static unsigned short* vgaVideoMemory = (unsigned short*)0xb8000;
+
+    for (unsigned int i = 0; string[i] != 0; i++) {
+        /*
+            The high byte in the VGA video memory contains colour info we don't want to overwrite.
+            So, we have to combine the high byte with the char we're writing.
+        */
+        vgaVideoMemory[i] = (vgaVideoMemory[i] & 0xFF00) | string[i];
+    }
+}

src/kernel/vga_console.h

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+#pragma once
+
+void vgaPrint(char* string);