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

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Message-ID: <20200427143442.14d929f0@gandalf.local.home>
Date:   Mon, 27 Apr 2020 14:34:42 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.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 Mon, 27 Apr 2020 10:23:05 +0300
Adrian Hunter <adrian.hunter@...el.com> wrote:

> 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?

Arnaldo deals with the userspace perf code. This looks like it needs to go
through the x86 tree.

-- Steve