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From: Steven Rostedt <>
To: Jiri Olsa <>
Subject: Re: [RFC 0/4] tracing,x86_64 - function/graph trace without mcount/-pg/framepointer
Date: Thu, 03 Feb 2011 11:33:25 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, 2011-02-03 at 16:42 +0100, Jiri Olsa wrote:
> hi,
> I recently saw the direct jump probing made for kprobes
> and tried to use it inside the trace framework.
> The global idea is patching the function entry with direct
> jump to the trace code, instead of using pregenerated gcc
> profile code.

Interesting, but ideally, it would be nice if gcc provided a better
"mcount" mechanism. One that calls mcount (or whatever new name it would
have) before it does anything with the stack.

> I started this just to see if it would be even possible
> to hook with new probing to the current trace code. It
> appears it's not that bad. I was able to run function
> and function_graph trace on x86_64.
> For details on direct jumps probe, please check:
> I realize using this way to hook the functions has some
> drawbacks, from what I can see it's roughly:
> - no all functions could be patched

What's the reason for not all functions?

> - need to find a way to say which function is safe to patch
> - memory consumption for detour buffers and symbol records
> but seems there're some advantages as well:
> - trace code could be in a module

What makes this allow module code?

ftrace could do that now, but it would require a separate handler. I
would need to disable preemption before calling the module code function

> - no profiling code is needed
> - framepointer can be disabled (framepointer is needed for
>   generating profile code)

Again ideally, gcc should fix this.

-- Steve

  parent reply	other threads:[~2011-02-03 16:33 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-03 15:42 Jiri Olsa
2011-02-03 15:42 ` [PATCH 1/4] kprobe - ktrace instruction slot cache interface Jiri Olsa
2011-02-03 15:42 ` [PATCH 2/4] tracing - adding size parameter to do_ftrace_mod_code Jiri Olsa
2011-02-03 15:42 ` [PATCH 3/4] ktrace - function trace support Jiri Olsa
2011-02-03 15:42 ` [PATCH 4/4] ktrace - function graph " Jiri Olsa
2011-02-03 16:33 ` Steven Rostedt [this message]
2011-02-03 17:35   ` [RFC 0/4] tracing,x86_64 - function/graph trace without mcount/-pg/framepointer Frederic Weisbecker
2011-02-03 19:00     ` Steven Rostedt
2011-02-04  6:03 ` Masami Hiramatsu
2011-02-07 21:22 Josh Triplett
2011-02-07 21:32 ` Steven Rostedt

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