Which version of Etherboot? I think I ran into a version with 5.2.4 where ELF/ZELF images were corrupt no matter which GCC I tried.
In the Old RH 9, gcc-3.2.2 works well.
[root@tst2723-rh9 xx]# /usr/bin/gcc --version gcc (GCC) 3.2.2 20030222 (Red Hat Linux 3.2.2-5) Copyright (C) 2002 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.