diff --git a/tools/generator.go b/tools/generator.go
new file mode 100644
index 0000000..02ca954
--- /dev/null
+++ b/tools/generator.go
@@ -0,0 +1,132 @@
+// Copyright 2015 Huan Du. All rights reserved.
+// Use of this source code is governed by a MIT
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type visitor func(node ast.Node) bool
+
+func (v visitor) Visit(node ast.Node) ast.Visitor {
+	if v(node) {
+		return v
+	}
+
+	return nil
+}
+
+// Generator stores progress of package parser.
+type Generator struct {
+	parsedPkgs map[string]bool
+	pkgs       []string
+	context    *Context
+}
+
+func (g *Generator) Parse() {
+	for i := 0; i < len(g.pkgs); i++ {
+		g.parsePkg(g.pkgs[i])
+	}
+}
+
+func (g *Generator) parsePkg(pkg string) {
+	pkgPath := filepath.Join(g.context.GoPackage, pkg)
+	fset := token.NewFileSet()
+	pkgs, err := parser.ParseDir(fset, pkgPath, func(info os.FileInfo) bool {
+		// Filter out all test files.
+		if strings.HasSuffix(info.Name(), "_test.go") {
+			return false
+		}
+
+		return true
+	}, parser.ParseComments)
+
+	if err != nil {
+		panic(err)
+	}
+
+    if _, ok := pkgs["main"]; ok {
+        delete(pkgs, "main")
+    }
+
+	if len(pkgs) != 1 {
+        keys := []string{}
+
+        for k, _ := range pkgs {
+            keys = append(keys, k)
+        }
+
+		panic(fmt.Errorf("there must be only one package name in a package. [pkgs:%v]", strings.Join(keys, ", ")))
+	}
+
+	//goDir := "go" + g.context.Version.Join("_")
+	//output := filepath.Join(g.context.Output, goDir, pkg)
+	//importPath := filepath.Join(g.context.ImportPath, goDir, pkg)
+
+	for _, p := range pkgs {
+		//name := p.Name
+		files := p.Files
+
+		for _, f := range files {
+			decls := f.Decls
+			neededDecls := []ast.Decl{}
+
+			for _, decl := range decls {
+				// Only type decl is needed.
+				if genDecl, ok := decl.(*ast.GenDecl); ok && genDecl.Tok == token.TYPE {
+					neededDecls = append(neededDecls, decl)
+					specs := genDecl.Specs
+
+					for _, spec := range specs {
+						ast.Walk(visitor(func(node ast.Node) bool {
+							if node == nil {
+								return false
+							}
+
+							switch n := node.(type) {
+							case *ast.TypeSpec:
+                                typeName := n.Name.Name
+								logTracef("Find type. [type:%v]", typeName)
+
+                            case *ast.SelectorExpr:
+                                pkgName := n.X.(*ast.Ident).Name
+                                typeName := n.Sel.Name
+
+                                if pkgName == "C" {
+                                    break
+                                }
+
+                                logTracef("Find type. [package-name:%v] [type:%v]", pkgName, typeName)
+							}
+
+							return true
+						}), spec)
+					}
+				}
+			}
+
+			f.Decls = neededDecls
+		}
+	}
+}
+
+// Generate hacked files for packages.
+// Basically, it extracts all types and generates hacked go files.
+//
+// Panic if it encounters any error.
+func GenerateHackedFiles(context *Context, pkgs ...string) {
+	generator := &Generator{
+		parsedPkgs: make(map[string]bool),
+		pkgs:       pkgs,
+		context:    context,
+	}
+	generator.Parse()
+}
diff --git a/tools/log.go b/tools/log.go
new file mode 100644
index 0000000..656a345
--- /dev/null
+++ b/tools/log.go
@@ -0,0 +1,23 @@
+// Copyright 2015 Huan Du. All rights reserved.
+// Use of this source code is governed by a MIT
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func logFatalf(format string, args ...interface{}) {
+	err := fmt.Errorf(format, args...)
+	panic(err)
+}
+
+func logErrorf(format string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, "ERROR: "+format+"\n", args...)
+}
+
+func logTracef(format string, args ...interface{}) {
+	fmt.Printf("TRACE: "+format+"\n", args...)
+}
diff --git a/tools/main.go b/tools/main.go
new file mode 100644
index 0000000..5803c90
--- /dev/null
+++ b/tools/main.go
@@ -0,0 +1,153 @@
+// Copyright 2015 Huan Du. All rights reserved.
+// Use of this source code is governed by a MIT
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"os"
+	"path/filepath"
+	"regexp"
+)
+
+var (
+	flagGoSrc      string
+	flagOutput     string
+	flagImportPath string
+
+	reImportPath = regexp.MustCompile(`^[a-zA-Z][a-zA-Z0-9_]*(\.[a-zA-Z0-9_]+)*(/[a-zA-Z0-9_]+)*$`)
+)
+
+type Context struct {
+	GoSrc      string  // Path to go src root directory.
+	GoPackage  string  // Path to package src in go src directory.
+	Version    Version // Version number.
+	Output     string  // Path to output directory.
+	ImportPath string  // The prefix of import path for output directory.
+}
+
+func init() {
+	flag.StringVar(&flagGoSrc, "go-src", "", "Path to go src directory.")
+	flag.StringVar(&flagOutput, "output", "", "Output path. Default is current directory.")
+	flag.StringVar(&flagImportPath, "import-path", "", "The prefix of import path for output directory.")
+}
+
+func validateGoSrc(context *Context) {
+	if flagGoSrc == "" {
+		logFatalf("Flag -go-src must be set.")
+	}
+
+	src, err := filepath.Abs(flagGoSrc)
+
+	if err != nil {
+		logFatalf("Fail to get absolute path of go src. [go-src:%v]", flagGoSrc)
+	}
+
+	info, err := os.Stat(src)
+
+	if err != nil {
+		logFatalf("Value of flag -go-src must be a valid directory name. [go-src:%v]", flagGoSrc)
+	}
+
+	if !info.Mode().IsDir() {
+		logFatalf("Value of flag -go-src must be a directory. [go-src:%v]", flagGoSrc)
+	}
+
+	srcsrc := filepath.Join(src, "src")
+	info, err = os.Stat(srcsrc)
+
+	if err != nil {
+		logFatalf("Fail to find `src` in go src directory. [go-src:%v]", flagGoSrc)
+	}
+
+	if !info.Mode().IsDir() {
+		logFatalf("The `src` in go src must be a directory. [go-src:%v]", flagGoSrc)
+	}
+
+	versionPath := filepath.Join(src, "VERSION")
+	versionFile, err := os.Open(versionPath)
+
+	if err != nil {
+		logFatalf("Fail to read VERSION in go src directory. Are you sure -go-src points to a valid go src directory? [go-src:%v]", flagGoSrc)
+	}
+
+	defer versionFile.Close()
+	versionBuf := &bytes.Buffer{}
+	versionBuf.ReadFrom(versionFile)
+
+	if versionBuf.Len() == 0 {
+		logFatalf("VERSION in go src is empty. [go-src:%v]", flagGoSrc)
+	}
+
+	version, err := ParseVersion(versionBuf.String())
+
+	if err != nil {
+		logFatalf("VERSION file content is not valid. [go-src:%v] [err:%v] [content:%v]", flagGoSrc, err, versionBuf.String())
+	}
+
+	context.GoSrc = src
+	context.GoPackage = srcsrc
+	context.Version = version
+}
+
+func validateOutput(context *Context) {
+	var err error
+
+	if flagOutput == "" {
+		flagOutput, err = os.Getwd()
+
+		if err != nil {
+			logFatalf("Value of flag -output is empty and current directory is not available.")
+		}
+	}
+
+	output, err := filepath.Abs(flagOutput)
+
+	if err != nil {
+		logFatalf("Fail to get absolute path of output. [output:%v]", flagOutput)
+	}
+
+	info, err := os.Stat(output)
+
+	if err != nil {
+		logFatalf("Value of flag -output must be a valid directory name. [output:%v]", flagOutput)
+	}
+
+	if !info.Mode().IsDir() {
+		logFatalf("Value of flag -output must be a directory. [output:%v]", flagOutput)
+	}
+
+	context.Output = output
+}
+
+func validateImportPath(context *Context) {
+	if flagImportPath == "" {
+		logFatalf("Flag -import-path must be set.")
+	}
+
+	if !reImportPath.MatchString(flagImportPath) {
+		logFatalf("Value of flag -import-path must be a valid import path. [import-path:%v]", flagImportPath)
+	}
+
+	context.ImportPath = flagImportPath
+}
+
+func main() {
+	defer func() {
+		if err := recover(); err != nil {
+			logErrorf("%v", err)
+			os.Exit(1)
+		}
+	}()
+
+	flag.Parse()
+
+	context := &Context{}
+	validateGoSrc(context)
+	validateOutput(context)
+	validateImportPath(context)
+
+	GenerateHackedFiles(context, "runtime")
+}
diff --git a/tools/version.go b/tools/version.go
new file mode 100644
index 0000000..5319034
--- /dev/null
+++ b/tools/version.go
@@ -0,0 +1,73 @@
+// Copyright 2015 Huan Du. All rights reserved.
+// Use of this source code is governed by a MIT
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+var reVersion = regexp.MustCompile(`^go(\d+)(\.(\d+))+`)
+
+type Version []string
+
+// Parse version string like "go1.6.3".
+func ParseVersion(version string) (Version, error) {
+	matches := reVersion.FindStringSubmatch(version)
+
+	if matches == nil {
+		return nil, fmt.Errorf("invalid version format")
+	}
+
+	v := Version{}
+
+	for i := 1; i < len(matches); i += 2 {
+		v = append(v, matches[i])
+	}
+
+	return v, nil
+}
+
+// Return a version string like "go1.6.3".
+func (v Version) String() string {
+	return "go" + v.Join(".")
+}
+
+// Join version numbers with sep.
+func (v Version) Join(sep string) string {
+	return strings.Join(([]string)(v), sep)
+}
+
+// Compare two versions.
+// Return 1 if a > b.
+// Return 0 if two versions equal.
+// Return -1 if a < b.
+func CompareVersions(a, b Version) int {
+	if a == nil && b != nil {
+		return -1
+	}
+
+	if a != nil && b == nil {
+		return 1
+	}
+
+	la := len(a)
+	lb := len(b)
+
+	for i := 0; i < la && i < lb; i++ {
+		if c := strings.Compare(a[i], b[i]); c != 0 {
+			return c
+		}
+	}
+
+	if la > lb {
+		return 1
+	} else if la < lb {
+		return -1
+	} else {
+		return 0
+	}
+}