config/tls.m4

   1 dnl Check whether the target supports TLS.
   2 AC_DEFUN([GCC_CHECK_TLS], [
   3   GCC_ENABLE(tls, yes, [], [Use thread-local storage])
   4   AC_CACHE_CHECK([whether the target supports thread-local storage],
   5                  have_tls, [
   6     AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
   7       [dnl If the test case passed with dynamic linking, try again with
   8        dnl static linking, but only if static linking is supported (not
   9        dnl on Solaris 10).  This fails with some older Red Hat releases.
  10       chktls_save_LDFLAGS="$LDFLAGS"
  11       LDFLAGS="-static $LDFLAGS"
  12       AC_LINK_IFELSE([int main() { return 0; }],
  13         AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
  14                       [have_tls=yes], [have_tls=no],[]),
  15         [have_tls=yes])
  16       LDFLAGS="$chktls_save_LDFLAGS"
  17       if test $have_tls = yes; then
  18         dnl So far, the binutils and the compiler support TLS.
  19         dnl Also check whether the libc supports TLS, i.e. whether a variable
  20         dnl with __thread linkage has a different address in different threads.
  21         dnl First, find the thread_CFLAGS necessary for linking a program that
  22         dnl calls pthread_create.
  23         chktls_save_CFLAGS="$CFLAGS"
  24         thread_CFLAGS=failed
  25         for flag in '' '-pthread' '-lpthread'; do
  26           CFLAGS="$flag $chktls_save_CFLAGS"
  27           AC_LINK_IFELSE(
  28             [AC_LANG_PROGRAM(
  29                [#include <pthread.h>
  30                 void *g(void *d) { return NULL; }],
  31                [pthread_t t; pthread_create(&t,NULL,g,NULL);])],
  32             [thread_CFLAGS="$flag"])
  33           if test "X$thread_CFLAGS" != Xfailed; then
  34             break
  35           fi
  36         done
  37         CFLAGS="$chktls_save_CFLAGS"
  38         if test "X$thread_CFLAGS" != Xfailed; then
  39           CFLAGS="$thread_CFLAGS $chktls_save_CFLAGS"
  40           AC_RUN_IFELSE(
  41             [AC_LANG_PROGRAM(
  42                [#include <pthread.h>
  43                 __thread int a;
  44                 static int *a_in_other_thread;
  45                 static void *
  46                 thread_func (void *arg)
  47                 {
  48                   a_in_other_thread = &a;
  49                   return (void *)0;
  50                 }],
  51                [pthread_t thread;
  52                 void *thread_retval;
  53                 int *a_in_main_thread;
  54                 if (pthread_create (&thread, (pthread_attr_t *)0,
  55                                     thread_func, (void *)0))
  56                   return 0;
  57                 a_in_main_thread = &a;
  58                 if (pthread_join (thread, &thread_retval))
  59                   return 0;
  60                 return (a_in_other_thread == a_in_main_thread);])],
  61              [have_tls=yes], [have_tls=no], [])
  62           CFLAGS="$chktls_save_CFLAGS"
  63         fi
  64       fi],
  65       [have_tls=no],
  66       [dnl This is the cross-compiling case. Assume libc supports TLS if the
  67        dnl binutils and the compiler do.
  68        AC_LINK_IFELSE([__thread int a; int b; int main() { return a = b; }],
  69                       [have_tls=yes], [have_tls=no])
  70       ]
  71     )])
  72   if test "$enable_tls $have_tls" = "yes yes"; then
  73     AC_DEFINE(HAVE_TLS, 1,
  74               [Define to 1 if the target supports thread-local storage.])
  75   fi])