Re: Getting empty callchain from perf_callchain_kernel()

From: Steven Rostedt
Date: Wed Jun 12 2019 - 09:15:03 EST

On Tue, 11 Jun 2019 22:05:01 -0500
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> 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?

-- Steve

> Though, hm, because of pt_regs I guess ORC would need to be able to
> decode an encoded frame pointer? I was hoping we could leave those
> encoded frame pointers behind in CONFIG_FRAME_POINTER-land forever...