[libc++] Generalize the customizeable assertion handler

[ldionne]

Summary

Instead of taking a fixed set of arguments, use variadics so that
we can pass arbitrary arguments to the handler. This is the first
step towards using the handler to handle other non-assertion-related
failures, like std::unreachable and an exception being thrown in
-fno-exceptions mode, which would improve user experience by including
additional information in crashes (right now, we call abort() without
additional information).

[ldionne]

I'd like to get this change (and the followups) into LLVM 15, since those will impact the ABI, so it's much simpler to do before we've actually released the current (pre-this-patch) ABI. I may have to cherry-pick this on release/15.x.

[philnik]

LGTM % nits.

libcxx/src/assert.cpp

28–61

Why are you __uglyfying the names inside the .cpp?

38–39

Duplicate comment?

[ldionne]

Address CI failures and comments.

[ldionne]

libcxx/src/assert.cpp

28–61

I'm used to it, I guess.

[ldionne]

Shipping, the CI issue is something else which I am fixing separately.

[thakis]

libcxx/src/assert.cpp

53

This requires API level 21. We still build for older Api levels in some configs. Can this use something that works in older Api levels?

(Also, this looks a bit unrelated to making the handler vararg?)

[thakis]

libcxx/src/assert.cpp

53

Ping?

[ldionne]

libcxx/src/assert.cpp

53

Thanks for the heads up, see D130708.

libcxx/docs/UsingLibcxx.rst

 platform where the compiled library is sufficiently recent. However, users can also override that
 assertion handler with their own, which can be useful to provide custom behavior, or when deploying
 to older platforms where the default assertion handler isn't available.
 
 Replacing the default assertion handler is done by defining the following function:
 
 .. code-block:: cpp
 
-  void __libcpp_assertion_handler(char const* file, int line, char const* expression, char const* message)
+  void __libcpp_assertion_handler(char const* format, ...)
 
 This mechanism is similar to how one can replace the default definition of ``operator new``
 and ``operator delete``. For example:
 
 .. code-block:: cpp
 
   // In HelloWorldHandler.cpp
   #include <version> // must include any libc++ header before defining the handler (C compatibility headers excluded)
 
-  void std::__libcpp_assertion_handler(char const* file, int line, char const* expression, char const* message) {
-    std::printf("Assertion %s failed at %s:%d, more info: %s", expression, file, line, message);
+  void std::__libcpp_assertion_handler(char const* format, ...) {
+    va_list list;
+    va_start(list, format);
+    std::vfprintf(stderr, format, list);
+    va_end(list);
+
     std::abort();
   }
 
   // In HelloWorld.cpp
   #include <vector>
 
   int main() {
     std::vector<int> v;

libcxx/include/__assert

 #if _LIBCPP_ENABLE_ASSERTIONS != 0 && _LIBCPP_ENABLE_ASSERTIONS != 1
 # error "_LIBCPP_ENABLE_ASSERTIONS must be set to 0 or 1"
 #endif
 
 #if _LIBCPP_ENABLE_ASSERTIONS
 # define _LIBCPP_ASSERT(expression, message)                                        \
     (__builtin_expect(static_cast<bool>(expression), 1) ?                           \
       (void)0 :                                                                     \
-      ::std::__libcpp_assertion_handler(__FILE__, __LINE__, #expression, message))
+      ::std::__libcpp_assertion_handler("%s:%d: assertion %s failed: %s", __FILE__, __LINE__, #expression, message))
 #elif !defined(_LIBCPP_ASSERTIONS_DISABLE_ASSUME) && __has_builtin(__builtin_assume)
 # define _LIBCPP_ASSERT(expression, message)                                        \
     (_LIBCPP_DIAGNOSTIC_PUSH                                                        \
     _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wassume")                                    \
     __builtin_assume(static_cast<bool>(expression))                                 \
     _LIBCPP_DIAGNOSTIC_POP)
 #else
 # define _LIBCPP_ASSERT(expression, message) ((void)0)
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-_LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_AVAILABILITY_ASSERTION_HANDLER
-void __libcpp_assertion_handler(char const* __file, int __line, char const* __expression, char const* __message);
+_LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_AVAILABILITY_ASSERTION_HANDLER _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2)
+void __libcpp_assertion_handler(const char *__format, ...);
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___ASSERT

libcxx/lib/abi/CHANGELOG.TXT

* f1c30135417f - [libc++] Drop the legacy debug mode symbols by default
   Symbol removed: _ZNSt3__18__c_nodeD2Ev
   Symbol removed: _ZNSt3__18__get_dbEv
   Symbol removed: _ZNSt3__18__i_nodeD1Ev
   Symbol removed: _ZNSt3__18__i_nodeD2Ev
   Symbol removed: _ZTINSt3__18__c_nodeE
   Symbol removed: _ZTSNSt3__18__c_nodeE
   Symbol removed: _ZTVNSt3__18__c_nodeE
 
-* b0fd9497af6d - [libc++] Add a lightweight overridable assertion handler
+* b0fd9497af6d and XXXXXXX - [libc++] Add a lightweight overridable assertion handler
 
   This patch adds a lightweight assertion handler mechanism that can be
   overriden at link-time in a fashion similar to `operator new`. A default
   assertion handler is provided in the shared library, hence the added
   symbol.
 
   All platforms
   -------------
-  Symbol added: _ZNSt3__126__libcpp_assertion_handlerEPKciS1_S1_
+  Symbol added: _ZNSt3__126__libcpp_assertion_handlerEPKcz
 
 ------------
 Version 14.0
 ------------
 
 * abb5dd6e99df - [libc++] `to_chars` for floating point.
 
   This commit added the `to_chars` implementation for floating point values.

libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist

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libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist

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 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIaaEEPaEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIccEEPcEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIddEEPdEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIeeEEPeEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIffEEPfEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIhhEEPhEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIiiEEPiEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIjjEEPjEEbT0_S5_T_', 'type': 'FUNC'}

 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIcNS_11char_traitsIcEEED0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIcNS_11char_traitsIcEEED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIwNS_11char_traitsIwEEED0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIwNS_11char_traitsIwEEED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__114basic_iostreamIcNS_11char_traitsIcEEED0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__114basic_iostreamIcNS_11char_traitsIcEEED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__19strstreamD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__19strstreamD1Ev', 'type': 'FUNC'}
 No newline at end of file

libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist

 {'is_defined': True, 'name': '_ZNSt3__121undeclare_no_pointersEPcm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_allEPVKNS_17__cxx_atomic_implIiNS_22__cxx_atomic_base_implIiEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_allEPVKv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__123__cxx_atomic_notify_oneEPVKNS_17__cxx_atomic_implIiNS_22__cxx_atomic_base_implIiEEEE', 'type': 'FUNC'}
 {'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__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__126__libcpp_assertion_handlerEPKciS1_S1_', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__126__libcpp_assertion_handlerEPKcz', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIaaEEPaEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIccEEPcEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIddEEPdEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIeeEEPeEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIffEEPfEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIhhEEPhEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIiiEEPiEEbT0_S5_T_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIjjEEPjEEbT0_S5_T_', 'type': 'FUNC'}

 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIcNS_11char_traitsIcEEED0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIcNS_11char_traitsIcEEED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIwNS_11char_traitsIwEEED0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__113basic_ostreamIwNS_11char_traitsIwEEED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__114basic_iostreamIcNS_11char_traitsIcEEED0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__114basic_iostreamIcNS_11char_traitsIcEEED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__19strstreamD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZTv0_n24_NSt3__19strstreamD1Ev', 'type': 'FUNC'}
 No newline at end of file

libcxx/src/assert.cpp

 //===----------------------------------------------------------------------===//
 //
 // 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 <__assert>
 #include <__config>
+#include <cstdarg>
 #include <cstdio>
 #include <cstdlib>
 
+#ifdef __BIONIC__
+#  include <android/api-level.h>
+#  include <syslog.h>
+extern "C" void android_set_abort_message(const char* msg);
+#endif
+
+#if defined(__APPLE__) && __has_include(<CrashReporterClient.h>)
+#  include <CrashReporterClient.h>
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 _LIBCPP_WEAK
-void __libcpp_assertion_handler(char const* __file, int __line, char const* __expression, char const* __message) {
-  std::fprintf(stderr, "%s:%d: libc++ assertion '%s' failed. %s\n", __file, __line, __expression, __message);
+void __libcpp_assertion_handler(char const* format, ...) {
+  // Write message to stderr. We do this before formatting into a
+  // buffer so that we still get some information out if that fails.
+  {
+    va_list list;
+    va_start(list, format);
+    std::vfprintf(stderr, format, list);
+    va_end(list);
+  }
+
+  // Format the arguments into an allocated buffer for CrashReport & friends.
+  // We leak the buffer on purpose, since we're about to abort() anyway.
+  char* buffer; (void)buffer;
+  va_list list;
+  va_start(list, format);
+
+#if defined(__APPLE__) && __has_include(<CrashReporterClient.h>)
+  // Note that we should technically synchronize accesses here (by e.g. taking a lock),
+  // however concretely we're only setting a pointer, so the likelihood of a race here
+  // is low.
+  vasprintf(&buffer, format, list);
+  CRSetCrashLogMessage(buffer);
+#elif defined(__BIONIC__)
+  // Show error in tombstone.
+  vasprintf(&buffer, format, list);
+  android_set_abort_message(buffer);
+
+  // Show error in logcat.
+  openlog("libc++", 0, 0);
+  syslog(LOG_CRIT, "%s", buffer);
+  closelog();
+#endif
+  va_end(list);
+
   std::abort();
 }
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/test/libcxx/assertions/customize_handler.backdeployment.pass.cpp

 // Note that this test isn't really different from customize_handler.pass.cpp when
 // run outside of back-deployment scenarios, but we still run it all the time.
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_ASSERTIONS=1 -D_LIBCPP_AVAILABILITY_CUSTOM_ASSERTION_HANDLER_PROVIDED
 
 #include <cassert>
 
 bool handler_called = false;
-void std::__libcpp_assertion_handler(char const*, int, char const*, char const*) {
+void std::__libcpp_assertion_handler(char const*, ...) {
   handler_called = true;
 }
 
 int main(int, char**) {
   _LIBCPP_ASSERT(false, "message");
   assert(handler_called);
   return 0;
 }

libcxx/test/libcxx/assertions/customize_handler.pass.cpp

 
 // We flag uses of the assertion handler in older dylibs at compile-time to avoid runtime
 // failures when back-deploying.
 // XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0|12.0}}
 
 #include <cassert>
 
 bool handler_called = false;
-void std::__libcpp_assertion_handler(char const*, int, char const*, char const*) {
+void std::__libcpp_assertion_handler(char const*, ...) {
   handler_called = true;
 }
 
 int main(int, char**) {
   _LIBCPP_ASSERT(false, "message");
   assert(handler_called);
   return 0;
 }

libcxx/test/libcxx/assertions/debug_mode_compatibility.pass.cpp

 
 // We flag uses of the assertion handler in older dylibs at compile-time to avoid runtime
 // failures when back-deploying.
 // XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0|12.0}}
 
 #include <cassert>
 
 bool handler_called = false;
-void std::__libcpp_assertion_handler(char const*, int, char const*, char const*) {
+void std::__libcpp_assertion_handler(char const*, ...) {
   handler_called = true;
 }
 
 int main(int, char**) {
   _LIBCPP_ASSERT(false, "message");
   assert(handler_called);
   return 0;
 }

libcxx/test/support/check_assertion.h

 //===----------------------------------------------------------------------===//
 //
 // 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 TEST_SUPPORT_CHECK_ASSERTION_H
 #define TEST_SUPPORT_CHECK_ASSERTION_H
 
 #include <cassert>
+#include <cstdarg>
 #include <cstddef>
 #include <cstdio>
 #include <cstdlib>
 #include <string>
 #include <string_view>
 #include <utility>
 
 #include <unistd.h>
private:
   pid_t child_pid_ = -1;
   int exit_code_ = -1;
   int stdout_pipe_fd_[2];
   int stderr_pipe_fd_[2];
   std::string stdout_from_child_;
   std::string stderr_from_child_;
 };
 
-void std::__libcpp_assertion_handler(char const* file, int line, char const* /*expression*/, char const* message) {
+void std::__libcpp_assertion_handler(char const* format, ...) {
   assert(!GlobalMatcher().empty());
+
+  // Extract information from the error message. This has to stay synchronized with
+  // how we format assertions in the library.
+  va_list list;
+  va_start(list, format);
+  char const* file = va_arg(list, char const*);
+  int line = va_arg(list, int);
+  char const* expression = va_arg(list, char const*); (void)expression;
+  char const* message = va_arg(list, char const*);
+  va_end(list);
+
   if (GlobalMatcher().Matches(file, line, message)) {
     std::exit(DeathTest::RK_MatchFound);
   }
   std::exit(DeathTest::RK_MatchFailure);
 }
 
 template <class Func>
 inline bool ExpectDeath(const char* stmt, Func&& func, AssertionInfoMatcher Matcher) {