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Date:   Fri, 1 Mar 2019 10:29:11 -0600
From:   Josh Poimboeuf <>
To:     Jann Horn <>
Cc:     Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,
        Andrew Morton <>,
        syzbot <>,
        "H. Peter Anvin" <>,,,
        Masahiro Yamada <>,
        Michal Marek <>,
Subject: Re: [PATCH 2/2] x86/unwind: add hardcoded ORC entry for NULL

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


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