Re: [GIT PULL] tracing/kprobes: Add dynamic tracepoints + instructiondecoder

[Masami Hiramatsu]

Frederic Weisbecker wrote:
> On Thu, Aug 27, 2009 at 11:00:38AM -0400, Masami Hiramatsu wrote:
> > Frederic Weisbecker wrote:
> > > Ingo,
> > >
> > > This is the kprobes tracing pile of patches. I've tested it
> > > successfully by setting some kprobes through debugfs by hand.
> > >
> > > It brings no known regressions.
> > >
> > > However, the stress test provided by Masami have revealed some
> > > unstable points. Some symbols are unsafe to probe and raise
> > > probing recursion.
> > >
> > > I've added a tiny patch in the series that helps identifying the
> > > kprobe that has raised such situation.
> > > For example it has learned me today that it's unsafe to trace
> > > ret_from_exception() (obviously: it's on the int 3 handler path).
> >
> > Thank you, Frederic.
> >
> > I'm currently fixing those problems on x86-64 (on kvm).
> > I'll also check it on x86-32, and fix it.
> >
> > Thanks
>
>
>
> Cool.
> Don't hesitate to interate through small patches that fix these
> sites.
>
> So that I can continue to test it over time and report you what I find,
> may be I can try to fix some of them too.
>
> I haven't fixed ret_from_exception because I wasn't sure about the
> right thing to do: putting it in the kprobes section or blacklist its
> name. It's a bit more delicate to put assembly code into sections so... :)

It depends on implementation, but I think blacklist is the last resort. :)
AFAIK, some assembly codes are already pushed into kprobes section.

Thank you,

--
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@xxxxxxxxxx

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