[llvm-dev] Minimal glibc version supported by LLVM build

[Davide Italiano via llvm-dev]

On Oct 4, 2017 2:31 PM, "Rui Ueyama via llvm-dev" <llvm-dev at lists.llvm.org>
wrote:

On Wed, Oct 4, 2017 at 2:19 PM, Philip Reames <listmail at philipreames.com>
wrote:

> Our build system is setup to deliberately use a very old environment.
> We've found that's one of the most reliable easy ways to ensure we don't
> accidentally introduce a dependency on a newer system library than
> intended.  This lets us ship prebuilt binaries which run on a wide spectrum
> of systems.  We're going to chat internally and check to see if we can roll
> this forward a bit, but supporting an older glibc is definitely going to be
> somewhat we want.  Exactly *how* old might be flexible, but I have to check.
>
> Rui, let me turn your question around on you.  What version of glibc would
> you like to be our minimum?  And why?  Is there a good reason to move this
> forward?
>
I don't have a clear answer to your question, and I don't think I'm a
person who can set a standard, but maybe, 11 years is a bit too old. I
don't think we want to intentionally break it, and if it can be supported
by adding a few lines to CMakeFiles, we probably should. However, IMO, this
should be done by best-effort basis. I don't think we need to immediately
revert a patch if broke a 11 year old system.


I don't necessarily agree with the last point.
I think a policy would help here, and it should be based on the number of
annoyances supporting an old version cause. This is akin to what we did
for, e.g. VS 2013. If supporting a old version doesn't allow the project to
reasonably move forward, we should consider an upgrade. FWIW, in this case
I don't think the feature introduced is worth the bump, but your mileage
may vary.
I'd like to add that "11 years old system" means nothing. In fact, I think
we should aim supporting even older systems whenever possible.

Thanks,

--
Davide


I think we need to establish and document a minimum supported version
> here.  I'm open to debating what that version should be, but the current
> lack of clarity is clearly problematic.
>
> Philip
>
> p.s. Sorry about the confusion earlier about CentOS.  I'd misunderstood an
> statement in internal conversation and repeated the information without
> checking.  While true that the build failed on a CentOS 6.4 system, it was
> being built against a non-default (older) glibc.
>
> p.p.s. This brought up the point internally that we really should have a
> public build bot for the configuration we care about.  I need to talk that
> over internally, but this seems like something we can make happen.
>
> On 10/04/2017 12:38 PM, Rui Ueyama via llvm-dev wrote:
>
> Serguei,
>
> glibc 2.5 was released 11 years ago, so I wonder what operating system you
> are using now.
>
> On Wed, Oct 4, 2017 at 12:08 AM, Serguei Katkov via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi All,
>>
>>
>>
>> The landed patch https://reviews.llvm.org/D38481 introduced the usage of
>> CPU_COUNT defined in glibc sched.h header.
>>
>> I failed to find this symbol in sched.h of glibc version 2.5-24, so
>> compilation just fails.
>>
>> /home/dolphin/merge-from-upstream-area/ws/pristine/lib/Support/Threading.cpp:
>> In function ‘unsigned int llvm::hardware_concurrency()’:
>>
>> /home/dolphin/merge-from-upstream-area/ws/pristine/lib/Support/Threading.cpp:80:26:
>> error: ‘CPU_COUNT’ was not declared in this scope
>>
>>      return CPU_COUNT(&Set);
>>
>>                           ^
>>
>>
>>
>> It is buildable with newest version of glibc.
>>
>> I tried to find a requirements for glibc version in LLVM documentation
>> but failed.
>>
>> So I wonder whether there is such requirement or not.
>>
>> Could anyone point me to this documentation?
>>
>>
>>
>> I'm trying to understand whether patch is wrong which relies on
>> availability of library but does not check the symbol itself or this
>> version of glibc is not supported.
>>
>>
>>
>> Thank you,
>>
>> Serguei.
>>
>>
>>
>> _______________________________________________
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>> llvm-dev at lists.llvm.org
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>>
>>
>
>
> _______________________________________________
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>
>

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