1// Copyright 2023 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 unix
6
7package runtime
8
9func checkfds() {
10	if islibrary || isarchive {
11		// If the program is actually a library, presumably being consumed by
12		// another program, we don't want to mess around with the file
13		// descriptors.
14		return
15	}
16
17	const (
18		// F_GETFD, EBADF, O_RDWR are standard across all unixes we support, so
19		// we define them here rather than in each of the OS specific files.
20		F_GETFD = 0x01
21		EBADF   = 0x09
22		O_RDWR  = 0x02
23	)
24
25	devNull := []byte("/dev/null\x00")
26	for i := 0; i < 3; i++ {
27		ret, errno := fcntl(int32(i), F_GETFD, 0)
28		if ret >= 0 {
29			continue
30		}
31
32		if errno != EBADF {
33			print("runtime: unexpected error while checking standard file descriptor ", i, ", errno=", errno, "\n")
34			throw("cannot open standard fds")
35		}
36
37		if ret := open(&devNull[0], O_RDWR, 0); ret < 0 {
38			print("runtime: standard file descriptor ", i, " closed, unable to open /dev/null, errno=", errno, "\n")
39			throw("cannot open standard fds")
40		} else if ret != int32(i) {
41			print("runtime: opened unexpected file descriptor ", ret, " when attempting to open ", i, "\n")
42			throw("cannot open standard fds")
43		}
44	}
45}
46