[PATCH] D41723: Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715, "Branch Target Injection", and is one of the two halves to Spectre..

[Chandler Carruth via Phabricator via llvm-commits]

chandlerc added a comment.

In https://reviews.llvm.org/D41723#987098, @samkellett wrote:

> @chandlerc is MacOS support omitted intentionally (ie. not implemented yet)?


Not at all, I just don't have a Mac system to test with...

> When I try using the `-mretpoline` flag on High Sierra I get the following:
> 
>   fatal error: error in backend: MachO doesn't support COMDATs, '__llvm_retpoline_r11' cannot be lowered.

This is just that I unconditionally used comdats and that doesn't work on MachO. We should use some other lowering strategy to ensure the thunks are merged by the Mac linker. I'm not an expert there, so would defer to others like Ahmed. Happy to review a patch fixing it though.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D41723