[Mesa-stable] [Mesa-dev] [PATCH 7/7] configure.ac: static link LLVM by default

[Emil Velikov]

On 5 October 2017 at 18:11, Tom Stellard <tstellar at redhat.com> wrote:
> On 10/05/2017 08:40 AM, Emil Velikov wrote:
>> On 5 October 2017 at 16:16, Tom Stellard <tstellar at redhat.com> wrote:
>>> On 10/05/2017 06:33 AM, Michel Dänzer wrote:
>>>> On 05/10/17 12:19 PM, Emil Velikov wrote:
>>>>> From: Emil Velikov <emil.velikov at collabora.com>
>>>>>
>>>>> A while back Michel reported that LLVM has symbol versioning to avoid
>>>>> symbol collisions. Based on observations LLVM 5.0 is the first upstream
>>>>> version to actually has it.
>>>>
>>>> Not exactly. Adam Jackson originally added symbol versioning in LLVM 3.6
>>>> (in SVN r214418), but it was only effective when LLVM was built with
>>>> autotools. As of 5.0, it's effective with cmake as well.
>>>>
>>>>
>>>>> Since symbol collisions do come up again and again (fortunately not so
>>>>> often) let's flip the switch back to static.
>>>>
>>>> It seems a bit weird to make this change now, that LLVM is solving the
>>>> issue for good. But I don't feel strongly about it.
>>>>
>>>>
>>>
>>> I agree with this, symbol versioning should solve the issues with  symbol
>>> collisions, so why change this now?
>>>
>> LLVM with symbol versioning as not so widely used as I/we hope it was.
>> See the list in my other reply.
>>
>
> I looked at the list, but my preference is still that LLVM shared libraries
> should remain the default.  What is motivating the change to static by
> default?  Do the symbol collision problems affect most users?
>
> Static linking really just works around a bug/deficiency in older versions
> of LLVM and I think this is something distros should be handling.
>
> static linking has the added downside of build breakage when LLVM changes
> the component names for it's static libraries, which can be a pain.  Not
> to mention the increase in library size.
>
> As a compromise, if shared libraries are really causing a lot of issues,
> then maybe you could make static the default for for LLVM < 5.0, but I really
> prefer using shared libraries for all versions.
>
Looking the whole thing from another angle:

I noticed that Fedora (RHEL?) has been using statlc libstdc++ for ~2 years.
In the packaging [1] there is this comment:

# C++ note: we never say "catch" in the source.  we do say "typeid" once,
# in an assert, which is patched out above.  LLVM doesn't use RTTI or throw.
#
# We do say 'catch' in the clover and d3d1x state trackers, but we're not
# building those yet.

d3d1x is long gone, but seemingly clover is build these days.
Thus static linking LLVM is the way right approach in that case.

Of course - everyone who knows the pros/cons of the toggle can adjust
it to their needs.

I hope that with these in mind I could get your blessing (ack) on the patch?

Thanks
Emil

[1] http://pkgs.fedoraproject.org/cgit/rpms/mesa.git/tree/mesa.spec#n387