+ AC_LINK_IFELSE([AC_LANG_SOURCE([int main() { return 0; }])],
+ [AC_RUN_IFELSE([AC_LANG_SOURCE([__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([AC_LANG_SOURCE([__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 $CFLAGS"
+ dnl If -shared works, test if TLS works in a shared library.
+ AC_LINK_IFELSE([AC_LANG_SOURCE([int f() { return 0; }])],
+ [AC_LINK_IFELSE([AC_LANG_SOURCE([__thread int a; int b; int f() { return a = b; }])],
+ [gcc_cv_have_tls=yes],
+ [gcc_cv_have_tls=no])],
+ [gcc_cv_have_tls=yes])
+ CFLAGS="$chktls_save_CFLAGS"
+ LDFLAGS="$chktls_save_LDFLAGS"], [gcc_cv_have_tls=no])
+ ]