[cmake-developers] VISIBILITY_DEFAULT target property

[Stephen Kelly]

Brad King wrote:

> On 05/20/2013 09:42 AM, Stephen Kelly wrote:
>>  set(CMAKE_DEFAULT_VISIBILITY hidden)
>>  
>>  add_library(foo ...)
>>  add_library(bar ...)
>>  add_library(bat ...)
>>  set_property(TARGET bat PROPERTY DEFAULT_VISIBILITY default)
>> 
>> I know this is only a bit nicer. It's an idea worth raising though if we
>> want to move away from strings for compile flags to lists of compile
>> options.
> 
> Thanks for the explanation.  (I assume you meant
> s/DEFAULT_VISIBILITY/VISIBILITY_DEFAULT/ in your example.)

Yes. I've been backward and forward over what to call that property while 
implementing it.

>>> Unlike PIC, visibility is not a usage requirement, is it?
>> 
>> I'm not sure either. My vague understanding is that it might be needed
>> for plugins. That seems to be true for Windows, but I haven't checked on
>> linux yet. According to a comment in a KDE cmake file, it is apparently.
>> kdelibs fails at cmake time if Qt is not built with hidden visibility.
> 
> That sounds like the other way around.  Qt is a dependency of kdelibs.
> If Qt wasn't built with hidden visiblity then kdelibs cannot change its
> build to make things work.  It is more of a usage check/error.

True. I guess making this a usage requirement doesn't make sense.

>>>> How should visibility-inlines-hidden be handled? Introduce
>>>> CMAKE_${lang}_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN and use it if
>>>> VISIBILITY_DEFAULT == "hidden"?
>> 
>> There is also an option for use with MinGW on Windows, which seems
>> roughly equivalent: -fno-keep-inline-dllexport.
>> 
>> Could I make CMAKE_${lang}_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN
>> apply that too?
> 
> They do look quite similar.  Might there ever be a reason one would
> want -fvisibility-inlines-hidden but not -fno-keep-inline-dllexport
> on the respective platforms?

The -fno-keep-inline-dllexport option has no effect on non MinGW:

 stephen at hal:~/cpp$ g++ -fno-keep-inline-dllexport
 g++: error: command line option ‘-fno-keep-inline-dllexport’ is not 
supported by this configuration
 g++: fatal error: no input files
 compilation terminated.

I don't know if MinGW ignores the visibility entirely (and relies only on 
the dllimport/dllexport setting). At least the compiler accepts the argument 
and the dirver passes it on to cc1plus.

> 
> In my understanding of your proposal, VISIBILITY_DEFAULT == "hidden"
> will add -fvisibility=hidden *and* -fvisibility-inlines-hidden.
> Should we have a way to skip the latter e.g. "hidden-no-inlines"?

Perhaps. If we can figure out how to name everything.

Thanks,

Steve.