From owner-freebsd-hackers@FreeBSD.ORG  Wed May 25 17:38:35 2011
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Date: Wed, 25 May 2011 19:20:32 +0200
From: Patrick Lamaiziere <patfbsd@davenulle.org>
To: freebsd-hackers@freebsd.org
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Subject: Re: DEBUG - analysing core dumps
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Le Wed, 25 May 2011 18:36:49 +0200,
Damien Fleuriot <ml@my.gd> a écrit :

Hello,

> Sadly, getting a backtrace with "bt" gives me more lines with "??",
> which is totally not helpful:
> [SNIP]
> #13 0x00007fffff1f9d70 in ?? ()
> #14 0x0000000000000000 in ?? ()
> #15 0x6f70732f7261762f in ?? ()
> #16 0x6c737973722f6c6f in ?? ()
> #17 0x5f6e70766f2f676f in ?? ()
> #18 0x746174732e676f6c in ?? ()
> #19 0x0000000000000065 in ?? ()
> #20 0x0000000000000000 in ?? ()
> [SNIP]
> 
> I am not sure what steps I should follow to get more information ?

You have to build the binary with debug symbols included.

The rsyslog port provides an option for this. Did you see this notice in
the port's makefile?

"
# XXX: 5.5.6+ seem to crash frequently with low-mid load 
# on FreeBSD, temporailiy enable debugging by default.
# Now we can send gdb backtraces into the list:
# rsyslog-users <rsyslog@lists.adiscon.com>
OPTIONS=        DEBUG   "Enable debugging"      on
"

Good luck...

Regards.