FLAT_DS_SELECTOR question - Minix

This is a discussion on FLAT_DS_SELECTOR question - Minix ; FLAT_DS_SELECTOR is defined in src/kernel/protect.h as 0x21, one bigger than ES_SELECTOR. It is then used in the phys_copy function defined in klib386.s (quoted below). > mov eax, FLAT_DS_SELECTOR > mox es, ax I do not understand the difference between using ...

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Thread: FLAT_DS_SELECTOR question

  1. FLAT_DS_SELECTOR question

    FLAT_DS_SELECTOR is defined in src/kernel/protect.h as 0x21, one bigger
    than ES_SELECTOR. It is then used in the phys_copy function defined in
    klib386.s (quoted below).
    > mov eax, FLAT_DS_SELECTOR
    > mox es, ax

    I do not understand the difference between using FLAT_DS_SELECTOR and
    using ES_SELECTOR. They seem to point to the same descriptor, except
    that FLAT_DS_SELECTOR appears misaligned in the gdt table, isn't it?


  2. Re: FLAT_DS_SELECTOR question

    FLAT_DS_SELECTOR is for flat space memory model

    ES_SELECTOR is for sememted memory model

    But the values should be different.


    Yunzhong wrote:
    > FLAT_DS_SELECTOR is defined in src/kernel/protect.h as 0x21, one bigger
    > than ES_SELECTOR. It is then used in the phys_copy function defined in
    > klib386.s (quoted below).
    > > mov eax, FLAT_DS_SELECTOR
    > > mox es, ax

    > I do not understand the difference between using FLAT_DS_SELECTOR and
    > using ES_SELECTOR. They seem to point to the same descriptor, except
    > that FLAT_DS_SELECTOR appears misaligned in the gdt table, isn't it?



  3. Re: FLAT_DS_SELECTOR question

    Thank you tmK.
    Can I assume that FLAT_DS_SELECTOR points to the same region of memory
    that ES_SELECTOR points to, but just with a lower RPL? Or is there any
    other difference with the flat space memory model?


  4. Re: FLAT_DS_SELECTOR question

    I think this reference might help you out

    http://groups.google.com/group/comp....58ae1d24a0b016

    tmK

    Yunzhong wrote:
    > Thank you tmK.
    > Can I assume that FLAT_DS_SELECTOR points to the same region of memory
    > that ES_SELECTOR points to, but just with a lower RPL? Or is there any
    > other difference with the flat space memory model?



  5. Re: FLAT_DS_SELECTOR question

    I think so
    Both ES_SELECTOR and FLAT_DS_SELECTOR point to the 4th entry in GDT
    with different privilege levels if they are used in protected mode.
    Actually ES_SELECTOR is never used except in boot process.

    I think this reference might help you out

    http://groups.google.com/group/comp..../thread/2f5f66...

    tmK

    Yunzhong wrote:
    > Thank you tmK.
    > Can I assume that FLAT_DS_SELECTOR points to the same region of memory
    > that ES_SELECTOR points to, but just with a lower RPL? Or is there any
    > other difference with the flat space memory model?




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