This is my first post to this list so ... HI !
I'm just starting out with sdcc on 18FXXX PICs.
I was having the problem with gplink that was mentioned on here where
linking fails with the message
"assertion "sym != NULL" failed: file "gpcofflink.c", line 203"
I raised this problem on the gnupic list, and the problem has now been
fixed in the latest nightly snapshots and in CVS.