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Date:   Wed, 12 Jun 2019 09:26:52 -0500
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Kairui Song <kasong@redhat.com>,
        Alexei Starovoitov <ast@fb.com>,
        Song Liu <songliubraving@fb.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Kernel Team <Kernel-team@fb.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>
Subject: Re: Getting empty callchain from perf_callchain_kernel()
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On Wed, Jun 12, 2019 at 09:10:23AM -0400, Steven Rostedt wrote:
> On Tue, 11 Jun 2019 22:05:01 -0500
> Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> 
> > Right now, ftrace has a special hook in the ORC unwinder
> > (orc_ftrace_find).  It would be great if we could get rid of that in
> > favor of the "always use frame pointers" approach.  I'll hold off on
> > doing the kpatch/kprobe trampoline conversions in my patches since it
> > would conflict with yours.
> 
> Basically, IIUC, what you are saying is that the ftrace trampoline
> should always store the %sp in %rb even when CONFIG_FRAME_POINTER is not
> enabled? And this can allow you to remove the ftrace specific code from
> the orc unwinder?

Basically, yes.  Though the frame pointer encoding which Peter is adding
to the ftrace/kprobes trampolines might complicate things a bit.

-- 
Josh