On Wed, Jul 12, 2000 at 10:05:03AM -0500, James Bottomley wrote:
> > So I looked in trampoline.S and discovered the answer to this
> > question - because each instance writes some magic number a5a5a5a5 to
> > its code. Ok, so then the answer becomes - why does it do that?
>
> If you look lower down in do_boot_cpu(), this is used as a diagnosis of a boot
> failure (the check at phys_to_virt(8192)). If we don't find the signature, we
> know the CPU failed to start, if we do find it, we know it started but got
> stuck somewhere after the switch to protected mode.
No. phys_to_virt(8192) != trampoline_base, at least in the general case.
It really looks like the code in smpboot.c is out of date to me.
> In the latter case, the CPU could happily have trashed the trampoline code
> before disappearing off into hyperspace, so it makes sense to set it up anew
> each time.
This doesn't seem to happen in practice. If it does, we probably want to
panic() anyway - we now have a random CPU executing random code but not
behaving as expected.
Philipp Rumpf
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