There is a test set on develop called BenPope x86_64 Ubuntu - phoenix - adapt_function / clang-linux-3.6~msan~c14_libc++ This runs this command line for example on the Phoenix test "adapt_function": "clang++-3.6" -c -x c++ -std=c++1y -stdlib=libc++ -fsanitize=memory -O0 -fno-inline -Wall -fPIC -m64 -DBOOST_ALL_NO_LIB=1 -I".." -o "/home/ben/development/boost/test/build/develop/results/boost/bin.v2/libs/phoenix/test/adapt_function.test/clang-linux-3.6~msan~c14_libc++/debug/address-model-64/architecture-x86/debug-symbols-off/function/adapt_function.o" "../libs/phoenix/test/function/adapt_function.cpp" There are numerous failures with this test set on Phoenix and I set out to find out why. Most of the failures are like this: SUMMARY: MemorySanitizer: use-of-uninitialized-value ??:0 std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) Exiting I think this is coming from the boost::report_errors function defined in boost/core/lightweight_test.hpp I have put some temporary tests on to develop for Phoenix which contain only various calls to test the lightweight test. These are called aa_test0 to 3 so they will come at the top of the table. Unfortunately tests are not reporting at the moment so I don't have any results. There are also failures on the testing of Boost Core with the same test set. I thought I would report this without waiting for the results in the hope that it can be sorted out for the 1.58.0 release. John