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

Hi LLVM developers,

Does it need to implement RetpolineThunksPass,
getOpcodeForRetpoline, EmitLoweredRetpoline, etc. for other Targets?
Or does it also need to implement RetpolinePic to inherit from
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.

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 :slight_smile:

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