OBJS = \
  entry.o \
  start.o \

# Try to infer the correct TOOLPREFIX if not set
ifndef TOOLPREFIX
TOOLPREFIX := $(shell if riscv64-unknown-elf-objdump -i 2>&1 | grep 'elf64-big' >/dev/null 2>&1; \
	then echo 'riscv64-unknown-elf-'; \
	elif riscv64-elf-objdump -i 2>&1 | grep 'elf64-big' >/dev/null 2>&1; \
	then echo 'riscv64-elf-'; \
	elif riscv64-linux-gnu-objdump -i 2>&1 | grep 'elf64-big' >/dev/null 2>&1; \
	then echo 'riscv64-linux-gnu-'; \
	elif riscv64-unknown-linux-gnu-objdump -i 2>&1 | grep 'elf64-big' >/dev/null 2>&1; \
	then echo 'riscv64-unknown-linux-gnu-'; \
	else echo "***" 1>&2; \
	echo "*** Error: Couldn't find a riscv64 version of GCC/binutils." 1>&2; \
	echo "*** To turn off this error, run 'gmake TOOLPREFIX= ...'." 1>&2; \
	echo "***" 1>&2; exit 1; fi)
endif

QEMU = qemu-system-riscv64
MIN_QEMU_VERSION = 7.2

CC = $(TOOLPREFIX)gcc
AS = $(TOOLPREFIX)gas
LD = $(TOOLPREFIX)ld
OBJCOPY = $(TOOLPREFIX)objcopy
OBJDUMP = $(TOOLPREFIX)objdump

CFLAGS = -Wall -Werror -O -fno-omit-frame-pointer -ggdb -gdwarf-2
CFLAGS += -MD
CFLAGS += -mcmodel=medany
CFLAGS += -ffreestanding
CFLAGS += -fno-common -nostdlib
CFLAGS += -fno-builtin-strncpy -fno-builtin-strncmp -fno-builtin-strlen -fno-builtin-memset
CFLAGS += -fno-builtin-memmove -fno-builtin-memcmp -fno-builtin-log -fno-builtin-bzero
CFLAGS += -fno-builtin-strchr -fno-builtin-exit -fno-builtin-malloc -fno-builtin-putc
CFLAGS += -fno-builtin-free
CFLAGS += -fno-builtin-memcpy -Wno-main
CFLAGS += -fno-builtin-printf -fno-builtin-fprintf -fno-builtin-vprintf
CFLAGS += -I.
CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)

# Disable PIE when possible (for Ubuntu 16.10 toolchain)
ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]no-pie'),)
CFLAGS += -fno-pie -no-pie
endif
ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]nopie'),)
CFLAGS += -fno-pie -nopie
endif

LDFLAGS = -z max-page-size=4096

kernel: $(OBJS) kernel.ld
	$(LD) $(LDFLAGS) -T kernel.ld -o kernel $(OBJS) 

%.o: %.S
	$(CC) -g -c -o $@ $<

clean: 
	rm -f ./*.o ./*.d ./kernel

qemu:
	qemu-system-riscv64 \
		-machine virt \
		-bios none \
		-nographic \
		-serial mon:stdio \
		--no-reboot \
		-kernel ./kernel
