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/*
* e820_bios.S: read e820 by int 15h call.
*
* The C language function exported by this file is:
* int get_e820_by_bios(void *e820_buf);
* @e820_buf: e820 mem map buffer, allocated by caller
* return: number of e820 entries
*
* Copyright (C) 2013 Intel Corporation.
* Author: Bin Gao <bin.gao@intel.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope 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
* this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
*
*/
#include "bootstub.h"
/* Real mode low memory layout */
#define IDT_START 0x0
#define RELOCATED_START 0xa000
#define STACK_START 0xb000
#define DATA_START 0xb200
#define SAVED_GDTR_ADDR 0xb100
#define SAVED_IDTR_ADDR 0xb110
#define COUNT_ADDR 0xb120
#define TOTAL_COUNT_ADDR 0xb130
#define MIN_BUF_LEN 20
#define BUF_LEN 2048
#define MAX_NR_ENTRIES 128
#define SMAP 0x534d4150
#define E820 0xe820
.text
.section ".text.head","ax",@progbits
.code32
.globl get_e820_by_bios
get_e820_by_bios:
jmp start_32bit
.balign 16
idtr:
.word 0xffff
.long IDT_START
.balign 16
gdt:
.quad 0
.quad GDT_ENTRY(0x009b, 0, 0xffff)
.quad GDT_ENTRY(0x0093, 0, 0xffff)
gdtr:
.word 3*8-1
.long gdt
saved_esp:
.long 0
start_32bit:
pushal
pushfl
/* Save ESP, GDTR and IDTR registers */
movl $saved_esp, %eax
movl %esp, (%eax)
xorl %eax, %eax
sidtl SAVED_IDTR_ADDR(%eax)
sgdtl SAVED_GDTR_ADDR(%eax)
/* Relocate real mode codes to 64k segment */
movl $relocated_end + 4, %ecx
subl $relocated_start, %ecx
shrl $2, %ecx
movl $relocated_start, %esi
movl $RELOCATED_START, %edi
rep movsl
/* Set up real mode IDT */
lidtl %cs:idtr
/* Set up real mode GDT */
lgdtl %cs:gdtr
movl $16, %ecx
movl %ecx, %ds
movl %ecx, %es
movl %ecx, %fs
movl %ecx, %gs
movl %ecx, %ss
/* Switch to 16bit segment */
ljmpl $8, $RELOCATED_START
.code16
relocated_start:
reloc_base = .
/* Switch to real mode */
andb $0x10, %al
movl %eax, %cr0
ljmpw $0, $realmode_entry - relocated_start + RELOCATED_START
realmode_entry = .
/* In real mode now, set up segment selectors */
movl $0, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
movl %eax, %gs
movl %eax, %fs
movl $STACK_START, %esp
/* Do int 15h call */
movl $COUNT_ADDR, %eax
movl $0, (%eax)
movl $TOTAL_COUNT_ADDR, %eax
movl $0, (%eax)
xorl %ebx, %ebx
movw $DATA_START, %di
again:
movw $E820, %ax
movw $BUF_LEN, %cx
movl $SMAP, %edx
int $0x15
jc error /* EFLGAS.CF is set */
cmpl $SMAP, %eax
jne error /* eax is not 'SMAP' */
cmpw $MIN_BUF_LEN, %cx
jl error /* returned buffer len < 20 */
cmpw $BUF_LEN, %cx
jg error /* returned buffer len > provided buffer len */
movl $TOTAL_COUNT_ADDR, %eax
addw %cx, (%eax)
movl $COUNT_ADDR, %eax
incl (%eax)
movl (%eax), %eax
cmpl $MAX_NR_ENTRIES, %eax /* max supported entries: 128 */
jge done
testl %ebx, %ebx /* ebx == 0: done, ebx != 0: continue */
je done
addw %cx, %di
jmp again
done:
jmp 2f
error:
movl $COUNT_ADDR, %eax
movl $~0, (%eax)
2:
/* Switch back to protected mode */
xorl %ebx, %ebx
lidtl SAVED_IDTR_ADDR(%ebx)
lgdtl SAVED_GDTR_ADDR(%ebx)
movl %cr0, %ebx
orb $1, %bl
movl %ebx, %cr0
.byte 0x66, 0xea /* opcode(JMP FAR) with operand size override */
.long resumed_protected_mode /* offset */
.word __BOOT_CS /* segment selector */
relocated_end = .
.code32
resumed_protected_mode:
cli /* in case real mode codes turn on interrrupt! */
/* Restore segment registers */
movl $__BOOT_DS, %ebx
movl %ebx, %ds
movl %ebx, %es
movl %ebx, %gs
movl %ebx, %fs
movl %ebx, %ss
/* Restore stack pointer */
movl $saved_esp, %eax
movl (%eax), %esp
/* Copy e820 data from our buffer to caller's buffer */
xorl %eax, %eax
movl TOTAL_COUNT_ADDR(%eax), %ecx
movl $DATA_START, %esi
movl 40(%esp), %edi
rep movsb
popfl
popal
/* Return number of e820 entries */
movl $COUNT_ADDR, %eax
movl (%eax), %eax
ret
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