Re: Troubles with debug info, using systemtap on debian.

[Eugeniy Meshcheryakov <eugen@debian.org>]

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Hello,

9 листопада 2009 о 20:18 -0500 James Y Knight написав(-ла):
> Systemtap was working fine, for symbols in vmlinux, but segfaulted
> when trying to probe modules. E.g., the simplest script segfaulted
> in the translator.
> 
> probe module("autofs4").function("autofs4_fill_super") {}
I never saw systemtap segfaulting. I do not have autofs4 module, but i
tried with snd module and it works. What version of
systemtap/libelf1/libdw1 do you use?

> debug package. Well, that failed, because the files there are
> apparently expected to be called: *.ko.debug, but I had a file
> called:
> /usr/lib/debug/lib/modules/2.6.31-jknight-1-amd64/kernel/fs/autofs4/
> autofs4.ko
> instead. So, I symlinked it to be called autofs4.ko.debug.
My bad, I rarely clean the build tree... Still I do not understand why
this .debug is needed... I'm going to ask kernel-package or elfutils
maintainers to change this...

> 3) The debian kernel's debuginfo does "objcopy --only-keep-
> debug"...That seems like it shouldn't cause systemtap to blow up,
> but it does. I guess that's a known bug?
No it is not. At least not for me.

> 4) Why does it blow up *differently* depending on whether it found
> the file in /usr/lib/debug or /lib/modules?
> 
> 5) Whose bug is it that systemtap doesn't look for
> /usr/lib/debug/.../autofs4.ko, but only autofs4.ko.debug?
> Apparently this is a difference between debian and Fedora. Fedora
> systems append .debug, Debian systems do not. My guess: debian
> should be patching their copy of elfutils to not append ".debug"?
> But maybe that's an upstream bug, and it should try both by default
> (or something).
> I dunno.
Me too.

> 
> Someone else discovered the ".debug" issue in another program:
> http://www.visophyte.org/rev_control/patches/chronicle-recorder/debian-usr-lib-debug-support.patch
> And here's the debian reference about how to install debuginfo:
> http://www.debian.org/doc/developers-reference/best-pkging-practices.html#bpp-dbg
If it is really Fedors's policy to append .debug to file names under
/usr/lib/debug (I did not know about that), then I guess Debian elfutils
should be modified to not append .debug to kernel modules names to
comply with Debian policy. Or hopefuly it can be done upstream.

> 
> 
> I guess all these except the first are probably bugs in elfutils,
> not systemtap, so perhaps I should be reporting it there instead.
> But despite what you might think, I actually have no clue about any
> of this crap: any clue you might infer from the above has all been
> gained by random flailing over the course of the last couple hours.
> So I figure it's safer to report here, first and redirect if
> requested. :)
> 
> James

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