Quiz 3

Following shows relevant part of xv6 bootasm.S from the p1-booting branch

Read carefully before answering. There may be some subtle changes from the xv6 bootasm.S. You can assume that the elided code in ... was unchanged.

.code16
start:
    ...
    lgdt gdtdesc
    ...
    ljmp $(SEG_KCODE<<3), $start32

.code32
start32:
    ...
    movw $(SEG_KDATA<<3), %ax   # Load data segment selector
    movw %ax, %ds               # DS points to data segment
    ...

    # Bootstrap GDT
    .p2align 2
    gdt:
    SEG_NULLASM                            # null segment
    SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff)  # code segment
    SEG_ASM(STA_W, 0x200000, 0xffffffff)   # data segment
    ...