[llvm-dev] FYI, we've posted a component of Spectre mitigation on llvm-commits

Leslie Zhai via llvm-dev llvm-dev at lists.llvm.org
Fri Jan 5 04:13:32 PST 2018

Hi Chandler,

Thanks for your kind response and teaching!

I just use the pass and function names to take an instance, just like 
Alex taught me that GlobalISel also needs to consider about supporting 
target-specific CCState[1], so it might factor a few minor things, for 
example implement a retpoline framework to fix speculative execution 
issues, code reusable for other targets is better :)

Thanks for your teaching! I will read relative articles and papers more 

[1] http://lists.llvm.org/pipermail/llvm-dev/2018-January/120098.html

在 2018年01月05日 16:53, Chandler Carruth 写道:
> On Fri, Jan 5, 2018 at 12:51 AM Leslie Zhai via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>     Hi LLVM developers,
>     Does it need to implement <Target>RetpolineThunksPass,
>     `getOpcodeForRetpoline`, `EmitLoweredRetpoline`, etc. for other
>     Targets?
>     Or does it also need to implement `RetpolinePic` to inherit from
>     <Target> for LLD's Backends? Alex is my mentor, he is leading me to
>     maintain RISCV target, so I have such question, please give me
>     suggestions, thanks for your teaching!
> What you need will highly depend on the architecture. We've worked to 
> ensure this is effective on x86, but other architectures may need 
> different approaches or may desire different approaches for performance.
> If you read the support article linked in the commit log that 
> describes retpoline's strategy in much more detail, you can see the 
> criteria that determine whether it would be effective for a particular 
> architecture.
> That said, about the only thing that I suspect would be usefully 
> shared in terms of code will be the feature flags. The implementation 
> is pretty much 100% target-specific anyways. We could factor a few 
> minor things if it proves useful.
> That said -- I would also only use the term `retpoline` if you in fact 
> build a return-based trampoline as the mitigation. Other potential 
> mitigation code sequences would (IMO) be better named something else.
>     --
>     Regards,
>     Leslie Zhai - https://reviews.llvm.org/p/xiangzhai/
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>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
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Leslie Zhai - https://reviews.llvm.org/p/xiangzhai/

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