diff --git a/cl/_testcgo/allocstr/in.go b/cl/_testcgo/allocstr/in.go
new file mode 100644
index 00000000..41bcdd61
--- /dev/null
+++ b/cl/_testcgo/allocstr/in.go
@@ -0,0 +1,13 @@
+package main
+
+import (
+	"github.com/goplus/llgo/internal/runtime/c"
+)
+
+func hello() string {
+	return "Hello world\n"
+}
+
+func main() {
+	c.Printf(c.AllocaCStr(hello()))
+}
diff --git a/cl/_testcgo/allocstr/out.ll b/cl/_testcgo/allocstr/out.ll
new file mode 100644
index 00000000..ddb4b10e
--- /dev/null
+++ b/cl/_testcgo/allocstr/out.ll
@@ -0,0 +1,43 @@
+; ModuleID = 'main'
+source_filename = "main"
+
+%"github.com/goplus/llgo/internal/runtime.String" = type { ptr, i64 }
+%"github.com/goplus/llgo/internal/runtime.Slice" = type { ptr, i64, i64 }
+
+@"main.init$guard" = global ptr null
+
+define %"github.com/goplus/llgo/internal/runtime.String" @main.hello() {
+_llgo_0:
+  ret [13 x i8] c"Hello world\0A\00"
+}
+
+define void @main.init() {
+_llgo_0:
+  %0 = load i1, ptr @"main.init$guard", align 1
+  br i1 %0, label %_llgo_2, label %_llgo_1
+
+_llgo_1:                                          ; preds = %_llgo_0
+  store i1 true, ptr @"main.init$guard", align 1
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  ret void
+}
+
+define void @main() {
+_llgo_0:
+  call void @main.init()
+  %0 = call %"github.com/goplus/llgo/internal/runtime.String" @main.hello()
+  %1 = call i64 @"github.com/goplus/llgo/internal/runtime.StringLen"(%"github.com/goplus/llgo/internal/runtime.String" %0)
+  %2 = add i64 %1, 1
+  %3 = alloca i8, i64 %2, align 1
+  %4 = call ptr @"github.com/goplus/llgo/internal/runtime.CStrCopy"(ptr %3, %"github.com/goplus/llgo/internal/runtime.String" %0)
+  %5 = call i32 (ptr, ...) @printf(ptr %4)
+  ret void
+}
+
+declare i64 @"github.com/goplus/llgo/internal/runtime.StringLen"(%"github.com/goplus/llgo/internal/runtime.Slice")
+
+declare ptr @"github.com/goplus/llgo/internal/runtime.CStrCopy"(ptr, %"github.com/goplus/llgo/internal/runtime.String")
+
+declare i32 @printf(ptr, ...)
diff --git a/cl/compile.go b/cl/compile.go
index b0a954be..a6e5b88f 100644
--- a/cl/compile.go
+++ b/cl/compile.go
@@ -275,6 +275,7 @@ func (p *context) checkVArgs(v *ssa.Alloc, t *types.Pointer) bool {
 	return false
 }
 
+// func cstr(string) *int8
 func cstr(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
 	if len(args) == 1 {
 		if c, ok := args[0].(*ssa.Const); ok {
@@ -287,6 +288,7 @@ func cstr(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
 	panic("cstr(<string-literal>): invalid arguments")
 }
 
+// func alloca(size uintptr) unsafe.Pointer
 func (p *context) alloca(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
 	if len(args) == 1 {
 		n := p.compileValue(b, args[0])
@@ -295,6 +297,15 @@ func (p *context) alloca(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
 	panic("alloca(size uintptr): invalid arguments")
 }
 
+// func allocaCStr(s string) *int8
+func (p *context) allocaCStr(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
+	if len(args) == 1 {
+		s := p.compileValue(b, args[0])
+		return b.AllocaCStr(s)
+	}
+	panic("allocaCStr(s string): invalid arguments")
+}
+
 func (p *context) compileInstrOrValue(b llssa.Builder, iv instrOrValue, asValue bool) (ret llssa.Expr) {
 	if asValue {
 		if v, ok := p.bvals[iv]; ok {
@@ -334,7 +345,9 @@ func (p *context) compileInstrOrValue(b llssa.Builder, iv instrOrValue, asValue
 				ret = cstr(b, call.Args)
 			case llgoAlloca:
 				ret = p.alloca(b, call.Args)
-			case llgoUnreachable:
+			case llgoAllocaCStr:
+				ret = p.allocaCStr(b, call.Args)
+			case llgoUnreachable: // func unreachable()
 				b.Unreachable()
 			default:
 				panic("todo")
diff --git a/cl/compile_test.go b/cl/compile_test.go
index 62f7bedb..c56355fa 100644
--- a/cl/compile_test.go
+++ b/cl/compile_test.go
@@ -29,7 +29,7 @@ func testCompile(t *testing.T, src, expected string) {
 }
 
 func TestFromTestcgo(t *testing.T) {
-	cltest.FromDir(t, "", "./_testcgo", true)
+	cltest.FromDir(t, "allocstr", "./_testcgo", true)
 }
 
 func TestFromTestdata(t *testing.T) {
diff --git a/cl/import.go b/cl/import.go
index 7cf32f7e..a2a380f7 100644
--- a/cl/import.go
+++ b/cl/import.go
@@ -178,9 +178,10 @@ const (
 	llgoInstr = -1
 
 	llgoInstrBase   = 0x80
+	llgoUnreachable = llgoInstrBase + 0
 	llgoCstr        = llgoInstrBase + 1
 	llgoAlloca      = llgoInstrBase + 2
-	llgoUnreachable = llgoInstrBase + 3
+	llgoAllocaCStr  = llgoInstrBase + 3
 )
 
 func (p *context) funcName(pkg *types.Package, fn *ssa.Function, ignore bool) (string, int) {
@@ -212,6 +213,8 @@ func (p *context) funcOf(fn *ssa.Function) (ret llssa.Function, ftype int) {
 			ftype = llgoCstr
 		case "alloca":
 			ftype = llgoAlloca
+		case "allocaCStr":
+			ftype = llgoAllocaCStr
 		case "unreachable":
 			ftype = llgoUnreachable
 		default:
diff --git a/internal/runtime/c/c.go b/internal/runtime/c/c.go
index 2bbccdd3..8605b157 100644
--- a/internal/runtime/c/c.go
+++ b/internal/runtime/c/c.go
@@ -29,6 +29,9 @@ func Str(string) *int8
 //go:linkname Alloca llgo.alloca
 func Alloca(size uintptr) unsafe.Pointer
 
+//go:linkname AllocaCStr llgo.allocaCStr
+func AllocaCStr(s string) *int8
+
 //go:linkname Unreachable llgo.unreachable
 func Unreachable()
 
diff --git a/internal/runtime/llgo_autogen.ll b/internal/runtime/llgo_autogen.ll
index 22268057..e60e4268 100644
--- a/internal/runtime/llgo_autogen.ll
+++ b/internal/runtime/llgo_autogen.ll
@@ -1,9 +1,9 @@
 ; ModuleID = 'github.com/goplus/llgo/internal/runtime'
 source_filename = "github.com/goplus/llgo/internal/runtime"
 
+%"github.com/goplus/llgo/internal/runtime.String" = type { ptr, i64 }
 %"github.com/goplus/llgo/internal/runtime.iface" = type { ptr, ptr }
 %"github.com/goplus/llgo/internal/runtime.itab" = type { ptr, ptr, i32, [4 x i8], [1 x i64] }
-%"github.com/goplus/llgo/internal/runtime.String" = type { ptr, i64 }
 %"github.com/goplus/llgo/internal/runtime.Slice" = type { ptr, i64, i64 }
 %"github.com/goplus/llgo/internal/abi.Type" = type { i64, i64, i32, i8, i8, i8, i8, ptr, ptr, i32, i32 }
 
@@ -25,6 +25,33 @@ _llgo_0:
   ret ptr %2
 }
 
+define ptr @"github.com/goplus/llgo/internal/runtime.CStrCopy"(ptr %0, %"github.com/goplus/llgo/internal/runtime.String" %1) {
+_llgo_0:
+  %2 = alloca %"github.com/goplus/llgo/internal/runtime.String", align 8
+  store %"github.com/goplus/llgo/internal/runtime.String" %1, ptr %2, align 8
+  %3 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %2, i32 0, i32 1
+  %4 = load i64, ptr %3, align 4
+  %5 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %2, i32 0, i32 0
+  %6 = load ptr, ptr %5, align 8
+  %7 = call ptr @memcpy(ptr %0, ptr %6, i64 %4)
+  %8 = getelementptr inbounds i8, ptr %0, i64 %4
+  store i8 0, ptr %8, align 1
+  ret ptr %0
+}
+
+define ptr @"github.com/goplus/llgo/internal/runtime.CStrDup"(%"github.com/goplus/llgo/internal/runtime.String" %0) {
+_llgo_0:
+  %1 = alloca %"github.com/goplus/llgo/internal/runtime.String", align 8
+  store %"github.com/goplus/llgo/internal/runtime.String" %0, ptr %1, align 8
+  %2 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %1, i32 0, i32 1
+  %3 = load i64, ptr %2, align 4
+  %4 = add i64 %3, 1
+  %5 = call ptr @"github.com/goplus/llgo/internal/runtime.Alloc"(i64 %4)
+  %6 = load %"github.com/goplus/llgo/internal/runtime.String", ptr %1, align 8
+  %7 = call ptr @"github.com/goplus/llgo/internal/runtime.CStrCopy"(ptr %5, %"github.com/goplus/llgo/internal/runtime.String" %6)
+  ret ptr %7
+}
+
 define { i64, i1 } @"github.com/goplus/llgo/internal/runtime.CheckI2Int"(%"github.com/goplus/llgo/internal/runtime.iface" %0, ptr %1) {
 _llgo_0:
   %2 = alloca %"github.com/goplus/llgo/internal/runtime.iface", align 8
@@ -216,6 +243,24 @@ _llgo_0:
   ret i64 %3
 }
 
+define ptr @"github.com/goplus/llgo/internal/runtime.StringData"(%"github.com/goplus/llgo/internal/runtime.String" %0) {
+_llgo_0:
+  %1 = alloca %"github.com/goplus/llgo/internal/runtime.String", align 8
+  store %"github.com/goplus/llgo/internal/runtime.String" %0, ptr %1, align 8
+  %2 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %1, i32 0, i32 0
+  %3 = load ptr, ptr %2, align 8
+  ret ptr %3
+}
+
+define i64 @"github.com/goplus/llgo/internal/runtime.StringLen"(%"github.com/goplus/llgo/internal/runtime.Slice" %0) {
+_llgo_0:
+  %1 = alloca %"github.com/goplus/llgo/internal/runtime.Slice", align 8
+  store %"github.com/goplus/llgo/internal/runtime.Slice" %0, ptr %1, align 8
+  %2 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Slice", ptr %1, i32 0, i32 1
+  %3 = load i64, ptr %2, align 4
+  ret i64 %3
+}
+
 define ptr @"github.com/goplus/llgo/internal/runtime.basicType"(i64 %0) {
 _llgo_0:
   %1 = call ptr @"github.com/goplus/llgo/internal/runtime.Alloc"(i64 16)
@@ -298,4 +343,6 @@ _llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
 
 declare ptr @malloc(i64)
 
+declare ptr @memcpy(ptr, ptr, i64)
+
 declare void @"github.com/goplus/llgo/internal/abi.init"()
diff --git a/internal/runtime/z_string.go b/internal/runtime/z_string.go
index a31f991a..d968d0d8 100644
--- a/internal/runtime/z_string.go
+++ b/internal/runtime/z_string.go
@@ -18,6 +18,8 @@ package runtime
 
 import (
 	"unsafe"
+
+	"github.com/goplus/llgo/internal/runtime/c"
 )
 
 // -----------------------------------------------------------------------------
@@ -38,4 +40,28 @@ func EmptyString() String {
 	return String{nil, 0}
 }
 
+// StringLen returns the length of a string.
+func StringLen(s Slice) int {
+	return s.len
+}
+
+// StringData returns the data pointer of a string.
+func StringData(s String) unsafe.Pointer {
+	return s.data
+}
+
+// CStrCopy copies a Go string to a C string buffer and returns it.
+func CStrCopy(dest unsafe.Pointer, s String) *int8 {
+	n := s.len
+	c.Memcpy(dest, s.data, uintptr(n))
+	arr := (*[1 << 30]int8)(dest)
+	arr[n] = 0
+	return (*int8)(dest)
+}
+
+func CStrDup(s String) *int8 {
+	dest := Alloc(uintptr(s.len + 1))
+	return CStrCopy(dest, s)
+}
+
 // -----------------------------------------------------------------------------
diff --git a/ssa/expr.go b/ssa/expr.go
index 55803500..79651d0f 100644
--- a/ssa/expr.go
+++ b/ssa/expr.go
@@ -537,6 +537,18 @@ func (b Builder) ArrayAlloca(telem Type, n Expr) (ret Expr) {
 }
 */
 
+// AllocaCStr allocates space for copy it from a Go string.
+func (b Builder) AllocaCStr(gostr Expr) (ret Expr) {
+	if debugInstr {
+		log.Printf("AllocaCStr %v\n", gostr.impl)
+	}
+	pkg := b.fn.pkg
+	n := b.InlineCall(pkg.rtFunc("StringLen"), gostr)
+	n1 := b.BinOp(token.ADD, n, b.Prog.Val(1))
+	cstr := b.Alloca(n1)
+	return b.InlineCall(pkg.rtFunc("CStrCopy"), cstr, gostr)
+}
+
 // -----------------------------------------------------------------------------
 
 // The ChangeType instruction applies to X a value-preserving type