netdev - Re: [PATCH v3 1/2] kretprobe: produce sane stack traces

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Message-ID: <20181102075818.fk55mxb3snqj5rjt@yavin>
Date:   Fri, 2 Nov 2018 18:58:18 +1100
From:   Aleksa Sarai <cyphar@...har.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Brendan Gregg <bgregg@...flix.com>,
        Christian Brauner <christian@...uner.io>,
        Aleksa Sarai <asarai@...e.de>, netdev@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v3 1/2] kretprobe: produce sane stack traces

On 2018-11-02, Aleksa Sarai <cyphar@...har.com> wrote:
> Unfortunately, I'm having a lot of trouble understanding how the current
> ftrace hooking works -- ORC has a couple of ftrace hooks that seem
> reasonable on the surface but I don't understand (for instance) how
> HAVE_FUNCTION_GRAPH_RET_ADDR_PTR *actually* works. Though your comment
> appears to indicate that it doesn't work for stack traces?

Sorry, I just figured out how it works! (To make sure I actually
understand -- retp is a pointer to the place in the stack where the
return address is stored, so it uniquely specifies what each trampoline
actually points to -- this trick could also be used for kretprobes).

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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