I've found this link which describes exactly what I'm experiencing in my K64. I've added a custom attribute section to Linker file for returning go and back from/to Kboot bootloader (by using a dedicated flag in specific location in flash).
Now the bin file has increased to 500MB (and using the blhost.exe, obviously takes forever...)
Alas, the startup.c does not have an 'init_data_bss' method.
Is the solution provided by Stanislav Sliva also works for the K64?
If so, what to change in the startup.c code?