[Mesa-dev] [PATCH] configure: simplify visibility compiler flag detection

[Emil Velikov]

On 1 March 2015 at 22:38, Sedat Dilek <sedat.dilek at gmail.com> wrote:
> On Sun, Mar 1, 2015 at 11:31 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>> On 01/03/15 21:05, Alan Coopersmith wrote:
>>> On 03/ 1/15 10:57 AM, Emil Velikov wrote:
>>>> On 01/03/15 18:30, Matt Turner wrote:
>>>>> On Sun, Mar 1, 2015 at 6:09 AM, Marc Dietrich <marvin24 at gmx.de> wrote:
>>>>>> This patch simplifies the visibility compiler flag detection in
>>>>>> configure and
>>>>>> makes it more generic to also support compilers other than gcc.
>>>>>
>>>>> This simplification relies on the assumption that compilers support
>>>>> -fvisibility=... if and only if they support
>>>>> attribute(visibility("...")).
>>>>>
>>>> Hmm you're correct. I've naively assumed they both go hand in hand.
>>>
>>> The latest Solaris Studio compilers support attribute(visibility), but
>>> not -fvisibility.  The absolute latest (12.4, released a few months back)
>>> also support the clang has_attribute() extension for checking what's
>>> supported (which is one of the reasons it's used in the X11/Xfuncproto.h
>>> header in xproto 7.0.27 & later).
>>>
>> Ouch... so I was quite naive indeed.
>>
>> So here are some interesting bits:
>>
>>  - HAVE_FUNC_ATTRIBUTE_VISIBILITY is likely to be undefined (0) with
>> Solaris Studio compilers, as the m4 macro checks for
>>
>> __attribute__((visibility("default")));
>> __attribute__((visibility("hidden")));
>> __attribute__((visibility("internal")));
>> __attribute__((visibility("protected")));
>>
>> As the last one does not appear in the 12.4 C User's Guide (linked
>> below) the compiler will likely error/warn.
>>
>> Perhaps we can nuke the latter two, as they are unused presently, and
>> add them back when needed ?
>>
>>  - Considering the lack of -fvisibility, what is the normal visibility
>> "level" - hidden or default ? If the latter this means that every
>> library/module built exports a ton of internal symbols.
>>
>
> From [1] for gcc:
>
> "Despite the nomenclature, ‘default’ always means public; i.e.,
> available to be linked against from outside the shared object.
> ‘protected’ and ‘internal’ are pretty useless in real-world usage so
> the only other commonly used option is ‘hidden’. The default if
> -fvisibility isn't specified is ‘default’, i.e., make every symbol
> public—this causes the same behavior as previous versions of GCC. "
>
I was talking/asking about the Solaris Studio compilers.

-Emil