/*
* Linux Boot Option ROM
*
* This program 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 2 of the License, or
* (at your option) any later version.
*
* This program 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 this program; if not, see <http://www.gnu.org/licenses/>.
*
* Copyright Novell Inc, 2009
* Authors: Alexander Graf <agraf@suse.de>
*
* Based on code in hw/pc.c.
*/
#include "optionrom.h"
BOOT_ROM_START
run_linuxboot:
cli
cld
jmp copy_kernel
boot_kernel:
read_fw FW_CFG_SETUP_ADDR
mov %eax, %ebx
shr $4, %ebx
/* All segments contain real_addr */
mov %bx, %ds
mov %bx, %es
mov %bx, %fs
mov %bx, %gs
mov %bx, %ss
/* CX = CS we want to jump to */
add $0x20, %bx
mov %bx, %cx
/* SP = cmdline_addr-real_addr-16 */
read_fw FW_CFG_CMDLINE_ADDR
mov %eax, %ebx
read_fw FW_CFG_SETUP_ADDR
sub %eax, %ebx
sub $16, %ebx
mov %ebx, %esp
/* Build indirect lret descriptor */
pushw %cx /* CS */
xor %ax, %ax
pushw %ax /* IP = 0 */
/* Clear registers */
xor %eax, %eax
xor %ebx, %ebx
xor %ecx, %ecx
xor %edx, %edx
xor %edi, %edi
xor %ebp, %ebp
/* Jump to Linux */
lret
copy_kernel:
/* We need to load the kernel into memory we can't access in 16 bit
mode, so let's get into 32 bit mode, write the kernel and jump
back again. */
/* Set DS to SS+SP - 0x10, so we can write our GDT descriptor there */
mov %ss, %eax
shl $4, %eax
add %esp, %eax
sub $0x10, %eax
shr $4, %eax
/* Now create the GDT descriptor */
mov %cs, %eax
shl $4, %eax
movw $((3 * 8) - 1), %bx
movw %bx, %gs:0
movl $gdt, %ebx
add %eax, %ebx
movl %ebx, %gs:2
/* And load the GDT */
data32 lgdt %gs:0
/* Get us to protected mode now */
mov $1, %eax
mov %eax, %cr0
/* So we can set DS to a 32-bit segment */
mov $0x10, %eax
mov %eax, %ds
/* We're now running in 16-bit CS, but 32-bit DS! */
/* Load kernel and initrd */
read_fw_blob(FW_CFG_KERNEL)
read_fw_blob(FW_CFG_INITRD)
read_fw_blob(FW_CFG_CMDLINE)
read_fw_blob(FW_CFG_SETUP)
/* And now jump into Linux! */
mov $0, %eax
mov %eax, %cr0
/* DS = CS */
mov %cs, %ax
mov %ax, %ds
jmp boot_kernel
/* Variables */
.align 4, 0
gdt:
/* 0x00 */
.byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
/* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */
.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00
/* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */
.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00
BOOT_ROM_END
