[libc++] Fix `std::atomic::wait` ulock wait UL_COMPARE_AND_WAIT64 (#92783)

in `atomic::wait`, when we call the platform wait ulock_wait , we are
using UL_COMPARE_AND_WAIT. But we should use UL_COMPARE_AND_WAIT64
instead as the address we are waiting for is a 64 bit integer.

fixes https://github.com/llvm/llvm-project/issues/85107

It is rather hard to test directly because in `atomic::wait`, before
calling into the platform wait, our c++ code has some poll logic which
checks the value not changing. Thus in this patch, the test is using the
internal function.

1 files changed, 32 insertions, 0 deletions

diff --git a/libcxx/test/libcxx/atomics/atomics.syn/wait.pass.cpp b/libcxx/test/libcxx/atomics/atomics.syn/wait.pass.cpp
new file mode 100644
index 0000000..f29dc6e
--- /dev/null
+++ b/libcxx/test/libcxx/atomics/atomics.syn/wait.pass.cpp
@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: no-threads
+// This bug was first fixed in LLVM 19
+// UNSUPPORTED: using-built-library-before-llvm-19
+// XFAIL: availability-synchronization_library-missing
+
+#include <atomic>
+#include <cassert>
+
+void test_85107() {
+  if constexpr (sizeof(std::__cxx_contention_t) == 8 && sizeof(long) > 4) {
+    // https://github.com/llvm/llvm-project/issues/85107
+    // [libc++] atomic_wait uses UL_COMPARE_AND_WAIT when it should use UL_COMPARE_AND_WAIT64 on Darwin
+    constexpr std::__cxx_contention_t old_val = 0;
+    constexpr std::__cxx_contention_t new_val = old_val + (1ll << 32);
+    std::__cxx_atomic_contention_t ct(new_val);
+    std::__libcpp_atomic_wait(&ct, old_val); // this will hang forever if the bug is present
+  }
+}
+
+int main(int, char**) {
+  test_85107();
+
+  return 0;
+}