20181103

VENIX/86 emulator taking shape...

Frequent readers will recall my obsession with Venix on the Rainbow.

For the past year or so in my off moments, I've been trying to put together a Venix binary emulator. This is part of a larger project to reconstruct the Venix sources from the ancient V7 sources plus clues left behind in various images found on the internet in time for the 50th anniversary of Unix next year.

Early in the summer I had the loader written. I could successfully load a VENIX image and start it executing. sync(1) was working, but it did little more than call the sync(2) and _exit(2) system calls. stdio programs were still basically not working, though odd things like ln(1) also worked.

My project is now one step closer to fruition. I have been able to get some of the basic programs in /bin working with my emulator. The last step before getting to this point was finding a bug in the 8086 CPU emulation where the pointers to things like AH and AL for the AX register were wrong so that "movb al, 1" would set ah to 1... To find that I ported ddb from FreeBSD over so I could print out registers and disassembled code that's about to execute and pore over the changes to the registers until I could spot a problem...

With that fixed, all the super simple programs run. echo(1), cat(1), tr(1), and basename(1) run. However, other simple ones like rm(1), touch(1), ls(1), and wc(1) all run into problems.

touch(1) seems to be related to a bad implementation of stat(2), for example, that I've not had the time to chase down. mv(1) and rm(1) seem that way as well. No clue what's up with wc(1) or ls(1).

I think I should come up with some kind of test script(s) to make sure the basics work.

Venix Github repo has the 86sim program in it.

I hope to soon be to the point where everything except maybe fork/exec works. I'll need those for not only /bin/sh, but also cc. cc(1) is the reason that I want to make this work so I can rebuild everything quickly for the VENIX restoration project....

No comments: