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    SubjectRe: [PATCH 2.4.24] Fix GDT limit in setup.S
    Richard B. Johnson wrote:

    > On Tue, 17 Feb 2004, Coywolf Qi Hunt wrote:
    >
    >
    >>Hello 2.4.xx hackers,
    >>
    >>In setup.S, i feel like that the gdt limit 0x8000 is not proper and it
    >>should be 0x800. How came 0x800 into 0x8000 in 2.4.xx code? Is there a
    >>story? It shouldn't be a careless typo. 256 gdt entries should be
    >>enough and since it's boot gdt, 256 is ok even if the code is run on SMP
    >>with 64 cpus.
    >>
    >
    >
    > The first element has nothing to do with the number of GDT entries.
    > It represents the LIMIT. Because the granularity bit is
    > set meaning 4 kilobyte pages and 0x8000 * 0x1000 = 0x8000000
    > | |
    > | |_______ Page size
    > |______________ GDT value
    > This is the size of address space that is unity-mapped for boot.
    >
    > The granularity is also not the number of GDT entries. It
    > represents the length for which the GDT definition applies.
    >
    > Because this GDT is used only for booting, somebody decided that
    > there would never be any boot code beyond 2 GB so there was no
    > reason to make room for it. If you change the number to 0x0800,
    > you are declaring that neither the boot code nor any RAM-disk
    > combination will ever exceed 0x800 * 0x1000 = 0x800000 bytes.
    > Therefore you broke my imbedded system. Do not do this.
    >
    >
    >>At least the comment doesn't match the code. Either fix the code or fix
    >>the comment. We really needn't so many GDT entries. Let's use the intel
    >>segmentation in a most limited way. Below follows a patch fixing the code.
    >>
    >>I don't have the latest 2.4.24, but setup.S isn't changed from 2.4.23 to
    >>2.4.24.
    >>
    >>Regards, Coywolf
    >>

    Thank you for you kindly reply, though I really don not agree with you.
    But thanks very much, since you are the only one replying me. I CCed to
    all the 2.0 2.2 2.4 maintainers.


    --
    Coywolf Qi Hunt
    Admin of http://GreatCN.org and http://LoveCN.org

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