AmigaStart is a small application that can show a colorful boot screen and system information during an Amiga computer's boot sequence. It was written in 1995 by Ian J. Einman and it's available on Aminet.
The original code has an issue, where if the Amiga has more than 640MiB (or more specifically more than 655350 KiB) of Fast Memory available, the number to string conversion code breaks, and displays the wrong amount or just garbage instead. This issue affects both emulators and high-end Amiga systems, where the amount of Zorro III Fast Memory can be potentially more than this limit as the Zorro III bus allows 1.5GiB of addressing range.
When as an experiment I expanded my Amiga 4000T beyond 640MiB, with the help of two BigRAM Z3 cards and a ZZ9000, my boot screen was broken. Annoying.
So I disassembled the app, found the error, fixed it, and wrote this quick & dirty patcher application to correct it.
Some Twitter links documenting the entire "drama" (with colorful pictures!):
- https://twitter.com/chainq/status/1551841506889187328
- https://twitter.com/chainq/status/1551846304925499392
- https://twitter.com/chainq/status/1552790394483757057
Contents of this repository:
testcode.pas- test code, containing the original code disassembly and the fixed versionpatchas.pas- patcher codebuild.sh- script that builds the test code and the patcherpatchmaker.sh- script that extracts the fixed function from the test code for inclusion in the patcher
Requirements to build the code:
- Free Pascal Compiler for Amiga
- Free Pascal Compiler for whatever host platform you're using
m68k-elf-objdump- the usual set of Un*x tools. The scripts were only tested on macOS.
After the patchas (or patchas.exe on Windows) was built, put the amigastart binary next to it, and execute it. The patched version will be in the same folder as amigastart.new. Use this binary from now on on your Amiga. The patcher was only ever tested with the AmigaStart version on Aminet.
Expected SHA-1 checksums for the amigastart and amigastart.new binaries:
e54db3ba57be8873381edc971f13d3ccc9845292 amigastart
acb112a8270dfa8d916cbb68e97b2020bd935336 amigastart.new
Use at your own risk. Precisely zero warranty that any of this will work for you, but for me it did. The contents of this repository are publised under WTFPL-2.
Q: I don't use AmigaStart, do I need this patcher?
A: No.
Q: I do use AmigaStart, but I don't have more than 640MiB Fast RAM, and probably never will, do I need this patcher?
A: No.
Q: Why did you write this in Pascal?
A: Because I wanted to.
Q: How many times did you rewrite the patcher, because you accidentally overwrote the code?
A: Twice.