I'm currently adding support for Two Level Linetables,
and noticed gdb going into an infinite loop on programs
compiled with them.
http://wiki.dwarfstd.org/index.php?title=TwoLevelLineTables

There are two bugs here:

1) gdb should punt when it sees a line table header version it doesn't
   understand.  The format could be different, there could be new fields
   or whatever, and blindly continuing is asking for trouble.

2) with the line table errantly read some fields like lh->range are
   getting a value of zero resulting in a SIGFPE (divide-by-zero).
   GDB's handling of SIGFPE it to mark the event with the async handler
   and return.  Eh?
   This results in an infinite loop of SIGFPE->handle_sigfpe->SIGFPE
   ->handle_sigfpe->...
   [filed as a separate bug, the number to be recorded once I know it]