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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
next prev parent reply other threads:[~2019-06-12 3:05 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-16 23:51 Song Liu
2019-05-17 7:46 ` Peter Zijlstra
2019-05-17 8:10 ` Peter Zijlstra
2019-05-17 8:15 ` Kairui Song
2019-05-17 8:32 ` Kairui Song
2019-05-17 16:22 ` Song Liu
2019-05-17 9:10 ` Peter Zijlstra
2019-05-17 18:40 ` 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
2019-05-22 18:07 ` Josh Poimboeuf
2019-05-22 21:55 ` Alexei Starovoitov
2019-05-17 16:32 ` Song Liu
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