[libcxx-commits] [libcxx] [libc++][hardening] Rework how the assertion handler can be overridden. (PR #77883)

[Mark de Wever via libcxx-commits]

================
@@ -69,6 +69,13 @@ if (NOT "${LIBCXX_HARDENING_MODE}" IN_LIST LIBCXX_SUPPORTED_HARDENING_MODES)
   message(FATAL_ERROR
     "Unsupported hardening mode: '${LIBCXX_HARDENING_MODE}'. Supported values are ${LIBCXX_SUPPORTED_HARDENING_MODES}.")
 endif()
+set(LIBCXX_ASSERTION_HANDLER_FILE
+  "${CMAKE_CURRENT_SOURCE_DIR}/vendor/llvm/default_assertion_handler.in"
+  CACHE STRING
+  "Specify the path to a header that contains a custom implementation of the
+   assertion handler that gets invoked when a hardening assertion fails. If
+   provided, the contents of this header will get injected into the library code
+   and override the default assertion handler.")
----------------
mordante wrote:

Looking at the code it feels somewhat clunky to me.
Why would the following approach not work?
```
set(LIBCXX_ASSERTION_HANDLER_FILE
  "${CMAKE_CURRENT_SOURCE_DIR}/vendor/llvm/default_assertion_handler.h"
  CACHE STRING
  "Specify the path to a header that contains a custom implementation of the
   assertion handler that gets invoked when a hardening assertion fails. If
   provided, this header will be used instead of libc++'s default handler.")
```

Then in `libcxx/include/CMakeLists.txt` you copy this file and no configuring at all.

The current approach would result in a file below or am I missing something.
```
// -*- C++ -*-
#ifndef _LIBCPP___ASSERTION_HANDLER
#define _LIBCPP___ASSERTION_HANDLER

#include <__config>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

// -*- C++ -*-
#include <__config>
#include <__verbose_abort>

#if _LIBCPP_HARDENING_MODE == _LIBCPP_HARDENING_MODE_DEBUG

#define _LIBCPP_ASSERTION_HANDLER(error_message, ...) ((void)error_message, _LIBCPP_VERBOSE_ABORT(__VA_ARGS__))

#else

// TODO(hardening): in production, trap rather than abort.
#define _LIBCPP_ASSERTION_HANDLER(error_message, ...) ((void)error_message, _LIBCPP_VERBOSE_ABORT(__VA_ARGS__))

#endif // #if _LIBCPP_HARDENING_MODE == _LIBCPP_HARDENING_MODE_DEBUG

#endif // _LIBCPP___ASSERTION_HANDLER
```

https://github.com/llvm/llvm-project/pull/77883