6 ms·

I couldn't tell, is a person doing this? or was this an LLM dissecting it?

xkcd-sucks 3mo ago
> Confidence is flagged: ..... > The big picture > The structural reverse-engineering is comprehensive (every subsystem mapped, both cross-page mechanisms resolved ... > Confidence summary / open items Probably an LLM wrote the docs. > (the GhidraMCP plugin reconnects for interactive work) Probably LLM+Ghidra for the actual RevEng. Ultimately does it matter if the end product is works though
- markus_zhang 3mo ago
  I think it’s fine as long as it works. Personally I prefer doing everything manually because that’s where the fun is, but everyone has their own fun.
deleted 3mo ago
[deleted]
siraben 3mo ago
This was made collaboratively by me directing coding agents at the binary, using Ghidra MCP extensively, disassembly and also dynamic analysis with an emulator. I don't have a writeup of the process but it was definitely not fully automatable (I wish though). I might prepare a blog post with transcripts and session history and things I learned along the way. Broad takeaways: - Ghidra MCP is not a silver bullet. Lots of opportunities for mis-decoding especially on older instruction sets (e.g. conflating code + data), which requires user input to flag data layout/structs. - Agents still need a lot of user direction otherwise the RE production is just kind of a random walk. With Z80 it's decent at reading code but I expect that it has much worse performance than reading x86 or ARM for instance. The TI-84+ has a bunch of hardware quirks as well. - GPT 5.5 is better than Opus 4.8 at RE. Opus 4.8 loves plausible-sounding RE'd logic without any checking. The gold standard is actually dynamically executing the binary and comparing the logic against the prose. - Maintaining consistency in style and prose is a PITA across the wiki. Hard to reconcile prose <-> code. Can be somewhat mitigated by agent loops. Was also in discussions with people in the TI calculator programming space who helped provide guidance as well. We previously did not have a catalogue of every subsystem in TI-OS yet alone most subroutines in the OS.
- analogpixel 3mo ago
  how much have you spent so far on this (for tokens)?
  - siraben 3mo ago
    The plans are heavily subsidized by the AI companies so I didn't end up needing to do API usage or buy another subscription. I have ChatGPT Pro and Claude Code Max.
    - xyst 3mo ago
      [flagged]
      - vitally3643 3mo ago
        That's not at all how that works
- deleted 3mo ago
  [deleted]
- hedgehog 3mo ago
  Do you have plans to generate a buildable version of the sources, and do you know the original implementation language (C?).
  - siraben 3mo ago
    It's highly likely that the original implementation language was assembly. The code is very idiomatic. Regarding source build, I think reverse engineering it to the point where you can reconstruct the source is possibly legally problematic, so I don't plan to do this, but maybe for certain subsystems like MathPrint (equation display) which was especially fun to RE. I have a PR up for it and it will be live at https://siraben.github.io/ti84p-re/mathprint https://siraben.github.io/ti84p-re/mathprint

> Confidence is flagged: ..... > The big picture > The structural reverse-engineering is comprehensive (every subsystem mapped, both cross-page mechanisms resolved ... > Confidence summary / open items Probably an LLM wrote the docs. > (the GhidraMCP plugin reconnects for interactive work) Probably LLM+Ghidra for the actual RevEng. Ultimately does it matter if the end product is works though

markus_zhang 3mo ago
I think it’s fine as long as it works. Personally I prefer doing everything manually because that’s where the fun is, but everyone has their own fun.

deleted 3mo ago

[deleted]

siraben 3mo ago

This was made collaboratively by me directing coding agents at the binary, using Ghidra MCP extensively, disassembly and also dynamic analysis with an emulator. I don't have a writeup of the process but it was definitely not fully automatable (I wish though). I might prepare a blog post with transcripts and session history and things I learned along the way. Broad takeaways: - Ghidra MCP is not a silver bullet. Lots of opportunities for mis-decoding especially on older instruction sets (e.g. conflating code + data), which requires user input to flag data layout/structs. - Agents still need a lot of user direction otherwise the RE production is just kind of a random walk. With Z80 it's decent at reading code but I expect that it has much worse performance than reading x86 or ARM for instance. The TI-84+ has a bunch of hardware quirks as well. - GPT 5.5 is better than Opus 4.8 at RE. Opus 4.8 loves plausible-sounding RE'd logic without any checking. The gold standard is actually dynamically executing the binary and comparing the logic against the prose. - Maintaining consistency in style and prose is a PITA across the wiki. Hard to reconcile prose <-> code. Can be somewhat mitigated by agent loops. Was also in discussions with people in the TI calculator programming space who helped provide guidance as well. We previously did not have a catalogue of every subsystem in TI-OS yet alone most subroutines in the OS.

analogpixel 3mo ago
how much have you spent so far on this (for tokens)?
- siraben 3mo ago
  The plans are heavily subsidized by the AI companies so I didn't end up needing to do API usage or buy another subscription. I have ChatGPT Pro and Claude Code Max.
  - xyst 3mo ago
    [flagged]
    - vitally3643 3mo ago
      That's not at all how that works
deleted 3mo ago
[deleted]
hedgehog 3mo ago
Do you have plans to generate a buildable version of the sources, and do you know the original implementation language (C?).
- siraben 3mo ago
  It's highly likely that the original implementation language was assembly. The code is very idiomatic. Regarding source build, I think reverse engineering it to the point where you can reconstruct the source is possibly legally problematic, so I don't plan to do this, but maybe for certain subsystems like MathPrint (equation display) which was especially fun to RE. I have a PR up for it and it will be live at https://siraben.github.io/ti84p-re/mathprint https://siraben.github.io/ti84p-re/mathprint