getrandom.go

     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  
     7  package unix
     8  
     9  import (
    10  	"sync/atomic"
    11  	"syscall"
    12  	"unsafe"
    13  )
    14  
    15  //go:linkname vgetrandom runtime.vgetrandom
    16  //go:noescape
    17  func vgetrandom(p []byte, flags uint32) (ret int, supported bool)
    18  
    19  var getrandomUnsupported atomic.Bool
    20  
    21  // GetRandomFlag is a flag supported by the getrandom system call.
    22  type GetRandomFlag uintptr
    23  
    24  // GetRandom calls the getrandom system call.
    25  func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
    26  	ret, supported := vgetrandom(p, uint32(flags))
    27  	if supported {
    28  		if ret < 0 {
    29  			return 0, syscall.Errno(-ret)
    30  		}
    31  		return ret, nil
    32  	}
    33  	if getrandomUnsupported.Load() {
    34  		return 0, syscall.ENOSYS
    35  	}
    36  	r1, _, errno := syscall.Syscall(getrandomTrap,
    37  		uintptr(unsafe.Pointer(unsafe.SliceData(p))),
    38  		uintptr(len(p)),
    39  		uintptr(flags))
    40  	if errno != 0 {
    41  		if errno == syscall.ENOSYS {
    42  			getrandomUnsupported.Store(true)
    43  		}
    44  		return 0, errno
    45  	}
    46  	return int(r1), nil
    47  }
    48
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