Case study

GEOS 2.0: source that rebuilds the cbmfiles KERNAL binaries

Reorganized cc65 source for GEOS 2.0 on the Commodore 64 and 128. The README says a standard compile generates binaries identical to the GEOS 64 2.0 and GEOS 128 2.0 distribution binaries, and make regress compares the bsw and wheels builds with the reference tree.

Targets: Binary
Category: Independent reconstruction cases
Relationship: Independent reconstruction project
Sources reviewed: 2026-11-04

Stars: 488
Last commit: 2026-04-05
Language: Assembly

GitHub data as of 2026-11-09

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Requirements & limits

Prerequisites: The README builds with make. reference/ holds the original binaries from the cbmfiles.com version. make regress builds the bsw and wheels variants and compares them with those references.
Scope: The README says this tree does not use the original encrypted loader and that the kernel is plaintext, matching the cbmfiles.com version it describes. It says the serial number 0x58B5 is pre-filled to match that version.
Testing evidence: make regress is the comparison named in the README.
License: The repository root has no LICENSE file. The README says the intellectual property added by the reverse-engineering and the subsequent improvements is in the public domain, asks to be credited, and says to respect the license of the underlying GEOS work.

Cite

BibTeX

@misc{geos-20-kernal-case,
  title = {{GEOS 2.0: source that rebuilds the cbmfiles KERNAL binaries}},
  howpublished = {\url{https://github.com/mist64/geos}},
  url = {https://github.com/mist64/geos},
  urldate = {2026-11-04},
  note = {Awesome REA entry: \url{https://awesomerea.org/resources/geos-20-kernal-case/}}
}

Plain text

GEOS 2.0: source that rebuilds the cbmfiles KERNAL binaries. https://github.com/mist64/geos (accessed 2026-11-04). Awesome REA entry: https://awesomerea.org/resources/geos-20-kernal-case/

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About this entry

The description was reviewed against primary sources.

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Primary sources

README.md GitHub · mist64/geos · Revision 617efdc
regress.sh GitHub · mist64/geos · Revision 617efdc
reference GitHub · mist64/geos · Revision 617efdc