gptmbr.S revision 1.2
1 /* ----------------------------------------------------------------------- 2 * 3 * Copyright 2007-2009 H. Peter Anvin - All Rights Reserved 4 * Copyright 2009-2010 Intel Corporation; author: H. Peter Anvin 5 * 6 * Permission is hereby granted, free of charge, to any person 7 * obtaining a copy of this software and associated documentation 8 * files (the "Software"), to deal in the Software without 9 * restriction, including without limitation the rights to use, 10 * copy, modify, merge, publish, distribute, sublicense, and/or 11 * sell copies of the Software, and to permit persons to whom 12 * the Software is furnished to do so, subject to the following 13 * conditions: 14 * 15 * The above copyright notice and this permission notice shall 16 * be included in all copies or substantial portions of the Software. 17 * 18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 19 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES 20 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 21 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT 22 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 23 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 24 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR 25 * OTHER DEALINGS IN THE SOFTWARE. 26 * 27 * ----------------------------------------------------------------------- */ 28 29 #include <machine/asm.h> 30 #include <sys/bootblock.h> 31 32 #ifdef CTRL_80 33 .macro ADJUST_DRIVE 34 testb $0x04, BIOS_kbdflags 35 jz 1f 36 movb $0x80, %dl 37 1: 38 .endm 39 #elif defined(FORCE_80) 40 .macro ADJUST_DRIVE 41 movb $0x80, %dl 42 .endm 43 #else 44 .macro ADJUST_DRIVE 45 .endm 46 #endif 47 48 .code16 49 .text 50 51 .globl bootsec 52 stack = 0x7c00 53 54 /* Partition table header here */ 55 phdr = stack /* Above the stack, overwritten by bootsect */ 56 /* Partition table sector here */ 57 /* To handle > 32K we need to play segment tricks... */ 58 psec = _phdr + 512 59 60 /* Where we put DS:SI */ 61 dssi_out = start + 0x1be 62 63 BIOS_kbdflags = 0x417 64 BIOS_page = 0x462 65 66 /* gas/ld has issues with doing this as absolute addresses... */ 67 .section ".bootsec", "a", @nobits 68 .globl bootsec 69 bootsec: 70 .space 512 71 72 .text 73 .globl start 74 start: 75 cli 76 xorw %ax, %ax 77 movw %ax, %ds 78 movw %ax, %ss 79 movw $stack, %sp 80 movw %sp, %si 81 pushw %es /* 4(%bp) es:di -> $PnP header */ 82 pushw %di /* 2(%bp) */ 83 movw %ax, %es 84 sti 85 cld 86 87 /* Copy down to 0:0x600 */ 88 movw $start, %di 89 movw $(512/2), %cx 90 rep; movsw 91 92 ljmpw $0, $next 93 next: 94 95 ADJUST_DRIVE 96 pushw %dx /* 0(%bp) = %dl -> drive number */ 97 98 /* Check to see if we have EBIOS */ 99 pushw %dx /* drive number */ 100 movb $0x41, %ah /* %al == 0 already */ 101 movw $0x55aa, %bx 102 xorw %cx, %cx 103 xorb %dh, %dh 104 stc 105 int $0x13 106 jc 1f 107 cmpw $0xaa55, %bx 108 jne 1f 109 shrw %cx /* Bit 0 = fixed disk subset */ 110 jnc 1f 111 112 /* We have EBIOS; patch in the following code at 113 read_sector_cbios: movb $0x42, %ah ; jmp read_common */ 114 movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ 115 (read_sector_cbios) 116 117 1: 118 popw %dx 119 120 /* Get (C)HS geometry */ 121 movb $0x08, %ah 122 int $0x13 123 andw $0x3f, %cx /* Sector count */ 124 movw %sp, %bp /* %bp -> frame pointer: LEAVE UNCHANGED */ 125 pushw %cx /* -2(%bp) Save sectors on the stack */ 126 movzbw %dh, %ax /* dh = max head */ 127 incw %ax /* From 0-based max to count */ 128 mulw %cx /* Heads*sectors -> sectors per cylinder */ 129 130 /* Save sectors/cylinder on the stack */ 131 pushw %dx /* -4(%bp) High word */ 132 pushw %ax /* -6(%bp) Low word */ 133 134 /* Load partition table header */ 135 xorl %eax,%eax 136 cltd 137 incw %ax /* %edx:%eax = 1 */ 138 movw $phdr, %bx 139 pushw %bx /* -8(%bp) phdr == bootsect */ 140 call read_sector 141 142 /* Number of partition sectors */ 143 /* We assume the partition table is 32K or less, and that 144 the sector size is 512. */ 145 /* Note: phdr == 6(%bp) */ 146 movw (80+6)(%bp),%cx /* NumberOfPartitionEntries */ 147 movw (84+6)(%bp),%ax /* SizeOfPartitionEntry */ 148 pushw %ax 149 pushw %cx 150 mulw %cx 151 shrw $9,%ax 152 xchgw %ax,%cx 153 incw %cx 154 155 /* Starting LBA of partition array */ 156 movl (72+6)(%bp),%eax 157 movl (76+6)(%bp),%edx 158 159 pushw %bx 160 get_ptab: 161 call read_sector 162 call inc64 163 loop get_ptab 164 165 /* Find the boot partition */ 166 xorw %si,%si /* Nothing found yet */ 167 popw %di /* Partition table in memory */ 168 popw %cx /* NumberOfPartitionEntries */ 169 popw %ax /* SizeOfPartitionEntry */ 170 171 find_part: 172 /* If the PartitionTypeGUID is all zero, it's an empty slot */ 173 movl (%di),%edx 174 orl 4(%di),%edx 175 orl 8(%di),%edx 176 orl 12(%di),%edx 177 jz not_this 178 testb $0x04,48(%di) 179 jz not_this 180 andw %si,%si 181 jnz found_multiple 182 movw %di,%si 183 not_this: 184 addw %ax,%di 185 loop find_part 186 187 andw %si,%si 188 jnz found_part 189 190 missing_os: 191 call error 192 .ascii "Missing OS\r\n" 193 194 found_multiple: 195 call error 196 .ascii "Multiple active partitions\r\n" 197 198 found_part: 199 xchgw %ax,%cx /* Set up %cx for rep movsb further down */ 200 201 movw $dssi_out,%di 202 pushw %di 203 204 /* 80 00 00 00 ee 00 00 00 205 - bootable partition, type EFI (EE), no CHS information */ 206 xorl %eax,%eax 207 movb $0x80,%al 208 stosl 209 movb $0xed,%al 210 stosl 211 movl 32(%si),%eax 212 movl 36(%si),%edx 213 call saturate_stosl /* Partition start */ 214 215 movl 40(%si),%eax 216 movl 44(%si),%edx 217 subl 32(%si),%eax 218 sbbl 36(%si),%edx 219 call inc64 220 call saturate_stosl /* Partition length */ 221 222 movzwl %cx,%eax /* Length of GPT entry */ 223 stosl 224 225 rep; movsb /* GPT entry follows MBR entry */ 226 popw %si 227 228 /* 229 * boot: invoke the actual bootstrap. %ds:%si points to the 230 * partition information in memory. The top word on the stack 231 * is phdr == 0x7c00 == the address of the boot sector. 232 */ 233 boot: 234 movl (32+20)(%si),%eax 235 movl (36+20)(%si),%edx 236 popw %bx 237 call read_sector 238 cmpw $0xaa55, -2(%bx) 239 jne missing_os /* Not a valid boot sector */ 240 movw %bp, %sp /* driveno == bootsec-6 */ 241 popw %dx /* dl -> drive number */ 242 popw %di /* es:di -> $PnP vector */ 243 popw %es 244 movl $0x54504721,%eax /* !GPT magic number */ 245 cli 246 jmpw *%sp /* %sp == bootsec */ 247 248 /* 249 * Store the value in %eax to %di iff %edx == 0, otherwise store -1. 250 * Returns the value that was actually written in %eax. 251 */ 252 saturate_stosl: 253 andl %edx,%edx 254 jz 1f 255 orl $-1,%eax 256 1: stosl 257 ret 258 259 /* 260 * Increment %edx:%eax 261 */ 262 inc64: 263 addl $1,%eax 264 adcl $0,%edx 265 ret 266 267 /* 268 * read_sector: read a single sector pointed to by %edx:%eax to 269 * %es:%bx. CF is set on error. All registers saved. 270 */ 271 read_sector: 272 pushal 273 pushl %edx /* MSW of LBA */ 274 pushl %eax /* LSW of LBA */ 275 pushw %es /* Buffer segment */ 276 pushw %bx /* Buffer offset */ 277 pushw $1 /* Sector count */ 278 pushw $16 /* Size of packet */ 279 movw %sp, %si 280 281 /* This chunk is skipped if we have ebios */ 282 /* Do not clobber %es:%bx or %edx:%eax before this chunk! */ 283 read_sector_cbios: 284 divl -6(%bp) /* secpercyl */ 285 shlb $6, %ah 286 movb %ah, %cl 287 movb %al, %ch 288 xchgw %dx, %ax 289 divb -2(%bp) /* sectors */ 290 movb %al, %dh 291 orb %ah, %cl 292 incw %cx /* Sectors are 1-based */ 293 movw $0x0201, %ax 294 295 read_common: 296 movb (%bp), %dl /* driveno */ 297 int $0x13 298 leaw 16(%si), %sp /* Drop DAPA */ 299 popal 300 jc disk_error 301 addb $2, %bh /* bx += 512: point to the next buffer */ 302 ret 303 304 disk_error: 305 call error 306 .ascii "Disk error on boot\r\n" 307 308 /* 309 * Print error messages. This is invoked with "call", with the 310 * error message at the return address. 311 */ 312 error: 313 popw %si 314 2: 315 lodsb 316 movb $0x0e, %ah 317 movb (BIOS_page), %bh 318 movb $0x07, %bl 319 int $0x10 /* May destroy %bp */ 320 cmpb $10, %al /* Newline? */ 321 jne 2b 322 323 int $0x18 /* Boot failure */ 324 die: 325 hlt 326 jmp die 327 328 mbr_space = end - . 329 . = MBR_DSN_OFFSET 330 end: 331
Indexes created Sat Oct 11 19:10:01 GMT 2025