Re: [PATCH 2/2] x86/unwind: add hardcoded ORC entry for NULL

[Josh Poimboeuf]

On Fri, Mar 01, 2019 at 10:24:18AM -0600, Josh Poimboeuf wrote:
> > Is there a reason why the top-level Makefile only sets
> > -fno-optimize-sibling-calls if CONFIG_FRAME_POINTER is set?
> > I suspect that this is just a historical thing, because reliable
> > unwinding didn't work without frame pointers until ORC came along.
> > I'm not quite sure how best to express "don't do tail optimization if
> > either frame pointers are used or ORC is used" in a Makefile, and
> > whether we want an indirection through Kconfig for that, so I'm not
> > doing anything about it in this series.
> > Can someone send a patch to deal with it properly?
> 
> Why would sibling calls be a problem for ORC?  Once a function does a
> sibling call, it has effectively returned and shouldn't show up on the
> stack trace anyway.

Answering my own question, I guess some people might find it confusing
to have a caller skipped in the stack trace.  But nobody has ever
complained about it.

It's not a problem for livepatch since we only care about the return
path.

-- 
Josh