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

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

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

#

# SYNOPSIS

#

#   AX_GCC_FUNC_ATTRIBUTE(ATTRIBUTE)

#

# DESCRIPTION

#

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

#   attributes; many other compilers also provide function 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_FUNC_ATTRIBUTE_<ATTRIBUTE>.

#

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

#   variable.

#

#   The macro currently supports the following function attributes:

#

#    alias

#    aligned

#    alloc_size

#    always_inline

#    artificial

#    cold

#    const

#    constructor

#    constructor_priority for constructor attribute with priority

#    deprecated

#    destructor

#    dllexport

#    dllimport

#    error

#    externally_visible

#    flatten

#    format

#    format_arg

#    gnu_inline

#    hot

#    ifunc

#    leaf

#    malloc

#    noclone

#    noinline

#    nonnull

#    noreturn

#    nothrow

#    optimize

#    pure

#    unused

#    used

#    visibility

#    warning

#    warn_unused_result

#    weak

#    weakref

#

#   Unsuppored function attributes will be tested with a prototype returning

#   an int and not accepting any arguments and the result of the 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_FUNC_ATTRIBUTE], [

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

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

        AC_LINK_IFELSE([AC_LANG_PROGRAM([

            m4_case([$1],

                [alias], [

                    int foo( void ) { return 0; }

                    int bar( void ) __attribute__(($1("foo")));

                ],

                [aligned], [

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

                ],

                [alloc_size], [

                    void *foo(int a) __attribute__(($1(1)));

                ],

                [always_inline], [

                    inline __attribute__(($1)) int foo( void ) { return 0; }

                ],

                [artificial], [

                    inline __attribute__(($1)) int foo( void ) { return 0; }

                ],

                [cold], [

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

                ],

                [const], [

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

                ],

                [constructor_priority], [

                    int foo( void ) __attribute__((__constructor__(65535/2)));

                ],

                [constructor], [

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

                ],

                [deprecated], [

                    int foo( void ) __attribute__(($1("")));

                ],

                [destructor], [

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

                ],

                [dllexport], [

                    __attribute__(($1)) int foo( void ) { return 0; }

                ],

                [dllimport], [

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

                ],

                [error], [

                    int foo( void ) __attribute__(($1("")));

                ],

                [externally_visible], [

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

                ],

                [flatten], [

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

                ],

                [format], [

                    int foo(const char *p, ...) __attribute__(($1(printf, 1, 2)));

                ],

                [format_arg], [

                    char *foo(const char *p) __attribute__(($1(1)));

                ],

                [gnu_inline], [

                    inline __attribute__(($1)) int foo( void ) { return 0; }

                ],

                [hot], [

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

                ],

                [ifunc], [

                    int my_foo( void ) { return 0; }

                    static int (*resolve_foo(void))(void) { return my_foo; }

                    int foo( void ) __attribute__(($1("resolve_foo")));

                ],

                [leaf], [

                    __attribute__(($1)) int foo( void ) { return 0; }

                ],

                [malloc], [

                    void *foo( void ) __attribute__(($1));

                ],

                [noclone], [

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

                ],

                [noinline], [

                    __attribute__(($1)) int foo( void ) { return 0; }

                ],

                [nonnull], [

                    int foo(char *p) __attribute__(($1(1)));

                ],

                [noreturn], [

                    void foo( void ) __attribute__(($1));

                ],

                [nothrow], [

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

                ],

                [optimize], [

                    __attribute__(($1(3))) int foo( void ) { return 0; }

                ],

                [pure], [

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

                ],

                [returns_nonnull], [

                    void *foo( void ) __attribute__(($1));

                ],

                [unused], [

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

                ],

                [used], [

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

                ],

                [visibility], [

                    int foo_def( void ) __attribute__(($1("default")));

                    int foo_hid( void ) __attribute__(($1("hidden")));

                    int foo_int( void ) __attribute__(($1("internal")));

                    int foo_pro( void ) __attribute__(($1("protected")));

                ],

                [warning], [

                    int foo( void ) __attribute__(($1("")));

                ],

                [warn_unused_result], [

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

                ],

                [weak], [

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

                ],

                [weakref], [

                    static int foo( void ) { return 0; }

                    static int bar( void ) __attribute__(($1("foo")));

                ],

                [

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

                 int foo( void ) __attribute__(($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_FUNC_ATTRIBUTE_$1), 1,

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

    AS_VAR_POPDEF([ac_var])

])