diff --git a/examples/ch2-xx/hello/.gitignore b/examples/ch2-xx/hello/.gitignore
new file mode 100644
index 0000000..f9cccb9
--- /dev/null
+++ b/examples/ch2-xx/hello/.gitignore
@@ -0,0 +1 @@
+!/_obj
diff --git a/examples/ch2-xx/hello/Makefile b/examples/ch2-xx/hello/Makefile
new file mode 100644
index 0000000..d09055d
--- /dev/null
+++ b/examples/ch2-xx/hello/Makefile
@@ -0,0 +1,2 @@
+default:
+	go tool cgo hello.go
diff --git a/examples/ch2-xx/hello/_obj/_cgo_export.c b/examples/ch2-xx/hello/_obj/_cgo_export.c
new file mode 100644
index 0000000..955b3be
--- /dev/null
+++ b/examples/ch2-xx/hello/_obj/_cgo_export.c
@@ -0,0 +1,58 @@
+/* Created by cgo - DO NOT EDIT. */
+#include <stdlib.h>
+#include "_cgo_export.h"
+
+extern void crosscall2(void (*fn)(void *, int, __SIZE_TYPE__), void *, int, __SIZE_TYPE__);
+extern __SIZE_TYPE__ _cgo_wait_runtime_init_done();
+extern void _cgo_release_context(__SIZE_TYPE__);
+
+extern char* _cgo_topofstack(void);
+#define CGO_NO_SANITIZE_THREAD
+#define _cgo_tsan_acquire()
+#define _cgo_tsan_release()
+
+extern void _cgoexp_16f1900c27a8_helloInt(void *, int, __SIZE_TYPE__);
+
+CGO_NO_SANITIZE_THREAD
+void helloInt(GoInt p0)
+{
+	__SIZE_TYPE__ _cgo_ctxt = _cgo_wait_runtime_init_done();
+	struct {
+		GoInt p0;
+	} __attribute__((__packed__)) a;
+	a.p0 = p0;
+	_cgo_tsan_release();
+	crosscall2(_cgoexp_16f1900c27a8_helloInt, &a, 8, _cgo_ctxt);
+	_cgo_tsan_acquire();
+	_cgo_release_context(_cgo_ctxt);
+}
+extern void _cgoexp_16f1900c27a8_helloString(void *, int, __SIZE_TYPE__);
+
+CGO_NO_SANITIZE_THREAD
+void helloString(GoString p0)
+{
+	__SIZE_TYPE__ _cgo_ctxt = _cgo_wait_runtime_init_done();
+	struct {
+		GoString p0;
+	} __attribute__((__packed__)) a;
+	a.p0 = p0;
+	_cgo_tsan_release();
+	crosscall2(_cgoexp_16f1900c27a8_helloString, &a, 16, _cgo_ctxt);
+	_cgo_tsan_acquire();
+	_cgo_release_context(_cgo_ctxt);
+}
+extern void _cgoexp_16f1900c27a8_helloSlice(void *, int, __SIZE_TYPE__);
+
+CGO_NO_SANITIZE_THREAD
+void helloSlice(GoSlice p0)
+{
+	__SIZE_TYPE__ _cgo_ctxt = _cgo_wait_runtime_init_done();
+	struct {
+		GoSlice p0;
+	} __attribute__((__packed__)) a;
+	a.p0 = p0;
+	_cgo_tsan_release();
+	crosscall2(_cgoexp_16f1900c27a8_helloSlice, &a, 24, _cgo_ctxt);
+	_cgo_tsan_acquire();
+	_cgo_release_context(_cgo_ctxt);
+}
diff --git a/examples/ch2-xx/hello/_obj/_cgo_export.h b/examples/ch2-xx/hello/_obj/_cgo_export.h
new file mode 100644
index 0000000..b6332d9
--- /dev/null
+++ b/examples/ch2-xx/hello/_obj/_cgo_export.h
@@ -0,0 +1,64 @@
+/* Created by "go tool cgo" - DO NOT EDIT. */
+
+/* package main */
+
+/* Start of preamble from import "C" comments.  */
+
+
+
+
+/* End of preamble from import "C" comments.  */
+
+
+/* Start of boilerplate cgo prologue.  */
+#line 1 "cgo-gcc-export-header-prolog"
+
+#ifndef GO_CGO_PROLOGUE_H
+#define GO_CGO_PROLOGUE_H
+
+typedef signed char GoInt8;
+typedef unsigned char GoUint8;
+typedef short GoInt16;
+typedef unsigned short GoUint16;
+typedef int GoInt32;
+typedef unsigned int GoUint32;
+typedef long long GoInt64;
+typedef unsigned long long GoUint64;
+typedef GoInt64 GoInt;
+typedef GoUint64 GoUint;
+typedef __SIZE_TYPE__ GoUintptr;
+typedef float GoFloat32;
+typedef double GoFloat64;
+typedef float _Complex GoComplex64;
+typedef double _Complex GoComplex128;
+
+/*
+  static assertion to make sure the file is being used on architecture
+  at least with matching size of GoInt.
+*/
+typedef char _check_for_64_bit_pointer_matching_GoInt[sizeof(void*)==64/8 ? 1:-1];
+
+typedef struct { const char *p; GoInt n; } GoString;
+typedef void *GoMap;
+typedef void *GoChan;
+typedef struct { void *t; void *v; } GoInterface;
+typedef struct { void *data; GoInt len; GoInt cap; } GoSlice;
+
+#endif
+
+/* End of boilerplate cgo prologue.  */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+extern void helloInt(GoInt p0);
+
+extern void helloString(GoString p0);
+
+extern void helloSlice(GoSlice p0);
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/examples/ch2-xx/hello/_obj/_cgo_flags b/examples/ch2-xx/hello/_obj/_cgo_flags
new file mode 100644
index 0000000..3c91b0f
--- /dev/null
+++ b/examples/ch2-xx/hello/_obj/_cgo_flags
@@ -0,0 +1 @@
+_CGO_CFLAGS=
diff --git a/examples/ch2-xx/hello/_obj/_cgo_gotypes.go b/examples/ch2-xx/hello/_obj/_cgo_gotypes.go
new file mode 100644
index 0000000..64ed703
--- /dev/null
+++ b/examples/ch2-xx/hello/_obj/_cgo_gotypes.go
@@ -0,0 +1,70 @@
+// Created by cgo - DO NOT EDIT
+
+package main
+
+import "unsafe"
+
+import _ "runtime/cgo"
+
+import "syscall"
+
+var _ syscall.Errno
+func _Cgo_ptr(ptr unsafe.Pointer) unsafe.Pointer { return ptr }
+
+//go:linkname _Cgo_always_false runtime.cgoAlwaysFalse
+var _Cgo_always_false bool
+//go:linkname _Cgo_use runtime.cgoUse
+func _Cgo_use(interface{})
+type _Ctype_void [0]byte
+
+//go:linkname _cgo_runtime_cgocall runtime.cgocall
+func _cgo_runtime_cgocall(unsafe.Pointer, uintptr) int32
+
+//go:linkname _cgo_runtime_cgocallback runtime.cgocallback
+func _cgo_runtime_cgocallback(unsafe.Pointer, unsafe.Pointer, uintptr, uintptr)
+
+//go:linkname _cgoCheckPointer runtime.cgoCheckPointer
+func _cgoCheckPointer(interface{}, ...interface{})
+
+//go:linkname _cgoCheckResult runtime.cgoCheckResult
+func _cgoCheckResult(interface{})
+
+//go:cgo_export_dynamic helloInt
+//go:linkname _cgoexp_16f1900c27a8_helloInt _cgoexp_16f1900c27a8_helloInt
+//go:cgo_export_static _cgoexp_16f1900c27a8_helloInt
+//go:nosplit
+//go:norace
+func _cgoexp_16f1900c27a8_helloInt(a unsafe.Pointer, n int32, ctxt uintptr) {
+	fn := _cgoexpwrap_16f1900c27a8_helloInt
+	_cgo_runtime_cgocallback(**(**unsafe.Pointer)(unsafe.Pointer(&fn)), a, uintptr(n), ctxt);
+}
+
+func _cgoexpwrap_16f1900c27a8_helloInt(p0 int) {
+	helloInt(p0)
+}
+//go:cgo_export_dynamic helloString
+//go:linkname _cgoexp_16f1900c27a8_helloString _cgoexp_16f1900c27a8_helloString
+//go:cgo_export_static _cgoexp_16f1900c27a8_helloString
+//go:nosplit
+//go:norace
+func _cgoexp_16f1900c27a8_helloString(a unsafe.Pointer, n int32, ctxt uintptr) {
+	fn := _cgoexpwrap_16f1900c27a8_helloString
+	_cgo_runtime_cgocallback(**(**unsafe.Pointer)(unsafe.Pointer(&fn)), a, uintptr(n), ctxt);
+}
+
+func _cgoexpwrap_16f1900c27a8_helloString(p0 string) {
+	helloString(p0)
+}
+//go:cgo_export_dynamic helloSlice
+//go:linkname _cgoexp_16f1900c27a8_helloSlice _cgoexp_16f1900c27a8_helloSlice
+//go:cgo_export_static _cgoexp_16f1900c27a8_helloSlice
+//go:nosplit
+//go:norace
+func _cgoexp_16f1900c27a8_helloSlice(a unsafe.Pointer, n int32, ctxt uintptr) {
+	fn := _cgoexpwrap_16f1900c27a8_helloSlice
+	_cgo_runtime_cgocallback(**(**unsafe.Pointer)(unsafe.Pointer(&fn)), a, uintptr(n), ctxt);
+}
+
+func _cgoexpwrap_16f1900c27a8_helloSlice(p0 []byte) {
+	helloSlice(p0)
+}
diff --git a/examples/ch2-xx/hello/_obj/_cgo_main.c b/examples/ch2-xx/hello/_obj/_cgo_main.c
new file mode 100644
index 0000000..f0ae18c
--- /dev/null
+++ b/examples/ch2-xx/hello/_obj/_cgo_main.c
@@ -0,0 +1,12 @@
+int main() { return 0; }
+void crosscall2(void(*fn)(void*, int, __SIZE_TYPE__), void *a, int c, __SIZE_TYPE__ ctxt) { }
+__SIZE_TYPE__ _cgo_wait_runtime_init_done() { return 0; }
+void _cgo_release_context(__SIZE_TYPE__ ctxt) { }
+char* _cgo_topofstack(void) { return (char*)0; }
+void _cgo_allocate(void *a, int c) { }
+void _cgo_panic(void *a, int c) { }
+void _cgo_reginit(void) { }
+#line 1 "cgo-generated-wrappers"
+int _cgoexp_16f1900c27a8_helloInt;
+int _cgoexp_16f1900c27a8_helloString;
+int _cgoexp_16f1900c27a8_helloSlice;
diff --git a/examples/ch2-xx/hello/_obj/hello.cgo1.go b/examples/ch2-xx/hello/_obj/hello.cgo1.go
new file mode 100644
index 0000000..d70d524
--- /dev/null
+++ b/examples/ch2-xx/hello/_obj/hello.cgo1.go
@@ -0,0 +1,24 @@
+// Created by cgo - DO NOT EDIT
+
+//line /Users/chai/go/src/github.com/chai2010/advanced-go-programming-book/examples/ch2-xx/hello/hello.go:1
+package main
+
+//line /Users/chai/go/src/github.com/chai2010/advanced-go-programming-book/examples/ch2-xx/hello/hello.go:5
+func main() {
+	helloString("hello")
+}
+
+//line /Users/chai/go/src/github.com/chai2010/advanced-go-programming-book/examples/ch2-xx/hello/hello.go:10
+func helloInt(s int) {
+	println(s)
+}
+
+//line /Users/chai/go/src/github.com/chai2010/advanced-go-programming-book/examples/ch2-xx/hello/hello.go:15
+func helloString(s string) {
+	println(s)
+}
+
+//line /Users/chai/go/src/github.com/chai2010/advanced-go-programming-book/examples/ch2-xx/hello/hello.go:20
+func helloSlice(s []byte) {
+	println(string(s))
+}
diff --git a/examples/ch2-xx/hello/_obj/hello.cgo2.c b/examples/ch2-xx/hello/_obj/hello.cgo2.c
new file mode 100644
index 0000000..0196be1
--- /dev/null
+++ b/examples/ch2-xx/hello/_obj/hello.cgo2.c
@@ -0,0 +1,31 @@
+
+
+#line 1 "cgo-gcc-prolog"
+/*
+  If x and y are not equal, the type will be invalid
+  (have a negative array count) and an inscrutable error will come
+  out of the compiler and hopefully mention "name".
+*/
+#define __cgo_compile_assert_eq(x, y, name) typedef char name[(x-y)*(x-y)*-2+1];
+
+/* Check at compile time that the sizes we use match our expectations. */
+#define __cgo_size_assert(t, n) __cgo_compile_assert_eq(sizeof(t), n, _cgo_sizeof_##t##_is_not_##n)
+
+__cgo_size_assert(char, 1)
+__cgo_size_assert(short, 2)
+__cgo_size_assert(int, 4)
+typedef long long __cgo_long_long;
+__cgo_size_assert(__cgo_long_long, 8)
+__cgo_size_assert(float, 4)
+__cgo_size_assert(double, 8)
+
+extern char* _cgo_topofstack(void);
+
+#include <errno.h>
+#include <string.h>
+
+
+#define CGO_NO_SANITIZE_THREAD
+#define _cgo_tsan_acquire()
+#define _cgo_tsan_release()
+
diff --git a/examples/ch2-xx/hello/hello.go b/examples/ch2-xx/hello/hello.go
new file mode 100644
index 0000000..0c93fcf
--- /dev/null
+++ b/examples/ch2-xx/hello/hello.go
@@ -0,0 +1,22 @@
+package main
+
+import "C"
+
+func main() {
+	helloString("hello") // _GoString_
+}
+
+//export helloInt
+func helloInt(s int) {
+	println(s)
+}
+
+//export helloString
+func helloString(s string) {
+	println(s)
+}
+
+//export helloSlice
+func helloSlice(s []byte) {
+	println(string(s))
+}