core not dumped

[James]

There is some underlying problem with imap-login but in order to debug 
it I'd like to see a core file.  On error dovecot reports "core not 
dumped".  If I put "abort()" in the code at the point it is reporting 
then a core file is written, so there is no OS reason why a core can not 
be written.  It appears to be dovecot's choice to control the child.  In 
an attempt to obtain a core file I have:

service imap-login {
   chroot =
   drop_priv_before_exec = yes
   user = dovecot
}

How can I make imap-login to produce a core file?


Syslog error report:
Mar 18 09:22:28 MAILHOST dovecot: [ID 583609 mail.crit] imap-login: 
Fatal: master: service(imap-login): child 10812 killed with signal 11 
(core not dumped) [last ip=111.222.333.444]



Should anyone care at this point (before I've looked at a core file) the 
error is related to;
imap-login: Disconnected (no auth attempts in 0 secs): user=<>,



James.