Messages in this thread | | | From | Dan Williams <> | Date | Wed, 19 May 2021 17:40:03 -0700 | Subject | Re: [RFC v2-fix 1/1] x86/boot: Add a trampoline for APs booting in 64-bit mode |
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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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