emacs/m4/dup2.m4

# dup2.m4
# serial 28
dnl Copyright (C) 2002, 2005, 2007, 2009-2025 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
dnl This file is offered as-is, without any warranty.

AC_DEFUN([gl_FUNC_DUP2],
[
  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
  AC_REQUIRE([AC_CANONICAL_HOST])
  AC_CACHE_CHECK([whether dup2 works], [gl_cv_func_dup2_works],
    [AC_RUN_IFELSE([
       AC_LANG_PROGRAM(
         [[#include <errno.h>
           #include <fcntl.h>
           #include <limits.h>
           #include <sys/resource.h>
           #include <unistd.h>
           ]GL_MDA_DEFINES[
           #ifndef RLIM_SAVED_CUR
           # define RLIM_SAVED_CUR RLIM_INFINITY
           #endif
           #ifndef RLIM_SAVED_MAX
           # define RLIM_SAVED_MAX RLIM_INFINITY
           #endif
         ]],
         [[int result = 0;
           int bad_fd = INT_MAX;
           struct rlimit rlim;
           if (getrlimit (RLIMIT_NOFILE, &rlim) == 0
               && 0 <= rlim.rlim_cur && rlim.rlim_cur <= INT_MAX
               && rlim.rlim_cur != RLIM_INFINITY
               && rlim.rlim_cur != RLIM_SAVED_MAX
               && rlim.rlim_cur != RLIM_SAVED_CUR)
             bad_fd = rlim.rlim_cur;
           #ifdef FD_CLOEXEC
             if (fcntl (1, F_SETFD, FD_CLOEXEC) == -1)
               result |= 1;
           #endif
           if (dup2 (1, 1) != 1)
             result |= 2;
           #ifdef FD_CLOEXEC
             if (fcntl (1, F_GETFD) != FD_CLOEXEC)
               result |= 4;
           #endif
           close (0);
           if (dup2 (0, 0) != -1)
             result |= 8;
           /* Many gnulib modules require POSIX conformance of EBADF.  */
           if (dup2 (2, bad_fd) == -1 && errno != EBADF)
             result |= 16;
           /* Flush out some cygwin core dumps.  */
           if (dup2 (2, -1) != -1 || errno != EBADF)
             result |= 32;
           dup2 (2, 255);
           dup2 (2, 256);
           /* On OS/2 kLIBC, dup2() does not work on a directory fd.  */
           {
             int fd = open (".", O_RDONLY);
             if (fd == -1)
               result |= 64;
             else if (dup2 (fd, fd + 1) == -1)
               result |= 128;
             close (fd);
           }
           return result;]])
      ],
      [gl_cv_func_dup2_works=yes], [gl_cv_func_dup2_works=no],
      [case "$host_os" in
         mingw* | windows*) # on this platform, dup2 always returns 0 for success
           gl_cv_func_dup2_works="guessing no" ;;
         cygwin*) # on cygwin 1.5.x, dup2(1,1) returns 0
           gl_cv_func_dup2_works="guessing no" ;;
         aix* | freebsd*)
                 # on AIX 7.1 and FreeBSD 6.1, dup2 (1,toobig) gives EMFILE,
                 # not EBADF.
           gl_cv_func_dup2_works="guessing no" ;;
         haiku*) # on Haiku alpha 2, dup2(1, 1) resets FD_CLOEXEC.
           gl_cv_func_dup2_works="guessing no" ;;
         *-android*) # implemented using dup3(), which fails if oldfd == newfd
           gl_cv_func_dup2_works="guessing no" ;;
         os2*) # on OS/2 kLIBC, dup2() does not work on a directory fd.
           gl_cv_func_dup2_works="guessing no" ;;
         *) gl_cv_func_dup2_works="guessing yes" ;;
       esac])
    ])
  case "$gl_cv_func_dup2_works" in
    *yes) ;;
    *)
      REPLACE_DUP2=1
      AC_CHECK_FUNCS([setdtablesize])
      ;;
  esac
  dnl Replace dup2() for supporting the gnulib-defined fchdir() function,
  dnl to keep fchdir's bookkeeping up-to-date.
  m4_ifdef([gl_FUNC_FCHDIR], [
    gl_TEST_FCHDIR
    if test $HAVE_FCHDIR = 0; then
      REPLACE_DUP2=1
    fi
  ])
])

# Prerequisites of lib/dup2.c.
AC_DEFUN([gl_PREREQ_DUP2], [])