root/arch/x86/boot/pmjump.S

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /* ----------------------------------------------------------------------- *
   3  *
   4  *   Copyright (C) 1991, 1992 Linus Torvalds
   5  *   Copyright 2007 rPath, Inc. - All Rights Reserved
   6  *
   7  * ----------------------------------------------------------------------- */
   8 
   9 /*
  10  * The actual transition into protected mode
  11  */
  12 
  13 #include <asm/boot.h>
  14 #include <asm/processor-flags.h>
  15 #include <asm/segment.h>
  16 #include <linux/linkage.h>
  17 
  18         .text
  19         .code16
  20 
  21 /*
  22  * void protected_mode_jump(u32 entrypoint, u32 bootparams);
  23  */
  24 GLOBAL(protected_mode_jump)
  25         movl    %edx, %esi              # Pointer to boot_params table
  26 
  27         xorl    %ebx, %ebx
  28         movw    %cs, %bx
  29         shll    $4, %ebx
  30         addl    %ebx, 2f
  31         jmp     1f                      # Short jump to serialize on 386/486
  32 1:
  33 
  34         movw    $__BOOT_DS, %cx
  35         movw    $__BOOT_TSS, %di
  36 
  37         movl    %cr0, %edx
  38         orb     $X86_CR0_PE, %dl        # Protected mode
  39         movl    %edx, %cr0
  40 
  41         # Transition to 32-bit mode
  42         .byte   0x66, 0xea              # ljmpl opcode
  43 2:      .long   in_pm32                 # offset
  44         .word   __BOOT_CS               # segment
  45 ENDPROC(protected_mode_jump)
  46 
  47         .code32
  48         .section ".text32","ax"
  49 GLOBAL(in_pm32)
  50         # Set up data segments for flat 32-bit mode
  51         movl    %ecx, %ds
  52         movl    %ecx, %es
  53         movl    %ecx, %fs
  54         movl    %ecx, %gs
  55         movl    %ecx, %ss
  56         # The 32-bit code sets up its own stack, but this way we do have
  57         # a valid stack if some debugging hack wants to use it.
  58         addl    %ebx, %esp
  59 
  60         # Set up TR to make Intel VT happy
  61         ltr     %di
  62 
  63         # Clear registers to allow for future extensions to the
  64         # 32-bit boot protocol
  65         xorl    %ecx, %ecx
  66         xorl    %edx, %edx
  67         xorl    %ebx, %ebx
  68         xorl    %ebp, %ebp
  69         xorl    %edi, %edi
  70 
  71         # Set up LDTR to make Intel VT happy
  72         lldt    %cx
  73 
  74         jmpl    *%eax                   # Jump to the 32-bit entrypoint
  75 ENDPROC(in_pm32)