# mmap-anon.m4 serial 10

dnl Copyright (C) 2005, 2007, 2009-2018 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.

# Detect how mmap can be used to create anonymous (not file-backed) memory

# mappings.

# - On Linux, AIX, OSF/1, Solaris, Cygwin, Interix, Haiku, both MAP_ANONYMOUS

#   and MAP_ANON exist and have the same value.

# - On HP-UX, only MAP_ANONYMOUS exists.

# - On Mac OS X, FreeBSD, NetBSD, OpenBSD, only MAP_ANON exists.

# - On IRIX, neither exists, and a file descriptor opened to /dev/zero must be

#   used.

AC_DEFUN([gl_FUNC_MMAP_ANON],

[

  dnl Persuade glibc <sys/mman.h> to define MAP_ANONYMOUS.

  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])

  # Check for mmap(). Don't use AC_FUNC_MMAP, because it checks too much: it

  # fails on HP-UX 11, because MAP_FIXED mappings do not work. But this is

  # irrelevant for anonymous mappings.

  AC_CHECK_FUNC([mmap], [gl_have_mmap=yes], [gl_have_mmap=no])

  # Try to allow MAP_ANONYMOUS.

  gl_have_mmap_anonymous=no

  if test $gl_have_mmap = yes; then

    AC_MSG_CHECKING([for MAP_ANONYMOUS])

    AC_EGREP_CPP([I cannot identify this map], [

#include <sys/mman.h>

#ifdef MAP_ANONYMOUS

    I cannot identify this map

#endif

],

      [gl_have_mmap_anonymous=yes])

    if test $gl_have_mmap_anonymous != yes; then

      AC_EGREP_CPP([I cannot identify this map], [

#include <sys/mman.h>

#ifdef MAP_ANON

    I cannot identify this map

#endif

],

        [AC_DEFINE([MAP_ANONYMOUS], [MAP_ANON],

          [Define to a substitute value for mmap()'s MAP_ANONYMOUS flag.])

         gl_have_mmap_anonymous=yes])

    fi

    AC_MSG_RESULT([$gl_have_mmap_anonymous])

    if test $gl_have_mmap_anonymous = yes; then

      AC_DEFINE([HAVE_MAP_ANONYMOUS], [1],

        [Define to 1 if mmap()'s MAP_ANONYMOUS flag is available after including

         config.h and <sys/mman.h>.])

    fi

  fi

])