diff --git a/cl/_testcgo/strlen/out.ll b/cl/_testcgo/strlen/out.ll
index 706fadc8..130d120f 100644
--- a/cl/_testcgo/strlen/out.ll
+++ b/cl/_testcgo/strlen/out.ll
@@ -1,7 +1,6 @@
 ; ModuleID = 'main'
 source_filename = "main"
 
-@main._Cgo_always_false = global ptr null
 @main.format = global ptr null
 @"main.init$guard" = global ptr null
 
diff --git a/cl/builtin_test.go b/cl/builtin_test.go
new file mode 100644
index 00000000..8daa7207
--- /dev/null
+++ b/cl/builtin_test.go
@@ -0,0 +1,27 @@
+/*
+ * 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 cl
+
+import (
+	"testing"
+)
+
+func TestIgnoreName(t *testing.T) {
+	if !ignoreName("runtime.foo") || !ignoreName("runtime/foo") || !ignoreName("internal/abi") {
+		t.Fatal("ignoreName failed")
+	}
+}
diff --git a/cl/compile.go b/cl/compile.go
index 60530630..631246c8 100644
--- a/cl/compile.go
+++ b/cl/compile.go
@@ -87,20 +87,26 @@ func ignorePkgInit(pkgPath string) bool {
 	return false
 }
 
-func ignoreFunc(name string, fn *ssa.Function) bool {
+func ignoreName(name string) bool {
 	/* TODO(xsw): confirm this is not needed more
 	if name == "unsafe.init" {
 		return true
 	}
 	*/
-	fnName := fn.Name()
-	if strings.HasPrefix(fnName, "_Cgo_") {
-		return true
+	if strings.HasPrefix(name, "internal/") || strings.HasPrefix(name, "crypto/") ||
+		strings.HasPrefix(name, "arena.") || strings.HasPrefix(name, "maps.") ||
+		strings.HasPrefix(name, "time.") || strings.HasPrefix(name, "syscall.") ||
+		strings.HasPrefix(name, "os.") || strings.HasPrefix(name, "plugin.") ||
+		strings.HasPrefix(name, "reflect.") || strings.HasPrefix(name, "errors.") {
+		return true // TODO(xsw)
 	}
-	const runtime = "runtime"
-	if strings.HasPrefix(name, runtime) {
-		left := name[len(runtime):]
-		return strings.HasPrefix(left, ".cgo") || strings.HasPrefix(left, "/cgo")
+	return inPkg(name, "runtime") || inPkg(name, "sync")
+}
+
+func inPkg(name, pkg string) bool {
+	if len(name) > len(pkg) && strings.HasPrefix(name, pkg) {
+		c := name[len(pkg)]
+		return c == '.' || c == '/'
 	}
 	return false
 }
@@ -131,8 +137,12 @@ type context struct {
 
 func (p *context) compileType(pkg llssa.Package, t *ssa.Type) {
 	tn := t.Object().(*types.TypeName)
+	tnName := tn.Name()
 	typ := tn.Type()
-	name := fullName(tn.Pkg(), tn.Name())
+	name := fullName(tn.Pkg(), tnName)
+	if ignoreName(name) {
+		return
+	}
 	if debugInstr {
 		log.Println("==> NewType", name, typ)
 	}
@@ -145,8 +155,9 @@ func (p *context) compileMethods(pkg llssa.Package, typ types.Type) {
 	mthds := prog.MethodSets.MethodSet(typ)
 	for i, n := 0, mthds.Len(); i < n; i++ {
 		mthd := mthds.At(i)
-		ssaMthd := prog.MethodValue(mthd)
-		p.compileFunc(pkg, mthd.Obj().Pkg(), ssaMthd)
+		if ssaMthd := prog.MethodValue(mthd); ssaMthd != nil {
+			p.compileFunc(pkg, mthd.Obj().Pkg(), ssaMthd)
+		}
 	}
 }
 
@@ -154,6 +165,9 @@ func (p *context) compileMethods(pkg llssa.Package, typ types.Type) {
 func (p *context) compileGlobal(pkg llssa.Package, gbl *ssa.Global) {
 	typ := gbl.Type()
 	name := fullName(gbl.Pkg.Pkg, gbl.Name())
+	if ignoreName(name) || checkCgo(gbl.Name()) {
+		return
+	}
 	if debugInstr {
 		log.Println("==> NewVar", name, typ)
 	}
@@ -163,13 +177,13 @@ 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 := p.funcName(pkgTypes, f)
-	if debugInstr {
-		log.Println("==> NewFunc", name, "type:", sig.Recv(), sig)
-	}
-	if ignoreFunc(name, f) {
+	name, ok := p.funcName(pkgTypes, f, true)
+	if !ok { // ignored
 		return
 	}
+	if debugInstr {
+		log.Println("==> NewFunc", f.Name(), name, "type:", sig.Recv(), sig)
+	}
 	fn := pkg.NewFunc(name, sig)
 	p.inits = append(p.inits, func() {
 		p.fn = fn
diff --git a/cl/import.go b/cl/import.go
index d73b236e..9a02ec0b 100644
--- a/cl/import.go
+++ b/cl/import.go
@@ -137,18 +137,27 @@ func funcName(pkg *types.Package, fn *ssa.Function) string {
 	return ret
 }
 
-func (p *context) funcName(pkg *types.Package, fn *ssa.Function) string {
+func checkCgo(fnName string) bool {
+	return len(fnName) > 4 && fnName[0] == '_' && fnName[2] == 'g' && fnName[3] == 'o' &&
+		(fnName[1] == 'C' || fnName[1] == 'c') &&
+		(fnName[4] == '_' || strings.HasPrefix(fnName[4:], "Check"))
+}
+
+func (p *context) funcName(pkg *types.Package, fn *ssa.Function, ignore bool) (string, bool) {
 	name := funcName(pkg, fn)
-	if v, ok := p.link[name]; ok {
-		return v
+	if ignore && ignoreName(name) || checkCgo(fn.Name()) {
+		return name, false
 	}
-	return name
+	if v, ok := p.link[name]; ok {
+		return v, true
+	}
+	return name, true
 }
 
 func (p *context) funcOf(fn *ssa.Function) llssa.Function {
 	pkgTypes := p.ensureLoaded(fn.Pkg.Pkg)
 	pkg := p.pkg
-	name := p.funcName(pkgTypes, fn)
+	name, _ := p.funcName(pkgTypes, fn, false)
 	if ret := pkg.FuncOf(name); ret != nil {
 		return ret
 	}