diff --git a/vendor/golang.org/x/sys/unix/mkasm_darwin.go b/vendor/golang.org/x/sys/unix/mkasm_darwin.go
new file mode 100644
index 0000000..4548b99
--- /dev/null
+++ b/vendor/golang.org/x/sys/unix/mkasm_darwin.go
@@ -0,0 +1,61 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+// mkasm_darwin.go generates assembly trampolines to call libSystem routines from Go.
+//This program must be run after mksyscall.go.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"strings"
+)
+
+func main() {
+	in1, err := ioutil.ReadFile("syscall_darwin.go")
+	if err != nil {
+		log.Fatalf("can't open syscall_darwin.go: %s", err)
+	}
+	arch := os.Args[1]
+	in2, err := ioutil.ReadFile(fmt.Sprintf("syscall_darwin_%s.go", arch))
+	if err != nil {
+		log.Fatalf("can't open syscall_darwin_%s.go: %s", arch, err)
+	}
+	in3, err := ioutil.ReadFile(fmt.Sprintf("zsyscall_darwin_%s.go", arch))
+	if err != nil {
+		log.Fatalf("can't open zsyscall_darwin_%s.go: %s", arch, err)
+	}
+	in := string(in1) + string(in2) + string(in3)
+
+	trampolines := map[string]bool{}
+
+	var out bytes.Buffer
+
+	fmt.Fprintf(&out, "// go run mkasm_darwin.go %s\n", strings.Join(os.Args[1:], " "))
+	fmt.Fprintf(&out, "// Code generated by the command above; DO NOT EDIT.\n")
+	fmt.Fprintf(&out, "\n")
+	fmt.Fprintf(&out, "// +build go1.12\n")
+	fmt.Fprintf(&out, "\n")
+	fmt.Fprintf(&out, "#include \"textflag.h\"\n")
+	for _, line := range strings.Split(in, "\n") {
+		if !strings.HasPrefix(line, "func ") || !strings.HasSuffix(line, "_trampoline()") {
+			continue
+		}
+		fn := line[5 : len(line)-13]
+		if !trampolines[fn] {
+			trampolines[fn] = true
+			fmt.Fprintf(&out, "TEXT ·%s_trampoline(SB),NOSPLIT,$0-0\n", fn)
+			fmt.Fprintf(&out, "\tJMP\t%s(SB)\n", fn)
+		}
+	}
+	err = ioutil.WriteFile(fmt.Sprintf("zsyscall_darwin_%s.s", arch), out.Bytes(), 0644)
+	if err != nil {
+		log.Fatalf("can't write zsyscall_darwin_%s.s: %s", arch, err)
+	}
+}