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# mmap-anon.m4
# serial 15
dnl Copyright (C) 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.
# Detect how mmap can be used to create anonymous (not file-backed) memory
# mappings.
# - On Linux, AIX, 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, Minix, only MAP_ANON exists.
AC_DEFUN_ONCE([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.
# Instead, assume that mmap() exists if and only if <sys/mman.h> exists.
# Code needs to tests HAVE_SYS_MMAN_H, not HAVE_MMAP.
AC_CHECK_HEADERS_ONCE([sys/mman.h])
# Try to allow MAP_ANONYMOUS.
gl_have_mmap_anonymous=no
if test $ac_cv_header_sys_mman_h = 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])
fi
])
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