arch/x86/boot/pmjump.S

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright (C) 1991, 1992 Linus Torvalds
   4  *   Copyright 2007 rPath, Inc. - All Rights Reserved
   5  *
   6  *   This file is part of the Linux kernel, and is made available under
   7  *   the terms of the GNU General Public License version 2.
   8  *
   9  * ----------------------------------------------------------------------- */
  10
  11 /*
  12  * The actual transition into protected mode
  13  */
  14
  15 #include <asm/boot.h>
  16 #include <asm/processor-flags.h>
  17 #include <asm/segment.h>
  18
  19         .text
  20
  21         .globl  protected_mode_jump
  22         .type   protected_mode_jump, @function
  23
  24         .code16
  25
  26 /*
  27  * void protected_mode_jump(u32 entrypoint, u32 bootparams);
  28  */
  29 protected_mode_jump:
  30         movl    %edx, %esi              # Pointer to boot_params table
  31
  32         xorl    %ebx, %ebx
  33         movw    %cs, %bx
  34         shll    $4, %ebx
  35         addl    %ebx, 2f
  36         jmp     1f                      # Short jump to serialize on 386/486
  37 1:
  38
  39         movw    $__BOOT_DS, %cx
  40         movw    $__BOOT_TSS, %di
  41
  42         movl    %cr0, %edx
  43         orb     $X86_CR0_PE, %dl        # Protected mode
  44         movl    %edx, %cr0
  45
  46         # Transition to 32-bit mode
  47         .byte   0x66, 0xea              # ljmpl opcode
  48 2:      .long   in_pm32                 # offset
  49         .word   __BOOT_CS               # segment
  50
  51         .size   protected_mode_jump, .-protected_mode_jump
  52
  53         .code32
  54         .type   in_pm32, @function
  55 in_pm32:
  56         # Set up data segments for flat 32-bit mode
  57         movl    %ecx, %ds
  58         movl    %ecx, %es
  59         movl    %ecx, %fs
  60         movl    %ecx, %gs
  61         movl    %ecx, %ss
  62         # The 32-bit code sets up its own stack, but this way we do have
  63         # a valid stack if some debugging hack wants to use it.
  64         addl    %ebx, %esp
  65
  66         # Set up TR to make Intel VT happy
  67         ltr     %di
  68
  69         # Clear registers to allow for future extensions to the
  70         # 32-bit boot protocol
  71         xorl    %ecx, %ecx
  72         xorl    %edx, %edx
  73         xorl    %ebx, %ebx
  74         xorl    %ebp, %ebp
  75         xorl    %edi, %edi
  76
  77         # Set up LDTR to make Intel VT happy
  78         lldt    %cx
  79
  80         jmpl    *%eax                   # Jump to the 32-bit entrypoint
  81
  82         .size   in_pm32, .-in_pm32