[curves] Distribution-ready optimized code

[Irene Knapp]

Ahh.  Thanks - that explains the problem a lot better.  In that case, I
don't have an easy solution for you. :)  I still wonder whether you can use
its backends without its bitcode or optimization passes, essentially just
as an assembler but without tying the ABI wrapping and such to text
transformations, which are always going to be very flaky.  But I see that
that's not as much of an advantage over using a traditional assembler as
I'd hoped it could be.

Irene

On Fri, Apr 3, 2015 at 11:42 AM Tony Arcieri <bascule at gmail.com> wrote:

> On Fri, Apr 3, 2015 at 11:35 AM, Irene Knapp <ireneista at gmail.com> wrote:
>
>> Surely, what you are describing is a lightweight tool that either
>> generates LLVM bitcode, or hooks into the LLVM backends at a slightly lower
>> level than that to output particular instructions when that's what you
>> really, really want - but I suspect its hinting system already makes that
>> unnecessary for this use-case.  LLVM bitcode is precisely this "mostly
>> concrete assembly" concept that you're describing.
>>
>
> The problem with using LLVM in this context is robust cryptographic
> implementations need to follow a very specific set of rules to avoid cache
> timing attacks, and LLVM is not designed to follow these rules:
>
> https://cryptocoding.net/index.php/Coding_rules
>
> LLVM has not been designed to support the generation of constant time code
> and is instead rather eager to do things like insert branches in otherwise
> branch free code if it thinks the code can be better optimized.
>
> --
> Tony Arcieri
>
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