* H. J. Lu: > On Mon, Jan 8, 2018 at 12:20 AM, Florian Weimer <f...@deneb.enyo.de> wrote: >> * H. J. Lu: >> >>> Add -mindirect-branch-loop= option to control loop filler in call and >>> return thunks generated by -mindirect-branch=. 'lfence' uses "lfence" >>> as loop filler. 'pause' uses "pause" as loop filler. 'nop' uses "nop" >>> as loop filler. The default is 'lfence'. >> >> Why is the loop needed? Doesn't ud2 or cpuid stop speculative >> execution? > > My understanding is that a loop works better.
Better how? What about far jumps? I think they prevent some forms of prefetch on i386, so perhaps long mode is similar in that regard?
