Makefile.kernel

# Makefile.kernel: Build a minimal Linux distro with custom Go utilities

ARCH ?= x86_64
KERNEL_VERSION ?= 6.14
KERNEL_URL = "https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-$(KERNEL_VERSION).tar.xz"
KERNEL_ARCHIVE = linux-$(KERNEL_VERSION).tar.xz
KERNEL_DIR = linux-$(KERNEL_VERSION)
ROOTFS_DIR = rootfs
INITRAMFS = initramfs.cpio.gz

# Directories for host system files - Be cautious with these!
BUSYBOX_DIR ?= /usr/bin/
GCC_DIR ?= /usr/bin/
MAKE_DIR ?= /usr/bin/
LIBS_DIR ?= /lib/
H_DIR=/usr/include/

# Set this to the password you want for dosu (required)
DOSU_PASS ?=

ISO_IMAGE = nebula.iso
ISO_DIR = iso

.PHONY: all kernel utils rootfs image clean iso quickreimage

all: kernel utils rootfs image iso
quickreimage: quickclean rootfs image iso

# Download and extract the Linux kernel
$(KERNEL_ARCHIVE):
	wget -c $(KERNEL_URL)

$(KERNEL_DIR): $(KERNEL_ARCHIVE)
	tar -xf "$<"

# Helper function to get the correct kernel image name based on ARCH
KERNEL_IMAGE_NAME = $(if $(filter x86_64,$(ARCH)),bzImage,Image)

kernel: $(KERNEL_DIR)
	@echo "--- Compiling the kernel for $(ARCH) ---"
	# Always start with a clean state to prevent stale files from causing issues
	@cd "$(KERNEL_DIR)" && make ARCH=$(ARCH) mrproper
	
	# Create a default configuration if it doesn't exist
	@cd "$(KERNEL_DIR)" && make ARCH=$(ARCH) defconfig
	
	# Compile the kernel using GCC 12 and required flags
	cd "$(KERNEL_DIR)" && make ARCH=$(ARCH) $(KERNEL_IMAGE_NAME) modules -j$(shell nproc) \
		CC=gcc \
		KBUILD_CFLAGS="-std=gnu11 -Wno-unterminated-string-initialization -Wno-error=attributes"

# Build all Go utilities using the main Makefile
utils:
	@echo "--- Building Go utilities ---"
	$(MAKE) -f Makefile

# Create a minimal root filesystem and copy utilities
rootfs: utils
	@echo "--- Creating root filesystem ---"
	rm -rf $(ROOTFS_DIR)
	mkdir -p $(ROOTFS_DIR)/bin $(ROOTFS_DIR)/etc $(ROOTFS_DIR)/root $(ROOTFS_DIR)/dev $(ROOTFS_DIR)/proc $(ROOTFS_DIR)/sys
	
	# Create necessary device nodes
	mknod -m 622 $(ROOTFS_DIR)/dev/console c 5 1
	mknod -m 666 $(ROOTFS_DIR)/dev/null c 1 3
	
	# Copy all built binaries from bin/ to rootfs/bin
	find bin -type f -executable -exec cp {} $(ROOTFS_DIR)/bin/ \;
	
	# Set up dosu password and permissions
	@if [ -z "$(DOSU_PASS)" ]; then \
		echo "ERROR: DOSU_PASS must be set (e.g. make rootfs DOSU_PASS=yourpassword)"; \
		exit 1; \
	fi
	echo -n "$(DOSU_PASS)" | sha256sum | awk '{print $$1}' > $(ROOTFS_DIR)/etc/dosu_passwd
	chmod 600 $(ROOTFS_DIR)/etc/dosu_passwd
	chown 0:0 $(ROOTFS_DIR)/etc/dosu_passwd
	
	# Set dosu binary permissions
	chown 0:0 $(ROOTFS_DIR)/bin/dosu || true
	chmod u+s $(ROOTFS_DIR)/bin/dosu || true
	
	# Prep emergency shell using built BusyBox
	cp "$(BUSYBOX_DIR)/busybox" "$(ROOTFS_DIR)/bin/sh"
	cp "$(GCC_DIR)/gcc" "$(ROOTFS_DIR)/bin/gcc"
	cp "$(MAKE_DIR)/make" "$(ROOTFS_DIR)/bin/make"
	mkdir -p "$(ROOTFS_DIR)/$(LIBS_DIR)"
	cp -r $(LIBS_DIR)/* "$(ROOTFS_DIR)/$(LIBS_DIR)"
	mkdir -p "$(ROOTFS_DIR)/$(H_DIR)"
	cp -r $(H_DIR)/* "$(ROOTFS_DIR)/$(H_DIR)"
	
	chmod +x $(ROOTFS_DIR)/bin/sh
	chmod +x $(ROOTFS_DIR)/bin/gcc
	chmod +x $(ROOTFS_DIR)/bin/make
	
	# Create init script
	echo '#!/bin/sh' > $(ROOTFS_DIR)/init
	echo '# Basic init script for gutils Linux' >>$(ROOTFS_DIR)/init
	echo 'mount -t proc none /proc' >>$(ROOTFS_DIR)/init
	echo 'mount -t sysfs none /sys' >>$(ROOTFS_DIR)/init
	echo 'mount -t devtmpfs none /dev' >>$(ROOTFS_DIR)/init
	echo 'export PATH=/bin:/sbin:/usr/bin:/usr/sbin' >> $(ROOTFS_DIR)/init
	echo 'export HOME=/root' >>$(ROOTFS_DIR)/init
	echo 'export TERM=linux' >>$(ROOTFS_DIR)/init
	echo 'echo "Booting gutils Linux..."' >>$(ROOTFS_DIR)/init
	echo 'echo "Starting highway shell..."' >>$(ROOTFS_DIR)/init
	echo 'exec /bin/highway || exec /bin/sh' >>$(ROOTFS_DIR)/init
	chmod +x $(ROOTFS_DIR)/init

# Create an initramfs image
image: rootfs
	@echo "--- Creating initramfs image ---"
	cd $(ROOTFS_DIR) && find . | cpio -o -H newc | gzip > ../$(INITRAMFS)

clean:
	@echo "--- Cleaning project ---"
	# Use make mrproper for a thorough cleanup of the kernel source tree
	-cd "$(KERNEL_DIR)" && make mrproper
	rm -rf $(KERNEL_DIR) $(KERNEL_ARCHIVE) $(ROOTFS_DIR) bin $(INITRAMFS) $(ISO_DIR) $(ISO_IMAGE)

quickclean:
	@echo "--- Quick cleaning rootfs and images ---"
	rm -rf $(ROOTFS_DIR) $(INITRAMFS) $(ISO_DIR) $(ISO_IMAGE)

iso: image kernel
	@echo "--- Creating bootable ISO image ---"
	rm -rf $(ISO_DIR)
	mkdir -p $(ISO_DIR)/boot/grub $(ISO_DIR)/EFI/BOOT
	
	# Copy kernel and initramfs to ISO directory
	cp "$(KERNEL_DIR)/arch/$(ARCH)/boot/$(KERNEL_IMAGE_NAME)" "$(ISO_DIR)/boot/vmlinuz"
	cp "$(INITRAMFS)" "$(ISO_DIR)/boot/initramfs.cpio.gz"
	
	# Create GRUB config
	printf 'set default=0\nset timeout=5\n\nmenuentry "NebuLa" { \n\tlinux /boot/vmlinuz root=/dev/ram0 rw \n\tinitrd /boot/initramfs.cpio.gz \n}\n' > $(ISO_DIR)/boot/grub/grub.cfg
	
	# Copy the GRUB EFI bootloader
	cp /usr/lib/grub/$(ARCH)-efi/grubx64.efi $(ISO_DIR)/EFI/BOOT/
	
	# Create a dummy grub.cfg for the EFI bootloader
	cp $(ISO_DIR)/boot/grub/grub.cfg $(ISO_DIR)/EFI/BOOT/
	
	# Create the ISO with grub-mkrescue
	grub-mkrescue -o $(ISO_IMAGE) $(ISO_DIR) --xorriso=/usr/bin/xorriso --install-modules="linux normal efi_gop"