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

Chandler Carruth via llvm-dev llvm-dev at lists.llvm.org
Fri Jan 5 00:53:41 PST 2018

On Fri, Jan 5, 2018 at 12:51 AM Leslie Zhai via llvm-dev <
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-dev at lists.llvm.org
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