The shipped gdb executable with FC4 can only debug ppc32 executables.

Even if one forcibly enables ppc64 support in bfd etc, a 32-bit gdb
executable has problems debugging 64-bit targets.  This can partially
be fixed by rewriting bits of code to use PPC_PTRACE_*_3264, but that
on its own does not (for some reason) fix the whole problem.  All of
this can be fixed, if one cares enough.

On the other hand, building a 64-bit gdb executable appears to 
successfully debug both 64 and 32-bit executables.  It seems like 
simply building another rpm is the easiest short-term way around
this problem.