Re: Userland instability in NetBSD 6.0.1 MacPPC

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> HOWEVER, I noticed that if I run the exact program with the same
> input twice, I get different crazy numbers. (!!)

My first inclination would be to suspect flaky hardware.

> This may well be due to some bug in analog where it is referencing
> some uninitialized data that just happens to be different on every
> run.

> It occurs to me, though that if single threaded (and analog is old,
> so I would expect that), even bugs should be deterministic.

True as far as it goes.  But...

> I wonder if the "different answers on different runs" might be caused
> by some OS behavior where it is not properly zeroing new vm pages, or
> some other anti-social, but not fatally incorrect behavior.

...this, while perhaps possible, is rather unlikely.  But there is
something I've seen called address space layout randomization, which
tries to put the various pieces of the address space at different
adresses each run.  It's intended, AIUI, to mostly-defeat
code-injection malware that has fixed addresses and/or offsets wired
into it.  If NetBSD has anything of the sort (you said 6.0.1, so it's
not a version I know), this could mean that the trash left on the stack
from one routine call to the next can differ from run to run.

> I have seen some strange behavior that seems non-reproducable, though
> it's hard to tell when bringing up a new box and debugging 12 things
> at once.

So true.

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