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: pledge_openbsd.go
    path of file: ./repos/teller/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.

package unix

import (
	"errors"
	"fmt"
	"strconv"
	"syscall"
	"unsafe"
)

// Pledge implements the pledge syscall.
//
// The pledge syscall does not accept execpromises on OpenBSD releases
// before 6.3.
//
// execpromises must be empty when Pledge is called on OpenBSD
// releases predating 6.3, ot
    
func PledgePromises(promises string) error {
	maj, min, err := majmin()
	if err != nil {
		return err
	}

	err = pledgeAvailable(maj, min, "")
	if err != nil {
		return err
	}

	// This variable holds the execpromises and is always nil.
	var expr unsafe.Pointer

	pptr, err := syscall.BytePtrFromString(promises)
	if err != nil {
		return err
	}

	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(unsafe.Pointer(pptr)), uintptr(expr), 0)
	if e != 0 {
		return e
	}

	return nil
}