[boost] [config] really, really sticky issue with BOOST_SYMBOL_IMPORT

Subject: [boost] [config] really, really sticky issue with BOOST_SYMBOL_IMPORT
From: Robert Ramey (ramey_at_[hidden])
Date: 2018-10-10 04:37:44

For many, many years we've built the Boost serialization library with 
the macros for BOOST_SYMBOL_IMPORT and BOOST_SYMBOL_EXPORT set according 
to the instructions included in the boost/config documentation written 
by John Maddock.  These set attributes for creating and using DLLS for 
windows and (used to) resolve to nothing on other systems.  So far so good.

At some point things changed for gcc compilers.  Now it seems that 
BOOST_SYMBOL_IMPORT resolves to nothing and BOOST_SYMBOL_EXPORT resolves 
to : __attribute__ ((visibility("default"))) and BOOST_SYMBOL_IMPORT 
still resolves to nothing.  OK - this has never been a problem.

Now we have an extremely subtle issue which appears on linux systems 
with gcc. It's related to sequence of shared library loading and 
unloading.  It shows up as a bunch of test failures for the test named 
test_exported_dll.  A very astute user has determined that this can be 
"fixed" by defining BOOST_SYMBOL_IMPORT as __attribute__ 
((visibility("default"))) as well.  Question. should config/gcc be 
updated in this way?  Also is it possible that this "fix" is just a 
fluke unrelated to the real source of the problem?

Note that this issue predates the recent change to make 
-visibility=default which has, as one might expect, caused some issues. 
I believe that this situation is unrelated.

Any help appreciated

Robert Ramey

reference: 
https://github.com/boostorg/serialization/issues/104#issuecomment-416948110