FreeBSD/Linux Kernel Cross Reference
sys/contrib/libsodium/m4/ax_tls.m4

     # ===========================================================================
     #          https://www.gnu.org/software/autoconf-archive/ax_tls.html
     # ===========================================================================
     #
     # SYNOPSIS
     #
     #   AX_TLS([action-if-found], [action-if-not-found])
     #
     # DESCRIPTION
    #
    #   Provides a test for the compiler support of thread local storage (TLS)
    #   extensions. Defines TLS if it is found. Currently knows about C++11,
    #   GCC/ICC, and MSVC. I think SunPro uses the same as GCC, and Borland
    #   apparently supports either.
    #
    # LICENSE
    #
    #   Copyright (c) 2008 Alan Woodland <ajw05@aber.ac.uk>
    #   Copyright (c) 2010 Diego Elio Petteno` <flameeyes@gmail.com>
    #
    #   This program is free software: you can redistribute it and/or modify it
    #   under the terms of the GNU General Public License as published by the
    #   Free Software Foundation, either version 3 of the License, or (at your
    #   option) any later version.
    #
    #   This program is distributed in the hope that it will be useful, but
    #   WITHOUT ANY WARRANTY; without even the implied warranty of
    #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
    #   Public License for more details.
    #
    #   You should have received a copy of the GNU General Public License along
    #   with this program. If not, see <https://www.gnu.org/licenses/>.
    #
    #   As a special exception, the respective Autoconf Macro's copyright owner
    #   gives unlimited permission to copy, distribute and modify the configure
    #   scripts that are the output of Autoconf when processing the Macro. You
    #   need not follow the terms of the GNU General Public License when using
    #   or distributing such scripts, even though portions of the text of the
    #   Macro appear in them. The GNU General Public License (GPL) does govern
    #   all other use of the material that constitutes the Autoconf Macro.
    #
    #   This special exception to the GPL applies to versions of the Autoconf
    #   Macro released by the Autoconf Archive. When you make and distribute a
    #   modified version of the Autoconf Macro, you may extend this special
    #   exception to the GPL to apply to your modified version as well.
    
    #serial 14
    
    AC_DEFUN([AX_TLS], [
      AC_MSG_CHECKING([for thread local storage (TLS) class])
      AC_CACHE_VAL([ac_cv_tls],
       [for ax_tls_keyword in thread_local _Thread_local __thread '__declspec(thread)' none; do
           AS_CASE([$ax_tls_keyword],
              [none], [ac_cv_tls=none ; break],
              [AC_TRY_COMPILE(
                  [#include <stdlib.h>
                   static void
                   foo(void) {
                   static ] $ax_tls_keyword [ int bar;
                   exit(1);
                   }],
                   [],
                   [ac_cv_tls=$ax_tls_keyword ; break],
                   ac_cv_tls=none
               )])
        done
      ])
      AC_MSG_RESULT([$ac_cv_tls])
    
      AS_IF([test "$ac_cv_tls" != "none"],
        [AC_DEFINE_UNQUOTED([TLS],[$ac_cv_tls],[If the compiler supports a TLS storage class define it to that here])
         m4_ifnblank([$1],[$1])],
        [m4_ifnblank([$2],[$2])])
    ])

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