Hi Finn,
Am 25.04.2024 um 18:32 schrieb Finn Thain:
This oops indicates that we are going to need the final NOP that was
in the first version of your patch. My test program seems inadequate
to show that it is safe to omit that NOP -- we would need a test which
doesn't jump over the MOVES.B.
We'd need a test using any number of longword moves expected to succeed,
followed by a byte move which is expected to fault. The current test
would attempt to do a byte move, but faults during the longword moves.
This requires running the test program in a directory whose absolute
path is a multiple of four characters long, and setting the start
address for the getcwd test accordingly, so the newline at the end of
the string is the single byte left to copy. Does that make sense?
Yes (I take it you meant NUL instead of LF). But my concern was that the
Yes, my bad ...
test program passes a pointer like 0xc0029000 - 1. That means the final
byte will land on a word that already faulted. I'll need to add a new test
that passes a pointer like 0xc0029000 - 5.
That's what I meant to say, yes.
Incidentally - what is the path this tests is run in? Any path longer
than five characters (including the newline) would have to had looped
back to the first movel, and faulted there?
It was /tmp.
Right - so if I'm right, running the test in /root would exercise the
movesw path, and fault on the movew. Using /var/tmp would loop back once
to repeat the movesl, and likely fault on the movel there.
As you said before - we'd need to know a lot more about
microarchitectural details here.
It's hard to be certain. We just have to experiment until we find
something that works on the CPUs we can test.
Right - I'll try a few of these ideas on my 030.
Cheers,
Michael
