pc-bios/optionrom/multiboot.S

   1 /*
   2  * Multiboot 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
  21 #include "optionrom.h"
  22
  23 #define BOOT_ROM_PRODUCT "multiboot loader"
  24
  25 #define MULTIBOOT_MAGIC         0x2badb002
  26
  27 #define GS_PROT_JUMP            0
  28 #define GS_GDT_DESC             6
  29
  30
  31 BOOT_ROM_START
  32
  33 run_multiboot:
  34
  35         cli
  36         cld
  37
  38         mov             %cs, %eax
  39         shl             $0x4, %eax
  40
  41         /* set up a long jump descriptor that is PC relative */
  42
  43         /* move stack memory to %gs */
  44         mov             %ss, %ecx
  45         shl             $0x4, %ecx
  46         mov             %esp, %ebx
  47         add             %ebx, %ecx
  48         sub             $0x20, %ecx
  49         sub             $0x30, %esp
  50         shr             $0x4, %ecx
  51         mov             %cx, %gs
  52
  53         /* now push the indirect jump decriptor there */
  54         mov             (prot_jump), %ebx
  55         add             %eax, %ebx
  56         movl            %ebx, %gs:GS_PROT_JUMP
  57         mov             $8, %bx
  58         movw            %bx, %gs:GS_PROT_JUMP + 4
  59
  60         /* fix the gdt descriptor to be PC relative */
  61         movw            (gdt_desc), %bx
  62         movw            %bx, %gs:GS_GDT_DESC
  63         movl            (gdt_desc+2), %ebx
  64         add             %eax, %ebx
  65         movl            %ebx, %gs:GS_GDT_DESC + 2
  66
  67         xor             %eax, %eax
  68         mov             %eax, %es
  69
  70         /* Read the bootinfo struct into RAM */
  71         read_fw_blob(FW_CFG_INITRD)
  72
  73         /* FS = bootinfo_struct */
  74         read_fw         FW_CFG_INITRD_ADDR
  75         shr             $4, %eax
  76         mov             %ax, %fs
  77
  78         /* ES = mmap_addr */
  79         mov             %fs:48, %eax
  80         shr             $4, %eax
  81         mov             %ax, %es
  82
  83         /* Initialize multiboot mmap structs using int 0x15(e820) */
  84         xor             %ebx, %ebx
  85         /* mmap start after first size */
  86         movl            $4, %edi
  87
  88 mmap_loop:
  89         /* entry size (mmap struct) & max buffer size (int15) */
  90         movl            $20, %ecx
  91         /* store entry size */
  92         /* old as(1) doesn't like this insn so emit the bytes instead:
  93         movl            %ecx, %es:-4(%edi)
  94         */
  95         .dc.b           0x26,0x67,0x66,0x89,0x4f,0xfc
  96         /* e820 */
  97         movl            $0x0000e820, %eax
  98         /* 'SMAP' magic */
  99         movl            $0x534d4150, %edx
 100         int             $0x15
 101
 102 mmap_check_entry:
 103         /* last entry? then we're done */
 104         jb              mmap_done
 105         and             %bx, %bx
 106         jz              mmap_done
 107         /* valid entry, so let's loop on */
 108
 109 mmap_store_entry:
 110         /* %ax = entry_number * 24 */
 111         mov             $24, %ax
 112         mul             %bx
 113         mov             %ax, %di
 114         movw            %di, %fs:0x2c
 115         /* %di = 4 + (entry_number * 24) */
 116         add             $4, %di
 117         jmp             mmap_loop
 118
 119 mmap_done:
 120 real_to_prot:
 121         /* Load the GDT before going into protected mode */
 122 lgdt:
 123         data32 lgdt     %gs:GS_GDT_DESC
 124
 125         /* get us to protected mode now */
 126         movl            $1, %eax
 127         movl            %eax, %cr0
 128
 129         /* the LJMP sets CS for us and gets us to 32-bit */
 130 ljmp:
 131         data32 ljmp     *%gs:GS_PROT_JUMP
 132
 133 prot_mode:
 134 .code32
 135
 136         /* initialize all other segments */
 137         movl            $0x10, %eax
 138         movl            %eax, %ss
 139         movl            %eax, %ds
 140         movl            %eax, %es
 141         movl            %eax, %fs
 142         movl            %eax, %gs
 143
 144         /* Read the kernel and modules into RAM */
 145         read_fw_blob(FW_CFG_KERNEL)
 146
 147         /* Jump off to the kernel */
 148         read_fw         FW_CFG_KERNEL_ENTRY
 149         mov             %eax, %ecx
 150
 151         /* EBX contains a pointer to the bootinfo struct */
 152         read_fw         FW_CFG_INITRD_ADDR
 153         movl            %eax, %ebx
 154
 155         /* EAX has to contain the magic */
 156         movl            $MULTIBOOT_MAGIC, %eax
 157 ljmp2:
 158         jmp             *%ecx
 159
 160 /* Variables */
 161 .align 4, 0
 162 prot_jump:      .long prot_mode
 163                 .short 8
 164
 165 .align 4, 0
 166 gdt:
 167         /* 0x00 */
 168 .byte   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
 169
 170         /* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */
 171 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00
 172
 173         /* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */
 174 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00
 175
 176         /* 0x18: code segment (base=0, limit=0x0ffff, type=16bit code exec/read/conf, DPL=0, 1b) */
 177 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x9e, 0x00, 0x00
 178
 179         /* 0x20: data segment (base=0, limit=0x0ffff, type=16bit data read/write, DPL=0, 1b) */
 180 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x00, 0x00
 181
 182 gdt_desc:
 183 .short  (5 * 8) - 1
 184 .long   gdt
 185
 186 BOOT_ROM_END