Re: [Boost-bugs] [Boost C++ Libraries] #12773: WINDOWS- Boost thread 1.63.0 strict aliasing warnings

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #12773: WINDOWS- Boost thread 1.63.0 strict aliasing warnings
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-02-19 13:29:04

#12773: WINDOWS- Boost thread 1.63.0 strict aliasing warnings
--------------------------------+----------------------
  Reporter:  alexandre.nunes@…  |      Owner:  anthonyw
      Type:  Bugs               |     Status:  new
 Milestone:  To Be Determined   |  Component:  thread
   Version:  Boost 1.63.0       |   Severity:  Problem
Resolution:                     |   Keywords:
--------------------------------+----------------------

Comment (by alexandre.nunes@…):

 You're absolutely right that type-punning leads to UB, and so does current
 implementation. It seems to me that other than checking member-by-member,
 the other option would be to - providing the structure is sufficiently
 sane - use std::memcmp() to check the data. Most compilers can optimize
 the call away, when that's safe.

 Here's the compiler report:
 {{{
     gcc.compile.c++ bin.v2/libs/type_erasure/build/gcc-mingw-6.3/release
 /link-static/runtime-link-static/target-os-windows/threadapi-win32
 /threading-multi/dynamic_binding.o
     In file included from ./boost/thread/shared_mutex.hpp:18:0,
                      from libs/type_erasure/src/dynamic_binding.cpp:14:
     ./boost/thread/win32/shared_mutex.hpp: In instantiation of 'T
 boost::shared_mutex::interlocked_compare_exchange(T*, T, T) [with T =
 boost::shared_mutex::state_data]':
     ./boost/thread/win32/shared_mutex.hpp:130:103:   required from here
     ./boost/thread/win32/shared_mutex.hpp:51:63: error: dereferencing
 type-punned pointer will break strict-aliasing rules [-Werror=strict-
 aliasing]
 *reinterpret_cast<long*>(&new_value),
 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     ./boost/thread/win32/shared_mutex.hpp:52:63: error: dereferencing
 type-punned pointer will break strict-aliasing rules [-Werror=strict-
 aliasing]
 *reinterpret_cast<long*>(&comparand));
 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     ./boost/thread/win32/shared_mutex.hpp:53:20: error: dereferencing
 type-punned pointer will break strict-aliasing rules [-Werror=strict-
 aliasing]
              return *reinterpret_cast<T const*>(&res);
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     ./boost/thread/win32/shared_mutex.hpp:53:52: error: dereferencing
 type-punned pointer will break strict-aliasing rules [-Werror=strict-
 aliasing]
              return *reinterpret_cast<T const*>(&res);
                                                     ^
     cc1plus: some warnings being treated as errors
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12773#comment:5>
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