Re: [RFC]-Approaches to user space probes

[fche at redhat dot com (Frank Ch. Eigler)]

anil.s.keshavamurthy wrote:

> [...]
> Sure, their is some advantange in 4, but the thing we need to see
> is whether this apporach suits probing different kinds of 
> application(mainly java apps).

Could you explain why you think Java would be harder to instrument
with kernel-space probes?  We may opt to compose user-kprobes along
the lines of #4, and static instrumentation (a libmudflap.so
containing hooks for language interpreters to hook up to and pass
event parameters).


> >   probe user.module("/lib/libc.so.6").function("strlen") {
> >       in_strlen[tid()] = 1
> Setting a variable in function entry probe and 
> later trying to reset in the function return probe
> is very problematic.	

> [...]
> >   probe user.module("/lib/libc.so.6").function("strlen").return {
> >       delete in_strlen[tid()]
> [...]  in_strlen[tid()] will never gets reset and the pagefault
> count will have wrong value.

That is not such a big problem.  Should such an unfortunate timing
glitch occur, the system would report a missed probe.  The user could
then try again.


- FChE