# ===========================================================================

#   https://www.gnu.org/software/autoconf-archive/ax_gcc_var_attribute.html

# ===========================================================================

#

# SYNOPSIS

#

#   AX_GCC_VAR_ATTRIBUTE(ATTRIBUTE)

#

# DESCRIPTION

#

#   This macro checks if the compiler supports one of GCC's variable

#   attributes; many other compilers also provide variable attributes with

#   the same syntax. Compiler warnings are used to detect supported

#   attributes as unsupported ones are ignored by default so quieting

#   warnings when using this macro will yield false positives.

#

#   The ATTRIBUTE parameter holds the name of the attribute to be checked.

#

#   If ATTRIBUTE is supported define HAVE_VAR_ATTRIBUTE_<ATTRIBUTE>.

#

#   The macro caches its result in the ax_cv_have_var_attribute_<attribute>

#   variable.

#

#   The macro currently supports the following variable attributes:

#

#    aligned

#    cleanup

#    common

#    nocommon

#    deprecated

#    mode

#    packed

#    tls_model

#    unused

#    used

#    vector_size

#    weak

#    dllimport

#    dllexport

#    init_priority

#

#   Unsupported variable attributes will be tested against a global integer

#   variable and without any arguments given to the attribute itself; the

#   result of this check might be wrong or meaningless so use with care.

#

# LICENSE

#

#   Copyright (c) 2013 Gabriele Svelto <gabriele.svelto@gmail.com>

#

#   Copying and distribution of this file, with or without modification, are

#   permitted in any medium without royalty provided the copyright notice

#   and this notice are preserved.  This file is offered as-is, without any

#   warranty.

#serial 5

AC_DEFUN([AX_GCC_VAR_ATTRIBUTE], [

    AS_VAR_PUSHDEF([ac_var], [ax_cv_have_var_attribute_$1])

    AC_CACHE_CHECK([for __attribute__(($1))], [ac_var], [

        AC_LINK_IFELSE([AC_LANG_PROGRAM([

            m4_case([$1],

                [aligned], [

                    int foo __attribute__(($1(32)));

                ],

                [cleanup], [

                    int bar(int *t) { return *t; };

                ],

                [common], [

                    int foo __attribute__(($1));

                ],

                [nocommon], [

                    int foo __attribute__(($1));

                ],

                [deprecated], [

                    int foo __attribute__(($1)) = 0;

                ],

                [mode], [

                    long foo __attribute__(($1(word)));

                ],

                [packed], [

                    struct bar {

                        int baz __attribute__(($1));

                    };

                ],

                [tls_model], [

                    __thread int bar1 __attribute__(($1("global-dynamic")));

                    __thread int bar2 __attribute__(($1("local-dynamic")));

                    __thread int bar3 __attribute__(($1("initial-exec")));

                    __thread int bar4 __attribute__(($1("local-exec")));

                ],

                [unused], [

                    int foo __attribute__(($1));

                ],

                [used], [

                    int foo __attribute__(($1));

                ],

                [vector_size], [

                    int foo __attribute__(($1(16)));

                ],

                [weak], [

                    int foo __attribute__(($1));

                ],

                [dllimport], [

                    int foo __attribute__(($1));

                ],

                [dllexport], [

                    int foo __attribute__(($1));

                ],

                [init_priority], [

                    struct bar { bar() {} ~bar() {} };

                    bar b __attribute__(($1(65535/2)));

                ],

                [

                 m4_warn([syntax], [Unsupported attribute $1, the test may fail])

                 int foo __attribute__(($1));

                ]

            )], [

            m4_case([$1],

                [cleanup], [

                    int foo __attribute__(($1(bar))) = 0;

                    foo = foo + 1;

                ],

                []

            )])

            ],

            dnl GCC doesn't exit with an error if an unknown attribute is

            dnl provided but only outputs a warning, so accept the attribute

            dnl only if no warning were issued.

            [AS_IF([test -s conftest.err],

                [AS_VAR_SET([ac_var], [no])],

                [AS_VAR_SET([ac_var], [yes])])],

            [AS_VAR_SET([ac_var], [no])])

    ])

    AS_IF([test yes = AS_VAR_GET([ac_var])],

        [AC_DEFINE_UNQUOTED(AS_TR_CPP(HAVE_VAR_ATTRIBUTE_$1), 1,

            [Define to 1 if the system has the `$1' variable attribute])], [])

    AS_VAR_POPDEF([ac_var])

])