[Ksummit-2008-discuss] DTrace

Frank Ch. Eigler fche at redhat.com
Mon Jun 30 13:42:19 PDT 2008

Hi -

On Mon, Jun 30, 2008 at 04:10:31PM -0400, Theodore Tso wrote:
> [...]
> > 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 [...]

OK, we'll have to think about how to support that well.

> Stupid question --- has anyone thought about writing tools to strip
> out specific debug information not needed by Systemtap?

Yes, but nothing so simple/workable as to have been done already.

> For example, I assume systemtap doesn't need the line number
> information, since you can't set probes on arbitrary line numbers

Actually, we can - and now with wildcards too if you want
source-line-by-line tracing.  See the top of the NEWS file.

> (and even if you could, such tapsets would be so brittle that it
> wouldn't be funny); [...]

Yes, this is not a good fit for tapsets, but is handy for exploring
one's known version of code.  Also, we can now use relative line
numbers (line #10 within this function), which might be stable enough
for some tapset use.  (This is all very recent stuff, beware.)

> [...]  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?

This is roughly what the Fedora/RHEL-style separated .ko.debug files
do, though I don't know if they are that complete.  (They'd need a
copy of the symbol tables, and probably other stuff.)

- FChE

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