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 "adjust.h" 30 31 .code16 32 .text 33 34 .globl bootsec 35stack = 0x7c00 36 37/* Partition table header here */ 38phdr = stack /* Above the stack, overwritten by bootsect */ 39/* Partition table sector here */ 40/* To handle > 32K we need to play segment tricks... */ 41psec = _phdr + 512 42 43/* Where we put DS:SI */ 44dssi_out = _start + 0x1be 45 46BIOS_kbdflags = 0x417 47BIOS_page = 0x462 48 49 /* gas/ld has issues with doing this as absolute addresses... */ 50 .section ".bootsec", "a", @nobits 51 .globl bootsec 52bootsec: 53 .space 512 54 55 .text 56 .globl _start 57_start: 58 .byte 0x33, 0xc0 /* xorw %ax, %ax */ 59 cli 60 movw %ax, %ds 61 movw %ax, %ss 62 movw $stack, %sp 63 movw %sp, %si 64 pushw %es /* 4(%bp) es:di -> $PnP header */ 65 pushw %di /* 2(%bp) */ 66 movw %ax, %es 67 sti 68 cld 69 70 /* Copy down to 0:0x600 */ 71 movw $_start, %di 72 movw $(512/2), %cx 73 rep; movsw 74 75 ljmpw $0, $next 76next: 77 78 ADJUST_DRIVE 79 pushw %dx /* 0(%bp) = %dl -> drive number */ 80 movw %sp, %bp /* %bp -> frame pointer: LEAVE UNCHANGED */ 81 82 /* prepare to read sector size */ 83 sub $0x1c, %sp /* -28(%bp) == %sp */ 84 pushw $0x1e /* -30(%bp) == %sp */ 85 movw $0x200, -6(%bp) /* -6(%bp) sector size */ 86 87 /* Check to see if we have EBIOS */ 88 pushw %dx /* drive number */ 89 movb $0x41, %ah /* %al == 0 already */ 90 movw $0x55aa, %bx 91 xorw %cx, %cx 92 xorb %dh, %dh 93 stc 94 int $0x13 95 popw %dx /* restore drive */ 96 movb $0x08, %ah /* get CHS geometry */ 97 jc 1f 98 cmpw $0xaa55, %bx 99 jne 1f 100 shrw %cx /* Bit 0 = fixed disk subset */ 101 jnc 1f 102 103 /* We have EBIOS; patch in the following code at 104 read_sector_cbios: movb $0x42, %ah ; jmp read_common */ 105 movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ 106 (read_sector_cbios) 107 108 /* 109 * read sector size. 110 * Should not fail but if it does I assume that at least 111 * previous 512 value is not overridden 112 */ 113 movb $0x48, %ah 114 movw %sp, %si 115 1161: 117 /* Get (C)HS geometry */ 118 int $0x13 119 120 /* here we computer CHS values or just do some dummy computation for EBIOS */ 121 andw $0x3f, %cx /* Sector count */ 122 pushw %cx /* -32(%bp) Save sectors on the stack */ 123 movzbw %dh, %ax /* dh = max head */ 124 incw %ax /* From 0-based max to count */ 125 mulw %cx /* Heads*sectors -> sectors per cylinder */ 126 127 /* Save sectors/cylinder on the stack */ 128 pushw %dx /* -34(%bp) High word */ 129 pushw %ax /* -36(%bp) Low word */ 130 131 /* Load partition table header */ 132 xorl %eax,%eax 133 cltd 134 incw %ax /* %edx:%eax = 1 */ 135 call read_sector_phdr 136 137 /* Number of partition sectors */ 138 /* We assume the partition table is 32K or less */ 139 movw (80+6)(%bp),%cx /* NumberOfPartitionEntries */ 140 movw (84+6)(%bp),%ax /* SizeOfPartitionEntry */ 141 pushw %ax 142 pushw %cx 143 mulw %cx 144 divw -6(%bp) /* %dx == 0 here */ 145 xchgw %ax,%cx 146 incw %cx 147 148 /* Starting LBA of partition array */ 149 movl (72+6)(%bp),%eax 150 movl (76+6)(%bp),%edx 151 152 pushw %bx 153get_ptab: 154 call read_sector 155 loopw get_ptab 156 157 /* Find the boot partition */ 158 xorw %si,%si /* Nothing found yet */ 159 popw %di /* Partition table in memory */ 160 popw %cx /* NumberOfPartitionEntries */ 161 popw %ax /* SizeOfPartitionEntry */ 162 163find_part: 164 /* If the PartitionTypeGUID is all zero, it's an empty slot */ 165 movl (%di),%edx 166 orl 4(%di),%edx 167 orl 8(%di),%edx 168 orl 12(%di),%edx 169 jz not_this 170 testb $0x04,48(%di) 171 jz not_this 172 andw %si,%si 173 jnz found_multiple 174 movw %di,%si 175not_this: 176 addw %ax,%di 177 loopw find_part 178 179 andw %si,%si 180 jnz found_part 181 182missing_os: 183 call error 184 .ascii "Missing OS\r\n" 185 186found_multiple: 187 call error 188 .ascii "Multiple active partitions\r\n" 189 190found_part: 191 xchgw %ax,%cx /* Set up %cx for rep movsb further down */ 192 193 movw $dssi_out,%di 194 pushw %di 195 196 /* 80 00 00 00 ee 00 00 00 197 - bootable partition, type EFI (EE), no CHS information */ 198 xorl %eax,%eax 199 movb $0x80,%al 200 stosl 201 movb $0xed,%al 202 stosl 203 movl 32(%si),%eax 204 movl 36(%si),%edx 205 call saturate_stosl /* Partition start */ 206 207 movl 40(%si),%eax 208 movl 44(%si),%edx 209 subl 32(%si),%eax 210 sbbl 36(%si),%edx 211 call inc64 212 call saturate_stosl /* Partition length */ 213 214 movzwl %cx,%eax /* Length of GPT entry */ 215 stosl 216 217 rep; movsb /* GPT entry follows MBR entry */ 218 popw %si 219 220/* 221 * boot: invoke the actual bootstrap. %ds:%si points to the 222 * partition information in memory. The top word on the stack 223 * is phdr == 0x7c00 == the address of the boot sector. 224 */ 225boot: 226 movl (32+20)(%si),%eax 227 movl (36+20)(%si),%edx 228 call read_sector_phdr 229 cmpw $0xaa55, (0x7c00+0x1fe) 230 jne missing_os /* Not a valid boot sector */ 231 movw %bp, %sp /* driveno == bootsec-6 */ 232 popw %dx /* dl -> drive number */ 233 popw %di /* es:di -> $PnP vector */ 234 popw %es 235 movl $0x54504721,%eax /* !GPT magic number */ 236 cli 237 jmpw *%sp /* %sp == bootsec */ 238 239/* 240 * Store the value in %eax to %di iff %edx == 0, otherwise store -1. 241 * Returns the value that was actually written in %eax. 242 */ 243saturate_stosl: 244 andl %edx,%edx 245 jz 1f 246 orl $-1,%eax 2471: stosl 248 ret 249 250read_sector_phdr: 251 movw $phdr, %bx 252 253 /* fall through and read sector */ 254 255/* 256 * read_sector: read a single sector pointed to by %edx:%eax to 257 * %es:%bx. CF is set on error. All registers saved. 258 * %edx:%eax and %es:%bx are incremented to read next sector 259 */ 260read_sector: 261 pushal 262 pushl %edx /* MSW of LBA */ 263 pushl %eax /* LSW of LBA */ 264 pushw %es /* Buffer segment */ 265 pushw %bx /* Buffer offset */ 266 pushw $1 /* Sector count */ 267 pushw $16 /* Size of packet */ 268 movw %sp, %si 269 270 /* This chunk is skipped if we have ebios */ 271 /* Do not clobber %es:%bx or %edx:%eax before this chunk! */ 272read_sector_cbios: 273 divl -36(%bp) /* secpercyl */ 274 shlb $6, %ah 275 movb %ah, %cl 276 movb %al, %ch 277 xchgw %dx, %ax 278 divb -32(%bp) /* sectors */ 279 movb %al, %dh 280 orb %ah, %cl 281 incw %cx /* Sectors are 1-based */ 282 movw $0x0201, %ax 283 284read_common: 285 movb (%bp), %dl /* driveno */ 286 int $0x13 287 leaw 16(%si), %sp /* Drop DAPA */ 288 popal 289 jc disk_error 290 addb -5(%bp), %bh /* bx += sector size: point to the next buffer */ 291 292 /* fall through and increment sector number */ 293 294/* 295 * Increment %edx:%eax 296 */ 297inc64: 298 addl $1,%eax 299 adcl $0,%edx 300 ret 301 302disk_error: 303 call error 304 .ascii "Disk error\r\n" 305 306/* 307 * Print error messages. This is invoked with "call", with the 308 * error message at the return address. 309 */ 310error: 311 popw %si 3122: 313 lodsb 314 movb $0x0e, %ah 315 movb (BIOS_page), %bh 316 movb $0x07, %bl 317 int $0x10 /* May destroy %bp */ 318 cmpb $10, %al /* Newline? */ 319 jne 2b 320 321 int $0x18 /* Boot failure */ 322die: 323 hlt 324 jmp die 325