pc-bios/optionrom/linuxboot.S

   1 /*
   2  * Linux Boot Option ROM
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  16  *
  17  * Copyright Novell Inc, 2009
  18  *   Authors: Alexander Graf <agraf@suse.de>
  19  *
  20  * Based on code in hw/pc.c.
  21  */
  22
  23 #include "optionrom.h"
  24
  25 #define BOOT_ROM_PRODUCT "Linux loader"
  26
  27 BOOT_ROM_START
  28
  29 run_linuxboot:
  30
  31         cli
  32         cld
  33
  34         jmp             copy_kernel
  35 boot_kernel:
  36
  37         read_fw         FW_CFG_SETUP_ADDR
  38
  39         mov             %eax, %ebx
  40         shr             $4, %ebx
  41
  42         /* All segments contain real_addr */
  43         mov             %bx, %ds
  44         mov             %bx, %es
  45         mov             %bx, %fs
  46         mov             %bx, %gs
  47         mov             %bx, %ss
  48
  49         /* CX = CS we want to jump to */
  50         add             $0x20, %bx
  51         mov             %bx, %cx
  52
  53         /* SP = cmdline_addr-real_addr-16 */
  54         read_fw         FW_CFG_CMDLINE_ADDR
  55         mov             %eax, %ebx
  56         read_fw         FW_CFG_SETUP_ADDR
  57         sub             %eax, %ebx
  58         sub             $16, %ebx
  59         mov             %ebx, %esp
  60
  61         /* Build indirect lret descriptor */
  62         pushw           %cx             /* CS */
  63         xor             %ax, %ax
  64         pushw           %ax             /* IP = 0 */
  65
  66         /* Clear registers */
  67         xor             %eax, %eax
  68         xor             %ebx, %ebx
  69         xor             %ecx, %ecx
  70         xor             %edx, %edx
  71         xor             %edi, %edi
  72         xor             %ebp, %ebp
  73
  74         /* Jump to Linux */
  75         lret
  76
  77
  78 copy_kernel:
  79
  80         /* We need to load the kernel into memory we can't access in 16 bit
  81            mode, so let's get into 32 bit mode, write the kernel and jump
  82            back again. */
  83
  84         /* Reserve space on the stack for our GDT descriptor. */
  85         mov             %esp, %ebp
  86         sub             $16, %esp
  87
  88         /* Now create the GDT descriptor */
  89         movw            $((3 * 8) - 1), -16(%bp)
  90         mov             %cs, %eax
  91         movzwl          %ax, %eax
  92         shl             $4, %eax
  93         addl            $gdt, %eax
  94         movl            %eax, -14(%bp)
  95
  96         /* And load the GDT */
  97         data32 lgdt     -16(%bp)
  98         mov             %ebp, %esp
  99
 100         /* Get us to protected mode now */
 101         mov             $1, %eax
 102         mov             %eax, %cr0
 103
 104         /* So we can set ES to a 32-bit segment */
 105         mov             $0x10, %eax
 106         mov             %eax, %es
 107
 108         /* We're now running in 16-bit CS, but 32-bit ES! */
 109
 110         /* Load kernel and initrd */
 111         read_fw_blob_addr32(FW_CFG_KERNEL)
 112         read_fw_blob_addr32(FW_CFG_INITRD)
 113         read_fw_blob_addr32(FW_CFG_CMDLINE)
 114         read_fw_blob_addr32(FW_CFG_SETUP)
 115
 116         /* And now jump into Linux! */
 117         mov             $0, %eax
 118         mov             %eax, %cr0
 119
 120         /* ES = CS */
 121         mov             %cs, %ax
 122         mov             %ax, %es
 123
 124         jmp             boot_kernel
 125
 126 /* Variables */
 127
 128 .align 4, 0
 129 gdt:
 130         /* 0x00 */
 131 .byte   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
 132
 133         /* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */
 134 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00
 135
 136         /* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */
 137 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00
 138
 139 BOOT_ROM_END