gdb source and symbol info for multiple files

If I try and debug a program under gdb where there are multiple source files
then gdb reports that no symbols are found and I cannot view variables or
source files.
I compile the sources with gcc -g option and and link the objects with
gcc -g as well.

If I create a SINGLE source file I can use gdb and access the source,
variable info etc. as expected.

What am I doing wrong?

Ian G