diff --git a/cl/_testdata/cstr/in.go b/cl/_testdata/cstr/in.go
new file mode 100644
index 00000000..a8285b4e
--- /dev/null
+++ b/cl/_testdata/cstr/in.go
@@ -0,0 +1,13 @@
+package main
+
+import _ "unsafe"
+
+//go:linkname cstr llgo.cstr
+func cstr(string) *int8
+
+//go:linkname printf C.printf
+func printf(format *int8, __llgo_va_list ...any)
+
+func main() {
+	printf(cstr("Hello, world\n"))
+}
diff --git a/cl/_testdata/cstr/out.ll b/cl/_testdata/cstr/out.ll
new file mode 100644
index 00000000..d5bfe25a
--- /dev/null
+++ b/cl/_testdata/cstr/out.ll
@@ -0,0 +1,26 @@
+; ModuleID = 'main'
+source_filename = "main"
+
+@"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()
+  call void (ptr, ...) @printf([14 x i8] c"Hello, world\0A\00")
+  ret void
+}
+
+declare void @printf(ptr, ...)
diff --git a/cl/builtin_test.go b/cl/builtin_test.go
index c947bdd5..bf83a119 100644
--- a/cl/builtin_test.go
+++ b/cl/builtin_test.go
@@ -25,6 +25,24 @@ import (
 	"golang.org/x/tools/go/ssa"
 )
 
+func TestCStrNoArgs(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fatal("cstr: no error?")
+		}
+	}()
+	cstr(nil, nil)
+}
+
+func TestCStrNonconst(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fatal("cstr: no error?")
+		}
+	}()
+	cstr(nil, []ssa.Value{&ssa.Parameter{}})
+}
+
 func TestPkgNoInit(t *testing.T) {
 	pkg := types.NewPackage("foo", "foo")
 	ctx := &context{
diff --git a/cl/compile.go b/cl/compile.go
index ed182b14..20ba4cdd 100644
--- a/cl/compile.go
+++ b/cl/compile.go
@@ -189,8 +189,9 @@ func (p *context) compileGlobal(pkg llssa.Package, gbl *ssa.Global) {
 
 func (p *context) compileFunc(pkg llssa.Package, pkgTypes *types.Package, f *ssa.Function) {
 	sig := f.Signature
-	name, ok := p.funcName(pkgTypes, f, true)
-	if !ok { // ignored
+	name, ftype := p.funcName(pkgTypes, f, true)
+	switch ftype {
+	case ignoredFunc, llgoInstr: // llgo extended instructions
 		return
 	}
 	if debugInstr {
@@ -269,6 +270,18 @@ func (p *context) checkVArgs(v *ssa.Alloc, t *types.Pointer) bool {
 	return false
 }
 
+func cstr(b llssa.Builder, args []ssa.Value) (ret llssa.Expr) {
+	if len(args) == 1 {
+		if c, ok := args[0].(*ssa.Const); ok {
+			if v := c.Value; v.Kind() == constant.String {
+				sv := constant.StringVal(v)
+				return b.Prog.CStringVal(sv)
+			}
+		}
+	}
+	panic("cstr(<string-literal>): 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 {
@@ -287,8 +300,9 @@ func (p *context) compileInstrOrValue(b llssa.Builder, iv instrOrValue, asValue
 		if debugGoSSA {
 			log.Println(">>> Call", cv, call.Args)
 		}
-		if builtin, ok := cv.(*ssa.Builtin); ok {
-			fn := builtin.Name()
+		switch cv := cv.(type) {
+		case *ssa.Builtin:
+			fn := cv.Name()
 			if fn == "ssa:wrapnilchk" { // TODO(xsw): check nil ptr
 				arg := call.Args[0]
 				ret = p.compileValue(b, arg)
@@ -297,7 +311,18 @@ func (p *context) compileInstrOrValue(b llssa.Builder, iv instrOrValue, asValue
 				args := p.compileValues(b, call.Args, kind)
 				ret = b.BuiltinCall(fn, args...)
 			}
-		} else {
+		case *ssa.Function:
+			fn, ftype := p.funcOf(cv)
+			switch ftype {
+			case goFunc, cFunc:
+				args := p.compileValues(b, call.Args, kind)
+				ret = b.Call(fn.Expr, args...)
+			case llgoCstr:
+				ret = cstr(b, call.Args)
+			default:
+				panic("todo")
+			}
+		default:
 			fn := p.compileValue(b, cv)
 			args := p.compileValues(b, call.Args, kind)
 			ret = b.Call(fn, args...)
@@ -421,7 +446,10 @@ func (p *context) compileValue(b llssa.Builder, v ssa.Value) llssa.Expr {
 			}
 		}
 	case *ssa.Function:
-		fn := p.funcOf(v)
+		fn, ftype := p.funcOf(v)
+		if ftype >= llgoInstrBase {
+			panic("can't use llgo instruction as a value")
+		}
 		return fn.Expr
 	case *ssa.Global:
 		g := p.varOf(v)
diff --git a/cl/import.go b/cl/import.go
index 249402a6..7cf32f7e 100644
--- a/cl/import.go
+++ b/cl/import.go
@@ -134,9 +134,9 @@ func (p *context) initLinkname(pkgPath, line string) {
 		text := strings.TrimSpace(line[len(linkname):])
 		if idx := strings.IndexByte(text, ' '); idx > 0 {
 			link := strings.TrimLeft(text[idx+1:], " ")
-			if strings.Contains(link, ".") { // eg. C.printf, C.strlen
+			if strings.Contains(link, ".") { // eg. C.printf, C.strlen, llgo.cstr
 				name := pkgPath + "." + text[:idx]
-				p.link[name] = link[2:]
+				p.link[name] = link
 			} else {
 				panic(line + ": no specified call convention. eg. //go:linkname Printf C.printf")
 			}
@@ -171,25 +171,56 @@ func checkCgo(fnName string) bool {
 		(fnName[4] == '_' || strings.HasPrefix(fnName[4:], "Check"))
 }
 
-func (p *context) funcName(pkg *types.Package, fn *ssa.Function, ignore bool) (string, bool) {
+const (
+	ignoredFunc = iota
+	goFunc
+	cFunc
+	llgoInstr = -1
+
+	llgoInstrBase   = 0x80
+	llgoCstr        = llgoInstrBase + 1
+	llgoAlloca      = llgoInstrBase + 2
+	llgoUnreachable = llgoInstrBase + 3
+)
+
+func (p *context) funcName(pkg *types.Package, fn *ssa.Function, ignore bool) (string, int) {
 	name := funcName(pkg, fn)
 	if ignore && ignoreName(name) || checkCgo(fn.Name()) {
-		return name, false
+		return name, ignoredFunc
 	}
 	if v, ok := p.link[name]; ok {
-		return v, true
+		if strings.HasPrefix(v, "C.") {
+			return v[2:], cFunc
+		}
+		if strings.HasPrefix(v, "llgo.") {
+			return v[5:], llgoInstr
+		}
+		return v, goFunc
 	}
-	return name, true
+	return name, goFunc
 }
 
-func (p *context) funcOf(fn *ssa.Function) llssa.Function {
+// funcOf returns a function by name and set ftype = goFunc, cFunc, etc.
+// or returns nil and set ftype = llgoCstr, llgoAlloca, llgoUnreachable, etc.
+func (p *context) funcOf(fn *ssa.Function) (ret llssa.Function, ftype int) {
 	pkgTypes := p.ensureLoaded(fn.Pkg.Pkg)
 	pkg := p.pkg
-	name, _ := p.funcName(pkgTypes, fn, false)
-	if ret := pkg.FuncOf(name); ret != nil {
-		return ret
+	name, ftype := p.funcName(pkgTypes, fn, false)
+	if ftype == llgoInstr {
+		switch name {
+		case "cstr":
+			ftype = llgoCstr
+		case "alloca":
+			ftype = llgoAlloca
+		case "unreachable":
+			ftype = llgoUnreachable
+		default:
+			panic("unknown llgo instruction: " + name)
+		}
+	} else if ret = pkg.FuncOf(name); ret == nil {
+		ret = pkg.NewFunc(name, fn.Signature)
 	}
-	return pkg.NewFunc(name, fn.Signature)
+	return
 }
 
 func (p *context) varOf(v *ssa.Global) llssa.Global {
diff --git a/internal/runtime/c/c.go b/internal/runtime/c/c.go
index 451d80b0..d3914551 100644
--- a/internal/runtime/c/c.go
+++ b/internal/runtime/c/c.go
@@ -22,13 +22,13 @@ const (
 	LLGoPackage = "decl"
 )
 
-//go:linkname String llgo.CString
+//go:linkname String llgo.cstr
 func String(string) *int8
 
-//go:linkname Alloca llgo.Alloca
+//go:linkname Alloca llgo.alloca
 func Alloca(size uintptr) unsafe.Pointer
 
-//go:linkname Unreachable llgo.Unreachable
+//go:linkname Unreachable llgo.unreachable
 func Unreachable()
 
 //go:linkname Malloc C.malloc
diff --git a/ssa/expr.go b/ssa/expr.go
index 4ea32c11..777f0da8 100644
--- a/ssa/expr.go
+++ b/ssa/expr.go
@@ -132,7 +132,7 @@ func (p Program) Val(v interface{}) Expr {
 
 // Const returns a constant expression.
 func (b Builder) Const(v constant.Value, typ Type) Expr {
-	prog := b.prog
+	prog := b.Prog
 	if v == nil {
 		return prog.Null(typ)
 	}
@@ -277,7 +277,7 @@ func (b Builder) BinOp(op token.Token, x, y Expr) Expr {
 		}
 		return Expr{llvm.CreateBinOp(b.impl, llop, x.impl, y.impl), x.Type}
 	case isPredOp(op): // op: == != < <= < >=
-		tret := b.prog.Bool()
+		tret := b.Prog.Bool()
 		kind := x.kind
 		switch kind {
 		case vkSigned:
@@ -318,7 +318,7 @@ func (b Builder) Load(ptr Expr) Expr {
 	if debugInstr {
 		log.Printf("Load %v\n", ptr.impl)
 	}
-	telem := b.prog.Elem(ptr.Type)
+	telem := b.Prog.Elem(ptr.Type)
 	return Expr{llvm.CreateLoad(b.impl, telem.ll, ptr.impl), telem}
 }
 
@@ -354,7 +354,7 @@ func (b Builder) FieldAddr(x Expr, idx int) Expr {
 	if debugInstr {
 		log.Printf("FieldAddr %v, %d\n", x.impl, idx)
 	}
-	prog := b.prog
+	prog := b.Prog
 	tstruc := prog.Elem(x.Type)
 	telem := prog.Field(tstruc, idx)
 	pt := prog.Pointer(telem)
@@ -377,7 +377,7 @@ func (b Builder) IndexAddr(x, idx Expr) Expr {
 	if debugInstr {
 		log.Printf("IndexAddr %v, %v\n", x.impl, idx.impl)
 	}
-	prog := b.prog
+	prog := b.Prog
 	telem := prog.Index(x.Type)
 	pt := prog.Pointer(telem)
 	indices := []llvm.Value{idx.impl}
@@ -407,7 +407,7 @@ func (b Builder) Alloc(t *types.Pointer, heap bool) (ret Expr) {
 	if debugInstr {
 		log.Printf("Alloc %v, %v\n", t, heap)
 	}
-	prog := b.prog
+	prog := b.Prog
 	telem := t.Elem()
 	if heap {
 		pkg := b.fn.pkg
@@ -452,7 +452,7 @@ func (b Builder) ChangeType(t Type, x Expr) (ret Expr) {
 	switch typ.(type) {
 	default:
 		ret.impl = b.impl.CreateBitCast(x.impl, t.ll, "bitCast")
-		ret.Type = b.prog.Type(typ)
+		ret.Type = b.Prog.Type(typ)
 		return
 	}
 }
@@ -488,7 +488,7 @@ func (b Builder) ChangeType(t Type, x Expr) (ret Expr) {
 //	t1 = convert []byte <- string (t0)
 func (b Builder) Convert(t Type, x Expr) (ret Expr) {
 	typ := t.t
-	ret.Type = b.prog.Type(typ)
+	ret.Type = b.Prog.Type(typ)
 	switch und := typ.Underlying().(type) {
 	case *types.Basic:
 		kind := und.Kind()
@@ -624,7 +624,7 @@ func (b Builder) TypeAssert(x Expr, assertedTyp Type, commaOk bool) (ret Expr) {
 		default:
 			panic("todo")
 		}
-		typ := b.InlineCall(pkg.rtFunc("Basic"), b.prog.Val(int(kind)))
+		typ := b.InlineCall(pkg.rtFunc("Basic"), b.Prog.Val(int(kind)))
 		return b.InlineCall(fn, x, typ)
 	}
 	panic("todo")
@@ -659,7 +659,7 @@ func (b Builder) Call(fn Expr, args ...Expr) (ret Expr) {
 	}
 	switch t := fn.t.(type) {
 	case *types.Signature:
-		ret.Type = b.prog.retType(t)
+		ret.Type = b.Prog.retType(t)
 	default:
 		panic("todo")
 	}
diff --git a/ssa/stmt_builder.go b/ssa/stmt_builder.go
index a8af71d4..bed0d537 100644
--- a/ssa/stmt_builder.go
+++ b/ssa/stmt_builder.go
@@ -50,7 +50,7 @@ func (p BasicBlock) Index() int {
 type aBuilder struct {
 	impl llvm.Builder
 	fn   Function
-	prog Program
+	Prog Program
 }
 
 // Builder represents a builder for creating instructions in a function.