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 "src/errno/libc_errno.h"
15#include <fcntl.h>
16#include <sys/syscall.h> // For syscall numbers.
17
18namespace LIBC_NAMESPACE {
19
20LLVM_LIBC_FUNCTION(int, dup2, (int oldfd, int newfd)) {
21#ifdef SYS_dup2
22 // If dup2 syscall is available, we make use of directly.
23 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_dup2, ts: oldfd, ts: newfd);
24#elif defined(SYS_dup3)
25 // If dup2 syscall is not available, we try using the dup3 syscall. However,
26 // dup3 fails if oldfd is the same as newfd. So, we handle that case
27 // separately before making the dup3 syscall.
28 if (oldfd == newfd) {
29 // Check if oldfd is actually a valid file descriptor.
30#if SYS_fcntl
31 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl, oldfd, F_GETFD);
32#elif defined(SYS_fcntl64)
33 // Same as fcntl but can handle large offsets
34 static_assert(sizeof(off_t) == 8);
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
56

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