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SubjectRe: System call instrumentation
* Ingo Molnar (mingo@elte.hu) wrote:
>
> * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:
>
> > > hm, i'm not sure about this. I've implemented system call tracing in
> > > -rt [embedded in the latency tracer] and it only needed changes in
> > > entry.S, not in every system call site. Now, granted, that tracer
> > > was simpler than what LTTng tries to do, but do we _really_ need
> > > more complexity? A trace point that simply expresses:
> > >
> > > sys_call_event(int sysno, long param1, long param2, long param3,
> > > long param4, long param5, long param6);
> > >
> >
> > That would work for all system calls that doesn't have parameters like
> > "const char __user *filename".
>
> what's the problem with them? Do you want to follow those parameters?
>
> Ingo

Ideally, I'd like to have this kind of high-level information :

event name : kernel syscall
syscall name : open
arg1 (%s) : "somefile" <-----
arg2 (%d) : flags
arg3 (%d) : mode

However, "somefile" has to be read from userspace. With the protection
involved, it would cause a performance impact to read it a second time
rather than tracing the string once it's been copied to kernel-space.

Mathieu

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


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