wakeup.S
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/*
* Copyright (C) 2017, Bin Meng <bmeng.cn@gmail.com>
*
* From coreboot src/arch/x86/wakeup.S
*
* SPDX-License-Identifier: GPL-2.0+
*/
#include <asm/acpi_s3.h>
#include <asm/processor.h>
#include <asm/processor-flags.h>
#define RELOCATED(x) ((x) - __wakeup + WAKEUP_BASE)
#define CODE_SEG (X86_GDT_ENTRY_16BIT_CS * X86_GDT_ENTRY_SIZE)
#define DATA_SEG (X86_GDT_ENTRY_16BIT_DS * X86_GDT_ENTRY_SIZE)
.code32
.globl __wakeup
__wakeup:
/* First prepare the jmp to the resume vector */
mov 0x4(%esp), %eax /* vector */
/* last 4 bits of linear addr are taken as offset */
andw $0x0f, %ax
movw %ax, (__wakeup_offset)
mov 0x4(%esp), %eax
/* the rest is taken as segment */
shr $4, %eax
movw %ax, (__wakeup_segment)
/* Activate the right segment descriptor real mode */
ljmp $CODE_SEG, $RELOCATED(1f)
1:
/* 16 bit code from here on... */
.code16
/*
* Load the segment registers w/ properly configured segment
* descriptors. They will retain these configurations (limits,
* writability, etc.) once protected mode is turned off.
*/
mov $DATA_SEG, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
/* Turn off protection */
movl %cr0, %eax
andl $~X86_CR0_PE, %eax
movl %eax, %cr0
/* Now really going into real mode */
ljmp $0, $RELOCATED(1f)
1:
movw $0x0, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %ss
movw %ax, %fs
movw %ax, %gs
/*
* This is a FAR JMP to the OS waking vector.
* The C code changes the address to be correct.
*/
.byte 0xea
__wakeup_offset = RELOCATED(.)
.word 0x0000
__wakeup_segment = RELOCATED(.)
.word 0x0000
.globl __wakeup_size
__wakeup_size:
.long . - __wakeup