Fix TLS detection: test with linker, add --disable-compiler-tls

NetBSD 5.1 and older, as well as Darwin, succeed to compile code
containing TLS, but cannot link it. Test with linker in addition to
compiler for TLS support.

Also add a --disable-compiler-tls configure option to allow users to
force using the pthread getspecific fall back.

Fixes #288

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

diff --git a/README b/README
index 81afe0e2757c8bceabef7c50ff4102d0600aa8d3..83330eab1e5ab82cd128dd6c68cdc247f1f272a8 100644 (file)
--- a/README
+++ b/README
@@ -274,3 +274,10 @@ Interaction with fork()
        call_rcu_after_fork_parent() after the fork().  The child
        process must invoke call_rcu_after_fork_child().
        These three APIs are suitable for passing to pthread_atfork().
+
+Thread Local Storage (TLS)
+
+       Userspace RCU can fall back on pthread_getspecific() to emulate
+       TLS variables on systems where it is not available. This behavior
+       can be forced by specifying --disable-compiler-tls as configure
+       argument.

diff --git a/config/ax_tls.m4 b/config/ax_tls.m4
index 5ab1a413d1414792e6b0098b7c13a42d56d9bdee..7c86daf147cdc8f068161f2dc128bbfd7ef2ebc2 100644 (file)
--- a/config/ax_tls.m4
+++ b/config/ax_tls.m4
@@ -69,16 +69,11 @@ AC_DEFUN([AX_TLS], [
     for ax_tls_keyword in $ax_tls_keywords; do
        AS_CASE([$ax_tls_keyword],
           [none], [ac_cv_tls=none ; break],
-          [AC_TRY_COMPILE(
-              [#include <stdlib.h>
-               static void
-               foo(void) {
-               static ] $ax_tls_keyword [ int bar;
-               exit(1);
-               }],
-               [],
+          [AC_TRY_LINK(
+               [$ax_tls_keyword int foo;],
+               [++foo;],
                [ac_cv_tls=$ax_tls_keyword ; break],
-               ac_cv_tls=none
+               [ac_cv_tls=none]
            )])
     done
   ])

diff --git a/configure.ac b/configure.ac
index 4d0c7f4131dfcaadcaa679e70c4bde421de0704f..1d04062f48f41d32022cb2adeec70c1628b95cea 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -28,7 +28,20 @@ AH_TEMPLATE([CONFIG_RCU_COMPAT_ARCH], [Compatibility mode for i386 which lacks c
 AH_TEMPLATE([CONFIG_RCU_ARM_HAVE_DMB], [Use the dmb instruction if available for use on ARM.])
 AH_TEMPLATE([CONFIG_RCU_TLS], [TLS provided by the compiler.])
 
-AX_TLS(AC_DEFINE_UNQUOTED([CONFIG_RCU_TLS], $ac_cv_tls), [:])
+# Allow overriding storage used for TLS variables.
+AC_ARG_ENABLE([compiler-tls],
+       AS_HELP_STRING([--disable-compiler-tls], [Use pthread_getspecific() to emulate Thread Local Storage (TLS) variables.]),
+       [def_compiler_tls=$enableval],
+       [def_compiler_tls="yes"])
+
+# 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)])
 
 # Checks for programs.
 AC_PROG_CC
@@ -252,3 +265,9 @@ AS_IF([test "x$def_smp_support" = "xyes"],[
 ],[
        AS_ECHO("SMP support disabled.")
 ])
+
+AS_IF([test "x$def_tls_detect" = "x"],[
+       AS_ECHO("Thread Local Storage (TLS): pthread_getspecific().")
+],[
+       AS_ECHO("Thread Local Storage (TLS): $def_tls_detect.")
+])