1 files changed, 55 insertions, 0 deletions
diff --git a/m4/mmap-anon.m4 b/m4/mmap-anon.m4
new file mode 100644
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+++ b/m4/mmap-anon.m4
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+# mmap-anon.m4 serial 12
+dnl Copyright (C) 2005, 2007, 2009-2023 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, Minix, only MAP_ANON exists.
+# - On IRIX, neither exists, and a file descriptor opened to /dev/zero must be
+#   used.
+
+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.
+  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
+])