diff --git a/c/pthread/sync/_pthd/pthd.c b/c/pthread/sync/_pthd/pthd.c
new file mode 100644
index 00000000..453bbe4d
--- /dev/null
+++ b/c/pthread/sync/_pthd/pthd.c
@@ -0,0 +1,6 @@
+#include <pthread.h>
+
+pthread_once_t llgoSyncOnceInitVal() {
+    pthread_once_t initVal = PTHREAD_ONCE_INIT;
+    return initVal;
+}
diff --git a/c/pthread/sync/llgo_autogen.lla b/c/pthread/sync/llgo_autogen.lla
new file mode 100644
index 00000000..e1b6d0eb
Binary files /dev/null and b/c/pthread/sync/llgo_autogen.lla differ
diff --git a/c/pthread/sync/sync.go b/c/pthread/sync/sync.go
new file mode 100644
index 00000000..2ddf2ee9
--- /dev/null
+++ b/c/pthread/sync/sync.go
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sync
+
+// #include <pthread.h>
+import "C"
+
+import (
+	_ "unsafe"
+
+	"github.com/goplus/llgo/c"
+)
+
+const (
+	LLGoFiles   = "_pthd/pthd.c"
+	LLGoPackage = "link"
+)
+
+type Once C.pthread_once_t
+
+//go:linkname onceInitVal C.llgoSyncOnceInitVal
+func onceInitVal() Once
+
+var OnceInit = onceInitVal()
+
+// llgo:link (*Once).Do C.pthread_once
+func (o *Once) Do(f func()) c.Int { return 0 }
diff --git a/cl/_testlibc/once/in.go b/cl/_testlibc/once/in.go
new file mode 100644
index 00000000..e7247122
--- /dev/null
+++ b/cl/_testlibc/once/in.go
@@ -0,0 +1,19 @@
+package main
+
+import (
+	"github.com/goplus/llgo/c"
+	"github.com/goplus/llgo/c/pthread/sync"
+)
+
+var once sync.Once = sync.OnceInit
+
+func f() {
+	once.Do(func() {
+		c.Printf(c.Str("Do once\n"))
+	})
+}
+
+func main() {
+	f()
+	f()
+}
diff --git a/cl/_testlibc/once/out.ll b/cl/_testlibc/once/out.ll
new file mode 100644
index 00000000..05ffcbc4
--- /dev/null
+++ b/cl/_testlibc/once/out.ll
@@ -0,0 +1,55 @@
+; ModuleID = 'main'
+source_filename = "main"
+
+%"github.com/goplus/llgo/c/pthread/sync.Once" = type { i64, [8 x i8] }
+
+@"main.init$guard" = global i1 false, align 1
+@main.once = global %"github.com/goplus/llgo/c/pthread/sync.Once" zeroinitializer, align 8
+@"github.com/goplus/llgo/c/pthread/sync.OnceInit" = external global %"github.com/goplus/llgo/c/pthread/sync.Once", align 8
+@__llgo_argc = global i32 0, align 4
+@__llgo_argv = global ptr null, align 8
+@0 = private unnamed_addr constant [9 x i8] c"Do once\0A\00", align 1
+
+define void @main.f() {
+_llgo_0:
+  %0 = call i32 @pthread_once(ptr @main.once, ptr @"main.f$1")
+  ret void
+}
+
+define void @main.init() {
+_llgo_0:
+  %0 = load i1, ptr @"main.init$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
+  %1 = load %"github.com/goplus/llgo/c/pthread/sync.Once", ptr @"github.com/goplus/llgo/c/pthread/sync.OnceInit", align 4
+  store %"github.com/goplus/llgo/c/pthread/sync.Once" %1, ptr @main.once, align 4
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  ret void
+}
+
+define i32 @main(i32 %0, ptr %1) {
+_llgo_0:
+  store i32 %0, ptr @__llgo_argc, align 4
+  store ptr %1, ptr @__llgo_argv, align 8
+  call void @"github.com/goplus/llgo/internal/runtime.init"()
+  call void @main.init()
+  call void @main.f()
+  call void @main.f()
+  ret i32 0
+}
+
+declare i32 @pthread_once(ptr, ptr)
+
+define void @"main.f$1"() {
+_llgo_0:
+  %0 = call i32 (ptr, ...) @printf(ptr @0)
+  ret void
+}
+
+declare void @"github.com/goplus/llgo/internal/runtime.init"()
+
+declare i32 @printf(ptr, ...)
diff --git a/internal/build/build.go b/internal/build/build.go
index d115f7c6..e1ed2f73 100644
--- a/internal/build/build.go
+++ b/internal/build/build.go
@@ -597,7 +597,7 @@ func llgoPkgLinkFiles(pkg *packages.Package, llFile string, procFile func(linkFi
 
 // files = "file1; file2; ..."
 func clFiles(files string, pkg *packages.Package, procFile func(linkFile string), verbose bool) {
-	dir := filepath.Dir(pkg.CompiledGoFiles[0])
+	dir := filepath.Dir(pkg.GoFiles[0])
 	expFile := pkg.ExportFile
 	for _, file := range strings.Split(files, ";") {
 		cFile := filepath.Join(dir, strings.TrimSpace(file))