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SubjectRe: [PATCH] tracing: Create generic syscall TRACE_EVENTs
* Ingo Molnar (mingo@elte.hu) wrote:
>
> * Josh Stone <jistone@redhat.com> wrote:
>
> > On 08/18/2009 06:32 PM, Li Zefan wrote:
> > > It would be much better to see a sample output of these TRACE_EVENTs,
> > > so we'll see the what's the output if a syscall has less than 6 args.
> > >
> > > And I guess it should be "(%lx, %lx, ..., %lx)"? Otherwise I think we'll
> > > see some negative values.
> >
> > Thanks, you're right -- the args should be unsigned long. Whether they
> > are hex or decimal doesn't matter to me, but I guess that does make
> > pointers easier to spot.
> >
> > Here's some output that I get on x86_64:
> >
> > > # tail trace
> > > tail-1106 [000] 113218.474657: syscall_enter: NR 2 (7f2d34dd38f0, 0, 7f2d35009010, 5, 4, ffffffffffffffb0)
> > >
> > > tail-1106 [000] 113218.474809: syscall_enter: NR 5 (3, 7f2d35009040, 7f2d35009040, 5, 4, ffffffffffffffb0)
> > >
> > > tail-1106 [000] 113218.474855: syscall_enter: NR 9 (0, 50d3ad0, 1, 2, 3, 0)
> > >
> > > tail-1106 [000] 113218.474946: syscall_enter: NR 3 (3, 7f2d2f9a0000, 5e22, 2, 3, 0)
> > >
> > > tail-1106 [000] 113218.475673: syscall_enter: NR 2 (7fff5e42a654, 0, 0, 7fff5e429600, 80, 3)
> >
> > It's very raw indeed, but that's what Ingo asked for. :) The
> > extra args show up as whatever happened to be in those registers.
>
> If the syscalls are handled as a single tracepoint, then they
> cannot really have per syscall properties.
>
> The per syscall tracepoints on the other hand give very finegrained
> information.
>

Hi Ingo,

Aiming to identify the event payload type with the event ID alone, I
would recommend either:

- one tracepoint per syscall argument set types (e.g. same syscall
prototype)
or
- one tracepoint per syscall (seems to be more straightforward)

Otherwise getting to fit a struct sockaddr into an integer might be
cumbersome.

Thanks,

Mathieu

> Note that via the use of filters one can limit the generic
> tracepoint to only output certain syscall NRs, and only with
> certain parameters.
>
> Ingo

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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