mirror of
https://github.com/xcat2/xNBA.git
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This should be much more elegant: we use flat real mode for the
highmem data, so decompress16 will be able to unpack blocks bigger than 64kB.
This commit is contained in:
Michael Brown
parent
cc8821a443
commit
d081d65d48
@ -1,178 +1,267 @@
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/*
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* Copyright (C) 2006 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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#define CR0_PE 1
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.arch i386
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.section ".prefix", "awx", @progbits
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.arch i386
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.section ".prefix.lib", "awx", @progbits
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/****************************************************************************
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* install_block (real-mode near call)
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*
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* Install block to specified address
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*
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* Parameters:
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* %esi : byte offset within loaded image (must be a multiple of 16)
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* %es:edi : destination address
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* %ecx : length to install
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* Returns:
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* none
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* Corrupts:
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* %esi, %edi, %ecx
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****************************************************************************
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*/
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.section ".prefix.lib"
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.code16
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install_block:
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/* Preserve registers */
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pushw %ds
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pushw %ax
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/* Starting segment => %ds */
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movw %cs, %ax
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shrl $4, %esi
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addw %si, %ax
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movw %ax, %ds
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xorl %esi, %esi
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/* Do the copy */
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cld
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addr32 rep movsb /* or "call decompress16" */
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/* Restore registers */
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popw %ax
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popw %ds
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ret
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.size install_block, . - install_block
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/****************************************************************************
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* alloc_basemem (real-mode near call)
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*
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* Allocate space from base memory via the BIOS free base memory
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* counter at 40: 13
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* Allocate space for .text16 and .data16 from top of base memory.
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* Memory is allocated using the BIOS free base memory counter at
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* 0x40:13.
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*
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* Parameters:
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* %cx : Number of bytes to allocate
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* none
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* Returns:
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* %es : Segment address of newly allocated memory
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* %ax : .text16 segment address
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* %bx : .data16 segment address
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* Corrupts:
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* none
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****************************************************************************
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*/
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.section ".prefix"
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.section ".prefix.lib"
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.code16
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alloc_basemem:
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/* Preserve registers */
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pushw %cx
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pushw %ax
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/* %fs = 0x40, %ax = fbms */
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/* FBMS => %ax as segment address */
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movw $40, %ax
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movw %ax, %fs
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/* Round up %cx to nearest kB, subtract from FBMS */
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addw $0x03ff, %cx
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andw $0xfc00, %cx
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shrw $10, %cx
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movw %fs:0x13, %ax
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subw %cx, %ax
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shlw $6, %ax
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/* .data16 segment address */
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subw $_data16_size, %ax
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pushw %ax
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/* .text16 segment address */
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subw $_text16_size, %ax
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pushw %ax
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/* Update FBMS */
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shrw $6, %ax
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movw %ax, %fs:0x13
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/* Convert to segment address in %es */
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shlw $6, %ax
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movw %ax, %es
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/* Restore registers and return */
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/* Return */
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popw %ax
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popw %cx
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popw %bx
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ret
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.size alloc_basemem, . - alloc_basemem
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/****************************************************************************
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* install_basemem (real-mode near call)
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*
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* Install .text16 and .data16 into base memory
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*
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* Parameters:
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* %ax : .text16 segment address
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* %bx : .data16 segment address
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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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.section ".prefix.lib"
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.code16
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install_basemem:
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/* Preserve registers */
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pushw %es
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pushl %esi
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pushl %edi
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pushl %ecx
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.section ".prefix"
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/* Install .text16 */
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movw %ax, %es
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xorl %edi, %edi
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movl $_text16_load_offset, %esi
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movl $_text16_size, %ecx
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call install_block
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/* Install .data16 */
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movw %bx, %es
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xorl %edi, %edi
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movl $_data16_load_offset_pgh, %esi
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movl $_data16_progbits_size, %ecx
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call install_block
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/* Restore registers */
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popl %ecx
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popl %edi
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popl %esi
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popw %es
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ret
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.size install_basemem, . - install_basemem
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/****************************************************************************
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* GDT for flat real mode
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*
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* We only ever use this GDT to set segment limits; the bases are
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* unused. Also, we only flatten data segments, so we don't need to
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* worry about the code or stack segments. This makes everything much
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* simpler.
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****************************************************************************
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*/
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.section ".prefix.lib"
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.align 16
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gdt:
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gdt_limit: .word gdt_length - 1
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gdt_base: .long gdt
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gdt_base: .long 0
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.word 0 /* padding */
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cs16: /* 16 bit code segment, base at real-mode %cs:0000 */
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.equ CS16, cs16 - gdt
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.word 0xffff, 0
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.byte 0, 0x9b, 0, 0
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ss16: /* 16 bit stack segment, base at real-mode %ss:0000 */
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.equ SS16, ss16 - gdt
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real_ds: /* Genuine real mode data segment */
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.equ REAL_DS, real_ds - gdt
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.word 0xffff, 0
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.byte 0, 0x93, 0, 0
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flat_ds: /* 16 bit data segment, zero base, 4GB limit */
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flat_ds: /* Flat real mode data segment */
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.equ FLAT_DS, flat_ds - gdt
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.word 0xffff, 0
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.byte 0, 0x9f, 0xcf, 0
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.byte 0, 0x93, 0xcf, 0
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gdt_end:
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.equ gdt_length, gdt_end - gdt
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.size gdt, . - gdt
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.section ".prefix"
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/****************************************************************************
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* set_segment_limits (real-mode near call)
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*
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* Sets limits on the data segments %ds and %es.
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*
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* Parameters:
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* %cx : Segment limit ($REAL_DS or $FLAT_DS)
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****************************************************************************
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*/
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.section ".prefix.lib"
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.code16
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prot16_call:
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set_segment_limits:
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/* Preserve real-mode segment values and temporary registers */
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pushw %es
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pushw %ds
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pushl %eax
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/* Install .data16 to top of base memory */
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movw %cs, %ax
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addw $_data16_load_offset_pgh, %ax
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movw %ax, %ds
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movw $_data16_size, %cx
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call alloc_basemem
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xorw %si, %si
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xorw %di, %di
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movw $_data16_progbits_size, %cx
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rep movsb /* or "call decompress16" */
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/* Install .code16 to top of base memory */
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movw %cs, %ax
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addw $_code16_load_offset_pgh, %ax
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movw %ax, %ds
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movw $_code16_size, %cx
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call alloc_basemem
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xorw %si, %si
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xorw %di, %di
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rep movsb /* or "call decompress16" */
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/* Push flags and real-mode segment registers */
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pushfl
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push %gs
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push %fs
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push %es
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push %ds
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push %ss
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push %cs
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/* Physical address of %cs:0000 to %ebx, of %ss:0000 to %eax */
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xorl %ebx, %ebx
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movw %cs, %bx
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shll $4, %ebx
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/* Set GDT base and load GDT */
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xorl %eax, %eax
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movw %ss, %ax
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shll $4, %eax
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/* Set up GDT and switch to protected mode */
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addl %ebx, %cs:gdt_base
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orl %ebx, %cs:(cs16+2)
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orl %eax, %cs:(ss16+2)
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cli
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data32 lgdt %cs:gdt
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movw %cs, %ax
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shrl $4, %eax
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addl $gdt, %eax
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movl %eax, %cs:gdt_base
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lgdt %cs:gdt
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/* Switch to protected mode, set segment limits, switch back */
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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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data32 ljmp $CS16, $1f
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1: movw $SS16, %ax
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movw %ax, %ss
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movw $FLAT_DS, %ax
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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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/* Install .text and .data to 2MB mark. Use 2MB to avoid
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* having to deal with A20.
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*/
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leal _text_load_offset(%ebx), %esi
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movl $( 2 * 1024 * 1024 ), %edi
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movl $_text_and_data_progbits_size, %ecx
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addr32 rep movsb /* or "call decompress16" */
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/* Restore real-mode segment limits */
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movw %ss, %ax
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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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/* Return to real mode, restore segment registers and flags */
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pushw $1f
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movl %cr0, %eax
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movw %cx, %ds
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movw %cx, %es
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andb $0!CR0_PE, %al
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movl %eax, %cr0
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lret /* used as equivalent of pop %cs */
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1: pop %ss
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pop %ds
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pop %es
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pop %fs
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pop %gs
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popfl
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/* Call init_gdt */
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pushw %cs
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pushw $1f
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pushw %es
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pushw $init_gdt
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lret /* lcall %es:init_gdt */
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1:
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/* Restore real-mode segment values and temporary registers */
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popl %eax
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popw %ds
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popw %es
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ret
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.size set_segment_limits, . - set_segment_limits
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/****************************************************************************
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* install_highmem (real-mode near call)
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*
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* Install .text and .data into high memory
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*
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* Parameters:
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* %edi : physical address in high memory
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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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.section ".prefix.lib"
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.code16
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install_highmem:
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/* Preserve registers and interrupt status */
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pushfl
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pushl %esi
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pushl %edi
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pushl %ecx
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/* Disable interrupts and flatten real mode */
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cli
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movw $FLAT_DS, %cx
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call set_segment_limits
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/* Install .text and .data to specified address */
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xorw %ax, %ax
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movw %ax, %es
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movl $_text_load_offset, %esi
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movl $_text_and_data_progbits_size, %ecx
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call install_block
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/* Unflatten real mode */
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movw $REAL_DS, %cx
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call set_segment_limits
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/* Restore registers and interrupt status */
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popl %ecx
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popl %edi
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popl %esi
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popfl
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ret
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.size install_highmem, . - install_highmem
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