add ostep homeworks

related_info/ostep/ostep11-threadintro/looping-race-nolock.s

@@ -0,0 +1,15 @@
+# assumes %bx has loop count in it
+
+.main
+.top	
+# critical section
+mov 2000, %ax  # get the value at the address
+add $1, %ax    # increment it
+mov %ax, 2000  # store it back
+
+# see if we're still looping
+sub  $1, %bx
+test $0, %bx
+jgt .top	
+
+halt