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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
101 lines
3.0 KiB
ReStructuredText
101 lines
3.0 KiB
ReStructuredText
==========
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Debug Mode
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==========
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.. contents::
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:local
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.. _using-debug-mode:
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Using Debug Mode
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================
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Libc++ provides a debug mode that enables assertions meant to detect incorrect
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usage of the standard library. By default these assertions are disabled but
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they can be enabled using the ``_LIBCPP_DEBUG`` macro.
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**_LIBCPP_DEBUG** Macro
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-----------------------
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**_LIBCPP_DEBUG**:
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This macro is used to enable assertions and iterator debugging checks within
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libc++. By default it is undefined.
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**Values**: ``0``, ``1``
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Defining ``_LIBCPP_DEBUG`` to ``0`` or greater enables most of libc++'s
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assertions. Defining ``_LIBCPP_DEBUG`` to ``1`` enables "iterator debugging"
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which provides additional assertions about the validity of iterators used by
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the program.
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Note that this option has no effect on libc++'s ABI
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**_LIBCPP_DEBUG_USE_EXCEPTIONS**:
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When this macro is defined ``_LIBCPP_ASSERT`` failures throw
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``__libcpp_debug_exception`` instead of aborting. Additionally this macro
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disables exception specifications on functions containing ``_LIBCPP_ASSERT``
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checks. This allows assertion failures to correctly throw through these
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functions.
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Handling Assertion Failures
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---------------------------
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When a debug assertion fails the assertion handler is called via the
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``std::__libcpp_debug_function`` function pointer. It is possible to override
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this function pointer using a different handler function. Libc++ provides two
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different assertion handlers, the default handler
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``std::__libcpp_abort_debug_handler`` which aborts the program, and
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``std::__libcpp_throw_debug_handler`` which throws an instance of
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``std::__libcpp_debug_exception``. Libc++ can be changed to use the throwing
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assertion handler as follows:
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.. code-block:: cpp
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#define _LIBCPP_DEBUG 1
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#include <string>
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int main() {
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std::__libcpp_debug_function = std::__libcpp_throw_debug_function;
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try {
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std::string::iterator bad_it;
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std::string str("hello world");
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str.insert(bad_it, '!'); // causes debug assertion
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} catch (std::__libcpp_debug_exception const&) {
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return EXIT_SUCCESS;
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}
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return EXIT_FAILURE;
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}
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Debug Mode Checks
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=================
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Libc++'s debug mode offers two levels of checking. The first enables various
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precondition checks throughout libc++. The second additionally enables
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"iterator debugging" which checks the validity of iterators used by the program.
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Basic Checks
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============
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These checks are enabled when ``_LIBCPP_DEBUG`` is defined to either 0 or 1.
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The following checks are enabled by ``_LIBCPP_DEBUG``:
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* FIXME: Update this list
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Iterator Debugging Checks
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=========================
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These checks are enabled when ``_LIBCPP_DEBUG`` is defined to 1.
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The following containers and STL classes support iterator debugging:
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* ``std::string``
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* ``std::vector<T>`` (``T != bool``)
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* ``std::list``
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* ``std::unordered_map``
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* ``std::unordered_multimap``
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* ``std::unordered_set``
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* ``std::unordered_multiset``
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The remaining containers do not currently support iterator debugging.
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Patches welcome.
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