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, 4 insertions, 2 deletions

diff --git a/misc.c b/misc.c
index bcf4c72d..7e0bef75 100644
--- a/misc.c
+++ b/misc.c
@@ -1258,7 +1258,8 @@ GC_API void GC_CALL GC_init(void)
 #   endif
 #   ifndef GC_DISABLE_INCREMENTAL
       if (GC_incremental || 0 != GETENV("GC_ENABLE_INCREMENTAL")) {
-#       if defined(CHECKSUMS) || defined(SMALL_CONFIG)
+#       if defined(BASE_ATOMIC_OPS_EMULATED) || defined(CHECKSUMS) \
+           || defined(SMALL_CONFIG)
           /* TODO: Implement CHECKSUMS for manual VDB. */
 #       else
           if (manual_vdb_allowed) {
@@ -1403,7 +1404,8 @@ GC_API void GC_CALL GC_enable_incremental(void)
           GC_init();
           LOCK();
         } else {
-#         if !defined(CHECKSUMS) && !defined(SMALL_CONFIG)
+#         if !defined(BASE_ATOMIC_OPS_EMULATED) && !defined(CHECKSUMS) \
+             && !defined(SMALL_CONFIG)
             if (manual_vdb_allowed) {
               GC_manual_vdb = TRUE;
               GC_incremental = TRUE;