# Build script for BIOS (legacy) boot.
#
# This compiles our bootloader as a static library,
# and wraps it in a multistage loader.


# Compile bootloader as library
LIB_SRC = ./bootloader/Cargo.toml ./bootloader/Cargo.lock $(shell find ./bootloader/src -type f)
$(BUILD_DIR)/bios.lib: $(LIB_SRC)
	@mkdir -p $(BUILD_DIR)
	env RUSTFLAGS="-C soft-float" \
	cargo rustc \
		--manifest-path="./bootloader/Cargo.toml" \
		-Z build-std=core,alloc \
		-Z build-std-features=compiler-builtins-mem \
		--target "./bootloader/targets/x86-unknown-none.json" \
		--lib \
		--release \
		-- \
		--emit link="$(CURDIR)/$@"

# Link bootloader
BIOS_LD = ./bootloader/linkers/x86-unknown-none.ld
$(BUILD_DIR)/bios.elf: $(BUILD_DIR)/bios.lib $(BIOS_LD)
	ld \
		-m elf_i386 \
		--gc-sections \
		-z max-page-size=0x1000 \
		-T "$(BIOS_LD)" \
		-o "$@" \
		"$<"

	objcopy --only-keep-debug "$@" "$@.sym"
	objcopy --strip-debug "$@"

# Wrap bootloader in three-stage BIOS loader
BIOS_SRC = ./bios
$(BUILD_DIR)/bios.bin: $(wildcard $(BIOS_SRC)/*.asm) $(BUILD_DIR)/bios.elf
	@mkdir -p "$(BUILD_DIR)"
	nasm \
		-f bin \
		-o "$@" \
		-l "$@.lst" \
		-D STAGE3="$(BUILD_DIR)/bios.elf" \
		-i "$(BIOS_SRC)" \
		"$(BIOS_SRC)/main.asm"

# Build demo disk image
$(BUILD_DIR)/bios.img: $(BUILD_DIR)/bios.bin
	rm -f "$@.partial"
	fallocate -l 256MiB "$@.partial"
	parted -s -a minimal "$@.partial" mklabel msdos
	parted -s -a minimal "$@.partial" mkpart primary 2MiB 100%
	dd if="$<" of="$@.partial" bs=1 count=512 conv=notrunc
	dd if="$<" of="$@.partial" bs=512 skip=1 seek=1 conv=notrunc
	mv "$@.partial" "$@"