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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: 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>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: Getting empty callchain from perf_callchain_kernel()
Date: Tue, 11 Jun 2019 22:05:01 -0500	[thread overview]
Message-ID: <20190612030501.7tbsjy353g7l74ej@treble> (raw)
In-Reply-To: <20190524085319.GE2589@hirez.programming.kicks-ass.net>

On Fri, May 24, 2019 at 10:53:19AM +0200, Peter Zijlstra wrote:
> > For ORC, I'm thinking we may be able to just require that all generated
> > code (BPF and others) always use frame pointers.  Then when ORC doesn't
> > recognize a code address, it could try using the frame pointer as a
> > fallback.
> 
> Yes, this seems like a sensible approach. We'd also have to audit the
> ftrace and kprobe trampolines, IIRC they only do framepointer setup for
> CONFIG_FRAME_POINTER currently, which should be easy to fix (after the
> patches I have to fix the FP generation in the first place:
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=x86/wip

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.

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...

Here are my latest BPF unwinder patches in case anybody wants a sneak
peek:

  https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=bpf-orc-fix

-- 
Josh

  parent reply	other threads:[~2019-06-12  3:05 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <3CD3EE63-0CD2-404A-A403-E11DCF2DF8D9@fb.com>
     [not found] ` <20190517074600.GJ2623@hirez.programming.kicks-ass.net>
     [not found]   ` <20190517081057.GQ2650@hirez.programming.kicks-ass.net>
     [not found]     ` <CACPcB9cB5n1HOmZcVpusJq8rAV5+KfmZ-Lxv3tgsSoy7vNrk7w@mail.gmail.com>
     [not found]       ` <20190517091044.GM2606@hirez.programming.kicks-ass.net>
2019-05-17 18:40         ` Getting empty callchain from perf_callchain_kernel() Song Liu
2019-05-17 21:06           ` Alexei Starovoitov
2019-05-17 21:48             ` Song Liu
2019-05-19 18:07               ` Kairui Song
2019-05-20 17:22                 ` Song Liu
2019-05-22 13:51                   ` Peter Zijlstra
2019-05-19 18:06         ` Kairui Song
2019-05-20 17:16           ` Song Liu
2019-05-20 17:19           ` Song Liu
2019-05-22 14:02           ` Peter Zijlstra
2019-05-22 14:49             ` Alexei Starovoitov
2019-05-22 17:45               ` Josh Poimboeuf
2019-05-22 23:46                 ` Josh Poimboeuf
2019-05-23  6:48                   ` Kairui Song
2019-05-23  8:27                     ` Song Liu
2019-05-23  9:11                       ` Kairui Song
2019-05-23 13:32                     ` Josh Poimboeuf
2019-05-23 14:50                       ` Kairui Song
2019-05-23 15:24                         ` Josh Poimboeuf
2019-05-23 16:41                           ` Kairui Song
2019-05-23 17:27                             ` Josh Poimboeuf
2019-05-24  2:20                               ` Kairui Song
2019-05-24 23:23                                 ` Josh Poimboeuf
2019-05-27 11:57                                   ` Kairui Song
2019-06-06 16:04                                     ` Song Liu
2019-06-06 23:58                                       ` Josh Poimboeuf
2019-06-11 21:03                                       ` Josh Poimboeuf
2019-05-24  8:53                           ` Peter Zijlstra
2019-05-24 13:05                             ` Josh Poimboeuf
2019-06-12  3:05                             ` Josh Poimboeuf [this message]
2019-06-12  8:54                               ` Peter Zijlstra
2019-06-12 14:50                                 ` Josh Poimboeuf
2019-06-13 20:26                                   ` Josh Poimboeuf
2019-06-12 13:10                               ` Steven Rostedt
2019-06-12 14:26                                 ` Josh Poimboeuf

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