From: Aleksa Sarai <cyphar@cyphar.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
"David S. Miller" <davem@davemloft.net>,
Masami Hiramatsu <mhiramat@kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Shuah Khan <shuah@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Brendan Gregg <bgregg@netflix.com>,
Christian Brauner <christian@brauner.io>,
Aleksa Sarai <asarai@suse.de>,
netdev@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v3 1/2] kretprobe: produce sane stack traces
Date: Thu, 8 Nov 2018 18:46:12 +1100 [thread overview]
Message-ID: <20181108074612.ldy6rozdpsdps6bf@yavin> (raw)
In-Reply-To: <20181106171501.59ccabbc@gandalf.local.home>
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On 2018-11-06, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Sun, 4 Nov 2018 22:59:13 +1100
> Aleksa Sarai <cyphar@cyphar.com> wrote:
>
> > The same issue is present in __save_stack_trace
> > (arch/x86/kernel/stacktrace.c). This is likely the only reason that --
> > as Steven said -- stacktraces wouldn't work with ftrace-graph (and thus
> > with the refactor both of you are discussing).
>
> By the way, I was playing with the the orc unwinder and stack traces
> from the function graph tracer return code, and got it working with the
> below patch. Caution, that patch also has a stack trace hardcoded in
> the return path of the function graph tracer, so you don't want to run
> function graph tracing without filtering.
Neat!
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 169b3c44ee97..aaeca73218cc 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -242,13 +242,16 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
> trace->calltime = current->ret_stack[index].calltime;
> trace->overrun = atomic_read(¤t->trace_overrun);
> trace->depth = index;
> +
> + trace_dump_stack(0);
Right, this works because save_stack is not being passed a pt_regs. But if
you pass a pt_regs (as happens with bpf_getstackid -- which is what
spawned this discussion) then the top-most entry of the stack will still
be a trampoline because there is no ftrace_graph_ret_addr call.
(I'm struggling with how to fix this -- I can't figure out what retp
should be if you have a pt_regs. ->sp doesn't appear to work -- it's off
by a few bytes.)
I will attach what I have at the moment to hopefully explain what the
issue I've found is (re-using the kretprobe architecture but with the
shadow-stack idea).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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next prev parent reply other threads:[~2018-11-08 7:46 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 8:35 [PATCH v3 0/2] kretprobe: produce sane stack traces Aleksa Sarai
2018-11-01 8:35 ` [PATCH v3 1/2] " Aleksa Sarai
2018-11-01 15:20 ` Masami Hiramatsu
2018-11-01 21:13 ` Aleksa Sarai
2018-11-02 3:04 ` Masami Hiramatsu
2018-11-02 4:37 ` Aleksa Sarai
2018-11-03 12:47 ` Masami Hiramatsu
2018-11-02 0:47 ` Steven Rostedt
2018-11-02 5:05 ` Aleksa Sarai
2018-11-02 6:59 ` Aleksa Sarai
2018-11-02 13:16 ` Steven Rostedt
2018-11-02 15:43 ` Josh Poimboeuf
2018-11-02 16:13 ` Steven Rostedt
2018-11-03 13:00 ` Masami Hiramatsu
2018-11-03 13:13 ` Steven Rostedt
2018-11-03 16:34 ` Masami Hiramatsu
2018-11-03 17:30 ` Steven Rostedt
2018-11-03 17:33 ` Steven Rostedt
2018-11-04 2:25 ` Masami Hiramatsu
2018-11-03 7:02 ` Aleksa Sarai
2018-11-04 11:59 ` Aleksa Sarai
2018-11-06 22:15 ` Steven Rostedt
2018-11-08 7:46 ` Aleksa Sarai [this message]
2018-11-08 8:04 ` Aleksa Sarai
2018-11-08 14:44 ` Josh Poimboeuf
2018-11-09 7:26 ` Masami Hiramatsu
2018-11-09 15:10 ` Aleksa Sarai
2018-11-09 7:15 ` Masami Hiramatsu
2018-11-09 15:06 ` Aleksa Sarai
2018-11-10 15:31 ` Masami Hiramatsu
2018-11-12 10:38 ` Aleksa Sarai
2018-11-03 13:23 ` Masami Hiramatsu
2018-11-02 7:58 ` Aleksa Sarai
2018-11-02 4:01 ` kbuild test robot
2018-11-01 8:35 ` [PATCH v3 2/2] trace: remove kretprobed checks Aleksa Sarai
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