diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 34
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong_explicit.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong_explicit.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong_explicit.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong_explicit.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 38
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 34
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak_explicit.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak_explicit.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak_explicit.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_weak_explicit.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 38
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... fails assertion line 31
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange_explicit.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange_explicit.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange_explicit.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_exchange_explicit.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 32
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_init.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_init.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_init.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_init.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 36
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_is_lock_free.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_is_lock_free.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_is_lock_free.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_is_lock_free.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 
 // <atomic>
 
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 35
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load_explicit.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load_explicit.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load_explicit.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_load_explicit.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 //  ... assertion fails line 31
 
 // <atomic>
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 
 // <atomic>
 
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store_explicit.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store_explicit.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store_explicit.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_store_explicit.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 
 // <atomic>
 
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_wait.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_wait.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_wait.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_wait.pass.cpp
@@ -17,6 +17,7 @@
 // XFAIL: with_system_cxx_lib=macosx10.11
 // XFAIL: with_system_cxx_lib=macosx10.10
 // XFAIL: with_system_cxx_lib=macosx10.9
+// XFAIL: freebsd && !freebsd-atomic-libcalls
 
 // <atomic>
 
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -115,5 +115,15 @@
   Feature(name='darwin', when=lambda cfg: '__APPLE__' in compilerMacros(cfg)),
   Feature(name='windows', when=lambda cfg: '_WIN32' in compilerMacros(cfg)),
   Feature(name='linux', when=lambda cfg: '__linux__' in compilerMacros(cfg)),
+  Feature(name='freebsd', when=lambda cfg: '__FreeBSD__' in compilerMacros(cfg)),
   Feature(name='netbsd', when=lambda cfg: '__NetBSD__' in compilerMacros(cfg))
 ]
+
+def _freebsdHasAtomicLibcalls(cfg):
+  freebsdVersion = int(compilerMacros(cfg, '-include sys/param.h').get('__FreeBSD_version', "0"))
+  # __atomic_* libcalls were added in SVN r364753 (__FreeBSD_version 1300113).
+  # On the stable/12 branch __atomic_* is available after 1202501.
+  return freebsdVersion >= 1300113 or (freebsdVersion < 1300000 and freebsdVersion >= 1202501)
+
+# Some atomic tests require __atomic_* libcalls, but older FreeBSD versions do not provide these functions.
+DEFAULT_FEATURES.append(Feature(name='freebsd-atomic-libcalls', when=_freebsdHasAtomicLibcalls))