Avoiding retpolines with static calls

January 2018 was a sad time in the kernel community. The Meltdown and Spectre vulnerabilities had finally been disclosed, and the required workarounds hurt kernel performance in a number of ways. One of those workarounds — retpolines — continues to cause pain, with developers going out of their way to avoid indirect calls, since they must now be implemented with retpolines. In some cases, though, there may be a way to avoid retpolines and regain much of the lost performance; after a long gestation period, the "static calls" mechanism may finally be nearing the point where it can be merged upstream.

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