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    SubjectRe: [RFC v2-fix 1/1] x86/boot: Add a trampoline for APs booting in 64-bit mode
    On Wed, May 19, 2021 at 5:19 PM Kuppuswamy, Sathyanarayanan
    <sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
    >
    > Hi Dan,
    >
    > On 5/17/21 9:08 PM, Dan Williams wrote:
    > >> SYM_DATA_START_LOCAL(tr_idt)
    > >> .short 0
    > >> .quad 0
    > >> SYM_DATA_END(tr_idt)
    > > This format implies that tr_idt is reserving space for 2 distinct data
    > > structure attributes of those sizes, can you just put those names here
    > > as comments? Otherwise the .fill format is more compact.
    >
    > Initially its 6 bytes (2 bytes for IDT limit, 4 bytes for 32 bit linear
    > start address). This patch extends it by another 4 bytes for supporting
    > 64 bit mode.
    >
    > 2 bytes IDT limit (.short)
    > 8 bytes for 64 bit IDT start address (.quad)
    >
    > This info is included in commit log. But I will add comment here as you
    > have mentioned.

    Thanks. I only read commit logs when code comments fail.

    >
    > Will following comment log do ?
    >
    > /* Use 10 bytes for IDT (in 64 bit mode), 8 bytes for IDT start address
    > 2 bytes for IDT limit size */

    I would clarify how the boot code uses this:

    "When a bootloader hands off to the kernel in 32-bit mode an IDT with
    a 2-byte limit and 4-byte base is needed. When a boot loader hands off
    to a kernel 64-bit mode the base address extends to 8-bytes. Reserve
    enough space for either scenario."

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