add step to create a UEFI-bootable image

Rsconscript

@@ -1,5 +1,24 @@
+configure do
+  check_command "mformat"
+end
+
 build do
+  class Image < Builder
+    def run(options)
+      unless @cache.up_to_date?(@target, nil, @sources, @env)
+        print_run_message("Image <target>#{@target}<reset>", nil)
+        system(*%W[dd if=/dev/zero of=#{@target} bs=1k count=1440])
+        system(*%W[mformat -i #{@target} -f 1440 ::])
+        system(*%W[mmd -i #{@target} ::/EFI])
+        system(*%W[mmd -i #{@target} ::/EFI/BOOT])
+        system(*%W[mcopy -i #{@target} #{@sources.first} ::/EFI/BOOT])
+        @cache.register_build(@target, nil, @sources, @env)
+      end
+      true
+    end
+  end
   Environment.new do |env|
+    env.add_builder(Image)
     env["CC"] = "x86_64-w64-mingw32-gcc"
     env["CPPPATH"] += %w[/usr/include/efi /usr/include/efi/x86_64]
     env["CFLAGS"] += %w[-ffreestanding]
@@ -7,5 +26,6 @@ build do
     env["LIBS"] += %w[gcc]
     env["sources"] = glob("*.c")
     env.Program("^/BOOTX64.EFI", "${sources}")
+    env.Image("^/efi-loader.img", "^/BOOTX64.EFI")
   end
 end