Build Configuration

This document explains the build configuration options available for SlayerOS. These settings control how the operating system is compiled and linked.

Makefile Options

The main Makefile supports several variables that can be set to customize the build:

Variable	Description	Default
DEBUG	Enable debug build	0 (disabled)
OPT_LEVEL	Optimization level (0-3)	2
WARNINGS	Warning level	all
QEMU_EXTRA	Extra QEMU options	(empty)

Example Usage

# Build with debug symbols and no optimization
make DEBUG=1 OPT_LEVEL=0

# Build with maximum optimization
make OPT_LEVEL=3

# Run with extra QEMU options
make run QEMU_EXTRA="-m 2G -smp 4"

Base Makefile Configuration

The misc/make/base.mk file defines common build settings:

# Compiler selection
CC = x86_64-elf-gcc
CXX = x86_64-elf-g++
LD = x86_64-elf-ld
AS = nasm

# Base flags
CFLAGS = -ffreestanding -O$(OPT_LEVEL) -Wall -Wextra -std=c11
CXXFLAGS = -ffreestanding -O$(OPT_LEVEL) -Wall -Wextra -std=c++17 -fno-exceptions -fno-rtti
LDFLAGS = -nostdlib
ASFLAGS = -f elf64

Compiler Flags

C/C++ Compiler Flags

Flag	Description
-ffreestanding	Compile for a freestanding environment (no standard library)
-O$(OPT_LEVEL)	Optimization level
-Wall -Wextra	Enable comprehensive warnings
-std=c++17	Use C++17 standard
-fno-exceptions	Disable C++ exceptions
-fno-rtti	Disable runtime type information
-g	Include debug symbols (when DEBUG=1)
-D_DEBUG	Define _DEBUG macro (when DEBUG=1)

Assembler Flags

Flag	Description
-f elf64	Output ELF64 format

Linker Flags

Flag	Description
-nostdlib	Don't use standard system startup files or libraries
-T $(LINKER_SCRIPT)	Use the specified linker script

Linker Script

The misc/linkage.ld script controls how the kernel is linked:

SECTIONS
{
    . = KERNEL_VIRT_BASE + KERNEL_PHYS_BASE;
    
    .text : AT(ADDR(.text) - KERNEL_VIRT_BASE)
    {
        *(.text*)
    }
    
    /* Other sections... */
}

Key aspects of the linker script:

• Places the kernel at the correct virtual address
• Organizes sections (.text, .rodata, .data, .bss)
• Sets up the entry point (_start)

ISO Configuration

The ISO build process is configured in the Makefile:

$(ISO_FILE): $(LIMINE_BIN) $(KERNEL_BIN)
	mkdir -p $(ISO_DIR)/boot/limine
	mkdir -p $(ISO_DIR)/EFI/BOOT
	cp $(KERNEL_BIN) $(ISO_DIR)/boot/slay.kernel
	cp -v $(LIMINE_CFG) $(LIMINE_DIR)/limine-bios.sys $(LIMINE_DIR)/limine-bios-cd.bin $(LIMINE_DIR)/limine-uefi-cd.bin $(ISO_DIR)/boot/limine
	cp -v $(LIMINE_DIR)/BOOTX64.EFI $(LIMINE_DIR)/BOOTIA32.EFI $(ISO_DIR)/EFI/BOOT
	xorriso -as mkisofs -b boot/limine/limine-bios-cd.bin \
		-no-emul-boot -boot-load-size 4 -boot-info-table \
		--efi-boot boot/limine/limine-uefi-cd.bin \
		-efi-boot-part --efi-boot-image --protective-msdos-label \
		$(ISO_DIR) -o $@
	$(LIMINE_BIN) bios-install $@

Customizing the Build

Adding New Source Files

When adding new source files, the build system automatically detects them:

SOURCE_FILES = $(shell find $(KERNEL_SRC) -name "*.cxx")
OBJECT_FILES = $(patsubst $(KERNEL_SRC)/%.cxx,$(OBJ_DIR)/%.o,$(SOURCE_FILES))

Adding New Include Directories

To add a new include directory:

INCLUDES += -I/path/to/new/include

Creating Custom Build Targets

You can add custom build targets to the Makefile:

custom_target: $(KERNEL_BIN)
	@echo "Running custom build steps..."
	# Custom commands here

Best Practices

1. Use make clean before changing build options
2. Start with debug builds during development
3. Use optimized builds for performance testing
4. Document any custom build configurations
5. Use version control to track build configuration changes