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 18 namespace LIBC_NAMESPACE { 19 20 LLVM_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, oldfd, 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