1//===-- Linux implementation of dup2 --------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "src/unistd/dup2.h"
10
11#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
12#include "src/__support/common.h"
13
14#include "hdr/fcntl_macros.h"
15#include "src/__support/libc_errno.h"
16#include "src/__support/macros/config.h"
17#include <sys/syscall.h> // For syscall numbers.
18
19namespace LIBC_NAMESPACE_DECL {
20
21LLVM_LIBC_FUNCTION(int, dup2, (int oldfd, int newfd)) {
22#ifdef SYS_dup2
23 // If dup2 syscall is available, we make use of directly.
24 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_dup2, oldfd, newfd);
25#elif defined(SYS_dup3)
26 // If dup2 syscall is not available, we try using the dup3 syscall. However,
27 // dup3 fails if oldfd is the same as newfd. So, we handle that case
28 // separately before making the dup3 syscall.
29 if (oldfd == newfd) {
30 // Check if oldfd is actually a valid file descriptor.
31#if SYS_fcntl
32 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl, oldfd, F_GETFD);
33#elif defined(SYS_fcntl64)
34 // Same as fcntl but can handle large offsets
35 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl64, oldfd, F_GETFD);
36#else
37#error "SYS_fcntl and SYS_fcntl64 syscalls not available."
38#endif
39 if (ret >= 0)
40 return oldfd;
41 libc_errno = -ret;
42 return -1;
43 }
44 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_dup3, oldfd, newfd, 0);
45#else
46#error "dup2 and dup3 syscalls not available."
47#endif
48 if (ret < 0) {
49 libc_errno = -ret;
50 return -1;
51 }
52 return ret;
53}
54
55} // namespace LIBC_NAMESPACE_DECL
56

source code of libc/src/unistd/linux/dup2.cpp