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, write to the Free Software
  16  * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  17  *
  18  * Copyright Novell Inc, 2009
  19  *   Authors: Alexander Graf <agraf@suse.de>
  20  */
  21
  22 #define NO_QEMU_PROTOS
  23 #include "../../hw/fw_cfg.h"
  24
  25 #define BIOS_CFG_IOPORT_CFG     0x510
  26 #define BIOS_CFG_IOPORT_DATA    0x511
  27
  28 #define MULTIBOOT_MAGIC         0x2badb002
  29
  30 /* Read a variable from the fw_cfg device.
  31    Clobbers:    %edx
  32    Out:         %eax */
  33 .macro read_fw VAR
  34         mov             $\VAR, %ax
  35         mov             $BIOS_CFG_IOPORT_CFG, %dx
  36         outw            %ax, (%dx)
  37         mov             $BIOS_CFG_IOPORT_DATA, %dx
  38         inb             (%dx), %al
  39         shl             $8, %eax
  40         inb             (%dx), %al
  41         shl             $8, %eax
  42         inb             (%dx), %al
  43         shl             $8, %eax
  44         inb             (%dx), %al
  45         bswap           %eax
  46 .endm
  47
  48 .code16
  49 .text
  50         .global         _start
  51 _start:
  52         .short          0xaa55
  53         .byte           1 /* (_end - _start) / 512 */
  54         push            %eax
  55         push            %ds
  56
  57         /* setup ds so we can access the IVT */
  58         xor             %ax, %ax
  59         mov             %ax, %ds
  60
  61         /* save old int 19 */
  62         mov             (0x19*4), %eax
  63         mov             %eax, %cs:old_int19
  64
  65         /* install our int 19 handler */
  66         movw            $int19_handler, (0x19*4)
  67         mov             %cs, (0x19*4+2)
  68
  69         pop             %ds
  70         pop             %eax
  71         lret
  72
  73 int19_handler:
  74         /* DS = CS */
  75         movw            %cs, %ax
  76         movw            %ax, %ds
  77
  78         /* fall through */
  79
  80 run_multiboot:
  81
  82         cli
  83         cld
  84
  85         mov             %cs, %eax
  86         shl             $0x4, %eax
  87
  88         /* fix the gdt descriptor to be PC relative */
  89         mov             (gdt_desc+2), %ebx
  90         add             %eax, %ebx
  91         mov             %ebx, (gdt_desc+2)
  92
  93         /* fix the prot mode indirect jump to be PC relative */
  94         mov             (prot_jump), %ebx
  95         add             %eax, %ebx
  96         mov             %ebx, (prot_jump)
  97
  98         /* FS = bootinfo_struct */
  99         read_fw         FW_CFG_INITRD_ADDR
 100         shr             $4, %eax
 101         mov             %ax, %fs
 102
 103         /* ES = mmap_addr */
 104         read_fw         FW_CFG_INITRD_SIZE
 105         shr             $4, %eax
 106         mov             %ax, %es
 107
 108         /* Initialize multiboot mmap structs using int 0x15(e820) */
 109         xor             %ebx, %ebx
 110         /* mmap start after first size */
 111         movl            $4, %edi
 112
 113 mmap_loop:
 114         /* entry size (mmap struct) & max buffer size (int15) */
 115         movl            $20, %ecx
 116         /* store entry size */
 117         movl            %ecx, %es:-4(%edi)
 118         /* e820 */
 119         movl            $0x0000e820, %eax
 120         /* 'SMAP' magic */
 121         movl            $0x534d4150, %edx
 122         int             $0x15
 123
 124 mmap_check_entry:
 125         /* last entry? then we're done */
 126         jb              mmap_done
 127         and             %bx, %bx
 128         jz              mmap_done
 129         /* valid entry, so let's loop on */
 130
 131 mmap_store_entry:
 132         /* %ax = entry_number * 24 */
 133         mov             $24, %ax
 134         mul             %bx
 135         mov             %ax, %di
 136         movw            %di, %fs:0x2c
 137         /* %di = 4 + (entry_number * 24) */
 138         add             $4, %di
 139         jmp             mmap_loop
 140
 141 mmap_done:
 142 real_to_prot:
 143         /* Load the GDT before going into protected mode */
 144 lgdt:
 145         data32 lgdt     %cs:gdt_desc
 146
 147         /* get us to protected mode now */
 148         movl            $1, %eax
 149         movl            %eax, %cr0
 150
 151         /* the LJMP sets CS for us and gets us to 32-bit */
 152 ljmp:
 153         data32 ljmp     *%cs:prot_jump
 154
 155 prot_mode:
 156 .code32
 157
 158         /* initialize all other segments */
 159         movl            $0x10, %eax
 160         movl            %eax, %ss
 161         movl            %eax, %ds
 162         movl            %eax, %es
 163         movl            %eax, %fs
 164         movl            %eax, %gs
 165
 166         /* Jump off to the kernel */
 167         read_fw         FW_CFG_KERNEL_ADDR
 168         mov             %eax, %ecx
 169
 170         /* EBX contains a pointer to the bootinfo struct */
 171         read_fw         FW_CFG_INITRD_ADDR
 172         movl            %eax, %ebx
 173
 174         /* EAX has to contain the magic */
 175         movl            $MULTIBOOT_MAGIC, %eax
 176 ljmp2:
 177         jmp             *%ecx
 178
 179 /* Variables */
 180 .align 4, 0
 181 old_int19:      .long 0
 182
 183 prot_jump:      .long prot_mode
 184                 .short 8
 185
 186 .align 4, 0
 187 gdt:
 188         /* 0x00 */
 189 .byte   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
 190
 191         /* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */
 192 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00
 193
 194         /* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */
 195 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00
 196
 197         /* 0x18: code segment (base=0, limit=0x0ffff, type=16bit code exec/read/conf, DPL=0, 1b) */
 198 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x9e, 0x00, 0x00
 199
 200         /* 0x20: data segment (base=0, limit=0x0ffff, type=16bit data read/write, DPL=0, 1b) */
 201 .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x00, 0x00
 202
 203 gdt_desc:
 204 .short  (5 * 8) - 1
 205 .long   gdt
 206
 207 .align 512, 0
 208 _end:
 209