Re: [PATCH tracing/kprobes 0/7] tracing/kprobes: kprobe-basedevent tracer update and perf support
From: Frederic Weisbecker
Date: Mon Sep 14 2009 - 16:53:04 EST
On Mon, Sep 14, 2009 at 01:16:13PM -0400, Masami Hiramatsu wrote:
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Frederic Weisbecker wrote:
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> On Fri, Sep 11, 2009 at 12:03:30PM -0400, Masami Hiramatsu wrote:
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>> Frederic Weisbecker wrote:
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>>> May be another step in the todo-list that would be nice: define the format
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>>> for a type. Like it's done from ftrace events.
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>>
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>> Thanks!
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>>
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>> BTW, I'm not sure what the type means. Each event already has its own
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>> event ID and event_call. Could you tell me which part of ftrace I should
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>> refer to ?
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>>
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>
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> Actually I meant the format for a field.
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> Say you define filename=arg1, it would be nice to have
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>
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> print "%s", filename
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> in the format file.
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Ah, indeed. It is better to support 'type' casting for each argument.
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I think type casting can be done as below syntax.
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NAME=ARG:TYPE
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e.g.
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jiffies64=@jiffies64:u64
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message=%ax:str
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Yeah looks good!
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> Hmm, now that I think about it, we can't dereference an array...for now :-)
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:-)
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BTW, currently, an entry of the array can be shown, e.g. +10(sa).
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Hmm, for more complex dereference(e.g. accessing a->b[a->c]), it might need
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another dereferencing syntax(e.g. "sa[16][sa[8]]"), or
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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.
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