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grub/grub-core/lib/i386/relocator16.S
Cao jin 27dd2885e1 relocator16: Comments update 
Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
2020-09-21 13:29:05 -04:00

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7.1 KiB
ArmAsm
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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 <grub/i386/relocator_private.h>
#include "relocator_common.S"
.p2align 4 /* force 16-byte alignment */
VARIABLE(grub_relocator16_start)
PREAMBLE
#ifdef __APPLE__
LOCAL(cs_base_bytes12_offset) = LOCAL (cs_base_bytes12) - LOCAL (base)
LOCAL(cs_base_byte3_offset) = LOCAL (cs_base_byte3) - LOCAL (base)
movl %esi, %eax
movw %ax, (LOCAL(cs_base_bytes12_offset)) (RSI, 1)
shrl $16, %eax
movb %al, (LOCAL (cs_base_byte3_offset)) (RSI, 1)
#else
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)
#endif
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
#ifdef __APPLE__
LOCAL(segment_offset) = LOCAL (segment) - LOCAL (base)
LOCAL(idt_offset) = LOCAL(relocator16_idt) - LOCAL (base)
LOCAL(cont2_offset) = LOCAL (cont2) - LOCAL(base)
movw %ax, LOCAL(segment_offset) (%esi, 1)
lidt LOCAL(idt_offset) (%esi, 1)
/* jump to a 16 bit segment */
ljmp $PSEUDO_REAL_CSEG, $(LOCAL(cont2_offset))
#else
movw %ax, (LOCAL (segment) - LOCAL (base)) (%esi, 1)
lidt (EXT_C(grub_relocator16_idt) - LOCAL (base)) (%esi, 1)
/* jump to a 16 bit segment */
ljmp $PSEUDO_REAL_CSEG, $(LOCAL (cont2) - LOCAL(base))
#endif
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
#ifdef __APPLE__
LOCAL(cont3_offset) = LOCAL(cont3) - LOCAL(base)
.word LOCAL(cont3_offset)
#else
.word LOCAL(cont3)-LOCAL(base)
#endif
LOCAL(segment):
.word 0
LOCAL(cont3):
/* movw imm16, %ax. */
.byte 0xb8
VARIABLE(grub_relocator16_keep_a20_enabled)
.word 0
test %ax, %ax
jnz LOCAL(gate_a20_done)
movw %cs, %ax
movw %ax, %ss
#ifdef __APPLE__
LOCAL(relocator16_end_offset) = LOCAL(relocator16_end) - LOCAL(base)
leaw LOCAL(relocator16_end_offset), %sp
#else
leaw LOCAL(relocator16_end) - LOCAL(base), %sp
#endif
addw $GRUB_RELOCATOR16_STACK_SIZE, %sp
/* second, try a BIOS call */
movw $0x2400, %ax
int $0x15
call LOCAL(gate_a20_check_state)
testb %al, %al
jz LOCAL(gate_a20_done)
/*
* In macbook, the keyboard test would hang the machine, so we move
* this forward.
*/
/* fourth, try the system control port A */
inb $0x92
andb $(~0x03), %al
outb $0x92
/* When turning off Gate A20, do not check the state strictly,
because a failure is not fatal usually, and Gate A20 is always
on some modern machines. */
jmp LOCAL(gate_a20_done)
LOCAL(gate_a20_check_state):
/* iterate the checking for a while */
movw $100, %cx
1:
xorw %ax, %ax
movw %ax, %ds
decw %ax
movw %ax, %es
xorw %ax, %ax
movw $0x8000, %ax
/* compare the byte at ADDR with that at 0x100000 + ADDR */
movw %ax, %si
addw $0x10, %ax
movw %ax, %di
/* save the original byte in DL */
movb %ds:(%si), %dl
movb %es:(%di), %al
/* try to set one less value at ADDR */
movb %al, %dh
decb %dh
movb %dh, %ds:(%si)
/* serialize */
outb %al, $0x80
outb %al, $0x80
/* obtain the value at 0x100000 + ADDR in CH */
movb %es:(%di), %dh
/* this result is 1 if A20 is on or 0 if it is off */
subb %dh, %al
xorb $1, %al
/* restore the original */
movb %dl, %ds:(%si)
testb %al, %al
jz LOCAL(gate_a20_done)
loop 1b
2:
ret
LOCAL(gate_a20_done):
/*
* We are in real mode now. Set up the real mode segment registers and
* all the other general purpose registers. cs is updated with ljmp.
*/
/* 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, %eax. */
.byte 0x66, 0xb8
VARIABLE(grub_relocator16_esi)
.long 0
movl %eax, %esi
/* movw imm32, %edx. */
.byte 0x66, 0xba
VARIABLE(grub_relocator16_edx)
.long 0
/* movw imm32, %ebx. */
.byte 0x66, 0xbb
VARIABLE(grub_relocator16_ebx)
.long 0
/* movl imm32, %ebp. */
.byte 0x66, 0xbd
VARIABLE(grub_relocator16_ebp)
.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 = filled by code, 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):
#ifdef __APPLE__
LOCAL(relocator16_idt):
#endif
VARIABLE(grub_relocator16_idt)
.word 0
.long 0
LOCAL(relocator16_end):
VARIABLE(grub_relocator16_end)
.byte 0
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