Re: [PATCH tracing/kprobes 0/7] tracing/kprobes: kprobe-based eventtracer update and perf support

[Masami Hiramatsu]

Frederic Weisbecker wrote:
> On Mon, Sep 14, 2009 at 01:16:13PM -0400, Masami Hiramatsu wrote:
> > Frederic Weisbecker wrote:
> > > On Fri, Sep 11, 2009 at 12:03:30PM -0400, Masami Hiramatsu wrote:
> > > > Frederic Weisbecker wrote:
> > > > > May be another step in the todo-list that would be nice: define the format
> > > > > for a type. Like it's done from ftrace events.
> > > >
> > > > Thanks!
> > > >
> > > > BTW, I'm not sure what the type means. Each event already has its own
> > > > event ID and event_call. Could you tell me which part of ftrace I should
> > > > refer to ?
> > >
> > >
> > > Actually I meant the format for a field.
> > > Say you define filename=arg1, it would be nice to have
> > >
> > > 	print "%s", filename
> > >
> > > in the format file.
> >
> > Ah, indeed. It is better to support 'type' casting for each argument.
> > I think type casting can be done as below syntax.
> >
> > NAME=ARG:TYPE
> > e.g.
> > jiffies64=@jiffies64:u64
> > message=%ax:str
>
>
> Yeah looks good!
>
>
>
> > > Hmm, now that I think about it, we can't dereference an array...for now :-)
> >
> > :-)
> > BTW, currently, an entry of the array can be shown, e.g. +10(sa).
> > Hmm, for more complex dereference(e.g. accessing a->b[a->c]), it might need
> > another dereferencing syntax(e.g. "sa[16][sa[8]]"), or
> > just allow to use braces(e.g. "+(+8(sa))(+16(sa))").
>
>
> Well, that may be too much complexity.
> I guess if we want multi level dereference, say you want a->b->c
> it should be sufficient to probe the point where b->c gets it's
> value (if any).
>
> But it would be nice to fetch a range: sa[begin:end]
> Or at least just giving the length of the range.

Hmm, I think it is better to treat the range as a type, because
we don't know how to express each entry without the type.

NAME=ARG:TYPE[LEN]
e.g.
regs=sa:u64[16]

Thank you,

--
Masami Hiramatsu

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

e-mail: mhiramat@xxxxxxxxxx

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