Messages in this thread | | | Date | Sat, 9 May 2009 16:06:29 +0200 | Subject | Re: [RFC] convert ftrace syscall tracer to TRACE_EVENT() | From | Frédéric Weisbecker <> |
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2009/5/9 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>: > * Ingo Molnar (mingo@elte.hu) wrote: >> >> * 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) >> > > I would expect to use copy_string_from_user (for strings) > and copy_from_user for structures, because without any strings > (especially), the trace information become much less useful.
Yeah, for structures we would just need the copy_from_user.
> This should probably be done at the TP_fast_assign level. > > Note that ftrace fields do not support variable length strings, AFAIK.
It does! Look at the __string() field :)
> Mathieu > >> Can you see any complication? >> >> Ingo > > -- > Mathieu Desnoyers > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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