Re: [Boost-users] questions about visibility/dlls under mingw

Subject: Re: [Boost-users] questions about visibility/dlls under mingw
From: John Maddock (jz.maddock_at_[hidden])
Date: 2018-11-19 19:07:22

> OK - due to some sleuthing on the part of one of the auxiliary 
> maintainers of the boost serialization library, it's seems that the 
> problem is that
>
> BOOST_SYMBOL_IMPORT is not defined to be 
> __attribute__((__dllimport__)) under MINGW and that is the source of 
> the problem. 

That's not true, gcc.hpp has:

#Â Â Â  define BOOST_SYMBOL_EXPORT __attribute__((__dllexport__))
#Â Â Â  define BOOST_SYMBOL_IMPORT __attribute__((__dllimport__))

when _Win32 is defined.

And if I modify config_info.cpp to print these out then I see:

 Â Â Â  BOOST_SYMBOL_EXPORT =__attribute__((__dllexport__))
 Â Â Â  BOOST_SYMBOL_IMPORT =__attribute__((__dllimport__))
 Â Â Â  BOOST_SYMBOL_VISIBLE =__attribute__((__visibility__("default")))

Which looks good to me.

John.

> It's totally plausible since gcc visibility attributes are only 
> applied to exports and it seems that in moving to windows this rule is 
> carried over.  So I'm thinking that BOOST_SYMBOL_EXPORT needs to be 
> updated for a special case of MINGW.
>
> Of course, this is subject to confirmation. Hope this is helpful.
>
> It's also been mentioned that the rules for application of these 
> attributes might be different for functions and variables.  The 
> thought of this makes me ill.  I don't know if it's true, but it's one 
> more thing to keep things interesting.
>
> Robert Ramey
>>
>> John.
>>
>>
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