arch/i386/kernel/trampoline.S

/* */
   1 !
   2 !       Trampoline.S    Derived from Setup.S by Linus Torvalds
   3 !
   4 !       Entry: CS:IP point to the start of our code, we are 
   5 !       in real mode with no stack, but the rest of the 
   6 !       trampoline page to make our stack and everything else
   7 !       is a mystery.
   8 !
   9 !       In fact we don't actually need a stack so we don't
  10 !       set one up.
  11 !
  12 !       We jump into the boot/compressed/head.S code. So you'd
  13 !       better be running a compressed kernel image or you
  14 !       won't get very far.
  15 !
  16 #define __ASSEMBLY__
  17 #include <linux/config.h>
  18 #include <asm/segment.h>
  19 
  20 .text
  21         extrn startup32
  22 
  23 entry start
  24 start:
  25 !       nop
  26 !       jmp start       !       Test
  27         mov ax,cs       !       Code and data in the same place
  28         mov ds,ax       !
  29         mov cx,ax       !       Pass stack info to the 32bit boot
  30         add cx,cx
  31         add cx,cx
  32         add cx,cx
  33         add cx,cx       !       Segment -> Offset
  34         add cx, #4096   !       End of page is wanted
  35         mov     bx,#1   !       Flag an SMP trampoline
  36         cli             !       We should be safe anyway
  37 
  38         lidt    idt_48  !       load idt with 0,0
  39         lgdt    gdt_48  !       load gdt with whatever is appropriate
  40 
  41         xor     ax,ax   
  42         inc     ax      !       protected mode (PE) bit
  43         lmsw    ax      !       Into protected mode
  44         jmp     flush_instr
  45 flush_instr:
  46         jmpi    8192+startup32,KERNEL_CS        !       Jump to the 32bit trampoline code
  47 !       jmpi    0x100000,KERNEL_CS              !       Jump into the 32bit startup
  48 !       .byte   0x66,0x67                       !       32bit
  49 !       .byte   0xea,0x00,0x00,0x10,0x00,0x10,0x00      !jmpi   .0x100000,KERNEL_CS
  50 
  51 gdt:
  52         .word   0,0,0,0         ! dummy
  53 
  54         .word   0,0,0,0         ! unused
  55 
  56         .word   0x07FF          ! 8Mb - limit=2047 (2048*4096=8Mb)
  57         .word   0x0000          ! base address=0
  58         .word   0x9A00          ! code read/exec
  59         .word   0x00C0          ! granularity=4096, 386
  60 
  61         .word   0x07FF          ! 8Mb - limit=2047 (2048*4096=8Mb)
  62         .word   0x0000          ! base address=0
  63         .word   0x9200          ! data read/write
  64         .word   0x00C0          ! granularity=4096, 386
  65 
  66 idt_48:
  67         .word   0                       ! idt limit=0
  68         .word   0,0                     ! idt base=0L
  69 
  70 gdt_48:
  71         .word   0x800           ! gdt limit=2048, 256 GDT entries
  72         .word   8192+gdt,0x0    ! gdt base = 8192+gdt (first SMP CPU)
  73                                 ! we load the others with the first table
  74                                 ! saves rewriting gdt_48 for each
  75
/* */
root/arch/i386/kernel/trampoline.S
