Improved Retpoline Code In The Linux 5.16 Kernel

Merged last week into the Linux 5.16 kernel is improved Retpoline "return trampoline" code.

Phoronix readers should be very familiar with Retpolines by now as being used for Spectre Variant Two mitigations. This improved Retpoline code in Linux 5.16 as part of the "objtool/core" changes rewrites Retpolines to indirect instructions in situations where Retpolines are not enabled. There is also a change for rewriting an indirect LFENCE for the AMD handling. The x86 BPF code is also better handled around its Retpoline behavior.

The updated objtool code should see a lower memory footprint and better optimizations around the run-time patching as a result. More details via the objtool pull of the material that made it into the kernel last week.