linux-kernel - Re: [PATCH V6 08/15] ftrace: Add perf text poke events for ftrace trampolines

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Message-ID: <76de871f-fb0a-6918-68a9-94aa7b049d6b@intel.com>
Date:   Mon, 27 Apr 2020 10:23:05 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>, Jiri Olsa <jolsa@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 08/15] ftrace: Add perf text poke events for ftrace
 trampolines

On 22/04/20 2:46 pm, Peter Zijlstra wrote:
> On Wed, Apr 22, 2020 at 10:39:06AM +0300, Adrian Hunter wrote:
>> On 21/04/20 4:45 pm, Peter Zijlstra wrote:
>>> On Sun, Apr 05, 2020 at 11:13:20PM +0300, Adrian Hunter wrote:
>>>> Add perf text poke events for ftrace trampolines when created and when
>>>> freed.
>>>
>>> Maybe also put in a little more detail on the various events. Because
>>> arch_ftrace_update_trampoline() can also generate text_poke_bp() events,
>>> to update an existing trampoline.
>>>
>>> A diagram, like with the kprobes thing perhaps.
>>
>> How about adding this:
>>
>> There can be 3 text_poke events for ftrace trampolines:
>>
>> 1. NULL -> trampoline
>>    By ftrace_update_trampoline() when !ops->trampoline
>>    Trampoline created
>>
>> 2. [e.g. on x86] CALL rel32 -> CALL rel32
>>    By arch_ftrace_update_trampoline() when ops->trampoline and
>>                         ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP
>>    [e.g. on x86] via text_poke_bp() which generates text poke events
>>    Trampoline-called function target updated
>>
>> 3. trampoline -> NULL
>>    By ftrace_trampoline_free() when ops->trampoline and
>>                  ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP
>>    Trampoline freed
> 
> Yes, very nice. Thanks!

Arnaldo, do you have this patchset on your radar?