Fix deadlocks in write and suspend handlers if AO test-and-set is emulated

This could be tested with -D AO_USE_PTHREAD_DEFS passed to CFLAGS.

* configure.ac (AO_TRYLINK_CFLAGS): New variable.
* configure.ac [$with_libatomic_ops!=none && $need_atomic_ops_asm!=true]
(BASE_ATOMIC_OPS_EMULATED): New AC_DEFINE (defined in case of failure
of AC_TRY_LINK of a code snippet calling AO_test_and_set_acquire,
AO_CLEAR, AO_compiler_barrier, AO_store, AO_load, AO_char_store,
AO_char_load, AO_store_release, AO_load_acquire); use AO_TRYLINK_CFLAGS;
add comment.
* include/private/gcconfig.h [BASE_ATOMIC_OPS_EMULATED] (MPROTECT_VDB):
Undefine.
* mark.c [AO_CLEAR] (GC_noop6): Do not call AO_compiler_barrier() if
BASE_ATOMIC_OPS_EMULATED.
* misc.c [!GC_DISABLE_INCREMENTAL] (GC_init, GC_enable_incremental):
Do not set GC_manual_vdb if BASE_ATOMIC_OPS_EMULATED.
* pthread_stop_world.c [!GC_OPENBSD_UTHREADS && !NACL]
(ao_load_acquire_async, ao_load_async, ao_store_release_async,
ao_store_async): New macro; undefine it after the usage.
* pthread_stop_world.c [!GC_OPENBSD_UTHREADS && !NACL]
(GC_store_stack_ptr): Use ao_store_async() instead of AO_store().
* pthread_stop_world.c [!GC_OPENBSD_UTHREADS && !NACL]
(GC_suspend_handler_inner): Use ao_load[_acquire]_async() and
ao_store_release_async() instead of AO_load[_acquire]() and
AO_store_release(), respectively.
* pthread_stop_world.c [!GC_OPENBSD_UTHREADS && !NACL
&& GC_ENABLE_SUSPEND_THREAD] (suspend_self_inner): Use
ao_load_acquire_async() instead of AO_load_acquire().

1 files changed, 1 insertions, 1 deletions

diff --git a/mark.c b/mark.c
index 12d927fe..283aa2f1 100644
--- a/mark.c
+++ b/mark.c
@@ -40,7 +40,7 @@ void GC_noop6(word arg1 GC_ATTR_UNUSED, word arg2 GC_ATTR_UNUSED,
               word arg5 GC_ATTR_UNUSED, word arg6 GC_ATTR_UNUSED)
 {
   /* Avoid GC_noop6 calls to be optimized away. */
-# ifdef AO_CLEAR
+# if defined(AO_CLEAR) && !defined(BASE_ATOMIC_OPS_EMULATED)
     AO_compiler_barrier(); /* to serve as a special side-effect */
 # else
     GC_noop1(0);