On Thu, Mar 24, 2016 at 03:44:55PM +0530, Kamalesh Babulal wrote: > * Torsten Duwe <duwe@xxxxxx> [2016-03-23 16:58:58]: > > > > > 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> > > Hi Torsten, > > Should this patch be applied over Petr Mladek's v4 ? Yes. Just omit the changes it makes to entry_64.S and use this instead. Torsten -- 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
