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    SubjectRe: 64bit port
       From: hpa@transmeta.com (H. Peter Anvin)
    Date: 1 May 1999 09:39:27 GMT

    I think that was only UltraSPARC I.

    Not true.

    All currently shipping UltraSparc's have at least one of the two
    64-bit lockup bugs. On the Ultra-I the user can do it no matter where
    the text section is mapped, this is why Solaris doesn't offer 64-bit
    installation by default on the < 250Mhz Ultra-I's which are the chips
    affected by this first bug.

    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.

    Later,
    David S. Miller
    davem@redhat.com

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