You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mkpost.go
    path of file: ./repos/dep/vendor/golang.org/x/sys/unix
    
    the code of the file until where you have to start completion: // Copyright 2016 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

// mkpost processes the output of cgo -godefs to
// modify the generated types. It is used to clean up
// the sys API in an architecture specific manner.
//
// mkpost is run after cgo -godefs; see README.md.
package main

import (
	"bytes"
	"fmt"
	"go/format"
	"io/ioutil"
	"log"
	"os"
	"regexp"
)

func main() {
	// Get the OS and architecture (using GOARCH_TARGET if it exists)
	goos := os.Getenv("GOOS")
	goarch := os.Getenv("GOARCH_TARGET")
	if goarch == "" {
		goarch = os.Getenv("GOARCH")
	}
	// Check that we are using the new build system if we should be.
	if goos == "linux" && goarch != "sparc64" {
		if os.Getenv("GOLANG_SYS_BUILD") != "docker" {
			os.Stderr.WriteString("In the new build system, mkpost should not be called directly.\n")
			os.Stderr.WriteString("See README.md\n")
			os.Exit(1)
		}
	}

	b, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		log.Fatal(err)
	}

	// If we have empty Ptrace structs, we should delete them. Only s390x emits
	// nonempty Ptrace structs.
	ptraceRexexp := regexp.MustCompile(`type Ptrace((Psw|Fpregs|Per) struct {\s*})`)
	b = ptraceRexexp.ReplaceAll(b, nil)

	// Replace the control_regs union with a blank identifier for now.
	controlRegsRegex := regexp.MustCompile(`(Control_regs)\s+\[0\]uint64`)
	b = controlRegsRegex.ReplaceAll(b, []byte("_ [0]uint64"))

	// Remove fields that are added by glibc
	// Note that this is unstable as the identifers are private.
	removeFieldsRegex := regexp.MustCompile(`X__glibc\S*`)
	b = removeFieldsRegex.ReplaceAll(b, []byte("_"))

	// We refuse to export private fields on s390x
	if goarch == "s390x" && goos == "linux" {
		// Remove cgo padding fields
		removeFieldsRegex := regexp.MustCompile(`Pad_cgo_\d+`)
		b = removeFieldsRegex.ReplaceAll(b, []byte("_"))

		// Remove padding, hidden, or unused fields
		removeFieldsRegex = regexp.MustCompile(`X_\S+`)
		b = removeFieldsRegex.ReplaceAll(b, []byte("_"))
	}

	// Re
    
func main() {
	// Get the OS and architecture (using GOARCH_TARGET if it exists)
	goos := os.Getenv("GOOS")
	goarch := os.Getenv("GOARCH_TARGET")
	if goarch == "" {
		goarch = os.Getenv("GOARCH")
	}
	// Check that we are using the new build system if we should be.
	if goos == "linux" && goarch != "sparc64" {
		if os.Getenv("GOLANG_SYS_BUILD") != "docker" {
			os.Stderr.WriteString("In the new build system, mkpost should not be called directly.\n")
			os.Stderr.WriteString("See README.md\n")
			os.Exit(1)
		}
	}

	b, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		log.Fatal(err)
	}

	// If we have empty Ptrace structs, we should delete them. Only s390x emits
	// nonempty Ptrace structs.
	ptraceRexexp := regexp.MustCompile(`type Ptrace((Psw|Fpregs|Per) struct {\s*})`)
	b = ptraceRexexp.ReplaceAll(b, nil)

	// Replace the control_regs union with a blank identifier for now.
	controlRegsRegex := regexp.MustCompile(`(Control_regs)\s+\[0\]uint64`)
	b = controlRegsRegex.ReplaceAll(b, []byte("_ [0]uint64"))

	// Remove fields that are added by glibc
	// Note that this is unstable as the identifers are private.
	removeFieldsRegex := regexp.MustCompile(`X__glibc\S*`)
	b = removeFieldsRegex.ReplaceAll(b, []byte("_"))

	// We refuse to export private fields on s390x
	if goarch == "s390x" && goos == "linux" {
		// Remove cgo padding fields
		removeFieldsRegex := regexp.MustCompile(`Pad_cgo_\d+`)
		b = removeFieldsRegex.ReplaceAll(b, []byte("_"))

		// Remove padding, hidden, or unused fields
		removeFieldsRegex = regexp.MustCompile(`X_\S+`)
		b = removeFieldsRegex.ReplaceAll(b, []byte("_"))
	}

	// Remove the first line of warning from cgo
	b = b[bytes.IndexByte(b, '\n')+1:]
	// Modify the command in the header to include:
	//  mkpost, our own warning, and a build tag.
	replacement := fmt.Sprintf(`$1 | go run mkpost.go
// Code generated by the command above; see README.md. DO NOT EDIT.

// +build %s,%s`, goarch, goos)
	cgoCommandRegex := regexp.MustCompile(`(cgo -godefs .*)`)
	b = cgoCommandRegex.ReplaceAll(b, []byte(replacement))

	// gofmt
	b, err = format.Source(b)
	if err != nil {
		log.Fatal(err)
	}

	os.Stdout.Write(b)
}