Re: [RFC] convert ftrace syscall tracer to TRACE_EVENT()

Ingo Molnar
2009-05-09T13:33:40Z

* Frédéric Weisbecker <fweisbec@gmail.com> wrote:

> > Secondly, we should reuse the information we get in
> > SYSCALL_DEFINE, to construct the TRACE_EVENT tracepoints
> > directly - without having to list all syscalls again in a
> > separate file.
>
> Indeed, that's not trivial though, but feasible. I'm not sure we
> can reuse the TRACE_EVENT macro directly inside SYSCALL_DEFINE.
> The resulting macro tempest effect that would occur confuses me
> and I have troubles to imagine the result.

Lets take an example. This syscall:

SYSCALL_DEFINE3(sched_setscheduler, pid_t, pid, int, policy,
struct sched_param __user *, param)

Is equivalent to:

SYSCALL_DEFINE3(name, t1, v1, t2, v2, t3, v3)

('t' for type, 'v' for variable/value).

This would transform into the following TRACE_EVENT() construct:

TRACE_EVENT_SYSCALL2():

TRACE_EVENT(sys_##name,
TP_PROTO(t1 v1, t2 v2),
TP_ARGS(v1, v2),
TP_STRUCT__entry(
__field(t1, v1)
__field(t2, v2)
),
TP_fast_assign(
__entry->v1 = v1;
__entry->v2 = v2;
),
TP_printk("%016Lx %016Lx", (u64)__entry->v1, (u64)__entry->v2)
);

We need TRACE_EVENT_SYSCALL[123456] definitions, and that's it.

The only place where we lose type information is the printk format -
but that's not a big issue, as i'd expect the event record to be the
main user of this.

[ In addition to this, we could extend DEFINE_SYSCALL[1..6] with a
(optional) format string definition field, and fill that in for
anything that matters. ]

Note, this assumes that all syscall types can be described via
__field() - i think that's correct. (we dont want to deref strings
as they are untrusted, and there are no arrays in syscall
parameters)

Can you see any complication?

Ingo