diff --git a/cl/_testcgo/alloca/in.go b/cl/_testcgo/alloca/in.go
new file mode 100644
index 00000000..83452977
--- /dev/null
+++ b/cl/_testcgo/alloca/in.go
@@ -0,0 +1,14 @@
+package main
+
+import (
+	"unsafe"
+
+	"github.com/goplus/llgo/internal/runtime/c"
+)
+
+func main() {
+	s := c.String("Hi\n")
+	s2 := c.Alloca(4)
+	c.Memcpy(s2, unsafe.Pointer(s), 4)
+	c.Printf(c.String("%s"), s)
+}
diff --git a/cl/_testcgo/alloca/out.ll b/cl/_testcgo/alloca/out.ll
new file mode 100644
index 00000000..44cd672d
--- /dev/null
+++ b/cl/_testcgo/alloca/out.ll
@@ -0,0 +1,36 @@
+; ModuleID = 'main'
+source_filename = "main"
+
+%"github.com/goplus/llgo/internal/runtime.String" = type { ptr, i64 }
+
+@"main.init$guard" = global ptr null
+
+define void @main.init() {
+_llgo_0:
+  %0 = load i1, ptr @"main.init$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 ptr @"github.com/goplus/llgo/internal/runtime/c.String"([4 x i8] c"Hi\0A\00")
+  %1 = alloca i8, i64 4, align 1
+  %2 = call ptr @memcpy(ptr %1, ptr %0, i64 4)
+  %3 = call ptr @"github.com/goplus/llgo/internal/runtime/c.String"([3 x i8] c"%s\00")
+  %4 = call i32 (ptr, ...) @printf(ptr %3, ptr %0)
+  ret void
+}
+
+declare ptr @"github.com/goplus/llgo/internal/runtime/c.String"(%"github.com/goplus/llgo/internal/runtime.String")
+
+declare ptr @memcpy(ptr, ptr, i64)
+
+declare i32 @printf(ptr, ...)
diff --git a/cl/_testdata/cstr/in.go b/cl/_testcgo/cstr/in.go
similarity index 100%
rename from cl/_testdata/cstr/in.go
rename to cl/_testcgo/cstr/in.go
diff --git a/cl/_testdata/cstr/out.ll b/cl/_testcgo/cstr/out.ll
similarity index 100%
rename from cl/_testdata/cstr/out.ll
rename to cl/_testcgo/cstr/out.ll
diff --git a/cl/compile.go b/cl/compile.go
index 1c10d564..4782e8b1 100644
--- a/cl/compile.go
+++ b/cl/compile.go
@@ -282,6 +282,14 @@ func cstr(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
 	panic("cstr(<string-literal>): invalid arguments")
 }
 
+func (p *context) alloca(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
+	if len(args) == 1 {
+		n := p.compileValue(b, args[0])
+		return b.Alloca(n)
+	}
+	panic("alloca(size uintptr): 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 {
@@ -319,6 +327,8 @@ func (p *context) compileInstrOrValue(b llssa.Builder, iv instrOrValue, asValue
 				ret = b.Call(fn.Expr, args...)
 			case llgoCstr:
 				ret = cstr(b, call.Args)
+			case llgoAlloca:
+				ret = p.alloca(b, call.Args)
 			default:
 				panic("todo")
 			}
diff --git a/internal/runtime/c/c.go b/internal/runtime/c/c.go
index d3914551..7c11ea9a 100644
--- a/internal/runtime/c/c.go
+++ b/internal/runtime/c/c.go
@@ -16,6 +16,7 @@
 
 package c
 
+import "C"
 import "unsafe"
 
 const (
@@ -38,4 +39,4 @@ func Malloc(size uintptr) unsafe.Pointer
 func Memcpy(dst, src unsafe.Pointer, n uintptr) unsafe.Pointer
 
 //go:linkname Printf C.printf
-func Printf(format *int8, __llgo_va_list ...any)
+func Printf(format *int8, __llgo_va_list ...any) C.int
diff --git a/ssa/expr.go b/ssa/expr.go
index e38961eb..817bb55c 100644
--- a/ssa/expr.go
+++ b/ssa/expr.go
@@ -420,6 +420,28 @@ func (b Builder) Alloc(t *types.Pointer, heap bool) (ret Expr) {
 	return
 }
 
+// Alloca allocates space for n bytes.
+func (b Builder) Alloca(n Expr) (ret Expr) {
+	if debugInstr {
+		log.Printf("Alloca %v\n", n.impl)
+	}
+	prog := b.Prog
+	telem := prog.tyInt8()
+	ret.impl = llvm.CreateArrayAlloca(b.impl, telem, n.impl)
+	ret.Type = &aType{prog.tyVoidPtr(), types.Typ[types.UnsafePointer], vkPtr}
+	return
+}
+
+// ArrayAlloca reserves space for an array of n elements of type telem.
+func (b Builder) ArrayAlloca(telem Type, n Expr) (ret Expr) {
+	if debugInstr {
+		log.Printf("ArrayAlloca %v, %v\n", telem.t, n.impl)
+	}
+	ret.impl = llvm.CreateArrayAlloca(b.impl, telem.ll, n.impl)
+	ret.Type = b.Prog.Pointer(telem)
+	return
+}
+
 // The ChangeType instruction applies to X a value-preserving type
 // change to Type().
 //