+#if HAVE_DUP2
+
+# undef dup2
+
+# if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+
+/* Get declarations of the native Windows API functions. */
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+
+# include "msvc-inval.h"
+
+/* Get _get_osfhandle. */
+# include "msvc-nothrow.h"
+
+static int
+ms_windows_dup2 (int fd, int desired_fd)
+{
+ int result;
+
+ /* If fd is closed, mingw hangs on dup2 (fd, fd). If fd is open,
+ dup2 (fd, fd) returns 0, but all further attempts to use fd in
+ future dup2 calls will hang. */
+ if (fd == desired_fd)
+ {
+ if ((HANDLE) _get_osfhandle (fd) == INVALID_HANDLE_VALUE)
+ {
+ errno = EBADF;
+ return -1;
+ }
+ return fd;
+ }
+
+ /* Wine 1.0.1 return 0 when desired_fd is negative but not -1:
+ http://bugs.winehq.org/show_bug.cgi?id=21289 */
+ if (desired_fd < 0)
+ {
+ errno = EBADF;
+ return -1;
+ }
+
+ TRY_MSVC_INVAL
+ {
+ result = dup2 (fd, desired_fd);
+ }
+ CATCH_MSVC_INVAL
+ {
+ errno = EBADF;
+ result = -1;
+ }
+ DONE_MSVC_INVAL;
+
+ if (result == 0)
+ result = desired_fd;
+
+ return result;
+}
+
+# define dup2 ms_windows_dup2
+
+# endif
+
+int
+rpl_dup2 (int fd, int desired_fd)
+{
+ int result;
+
+# ifdef F_GETFL
+ /* On Linux kernels 2.6.26-2.6.29, dup2 (fd, fd) returns -EBADF.
+ On Cygwin 1.5.x, dup2 (1, 1) returns 0.
+ On Cygwin 1.7.17, dup2 (1, -1) dumps core.
+ On Cygwin 1.7.25, dup2 (1, 256) can dump core.
+ On Haiku, dup2 (fd, fd) mistakenly clears FD_CLOEXEC. */
+# if HAVE_SETDTABLESIZE
+ setdtablesize (desired_fd + 1);
+# endif
+ if (desired_fd < 0)
+ fd = desired_fd;
+ if (fd == desired_fd)
+ return fcntl (fd, F_GETFL) == -1 ? -1 : fd;
+# endif
+
+ result = dup2 (fd, desired_fd);
+
+ /* Correct an errno value on FreeBSD 6.1 and Cygwin 1.5.x. */
+ if (result == -1 && errno == EMFILE)
+ errno = EBADF;
+# if REPLACE_FCHDIR
+ if (fd != desired_fd && result != -1)
+ result = _gl_register_dup (fd, result);
+# endif
+ return result;
+}
+
+#else /* !HAVE_DUP2 */
+
+/* On older platforms, dup2 did not exist. */
+
+# ifndef F_DUPFD