[Mesa-dev] [PATCH v3 25/25] configure.ac: Add required LLVM versions to the top

[Michel Dänzer]

On 18/10/16 11:39 PM, Emil Velikov wrote:
> On 17 October 2016 at 08:56, Michel Dänzer <michel at daenzer.net> wrote:
>> On 14/10/16 07:02 PM, Emil Velikov wrote:
>>
>>> * src/gallium/drivers/radeon/r600_pipe_common.c
>>> No actual bug, yet misleading.
>>
>> If you want to call it that... I'd say this can be useful for detecting
>> the problems you're thinking of. :)
>>
> On the contrary, for example:
> Building against shared llvm 3.6.0, later one updates to 3.6.2.
> 
> Mesa is not rebuild, thus the above message says "3.6.0" and they
> don't get any tessellation.
> Then they check with their package/install - Why is Mesa showing
> 3.6.0, I have 3.6.2 installed. Should I reinstall LLVM, are there any
> parts of 3.6.0 still around ?"

My point is that all the information is there; even if not everybody can
make sense of it, *somebody* can and explain to others what needs to be
done.

> This in itself is because people don't expect that one should rebuild
> package X when one its dependencies gets a patch version change.

The same thing applies with static linking, though. Except then one
doesn't get the benefit of any other additional fixes in the newer LLVM
either without rebuilding Mesa.


>>> Downgrade - TBD, depending on the (fixed) LLVM bugs.
>>
>> Building against one version of LLVM and then downgrading the shared
>> library to an older version is indeed the only case we're currently not
>> handling gracefully. It should be rather rare though.

[...]

>>> That or just bump the requirement ?
>>
>> That wouldn't protect against the shared library being downgraded to an
>> older version.
>>
> Almost. AFAICT Mesa has (had for a long time) the implicit agreement
> that the build-time requirements are identical to the run-time ones.
> 
> If people use a lower [runtime] versions, things will explode in many
> places. This is not specific/isolated to LLVM.

Right, but this principle generally applies to the effective version of
a shared library compiled against instead of its minimum required
version. I'm not sure raising the minimum required version would provide
enough benefit to offset artificially preventing users with older
versions from building Mesa. Have you seen any actual reports of users
running into trouble because of this? I don't remember seeing any.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer