Re: Systemtap userspace probing: status and roadmap?

[Mark Wielaard <mjw at redhat dot com>]

Hi,

On Wed, 2008-11-05 at 14:00 +0100, Mark Wielaard wrote:
> Note, that Fedora 9 kernels (2.6.26 based) contain an alternative
> utrace version that doesn't seem very stable combined with the new
> uprobes version 2 (and doesn't work at all against uprobes version 1).
> So you really want either a CentOS or Fedora 10/rawhide kernel for now
> to play with the user space probes.

This seems untrue. It must have been my local changes that made it not
work. There is an issue currently with utrace as in the fedora kernel
(any version) as described in bug #6964. The workaround for that
(currently committed in git 1b1d63) makes that -c doesn't work reliably.
I had that workaround disabled which seems to have caused my
instability. So the latest Fedora 9 kernel should be enough.

With current trunk systemtap and 2.6.26.6-79.fc9.x86_64
things like stap -v -e 'probe process("/bin/ls").function("*").call
{printf("%s=>%s(%s)\n", thread_indent(1),probefunc(), $$parms)} probe
process("/bin/ls").function("*").return {printf("%s<=%s %s\n",
thread_indent(-1), probefunc(), $$return)}' work just fine (given that
you have core-utils-debuginfo installed). And look pretty spectacular :)

Cheers,

Mark