mattst88's blog - Reverse Engineering the PROM for the SGI O2

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A detailed account of reverse engineering the SGI O2 workstation's PROM firmware to enable CPU upgrades. The author built a decompiler that converts the 512 KiB binary into modifiable assembly by discovering the firmware's structure: section headers (SHDRs), checksums, code/data boundaries, and virtual memory layout. Key discoveries included identifying the five firmware sections, understanding MIPS jump instructions and memory regions, recognizing overlaid ELF headers, and implementing two's complement checksums. The decompiler now produces bit-identical reassemblable output with annotations, making the 1996 firmware comprehensible and modifiable without SGI's original source code.

Reverse Engineering the PROM for the SGI O2