diff --git a/lib/arm/constants.rb b/lib/arm/constants.rb
index 2ab95c4e..a2e2fa8c 100644
--- a/lib/arm/constants.rb
+++ b/lib/arm/constants.rb
@@ -59,7 +59,12 @@ module Arm
       if name.is_a? Vm::Word
         name = "r#{name.register}"
       end
-      REGISTERS[name.to_s]
+      if name.is_a? Fixnum
+        name = "r#{name}"
+      end
+      r = REGISTERS[name.to_s]
+      raise "no reg #{name}" if r == nil
+      r
     end
 
    def calculate_u8_with_rr(arg)
diff --git a/lib/arm/stack_instruction.rb b/lib/arm/stack_instruction.rb
index 6f0a7195..cd20ab03 100644
--- a/lib/arm/stack_instruction.rb
+++ b/lib/arm/stack_instruction.rb
@@ -58,8 +58,8 @@ module Arm
       regs = @first
       if (regs.is_a?(Array))
         @operand = 0
-        regs.each do |reg |
-          next unless reg
+        regs.each_with_index do |reg , index|
+          raise "nil register in push, index #{index}" if reg == nil
           @operand |= (1 << reg_code(reg))
         end
       else
diff --git a/lib/ast/call_site_expression.rb b/lib/ast/call_site_expression.rb
index 71a19e2f..3bf0d517 100644
--- a/lib/ast/call_site_expression.rb
+++ b/lib/ast/call_site_expression.rb
@@ -11,25 +11,14 @@ module Ast
       function = context.program.get_or_create_function(name)
       raise "Forward declaration not implemented (#{name}) #{inspect}" if function == nil
       call = Vm::CallSite.new( name ,  params  , function)
-      save_locals context , into
+      current_function = context.function
+      current_function.save_locals(context , into) if current_function
       call.load_args into
       call.do_call into
-      restore_locals context , into
+      current_function.restore_locals(context , into) if current_function
       function.return_type
     end
 
-    def save_locals context , into
-      into.instance_eval do 
-        push [:r0,:r1 , :r2 , :r3]
-      end
-    end
-
-    def restore_locals context , into
-      into.instance_eval do 
-        pop [:r0,:r1, :r2 , :r3]
-      end
-    end
-
     def inspect
       self.class.name + ".new(" + name.inspect + ", ["+ 
         args.collect{|m| m.inspect }.join( ",") +"] )"  
diff --git a/lib/vm/function.rb b/lib/vm/function.rb
index 3639c019..5f0c6e06 100644
--- a/lib/vm/function.rb
+++ b/lib/vm/function.rb
@@ -67,6 +67,16 @@ module Vm
       l
     end
 
+    def save_locals context , into
+      save = args.collect{|a| a.register } + @locals.collect{|l| l.register}
+      into.push save
+    end
+
+    def restore_locals context , into
+      restore = args.collect{|a| a.register } + @locals.collect{|l| l.register}
+      into.pop restore
+    end
+
     def new_block name
       block = Block.new(name , self)
       @blocks << block
diff --git a/lib/vm/values.rb b/lib/vm/values.rb
index b019d77c..72a95518 100644
--- a/lib/vm/values.rb
+++ b/lib/vm/values.rb
@@ -59,6 +59,7 @@ module Vm
     end
     def initialize reg
       @register = reg
+      raise inspect if reg == nil
     end
     def length
       4