20181104

Even more VENIX emulator progress

So in looking at the traces for why cal wasn't working, I noticed something odd:

0212:100D: jmp 0x109e
0212:109C: rcrw $0xff,0xdceb(%bx,%si)
Invalid opcode c1
What? I'm not super-duper strong on Intel assembler, but I sure know that 109e is not 109c. So what's going on here. After adding some more debugging, I discovered this was opcode 0xe9, which is a jump relative with word (so take IP and add the next two bytes to it). So, the code looked OK:
                doJump(ip + fetchWord()); 
But looking more closely. It's oddly off by 2. Sow what's inside fetchWord()? Inside it effectively does ip++, twice. So, on the other compiler that was used for this code that I obtained from tkchia's reenigne repo had this flaw. it did fetchWord() + ip, rather than clang's ip + fetchWord(). So the fix was simple:
                t = fetchWord();
                doJump(ip + t);
which made the order of operations well defined. A quick audit of the code shows no other places where this is done.

I did that, and nothing else, and now cal(1) works. It produces correct calendars. As does od(1), uniq(1), pr(1) and others.

I've also implemented alarm(2), signal(2), lseek(2) and pause(2). With that, sleep(1) works (although it says 'Alarm clock' which suggests I need to actually establish a SIGALRM handler).

There's enough working I'm starting to need some kind of regression suite to make sure I don't regress and can publish the status of all the binaries... Maybe I could leverage an existing something...

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