[Mesa-dev] [PATCH 00/11] glapi fixes - build whole of mesa with

[Emil Velikov]

On 22 June 2015 at 15:01, Jose Fonseca <jfonseca at vmware.com> wrote:
> On 19/06/15 23:09, Emil Velikov wrote:
>>
>> On 19 June 2015 at 21:26, Jose Fonseca <jfonseca at vmware.com> wrote:
>>>
>>> On 19/06/15 20:56, Emil Velikov wrote:
>>>>
>>>>
>>>> Hi all,
>>>>
>>>> A lovely series inspired (more like 'was awaken to send these out') by
>>>> Pal Rohár, who was having issues when building xlib-libgl (plus the now
>>>> enabled gles*)
>>>>
>>>> So here, we teach the final two static glapi users about shared-glapi,
>>>> plus some related fixes. After this is done we can finally start
>>>> transitioning to shared-only glapi, with some more details as mentioned
>>>> in one of the patches:
>>>>
>>>>       XXX: With this one done, we can finally transition with enforcing
>>>>       shared-glapi, and
>>>>
>>>>        - link the dri modules against libglapi.so, add --no-undefined to
>>>>       the LDFLAGS
>>>>        - drop the dlopen(libglapi.so/libGL.so, RTLD_GLOBAL) workarounds
>>>>       in the loaders - libGL, libEGL and libgbm.
>>>>        - start killing off/cleaning up the dispatch ?
>>>>
>>>>       The caveats:
>>>>       1) up to what stage do we care about static libraries
>>>>        - libgl (either dri or xlib based)
>>>>        - osmesa
>>>>        - libEGL
>>>>
>>>>       2) how about other platforms (scons) ?
>>>>        - currently the scons uses static glapi,
>>>>        - would we need the dlopen(...) on windows ?
>>>>
>>>> Hope everyone is excited about this one as I am :-)
>>>
>>>
>>>
>>> Maybe I missed the context of this changes, but why this matters or is an
>>> improvement?
>>>
>> If one goes the extra mile (which this series doesn't) - one configure
>> option less, substantial some code de-duplication and consistent use
>> of the code amongst all components provided. This way any
>> improvements/cleanups made to the shared glapi will be available to
>> osmesa/xlib-libgl.
>
>
> I'm perfectly happy with removing the configure option.
>
> And I understand the benefits of unified code paths, but I believe that for
> this particular case, the difference in requirements really demands the
> separate code paths.
>
>>> In summary, having the ability of using a shared glapi sounds great, but
>>> forcing shared glapi everywhere, sounds a bad idea.
>>>
>> I'm suspecting that people might be keen on the following idea - use
>> static glapi for osmesa/xlib-libgl and shared one everywhere else?
>
>
> Yes, that sounds reasonable for me.  (Needs libgl-gdi too.)
>
Indeed. Everything gdi is build only via scons so we'll touch it only if needed.

>>
>> I fear that this will lead to further separation/bit-rot between the
>> different implementations, but it seems like the bester compromise.
>
>
> I don't feel strongly between: a) using the same source code for both
> static/shared glapi (switched by a pre-processor define), or b) only share
> the interface but have shared/static glapi implementations.  I'm actually
> not that familiar with that code.
>
>
> Either way, we can have two glapi build targets (a shared-glapi and a
> static-glapipe) side-by-side, so that there are no more source-wide
> configure flags.
>
In theory it should be fine, in practise... I'm rather cautious as
mapi is the most convoluted part in mesa, and with the
"subdir-objects" option being toggled soon things may go (albeit
unlikely) subtly haywire.

>
> I believe a lot of the complexity of that code comes from assembly.  I
> wonder if it's really justified nowadays (and even if it is, whether it
> would be better served with GNU C assembly.) Futhermore, I believe on
> Windows we use any assembly, so if we split shared/static glapi source code,
> we could probably abandon assembly from the static-glapi.
>
I'm not 100% sure but I'd suspect that Cygwin might use it when
combined with swrast_dri. Don't know what others use - iirc some of
the BSD folks are moving over to llvm. That I aside there is a massive
amount of #ifdef spaghetti, apart from the assembly code.

Can I have your ack/nack on the idea of having shared-glapi available
for xlib-libgl (patches 2, 3 and 4), until we have both glapi's built
in in parallel ? As mentioned originally, currently we fail to build
if one enabled gles* and xlib-libgl and adding another hack in
configure.ac is feel like flocking up a dead horse.

-Emil