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!

!       Trampoline.S    Derived from Setup.S by Linus Torvalds

!

!       Entry: CS:IP point to the start of our code, we are

!       in real mode with no stack, but the rest of the

!       trampoline page to make our stack and everything else

!       is a mystery.

!

!       In fact we don't actually need a stack so we don't

!       set one up.

!

!       We jump into the boot/compressed/head.S code. So you'd

!       better be running a compressed kernel image or you

!       won't get very far.

!

#define __ASSEMBLY__

#include 

.text

        extrn startup32

entry start

start:

!       nop

!       jmp start       !       Test

        mov ax,cs       !       Code and data in the same place

        mov ds,ax       !

        mov cx,ax       !       Pass stack info to the 32bit boot

        add cx,cx

        add cx,cx

        add cx,cx

        add cx,cx       !       Segment -> Offset

        add cx, #4096   !       End of page is wanted

        mov     bx,#1   !       Flag an SMP trampoline

        cli             !       We should be safe anyway

        lidt    idt_48  !       load idt with 0,0

        lgdt    gdt_48  !       load gdt with whatever is appropriate

        xor     ax,ax

        inc     ax      !       protected mode (PE) bit

        lmsw    ax      !       Into protected mode

        jmp     flush_instr

flush_instr:

        jmpi    8192+startup32,KERNEL_CS        !       Jump to the 32bit trampoline code

!       jmpi    0x100000,KERNEL_CS              !       Jump into the 32bit startup

!       .byte   0x66,0x67                       !       32bit

!       .byte   0xea,0x00,0x00,0x10,0x00,0x10,0x00      !jmpi   .0x100000,KERNEL_CS

gdt:

        .word   0,0,0,0         ! dummy

        .word   0,0,0,0         ! unused

        .word   0x07FF          ! 8Mb - limit=2047 (2048*4096=8Mb)

        .word   0x0000          ! base address=0

        .word   0x9A00          ! code read/exec

        .word   0x00C0          ! granularity=4096, 386

        .word   0x07FF          ! 8Mb - limit=2047 (2048*4096=8Mb)

        .word   0x0000          ! base address=0

        .word   0x9200          ! data read/write

        .word   0x00C0          ! granularity=4096, 386

idt_48:

        .word   0                        ! idt limit=0

        .word   0,0                     ! idt base=0L

gdt_48:

        .word   0x800           ! gdt limit=2048, 256 GDT entries

        .word   8192+gdt,0x0    ! gdt base = 8192+gdt (first SMP CPU)

                                ! we load the others with the first table

                                ! saves rewriting gdt_48 for each