[ Adding Ingo to cc because I believe it was his suggestion to hide the guess unwinder behind CONFIG_EXPERT. ] On Mon, Nov 06, 2017 at 06:27:53PM -0500, Mikulas Patocka wrote: > This patch fixes building of 64-bit kernel on 32-bit userspace (I tested > it on RHEL-6-i686 and Debian-Sid-x32). Thanks, I'll review the patch. > There are still some more bugs - when building 64-bit kernel on 32-bit > Debian 7 distribution, objtool corrupts object files so that the linker > doesn't recognize them (ld doesn't recognize the format of the file at all > and gold prints a lot of errors). Hm, we should figure out what's going on there... > Another problem - when building 32-bit kernel, why do you force frame > pointers on and why did you hide CONFIG_GUESS_UNWINDER behind > CONFIG_EXPERT? Frame pointers increase code size and register pressure, > most users don't need precise stacktraces, so CONFIG_GUESS_UNWINDER should > be default for non-expert users just like it was before. > > Is there some technical reason why do you want to avoid > CONFIG_GUESS_UNWINDER? The technical reason for avoiding the guess unwinder is that it's sketchy: it gives false positive results. Not only for oopses, but for all the other users of the unwinder: /proc/<pid>/stack, perf, lockdep, etc. So it's a correctness issue. I agree with you that the frame pointer unwinder has drawbacks, but if somebody cares about those drawbacks, I would consider that person an "expert" ;-) -- Josh -- 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
