Implement a throwing version of _LIBCPP_ASSERT.

This patch implements changes to allow _LIBCPP_ASSERT to throw on failure
instead of aborting. The main changes needed to do this are:

1. Change _LIBCPP_ASSERT to call a handler via a replacable function pointer
   instead of calling abort directly. Additionally this patch implements two
   handler functions, one which aborts and another that throws an exception.

2. Add _NOEXCEPT_DEBUG macro for disabling noexcept spec on function which
   contain _LIBCPP_ASSERT. This is required in order to prevent assertion
   failures throwing through a noexcept function. This macro has no effect
   unless _LIBCPP_DEBUG_USE_EXCEPTIONS is defined.

Having a non-aborting _LIBCPP_ASSERT is very important to allow sane testing of
debug mode. Currently we can only have one test case per file, since the test
case will cause the program to abort. Testing debug mode this way would require
thousands of test files, most of which would be 95% boiler plate. I don't think
this is a feasible strategy. Fortunately using a throwing debug handler solves
these issues.

Additionally this patch rewrites the documentation for debug mode.

llvm-svn: 290651

14 files changed, 389 insertions, 186 deletions

diff --git a/libcxx/docs/DesignDocs/DebugMode.rst b/libcxx/docs/DesignDocs/DebugMode.rst
new file mode 100644
index 00000000000..166c733e663
--- /dev/null
+++ b/libcxx/docs/DesignDocs/DebugMode.rst
@@ -0,0 +1,100 @@
+==========
+Debug Mode
+==========
+
+.. contents::
+   :local
+
+.. _using-debug-mode:
+
+Using Debug Mode
+================
+
+Libc++ provides a debug mode that enables assertions meant to detect incorrect
+usage of the standard library. By default these assertions are disabled but
+they can be enabled using the ``_LIBCPP_DEBUG`` macro.
+
+**_LIBCPP_DEBUG** Macro
+-----------------------
+
+**_LIBCPP_DEBUG**:
+  This macro is used to enable assertions and iterator debugging checks within
+  libc++. By default it is undefined.
+
+  **Values**: ``0``, ``1``
+
+  Defining ``_LIBCPP_DEBUG`` to ``0`` or greater enables most of libc++'s
+  assertions. Defining ``_LIBCPP_DEBUG`` to ``1`` enables "iterator debugging"
+  which provides additional assertions about the validity of iterators used by
+  the program.
+
+  Note that this option has no effect on libc++'s ABI
+
+**_LIBCPP_DEBUG_USE_EXCEPTIONS**:
+  When this macro is defined ``_LIBCPP_ASSERT`` failures throw
+  ``__libcpp_debug_exception`` instead of aborting. Additionally this macro
+  disables exception specifications on functions containing ``_LIBCPP_ASSERT``
+  checks. This allows assertion failures to correctly throw through these
+  functions.
+
+Handling Assertion Failures
+---------------------------
+
+When a debug assertion fails the assertion handler is called via the
+``std::__libcpp_debug_function`` function pointer. It is possible to override
+this function pointer using a different handler function. Libc++ provides two
+different assertion handlers, the default handler
+``std::__libcpp_abort_debug_handler`` which aborts the program, and
+``std::__libcpp_throw_debug_handler`` which throws an instance of
+``std::__libcpp_debug_exception``. Libc++ can be changed to use the throwing
+assertion handler as follows:
+
+.. code-block:: cpp
+
+  #define _LIBCPP_DEBUG 1
+  #include <string>
+  int main() {
+    std::__libcpp_debug_function = std::__libcpp_throw_debug_function;
+    try {
+      std::string::iterator bad_it;
+      std::string str("hello world");
+      str.insert(bad_it, '!'); // causes debug assertion
+    } catch (std::__libcpp_debug_exception const&) {
+      return EXIT_SUCCESS;
+    }
+    return EXIT_FAILURE;
+  }
+
+Debug Mode Checks
+=================
+
+Libc++'s debug mode offers two levels of checking. The first enables various
+precondition checks throughout libc++. The second additionally enables
+"iterator debugging" which checks the validity of iterators used by the program.
+
+Basic Checks
+============
+
+These checks are enabled when ``_LIBCPP_DEBUG`` is defined to either 0 or 1.
+
+The following checks are enabled by ``_LIBCPP_DEBUG``:
+
+  * FIXME: Update this list
+
+Iterator Debugging Checks
+=========================
+
+These checks are enabled when ``_LIBCPP_DEBUG`` is defined to 1.
+
+The following containers and STL classes support iterator debugging:
+
+  * ``std::string``
+  * ``std::vector<T>`` (``T != bool``)
+  * ``std::list``
+  * ``std::unordered_map``
+  * ``std::unordered_multimap``
+  * ``std::unordered_set``
+  * ``std::unordered_multiset``
+
+The remaining containers do not currently support iterator debugging.
+Patches welcome.
diff --git a/libcxx/docs/UsingLibcxx.rst b/libcxx/docs/UsingLibcxx.rst
index d6d1095b83c..de87c9c159d 100644
--- a/libcxx/docs/UsingLibcxx.rst
+++ b/libcxx/docs/UsingLibcxx.rst
@@ -133,17 +133,7 @@ or disable extended libc++ behavior, including enabling "debug mode" or
 thread safety annotations.
 
 **_LIBCPP_DEBUG**:
-  This macro is used to enable assertions and other debugging checks within
-  libc++. All debugging checks are disabled by default.
-
-  **Values**: ``0``, ``1``
-
-  Defining ``_LIBCPP_DEBUG`` to ``0`` or greater enables most of libc++'s
-  assertions. Defining ``_LIBCPP_DEBUG`` to ``1`` enables "iterator debugging"
-  which provides additional assertions about the validity of iterators used by
-  the program.
-
-  Note that this option has no effect on libc++'s ABI
+  See :ref:`using-debug-mode` for more information.
 
 **_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS**:
   This macro is used to enable -Wthread-safety annotations on libc++'s
diff --git a/libcxx/docs/index.rst b/libcxx/docs/index.rst
index 0cac7fe98a9..c62dfe83392 100644
--- a/libcxx/docs/index.rst
+++ b/libcxx/docs/index.rst
@@ -127,6 +127,7 @@ Design Documents
 .. toctree::
    :maxdepth: 1
 
+   DesignDocs/DebugMode
    DesignDocs/CapturingConfigInfo
    DesignDocs/ABIVersioning
    DesignDocs/VisibilityMacros
diff --git a/libcxx/include/__config b/libcxx/include/__config
index d6ab2345ca5..868914d9899 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -651,6 +651,17 @@ namespace std {
 #  define _NOEXCEPT_(x)
 #endif
 
+#if defined(_LIBCPP_DEBUG_USE_EXCEPTIONS)
+# if !defined(_LIBCPP_DEBUG)
+#   error cannot use _LIBCPP_DEBUG_USE_EXCEPTIONS unless _LIBCPP_DEBUG is defined
+# endif
+# define _NOEXCEPT_DEBUG noexcept(false)
+# define _NOEXCEPT_DEBUG_(x) noexcept(false)
+#else
+# define _NOEXCEPT_DEBUG _NOEXCEPT
+# define _NOEXCEPT_DEBUG_(x) _NOEXCEPT_(x)
+#endif
+
 #ifdef _LIBCPP_HAS_NO_UNICODE_CHARS
 typedef unsigned short char16_t;
 typedef unsigned int   char32_t;
diff --git a/libcxx/include/__debug b/libcxx/include/__debug
index e67dd086bf6..e3a5ec965b4 100644
--- a/libcxx/include/__debug
+++ b/libcxx/include/__debug
@@ -17,13 +17,16 @@
 #pragma GCC system_header
 #endif
 
-#if _LIBCPP_DEBUG_LEVEL >= 1
+#if _LIBCPP_DEBUG_LEVEL >= 1 || defined(_LIBCPP_BUILDING_LIBRARY)
 #   include <cstdlib>
 #   include <cstdio>
 #   include <cstddef>
-#   ifndef _LIBCPP_ASSERT
-#      define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : (_VSTD::fprintf(stderr, "%s\n", m), _VSTD::abort()))
-#   endif
+#   include <exception>
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 1 && !defined(_LIBCPP_ASSERT)
+# define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : \
+  _VSTD::__libcpp_debug_function(_VSTD::__libcpp_debug_info{__FILE__, __LINE__, #x, m}))
 #endif
 
 #if _LIBCPP_DEBUG_LEVEL >= 2
@@ -43,10 +46,61 @@
 #define _LIBCPP_DEBUG_MODE(...) ((void)0)
 #endif
 
-#if _LIBCPP_DEBUG_LEVEL >= 2
+#if _LIBCPP_DEBUG_LEVEL < 1
+class _LIBCPP_EXCEPTION_ABI __libcpp_debug_exception;
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+struct _LIBCPP_TYPE_VIS_ONLY __libcpp_debug_info {
+  const char* __file_;
+  int __line_;
+  const char* __pred_;
+  const char* __msg_;
+};
+
+/// __libcpp_debug_function_type - The type of the assertion failure handler.
+typedef void(*__libcpp_debug_function_type)(__libcpp_debug_info const&);
+
+/// __libcpp_debug_function - The handler function called when a _LIBCPP_ASSERT
+///    fails.
+extern __libcpp_debug_function_type __libcpp_debug_function;
+
+/// __libcpp_abort_debug_function - A debug handler that aborts when called.
+_LIBCPP_NORETURN _LIBCPP_FUNC_VIS
+void __libcpp_abort_debug_function(__libcpp_debug_info const&);
+
+/// __libcpp_throw_debug_function - A debug handler that throws
+///   an instance of __libcpp_debug_exception when called.
+ _LIBCPP_NORETURN _LIBCPP_FUNC_VIS
+void __libcpp_throw_debug_function(__libcpp_debug_info const&);
+
+/// __libcpp_set_debug_function - Set the debug handler to the specified
+///    function.
+_LIBCPP_FUNC_VIS
+bool __libcpp_set_debug_function(__libcpp_debug_function_type __func);
+
+// Setup the throwing debug handler during dynamic initialization.
+#if _LIBCPP_DEBUG_LEVEL >= 1 && defined(_LIBCPP_DEBUG_USE_EXCEPTIONS)
+static bool __init_dummy = __libcpp_set_debug_function(__libcpp_throw_debug_function);
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 1 || defined(_LIBCPP_BUILDING_LIBRARY)
+class _LIBCPP_EXCEPTION_ABI __libcpp_debug_exception : public exception {
+public:
+  __libcpp_debug_exception() _NOEXCEPT;
+  explicit __libcpp_debug_exception(__libcpp_debug_info const& __i);
+  __libcpp_debug_exception(__libcpp_debug_exception const&);
+  ~__libcpp_debug_exception() _NOEXCEPT;
+  const char* what() const _NOEXCEPT;
+private:
+  struct __libcpp_debug_exception_imp;
+  __libcpp_debug_exception_imp *__imp_;
+};
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 2 || defined(_LIBCPP_BUILDING_LIBRARY)
+
 struct _LIBCPP_TYPE_VIS __c_node;
 
 struct _LIBCPP_TYPE_VIS __i_node
@@ -115,7 +169,7 @@ struct _C_node
 };
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__dereferenceable(const void* __i) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -125,7 +179,7 @@ _C_node<_Cont>::__dereferenceable(const void* __i) const
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__decrementable(const void* __i) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -135,7 +189,7 @@ _C_node<_Cont>::__decrementable(const void* __i) const
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__addable(const void* __i, ptrdiff_t __n) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -145,7 +199,7 @@ _C_node<_Cont>::__addable(const void* __i, ptrdiff_t __n) const
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__subscriptable(const void* __i, ptrdiff_t __n) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -227,9 +281,9 @@ _LIBCPP_FUNC_VIS __libcpp_db* __get_db();
 _LIBCPP_FUNC_VIS const __libcpp_db* __get_const_db();
 
 
-_LIBCPP_END_NAMESPACE_STD
+#endif // _LIBCPP_DEBUG_LEVEL >= 2 || defined(_LIBCPP_BUILDING_LIBRARY)
 
-#endif
+_LIBCPP_END_NAMESPACE_STD
 
 #endif  // _LIBCPP_DEBUG_H
 
diff --git a/libcxx/lib/abi/CHANGELOG.TXT b/libcxx/lib/abi/CHANGELOG.TXT
index 488d7b76ea7..bccca2e085e 100644
--- a/libcxx/lib/abi/CHANGELOG.TXT
+++ b/libcxx/lib/abi/CHANGELOG.TXT
@@ -16,6 +16,28 @@ New entries should be added directly below the "Version" header.
 Version 4.0
 -----------
 
+* rTBD - Add _LIBCPP_ASSERT debug handling functions
+
+  All Platforms
+  -------------
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC2ERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionD1Ev
+  Symbol added: _ZTINSt3__124__libcpp_debug_exceptionE
+  Symbol added: _ZNSt3__129__libcpp_throw_debug_functionERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionD2Ev
+  Symbol added: _ZNSt3__129__libcpp_abort_debug_functionERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC2ERKS0_
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC1Ev
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC1ERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC2Ev
+  Symbol added: _ZTSNSt3__124__libcpp_debug_exceptionE
+  Symbol added: _ZNSt3__123__libcpp_debug_functionE
+  Symbol added: _ZNKSt3__124__libcpp_debug_exception4whatEv
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC1ERKS0_
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionD0Ev
+  Symbol added: _ZTVNSt3__124__libcpp_debug_exceptionE
+  Symbol added: _ZNSt3__127__libcpp_set_debug_functionEPFvRKNS_19__libcpp_debug_infoEE
+
 * r288547 - Implement C++17 <variant>
 
   All Platforms
diff --git a/libcxx/lib/abi/x86_64-apple-darwin16.0.0.abilist b/libcxx/lib/abi/x86_64-apple-darwin16.0.0.abilist
index 1b6acad008a..f7218a45fbb 100644
--- a/libcxx/lib/abi/x86_64-apple-darwin16.0.0.abilist
+++ b/libcxx/lib/abi/x86_64-apple-darwin16.0.0.abilist
@@ -262,6 +262,7 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__121__basic_string_commonILb1EE20__throw_out_of_rangeEv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__123__match_any_but_newlineIcE6__execERNS_7__stateIcEE'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__123__match_any_but_newlineIwE6__execERNS_7__stateIwEE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__124__libcpp_debug_exception4whatEv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__15ctypeIcE10do_tolowerEPcPKc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__15ctypeIcE10do_tolowerEc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__15ctypeIcE10do_toupperEPcPKc'}
@@ -1212,6 +1213,16 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121recursive_timed_mutexD1Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121recursive_timed_mutexD2Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121undeclare_no_pointersEPcm'}
+{'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__123__libcpp_debug_functionE', 'size': 0}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC1ERKNS_19__libcpp_debug_infoE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC1ERKS0_'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC1Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC2ERKNS_19__libcpp_debug_infoE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC2ERKS0_'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC2Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionD0Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionD1Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionD2Ev'}
 {'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__insertion_sort_incompleteIRNS_6__lessIaaEEPaEEbT0_S5_T_'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIccEEPcEEbT0_S5_T_'}
@@ -1228,6 +1239,9 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIwwEEPwEEbT0_S5_T_'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIxxEEPxEEbT0_S5_T_'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIyyEEPyEEbT0_S5_T_'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__libcpp_set_debug_functionEPFvRKNS_19__libcpp_debug_infoEE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__129__libcpp_abort_debug_functionERKNS_19__libcpp_debug_infoE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__129__libcpp_throw_debug_functionERKNS_19__libcpp_debug_infoE'}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__13cinE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__14cerrE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__14clogE', 'size': 0}
@@ -1651,6 +1665,7 @@
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__120__codecvt_utf8_utf16IwEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__120__time_get_c_storageIcEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__120__time_get_c_storageIwEE', 'size': 0}
+{'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__124__libcpp_debug_exceptionE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__15ctypeIcEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__15ctypeIwEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__16locale5facetE', 'size': 0}
@@ -2182,6 +2197,7 @@
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__120__codecvt_utf8_utf16IDiEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__120__codecvt_utf8_utf16IDsEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__120__codecvt_utf8_utf16IwEE', 'size': 0}
+{'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__124__libcpp_debug_exceptionE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__15ctypeIcEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__15ctypeIwEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__16locale5facetE', 'size': 0}
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.abilist
index a802ae46265..7282fa7b219 100644
--- a/libcxx/lib/abi/x86_64-unknown-linux-gnu.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-linux-gnu.abilist
@@ -252,6 +252,7 @@
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__121__basic_string_commonILb1EE20__throw_out_of_rangeEv'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__123__match_any_but_newlineIcE6__execERNS_7__stateIcEE'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__123__match_any_but_newlineIwE6__execERNS_7__stateIwEE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__124__libcpp_debug_exception4whatEv'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__15ctypeIcE10do_tolowerEPcPKc'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__15ctypeIcE10do_tolowerEc'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__15ctypeIcE10do_toupperEPcPKc'}
@@ -1136,6 +1137,16 @@
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__121recursive_timed_mutexD1Ev'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__121recursive_timed_mutexD2Ev'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__121undeclare_no_pointersEPcm'}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__123__libcpp_debug_functionE', 'size': 8}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC1ERKNS_19__libcpp_debug_infoE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC1ERKS0_'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC1Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC2ERKNS_19__libcpp_debug_infoE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC2ERKS0_'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC2Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionD0Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionD1Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionD2Ev'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__125__num_get_signed_integralIlEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__125__num_get_signed_integralIxEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE'}
@@ -1154,10 +1165,13 @@
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIwwEEPwEEbT0_S5_T_'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIxxEEPxEEbT0_S5_T_'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIyyEEPyEEbT0_S5_T_'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__libcpp_set_debug_functionEPFvRKNS_19__libcpp_debug_infoEE'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralIjEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralImEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralItEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralIyEET_PKcS3_Rji'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__129__libcpp_abort_debug_functionERKNS_19__libcpp_debug_infoE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__129__libcpp_throw_debug_functionERKNS_19__libcpp_debug_infoE'}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__13cinE', 'size': 168}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__14cerrE', 'size': 160}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__14clogE', 'size': 160}
@@ -1554,6 +1568,7 @@
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__120__codecvt_utf8_utf16IwEE', 'size': 24}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__120__time_get_c_storageIcEE', 'size': 16}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__120__time_get_c_storageIwEE', 'size': 16}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__124__libcpp_debug_exceptionE', 'size': 24}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__15ctypeIcEE', 'size': 56}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__15ctypeIwEE', 'size': 56}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__16locale5facetE', 'size': 24}
@@ -1679,6 +1694,7 @@
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__120__codecvt_utf8_utf16IwEE', 'size': 34}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__120__time_get_c_storageIcEE', 'size': 34}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__120__time_get_c_storageIwEE', 'size': 34}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__124__libcpp_debug_exceptionE', 'size': 35}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__15ctypeIcEE', 'size': 18}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__15ctypeIwEE', 'size': 18}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__16locale5facetE', 'size': 22}
@@ -1790,6 +1806,7 @@
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__120__codecvt_utf8_utf16IDiEE', 'size': 96}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__120__codecvt_utf8_utf16IDsEE', 'size': 96}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__120__codecvt_utf8_utf16IwEE', 'size': 96}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__124__libcpp_debug_exceptionE', 'size': 40}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__15ctypeIcEE', 'size': 104}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__15ctypeIwEE', 'size': 136}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__16locale5facetE', 'size': 40}
diff --git a/libcxx/src/debug.cpp b/libcxx/src/debug.cpp
index d46935cc9ed..fe27dc82ca6 100644
--- a/libcxx/src/debug.cpp
+++ b/libcxx/src/debug.cpp
@@ -7,16 +7,75 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_DEBUG 1
 #include "__config"
 #include "__debug"
 #include "functional"
 #include "algorithm"
+#include "string"
+#include "cstdio"
 #include "__hash_table"
 #include "mutex"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+static std::string make_what_str(__libcpp_debug_info const& info) {
+  string msg = info.__file_;
+  msg += ":" + to_string(info.__line_) + ": _LIBCPP_ASSERT '";
+  msg += info.__pred_;
+  msg += "' failed. ";
+  msg += info.__msg_;
+  return msg;
+}
+
+_LIBCPP_SAFE_STATIC __libcpp_debug_function_type
+    __libcpp_debug_function = __libcpp_abort_debug_function;
+
+bool __libcpp_set_debug_function(__libcpp_debug_function_type __func) {
+  __libcpp_debug_function = __func;
+  return true;
+}
+
+_LIBCPP_NORETURN void __libcpp_abort_debug_function(__libcpp_debug_info const& info) {
+  std::fprintf(stderr, "%s\n", make_what_str(info).c_str());
+  std::abort();
+}
+
+_LIBCPP_NORETURN void __libcpp_throw_debug_function(__libcpp_debug_info const& info) {
+  throw __libcpp_debug_exception(info);
+}
+
+struct __libcpp_debug_exception::__libcpp_debug_exception_imp {
+  __libcpp_debug_info __info_;
+  std::string __what_str_;
+};
+
+__libcpp_debug_exception::__libcpp_debug_exception() _NOEXCEPT
+    : __imp_(nullptr) {
+}
+
+__libcpp_debug_exception::__libcpp_debug_exception(
+    __libcpp_debug_info const& info) : __imp_(new __libcpp_debug_exception_imp)
+{
+  __imp_->__info_ = info;
+  __imp_->__what_str_ = make_what_str(info);
+}
+__libcpp_debug_exception::__libcpp_debug_exception(
+    __libcpp_debug_exception const& other) : __imp_(nullptr) {
+  if (other.__imp_)
+    __imp_ = new __libcpp_debug_exception_imp(*other.__imp_);
+}
+
+__libcpp_debug_exception::~__libcpp_debug_exception() _NOEXCEPT {
+  if (__imp_)
+    delete __imp_;
+}
+
+const char* __libcpp_debug_exception::what() const _NOEXCEPT {
+  if (__imp_)
+    return __imp_->__what_str_.c_str();
+  return "__libcpp_debug_exception";
+}
+
 _LIBCPP_FUNC_VIS
 __libcpp_db*
 __get_db()
diff --git a/libcxx/test/libcxx/debug/debug_abort.pass.cpp b/libcxx/test/libcxx/debug/debug_abort.pass.cpp
new file mode 100644
index 00000000000..cfe63202705
--- /dev/null
+++ b/libcxx/test/libcxx/debug/debug_abort.pass.cpp
@@ -0,0 +1,30 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Test that the default debug handler aborts the program.
+
+#define _LIBCPP_DEBUG 0
+
+#include <csignal>
+#include <cstdlib>
+#include <__debug>
+
+void signal_handler(int signal)
+{
+    if (signal == SIGABRT)
+      std::_Exit(EXIT_SUCCESS);
+    std::_Exit(EXIT_FAILURE);
+}
+
+int main()
+{
+  if (std::signal(SIGABRT, signal_handler) != SIG_ERR)
+    _LIBCPP_ASSERT(false, "foo");
+  return EXIT_FAILURE;
+}
diff --git a/libcxx/test/libcxx/debug/debug_throw.pass.cpp b/libcxx/test/libcxx/debug/debug_throw.pass.cpp
new file mode 100644
index 00000000000..109f9e93b03
--- /dev/null
+++ b/libcxx/test/libcxx/debug/debug_throw.pass.cpp
@@ -0,0 +1,36 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: libcpp-no-exceptions
+
+// Test that the default debug handler can be overridden and test the
+// throwing debug handler.
+
+#define _LIBCPP_DEBUG 0
+
+#include <cstdlib>
+#include <exception>
+#include <type_traits>
+#include <__debug>
+
+int main()
+{
+  {
+    std::__libcpp_debug_function = std::__libcpp_throw_debug_function;
+    try {
+      _LIBCPP_ASSERT(false, "foo");
+    } catch (std::__libcpp_debug_exception const&) {}
+  }
+  {
+    // test that the libc++ exception type derives from std::exception
+    static_assert(std::is_base_of<std::exception,
+                                  std::__libcpp_debug_exception
+                  >::value, "must be an exception");
+  }
+}
diff --git a/libcxx/test/libcxx/debug/debug_throw_register.pass.cpp b/libcxx/test/libcxx/debug/debug_throw_register.pass.cpp
new file mode 100644
index 00000000000..21b1d5255d3
--- /dev/null
+++ b/libcxx/test/libcxx/debug/debug_throw_register.pass.cpp
@@ -0,0 +1,30 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: libcpp-no-exceptions
+
+// Test that defining _LIBCPP_DEBUG_USE_EXCEPTIONS causes _LIBCPP_ASSERT
+// to throw on failure.
+
+#define _LIBCPP_DEBUG 1
+#define _LIBCPP_DEBUG_USE_EXCEPTIONS
+
+#include <cstdlib>
+#include <exception>
+#include <type_traits>
+#include <__debug>
+#include <cassert>
+
+int main()
+{
+  try {
+    _LIBCPP_ASSERT(false, "foo");
+    assert(false);
+  } catch (...) {}
+}
diff --git a/libcxx/www/debug_mode.html b/libcxx/www/debug_mode.html
deleted file mode 100644
index 943c47db011..00000000000
--- a/libcxx/www/debug_mode.html
+++ /dev/null
@@ -1,162 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
-        "http://www.w3.org/TR/html4/strict.dtd">
-<html>
-<head>
-	<title>libc++ debug mode status</title>
-</head>
-<body>
-
-<p>
-Work is beginning on a libc++ debug mode.  The purpose of this table is to
-record which parts of libc++ have debug mode support.
-</p>
-
-<p>
-Note: Debug mode is currently not functional. Defining _LIBCPP_DEBUG will result
-in fairly nasty compile errors.
-</p>
-
-<table border=1>
-<tr>
-<th>Section</th>
-<th>Completed ?</th>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>vector&lt;T&gt;, T != bool</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;list&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;unordered_set&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;unordered_map&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;string&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;set&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;map&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>vector&lt;bool&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;deque&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;forward_list&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;array&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;stack&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;queue&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;algorithm&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-
-</table>
-
-<p>
-At present the table is known to not be a complete list.  It is currently ordered
-in approximate priority order.
-</p>
-
-<p>Last Updated: 3-June-2014</p>
-
-</body>
-</html>
diff --git a/libcxx/www/index.html b/libcxx/www/index.html
index e0f02f2de2e..6b464ebec4e 100644
--- a/libcxx/www/index.html
+++ b/libcxx/www/index.html
@@ -220,7 +220,6 @@
 <li><a href="atomic_design.html"><tt>&lt;atomic&gt;</tt></a></li>
 <li><a href="type_traits_design.html"><tt>&lt;type_traits&gt;</tt></a></li>
 <li><a href="http://cplusplusmusings.wordpress.com/2012/07/05/clang-and-standard-libraries-on-mac-os-x/">Excellent notes by Marshall Clow</a></li>
-<li><a href="debug_mode.html">Status of debug mode</a></li>
 </ul>
 
 </div>