{... booting trouble on an RS/6000 B50...}
With the correctly sized /dev/sda1 of 4 Megabytes and yaboot (written bymkofboot) it gives: boot: failsafe Please wait, loading kernel... Elf32 kernel loaded... chrpboot starting: loaded at 0x00400000 gunzipping (0x00010000 <- 0x00416470:0x004d96ec)...done 1924340 bytes 48568 bytes of heap consumed, max in use 40848 start address = 0x10000 instantiating rtas at 00600000 ... done copying OF device tree...done Calling quiesce ... returning 00010000 from prom_init and it hangs with code "7777".
Are you sure it doesn't boot? 7777 is the normal display when the system is running.
My temporary solution: I dd your kernel linux.bin (the one without the modules) directly into /dev/sda1 -> then it boots directly with no problem, so I guess yaboot 1.3.9 has difficulties.
That should work with the modularized kernel, too. Cheers, Jens.