1// Copyright 2021 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5//go:build dragonfly || freebsd || linux
6
7package unix
8
9import (
10	"sync/atomic"
11	"syscall"
12	"unsafe"
13)
14
15var getrandomUnsupported atomic.Bool
16
17// GetRandomFlag is a flag supported by the getrandom system call.
18type GetRandomFlag uintptr
19
20// GetRandom calls the getrandom system call.
21func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
22	if len(p) == 0 {
23		return 0, nil
24	}
25	if getrandomUnsupported.Load() {
26		return 0, syscall.ENOSYS
27	}
28	r1, _, errno := syscall.Syscall(getrandomTrap,
29		uintptr(unsafe.Pointer(&p[0])),
30		uintptr(len(p)),
31		uintptr(flags))
32	if errno != 0 {
33		if errno == syscall.ENOSYS {
34			getrandomUnsupported.Store(true)
35		}
36		return 0, errno
37	}
38	return int(r1), nil
39}
40