source: trunk/libs/newlib/src/config/tls.m4 @ 499

dnl Check whether the target supports TLS.
AC_DEFUN([GCC_CHECK_TLS], [
  AC_REQUIRE([AC_CANONICAL_HOST])
  GCC_ENABLE(tls, yes, [], [Use thread-local storage])
  AC_CACHE_CHECK([whether the target supports thread-local storage],
                 gcc_cv_have_tls, [
    AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
      [dnl If the test case passed with dynamic linking, try again with
       dnl static linking, but only if static linking is supported (not
       dnl on Solaris 10).  This fails with some older Red Hat releases.
      chktls_save_LDFLAGS="$LDFLAGS"
      LDFLAGS="-static $LDFLAGS"
      AC_LINK_IFELSE([int main() { return 0; }],
        [AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
                       [gcc_cv_have_tls=yes], [gcc_cv_have_tls=no],[])],
        [gcc_cv_have_tls=yes])
      LDFLAGS="$chktls_save_LDFLAGS"
      if test $gcc_cv_have_tls = yes; then
        dnl So far, the binutils and the compiler support TLS.
        dnl Also check whether the libc supports TLS, i.e. whether a variable
        dnl with __thread linkage has a different address in different threads.
        dnl First, find the thread_CFLAGS necessary for linking a program that
        dnl calls pthread_create.
        chktls_save_CFLAGS="$CFLAGS"
        thread_CFLAGS=failed
        for flag in '' '-pthread' '-lpthread'; do
          CFLAGS="$flag $chktls_save_CFLAGS"
          AC_LINK_IFELSE(
            [AC_LANG_PROGRAM(
               [#include <pthread.h>
                void *g(void *d) { return NULL; }],
               [pthread_t t; pthread_create(&t,NULL,g,NULL);])],
            [thread_CFLAGS="$flag"])
          if test "X$thread_CFLAGS" != Xfailed; then
            break
          fi
        done
        CFLAGS="$chktls_save_CFLAGS"
        if test "X$thread_CFLAGS" != Xfailed; then
          CFLAGS="$thread_CFLAGS $chktls_save_CFLAGS"
          dnl Test for an old glibc bug that violated the __thread property.
          dnl Use volatile to ensure the compiler won't optimize away pointer
          dnl accesses it might otherwise assume to be redundant, or reorder 
          dnl them and reuse storage, which might lead to them pointing to
          dnl the same location.
          AC_RUN_IFELSE(
            [AC_LANG_PROGRAM(
               [#include <pthread.h>
                __thread int a;
                static int *volatile a_in_other_thread;
                static void *
                thread_func (void *arg)
                {
                  a_in_other_thread = &a;
                  return (void *)0;
                }],
               [pthread_t thread;
                void *thread_retval;
                int *volatile a_in_main_thread;
                a_in_main_thread = &a;
                if (pthread_create (&thread, (pthread_attr_t *)0,
                                    thread_func, (void *)0))
                  return 0;
                if (pthread_join (thread, &thread_retval))
                  return 0;
                return (a_in_other_thread == a_in_main_thread);])],
             [gcc_cv_have_tls=yes], [gcc_cv_have_tls=no], [])
          CFLAGS="$chktls_save_CFLAGS"
        fi
      fi],
      [gcc_cv_have_tls=no],
      [dnl This is the cross-compiling case. Assume libc supports TLS if the
       dnl binutils and the compiler do.
       AC_LINK_IFELSE([__thread int a; int b; int main() { return a = b; }],
         [chktls_save_LDFLAGS="$LDFLAGS"
          dnl Shared library options may depend on the host; this check
          dnl is only known to be needed for GNU/Linux.
          case $host in
            *-*-linux*)
              LDFLAGS="-shared -Wl,--no-undefined $LDFLAGS"
              ;;
          esac
          chktls_save_CFLAGS="$CFLAGS"
          CFLAGS="-fPIC $CFLAGS"
          dnl If -shared works, test if TLS works in a shared library.
          AC_LINK_IFELSE([int f() { return 0; }],
            [AC_LINK_IFELSE([__thread int a; int b; int f() { return a = b; }],
              [gcc_cv_have_tls=yes],
              [gcc_cv_have_tls=no])],
            [gcc_cv_have_tls=yes])
          CFLAGS="$chktls_save_CFLAGS"
          LDFLAGS="$chktls_save_LDFLAGS"], [gcc_cv_have_tls=no])
      ]
    )])
  if test "$enable_tls $gcc_cv_have_tls" = "yes yes"; then
    AC_DEFINE(HAVE_TLS, 1,
              [Define to 1 if the target supports thread-local storage.])
  fi])

dnl Check whether the target assembler supports TLS.
AC_DEFUN([GCC_CHECK_CC_TLS], [
  GCC_ENABLE(tls, yes, [], [Use thread-local storage])
  AC_CACHE_CHECK([whether the target assembler supports thread-local storage],
                 gcc_cv_have_cc_tls, [
    AC_COMPILE_IFELSE([__thread int a; int b; int main() { return a = b; }],
      [gcc_cv_have_cc_tls=yes], [gcc_cv_have_cc_tls=no])]
    )])
  if test "$enable_tls $gcc_cv_have_cc_tls" = "yes yes"; then
    AC_DEFINE(HAVE_CC_TLS, 1,
              [Define to 1 if the target assembler supports thread-local storage.])
  fi])

dnl Check whether TLS is emulated.
AC_DEFUN([GCC_CHECK_EMUTLS], [
  AC_CACHE_CHECK([whether the thread-local storage support is from emutls],
                 gcc_cv_use_emutls, [
    gcc_cv_use_emutls=no
    echo '__thread int a; int b; int main() { return a = b; }' > conftest.c
    if AC_TRY_COMMAND(${CC-cc} -Werror -S -o conftest.s conftest.c 1>&AS_MESSAGE_LOG_FD); then
      if grep __emutls_get_address conftest.s > /dev/null; then
        gcc_cv_use_emutls=yes
      fi
    fi
    rm -f conftest.*
    ])
  if test "$gcc_cv_use_emutls" = "yes" ; then
    AC_DEFINE(USE_EMUTLS, 1,
              [Define to 1 if the target use emutls for thread-local storage.])
  fi])