From: Peter Zijlstra <peterz@infradead.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Borislav Petkov <bp@alien8.de>, "H . Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Mathieu Poirier <mathieu.poirier@linaro.org>,
Leo Yan <leo.yan@linaro.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Jiri Olsa <jolsa@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V4 08/13] ftrace: Add perf text poke events for ftrace trampolines
Date: Wed, 1 Apr 2020 13:14:33 +0200 [thread overview]
Message-ID: <20200401111433.GD20713@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <7e54c145-28d2-5175-6882-9f19e3939f13@intel.com>
On Wed, Apr 01, 2020 at 01:42:50PM +0300, Adrian Hunter wrote:
> On 1/04/20 1:09 pm, Peter Zijlstra wrote:
> > On Wed, Mar 04, 2020 at 11:06:28AM +0200, Adrian Hunter wrote:
> >> Add perf text poke events for ftrace trampolines when created and when
> >> freed.
> >
> > If I'm not mistaken that ends up like so:
> >
> > static void ftrace_update_trampoline(struct ftrace_ops *ops)
> > {
> > + unsigned long trampoline = ops->trampoline;
> > +
> > arch_ftrace_update_trampoline(ops);
> > + if (ops->trampoline && ops->trampoline != trampoline &&
> >> + (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP)) {
> >> + /* Add to kallsyms before the perf events */
> > + ftrace_add_trampoline_to_kallsyms(ops);
> >> + perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_OOL,
> >> + ops->trampoline, ops->trampoline_size, false,
> >> + FTRACE_TRAMPOLINE_SYM);
> >> + /*
> >> + * Record the perf text poke event after the ksymbol register
> >> + * event.
> >> + */
> >> + perf_event_text_poke((void *)ops->trampoline, NULL, 0,
> >> + (void *)ops->trampoline,
> >> + ops->trampoline_size);
> > }
> > }
> >
> > And afaict, that is wrong.
> >
> > The thing is; arch_ftrace_update_trampoline() can actually *update* an
> > existing trampoline, as per the name. Yes it also creates a trampoline
> > if there isn't one already, but if there already is one, it will modify
> > it in-place.
> >
> > I see the appeal of having this event in generic code; but I'm thinking
> > you'll need the update even in arch code anyway, at which point it'd
> > probably be easier to do all of this in arch code.
>
> For x86, we use text_poke_bp for updates which already does text_poke events
> via text_poke_bp_batch.
Ah, indeed! Damn, I even wrote that code :/
> It might be reasonable to assume other architectures will also need to put
> updates through a common text poker which will take care of text_poke events.
You'd better look, I recently rewrote the x86/ftrace code to be 'sane'
and not re-implement all the text poking stuff itself.
But I suppose that any arch adding support for this can fix that up if
needed.
next prev parent reply other threads:[~2020-04-01 11:14 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-04 9:06 [PATCH V4 00/13] perf/x86: Add perf text poke events Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 01/13] perf: Add perf text poke event Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 02/13] perf/x86: Add support for perf text poke event for text_poke_bp_batch() callers Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 03/13] kprobes: Add symbols for kprobe insn pages Adrian Hunter
2020-03-05 5:58 ` Masami Hiramatsu
2020-03-05 6:10 ` Alexei Starovoitov
2020-03-05 9:04 ` Masami Hiramatsu
2020-03-24 12:31 ` Peter Zijlstra
2020-03-24 12:54 ` Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 04/13] kprobes: Add perf ksymbol events " Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 05/13] perf/x86: Add perf text poke events for kprobes Adrian Hunter
2020-03-24 12:21 ` Peter Zijlstra
2020-03-26 1:58 ` Masami Hiramatsu
2020-03-26 7:42 ` Adrian Hunter
2020-03-27 8:36 ` [PATCH V5 " Adrian Hunter
2020-03-31 23:44 ` Masami Hiramatsu
2020-04-01 10:13 ` Peter Zijlstra
2020-03-04 9:06 ` [PATCH V4 06/13] ftrace: Add symbols for ftrace trampolines Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 07/13] ftrace: Add perf ksymbol events " Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 08/13] ftrace: Add perf text poke " Adrian Hunter
2020-04-01 10:09 ` Peter Zijlstra
2020-04-01 10:42 ` Adrian Hunter
2020-04-01 11:14 ` Peter Zijlstra [this message]
2020-03-04 9:06 ` [PATCH V4 09/13] perf kcore_copy: Fix module map when there are no modules loaded Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 10/13] perf evlist: Disable 'immediate' events last Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 11/13] perf tools: Add support for PERF_RECORD_TEXT_POKE Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 12/13] perf tools: Add support for PERF_RECORD_KSYMBOL_TYPE_OOL Adrian Hunter
2020-03-04 9:06 ` [PATCH V4 13/13] perf intel-pt: Add support for text poke events Adrian Hunter
2020-03-16 7:07 ` [PATCH V4 00/13] perf/x86: Add perf " Adrian Hunter
2020-03-24 9:29 ` Adrian Hunter
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