How to dynamically build and link boost::regex with hidden inlines? - c++

Question

As part of my (OSX) project, I am building boost::regex as a dynamic library. When I build and link without -fvisibility-inlines-hidden, everything works as expected.
To work around a bug in another external dependency, I need to turn this compiler switch on, however. Doing so results in lots of linker errors like this one
Undefined symbols for architecture x86_64:
"boost::re_detail::perl_matcher<__gnu_cxx::__normal_iterator<char const*,
std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<
char const*, std::string> > >, boost::regex_traits<char,
boost::cpp_regex_traits<char> > >::find()", referenced from:
bool boost::regex_search<__gnu_cxx::__normal_iterator<char const*,
std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<
char const*, std::string> > >, char, boost::regex_traits<char,
boost::cpp_regex_traits<char> > >(__gnu_cxx::__normal_iterator<char const*,
std::string>, __gnu_cxx::__normal_iterator<char const*, std::string>,
boost::match_results<__gnu_cxx::__normal_iterator<char const*, std::string>,
std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*,
std::string> > > >&, boost::basic_regex<char, boost::regex_traits<char,
boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags,
__gnu_cxx::__normal_iterator<char const*, std::string>) in Regex.o
when I try to link boost to my project (the file "Regex.o" is part of the boost dylib). As I understand Apple's documentation, limiting inline visibility should just cause every dynamic lib to get its own instance of the inlined function, but should never cause linker errors.
It seems there is a related compiler bug for virtual methods, but neither perl_matcher::find() nor regex_search() are virtual methods.
Any suggestions/ideas?
$ clang --version
Apple clang version 3.1 (tags/Apple/clang-318.0.58) (based on LLVM 3.1svn)
Target: x86_64-apple-darwin11.4.0
Thread model: posix

Answer 1

It turns out that this is a compiler bug in clang 3.1. Boost declares the template inline member function perl_matcher<...>::find() (and others) as external; only the instance linked into the boost dylib is not marked as external. Because it is inline, clang 3.1 hides this instance from the dylib's export table with -fvisibility-inlines-hidden.
It seems that this bug is fixed in the current trunk of clang (3.2.x). Until then, defining BOOST_REGEX_NO_EXTERNAL_TEMPLATES works around this bug (if it is acceptable to possibly have multiple instances of these inline functions in your binary). Otherwise, patching boost::regex to explicitly export the symbols defined in boost/regex/v4/instances.hpp using __attribute__ ((visibility("default"))) when BOOST_REGEX_INSTANTIATE is defined should also do the job (see the #define template hack at the top of instances.hpp).