[PATCH libICE] Enable visibility annotations

[Yury Gribov]

On 05/12/2016 04:16 PM, Emil Velikov wrote:
> On 10 May 2016 at 13:00, Yury Gribov <y.gribov at samsung.com> wrote:
>> On 05/06/2016 07:25 PM, Alan Coopersmith wrote:
>>>
>>> On 05/ 6/16 04:18 AM, Yury Gribov wrote:
>>>>
>>>> Unfortunately I don't see any good approach. We could move definitions of
>>>> _X_EXPORT and friends to configure.ac but this would need to be done
>>>> for all X11 packages (not just libICE) which just does not scale.
>>>
>>>
>>> And then you'd require any package that #includes an X11 header to use
>>> autoconf and add those to configure.ac and that really doesn't scale.
>>
>>
>> There is a way around this: you can strip internal defines from public
>> headers and replace it with e.g. extern. This is how visibility was enabled
>> for acl and libattr some time ago
>> (http://lists.nongnu.org/archive/html/acl-devel/2016-02/msg00020.html).
>>
> If you're suggesting that we should remove all the internal prototypes
> (declarations) from the exported headers, yes that would be great. If
> you're thinking about defining _X_EXPORT via extern that won't work,
> as it will break way too many applications that set
> -fvisibility=hidden or alike.

The libacl way is to use proper _X_EXPORT (actually they have 
ACL_PUBLIC_API or something like that) when building X11 libraries but 
replace it with 'extern' in installed devel headers. Funny enough, this 
works with -fvisibility=hidden (if you declare some function extern and 
it's not defined in the application code, the linker will resolve the 
call to PLT).

 > Or perhaps you're thinking about nuking
> the macro all together ? Sadly that won't work either, as it will
> break way too many other (sub)projects that depend on it.
>
> On the WIN32 (original?) topic
>   - _X_EXPORT implemented via __declspec dllimport/dllexport
> Works fine on mingw-w64 - and the resulting binary has only the
> annotated symbols as exported.
>   - fvisibility=hidden
> Does nothing on mingw64, although it does not cause any warning/errors.
>
> So in general something like the following should work
> Note: mingw and cygwin will need to drop fvisibility and/or alike and
> set the BUILDING_DLL define
>
> --- a/Xfuncproto.h.orig
> +++ b/Xfuncproto.h.new
> @@ -89,8 +89,15 @@ in this Software without prior written
> authorization from The Open Group.
> #endif /* GNUC >= 4 */
>
> /* Added in X11R6.9, so available in any version of modular xproto */
> -#if (__has_attribute(visibility) || (defined(__GNUC__) && (__GNUC__ >= 4))) \
> -    && !defined(__CYGWIN__) && !defined(__MINGW32__)
> +#if defined(_WIN32) || defined(__CYGWIN__) && defined(__MINGW32__)
> +# ifdef BUILDING_DLL // should we prefix this with _X_ ?
> +#  define _X_EXPORT __declspec(dllexport)
> +# else
> +#  define _X_EXPORT __declspec(dllimport)
> +# endif
> +# define _X_HIDDEN
> +# define _X_INTERNAL
> +#elif __has_attribute(visibility) || (defined(__GNUC__) && (__GNUC__ >= 4))
> # define _X_EXPORT      __attribute__((visibility("default")))
> # define _X_HIDDEN      __attribute__((visibility("hidden")))
> # define _X_INTERNAL    __attribute__((visibility("internal")))
>
>
> Jon, have I lost the plot with any of the above ? Please don't be shy
> to say "yes you have" ;-)
> Can you give it a quick test on your end ?
>
> Thanks
> Emil
>
>