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    SubjectRe: [PATCH 08/12] add trace events for each syscall entry/exit
    On Tue, Aug 11, 2009 at 01:45:12PM +0200, Ingo Molnar wrote:
    >
    > * Frederic Weisbecker <fweisbec@gmail.com> wrote:
    >
    > > > +struct trace_event event_syscall_enter = {
    > > > + .trace = print_syscall_enter,
    > > > + .type = TRACE_SYSCALL_ENTER
    > > > +};
    > > > +
    > > > +struct trace_event event_syscall_exit = {
    > > > + .trace = print_syscall_exit,
    > > > + .type = TRACE_SYSCALL_EXIT
    > > > +};
    > > > --
    > > > 1.6.2.5
    > > >
    > >
    > > Nice.
    > >
    > > It's a bit too bad that enter and exit must be that separated
    > > whereas their callbacks are pretty the same.
    > >
    > > But I guess if we want to nicely decouple both, we don't have the
    > > choice.
    >
    > Yeah - and enter and exit are different, in terms of state.
    >
    > One thing that would be nice in the future (as an add-on - this
    > patch-set looks useful already) is to allow the sampling of user
    > register state as well via these tracepoints. That way we'd have a
    > much faster (and completely transparent) implementation of strace in
    > essence, with unique features such as system-wide or per cpu
    > strace-ing.
    >
    > Ingo


    Indeed, a missing piece is the syscall record sampling with registers.
    Actually, IMO the registers themselves are not the right piece to export
    to perfcounter. It's too low-level.

    What we need are the fetched arguments, because a lot of them are adresses
    (even user adresses), pretty useless for perf tools.

    We can already and easily implement that simple args, like we do for ftrace.
    That's pretty trivial.



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