Fix: tls-compat.h exposes compiler-dependent public configuration

Exposing the storage class chosen by ax_tls.m4 in a public header is
a bad idea, because if a recent gcc is used when configuring
liburcu, thus detecting C11, it will choose _Thread_local. Then, if an
external project uses urcu/tls-compat.h with an older gcc (e.g. 4.8),
it will fail to build, because that storage class is unknown, and
__thread should be used instead.

Therefore, use a preprocessor conditional on __cplusplus to detect C++11
(and use thread_local). Else, the STDC version is used to select
_Thread_local. Else check if _MSC_VER is defined to select
__declspec(thread), or else rely on __thread as fallback.

Remove ax_tls.m4 because it is now unused.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/configure.ac b/configure.ac
index c80b918356a4372db8d4951e2a81de9a4f991182..b62f587e8d8e42de3394beb74ad0f1819eb47bfb 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -50,14 +50,7 @@ AC_USE_SYSTEM_EXTENSIONS
 AC_PROG_CC
 AC_PROG_CC_STDC
 
-# If not overridden, use ax_tls.m4 to check if TLS is available.
-AS_IF([test "x$def_compiler_tls" = "xyes"],
-       [AX_TLS([def_tls_detect=$ac_cv_tls], [:])],
-       [:])
-
-AS_IF([test "x$def_tls_detect" = "x"],
-       [:],
-       [AC_DEFINE_UNQUOTED([CONFIG_RCU_TLS], $def_tls_detect)])
+AS_IF([test "x$def_compiler_tls" = "xyes"], AC_DEFINE([CONFIG_RCU_TLS], [1]), [:])
 
 # Checks for programs.
 AC_PROG_AWK
@@ -501,7 +494,7 @@ test "x$compat_futex_test" = "x0" && value=1 || value=0
 PPRINT_PROP_BOOL([Futex support], $value)
 
 # TLS
-test "x$def_tls_detect" = "x" && value="pthread_getspecific()" || value="$def_tls_detect"
+test "x$def_compiler_tls" = "xyes" && value="compiler TLS" || value="pthread_getspecific()"
 PPRINT_PROP_STRING([Thread Local Storage (TLS)], [$value])
 
 # clock_gettime() available

diff --git a/include/urcu/tls-compat.h b/include/urcu/tls-compat.h
index c17aca36b2c86a4b94f95e1c97c8aaa327f1f4a7..db22dde6758550cad1dbf329ef050c7916706ffd 100644 (file)
--- a/include/urcu/tls-compat.h
+++ b/include/urcu/tls-compat.h
@@ -32,7 +32,17 @@
 extern "C" {
 #endif
 
-#ifdef CONFIG_RCU_TLS  /* Based on ax_tls.m4 */
+#ifdef CONFIG_RCU_TLS
+
+#if defined (__cplusplus) && __cplusplus >= 201103L
+# define URCU_TLS_STORAGE_CLASS        thread_local
+#elif defined (__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L)
+# define URCU_TLS_STORAGE_CLASS        _Thread_local
+#elif defined (_MSC_VER)
+# define URCU_TLS_STORAGE_CLASS        __declspec(thread)
+#else
+# define URCU_TLS_STORAGE_CLASS        __thread
+#endif
 
 /*
  * Hint: How to define/declare TLS variables of compound types
@@ -65,13 +75,13 @@ extern "C" {
  */
 
 # define DECLARE_URCU_TLS(type, name)  \
-       CONFIG_RCU_TLS type name
+       URCU_TLS_STORAGE_CLASS type name
 
 # define DEFINE_URCU_TLS(type, name)   \
-       CONFIG_RCU_TLS type name
+       URCU_TLS_STORAGE_CLASS type name
 
 # define DEFINE_URCU_TLS_INIT(type, name, init)        \
-       CONFIG_RCU_TLS type name = (init)
+       URCU_TLS_STORAGE_CLASS type name = (init)
 
 # define URCU_TLS(name)                (name)
 

diff --git a/m4/ax_tls.m4 b/m4/ax_tls.m4
deleted file mode 100644 (file)
index 51edee8..0000000
--- a/m4/ax_tls.m4
+++ /dev/null
@@ -1,74 +0,0 @@
-# ===========================================================================
-#          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])])
-])