On 10/10/2018 17:37, Robert Ramey wrote:
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?
While I know next to nothing about how Linux DSOs work, my reading of https://gcc.gnu.org/wiki/Visibility suggests that you're supposed to specify the same visibility level for both definition and usage of any given symbol. (See in particular the example code in the step-by-step guide, and some of the admonishments against using different visibility in the section on exceptions.)