In my 68K Mac emulator running on modern (or even decade-old) hardware, performance in the traditional sense is less of a concern, but other issues arise. The big ones include CPU-burning loops that wait for a length of time or for an interrupt-decremented counter to reach zero, as well as invalid memory accesses (which I've made crash — no NULL deref for you).
> We considered creating a plugin that fixed all these things, it would have been hard to maintain, in the end we travelled around to the people who made these apps and talked them through their problems
Since talking to developers is no longer an option, I actually do write "Such-and-such Tune-up" extensions that patch applications dynamically to make them run better (or at all) in Advanced Mac Substitute, or even Mac OS itself.
I knew of Executor, but never saw it in action. Winning back performance lost to emulation was critical when competing with contemporary real hardware, and kudos to ctm and ARDI for their clever solution.
Decades later, though, emulation performance is mostly a non-issue (and even improves automatically with faster hosts). What matters now is portability (which requires ongoing maintenance) and renovation of programs designed around having the CPU to themselves (via dynamically applied patches).
It's not you; it's me. My implementation of LoadScrap() (which is called at startup) is calling FSOpen(), and it turns out the glue code for that tries OpenDF() before falling back to PBOpen(). TIL.
You want to talk trap patches? Your Mac's INITs have minimal trap patches, touch the Toolbox in boring places like SysBeep() and GetNextEvent(). The Developator's Mac has big, tricky INITs with trap patches that hook into half of the Device Manager.[1] The Developator is in touch with the metal, starts like a warm boot off the ROM reset vector, stops on an NMI.
Oh wow. Once I saw the smiling machine and empty progress bar, I went straight to NoScript and enabled your domain without a moment's hesitation — highly unusual for me. It's charming! I laughed out loud when I saw your screen-saver.
It's familiar and alien at the same time, like I'm seeing an alternate universe.
It was a way to become more familiar with CSS and JS (and indulge my classic Mac OS nostalgia), but my biggest takeaway was that the web wasn't a foundation I wanted to build complex structures on, and indirectly helped spur me to create Advanced Mac Substitute.
Advanced Mac Substitute uses a factored approach. 68K emulation happens in the back end, which is a collection of processes connected by Unix-domain sockets, portable to basically any POSIX system.
The front end deals with displaying graphics and forwarding user input to the back end. Working front ends include SDL2 (by a contributor), X11, Linux fbdev, VNC, and five different macOS APIs (Cocoa/OpenGL, CGL, AGL, Quartz, and QuickDraw).
The front and back ends communicate using FIFOs and shared memory. I'm aware that certain platforms will require refactoring all of this to run in a single process. If Emscripten is one of them, then it won't be as simple as you suggest.
In any case, if I were the one doing the port, I might write a bare-bones front end just for this purpose, possibly using the fbdev one as a starting point.
Correction: 68K Mac OS calls were A-line traps — in other words, they had opcodes of the form `$Axxx`. To the processor, they're unimplemented instructions that each take an exception through the same vector. The exception handler is the Mac OS trap dispatcher.
`TRAP` is a different instruction, with opcodes `$4E4x`. Each one gets its own exception vector.
It's not just trap calls, though — sometimes applications write directly to the sound buffer or use hardware page flipping.
The FSSpec calls added in System 7 are mostly new interfaces to existing File Manager functionality. There's an actual high-level `OpenDF()` call, which is like `FSOpen()` except that it won't try to open a driver when the name begins with `.`.
Some applications call `OpenDF()` without checking its availability, but fall back to `FSOpen()` or equivalent if `OpenDF()` returns `paramErr`, which is what the parent is witnessing. See `68k/modules/ams-fs/Files.cc` in the `metamage_1` repo.
If the error message is confusing people, maybe it's time to implement `OpenDF()` for real.
Implementing fork() without address translation is possible — it's just expensive.
In MacRelix (a POSIX-like environment for classic Mac OS), when a process calls fork(), the system allocates backup memory regions for it and its child. Whenever one of them is switched in after its counterpart was the last of the two to run, the old one's regions are backed up and the new one's regions restored.
Rhapsody DR2 is not a solution for classic Mac OS on x86. Lunduke writes:
"Unfortunately [the Blue Box] was only available on PowerPC versions of Rhapsody"
Another option is Advanced Mac Substitute. It doesn't run everything, but what it does run it runs really well. One of my goals is that you can use a 68K Mac application (e.g. MacPaint) as part of your personal computing workflow, if you wish.
My own high-level language, Varyx, has somewhat LISPy internals and is very dynamic — for example, you can annotate a variable with a type that's determined only at run time — and has an eval() that insulates the caller from the payload and vice versa. You can sequester mutable state within a closure, which can't be cracked open. Using an experimental Varyx build with some bindings for Apple's Core Graphics API, I wrote a script that rendered an arrow cursor (which I donated to the ravynOS project).
> We considered creating a plugin that fixed all these things, it would have been hard to maintain, in the end we travelled around to the people who made these apps and talked them through their problems
Since talking to developers is no longer an option, I actually do write "Such-and-such Tune-up" extensions that patch applications dynamically to make them run better (or at all) in Advanced Mac Substitute, or even Mac OS itself.