diff --git a/cl/_testrt/concat/in.go b/cl/_testrt/concat/in.go
new file mode 100644
index 00000000..5328026a
--- /dev/null
+++ b/cl/_testrt/concat/in.go
@@ -0,0 +1,9 @@
+package main
+
+import (
+	"github.com/goplus/llgo/internal/runtime/c"
+)
+
+func main() {
+	c.Fprintf(c.Stderr, c.Str("Hello %d\n"), 100)
+}
diff --git a/cl/_testrt/concat/out.ll b/cl/_testrt/concat/out.ll
new file mode 100644
index 00000000..ee0cd9d7
--- /dev/null
+++ b/cl/_testrt/concat/out.ll
@@ -0,0 +1,32 @@
+; ModuleID = 'main'
+source_filename = "main"
+
+@"main.init$guard" = global ptr null
+@__stderrp = external global ptr
+@0 = private unnamed_addr constant [10 x i8] c"Hello %d\0A\00", align 1
+
+define void @main.init() {
+_llgo_0:
+  %0 = load i1, ptr @"main.init$guard", align 1
+  br i1 %0, label %_llgo_2, label %_llgo_1
+
+_llgo_1:                                          ; preds = %_llgo_0
+  store i1 true, ptr @"main.init$guard", align 1
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  ret void
+}
+
+define void @main() {
+_llgo_0:
+  call void @"github.com/goplus/llgo/internal/runtime.init"()
+  call void @main.init()
+  %0 = load ptr, ptr @__stderrp, align 8
+  %1 = call i32 (ptr, ptr, ...) @fprintf(ptr %0, ptr @0, i64 100)
+  ret void
+}
+
+declare void @"github.com/goplus/llgo/internal/runtime.init"()
+
+declare i32 @fprintf(ptr, ptr, ...)
diff --git a/cl/_testrt/fprintf/in.go b/cl/_testrt/fprintf/in.go
new file mode 100644
index 00000000..b6821913
--- /dev/null
+++ b/cl/_testrt/fprintf/in.go
@@ -0,0 +1,16 @@
+package main
+
+import "unsafe"
+
+//go:linkname cstr llgo.cstr
+func cstr(string) *int8
+
+//go:linkname stderr __stderrp
+var stderr unsafe.Pointer
+
+//go:linkname fprintf C.fprintf
+func fprintf(fp unsafe.Pointer, format *int8, __llgo_va_list ...any)
+
+func main() {
+	fprintf(stderr, cstr("Hello %d\n"), 100)
+}
diff --git a/cl/_testrt/fprintf/out.ll b/cl/_testrt/fprintf/out.ll
new file mode 100644
index 00000000..03f4adf7
--- /dev/null
+++ b/cl/_testrt/fprintf/out.ll
@@ -0,0 +1,32 @@
+; ModuleID = 'main'
+source_filename = "main"
+
+@"main.init$guard" = global ptr null
+@__stderrp = external global ptr
+@0 = private unnamed_addr constant [10 x i8] c"Hello %d\0A\00", align 1
+
+declare void @fprintf(ptr, ptr, ...)
+
+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 @"github.com/goplus/llgo/internal/runtime.init"()
+  call void @main.init()
+  %0 = load ptr, ptr @__stderrp, align 8
+  call void (ptr, ptr, ...) @fprintf(ptr %0, ptr @0, i64 100)
+  ret void
+}
+
+declare void @"github.com/goplus/llgo/internal/runtime.init"()
diff --git a/cl/builtin_test.go b/cl/builtin_test.go
index a3fa722a..66d0e839 100644
--- a/cl/builtin_test.go
+++ b/cl/builtin_test.go
@@ -122,7 +122,7 @@ func TestErrInitLinkname(t *testing.T) {
 		}
 	}()
 	var ctx context
-	ctx.initLinkname("foo", "//go:linkname Printf printf")
+	ctx.initLinkname("foo", "//go:linkname Printf printf", false)
 }
 
 func TestErrVarOf(t *testing.T) {
diff --git a/cl/compile.go b/cl/compile.go
index c70c59c6..c374a5d5 100644
--- a/cl/compile.go
+++ b/cl/compile.go
@@ -177,7 +177,7 @@ func (p *context) compileMethods(pkg llssa.Package, typ types.Type) {
 // Global variable.
 func (p *context) compileGlobal(pkg llssa.Package, gbl *ssa.Global) {
 	typ := gbl.Type()
-	name := llssa.FullName(gbl.Pkg.Pkg, gbl.Name())
+	name, isDef := p.varName(gbl.Pkg.Pkg, gbl)
 	if ignoreName(name) || checkCgo(gbl.Name()) {
 		return
 	}
@@ -185,7 +185,9 @@ func (p *context) compileGlobal(pkg llssa.Package, gbl *ssa.Global) {
 		log.Println("==> NewVar", name, typ)
 	}
 	g := pkg.NewVar(name, typ)
-	g.Init(p.prog.Null(g.Type))
+	if isDef {
+		g.Init(p.prog.Null(g.Type))
+	}
 }
 
 func (p *context) compileFunc(pkg llssa.Package, pkgTypes *types.Package, f *ssa.Function) {
diff --git a/cl/import.go b/cl/import.go
index a2a380f7..bdfa1050 100644
--- a/cl/import.go
+++ b/cl/import.go
@@ -90,19 +90,14 @@ func (p *context) importPkg(pkg *types.Package, i *pkgInfo) {
 	for _, name := range names {
 		if token.IsExported(name) {
 			obj := scope.Lookup(name)
-			if obj, ok := obj.(*types.Func); ok {
+			switch obj := obj.(type) {
+			case *types.Func:
 				if pos := obj.Pos(); pos != token.NoPos {
-					f := fset.File(pos)
-					if fp := f.Position(pos); fp.Line > 2 {
-						lines, err := contentOf(contents, fp.Filename)
-						if err != nil {
-							panic(err)
-						}
-						if i := fp.Line - 2; i < len(lines) {
-							line := string(lines[i])
-							p.initLinkname(pkgPath, line)
-						}
-					}
+					p.initLinknameByPos(fset, pos, pkgPath, contents, false)
+				}
+			case *types.Var:
+				if pos := obj.Pos(); pos != token.NoPos {
+					p.initLinknameByPos(fset, pos, pkgPath, contents, true)
 				}
 			}
 		}
@@ -112,21 +107,44 @@ func (p *context) importPkg(pkg *types.Package, i *pkgInfo) {
 func (p *context) initFiles(pkgPath string, files []*ast.File) {
 	for _, file := range files {
 		for _, decl := range file.Decls {
-			if decl, ok := decl.(*ast.FuncDecl); ok {
+			switch decl := decl.(type) {
+			case *ast.FuncDecl:
 				if decl.Recv == nil {
-					if doc := decl.Doc; doc != nil {
-						if n := len(doc.List); n > 0 {
-							line := doc.List[n-1].Text
-							p.initLinkname(pkgPath, line)
-						}
-					}
+					p.initLinknameByDoc(decl.Doc, pkgPath, false)
+				}
+			case *ast.GenDecl:
+				if decl.Tok == token.VAR && len(decl.Specs) == 1 {
+					p.initLinknameByDoc(decl.Doc, pkgPath, true)
 				}
 			}
 		}
 	}
 }
 
-func (p *context) initLinkname(pkgPath, line string) {
+func (p *context) initLinknameByDoc(doc *ast.CommentGroup, pkgPath string, isVar bool) {
+	if doc != nil {
+		if n := len(doc.List); n > 0 {
+			line := doc.List[n-1].Text
+			p.initLinkname(pkgPath, line, isVar)
+		}
+	}
+}
+
+func (p *context) initLinknameByPos(fset *token.FileSet, pos token.Pos, pkgPath string, contents contentMap, isVar bool) {
+	f := fset.File(pos)
+	if fp := f.Position(pos); fp.Line > 2 {
+		lines, err := contentOf(contents, fp.Filename)
+		if err != nil {
+			panic(err)
+		}
+		if i := fp.Line - 2; i < len(lines) {
+			line := string(lines[i])
+			p.initLinkname(pkgPath, line, isVar)
+		}
+	}
+}
+
+func (p *context) initLinkname(pkgPath, line string, isVar bool) {
 	const (
 		linkname = "//go:linkname "
 	)
@@ -134,7 +152,7 @@ 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, llgo.cstr
+			if isVar || strings.Contains(link, ".") { // eg. C.printf, C.strlen, llgo.cstr
 				name := pkgPath + "." + text[:idx]
 				p.link[name] = link
 			} else {
@@ -201,6 +219,14 @@ func (p *context) funcName(pkg *types.Package, fn *ssa.Function, ignore bool) (s
 	return name, goFunc
 }
 
+func (p *context) varName(pkg *types.Package, v *ssa.Global) (vName string, isDef bool) {
+	name := llssa.FullName(pkg, v.Name())
+	if v, ok := p.link[name]; ok {
+		return v, false
+	}
+	return name, true
+}
+
 // 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) {
@@ -226,14 +252,14 @@ func (p *context) funcOf(fn *ssa.Function) (ret llssa.Function, ftype int) {
 	return
 }
 
-func (p *context) varOf(v *ssa.Global) llssa.Global {
+func (p *context) varOf(v *ssa.Global) (ret llssa.Global) {
 	pkgTypes := p.ensureLoaded(v.Pkg.Pkg)
 	pkg := p.pkg
-	name := llssa.FullName(pkgTypes, v.Name())
-	if ret := pkg.VarOf(name); ret != nil {
-		return ret
+	name, _ := p.varName(pkgTypes, v)
+	if ret = pkg.VarOf(name); ret == nil {
+		ret = pkg.NewVar(name, v.Type())
 	}
-	return pkg.NewVar(name, v.Type())
+	return
 }
 
 func (p *context) ensureLoaded(pkgTypes *types.Package) *types.Package {
diff --git a/internal/runtime/c/c.go b/internal/runtime/c/c.go
index 79763a1b..05bd8ec6 100644
--- a/internal/runtime/c/c.go
+++ b/internal/runtime/c/c.go
@@ -27,8 +27,18 @@ type (
 	Char    = int8
 	Int     = C.int
 	Pointer = unsafe.Pointer
+	FilePtr = unsafe.Pointer
 )
 
+//go:linkname Stdin __stdinp
+var Stdin FilePtr
+
+//go:linkname Stdout __stdoutp
+var Stdout FilePtr
+
+//go:linkname Stderr __stderrp
+var Stderr FilePtr
+
 //go:linkname Str llgo.cstr
 func Str(string) *Char
 
@@ -52,3 +62,6 @@ func Memcpy(dst, src Pointer, n uintptr) Pointer
 
 //go:linkname Printf C.printf
 func Printf(format *Char, __llgo_va_list ...any) Int
+
+//go:linkname Fprintf C.fprintf
+func Fprintf(fp FilePtr, format *Char, __llgo_va_list ...any) Int