[llvm-dev] Need help with code generation

[Rui Ueyama via llvm-dev]

On Tue, Mar 22, 2016 at 8:40 PM, Hal Finkel <hfinkel at anl.gov> wrote:

>
> ------------------------------
>
> *From: *"Rui Ueyama" <ruiu at google.com>
> *To: *"Hal Finkel" <hfinkel at anl.gov>
> *Cc: *"David Blaikie" <dblaikie at gmail.com>, "llvm-dev" <
> llvm-dev at lists.llvm.org>, "Bruce Hoult" <bruce at hoult.org>
> *Sent: *Tuesday, March 22, 2016 2:36:34 PM
> *Subject: *Re: [llvm-dev] Need help with code generation
>
> On Tue, Mar 22, 2016 at 7:36 PM, Rui Ueyama <ruiu at google.com> wrote:
>
>> I have a question. If there is a ELF verifier function that walks every
>> part of an ELF file to verify that the file is sane, and if you can call
>> that before calling LLD's function, are you guys happy with that?
>>
>
> I'd like to get you guys opinion on this question.
>
>
> I'll echo Rafael here. What does "sane" mean? If I define sane to mean,
> "will not cause lld to exhibit undefined behavior if later run over the
> same input", then this seems like the most efficient way of satisfying that
> goal (perhaps staged to avoid cache thrashing), and I'd like to know how
> much overhead it would add to run it in lld by default (even if we have an
> option to disable it for absolute speed).
>

ELF is a documented file format so if you are not sure if something should
be considered valid, you can take a look at the spec to determine whether
it is valid or not. File validity is an independent concept from LLD and I
think we can determine it according to the spec.

I have a different opinion about how it could be implemented. We have no
idea if it'd be faster if it is "embedded" to LLD, at least. And usually
separating passes leads to cleaner and more readable code.

Thanks again,
> Hal
>
>
>
>
>> On Tue, Mar 22, 2016 at 6:39 PM, Hal Finkel via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>>
>>> ------------------------------
>>>
>>> *From: *"David Blaikie via llvm-dev" <llvm-dev at lists.llvm.org>
>>> *To: *"Rafael Espíndola" <rafael.espindola at gmail.com>
>>> *Cc: *"llvm-dev" <llvm-dev at lists.llvm.org>, "Bruce Hoult" <
>>> bruce at hoult.org>
>>> *Sent: *Tuesday, March 22, 2016 10:18:03 AM
>>> *Subject: *Re: [llvm-dev] Need help with code generation
>>>
>>>
>>>
>>> On Tue, Mar 22, 2016 at 4:27 AM, Rafael Espíndola <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> > Maybe not, but it's not impossible either - browsers manage to harden
>>>> themselves against malicious input and they operate in a far hostile
>>>> environment with many more input formats than we do.
>>>>
>>>> It is important to note how different they are. Both Firefox and
>>>> Chromium have people working just to try to make them more secure.
>>>> Compare that with LLVM: One week ago I pointed out that your patch
>>>> (r263521) introduces a crash. It still hasn't been reverted or even
>>>> acknowledge yet.
>>>>
>>>>
>>>> > I'm not trying to shift your personal goal, or to direct the features
>>>> that you choose to put your time into, but I am interested in project
>>>> policy.
>>>>
>>>> Why do you care about policy that is not followed? A policy saying
>>>> llvm should not crash on any input is as relevant as one that says
>>>> that clang should keep bootstrapping in under one second.
>>>>
>>>
>>> It's pretty different when you say, essentially, that patches to address
>>> these things are unlikely to be accepted. It doesn't seem surprising that
>>> people wouldn't try to provide those patches and would choose not to use
>>> the project if that's the expressed policy of the developers on the project
>>> and doesn't line up with the needs of other people.
>>>
>>>
>>> +1
>>>
>>>  -Hal
>>>
>>>
>>>
>>>>
>>>> So, if we stick to reality, what we have is that lld (ELF and COFF)
>>>> are already the most reliable parts of the toolchain. If not for Rui
>>>> and I being upfront about it most people would not even know that you
>>>> could crash it. So please, just let us keep working on the most
>>>> reliable part of the toolchain.
>>>>
>>>> Cheers,
>>>> Rafael
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>
>>>
>>> _______________________________________________
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>>>
>>>
>>>
>>> --
>>> Hal Finkel
>>> Assistant Computational Scientist
>>> Leadership Computing Facility
>>> Argonne National Laboratory
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>
>
>
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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