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    SubjectRe: [RFD] Kprobes/Kretprobes perf support

    Frederic Weisbecker wrote:
    > On Wed, Aug 12, 2009 at 01:02:24PM -0400, Masami Hiramatsu wrote:
    >> Masami Hiramatsu wrote:
    >>> Hi Frederic and Jason,
    >>> Frederic Weisbecker wrote:
    >>>> Frederic Weisbecker (3):
    >>>> tracing: Add ftrace event call parameter to its field descriptor handler
    >>>> Jason Baron (12):
    >>>> tracing: Add ftrace_event_call void * 'data' field
    >>> Both of you added a parameter to ftrace_event_call for passing
    >>> sycall name (call->data) to handlers, but one passes 'ftrace_event_call *'
    >>> and another passes 'void *'. It seems not enough unified.
    >>> And also, I'm now updating my patch for 'dynamic ftrace_event_call'
    >>> which adds 'ftrace_event_call *' for all handlers.
    >>> I think passing 'ftrace_event_call *' is more generic way
    >>> to do that. What would you think about that?
    >> Hmm, I changed my mind that passing 'void *' is enough, since
    >> all other fields of ftrace_event_call will be handled in
    >> trace_events.c.
    >> Thank you,
    > Well, actually I agree with you because:
    > - struct ftrace_event_call * is typed and let the compiler
    > be able to perform basic type checks.
    > (Even though that only delays the use of a void * type through
    > call->data)
    > - Further dynamic trace events might need other fields of struct ftrace_event_call *

    Hmm, so would you think passing 'struct ftrace_event_call *' is better?

    > While adding the struct ftrace_event_call * as parameter in the show_format
    > callback yesterday, I first thought about applying your "dynamic ftrace
    > event creation" patch.
    > But it was just too much for what I needed.

    Sure, syscall events can be defined in build time.

    > Speaking about your patches. You told recently you would be willing
    > to implement a perf support for kprobes, right? :-)

    Hmm, perhaps, I meant a profiling interface(
    However, that is interesting idea too.

    > I've thought about how to do that.
    > Ftrace events are supported by perfcounter currently but Kprobes
    > dynamic ftrace events are of a different nature: we must create them
    > before any toggling.
    > So a large part is already done through the ftrace events and the fact
    > that you create one dynamically for each kprobes (we'll just need
    > a little callback for perf sample submission but that's a small
    > point).

    Sure, even current implementation has some difference from tracepoint
    events... (currently, all of those kprobes events shares same event id,
    and each event can be identified by the event ip address)

    > The largest work that remains is to port the current powerful interface
    > to create these k{ret}probes (with requested arguments, etc...) through
    > ftrace but using perf open syscall.
    > And I imagine it won't be trivial.
    > Ingo, Peter do you have an idea on how we could do that?
    > We should be able to choose between a kprobe and kretprobe (these can
    > be two separate counters). And also one must be able to request the dump
    > of random desired parameters (or return values in case of kretprobe)
    > or registers...
    > May be we should use the perf attr by passing a __user address to a buffer
    > that contains all these options?
    > Once we get that to the kernel, that can be passed to ftrace-kprobe that
    > can parse it, create the desired trace event and rely on perf to create
    > a counter for it.
    > I guess that won't imply so much adds to Masami's patchset. Most of
    > the work is on the perf tools (parsing the user request).
    > ./perf kprobes -e (func|addr):(c|r):(a1,a2,a3,... | rax,rbx,rcx,...)
    > ^ ^
    > c = call = kprobe
    > r = return = kretprobe

    It could work. can it support some dereference format, like as +4(%sp)?

    Thank you,

    Masami Hiramatsu

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


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