diff --git a/ast.go b/ast.go
index 6fb60fc..b4f5cd5 100644
--- a/ast.go
+++ b/ast.go
@@ -10,10 +10,6 @@ type Asm interface {
 	Asm() string
 }
 
-type Operand interface {
-	Asm
-}
-
 type Node interface {
 	node()
 }
@@ -90,15 +86,29 @@ func (i Instruction) OutputRegisters() []reg.Register {
 	return rs
 }
 
+type Section interface {
+	section()
+}
+
 // File represents an assembly file.
 type File struct {
-	Functions []*Function
+	Sections []Section
 }
 
 func NewFile() *File {
 	return &File{}
 }
 
+func (f *File) Functions() []*Function {
+	var fns []*Function
+	for _, s := range f.Sections {
+		if fn, ok := s.(*Function); ok {
+			fns = append(fns, fn)
+		}
+	}
+	return fns
+}
+
 // Function represents an assembly function.
 type Function struct {
 	Name      string
@@ -114,6 +124,8 @@ type Function struct {
 	Allocation reg.Allocation
 }
 
+func (f Function) section() {}
+
 func NewFunction(name string) *Function {
 	return &Function{
 		Name:      name,
diff --git a/build/context.go b/build/context.go
index 4891376..429bd00 100644
--- a/build/context.go
+++ b/build/context.go
@@ -47,7 +47,7 @@ func (c *Context) Package(path string) {
 
 func (c *Context) Function(name string) {
 	c.function = avo.NewFunction(name)
-	c.file.Functions = append(c.file.Functions, c.function)
+	c.file.Sections = append(c.file.Sections, c.function)
 }
 
 func (c *Context) Signature(s *gotypes.Signature) {
diff --git a/pass/pass.go b/pass/pass.go
index b9e2a9f..530bd1e 100644
--- a/pass/pass.go
+++ b/pass/pass.go
@@ -29,7 +29,7 @@ func (p Func) Execute(f *avo.File) error {
 type FunctionPass func(*avo.Function) error
 
 func (p FunctionPass) Execute(f *avo.File) error {
-	for _, fn := range f.Functions {
+	for _, fn := range f.Functions() {
 		if err := p(fn); err != nil {
 			return err
 		}
diff --git a/pass/reg_test.go b/pass/reg_test.go
index 901a2cd..59e2aa1 100644
--- a/pass/reg_test.go
+++ b/pass/reg_test.go
@@ -65,10 +65,11 @@ func ConstructLiveness(t *testing.T, ctx *build.Context) *avo.Function {
 		t.FailNow()
 	}
 
-	if len(f.Functions) != 1 {
+	fns := f.Functions()
+	if len(fns) != 1 {
 		t.Fatalf("expect 1 function")
 	}
-	fn := f.Functions[0]
+	fn := fns[0]
 
 	passes := []func(*avo.Function) error{
 		pass.LabelTarget,
diff --git a/printer/goasm.go b/printer/goasm.go
index bb3f663..3680368 100644
--- a/printer/goasm.go
+++ b/printer/goasm.go
@@ -22,8 +22,13 @@ func NewGoAsm(cfg Config) Printer {
 
 func (p *goasm) Print(f *avo.File) ([]byte, error) {
 	p.header()
-	for _, fn := range f.Functions {
-		p.function(fn)
+	for _, s := range f.Sections {
+		switch s := s.(type) {
+		case *avo.Function:
+			p.function(s)
+		default:
+			panic("unknown section type")
+		}
 	}
 	return p.Result()
 }
diff --git a/printer/stubs.go b/printer/stubs.go
index b1ae7a6..7a25332 100644
--- a/printer/stubs.go
+++ b/printer/stubs.go
@@ -18,7 +18,7 @@ func (s *stubs) Print(f *avo.File) ([]byte, error) {
 	s.Comment(s.cfg.GeneratedWarning())
 	s.NL()
 	s.Printf("package %s\n", s.cfg.Pkg)
-	for _, fn := range f.Functions {
+	for _, fn := range f.Functions() {
 		s.NL()
 		s.Printf("%s\n", fn.Stub())
 	}