Re: [lld] r271569 - Start adding tlsdesc support for aarch64.

[Renato Golin]

On 3 June 2016 at 21:02, Rui Ueyama  wrote:
>> Is the LLD community in agreement that a few core developers can and
>> will continue to block contributions, while doing all the work
>> themselves until such a day that it's deemed ready by the same
>> developers, in which time that everyone else will then, be allowed to
>> collaborate?
>
>
> No, and I think I've never blocked any contributions for such reason. I
> apologize I didn't review Adhemerval patch. My knowledge of AArch64 and TLS
> optimizations is limited, and since Rafael (who knows most about relocation
> handling in LLD) was reviewing it, I deferred it to him. I'll try to review
> it next time.
>
>>
>> Or is the community in disagreement with Rafael's behaviour and will
>> try to not only curb it, but openly and actively promote more
>> collaboration by allowing other people to participate in the design
>> and implementation of their own targets?
>
>
> Yes, including the part that Rafael should have done this differently.
>
> Rafael, I think you want to slow down a little bit and take more time on
> getting consensus on commits, even for things that you think "too obvious".
> Code review for LLD is usually fast, and overall it would make the
> development even faster because of smooth communication between
> collaborators.

Rui,

Thank you very much for your response.

I'm relieved that I had not made the wrong decision about LLD some
years back, and I really appreciate the work you have being putting on
it.

Looking forward to more collaborations in the present and future!

cheers,
--renato
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Re: [lld] r271569 - Start adding tlsdesc support for aarch64.

[Renato Golin]

On 3 June 2016 at 18:47, Rui Ueyama  wrote:
> Renato, it is not appropriate to call it my and Rafael's pet project.

Hi Rui,

I apologise, that was wrong in all levels.

I know how much other people have contributed, but these people are on
the inside already, so their contributions are more easily accepted.

We have been trying to contribute for more than a year and have yet
failed to get in the loop. We were asked to wait for 2 years until the
core linker was ready, we did. Last year we wasted 3 months on the old
back end, and were told to wait again. Now we wasted another 4 months
this year, and all we did was re-written without warning. I cannot
recommend Linaro to continue wasting any more time.


> I have never declined contributions by saying that "I know better." I
> requested design documents (because I don't know better!) when contributors
> seem to be starting large design changes, but that was needed for
> discussion. If you want to do some large change, you want to convince other
> collaborators that your design will work. It is I think a usual process.

Again, I apologise. Your behaviour is by no means comparable to Rafael's.

But he's taking the stance and speaking for the LLD community, at
least that's what it looks like to me.

Linaro is not a drive-by contributor to LLVM, or even to LLD. And if
even long time contributors to LLVM, and professional developers with
decades of experience in linker technology, are getting this
treatment, what does that say about others?


> I sincerely request you to retract your recommendation to not collaborate
> with us.

Those are based on facts. Not about you, but about interacting the the
LLD community, which unfortunately, you're part of.

I don't want to blame people, I want to produce software, and the LLD
community is blocking our progress for 3 years already.


> I had totally no intention to say that you should try something outside LLD. 
> I'm sorry for the confusion.

That's what I meant, yes. :)

Let me re-write my question to make sure we get over the language barrier:

Is the LLD community in agreement that a few core developers can and
will continue to block contributions, while doing all the work
themselves until such a day that it's deemed ready by the same
developers, in which time that everyone else will then, be allowed to
collaborate?

Or is the community in disagreement with Rafael's behaviour and will
try to not only curb it, but openly and actively promote more
collaboration by allowing other people to participate in the design
and implementation of their own targets?

If the former, than I'll respectfully move to MCLinker. If the latter,
than I expect due process and future collaborations, including letting
Adhemerval complete the AArch64 TLS implementation with proper code
review, not bypass re-writes.

As I said earlier, we'll continue to collaborate on LLD for the time
being on both ARM and AArch64 targets, and the next months will be a
test of how the LLD community will respond to this incident.

Peter Smith has just sent an initial implementation for the ARM target
(D20951), and he's working on improving it to be able to self-host
Clang on ARM in the next few months. I seriously hope that this
doesn't end up as another bad decision.

cheers,
--renato
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[ACTIVITY] 1st June - 3rd June 2016

[Peter Smith]

== Progress ==

- Holiday Monday/Tuesday
- Finished writing initial support for ARM in lld. Posted upstream as
RFC, no comments so far.
- Implemented, but not tested the static Thumb relocations present in
the arm-linux-gnueabihf-gcc
-- I'd forgotten how much I hated the Thumb 2 instruction encodings.

== Plan ==

- Add tests for Thumb relocations
- Start thinking about how interworking can be implemented in lld
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Re: [lld] r271569 - Start adding tlsdesc support for aarch64.

[Renato Golin]

On 3 June 2016 at 17:10, Rafael Espíndola  wrote:
> Do keep in mind you are comparing a 11 year old project and a 11 month
> old one. There is a lot more churn on the 11 month old one.

LLD is at least 5 years old. Every time you re-write it doesn't reset history.


> Again, I am truly sorry we were unable to come up with a perfect
> design the first time. For the record, I don't think it is perfect
> yet. There will likely be more big changes to lld. That is the cost of
> trying to build as good a linker as we can.

This is not about what you do. It's about *how* you do it.

We have developers trying to create a linker. They are working on LLD
because Chris wanted a true LLVM linker. But it seems that you want a
project that you can do whatever you want, whenever you want.

This is *NOT* open source. Right now, LLD is *nothing more* than Rui's
and Rafael's pet project. I cannot recommend Linaro to collaborate on
those terms, and I sincerely recommend anyone that is listening to
this thread to not do so either.


> Being open source doesn't mean I get to implement what someone else
> wants. You are more than welcome to send patches, but they have avoid
> harming the rest of the linker. In particular, at this early stage
> they cannot harm its development. Once we have a mature project we can
> actually evaluate tradeoff.

We're clearly not welcome to send patches. We did, and you re-wrote it
and committed without asking the original author.

So, the plan is to wait for you to finish the initial implementation
alone? Again? What do we do in the interim? How many times are we
going to go through this?

I have waited 2 years before LLD was barely useful, then Adhemerval
implemented the AArch64 back-end. Then you destroyed and now we have
waited another year, but we're still unable to collaborate. If
anything, now it's even harder than it was last year.

Why can't we help with the design, too? We know about ARM and AArch64,
that's what we do, and we can provide you with the expertise without
having to go on your own doing everything. That is the whole point of
collaborative development, and it seems that you're missing this
point.


> And just like we did, you are more than welcome to try to write
> something better. Please let us know how it goes.

Is this the position of every LLD developer?

Rui, Nick, Chris?

I'm seriously looking for others to chime in and let me know if that
is the final stance on LLD, so that I can finally write it off and go
work on another linker.

If the official position is that LLD is a project that only Rui and
Rafael can design and implement for another 2~3 years, I *cannot*
recommend Linaro and its members to participate.

cheers,
--renato
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[ACTIVITY] 30 May-3 June 2016

[Diana Picus]

== Progress ==

* Remove exit-on-error flag from CodeGen tests [TCWG-604] [4/10]
  - This is a follow-up of TCWG-592: when changing the diag handler,
some of the tests started to fail, so we had to add an exit-on-error
flag to preserve the old behaviour until we can fix the tests.
  - Patch fixing the MIR tests (PR27770) - still in upstream review
  - Submitted another patch fixing two other BPF tests (PR27768/9) -
committed upstream
  - Submitted a patch fixing one of the AMDGPU tests (PR27761) - in
upstream review
  - Investigating the ARM test (PR27765)

* Use git worktree in llvm helper scripts [TCWG-587] [4/10]
  - In review, hopefully we can wrap it up soon

* Misc [2/10]
  - More LLVM backend education (MI level), ARM ARM etc

== Plan ==

* Remove exit-on-error flag from CodeGen tests [TCWG-604]
  - Fix the ARM test

* Use git worktree in llvm helper scripts [TCWG-587]
  - Fix a regression in the error-handling
  - Address review comments
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[ACTIVITY] 30 May-3 June 2016

[Christophe Lyon]

== Progress ==
* Validation
  - trying to improve cleanup job such that they skip offline nodes
  - reviews

* Backports
  - successful backport for our gcc-6 branch

* GCC
  - regressions reports on trunk
  - preparing removal of neon-testgen.ml

* Misc (conf-calls, meetings, emails, )

== Next ==
* Validation
  - prepare switch to docker for buildfarm job
  - cleanup

* Backports

* GCC
  - trunk monitoring
  - more on AdvSIMD intrinsics
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Re: [lld] r271569 - Start adding tlsdesc support for aarch64.

[Renato Golin]

On 3 June 2016 at 01:53, Rui Ueyama  wrote:
> Not so fast to conclude that the community is not trustworthy, it doesn't
> consist of a single person or a single action.

This is not an isolated incident. This seems to be the general
behaviour around LLD, which is less so in the rest of the LLVM
projects.

The obliteration of the old ELF back-end was discussed only between a
few people, not on the list. The technical reasoning could have been
solid for a new back-end, but not for destroying fresh code. The
removal was weeks after Adhemerval had LLD bootstrapping Clang on
AArch64 upstream.

There were backlashes to that decision, as well as other decisions in
this list, and many people have already demonstrated discontent with
how LLD patches and decisions are handled.

During EuroLLVM's LLD presentation, a lot of people asked technical
questions about the implementation of wanted features like library
order, linker scripts, version scripts, and all answers were "it's not
that hard, it's all in my head, don't worry about it".

If this was a closed source project, and you, Rafael, Nick and PCC
were the team developing it, it'd be expected that the team lead would
have some leeway on the implementation and the consumers would have to
wait until it's ready. But this is open source, and that's absolutely
*not* how things work out here. That is *precisely* the problem, not
this one incident. This incident was just the tipping point.

That is why I personally don't trust the LLD community to act in the
open source way. I have seen it consistently repeated over the last
two years that I'm following. It makes no difference if this is a new
project or not, this is open source, and in open source we work
collaboratively. If you refuse people's patches because "you know
better", you're not doing open source and people doing it will move
elsewhere. This is not about you, me or Rafael, this is about the LLVM
linker.

So, I'll now be going back looking at MCLinker and see if we can make
a Linux/BSD ARM/AArch64 upstream linker out of it, compatible with the
GNU environment. As you can see [1], the development is still active,
up-to-date with modern LLVM and there are ARM and MIPS support
already, and the community there is far more receptive than LLD's.

We'll continue to work on ARM and AArch64 patches to LLD, but if
MCLinker proves an easier route to achieve our final goal, which is to
have a Lesser-licensed open source ARM/AArch64 linker for GNU/BSD
environments, and LLD's community continues to offer resistance and
bad behaviour, we'll slowly de-phase LLD in favour of MCLinker, at
least at Linaro.

Such is the nature of open source.

cheers,
--renato

[1] https://github.com/mclinker/mclinker
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