On Wed, Feb 03, 2016 at 09:55:11AM +0100, Jiri Kosina wrote: > On Wed, 3 Feb 2016, AKASHI Takahiro wrote: > > those efforts, we are proposing[1] a new *generic* gcc option, -fprolog-add=N. > > This option will insert N nop instructions at the beginning of each function. > The interesting part of the story with ppc64 is that you indeed want to > create the callsite before the *most* of the prologue, but not really :) I was silently assuming that GCC would do this right on ppc64le; add the NOPs right after the TOC load. Or after TOC load and LR save? ... > The part of the prologue where TOC pointer is saved needs to happen before > the fentry/profiling call. Yes, any call, to any profiler/tracer/live patcher is potentially global and needs the _new_ TOC value. This proposal, if implemented in a too naive fashion, will worsen the problem we currently discuss: a few NOPs _never_ cause any global reference. GCC might be even more inclined to not load a new TOC value. That change would need to be fairly smart on ppc64le. 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
