mirror of
https://github.com/ipxe/ipxe
synced 2025-12-31 06:49:20 +03:00
142 lines
3.2 KiB
ArmAsm
142 lines
3.2 KiB
ArmAsm
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/*
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* Copyright (C) 2010 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*/
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FILE_LICENCE ( GPL2_OR_LATER )
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.arch i386
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#define CR0_PE 1
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/****************************************************************************
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* flatten_real_mode (real-mode far call)
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*
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* Set up 4GB segment limits
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*
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* Parameters:
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* none
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* Returns:
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* none
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* Corrupts:
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* none
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****************************************************************************
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*/
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/* GDT for protected-mode calls */
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.section ".text16.early.data", "aw", @progbits
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.align 16
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flatten_gdt:
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flatten_gdt_limit: .word flatten_gdt_length - 1
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flatten_gdt_base: .long 0
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.word 0 /* padding */
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flatten_cs: /* 16-bit protected-mode flat code segment */
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.equ FLAT_CS, flatten_cs - flatten_gdt
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.word 0xffff, 0
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.byte 0, 0x9b, 0x8f, 0
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flatten_ss: /* 16-bit protected-mode flat stack segment */
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.equ FLAT_SS, flatten_ss - flatten_gdt
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.word 0xffff, 0
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.byte 0, 0x93, 0x8f, 0
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flatten_gdt_end:
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.equ flatten_gdt_length, . - flatten_gdt
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.size flatten_gdt, . - flatten_gdt
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.section ".text16.early.data", "aw", @progbits
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.align 16
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flatten_saved_gdt:
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.long 0, 0
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.size flatten_saved_gdt, . - flatten_saved_gdt
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.section ".text16.early", "awx", @progbits
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.code16
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.globl flatten_real_mode
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flatten_real_mode:
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/* Preserve registers and flags */
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pushfl
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pushl %eax
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pushw %si
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pushw %gs
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pushw %fs
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pushw %es
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pushw %ds
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pushw %ss
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/* Set %ds for access to .text16.early.data variables */
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pushw %cs
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popw %ds
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/* Preserve original GDT */
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sgdt flatten_saved_gdt
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/* Set up GDT bases */
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xorl %eax, %eax
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movw %cs, %ax
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shll $4, %eax
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addl $flatten_gdt, %eax
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movl %eax, flatten_gdt_base
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movw %cs, %ax
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movw $flatten_cs, %si
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call set_seg_base
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movw %ss, %ax
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movw $flatten_ss, %si
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call set_seg_base
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/* Switch temporarily to protected mode and set segment registers */
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pushw %cs
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pushw $2f
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cli
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data32 lgdt flatten_gdt
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movl %cr0, %eax
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orb $CR0_PE, %al
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movl %eax, %cr0
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ljmp $FLAT_CS, $1f
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1: movw $FLAT_SS, %ax
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movw %ax, %ss
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %fs
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movw %ax, %gs
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movl %cr0, %eax
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andb $0!CR0_PE, %al
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movl %eax, %cr0
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lret
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2: /* lret will ljmp to here */
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/* Restore GDT, registers and flags */
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data32 lgdt flatten_saved_gdt
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popw %ss
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popw %ds
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popw %es
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popw %fs
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popw %gs
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popw %si
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popl %eax
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popfl
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lret
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.size flatten_real_mode, . - flatten_real_mode
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.section ".text16.early", "awx", @progbits
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.code16
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set_seg_base:
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rolw $4, %ax
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movw %ax, 2(%si)
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andw $0xfff0, 2(%si)
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movb %al, 4(%si)
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andb $0x0f, 4(%si)
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ret
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.size set_seg_base, . - set_seg_base
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