Re: Cross instrumentation with user space tracing enabled

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

Hi -

hpatel05 wrote:

> [...]
> My setup is one of the most complex use case for systemtap :)
> - Cross Instrumentation with user space trace support required.
> - Host : Running CentOS 5.4 with 2.6.18-164.el5 i686
> - Target : Self compiled Kernel 2.6.32.10 i686, image size max 512 mb.

Sounds fine.

> My queries are as follows :
> 1) I was able to run normal kernel scripts successfully on target, but
> user space script is having issue.. [...]

You found the uprobes.ko bit.  git systemtap contains a fix to the
client/server code to automate this aspect too.

> 2) Is it possible to use for Systemtap without debuginfo ? e.g. Only
> with Kernel Markers support and User space traces enabled.

Kernel markers & tracepoints don't require kernel-debuginfo on the
systemtap compile (host) side.  Modern user-space markers (sys/sdt.h)
usually don't require userspace debuginfo either.  General user-space
probes may require userspace debuginfo (for the probed processes).

> As of now, I am working the long way of keeping debuginfo for target
> on Host box itself, I can't afford debuginfo on target as it goes
> beyond max image size.

Of course.  None of this is needed on the target.

> 3) This is with performance related. Pardon my kernel knowledge. How
> the dynamic filtering of traces actually works?

Each kernel & user-space marker/tracepoint is individually controlled.
Only those you attach to with live stap scripts represent any run-time
overhead.


- FChE