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    SubjectRe: bzImage ~ 900K with i386 test11-pre2
    [This is quite a bizarre discussion, but I'll answer anyways. I am not exactly
    sure what your point is]

    On Sun, Nov 12, 2000 at 11:57:15AM -0700, Eric W. Biederman wrote:
    >
    > > > I can tell you don't have real hardware. The non obviousness
    >
    > I need to retract this a bit. You are still building a compressed image,
    > and the code in the boot/compressed/head.S remains unchanged and loads
    > segment registers, so it works by luck. If you didn't build a
    > compressed image you would be in trouble.

    boot/compressed/head.S does run in 32bit legacy mode, where you of course
    need segment registers. After you got into long mode segments are only
    needed to jump between 32/64bit code segments and and for a the data segment
    of the 32bit emulation (+ the iretd bug currently which I hope will be fixed
    in final hardware)

    Also note that boot/compressed/* currently does not even link, because the
    x86-64 toolchain cannot generate relocated 32bit code ATM (the linker chokes
    on the 32bit relocations) The tests we did so far used a precompiled
    relocated binary compressed/{head,misc}.o from a IA32 build.

    > > In 64-bit mode, the contents of the ES, DS, and SS segment registers
    > > are ignored. All fields (base, limit, and attribute) in the
    > > corresponding segment descriptor registers (hidden part) are also
    > > ignored.
    >
    > Hmm. I'll have to look and see if FS & GS are also ignored.

    They are not, you to fully use them you need privileged MSRs.
    Their limit is ignored.

    > > Sure, go ahead if you weren't missing that basic part of the long mode specs.
    > > Thanks.
    >
    > Nope. Though I suspect we should do the switch to 64bit mode in
    > setup.S and not have these issues pollute head.S at all.

    I see no advantage in doing it there instead of in head.S



    -Andi
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