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

[Emil Velikov]

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.

 - Using the __has_attribute macro looks great, although I would suspect
that it will take a while for GCC and others to adopt(?).

Thanks for the insightful input Alan.

-Emil

> https://docs.oracle.com/cd/E37069_01/html/E37074/gjzke.html
> https://docs.oracle.com/cd/E37069_01/html/E37074/gopqx.html
> http://cgit.freedesktop.org/xorg/proto/x11proto/commit/?id=ffd4a13042d24cb5c913207585191801a9a1603e
> 
>