[Ksummit-2008-discuss] DTrace

Theodore Tso tytso at mit.edu
Mon Jun 30 13:10:31 PDT 2008

On Mon, Jun 30, 2008 at 03:25:33PM -0400, Frank Ch. Eigler wrote:
> > The problem is that kernel developers are often juggling multiple
> > kernels, so kernel developers need to learn how to package up this
> > bulky data as well.
> They shouldn't have to repackage it at all - just leave it in the
> build tree.

The problem is that I am often juggling multiple kernel builds, and so
I don't want to keep the full build tree around.  So I just want to
extract out the specific files needed by Systemtap, especially becuase
they are so bulky.  So normally I actually do create specific packages
for the kernels I use (so I can give them to others or put them on my
server machines if they prove to be stable), and I want to be able to
package up the debuginfo files as well --- and only exactly the
debuginfo files which are needed to make systemtap work.

Stupid question --- has anyone thought about writing tools to strip
out specific debug information not needed by Systemtap?  For example,
I assume systemtap doesn't need the line number information, since you
can't set probes on arbitrary line numbers (and even if you could,
such tapsets would be so brittle that it wouldn't be funny); so would
the debuginfo files be smaller if that information were stripped out?
I understand that this would make the files less useful for
kdump/crash, but for systemtap only users, it might be quite useful.
What about stripping out the text segment of the object files, so you
aren't storing the information twice on disk, or compressing the
debuginfo files so they take up less room on disk?

> > [...] since the Wiki is filled with assertions (echoed by Ulrich in
> > the recent ksummit-discuss thread) about how Systemtap is a fast
> > moving project, and why it's absolutely necessary to grab the latest
> > bleeding edge sources from the git tree.
> That's been generally true - but that does not apply to elfutils.
> Some of us run with rather old elfutils just fine.

Hmm, well it doesn't work with the version of elfutils shipped with
the latest (8.04) Ubuntu.  <Checking to get the exact message
configure blew up with...>  Ah, now it does.  The wiki didn't say
anyting about needing --enable-staticdw, and I see with a recent
commit from last Friday you don't even need to specify
--enable-staticdw any more, it DTRT automatcally.  Nice!  Thanks for
fixing this!

							- Ted

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