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 5package unix 6 7import ( 8 "sync/atomic" 9 "syscall" 10 "unsafe" 11) 12 13//go:cgo_import_dynamic libc_getrandom getrandom "libc.so" 14 15//go:linkname procGetrandom libc_getrandom 16 17var procGetrandom uintptr 18 19var getrandomUnsupported atomic.Bool 20 21// GetRandomFlag is a flag supported by the getrandom system call. 22type GetRandomFlag uintptr 23 24const ( 25 // GRND_NONBLOCK means return EAGAIN rather than blocking. 26 GRND_NONBLOCK GetRandomFlag = 0x0001 27 28 // GRND_RANDOM means use the /dev/random pool instead of /dev/urandom. 29 GRND_RANDOM GetRandomFlag = 0x0002 30) 31 32// GetRandom calls the getrandom system call. 33func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) { 34 if len(p) == 0 { 35 return 0, nil 36 } 37 if getrandomUnsupported.Load() { 38 return 0, syscall.ENOSYS 39 } 40 r1, _, errno := syscall6(uintptr(unsafe.Pointer(&procGetrandom)), 41 3, 42 uintptr(unsafe.Pointer(&p[0])), 43 uintptr(len(p)), 44 uintptr(flags), 45 0, 0, 0) 46 if errno != 0 { 47 if errno == syscall.ENOSYS { 48 getrandomUnsupported.Store(true) 49 } 50 return 0, errno 51 } 52 return int(r1), nil 53} 54