[libc++][hardening] Add an experimental function to log hardening errors (#149452)

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.

2 files changed, 32 insertions, 0 deletions

diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
index 97fe57a..f59fe0e 100644
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -309,6 +309,7 @@ add_custom_target(cxx DEPENDS ${LIBCXX_BUILD_TARGETS})
 # Build the experimental static library
 set(LIBCXX_EXPERIMENTAL_SOURCES
   experimental/keep.cpp
+  experimental/log_hardening_failure.cpp
   )
 
 if (LIBCXX_PSTL_BACKEND STREQUAL "libdispatch")
diff --git a/libcxx/src/experimental/log_hardening_failure.cpp b/libcxx/src/experimental/log_hardening_failure.cpp
new file mode 100644
index 0000000..f836c15
--- /dev/null
+++ b/libcxx/src/experimental/log_hardening_failure.cpp
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// 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>
+#endif // __BIONIC__
+
+_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);
+
+#if defined(__BIONIC__)
+  // 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