[libc++][hardening] Introduce a dylib function to log hardening errors.

var-const · var-const · commit 74fc2ece44eb · 2025-07-17T22:58:07.000-07:00
Unlike `verbose_abort`, this function merely logs the error but does not
terminate execution. It is intended to make it possible to implement the
`observe` semantic for Hardening.
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
@@ -535,6 +535,7 @@ set(files
   __locale_dir/time.h
   __locale_dir/wbuffer_convert.h
   __locale_dir/wstring_convert.h
+  __log_hardening_failure
   __math/abs.h
   __math/copysign.h
   __math/error_functions.h
diff --git a/libcxx/include/__config b/libcxx/include/__config
@@ -207,6 +207,7 @@ _LIBCPP_HARDENING_MODE_DEBUG
 #  define _LIBCPP_HAS_EXPERIMENTAL_PSTL _LIBCPP_HAS_EXPERIMENTAL_LIBRARY
 #  define _LIBCPP_HAS_EXPERIMENTAL_TZDB _LIBCPP_HAS_EXPERIMENTAL_LIBRARY
 #  define _LIBCPP_HAS_EXPERIMENTAL_SYNCSTREAM _LIBCPP_HAS_EXPERIMENTAL_LIBRARY
+#  define _LIBCPP_HAS_EXPERIMENTAL_HARDENING_OBSERVE_SEMANTIC _LIBCPP_HAS_EXPERIMENTAL_LIBRARY
 
 #  if defined(__MVS__)
 #    include <features.h> // for __NATIVE_ASCII_F
diff --git a/libcxx/include/__configuration/availability.h b/libcxx/include/__configuration/availability.h
@@ -304,6 +304,11 @@
 #define _LIBCPP_AVAILABILITY_HAS_VERBOSE_ABORT _LIBCPP_INTRODUCED_IN_LLVM_15
 #define _LIBCPP_AVAILABILITY_VERBOSE_ABORT _LIBCPP_INTRODUCED_IN_LLVM_15_ATTRIBUTE
 
+// This controls whether the library provides a function to log errors without terminating the program (used in
+// particular by the `observe` assertion semantic).
+#define _LIBCPP_AVAILABILITY_HAS_LOG_HARDENING_FAILURE _LIBCPP_INTRODUCED_IN_LLVM_21
+#define _LIBCPP_AVAILABILITY_LOG_HARDENING_FAILURE _LIBCPP_INTRODUCED_IN_LLVM_21_ATTRIBUTE
+
 // This controls the availability of the C++17 std::pmr library,
 // which is implemented in large part in the built library.
 //
diff --git a/libcxx/include/__log_hardening_failure b/libcxx/include/__log_hardening_failure
@@ -0,0 +1,49 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___LOG_HARDENING_FAILURE
+#define _LIBCPP___LOG_HARDENING_FAILURE
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_HAS_EXPERIMENTAL_HARDENING_OBSERVE_SEMANTIC
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// This function should never be called directly from the code -- it should only be called through the
+// `_LIBCPP_LOG_HARDENING_FAILURE` macro.
+_LIBCPP_AVAILABILITY_LOG_HARDENING_FAILURE _LIBCPP_EXPORTED_FROM_ABI void
+__log_hardening_failure(const char* __message) _NOEXCEPT;
+
+// _LIBCPP_LOG_HARDENING_FAILURE(message)
+//
+// This macro is used to log an error without terminating the program (as is the case for hardening failures if the
+// `observe` assertion semantic is used).
+
+#  if !defined(_LIBCPP_LOG_HARDENING_FAILURE)
+
+#    if !_LIBCPP_AVAILABILITY_HAS_LOG_HARDENING_FAILURE
+// The decltype is there to suppress -Wunused warnings in this configuration.
+void __use(const char*);
+#      define _LIBCPP_LOG_HARDENING_FAILURE(__message) (decltype(::std::__use(__message))())
+#    else
+#      define _LIBCPP_LOG_HARDENING_FAILURE(__message) ::std::__log_hardening_failure(__message)
+#    endif
+
+#  endif // !defined(_LIBCPP_LOG_HARDENING_FAILURE)
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_EXPERIMENTAL_HARDENING_OBSERVE_SEMANTIC
+
+#endif // _LIBCPP___LOG_HARDENING_FAILURE
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
@@ -2353,6 +2353,9 @@ module std [system] {
     header "__std_mbstate_t.h"
     export *
   }
+  module log_hardening_failure {
+    header "__log_hardening_failure"
+  }
   module verbose_abort {
     header "__verbose_abort"
   }
diff --git a/libcxx/lib/abi/CHANGELOG.TXT b/libcxx/lib/abi/CHANGELOG.TXT
@@ -36,6 +36,14 @@ Version 21.0
   -------------
   Symbol added: _ZNSt3__113__hash_memoryEPKvm
 
+* [libc++][hardening] Introduce a dylib function to log hardening errors.
+
+  This patch added a function to log hardening failures to the dylib.
+
+  All platforms
+  -------------
+  Symbol added: _ZNSt3__123__log_hardening_failureEPKc
+
 ------------
 Version 20.0
 ------------
diff --git a/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1581,6 +1581,7 @@
 {'is_defined': True, 'name': '__ZNSt3__123__cxx_atomic_notify_oneEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIxNS_22__cxx_atomic_base_implIxEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__123__libcpp_atomic_monitorEPVKv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '__ZNSt3__123__log_hardening_failureEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__127__from_chars_floating_pointIdEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__127__from_chars_floating_pointIfEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1217,6 +1217,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk123__cxx_atomic_notify_oneEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIiNS_22__cxx_atomic_base_implIiEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk123__libcpp_atomic_monitorEPVKv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt6__ndk123__log_hardening_failureEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk127__from_chars_floating_pointIdEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk127__from_chars_floating_pointIfEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -569,6 +569,7 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_oneEPVKv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIiNS_22__cxx_atomic_base_implIiEEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__log_hardening_failureEPKc', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__131__arrive_barrier_algorithm_baseEPNS_24__barrier_algorithm_baseEh', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__132__destroy_barrier_algorithm_baseEPNS_24__barrier_algorithm_baseE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -569,6 +569,7 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_oneEPVKv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIlNS_22__cxx_atomic_base_implIlEEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__123__log_hardening_failureEPKc', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__131__arrive_barrier_algorithm_baseEPNS_24__barrier_algorithm_baseEh', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__132__destroy_barrier_algorithm_baseEPNS_24__barrier_algorithm_baseE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1580,6 +1580,7 @@
 {'is_defined': True, 'name': '__ZNSt3__123__cxx_atomic_notify_oneEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIxNS_22__cxx_atomic_base_implIxEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__123__libcpp_atomic_monitorEPVKv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '__ZNSt3__123__log_hardening_failureEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__127__from_chars_floating_pointEPKcS1_RdNS_12chars_formatE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__127__from_chars_floating_pointEPKcS1_RfNS_12chars_formatE', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1217,6 +1217,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk123__cxx_atomic_notify_oneEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIiNS_22__cxx_atomic_base_implIiEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk123__libcpp_atomic_monitorEPVKv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt6__ndk123__log_hardening_failureEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk127__from_chars_floating_pointIdEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk127__from_chars_floating_pointIfEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1231,6 +1231,7 @@
 {'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_oneEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIlNS_22__cxx_atomic_base_implIlEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__123__log_hardening_failureEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__from_chars_floating_pointIdEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__from_chars_floating_pointIfEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1229,6 +1229,7 @@
 {'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_oneEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIiNS_22__cxx_atomic_base_implIiEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__123__log_hardening_failureEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__from_chars_floating_pointIdEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__from_chars_floating_pointIfEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
@@ -1200,6 +1200,7 @@
 {'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_oneEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKNS_17__cxx_atomic_implIiNS_22__cxx_atomic_base_implIiEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__libcpp_atomic_monitorEPVKv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__123__log_hardening_failureEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__from_chars_floating_pointIdEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__from_chars_floating_pointIfEENS_19__from_chars_resultIT_EEPKcS5_NS_12chars_formatE', 'type': 'FUNC'}
diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
@@ -30,6 +30,7 @@ set(LIBCXX_SOURCES
   include/ryu/ryu.h
   include/to_chars_floating_point.h
   include/from_chars_floating_point.h
+  log_hardening_failure.cpp
   memory.cpp
   memory_resource.cpp
   new_handler.cpp
diff --git a/libcxx/src/log_hardening_failure.cpp b/libcxx/src/log_hardening_failure.cpp
@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <__config>
+#include <__log_hardening_failure>
+#include <cstdio>
+
+#ifdef __BIONIC__
+#  include <syslog.h>
+extern "C" void android_set_abort_message(const char* msg);
+#endif // __BIONIC__
+
+#if defined(__APPLE__) && __has_include(<os/reason_private.h>)
+#  include <TargetConditionals.h>
+#  include <os/reason_private.h>
+#endif
+
+#if _LIBCPP_HAS_EXPERIMENTAL_HARDENING_OBSERVE_SEMANTIC
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+void __log_hardening_failure(const char* message) noexcept {
+  // Always log the message to `stderr` in case the platform-specific system calls fail.
+  std::fputs(message, stderr);
+
+  // On Apple platforms, use the `os_fault_with_payload` OS function that simulates a crash.
+#  if defined(__APPLE__) && __has_include(<os/reason_private.h>) && !TARGET_OS_SIMULATOR
+  os_fault_with_payload(
+      /*reason_namespace=*/OS_REASON_SECURITY,
+      /*reason_code=*/0,
+      /*payload=*/nullptr,
+      /*payload_size=*/0,
+      /*reason_string=*/message,
+      /*reason_flags=*/0);
+
+#  elif defined(__BIONIC__)
+  // Show error in tombstone.
+  android_set_abort_message(message);
+
+  // Show error in logcat. The latter two arguments are ignored on Android.
+  openlog("libc++", 0, 0);
+  syslog(LOG_CRIT, "%s", message);
+  closelog();
+#  endif
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_EXPERIMENTAL_HARDENING_OBSERVE_SEMANTIC
diff --git a/libcxx/test/libcxx/assertions/log_hardening_failure.pass.cpp b/libcxx/test/libcxx/assertions/log_hardening_failure.pass.cpp
@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// Basic smoke test for `__log_hardening_failure`.
+//
+// UNSUPPORTED: libcpp-has-no-experimental-hardening-observe-semantic
+// XFAIL: availability-log_hardening_failure-missing
+// UNSUPPORTED: FROZEN-CXX03-HEADERS-FIXME
+
+#include <__log_hardening_failure>
+
+#include "test_macros.h"
+
+ASSERT_NOEXCEPT(std::__log_hardening_failure(""));
+
+int main(int, char**) {
+  std::__log_hardening_failure("Some message");
+  // It's difficult to properly test platform-specific logging behavior of the function; just make sure it exists and
+  // can be called at runtime.
+
+  return 0;
+}
diff --git a/libcxx/test/libcxx/experimental/fexperimental-library.compile.pass.cpp b/libcxx/test/libcxx/experimental/fexperimental-library.compile.pass.cpp
@@ -29,3 +29,7 @@
 #if !_LIBCPP_HAS_EXPERIMENTAL_SYNCSTREAM
 #  error "-fexperimental-library should enable the syncstream header"
 #endif
+
+#if !_LIBCPP_HAS_EXPERIMENTAL_HARDENING_OBSERVE_SEMANTIC
+#  error "-fexperimental-library should enable the Hardening observe semantic"
+#endif
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
@@ -926,4 +926,12 @@ def check_gdb(cfg):
             cfg.available_features,
         ),
     ),
+    # Tests that require __log_hardening_failure support in the built library
+    Feature(
+        name="availability-log_hardening_failure-missing",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "!libcpp-has-no-availability-markup && (stdlib=apple-libc++ && !_target-has-llvm-21)",
+            cfg.available_features,
+        ),
+    ),
 ]
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
@@ -361,6 +361,7 @@ def getSuitableClangTidy(cfg):
             AddFeature("libcpp-has-no-incomplete-pstl"),
             AddFeature("libcpp-has-no-experimental-tzdb"),
             AddFeature("libcpp-has-no-experimental-syncstream"),
+            AddFeature("libcpp-has-no-experimental-hardening-observe-semantic"),
         ],
     ),
     # TODO: This can be improved once we use a version of GoogleBenchmark that supports the dry-run mode.

Original file line number	Diff line number	Diff line change
`@@ -2353,6 +2353,9 @@ module std [system] {`
`2353`	`2353`	`header "__std_mbstate_t.h"`
`2354`	`2354`	`export *`
`2355`	`2355`	`}`
	`2356`	`+ module log_hardening_failure {`
	`2357`	`+ header "__log_hardening_failure"`
	`2358`	`+ }`
`2356`	`2359`	`module verbose_abort {`
`2357`	`2360`	`header "__verbose_abort"`
`2358`	`2361`	`}`