I think i found problem.
Your boot.img is ELF:
> $ file sid.img
> sid.img: ELF 64-bit MSB executable, SPARC V9, Sun UltraSPARC1 Extensions Required, relaxed memory ordering, version 1 (SYSV), statically linked, BuildID[sha1]=18bd92546b393062ab1864a0ec7b910cf32cf7ad, not stripped, with debug_info