On 24/03/16 02:58, Torsten Duwe wrote: > Since nobody liked the extra stack frame nor its workarounds, here is > the next attempt. Assumptions: > > 1. Heuristics are bad. The better they are, the more subtly the > way they might fail. > > 2. The TOC pointer is usually dividable by 4, if not by 8. An odd > value never occurs. > > Conclusively, this patch unambiguously creates an odd TOC value when > an ftraced function's global entry point is used. Ftrace_caller will > then immediately fix it, and alongside gather the information whether > the made call was local or global. > > In case of live patching this information is furthermore used to decide > whether a klp_return_helper needs to be inserted or not. > CAVEAT: any frameless klp_return_helper does not play well with > sibling calls! There's an emergency exit that might work, at worst > it will cause an oops, but it surely avoids a lockup. > At least the live patching modules on ppc64le will need to be compiled > using the -fno-optimize-sibling-calls compiler flag! > > Thanks go to Michael Matz and Richard Biener for reassurance about > heuristics and pointers to the compiler flag. > > Signed-off-by: Torsten Duwe <duwe@xxxxxxx> > > I missed this yesterday, not on cc, but caught it on the list today Thanks for working on this. I did a quick look, so the CR+4 code plus heuristics for global/local call detection? I'll review this soon - hopefully tonight, but we have a long weekend coming up, so there might be delays. In the meanwhile feel free to add my signed-off-by for the CR+4 code. I am also looking at a different approach -- per thread lr0 stack. Balbir Singh. -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
