[Help-gsl] debugging with gdb

[Joe Bloggs]

I am using gdb to debug my code, and I want to step into a gsl function to see 
what's going on exactly (gsl_multimin_fdfminimizer_iterate).
I have installed the debug symbols and development packages, but gdb can't find 
the associated source code, and neither can I:

gsl_multimin_fdfminimizer_iterate (s=0x80a8f70) at fdfminimizer.c:133
133     fdfminimizer.c: No such file or directory.
        in fdfminimizer.c

I am using Debian etch.
Can anyone help?