Single stepping and "no line information"

[Stefano Sabatini]

I'm debugging an application which use a shared lib.

That library has been compiled on my system, and I added to the CFLAGS
used the -ggdb -O0 flags, so I'm quite sure that lib should contain
the source line symbol informations.

Nonetheless when I try to step into the library functions I get:

(gdb) s
Single stepping until exit from function su_clone_start, 
which has no line number information.

stefano@geppetto ~/s/ptlib> gdb --version
GNU gdb 6.8-debian
Copyright (C) 2008 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 "i486-linux-gnu".

Why gdb can't find the source line informations?

How can I verify (e.g. with a commandline tool) wether that
information is present directly analyzing the library files?

TIA.

Best regards.