[Boost-bugs] [Boost C++ Libraries] #13121: std_fenced_block gets used for g++ 4.6.4 and hence buggy std::atomic_thread_fence

Subject: [Boost-bugs] [Boost C++ Libraries] #13121: std_fenced_block gets used for g++ 4.6.4 and hence buggy std::atomic_thread_fence
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-07-13 10:52:37

#13121: std_fenced_block gets used for g++ 4.6.4 and hence buggy
std::atomic_thread_fence
-----------------------------------------+----------------------------
 Reporter:  Richard Hazlewood <boost@…>  |      Owner:  chris_kohlhoff
     Type:  Bugs                         |     Status:  new
Milestone:  To Be Determined             |  Component:  asio
  Version:  Boost 1.64.0                 |   Severity:  Problem
 Keywords:  g++ 4.6                      |
-----------------------------------------+----------------------------
 With g++ 4.6.4: using {{{asio}}} code that results in
 {{{detail::fenced_block}}} being used results in
 {{{detail::std_fenced_block}}} being used.
 This uses {{{std::atomic_thread_fence}}} but that has link issues with 4.6
 (maybe https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51038).

 {{{g++4.6 -std=c++0x -I boost... }}}

 {{{
 #include <boost/asio/detail/fenced_block.hpp>

 #ifdef BOOST_ASIO_HAS_STD_ATOMIC
 # pragma message("Will use asio std_fenced_block")
 #endif

 int main(int argc, char *argv[])
 {
   (void)argc; (void)argv;

   boost::asio::detail::fenced_block
 block(boost::asio::detail::fenced_block::full);
 }
 }}}

 boost_asio.cpp:4:51: note: #pragma message: Will use asio std_fenced_block
 /tmp/ccNS0287.o: In function
 `boost::asio::detail::std_fenced_block::std_fenced_block(boost::asio::detail::std_fenced_block::full_t)':
 boost_asio.cpp:(.text._ZN5boost4asio6detail16std_fenced_blockC2ENS2_6full_tE[_ZN5boost4asio6detail16std_fenced_blockC5ENS2_6full_tE]+0x22):
 undefined reference to `std::atomic_thread_fence(std::memory_order)'
 /tmp/ccNS0287.o: In function
 `boost::asio::detail::std_fenced_block::~std_fenced_block()':
 boost_asio.cpp:(.text._ZN5boost4asio6detail16std_fenced_blockD2Ev[_ZN5boost4asio6detail16std_fenced_blockD5Ev]+0x13):
 undefined reference to `std::atomic_thread_fence(std::memory_order)'
 collect2: ld returned 1 exit status

 It looks like between 1.63 and 1.64, in ''detail/fenced_block.hpp'', the
 {{{#elif defined(BOOST_ASIO_HAS_STD_ATOMIC)}}} line takes precedence over
 the specific gcc test.  However, {{{BOOST_ASIO_HAS_STD_ATOMIC}}} is
 defined for 4.6.4.

-- 
Ticket URL: <https://svn.boost.org/trac10/boost/ticket/13121>
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