Add a Makefile

It provides `make` (builds the kernel), `make iso` (builds kernel+ISO), and `make run` (builds kernel+ISO and starts qemu). All assembly files from the arch subdirectories are compiled and linked. It also provides basic multi-architecture support through e.g. `make arch=mips iso`.

Makefile

@@ -0,0 +1,50 @@
+# Copyright 2015 Philipp Oppermann
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+arch ?= x86_64
+kernel := build/kernel-$(arch).bin
+iso := build/os-$(arch).iso
+
+linker_script := src/arch/$(arch)/linker.ld
+grub_cfg := src/arch/$(arch)/grub.cfg
+assembly_source_files := $(wildcard src/arch/$(arch)/*.asm)
+assembly_object_files := $(patsubst src/arch/$(arch)/%.asm, \
+	build/arch/$(arch)/%.o, $(assembly_source_files))
+
+.PHONY: all clean run iso
+
+all: $(kernel)
+
+clean:
+	@rm -r build
+
+run: $(iso)
+	@qemu-system-x86_64 -hda $(iso)
+
+iso: $(iso)
+
+$(iso): $(kernel)
+	@mkdir -p build/isofiles/boot/grub
+	@cp $(kernel) build/isofiles/boot/
+	@cp $(grub_cfg) build/isofiles/boot/grub
+	@grub-mkrescue -o $(iso) build/isofiles 2> /dev/null
+	@rm -r build/isofiles
+
+$(kernel): $(assembly_object_files) $(linker_script)
+	@ld -n -T $(linker_script) -o $(kernel) $(assembly_object_files)
+
+# compile assembly files
+build/arch/$(arch)/%.o: src/arch/$(arch)/%.asm
+	@mkdir -p $(shell dirname $@)
+	@nasm -felf64 $< -o $@