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/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2009,2010 Free Software Foundation, Inc.
*
* GRUB is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GRUB is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
*/
/* The code segment of the protected mode. */
#define CODE_SEGMENT 0x08
/* The data segment of the protected mode. */
#define DATA_SEGMENT 0x10
#define PSEUDO_REAL_CSEG 0x18
#define PSEUDO_REAL_DSEG 0x20
#include "relocator_common.S"
.p2align 4 /* force 16-byte alignment */
VARIABLE(grub_relocator16_start)
PREAMBLE
movl %esi, %eax
movw %ax, (LOCAL (cs_base_bytes12) - LOCAL (base)) (RSI, 1)
shrl $16, %eax
movb %al, (LOCAL (cs_base_byte3) - LOCAL (base)) (RSI, 1)
RELOAD_GDT
.code32
/* Update other registers. */
movl $DATA_SEGMENT, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %fs
movl %eax, %gs
movl %eax, %ss
DISABLE_PAGING
#ifdef __x86_64__
/* Disable amd64. */
movl $GRUB_MEMORY_CPU_AMD64_MSR, %ecx
rdmsr
andl $(~GRUB_MEMORY_CPU_AMD64_MSR_ON), %eax
wrmsr
#endif
/* Turn off PAE. */
movl %cr4, %eax
andl $(~GRUB_MEMORY_CPU_CR4_PAE_ON), %eax
movl %eax, %cr4
/* Update other registers. */
movl $PSEUDO_REAL_DSEG, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %fs
movl %eax, %gs
movl %eax, %ss
movl %esi, %eax
shrl $4, %eax
movw %ax, (LOCAL (segment) - LOCAL (base)) (%esi, 1)
/* jump to a 16 bit segment */
ljmp $PSEUDO_REAL_CSEG, $(LOCAL (cont2) - LOCAL(base))
LOCAL(cont2):
.code16
/* clear the PE bit of CR0 */
movl %cr0, %eax
andl $(~GRUB_MEMORY_CPU_CR0_PE_ON), %eax
movl %eax, %cr0
/* flush prefetch queue, reload %cs */
/* ljmp */
.byte 0xea
.word LOCAL(cont3)-LOCAL(base)
LOCAL(segment):
.word 0
LOCAL(cont3):
/* we are in real mode now
* set up the real mode segment registers : DS, SS, ES
*/
/* movw imm16, %ax. */
.byte 0xb8
VARIABLE(grub_relocator16_ds)
.word 0
movw %ax, %ds
/* movw imm16, %ax. */
.byte 0xb8
VARIABLE(grub_relocator16_es)
.word 0
movw %ax, %es
/* movw imm16, %ax. */
.byte 0xb8
VARIABLE(grub_relocator16_fs)
.word 0
movw %ax, %fs
/* movw imm16, %ax. */
.byte 0xb8
VARIABLE(grub_relocator16_gs)
.word 0
movw %ax, %gs
/* movw imm16, %ax. */
.byte 0xb8
VARIABLE(grub_relocator16_ss)
.word 0
movw %ax, %ss
/* movw imm16, %ax. */
.byte 0xb8
VARIABLE(grub_relocator16_sp)
.word 0
movzwl %ax, %esp
/* movw imm32, %edx. */
.byte 0x66, 0xba
VARIABLE(grub_relocator16_edx)
.long 0
/* Cleared direction flag is of no problem with any current
payload and makes this implementation easier. */
cld
/* ljmp */
.byte 0xea
VARIABLE(grub_relocator16_ip)
.word 0
VARIABLE(grub_relocator16_cs)
.word 0
.code32
/* GDT. Copied from loader/i386/linux.c. */
.p2align 4
LOCAL(gdt):
.word 0, 0
.byte 0, 0, 0, 0
/* -- code segment --
* base = 0x00000000, limit = 0xFFFFF (4 KiB Granularity), present
* type = 32bit code execute/read, DPL = 0
*/
.word 0xFFFF, 0
.byte 0, 0x9A, 0xCF, 0
/* -- data segment --
* base = 0x00000000, limit 0xFFFFF (4 KiB Granularity), present
* type = 32 bit data read/write, DPL = 0
*/
.word 0xFFFF, 0
.byte 0, 0x92, 0xCF, 0
/* -- 16 bit real mode CS --
* base = 0x00000000, limit 0x0FFFF (1 B Granularity), present
* type = 16 bit code execute/read only/conforming, DPL = 0
*/
.word 0xFFFF
LOCAL(cs_base_bytes12):
.word 0
LOCAL(cs_base_byte3):
.byte 0
.byte 0x9E, 0, 0
/* -- 16 bit real mode DS --
* base = 0x00000000, limit 0x0FFFF (1 B Granularity), present
* type = 16 bit data read/write, DPL = 0
*/
.word 0xFFFF, 0
.byte 0, 0x92, 0, 0
LOCAL(gdt_end):
VARIABLE(grub_relocator16_end)
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