Entry point publishing in Truffle OptimizedCallTarget, on AArch64

[Andrew Dinn]

Hi Aleksander,

I have quickly eyeballed your patch and it looks ok. I'll try applying
the patch and building it this afternoon (once I have got some other
graal fixes I am working on out of the way).

If it builds ok I will then take out the disabling check and try to run
it. Is there a specific test I can use to ensure I exercise the changed
code?

regards,


Andrew Dinn
-----------

On 14/06/17 09:09, Aleksandar Prokopec wrote:
> Dear Andrew,
> 
> I have yesterday submitted a pull request to the Graal compiler, which
> should resolve a rare race condition that happens during Truffle's code
> installation. In short, the race condition existed because: after the
> code got installed with JVMCI, the "entryPoint" field in the
> "InstalledCode" class became visible to other threads, but the
> Truffle-level assumptions were not yet associated with that code [2].
> 
> My fix solves this by introducing the rule that Truffle
> OptimizedCallTarget's entry points addresses can only be jumped to if
> the lowest bit of the "entryPoint" field is set to "1". In other words,
> setting the lowest bit means that the "entryPoint" is published. The
> tail call code that gets patched at the beginning of the code of every
> OptimizedCallTarget must now not only check that the "entryPoint" is
> non-null, but also check that the lowest bit is "1".
> 
> I have implemented the fix on x86, SPARC and AArch64. However, I was
> only able to run and test this x86 and SPARC, since we have no AArch64
> machines. Since you've been involved with a lot of AArch64 maintenance
> in the past, I am assuming that you have access to a proper machine. If
> so, could you perhaps validate that my fix on AArch64 is correct (files
> under links [3] [4] [5]), or suggest changes?
> 
> Note that the new functionality, "entryPoint" tagging, is currently
> disabled [6] on AArch64, since I was not sure about my fix.
> 
> Thanks a lot,
> Alex
> 
> [1]
> https://github.com/graalvm/graal/commit/28b5474a1f6882f30c883c33012cd1bac8c2a646
> 
> 
> [2]
> https://github.com/graalvm/graal/blob/master/compiler/src/org.graalvm.compiler.truffle/src/org/graalvm/compiler/truffle/TruffleCompiler.java#L234
> 
> 
> [3]
> https://github.com/graalvm/graal/commit/28b5474a1f6882f30c883c33012cd1bac8c2a646#diff-d53ecccd225be6a6ece41d8c64579c7a
> 
> 
> [4]
> https://github.com/graalvm/graal/commit/28b5474a1f6882f30c883c33012cd1bac8c2a646#diff-7a3deff5793b399e8a3b008e14fb14cf
> 
> 
> [5]
> https://github.com/graalvm/graal/commit/28b5474a1f6882f30c883c33012cd1bac8c2a646#diff-6a1d15e2ba69aa5ed34a906ecf895a1f
> 
> 
> [6]
> https://github.com/graalvm/graal/commit/28b5474a1f6882f30c883c33012cd1bac8c2a646#diff-b171c7113ea386f9a5af29d46cd4e7bcR238
> 
> 
> 

-- 
regards,


Andrew Dinn
-----------
Senior Principal Software Engineer
Red Hat UK Ltd
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