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       save_LDFLAGS="$LDFLAGS"
  11       LDFLAGS="-static $LDFLAGS"
  12       AC_LINK_IFELSE([int main() { return 0; }],
  13         AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
  14                       [have_tls=yes], [have_tls=no],[]),
  15         [have_tls=yes])
  16       LDFLAGS="$save_LDFLAGS"],
  17       [have_tls=no],
  18       [AC_LINK_IFELSE([__thread int a; int b; int main() { return a = b; }],
  19         [have_tls=yes], [have_tls=no])]
  20     )])
  21   if test "$enable_tls $have_tls" = "yes yes"; then
  22     AC_DEFINE(HAVE_TLS, 1,
  23               [Define to 1 if the target supports thread-local storage.])
  24   fi])