github.com/hxx258456/ccgo@v0.0.5-0.20230213014102-48b35f46f66f/internal/syscall/unix/getrandom.go (about)

     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  // +build dragonfly freebsd linux
     7  
     8  package unix
     9  
    10  import (
    11  	"sync/atomic"
    12  	"syscall"
    13  	"unsafe"
    14  )
    15  
    16  var getrandomUnsupported int32 // atomic
    17  
    18  // GetRandomFlag is a flag supported by the getrandom system call.
    19  type GetRandomFlag uintptr
    20  
    21  // GetRandom calls the getrandom system call.
    22  func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
    23  	if len(p) == 0 {
    24  		return 0, nil
    25  	}
    26  	if atomic.LoadInt32(&getrandomUnsupported) != 0 {
    27  		return 0, syscall.ENOSYS
    28  	}
    29  	r1, _, errno := syscall.Syscall(getrandomTrap,
    30  		uintptr(unsafe.Pointer(&p[0])),
    31  		uintptr(len(p)),
    32  		uintptr(flags))
    33  	if errno != 0 {
    34  		if errno == syscall.ENOSYS {
    35  			atomic.StoreInt32(&getrandomUnsupported, 1)
    36  		}
    37  		return 0, errno
    38  	}
    39  	return int(r1), nil
    40  }