libc/src/unistd/linux/dup2.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-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