Re: 64bit port
H. Peter Anvin (hpa@transmeta.com)
Sat, 01 May 1999 03:05:51 -0700
David Miller wrote:
>
> All UltraSparc chips (to my knowledge) are effected by the second hw
> bug, which can only be triggered if the user can execute code in the
> top of low 2GB of the 64-bit address space (it involves doing a PC
> relative call which over/under-flows the program counter across the
> 64-bit top/bottom addresses, while doing an access into the VA space
> hole in the delay slot, or something like this, I don't know the exact
> trigger sequence yet). This is why Solaris-7 does not allow 64-bit
> userspace to map anything in these areas in 64-bit mode, which as a
> side-effect makes the medium-low code model close to useless.
>
> When Jakub and I get the 64-bit userland bootstrapped, I'll start
> running crashme to learn what the exact instruction sequences are so
> we have a chance at coding a more suitable workaround than what
> Solaris has chosen.
>
I don't know what you mean with "medium-low code model"; I guess if it
was up to me I'd say to heck with it, and waste 1/4294967296 of the
address space as a 4 GB "null pointer check region"...
I presume the only reason you want that is to run 32-bit code/64-bit
data or something like that (shades of DOS.)
-hpa
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