56 lines · cpp
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-exception6//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_dup223 // 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 case28 // separately before making the dup3 syscall.29 if (oldfd == newfd) {30 // Check if oldfd is actually a valid file descriptor.31#if SYS_fcntl32 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 offsets35 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl64, oldfd, F_GETFD);36#else37#error "SYS_fcntl and SYS_fcntl64 syscalls not available."38#endif39 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#else46#error "dup2 and dup3 syscalls not available."47#endif48 if (ret < 0) {49 libc_errno = -ret;50 return -1;51 }52 return ret;53}54 55} // namespace LIBC_NAMESPACE_DECL56