start on a printf call

test/extern_test.rb

@@ -0,0 +1,28 @@
+require_relative 'helper'
+
+#try to call an extern function
+
+class TestExtern < MiniTest::Test
+  # need a code generator, for arm 
+  def setup
+    @generator = Asm::Arm::CodeGenerator.new
+  end
+
+  def test_generate_small
+    @generator.instance_eval {
+      mov r0, 5                #1
+      loop_start = label
+      loop_start.set!
+      subs r0, r0, 1          #2
+      bne loop_start          #3
+    	mov r7, 1               #4
+    	swi 0                   #5  5 instruction x 4 == 20
+    }
+
+    writer = Asm::ObjectWriter.new(Elf::Constants::TARGET_ARM)
+    assembly = @generator.assemble
+    assert_equal 20 , assembly.length 
+    writer.set_text assembly
+    writer.save('small_test.o')    
+  end
+end