linux-kernel - Re: [PATCH 2/4] ftrace - add function

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20091210202317.GA6135@nowhere>
Date:	Thu, 10 Dec 2009 21:23:20 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Tim Bird <tim.bird@...sony.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] ftrace - add function_duration tracer

On Thu, Dec 10, 2009 at 09:29:27AM -0500, Steven Rostedt wrote:
> On Thu, 2009-12-10 at 13:03 +0100, Frederic Weisbecker wrote:
> 
> > This makes me feel I'm going to try converting the function graph tracer
> > into an event during the next cycle. It does not mean I could make it
> > usable as a perf event right away in the same shot that said, as you can
> > guess this is not a trivial plug. The current perf fast path is not yet
> > adapted for that.
> 
> I curious how you plan on doing this. The current event system shows one
> event per trace point. A straight forward approach would make every
> entry and exit of a function a trace point and that would lead to a very
> large kernel to handle that.

Oh no, I'm not planning to use tracepoints for that.

> Perhaps we could abstract out all entries and exits. We need to be able
> to link to a single point (entry or exit) not all.  This also has the
> added issue of using the ftrace infrastructure of nop the mcount call.
> We also need a way to enable a set of functions.
> 
> We may be able to abstract this out, but I'm hesitant on making this the
> only interface.

Hmm, yeah. The idea was just to move the use the struct trace to struct
trace_event. This would be about straightforward. A bit like kprobes: by
not using the TRACE_EVENT macros (would be impossible anyway) but
specific callbacks.

It would be one event.

set_ftrace_filter and set_graph_function can still be used to further
control dynamic patching. That's what I intended for a first conversion.

Another idea would be to abstract it through one trace event subsystem
that has one event per function. But that sounds a bit too much in term
of memory footprint. Also it's perhaps sufficient to abstract the
dynamic patching, but not enough to abstract set_graph_function.

But later on, a full trace event integration would probably imply
dicossiating dynamic tracing from the two function tracers.
For example if the function graph tracer asks to nop a function,
this shouldn't be propagated to a parallel function tracer user.
That's even worse once we get a perf integration, we can have
multiple parallel users of the function tracer. And patching
should probably adapt to parallel uses, maintaining a kind of
refcounting, extending the current function hashlist we have
for function profiling could probably help for that.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/