Boot to C in 64-bit long mode

Makefile

@@ -0,0 +1,60 @@
+# Nadir Kernel build.
+#
+# Toolchain: host gcc/binutils (x86-64) with strict freestanding flags.
+# A dedicated x86-64-elf cross-compiler is the planned next step; until
+# then CC/LD/OBJCOPY stay overridable so it drops in without edits.
+# Requires GNU coreutils (truncate -s %N).
+
+NASM    ?= nasm
+CC      ?= gcc
+LD      ?= ld
+OBJCOPY ?= objcopy
+QEMU    ?= qemu-system-x86_64
+
+ARCH_DIR := kernel/arch/x86_64
+BUILD    := build
+IMG      := nadir.img
+
+CFLAGS := -std=c17 -ffreestanding -nostdlib -fno-builtin \
+          -m64 -mno-red-zone -mno-mmx -mno-sse \
+          -fno-pic -fno-pie -fno-stack-protector \
+          -Wall -Wextra -Werror -O2 -Iinclude
+
+OBJS := $(BUILD)/entry.o $(BUILD)/kmain.o $(BUILD)/console.o
+
+all: $(IMG)
+
+$(BUILD):
+	mkdir -p $(BUILD)
+
+$(BUILD)/entry.o: $(ARCH_DIR)/entry.asm | $(BUILD)
+	$(NASM) -f elf64 $< -o $@
+
+$(BUILD)/kmain.o: kernel/core/kmain.c include/console.h | $(BUILD)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+$(BUILD)/console.o: $(ARCH_DIR)/console.c include/console.h | $(BUILD)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+$(BUILD)/kernel.elf: $(OBJS) $(ARCH_DIR)/link.ld
+	$(LD) -m elf_x86_64 -T $(ARCH_DIR)/link.ld -o $@ $(OBJS)
+
+$(BUILD)/kernel.bin: $(BUILD)/kernel.elf
+	$(OBJCOPY) -O binary $< $@
+	truncate -s %512 $@
+
+# The boot sector needs the kernel size up front, so it builds last.
+$(BUILD)/boot.bin: $(ARCH_DIR)/boot.asm $(BUILD)/kernel.bin | $(BUILD)
+	SECTORS=$$(( ($$(stat -c%s $(BUILD)/kernel.bin) + 511) / 512 )); \
+	$(NASM) -f bin -D KERNEL_SECTORS=$$SECTORS $< -o $@
+
+$(IMG): $(BUILD)/boot.bin $(BUILD)/kernel.bin
+	cat $^ > $@
+
+run: $(IMG)
+	$(QEMU) -fda $(IMG)
+
+clean:
+	rm -rf $(BUILD) $(IMG)
+
+.PHONY: all run clean