Re: Fwd: newb question : list of elligible computers to debian-68k
On Wed, 22 Oct 2008, Michael Schmitz wrote:
> > [exception for the unimplemented instruction] may or may not have been
> > raised and handled already, depending on whether the bug lost the
> > exception or not (the bug is apparently not dependable).
>
> That would indeed vastly complicate matters. Are you sure the unreliable
> bug isn't due to the page in question having been mapped in nonetheless?
No. Would the kernel map 16 or 17 pages following a mmap? Maybe glibc is
causing them to be paged in too early?
But this is a secondary problem anyway.
> > No idea what to do about (1). Since I don't understand the
> > implications of "overlapped execution", I can't hazard a guess as to
> > whether this kind of fix is even theoretically feasible.
>
> What this means is that one instruction is in the process of being
> executed while another one is being loaded and decoded at the same time.
That's what I thought.
> Loading it would trigger the page fault while executing of the previous
> one had triggered the unimplemented instruction exception just
> previously. Only guessing here...
Thing is, we have to know exactly what the saved PC will be when either,
a. ATC fault at unimplemented fpu op and bug may or may not take effect
b. ATC fault with no unimplemented fpu op
The point I was trying to make is that only for (a) is the saved PC
determined (that's what the docs I quoted tell me, anyway). Which means,
the fault handler can't tell (a) and (b) apart.
Finn
>
> Michael
>
>
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