title: Problems Linking boost log 1_60 with MinGw on Windows 7
body: <p>On upgrading to <a href="http://www.boost.org/" rel="noreferrer">boost 1.60.0</a> some applications are failing to link with <a href="http://www.boost.org/doc/libs/1_60_0/libs/log/doc/html/index.html" rel="noreferrer">boost log</a> when built with MinGw 4.9.2 on Windows 7.</p>
  
  <p>I get the following linker errors:</p>
  
  <pre><code>undefined reference to `_imp___ZN5boost3log9v2_mt_nt67trivial6logger3getEv'
  undefined reference to `_imp___ZN5boost3log9v2_mt_nt63aux15stream_providerIcE17allocate_compoundERNS1_6recordE'
  undefined reference to `_imp___ZN5boost3log9v2_mt_nt63aux25unhandled_exception_countEv'
  undefined reference to `_imp___ZN5boost3log9v2_mt_nt611record_view11public_data7destroyEPKS3_'
  bad reloc address 0x1 in section `.text$_ZNK5boost4asio5error6detail13misc_category4nameEv[__ZNK5boost4asio5error6detail13misc_category4nameEv]'
  </code></pre>
  
  <p>Note: BOOST_LOG_DYN_LINK is defined:  </p>
  
  <pre><code>g++ -c -pipe -fno-keep-inline-dllexport -Wall -Wextra -Wpedantic -Ofast -std=c++1y -frtti -fexceptions -mthreads -DUNICODE -DLOGGING_ENABLED -DNTDDI_VERSION=NTDDI_WIN7 -D_WIN32_WINNT=_WIN32_WINNT_WIN7 -DBOOST_THREAD_USE_LIB=1 -DBOOST_LOG_DYN_LINK=1
  </code></pre>
  
  <p>The boost 1.60.0 build log file shows that both boost log and boost log_setup built without any errors or warnings, including some of the files that it's failing to link with e.g.:</p>
  
  <pre><code>gcc.compile.c++ bin.v2\libs\log\build\gcc-mingw-4.9.2\release\threading-multi\trivial.o
  gcc.compile.c++ bin.v2\libs\log\build\gcc-mingw-4.9.2\release\threading-multi\unhandled_exception_count.o   
  </code></pre>
  
  <p>The applications link OK using boost 1.59.0 with MinGw 4.9.2 on Windows 7 and also link OK using boost 1.60.0 with gcc 5.1.1 on Fedora 23.</p>
  
  <p><a href="http://www.boost.org/doc/libs/1_60_0/doc/html/boost_asio.html" rel="noreferrer">boost asio</a> hasn't changed since boost 1.58.0. So what's changed in <a href="http://www.boost.org/doc/libs/1_60_0/libs/log/doc/html/index.html" rel="noreferrer">boost log</a> between boost 1.59.0 and boost 1.60.0 to cause MinGw linking to fail on Windows?</p>