Add stages and a rakefile

Rakefile

@@ -0,0 +1,41 @@
+require 'open3'
+require 'rake/clean'
+
+CLOBBER.include 'build'
+
+CROSS_GCC = '../riscv32-ilp32d--glibc/bin/riscv32-linux-gcc'
+SYSROOT = '../riscv32-ilp32d--glibc/riscv32-buildroot-linux-gnu/sysroot'
+QEMU = 'qemu-riscv32'
+
+desc 'Final stage'
+task default: 'build/stage2'
+
+directory 'build'
+
+desc 'Initial stage'
+file 'build/stage1' => ['boot/echo-boot.s', 'boot/common-boot.s', 'build'] do |t|
+  assembler = t.prerequisites.filter { |prerequisite| prerequisite.end_with? '.s' }
+
+  sh CROSS_GCC, '-nostdlib', '-o', t.name, *assembler
+end
+
+file 'build/stage2.s' => ['build/stage1', 'boot/stage2.elna'] do |t|
+  assembler, exe = t.prerequisites.partition { |prerequisite| prerequisite.end_with? '.elna' }
+  arguments = [QEMU, '-L', SYSROOT, *exe]
+
+  puts(arguments * ' ')
+  puts
+  Open3.popen2(*arguments) do |qemu_in, qemu_out|
+    qemu_in.write File.read(*assembler)
+    qemu_in.close
+
+    File.open t.name, 'w' do |output|
+      IO.copy_stream qemu_out, output
+    end
+    qemu_out.close
+  end
+end
+
+file 'build/stage2' => ['build/stage2.s', 'boot/common-boot.s'] do |t|
+  sh CROSS_GCC, '-nostdlib', '-o', t.name, *t.prerequisites
+end