Tim, I have tried it twice, both times I seem to run into a bug of gdb:

till@till:~$ sudo gdb avahi-daemon
[sudo] password for till: 
GNU gdb (GDB) 7.5-ubuntu
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/sbin/avahi-daemon...Reading symbols from /usr/lib/debug/.build-id/47/c734e7af8803ff790794348387df57e5843b67.debug...done.
done.
(gdb) finish
The program is not being run.
(gdb) help finish
Execute until selected stack frame returns.
Upon return, the value returned is printed and put in the value history.
(gdb) run
Starting program: /usr/sbin/avahi-daemon 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Process 29509 died: No such process; trying to remove PID file. (/var/run/avahi-daemon//pid)
Found user 'avahi' (UID 111) and group 'avahi' (GID 120).
Successfully dropped root privileges.
avahi-daemon 0.6.31 starting up.
Successfully called chroot().
Successfully dropped remaining capabilities.
Loading service file /services/nut.service.
Loading service file /services/udisks.service.
Joining mDNS multicast group on interface virbr0.IPv4 with address 192.168.122.1.
New relevant interface virbr0.IPv4 for mDNS.
Joining mDNS multicast group on interface eth2.IPv4 with address 192.168.178.26.
New relevant interface eth2.IPv4 for mDNS.
Network interface enumeration completed.
Registering new address record for fe80::fc54:ff:feaa:6be4 on vnet1.*.
Registering new address record for fe80::fc54:ff:fe36:4ab on vnet0.*.
Registering new address record for 192.168.122.1 on virbr0.IPv4.
Registering new address record for 2002:5ddb:93a1:0:222:4dff:fe84:44d7 on eth2.*.
Registering new address record for 2002:5ddb:93a1:0:e904:5d60:fd49:58c8 on eth2.*.
Registering new address record for 192.168.178.26 on eth2.IPv4.
Server startup complete. Host name is till.local. Local service cookie is 3725523792.
Registering HINFO record with values 'X86_64'/'LINUX'.
Received response from host 192.168.122.1 with invalid source port 1048 on interface 'virbr0.0'
Received response from host 192.168.122.1 with invalid source port 1049 on interface 'virbr0.0'
^C
Program received signal SIGINT, Interrupt.
avahi_utf8_valid (
    str=str@entry=0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till")
    at utf8.c:59
59	utf8.c: No such file or directory.
(gdb) bt
#0  avahi_utf8_valid (
    str=str@entry=0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till")
    at utf8.c:59
#1  0x00007ffff7bd30f8 in avahi_unescape_label (
    name=name@entry=0x7fffffffe408, 
    dest=dest@entry=0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till", 
    size=size@entry=64) at domain.c:109
#2  0x00007ffff7bd3674 in avahi_domain_equal (a=0x6770ba "_ipp._tcp.local", 
    b=0x64bd00 "Hewlett-Packard\\032HP\\032Color\\032LaserJet\\0322600n\\032\\064\\032till._ipp._tcp.local") at domain.c:239
#3  0x00007ffff79b1bdf in packet_add_probe_query (s=s@entry=0x62b200, 
    p=p@entry=0x676590, pj=0x66f6f0, pj@entry=0x670d70) at probe-sched.c:201
#4  0x00007ffff79b1ece in elapse_callback (e=<optimized out>, 
    data=<optimized out>) at probe-sched.c:281
#5  0x00007ffff79a2093 in expiration_event (timeout=<optimized out>, 
    userdata=0x623ad0) at timeeventq.c:94
#6  0x00007ffff7bd56c8 in avahi_simple_poll_dispatch (s=0x6229c0)
    at simple-watch.c:570
#7  0x00007ffff7bd5785 in avahi_simple_poll_iterate (s=<optimized out>, 
    timeout=timeout@entry=-1) at simple-watch.c:605
#8  0x000000000040676c in run_server (c=<optimized out>) at main.c:1217
#9  main (argc=<optimized out>, argv=<optimized out>) at main.c:1635
(gdb) finish
Run till exit from #0  avahi_utf8_valid (
    str=str@entry=0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till")
    at utf8.c:59
0x00007ffff7bd30f8 in avahi_unescape_label (name=name@entry=0x7fffffffe408, 
    dest=dest@entry=0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till", 
    size=size@entry=64) at domain.c:109
109	domain.c: No such file or directory.
Value returned is $1 = 0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till"
(gdb) finish
Run till exit from #0  0x00007ffff7bd30f8 in avahi_unescape_label (
    name=name@entry=0x7fffffffe408, 
    dest=dest@entry=0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till", 
    size=size@entry=64) at domain.c:109
avahi_domain_equal (a=0x6770ba "_ipp._tcp.local", 
    b=0x64bd00 "Hewlett-Packard\\032HP\\032Color\\032LaserJet\\0322600n\\032\\064\\032till._ipp._tcp.local") at domain.c:240
240	in domain.c
Value returned is $2 = 0x7fffffffe410 "Hewlett-Packard HP LaserJet 1020 @ till"
(gdb) finish
Run till exit from #0  avahi_domain_equal (a=0x6770ba "_ipp._tcp.local", 
    b=0x64bd00 "Hewlett-Packard\\032HP\\032Color\\032LaserJet\\0322600n\\032\\064\\032till._ipp._tcp.local") at domain.c:240
0x00007ffff79b1bdf in packet_add_probe_query (s=s@entry=0x62b200, 
    p=p@entry=0x676590, pj=0x66f6f0, pj@entry=0x670d70) at probe-sched.c:201
201	probe-sched.c: No such file or directory.
Value returned is $3 = 0
(gdb) finish
Run till exit from #0  0x00007ffff79b1bdf in packet_add_probe_query (
    s=s@entry=0x62b200, p=p@entry=0x676590, pj=0x66f6f0, pj@entry=0x670d70)
    at probe-sched.c:201
0x00007ffff79b1ece in elapse_callback (e=<optimized out>, data=<optimized out>)
    at probe-sched.c:281
281	in probe-sched.c
Value returned is $4 = 1
(gdb) finish
Run till exit from #0  0x00007ffff79b1ece in elapse_callback (
    e=<optimized out>, data=<optimized out>) at probe-sched.c:281
expiration_event (timeout=<optimized out>, userdata=0x623ad0)
    at timeeventq.c:96
96	timeeventq.c: No such file or directory.
(gdb) finish
Run till exit from #0  expiration_event (timeout=<optimized out>, 
    userdata=0x623ad0) at timeeventq.c:96
avahi_simple_poll_dispatch (s=0x6229c0) at simple-watch.c:571
571	simple-watch.c: No such file or directory.
(gdb) finish
Run till exit from #0  avahi_simple_poll_dispatch (s=0x6229c0)
    at simple-watch.c:571
/build/buildd/gdb-7.5/gdb/breakpoint.c:8592: internal-error: set_momentary_breakpoint: Assertion `!frame_id_inlined_p (frame_id)' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n) n

/build/buildd/gdb-7.5/gdb/breakpoint.c:8592: internal-error: set_momentary_breakpoint: Assertion `!frame_id_inlined_p (frame_id)' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Create a core file of GDB? (y or n) n
(gdb) quit
A debugging session is active.

	Inferior 1 [process 31221] will be killed.

Quit anyway? (y or n) 
Please answer y or n.
A debugging session is active.

	Inferior 1 [process 31221] will be killed.

Quit anyway? (y or n) 
Please answer y or n.
A debugging session is active.

	Inferior 1 [process 31221] will be killed.

Quit anyway? (y or n) 
Please answer y or n.
A debugging session is active.

	Inferior 1 [process 31221] will be killed.

Quit anyway? (y or n) y
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ 
till@till:~$ sudo gdb avahi-daemon
GNU gdb (GDB) 7.5-ubuntu
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/sbin/avahi-daemon...Reading symbols from /usr/lib/debug/.build-id/47/c734e7af8803ff790794348387df57e5843b67.debug...done.
done.
(gdb) run
Starting program: /usr/sbin/avahi-daemon 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Process 31221 died: No such process; trying to remove PID file. (/var/run/avahi-daemon//pid)
Found user 'avahi' (UID 111) and group 'avahi' (GID 120).
Successfully dropped root privileges.
avahi-daemon 0.6.31 starting up.
Successfully called chroot().
Successfully dropped remaining capabilities.
Loading service file /services/nut.service.
Loading service file /services/udisks.service.
Joining mDNS multicast group on interface virbr0.IPv4 with address 192.168.122.1.
New relevant interface virbr0.IPv4 for mDNS.
Joining mDNS multicast group on interface eth2.IPv4 with address 192.168.178.26.
New relevant interface eth2.IPv4 for mDNS.
Network interface enumeration completed.
Registering new address record for fe80::fc54:ff:feaa:6be4 on vnet1.*.
Registering new address record for fe80::fc54:ff:fe36:4ab on vnet0.*.
Registering new address record for 192.168.122.1 on virbr0.IPv4.
Registering new address record for 2002:5ddb:93a1:0:222:4dff:fe84:44d7 on eth2.*.
Registering new address record for 2002:5ddb:93a1:0:e904:5d60:fd49:58c8 on eth2.*.
Registering new address record for 192.168.178.26 on eth2.IPv4.
Server startup complete. Host name is till.local. Local service cookie is 712852784.
Registering HINFO record with values 'X86_64'/'LINUX'.
Received response from host 192.168.122.1 with invalid source port 1049 on interface 'virbr0.0'
Invalid legacy unicast query packet.
Invalid legacy unicast query packet.
Invalid legacy unicast query packet.

Received response from host 192.168.122.1 with invalid source port 1049 on interface 'virbr0.0'
Received response from host 192.168.122.1 with invalid source port 1049 on interface 'virbr0.0'

Received response from host 192.168.122.1 with invalid source port 1049 on interface 'virbr0.0'
^C
Program received signal SIGINT, Interrupt.
__ctype_b_loc () at ../include/ctype.h:33
33	../include/ctype.h: No such file or directory.
(gdb) bt
#0  __ctype_b_loc () at ../include/ctype.h:33
#1  0x00007ffff7bd3062 in avahi_unescape_label (
    name=name@entry=0x7fffffffe400, 
    dest=dest@entry=0x7fffffffe450 "Hewlett-Packard HP Color LaserJet CM3530 MFP @ till", size=size@entry=64) at domain.c:76
#2  0x00007ffff7bd368f in avahi_domain_equal (a=0x6761ba "_ipps._tcp.local", 
    b=0x64e41c "032\\064\\032till._ipp._tcp.local") at domain.c:241
#3  0x00007ffff79b1bdf in packet_add_probe_query (s=s@entry=0x62b1f0, 
    p=p@entry=0x675690, pj=0x66f300, pj@entry=0x670230) at probe-sched.c:201
#4  0x00007ffff79b1ece in elapse_callback (e=<optimized out>, 
    data=<optimized out>) at probe-sched.c:281
#5  0x00007ffff79a2093 in expiration_event (timeout=<optimized out>, 
    userdata=0x623ad0) at timeeventq.c:94
#6  0x00007ffff7bd56c8 in avahi_simple_poll_dispatch (s=0x6229c0)
    at simple-watch.c:570
#7  0x00007ffff7bd5785 in avahi_simple_poll_iterate (s=<optimized out>, 
    timeout=timeout@entry=-1) at simple-watch.c:605
#8  0x000000000040676c in run_server (c=<optimized out>) at main.c:1217
#9  main (argc=<optimized out>, argv=<optimized out>) at main.c:1635
(gdb) finish
Run till exit from #0  __ctype_b_loc () at ../include/ctype.h:33
0x00007ffff7bd3062 in avahi_unescape_label (name=name@entry=0x7fffffffe400, 
    dest=dest@entry=0x7fffffffe450 "Hewlett-Packard HP Color LaserJet CM3530 MFP @ till", size=size@entry=64) at domain.c:76
76	domain.c: No such file or directory.
Value returned is $1 = (const short unsigned int **) 0x7ffff7fd76b8
(gdb) finish
Run till exit from #0  0x00007ffff7bd3062 in avahi_unescape_label (
    name=name@entry=0x7fffffffe400, 
    dest=dest@entry=0x7fffffffe450 "Hewlett-Packard HP Color LaserJet CM3530 MFP @ till", size=size@entry=64) at domain.c:76
avahi_domain_equal (a=0x6761ba "_ipps._tcp.local", 
    b=0x64e42c "_ipp._tcp.local") at domain.c:242
242	in domain.c
Value returned is $2 = 0x7fffffffe450 "Hewlett-Packard HP Color LaserJet CM3530 MFP @ till"
(gdb) finish
Run till exit from #0  avahi_domain_equal (a=0x6761ba "_ipps._tcp.local", 
    b=0x64e42c "_ipp._tcp.local") at domain.c:242
0x00007ffff79b1bdf in packet_add_probe_query (s=s@entry=0x62b1f0, 
    p=p@entry=0x675690, pj=0x66f300, pj@entry=0x670230) at probe-sched.c:201
201	probe-sched.c: No such file or directory.
Value returned is $3 = 0
(gdb) finish
Run till exit from #0  0x00007ffff79b1bdf in packet_add_probe_query (
    s=s@entry=0x62b1f0, p=p@entry=0x675690, pj=0x66f300, pj@entry=0x670230)
    at probe-sched.c:201
0x00007ffff79b1ece in elapse_callback (e=<optimized out>, data=<optimized out>)
    at probe-sched.c:281
281	in probe-sched.c
Value returned is $4 = 1
(gdb) finish
Run till exit from #0  0x00007ffff79b1ece in elapse_callback (
    e=<optimized out>, data=<optimized out>) at probe-sched.c:281
expiration_event (timeout=<optimized out>, userdata=0x623ad0)
    at timeeventq.c:96
96	timeeventq.c: No such file or directory.
(gdb) finish
Run till exit from #0  expiration_event (timeout=<optimized out>, 
    userdata=0x623ad0) at timeeventq.c:96
avahi_simple_poll_dispatch (s=0x6229c0) at simple-watch.c:571
571	simple-watch.c: No such file or directory.
(gdb) finish
Run till exit from #0  avahi_simple_poll_dispatch (s=0x6229c0)
    at simple-watch.c:571
/build/buildd/gdb-7.5/gdb/breakpoint.c:8592: internal-error: set_momentary_breakpoint: Assertion `!frame_id_inlined_p (frame_id)' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)