Re: Wrong class export/visibility setting for shared libs in many Boost libs

From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2021-02-02 14:05:46

On 02/02/2021 13:02, Andrey Semashev via Boost wrote:
> On 2/2/21 3:34 PM, Niall Douglas via Boost wrote:
>> On 02/02/2021 11:51, Andrey Semashev via Boost wrote:
>>
>>> So, the bottom line, BOOST_PROGRAM_OPTIONS_DECL must be defined to:
>>>
>>> - BOOST_SYMBOL_EXPORT - on Windows, when the library is being built;
>>> - BOOST_SYMBOL_IMPORT - on Windows, when the library is being consumed
>>> by user;
>>> - BOOST_SYMBOL_VISIBLE - in any other case.
>>
>> This causes Boost.ProgramOptions symbols to be exported in any shared
>> object or executable which links in Boost.ProgramOptions i.e. you
>> reexport the same symbols.
> 
> It does not because the symbols to be exported are (supposed to be) only
> defined in Boost.ProgramOptions library.

BOOST_SYMBOL_VISIBLE is always default visibility, no matter what.

Therefore anything in a Boost.ProgramOptions header would be made
visible and thus exported, which equals exporting all the extern
declarations. That, in turn, would cause ABI collision if somebody tries
linking in a non-matching Boost, under the assumption that an internal
Boost has been hidden from linkage (which "works", so far).

ELF is generally completely borked when it comes to this stuff. We made
it quack like a dog fifteen years ago, but a duck it never can be
without fixing the ELF specification.

Niall