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Subject: Re: [boost] [config] really, really sticky issue with BOOST_SYMBOL_IMPORT
From: Gavin Lambert (boost_at_[hidden])
Date: 2018-10-10 05:33:28

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 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.)

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