On Sun, Dec 30, 2018 at 11:20 PM Nadav Amit <[email protected]> wrote: > > During runtime, we collect the targets of indirect branch targets and > patch them in. Patching is done asynchronously, by modifying each of the > relpoline code-paths separately while diverting code execution to the > other path during patching. Preemption is disabled while the code runs, > and we wait for preemption to occur on each core to ensure no core is > executing the patched code. > > To make use of relpolines, a worker goes over the experienced indirect > calls targets and sorts them according to frequency. The target that > was encountered most times is patched in. > > Periodically, the indirect branches are set back into learning mode to > see whether the targets have changed. The current policy might be too > aggressive. >
Can you put, in a comment somewhere, a clear description of the actual optpoline assembly sequence? I'm finding this code very hard to follow as is. Something like: /* * An optpoline is: * * cmp something, something else * je somewhere * [repeats of the above] * RETPOLINE (i.e. call some thunk) */ And please make it correct. Your comment says that preemption is disabled, but it's not obvious to me where this happens. Also, you define REX_B and don't use it. Are there other cases of that?
